RECOMMENDED WORKING PROCEDURES AND NOTES FOR GUIDANCE FOR APPLICATION OF ORGANIC WATER-BORNE COATINGS

Transcription

1 Waterbased Coatings Working Procedures DEFG RECOMMENDED WORKING PROCEDURES AND NOTES FOR GUIDANCE FOR APPLICATION OF ORGANIC WATER-BORNE COATINGS 1. INTRODUCTION The use of water-borne protective coatings is increasing due to legislation on the emission of solvents (volatile organic compound) from paints. The aim is to limit the volatile organic compound (VOC) content of the paint and subsequent emission into the atmosphere. Water-borne paints are one class of coatings that normally have VOC levels below any regulatory limits and can be used to reduce overall emissions compared to solvent-borne paints. Different types of coatings go by the name of water-borne. For example there are coatings in which water is the solvent, there are coatings containing resin dispersions and lattices. These working procedures and notes for guidance are intended as a guide to the experienced contractor and the interested specifier/end user covering the key points in the selection and application of International Protective Coatings water-borne systems. The durability of any applied coating system is dependent on:- i) The selection of the coating specification. ii) Correct preparation. iii) Correction application. General guidance notes on these principal areas are given below. 2. THE SELECTION OF THE COATING There is a wide range of International Protective Coatings water-borne systems, each with it s own properties. In addition, there are many further options available as the water-borne systems are compatible with both conventional solvent-borne systems and high solids coatings (for further details consult International Protective Coatings Systems Guide). Prior to selection of the coating system the following are some of the questions which should be answered before adopting any particular coating specification. What is the type of substrate? Blast cleaned steel (Sa 2½) (SSPC SP6), gingered steel, aged coatings, hand prepared steel. Why is the substrate being coated? Protection, cosmetics? What is the expected life to first maintenance? What is the expected environment of the final system? Exterior/interior, exposure to chemicals, severe corrosion environment? What are the anticipated conditions during application?

2 Our Sales and Technical staff will be pleased to help with particular specification requirements. 3. PREPARATION 3.1 Where to Apply Water-borne Systems At Works International Protective Coatings water-borne systems are best suited for application in the steel fabrication shop or at an applicator's works. Sufficient time should be allowed for through drying before handling. This hardening time must be under cover, and will vary with dry film thickness and conditions in the shop. Humidity, temperature and air movement have a significant effect on the drying of water-borne paints. Cure of water-borne products requires moisture to evaporate from the film. When the relative humidity is high (>70%), curing times will be longer than the data presented in the Technical Data Sheet, as water will be retained in the film in high humidity conditions. At low temperatures the drying time is increased. The air temperature and surface temperature must be above 8 C (46 F) or 10 C (50 F) depending upon the product, during cure and not just during application. Water-borne products should not be applied when the relative humidity is greater than 80% and/or the ambient temperature is below 10 C (50 F). Application under these conditions will compromise the ultimate coating performance. Application Conditions for Water-borne Paints Possible application and drying conditions Relative Humidity (%) 60 Recommended conditions for application and drying Application not recommended C 50 F 20 C 68 F 30 C 86 F 40 C 104 F 50 C 122 F 60 C 140 F Temperature ( C + F)

3 The Effect of Humidity and Air Flow in Touch Dry Times of Water-borne Paints (Finish Coat 50 microns dft (2 mils)) 50 30% 30% 50% 50% 70% 70% 40 Temperature (Degrees Centrigrade) Time (minutes) Air flow 0.5ms -1 Air flow 0.2ms -1 Air movement is probably the most significant factor affecting the drying of water-borne paints. With little air movement a local increase in relative humidity will soon reach unacceptable levels while spraying water-borne paints, resulting in poor performance. Product drying times should be strictly followed. Too early exposure to the environment may result in damage to the coating if not fully cured. Localised forced heating (>60 C) (>140 F) is not recommended as this can result in skinning of the surface and subsequent retention of the water in the film. To determine whether an application area will be suitable or what modifications will be required to use water-borne paints, consult your local International Protective Coatings representative On Site The same environmental considerations as outlined for application in fabrication shops, are necessary. On site the application should be protected from rain and dampness. If water-borne coatings become wet before full cure, damage will occur. Soft coatings may be cratered by rain droplets and are likely to become soft, blistered or water logged. Such coatings must be removed and re-applied. The water-borne products may become wet after initial set without being obviously affected, remaining firm and intact. However, due to the early water sensitivity of the products, the adhesion properties may have been affected. If in doubt, consult International Protective Coatings.

4 3.2 Surface Preparation With all coatings, the surface preparation is critical to the coating s performance and this is especially so in the case of water-borne products. The steelwork should be blast cleaned to a minimum of grade Sa2½ (ISO : 1988 Swedish Standard SIS : 1989) or SSPC SP6 before application of the priming system. The steelwork should be free from soluble salts to prevent flash rusting and all excess blasting grit or dust should also be removed to prevent the possibility of pinholing. Oil and grease must be removed from all surfaces to be coated. Water-borne materials will not tolerate cutting oils and grease on the steel surface. For water-borne intermediate and finish coats the priming coat must be clean and dry within its specified overcoating period, and compatible with the top coat. 4. APPLICATION 4.1 Method of Application Airless Spray Airless spray is the recommended method of application. However, as with all waterborne paints, initial cleaning of spray equipment is crucial. Prior to application, spray equipment, pump, lines and guns, which have previously been used for solvent-borne paints must be initially cleaned with International thinners GTA822 followed by International thinners GTA991. This should be followed by flushing with clean potable* water. The equipment is then suitable for use with water-borne paints. * Potable means drinking water, so as a guide, if you would not drink the water it is not clean enough to be used. Upon completion of spray application, similar cleaning precautions should be taken. The equipment should be initially flushed with potable water. This is then followed by GTA991. In the event of the paint temperature being greater than 30 C (86 F), GTA991 should be used immediately after paint application. Finally to remove any water from the system and prevent rusting of the spray equipment occurring, it should be thoroughly flushed through with International Thinners GTA822. The equipment is then available for use with either solvent-borne or water-borne paints again Brush/Roller Brush application should be undertaken using synthetic bristles, such as nylon or polyester. Do not use natural bristle brushes, such as those with horse hair bristles as the bristles will absorb the water and swell. The brush will lose its shape quickly. Similarly rollers should also be made of a synthetic fabric such as polyester rather than a natural fabric such as lambskin. Brush or roller application should be performed at an average rate using only moderate pressure. Too high a pressure or over-working the material will result in foaming. For suitability of each of the water-borne products to brush/roller application, consult individual Technical Data Sheets.

5 4.2 Thinning Thinning should not normally be required. If the material is cold, or equipment is not in optimum condition, application may be improved by thinning with up to 5% water. Holdup properties may then be reduced and drying times extended. Solvent based thinner should not be used for thinning water-borne paints. 4.3 Potlife Water-based epoxy paints show an increase in pot life with increasing temperature. Paints containing water-borne epoxy resins have particles of resin which must deform and stick together to form films. The higher the temperature, the softer the particles and the easier they deform and stick together. As the particles cure they get harder still. At low temperatures, the particles require less cure before they fail to deform and stick together. This results in powdery films being formed at shorter pot lives as the paint temperature reduces. 4.4 Thickness Build-up The specified thickness of each of the water-borne products may be achieved in one spray coat. For difficult areas which are likely to be under-applied, a stripe coat should be applied, prior to application of a full coat. For brush/roller application, in some cases, two coats may be required to achieve the required thickness. Care must be taken not to over apply water-borne products. Application of thick films will greatly extend the drying times and may result in powdery or cracked films. The time before removal to the environment will also be extended. 4.5 Overcoating Water-borne coatings can be overcoated with themselves with no unusual problems and the Technical Data Sheets for each particular product should be consulted for specific overcoating times. However in cases where poor application conditions have been experienced the overcoating times will be extended. 4.6 Storage of Materials Water-borne products should be stored in covered, dry conditions and stored in the temperature range 4 C (40 F) to 35 C (95 F). Ideal application temperature and hence storage temperature is between 15 C (60 F) and 25 C (77 F). At lower temperatures, materials will be thicker and may require adaption of the application procedure. At higher temperatures and low humidities materials will flow more easily and dry more rapidly, perhaps causing greater dry-spray. 4.7 Health and Safety

6 International Protective Coatings water-borne products are intended for use only by professional applicators in industrial situations in accordance with the advice given in this leaflet and on containers, and should not be used without reference to the Health and Safety Data Sheets which International Protective Coatings has provided to its customers. If for any reason a copy of the relevant Health and Safety Data Sheets are not immediately available to the end user, one should be obtained before using the product. Safe handling and use are as important with water-borne paints as they are with solvent borne paints. The minimum safety precautions in dealing with all paints are: - Take precautions to avoid skin and eye contact (i.e. use overalls, gloves, goggles, face mask, barrier creams, etc.). - Provide adequate ventilation. - If product comes in contact with the skin, wash thoroughly with lukewarm water and soap or suitable industrial cleaner. Do not wash with solvents. If the eyes are contaminated. flush with water (minimum 10 minutes) and obtain medical attention at once. - Observe all precautionary notice on containers. Water-borne paints have a higher flash point than solvent-borne paints. The safety hazard from fire and explosion is low, but do not assume there is no fire hazard. Therefore the following precautions should still be followed: - Keep away from sparks and open flames. Smoking should be prohibited in the area. All products supplied and any advice given by International Protective Coatings is subject to their standard conditions of sale. Disclaimer The information given in this sheet is not intended to be exhaustive and any person using the product for any purpose other than that specifically recommended in this sheet without first obtaining written confirmation from us as to the suitability of the product for the intended purpose does so at his own risk. Any warranty, if given, or specific Terms & Conditions of Sale are contained in International s Terms & Conditions of Sale, a copy of which can be obtained on request. Whilst we endeavour to ensure that all advice we give about the product (whether in this sheet or otherwise) is correct we have no control over either the quality or condition of the substrate or the many factors affecting the use and application of the product. Therefore, unless we specifically agree in writing to do so, we do not accept any liability whatsoever or howsoever arising for the performance of the product or for any loss or damage (other than death or personal injury resulting from our negligence) arising out of the use of the product. The information contained in this sheet is liable to modification from time to time in the light of experience and our policy of continuous product development. It is the user s responsibility to check that this sheet is current prior to using the product Issue date: 21/12/2001