Table of contents
Introduction
pag.2
Elettrodeposition n What is it? n The young history of ED n Cathodic/anodic deposition
pag.3 pag.3 pag.4 pag.5
1 Fundamentals 1.1 Paint components and composition 1.2 Resin Chemistry 1.3 Application 1.3.1 Anode and cathode reaction 1.3.2 Film formation 1.3.3 Throwing power 1.3.4 Crosslinking 1.4 ED Development from laboratory to marketplace
pag.6 pag.6 pag.7 pag.8 pag.8 pag.9 pag.10 pag.10 pag.11
2 BASF’s portfolio 2.1 Eco-efficient innovations in ED 2.2 BASF Products
pag.12 pag.12 pag.14
BASF Industrial Coatings Solutions 3.1 Coatings Solutions
pag.16 pag.16
Surface treatment has continuously increasing needs. Such needs can only be met by supplying reliable coating systems that grant efficiency, energy saving and environmental friendliness. BASF Coatings has the expertise and experience necessary to the research and develop of tailor-made products for its customers and support them with effective consulting for all types of applications. BASF provides reliable, innovative products, that goes far beyond the supply of paints.
e c a f r u s d n Beyo Sustainable development Innovative solutions from BASF Coatings give our customers a competitive edge in the global marketplace. Highly efficient, high quality coating technologies created by BASF Coatings form the foundation for the continued success of our customers. BASF Coatings unites the interdisciplinary research activities of the BASF Group world-wide, guaranteeing the utmost technological development available in the coating industry. The result is a unique, synergic blend of expertise that gives BASF Coatings its special strength. BASF Group, and in particular BASF Coatings, has continuously dedicated research and development resources to innovative coating solutions in order to create coatings with fundamental technical improvements; this results in advantages for the ecology of our partners, providing them with the right support in their efforts to succeed while respecting the environment.
Contribute to the success of our customers Innovation + Global Vision + Partnership. The successful formula for the coatings of the future. Acting as partners, we work closely with our customers to develop pioneering coating processes that yield impressive results on both the production line and bottom line. At BASF Coatings we see partnership as essential to the success of our customers. As a systems supplier, we work closely with our customers in designing total coating solutions and excel at coatings processes and quality products. BASF Coatings’ future is in its customers and this is the force that pushes our organization to create and sustain the success of our partners day after day.
Form the best team in the industry BASF Coatings supports the continuous improvement of its collaborators, in order to create and to renovate the essential competences to improve its contribution to the marketplace. Our international presence ensures a high degree of customer proximity that allows us to assist our customers quickly and effectively in the optimization of their products and manufacturing procedures. A world-wide network for marketing, sales and operation, attention to the market and to its requirements and technological coordination are the instruments with which the team of BASF Coatings has become the best choice for Industrial Coatings in Europe.
We help our customers face the future and open up new successful markets by providing them with total coating solutions and state-of-the-art paint technologies.
ELECTRODEPOSITION ED – What is it? ED is the abbreviation for electrodeposition and describes the modern and effective way of coating complex metal shapes by means of DC electricity. These days it is becoming almost impossible to avoid contact with products coated in ED systems – Cars, steel furniture, domestic appliances to name a few examples. By its ability to prime and finish large numbers of mass-produced goods, the introduction of ED signaled the impending demise of the brush and spray gun and not before time, when you consider the environmental and health implications. In this brochure on the subject of “ED Processes”, we are able to provide all the basic information on paint chemistry and systems, and answer your questions concerning plant design and process control. However, because precise requirements vary from application to application we recommend that you also consult one of our specialists too.
Chart 1. Electrodeposition line used air
UF rinse
oven
conveyor belt
anolyte circulation system
ED tank
to waste-water treatment
ultrafiltration
3
The young history of ED Electrodeposition first stepped into the spotlight in the 1960’s when Ford USA started the first plant for the electrophoretic painting of car bodies. Within a short time the new process reached Europe. The term “electrophoresis” is no longer commonly used, since we now know that the deposition mechanism has more to do with the electrolysis of water and electrical de-stabilization of polymer particles than with the simple movement of the polymer in the electric field. In the mid-70’s anodic coatings (AED) gave way to cathodic systems (CED). The automobile manufacturers had already made the change and the auto-component and other industries one by one abandoned the anodic system. Despite this change, anodic products are still the preferred choice for certain applications, for example weather-resistant one-coat finishes, radiators, etc. Cathodic/anodic deposition Before we discuss the difference we should first answer the following question: Why electrocoat at all? ED offers these important advantages: Environmental acceptability High painting efficiency n Excellent corrosion protection n Excellent throwing power n Even film thickness n High degree of automation of the process n n
In anodic coating the paint film is deposited at the anode, that is to say the work piece is connected to the positive side of the rectifier. It follows therefore that the paint resin has negative charge. This process will be seen at page 8. Cathodic coating is just the opposite; the work piece is the cathode and the paint resin of course has positive charge. The different anodic/cathodic coating mechanisms and therefore the different resin systems required result in paint-film properties which are also quite different.
4
Electrodeposition
Also introducing differences in terms of chemical resistances, the two systems have very specific advantages: Cathodic - CED No dissolution of work piece Basic polymers are inherently corrosion inhibiting and resist saponification n In cycle with nanotechnological pretreatments and/or pho phates it is almost un-attackable n n
Anodic - AED Availability of one-layer finishes in different colors Excellent colour stability over time n Simple and versatile application process with diverse applic tion conditions n n
For these basic reasons the two processes find themselves used in particular applications: CED is generally used where high corrosion resistance is required. The high voltages employed give good throwing power so that the hidden areas are also well protected. AED products are used, conversely, where corrosion-resistance is not as important as the mechanical film properties and where a decorative one-coat finish is desired. Acrylics are particularly popular because their excellent resistance to UV enables the formulation of a wide colour range. Chart 2. Properties of cathodic/anodic products Property
Cathodic
Anodic
Salt-spray resistance up to 240 hrs
yes
yes
Salt-spray resistance up to 1000 hrs
yes
no
UV resistance
no/yes*
no/yes*
Alkali resistance
yes
no
Throwing power
very good
poor
Colour range
low
good
Chemical resistance
yes
poor
*Some special products are available which meet these requirements
5
1
Fundamentals 1.1 Paint components and composition
An ED bath comprises 80-90% water. The remainder consists of resin, pigment, a small quantity of organic solvent and additives. In the following table the most important characteristics of AED and CED resins are shown. To find out which product belongs to which resin class please refer to tables provided in the following sections. Other information about properties, supplies and bath make-up procedures can be provided by one of our technical representatives.
Chart 3. Blinders, pigments and organic solvent for electrodeposition coating Binders CED
Organic solvents
Titanium dioxide, carbon black, iron oxide, kaolin, talcum, lead pigment, blanc fixe, aluminium
The solvents used are easily degradable. We might name the product categories listed below: n low-molecular alcohols n aliphatic and aromatic glycol n ketones
AED
Acrylate n UV resistant n better anti-corrosion than AED acrylates n suitable for single-coat systems Epoxy n mainly employed as primer n excellent anti-corrosion n good coating of cavities (throwing power) n can be recoated with 2C topcoats n alkali/acid resistant
Acrylate overbake resistance n all colours available n high bath stability n non-critical anti-corrosion n suitable for single-coat systems n
Phenolic modified acrylate n improved corrosion protection n dark colours only Epoxy/polyesters n lighter colours n medium anticorrosion n good adhesion on zinc n can be recoated, even with air-drying paints Polybutadiene oils n subject to yellowing n good anti-corrosion, especially when phenolic resins are used n tends to chalk when exposed to weathering
6
Pigments
Electrodeposition
Common inorganic or organic colour pigments may be used to achieve the desired colour in single-coat systems. As a matter of principle, ED pigments should be neither reactive nor contaminated with water-soluble substances (such as chloride, sulphate, etc.). Heavy-metal pigments are avoided to the greatest possible extend.
1.2 Resin Chemistry
As you can see from Chart 3, a number of different polymer types can be used to make ED resins. One thing applies to all of them; they must possess functional (reactive) groups that can form salts by reacting with acids (CED types) or bases (AED types). Only then can they achieve their very important compatibility with water. Resins for use in anodic electrodeposition have in the backbone carboxyl or sulphuric acid groups. Chart 4 shows the salt formation from the polymer with an alkali or organic amine. When this resin is mixed with an acid (e.g. lactic, acetic, formic) it becomes water dispersible (Chart 6). Often only a portion of the functional groups combine with the neutralizing agent. The molar ratio of neutralizer to functional group is known as the neutralization number, and a value of 30-40% is usually high enough to achieve compatibility with water.
Chart 4. Solution reaction fot AED resin
or:
acid, insoluble
base, amine
salt, soluble
Chart 5. Addition of an amino group in an epoxy resin
epoxy
amine
Chart 6. Neutralisation reaction in CED resin
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Chart 7. Cathodic Electrodeposition
1.3 Application
1.3.1 Anode and cathode reaction During the electrolytic breakdown of water at the anode and cathode, secondary products develop which begin the process of coagulation of the resin solution: In CED systems these are OH (hydroxyl) ions which, in a secondary reaction, combine with the charged resin molecules. It is hydrogen ions (H+), in the case of AED processes, which react at the anode with the negatively charged resin. The following equations and figures show these reactions schematically. Chart 7 shows diagrammatically what happens in cathodic deposition. The newly released hydrogen and oxygen play an important part in the film-forming process. On the applied “wet film� they form foam which is electrically resistant and which therefore limits film thickness.
Chart 8. Anodic Electrodeposition
8
Electrodeposition
1.3.2 Film formation The quantity of paint deposited is determined by the current flow. Thanks to the applied paint and the foams that generate, film resistance builds up which exceeds that of the bath many times. According to Ohm’s Law the current falls and the deposition process slows down.
Chart 9. Schematic diagram of an ED installation
Film resistance & bath temperature By varying the bath temperature one also varies the film resistance. The origin of this strong dependency lies in the viscosity of the deposited polymer. If it is very high (at low temperatures) the wet film is porous and the resistance remains low. At a coating time of 120 secs the current flow at 12°C and 28°C is similar, although the route is completely different; at a lower temperature almost 90% of current flow occurs in the first 5 secs, after which nothing changes very much. In contrast, the current flow at 28°C is more
9
continuous, increasing evenly over the whole coating time. If you were to continue coating, the film thickness at 28°C would be significantly higher than at 12°C. The current curve for 20°C shows the transition to a more continuous deposition process. Here the attainable current levels are very low and thus also the film thickness. Chart 10. Coating of box sections
Box section
Start of coating: outer coating
Box section
After a short time: start of inner coating, film resistance development outside
Box section
At the end: further slight coating inside, no coating at all outside
10
Electrodeposition
1.3.3 Throwing power One of the most important properties of electrodeposition paints is the possibility to coat difficult areas. This is how, for example, some parts of car bodies, as well as the chassis of appliances or the hidden parts of the radiators are coated, a basic requirement for the prevention of perforation by corrosion from inside How does it work? On application of DC voltage between work piece and electrode the current seeks the path of least resistance. This means that the parts nearest the electrode are coated first, i.e. the outer surfaces. During the coating of the outer areas the electrical resistance increases and the current now has to find a path to areas of lower resistance. In this way the coating process proceeds further. The coating process does not stop until the distance has become so great that the path resistance is too high for the required current density. In these cases, the work pieces must conduct so that the electric field can get into the cavity (through holes or slots). Chart 10 shows the dynamics of the coating progress from start to finish. 1.3.4 Crosslinking Once the paint has been applied and the cream-coat rinsed, the film appears to be complete; it can be handled – it is not sticky and feels quite dry. This gives the illusion of resistance when, in fact, solvents like MEK or acetone can easily remove the film. Under mechanical testing (e.g. Erichsen cupping) the film cracks very easily. It is basically the chemical crosslinking of the resin molecules that leads to a solvent-resistant film with good physical/ mechanical properties. On this basis the paint is joined to a crosslinker which, at elevated temperatures, brings about a chemical bonding between the individual resin molecules. There are three different types of crosslink reactions: melamine/hydroxyl crosslinking, Mannich-base and urethanisation. The melamine or phenolic crosslinking mechanisms are usually found in AED systems while urethanizing ones characterize CED systems. The proportion of functional (reactive) groups (OH or NH2) is very important for good crosslinking because the nature of the crosslinker may have a decisive impact on the end properties of the film.
1.4 ED Development from laboratory to marketplace
Picture 1. Italian Electrodeposition Laboratory
The development of a new ED product requires extensive laboratory work. The main goal of new development projects often stems from customer requirements; it may be about either of the following features: Corrosion Protection Finish (gloss, flow) n Colour n Mechanical properties n Film thickness n Process reliability n Ease of handling n Cost n Production reliability n n
For the developer the next question is whether the available resin and crosslinker can be used to meet the required specifications. If this is the case, formulation work begins in the lab. The following parameters may be influenced. ED bath Pigment Additives n Solids content n Pigment/binder ratio n Solvent content/flow agent n n
Application Bath temperature Application voltage n Application time n Curing temperature and time n n
11
In the occurrence of special requests from the customer or of a particular product adjustment, it is possible to re-design from scratch the resin, or the crosslinker. The products are prepared in the resin laboratory and then tested in the EDP laboratory. It is also possible to design alternative bath formulations. The manufacturing process for resins is performed in the resin department. The development and manufacturing of the pastes is also directly carried out by BASF Coatings.
2
BASF’s portfolio 2.1 Eco-efficient innovations in ED
Innovation with built-in eco-efficiency: key to tomorrow’s success. To succeed in the current global marketplace as well as in the future, innovative paint systems must offer outstanding product and process performance combined with eco-efficiency. That is, they must make the overall process more profitable while at the same time contributing to improved environmental compatibility.
BASF Coatings undertakes specifically targeted research and development projects with the aim of readying eco-efficient innovations for the marketplace. The driving force for innovation is the improvement of: Efficiency in the application process Reduction of solvent content n Elimination of heavy metals n Improvement of the performance of the film n n
Chart 11. Coating of box sections
Heavy metal
introduction
12
Electrodeposition
Solvent
Efficiency
present and future
And of course, such characteristics must maintain the current performance in terms of corrosion protection. The results of development work at BASF Coatings clearly demonstrate progress in the fields of efficiency and the reduction of solvent and heavy metal contents. Appliances In order to meet the strict quality standards of the appliance industry, the chassis and some of the components of large appliances are painted with electrodeposition systems. All the parts of the appliance, above all in the �wet segment�, (washing machines, dryers, dishwashers, etc.), exposed to the risk of corrosion due to the contact with chemical agents, like detergents, alkali, etc., are protected for their whole life cycle with Cathodic systems (CED). In addition to the appropriate electrodeposition products, BASF Coatings is able to provide a complete coating system, including suitable liquid topcoats and powder coatings. The advantages for the customer are obvious: the coatings layers are perfectly matched and they have to stand strict homologation tests. Do not forget that BASF Coatings guarantees the whole coating cycle in total. Radiator coating Today, radiator production always includes coating by the manufacturer. Normally, the uncoated radiators are degreased and pretreated generally in a single process stage. In the subsequent priming stage, there are mainly three environmentally compatible options: 1. Water-based dipping coating 2. Anodic electrodeposition (AED) 3. Cathodic electrodeposition (CED) BASF Coatings suggests CED for the priming of steel-plate radiators, since it offers good throwing power, high corrosion resistance and improved cost efficiency of the coating material; on the other hand, for aluminium and design radiators we recommend the use of Anaphoresis, due to the great stability, the reduced sensibility to the bleeding when used as primer or the chromatic versatility in one-layer cycles. The product range has been specifically developed for this application, and it is characterized by: High efficiency High throwing power n Excellent colour stability n Safe re-coating n Ease of management of the process n n
The preferred finish is a powder product.
13
Main radiator pretreatments Steel: Cast iron: Aluminum:
iron phosphate sand-blasting F-Zr treatment
BASF offers its competences not only for the final part of the painting but for the entire coating process, including pretreatment. This approach allows an optimal management of the cycle and the efficiency of the whole process. BASF Acrylic Anaphoresis (AED) is recommended for the coating of all the goods that require elevated automation of the process and easy management of the line, and hence a punctual control of the application costs and remarkable quality of the finished goods. Such system is currently widely employed for onelayer applications for metallic furniture and shelving, tools, post boxes, and so on. Another common application is the use of ED for small parts that are supplied as bulk goods and must therefore no longer be laboriously separated and handled one by one. On a special conveyor, they are fed through the ED bath and the subsequent rinsing zones and are then transferred to a second conveyor that takes them through the drying oven. The first conveyor returns to the feed point via a cleaning station. This process will in future be able to replace galvanic coating in certain applications and will therefore contribute to achieving considerable reductions in the effluent currently discharged from galvanization plants. This method can be used for screws, nails, window and door fittings, washers, springs, hooks, expansion fixings etc.
2.2 BASF Products
BASF Coatings provides a product range tailored to a wide variety of applications. Our product laboratory and our sales units are always available to assist you in selecting the right product. Nevertheless, the following overview shows the main differences to help you narrow down the preliminary choice.
14
Electrodeposition
Chart 12. Cathodic system BRAND
Product-line
Resin base
Colours
Film thickness
Baking conditions
Main properties
Cathoguard® 570 (HFB)
QT30
Epoxy
up to 35 µm
15 min at 160 / 180°C
Cathoguard® 580 (LFB)
QT33
grey, black
Good corrosion protection and edge protection optimized flow (outlets, bridging)
Cathoprime® (HFB)
QT80
Epoxy
grey, black, off-white
up to 35 µm
15 min at 170 / 180°C
Good corrosion protection and edge protection Honda-Test Very good appearace High yield Low solvent content
Cathoprime® (LFB)
QT80
Epoxy
grey, black off-white
up to 22 µm
15 min at 170 / 180°C
Good corrosion protection Low gloss Broad film-build range
Cathocryl®
GY21
Acrylic
All colours
up to 35 µm
15 min at 160 / 170°C
Good corrosion protection and edge protection
Glassodip®
GV87
Epoxy
Off-white
up to 15 µm
15 min at 160 / 170°C
Very good throwing power Colour Stability Low film-build possible
up to 22 µm
Nanotechnology BASF is an active part in the development of new nano-technologies, both for the treatment and the coating of surfaces. Chart 13. Anodic system BRAND
Product-line
Resin base
Colours
Film thickness
Baking conditions
Main properties
Glassophor® repair
GV88
Epoxy-ester
Clear
not applicable
15 min at 200°C
Good corrosion protection Good coverage Not sensitive to pre-treatment defects
Glassophor®
GW88
Acrylic
All colours
up to 30 µm
15 min at 170 / 180°C
UV-resistance Single layer High gloss
Glassophor® Top
GW89
Epoxy polyester
Grey, off-white
up to 30 µm
15 min at 180 / 200°C
Good adhesion to Zinc Good primer for comon decorative paint Good chemical resistances
15
3
BASF Industrial Coatings Solutions 3.1 Coatings Solutions
BASF Coatings aims at providing innovative and eco-efficient coating systems and processes that cover a wide variety of applications in industrial coating and industrial goods production.
Today it is no longer sufficient to be an expert in one paint technology because most finishing jobs require extensive expertise. This is why every time BASF Coatings develops new coating solutions it always has in mind to design total coating solutions instead of simple products. BASF Coatings is one of the few european paint suppliers with a comprehensive product portfolio comprising: Electrocoat paints Powder coatings n Liquid solvent coatings, high solid and water based n n
Tailor-made system concepts BASF Coatings combines products, for example electrocoat paints and powder coatings, to obtain intelligent solutions which we can offer our customers as eco-efficient and economically interesting coating system from one single source with extensive know-how. The competence that BASF Coatings offers in the research and development laboratories guarantees always the best results obtainable into the market. There is more to coating than just the paint To form a genuine system, paint and process must interact perfectly with each other. This means that we at BASF Coatings proactively support the development of new application technology by sharing our knowledge with machine and equipment manufacturers and by providing innovation impetus.
16
Electrodeposition
The statements in this publication are based on the present state of our technical knowledge and experience. Due to the great variety of conditions that many influence processing and application of our products, these statements do not exempt the user from making his own tests and experiments. This publication is not to be interpreted as a legally binding guarantee of specific properties or fitness for use. Any existing industrial property rights as well as pertinent laws and regulations have to be observed at the responsibility of the user.
BASF Industrial Coatings Europe Postcoatings
BASF Coatings AG
BASF Coatings S.A
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ZAO BASF
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Contact person: Luca Cerini / luca.cerini@basf.com