Original article date: May 19, 2016
Updated November 2022
Since this article was written in 2016, I have received almost 30 requests for information. I will address this later in the article, but other than defoamers, this is the most widely requested topic for information that I have written, and one that I decided to update.
Adhesion promoters (AP), are bi-functional materials that increase adhesive strength between the coating and the substrate, and sometimes are referred to as “coupling agents”. Unlike priming systems, adhesion promoters are largely applied at thinner film thicknesses and are generally thought more of as a surface treatment than an actual coating. An adhesion promoter’s effectiveness depends on both the substrate and the adhesive being used. Surface pretreatments, such as solvent cleaning or mechanical etching and corona treatment, can be used with adhesion promoters as part of a pretreatment method.
Within a class of materials, the functionality on the backbone of the molecule will vary based on the resin system employed as well as the substrate to which it is attached. Organic and inorganic materials are very different in many ways, for example, compatibility, chemical reactivity, surface properties, and coefficient of thermal expansion, such that forming a strong adhesive bond between these two dissimilar materials is difficult. An adhesion promoter, in its optimal sense, will act effectively at the organic-inorganic interface to chemically and physically wed these dissimilar materials into a strong cohesive bond structure.
Adhesion is one of the most important properties of both decorative and protective coatings. Many of the additives used in coating formulations can have a negative impact on the overall adhesion behavior, even on surfaces that would not be considered difficult for adhesion. As in most coatings formulations, there are a variety of materials used for different performance parameters or applications, etc. Avoidance of deleterious additives is preferred, but at times their need to impart other properties to the coating is required.
Before discussing the classes of adhesion promoters, a word about their use. There are literally hundreds of materials that are used for this application. It would be nice if there was a guide that would automatically tell you how to achieve perfect adhesion under whatever conditions the coating will be used. Unfortunately, that is not the case. Use of selection guides, such as with UL Prospector, will provide some guidance to what will work. In the brief writing of the material, it is generally indicated what substrate is appropriate with which AP. At the end of this article are several links to companies’ adhesion promoters. There are more, and I am not saying these are particularly the best, but just examples. Do not be afraid to contact the companies and ask them for help. They will have evaluated the type of substrate and type of coating and may have some recommendations for you to try. Generally speaking, it is necessary to test them under all that conditions and not take the word of the supplier. Very slight differences in formulation of either substrate or topcoat can affect the performance.
Titanates and zirconates
Titanates and zirconates are coupling agents and adhesion promoters that increase impact strength and chemical resistance, and enhance physical, compounding, and application properties. Common applications include polymers in industrial coatings, silicone and rubber sealants, adhesives, surface primers, oil and gas, electronics, printing, ceramics, glass, catalysts in esterifications and transesterification. Zircoaluminates are manufactured by several suppliers, such as Manchem and Solvay.
I. Monomeric phosphate chemistries and Phosphate esters
Monomeric phosphates are materials used in free radical emulsion polymerization, that provide wet adhesion bonding to the substrate. The phosphorus-containing functional groups can be incorporated into the polymers during the polymerization; usually through delayed addition from the start of the polymerization. When these resins are used in coatings or adhesives, the adhesion and anticorrosion performance of the final products are significantly improved.
Several companies, such as LANXESS, Solvay, Eastman and Dow, produce phosphate ester surfactants and phosphate acids precursors to the esters. These have been found to benefit adhesion as well as improve corrosion inhibition of coatings over ferrous surfaces.
II. Silanes
Silanes are effective AP’s for glass and silica-containing materials. Hence, they are used widely for Ultrahydrophobic treatments that rely on a system package of a silanol and silica, with silane adhesion used in epoxy, urethane and acrylic systems. One of the concepts used to obtain excellent adhesion is to assure that covalent bonds are formed between the substrate and the coating. This concept is called coupling or chemisorption. Silanes can be used as additives to couple substrates that contain hydroxyl (-OH) groups, like metals, and coatings. Apart from an alkoxy (-OR) group, that forms a covalent bond with the metal surface, the silane additive contains a chemical group that can crosslink with the binder system of the coating during film formation.
The effectiveness of silanes depends on the substrate being used; smooth, high-surface-energy substrates are better than low-surface-energy or discontinuous substrates.
III. Oligomeric Silanesi
The first generation coupling agents, that are still used to improve adhesion, are mono-functional. These mono-functional silane adhesion promoters are more and more substituted by oligomers.
The oligomer molecules have a moderately high molecular weight and multiple functionality in both types of reactive groups:
-
- Methoxy (-O-CH3) groups, directly linked to silicon (Si) atoms, that form a covalent bond with the hydroxyl (-OH) groups of the metal substrate.
- Epoxy groups that co-crosslink with the binder system during film formation.
The core of the additive is formed by a strong siloxane network that has excellent resistance against, for example, hydrolysis, chemicals and UV radiation. Despite the increased molecular weight, compared to mono-functional silanes, the oligomer has a low viscosity and broad compatibility.
IV. Chlorinated and Non-Chlorinated Polyolefin Chemistries
For plastic adhesion, some chlorinated polyolefin (CPO) chemistries are effective in the improvement in adhesion of coatings to thermoplastic olefin (TPO). This is particularly important in automotive coatings, as an increasing amount of the external portion of the vehicle is composed of plastics.
There are also non-chlorinated adhesion promoters that provide excellent adhesion to TPO and polypropylene substrates.
[1] Mittal, KL, Advances in Contact Angle, Wettability and Adhesion, Volume One, July 2013
Manchem Zircoaluminates | Adhesion Promoter
AdhesionPromoterGuide_1.pdf.aspx (ppgaerospace.com)
Adhesion Promoters – Lubrizol
Auto Primers Adhesion Promoter Product Page (rustoleum.com)
Adhesion promoters – Atotech
Adhesion Promoters | Product Types | Eastman
DOWSIL™ P5200 Adhesion Promoter
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hi, my work content is about the powder coating.i am very interested in Zircoaluminates . the good performance of the adhesive additive in pipline industry is critical factor.so i want to the address to apply that.
if someone knows ,i really appriciate the email from you.
I would start with Manchem zircoaluminates: http://www.manchem.com/
I am interested in finding an adhesion promoting agent for aqueous based resin to a wood substrate. Hopefully this would be incorporated into the resin itself. Has anyone got any suggestions?
I doubt that a raw material supplier will respond, so I will suggest that you contact companies who supply adhesion promoters and ask them for help. The chemistry of the resin is as important as the substrate and aqueous vs solvent (or solvent-free).
Aderência:
Para obter um desempenho satisfatório, o revestimento deve aderir aos substratos sobre os quais são aplicados. Na prática, são usados três procedimentos de testes diferentes para avaliar a resistência ou aderência de tintas e revestimentos nos substratos.
Teste de Corte Cruzado (Cross-Cut Tester) Este método de ensaio especifica um procedimento para avaliação da aderência de tintas e revestimentos pela separação dos substratos quando um padrão reticulado em ângulo reto é cortado para dentro do revestimento, penetrando através do substrato.
O método pode ser usado para um teste rápido de passa/falha. Quanto aplicado a um sistema de multi-camadas, a avaliação da aderência pode ser feita em camadas individuais.
Ensaio de Aderência Resistente a Raspagem (SCRAPER TESTER)
Este método de ensaio abrange a determinação de aderência de revestimentos orgânicos como tinta, verniz e laca quando aplicados sobre superfícies de painéis lisos e planos. Este ensaio tem sido útil no fornecimento de classificações relativas para uma série de painéis revestidos que exibem diferenças significativas em aderência.
Ensaio de Arrancamento (PUL-OFF TEST)
A aderência de um sistema de pintura de revestimento simples ou de múltiplas camadas de pintura, verniz ou produtos relacionados é avaliada pela medição da tensão de tração mínima necessária para descolar ou romper o revestimento em uma direção perpendicular ao substrato. Este método maximiza a tensão de tração quando comparado à tensão de cisalhamento aplicado por outros métodos, tais como resistência da aderência ao risco e os resultados podem não ser comparáveis.
O ensaio é executado ao prender um corpo de prova (dolly) perpendicular à superfície do revestimento com um adesivo. Após a cura do adesivo, um aparelho de ensaio é ligado ao corpo de proa e alinhado para aplicar tensão
perpendicular à superfície de teste. A força aplicada é gradualmente aumentada e monitorada até que uma placa do material do revestimento se desprenda, ou um valor determinado seja alcançado.
Translation per Google:
adhesion:
For satisfactory performance, the coating must adhere to the substrates on which they are applied. In practice, they use three different test procedures to evaluate the resistance and adhesion of paints and coatings on substrates.
Cross-cut test (cross-cut tester) This test method specifies a procedure for evaluating the adhesion of paints and coatings for the separation of the substrates when a right angle lattice pattern is cut into the coating, penetrating through the substrate.
The method can be used for a quick test pass / fail. As applied to a multi-layer system, the evaluation of adherence can be made on individual layers.
Adhesion test resistant Scraping (SCRAPER TESTER)
This test method covers the determination of adhesion of organic coatings such as paint, varnish and lacquer when applied to smooth surfaces and flat panels. This test has been useful in providing relative ratings for a series of coated panels exhibit significant differences in adhesion.
Pullout test (PUL-OFF TEST)
Adhesion of a single coat paint system or multiple layers of paint, varnish or related product is evaluated by measuring the minimum tensile strength required to peel off or break the coating in a direction perpendicular to the substrate. This method maximizes tensile stress as compared to the shear stress applied by other methods such as adhesion of the scratch resistance and the results may not be comparable.
The test is performed while holding a specimen (dolly) perpendicular to the coating surface with an adhesive. After adhesive curing a test apparatus is attached to the body of the bow and aligned to apply tension
perpendicular to the test surface. The applied force is gradually increased and monitored until a plate of the cladding material becomes detached, or a certain value is reached.
It doesn’t appear that you have a question. There are ASTM and DIN tests as well as some ISO that address the different types of test that you provided, specific to various coatings and substrates. I approved your comment, since you have provided information.
Hi.
I’m looking for an additive to a single component epoxy adhesive to enhance adhesion over corona treated polypropylene. Can you suggest any?
I have found that for water-borne filled systems (ATH, CaCO2) adhesion promoters don’t work. I have tried a variety of them, I think that the presence of the Inorganic filler mimics the surface and the promoter adheres to the fillers instead of the substrate. Has anyone had a similar experience. How do I overcome this problem?
My apologies for not having seen this for a year. I hope that you were able to find a successful solution. If not, Eastman Chemical has adhesion promoters that may be of use. The addition of an AP doesn’t always work, and sometimes a tie-coating is needed between the substrate and coating. Not a true primer in the normal sense, but it does prepare the surface for adhesion; just better than you can accomplish with corona discharge.
My guess based on those two components is that this is some sort of fire retardant coating. Regardless, adhesion promoters are surfactants as are any surface active agents. As such, they have the ability to attach to pigments, etc. So the trick is to encourage the AP to remain in the solvent portion of the coating or promote the AP to anchor. You also have to be aware of reactivities. Silanes are great adhesion promoters, but react with water and are rendered ineffective as AP.
So part of this is formulation-dependent and part is choosing the right AP for the system and substrate.
i can search those additive whisch adhesionn property is good for paint plz tell me about this?
I am not sure of your question. It appears you are asking what adhesion promoters are good for paint? The article covers many different kinds. And as I have stated, the choice of adhesion promoter is dependent on the substrate, the resin in the coating, and the other components in the coating formula.
I suggest that you search “Adhesion Promoters” https://www.ulprospector.com/en/na/Coatings/search?k=adhesion+promoters&st=1 , collect the names of the suppliers, determine which supply your geography, and contact them to recommend one(s) for your specific system. Just realize that you will have to provide them with a bit of information. The more you provide, the better job they can do to recommend something to you, how to use it in your system (incorporate it), etc.
If I did not answer your question, please re-post in your native language and also post with whatever Google provides as translation for that language.
We have a 200 year old church the has a very bad peeling of paint. The church has been painted several times by professionals and yet peeling of paint begins just 3-4 years after painting. the siding material is shiplap wood siding (very old). Is there new technology that would help paint adhere to this historic structure?
This is a case where the paint won’t adhere to the substrate. I will assume that it is wood and the wood has a glaze on it. I will also assume that the paint is many mils thick.
To get a good finish you will need to strip the paint down to the substrate and rough in the substrate, preferably with a power-washer.
I WANT TO MAKE A SOLVENT BASED ADHESIVE INCREASE PRIMER BEHIND THE PVC EDGE BAND USED IN THE FURNITURE SECTOR.
You really haven’t posed the question. If you’re looking to formulate something specific, you can contact me directly or talk to an adhesive consultant. I don’t think what you’re asking is directly available through Prospector
Do you have specific adhesion promoter chemistry recommendation for polyester substrates?
Hi Marc,
We have identified a product called “Bl;ack 3.0”. It is an acrylic water based paint the exhibits less than 1% reflectivity. Our industrial application of this paint to metal substrates will require finding an adhesion promoter that can be laid down in a very thin layer. We hope to keep the total paint and promoter thickness below 10 microns!
Do you have any idea where we should start looking?
Regards,
Dennis
Hi Marc,
We have identified a product called “Black 3.0”. It is an acrylic water based paint the exhibits less than 1% reflectivity. Our industrial application of this paint to metal substrates will require finding an adhesion promoter that can be laid down in a very thin layer. We hope to keep the total paint and promoter thickness below 10 microns!
Do you have any idea where we should start looking?
Regards,
Dennis
I’m sorry. I was not aware that there was a question posed on the site. It depends on what you would like to use and what kind of paint will be applied to the polyester. It really is a matter of the crystallinity of the polyester
According to their website, their Black 2.0 would be their choice of primer. It may be a way for them to have more business and not have someone else’s adhesion promoter. Since you want very thin thicknesses, I suggest you look at the silanes as a whole, and TEOS specifically. I’m not sure that you’re going to have success at that film thickness. Part of the Black 3.0 works on light reflection/refraction/absorption. In a particularly thin film I’m not sure you will achieve that. But you can try
Hi there! Do you know what adhesive shoe manufacturers use to adhere glitter to fabric/leather? Something that’s a strong hold, yet flexible? TIA
Hi, Erika:
There are many adhesives that work acceptably, so it is best to work with the manufacturers of the adhesives to get their recommendations. It also depends on where you are located and what manufacturers are available.
Thanks for reading!
Marc
Can you suggest adhesion promotors for Non Treated Polypropylene for polyamide based surface printing inks. It should pass tape test.
Silanes, Tyzor® Organic Titanates and Zirconates, Zircoaluminates. Eastman sells 550-1 and 510W.Unfortunately with the adhesion promoters no one can say for sure what will work until you actually try it in the laboratory.
Hello.
Thank you for putting out this quality information, and also for taking time to answer questions.
Please, can you recommend for me material to use to adhere a kaolin substrate and graphene oxide together? I’m making a filtration membrane.
Unless you treat one material or the other with an adhesion promoter, they won’t stick. Your best bet for something like this is to contact the companies that make adhesion promoters since they have assuredly had instances where other people may have requested the materials in question.
We are looking Additive to adhere the paint (Automotive paint) over PVC based sealer (thermosetting coating) after run high pressure wash system(1025psi) at 60C Water temperature,
could you please suggest any Additive will enhance the paint adhesion?
The article is designed to give you an explanation of what adhesion promoters are. No one person is an expert on every type of promoter. I think there been almost 30 questions similar to yours in the past six years. I know you don’t want to hear this, but it would be best if you were to contact any or some of the companies that make AP, and you can screen some yourself by looking at their explanation of the materials.
Nice article that touches all the bases. Glad to see you’re still active in the industry.
Is there any particular AP for PVC if my material is based on saturated polyester + catalyst (2K)
It would be nice if there were a simple answer. It depends on both of the materials. PVC can have slightly different compositions, and the polyester and catalyst is dependent as well. You probably are best served by contacting several adhesion promoter companies and they may test applications for you and not just suggest something. Residual exuding material, etc. all makes a difference. It also depends on what type of adhesion that is required. Something as simple as a tape test, or as complex as actual use.
Is there any adhesion promoter chemistry that improves scrub resistance in architectural coatings without any contribution in VOC?
I don’t know that anyone has looked at adhesion promoters to improve scrub resistance. Generally, you balance the pigments as well as a resin type. Typically, smaller particle latexes perform better in the use of hydrophobic monomers helps as well in addition to minimizing the water soluble fraction which can be your surfactants etc. There are many formulas prescribed resistance and some suppliers still maintain data that has ladders of pigment etc. I would start there
Hi
I am planning to create a very strong structural bond between the steel and the polyurethane with the help of adhesive promoters(AP), I have already found a special primer for this job (PU to Metal Bonding) but I don’t know if this primer contains AP or not. ? If the answer is negative, I will apply it separately in the bonding process. Would it please me if I could get your opinion on this?
Most primers have some sort of adhesion promotion system but may not necessarily be a silane or a zircoaluminate or other. If you have good adhesion that meets the requirements of what you want without adding anything, I would just do that. You are suggesting adhesion promotion as a separate step and in this case you could also check to see if it is compatible with the primer over a period of time. I would suggest testing the stability such as viscosity increase as well as gellation.
Thank you for your answer. I agree with you because I have achieved sufficient bond strength without using AP, but my main purpose for using AP in the PU to Metal bonding is to increase the durability of the joint because I want to make a joint that will last about 50 years.
Will using the AP help me in this regard?
I don’t know of any accelerated tests that will guarantee 50 years adhesion for your product. In general, I would not want to guarantee that. But if you write your claims correctly, you can probably indicate you will supply product if there is failure and that’s about it. I think that is what most other people do for long durability products.
You are getting into the legal area and play from performance