AUXILIARY ADDITIVES

Screen Printing inks are generally delivered in a consistency which, apart from thinner, does not require any further addition of additives for modification. As the screen printing process varies, depending on the materials to be printed it cannot be avoided to modify the inks slightly in order to achieve the desired result. Coates Screen printing inks offers a number of auxiliary agents. A general overview of these additives is given in this document.

Which additive to use depends on individual circumstances. In certain situations it is suitable to use auxiliary agents. However, overdosage may have adverse effects. Therefore pretest should be performed under local conditions in order to determine the most favorable addition amount within the values stated above.

The information given in this document can only be understood as non-obligatory advise for the elimination of certain problems occurring during printing.

RETARDERS:  Retarders are auxiliary agents which prevent quick drying in the mesh. They reduce the evaporation rate of the solvent contained in the screen ink and also show good solving properties concerning the binding agents of the screen inks. Retarding agents not only delay drying of the ink, they also retard drying on the substrate. If solvent are retained, there is a risk of blocking. Therefore, retarders must be measured out carefully. Drying tests are recommended.

LIQUID RETARDERS:  Besides the special retarders available, there are the so called "Universal Retarders" which can be used for many ink types. Such universal retarders have to be compatible to many different binding agents. We have 4 universal retarders which can be used for almost all Coates Screen printing ink types. Exceptions are UV curing inks, water dilutable inks and some two-component ink systems.

UNIVERSAL RETARDER UV1:  Universal retarder UV1 has good solving properties and medium retardation. Depending on the required degree of retardation and drying possibilities, addition to the screen printing ink is approx. 5-10%

UNIVERSAL RETARDER UV2:  Universal retarder UV2 is also suitable for almost all screen printing ink types, except for those mentioned above. It shows good retardation properties and medium solving properties against binding agents contained in the inks. Addition to the screen printing ink is approx. 5%

UNIVERSAL RETARDER UV3:  Compared to UV1 and UV2, the universal retarder UV3 shows minor solving properties and has strong retardation effect. Addition is approx. 3-5%. If more UV3 is added, drying could be impaired. Due to its low solving property, it is sometimes difficult to mix UV 3 into the ink. In such cases addition of a small amount of UV1 will help.

UNIVERSAL RETARDER UV4:  Universal Retarder UV4 shows strong retardation properties and good solving properties. This results in very long screen openness but also slow curing of the screen printing ink film. Recommended addition of UV4 is approx. 3-5%. Contrary to the UV1, UV2 and UV3 retarders, UV4 can be used to retard the initial drying time of two-component systems.

RETARDER PASTES:  As liquid retarders often also reduce viscosity of screen printing inks, it is often suitable to use retarder pastes. These are transparent and do not change the ink shade significantly. Retarder pastes should not be used as transparent pastes. Addition of retarder paste should not exceed the amount indicated.

RETARDER PASTE VPK:  VPK is suitable for all plastic inks, such as, CP, HG, J, PK, PK JET, SG and process inks RF-K

RETARDER PASTE VPP:  Retarder paste VPP is used for paper inks, such as, M, ZA and DA. Addition is approx 5-10%. Except for the inks mentioned above, retarder paste VPK cannot be used for paper inks other than Coates Screen.

FLOW AGENTS:  Problems which occur on the surface of a screen printing ink film are bubbles, pin holes, orange-peel or similar effects. In order to avoid such undesired effects in some cases certain auxiliary agents, so-called flow agents, have to be added to the screen ink. The amount specified should not be exceeded.

Proceed cautiously when overprinting inks mixed with silicone containing flow agents.

FLOW AGENT VM 1:  Silicone containing flow agent for a broad field of applications. It is suitable for all ink types except water based and UV curing inks.

Eliminates flow problems in the screen ink film such as orange-peel, bubbles, pin holes and similar effects.

Addition approx. 1-5%, not overprintable.

FLOW AGENT VM2:  Effect of flow agent VM2 is basically the same as VM1. This additive is more concentrated and therefore more effective.

Addition should not exceed 0.3-0.5%. Only exceptional cases up to 2% of VM2 can be added to the screen printing ink. Not overprintable.

FLOW AGENT VM3:  It is only suitable to use VM3 if no other silicone containing flow agents have already be added to the ink. Flow agent VM3 is preferably used for overprinting applications for long term outdoor use. This flow agent has shown excellent results as additive for two-component inks. VM3 can be also used for all Coates Screen printing ink types, except for UV curing and water dilutable inks.

Addition is approx. 1-5%. Overdosage will not achieve any improvement.

ELASTIFYING AGENT:  Increased elasticity is sometimes necessary for special applications. Also the cracking of highly opaque screen printing inks on glossy substrates. In such cases addition of an elastifying agent or plasticizer is suitable in order to solve the problem.

ELASTIFYING AGENT NL8949T:  Can be used for many applications. With the exception of UV curing and water dilutable inks, this elastifying agent can be mixed with all Coates Screen inks. Besides increased elasticity of the screen printing ink film, adhesion on various substrates (oven curing inks on metals as well as etch plate resists) is also improved. Addition of NL8949 is approx. 5-10%.

There is a risk of blocking if dosage is exceeded. NL8949 shows no tendency to migrate.

THICKENING POWDER:  Thickening powder is used to make screen inks more thixotropic. Sometimes this will be necessary, especially when printing fine details, characters, halftones lines etc. The thickening powder is a very light powdery substance. Addition of Filler 13 is approx. 2-3%.

A good dispersion of the Filler 13 in the ink is important. We recommend a high speed mixer.

MATTE POWDER:  The matting powder looks like thickening powder. However, it is used to matte the screen ink and not to increase the thixotropy. Depending on the amount added, the gloss of the ink film is changed and the viscosity may increase. Addition of Filler 33 is approx. 3-6%.

A good dispersion of the Filler 33 in the ink is important. We recommend a high speed mixer.

ANTISTATIC AGENTS:  Static electricity is often a big problem when printing onto plastics. Static electricity shows in form of irregular ink deposit, dulling, spin-webbing, sticking of the substrate or other problems occurring during laying and stacking of the prints.

The cause of static electricity is the separation of surfaces, during which charge separation occurs. The surplus of positive and negative charge on the surface cannot flow the non conductors (plastic) or the isolated conductors and remain as static or resting electricity. In order to avoid static charge, the surface of the material, the environment must have sufficient conductivity. Static charge can be eliminated most efficiently with high humidity, as this will reduce surface resistance. Another possibility would be the use of antistatic agents.

WIECOSTAT W:  Wiecostat W is a watery solution. It is mainly used to make floors conductive and to treat substrates sensitive to tension cracks and solvents.

In order to apply the antistatic coating, three methods are possible:

1. Wiping with soaked cloth or spreading with brush.

2. Dipping the material into the antistatic solution.

3. Spraying the material using a spray gun.

In many cases cleaning and de-electrification can be done in one step by adding Wiecostat W at a ratio 1:20 to the cleaning water.

Usually only small amounts of plastic boards are printed. It is possible to wash plastic boards with thinned solution of Wiecostat W.

WIECOSTAT A:  Wiecostat A contains the same active substances as Wiecostat W. As Wiecostat A is an alcoholic solution, it dries faster than watery solutions. As Wiecostat A is flammable, the usual safety precaution have to be considered during processing.

WIECOSTAT-SPRAY:  The active substance of Wiecostat spray correspond to those contained in the Wiecostat W and A. This antistatic agent is delivered in spray form with a high concentration. This spray is also free of FCKW.

WIECOSTAT N:  Wiecostat N is a special antistatic agent, which is mainly used to increase conductivity of a screen printing ink. Wiecostat N is also solved in an organic solvent. Addition of approx. 1-3% to the screen ink will often eliminate printing problems caused by static charge. Drying properties of the ink will change if this amount is exceeded. All above mentioned antistatic agents can not only be used for screen printing. Wiecostat may also be useful for other problems caused by static charge.

1. Fight dust attraction.

2. To renew used antistatic cloths.

3. To avoid problems in pneumatic dispatch equipment made of PVC pipes.

4. To avoid sparks during the production on processing of plastics.

5. To impregnate textiles, carpets etc...

6. To secure continuous processing in the graphic industry.

HEALTH AND SAFETY: As with all inks, gloves and safety goggles should be used when handling these products. For more complete information, refer to the relevant Material Safety Data Sheets.