NL1042005B1

NL1042005B1 - Adhesion promoter for coatings on metal surfaces

Info

Publication number: NL1042005B1
Application number: NL1042005A
Authority: NL
Inventors: Maslow Alexander; Alexander Bijpost Erik
Original assignee: Holland Novochem Technical Coatings Bv
Priority date: 2016-08-03
Filing date: 2016-08-03
Publication date: 2018-02-14

Abstract

F r o m : O c t r o o i b u r e a u G r i e b l i n g T o : N L O c t r o o i C e n t r u m 0 3 / 0 8 / 2 0 1 6 1 5 : 2 4 # 8 2 0 P . 0 1 4 / 0 1 4 ABSTRACT Coating or resin compositions substantially free of bisphenol A with excellent surface adhesion comprising a compound in an effective amount of less than 10 % w/w based on the resin with the following structure: Y The adhesion promoters are preferably aldehyde condensation products of aromatic carboxylic acid, phosphonic acid, phosphinic acid, sulphonic acid or sulphinic acid or its corresponding ionic form. 1042005

Description

ref.: P 2016 NL 017 TITLE: Adhesion promoter for coatings on metal surfaces Introduction

Many metal objects are treated with a coating to establish an aesthetic effect, to maintain the original quality over a long period of time, to improve the performance and so on. Adhesion is a crucial factor for the success of the coating. Due to the complexity of the adhesion, especially on metal alloys, it appeared difficult to obtain robust adhesion promoting systems. Well known successful products are silanes, carboxylic acids, sulphonates and phosphates, in particular epoxy phosphate esters of bisphenol A (BPA) resins.

Those skilled-in-the-art are familiar with the high regulatory pressure on BPA as it is considered as an endocrinic disruptor. Consequently, BPA-containing compounds are about to be expelled from coatings coming into direct contact with food or beverages, for example in two- and three piece cans, starting from internal, but it is likely that the external coatings, including inks, will be demanded to be BPA-free as well.

New adhesion promoters for coatings to be applied for direct food contact have to meet the criteria for FDA and the European Food Safety Authority (EFSA). In addition, they have to comply with REACH and other regional registrations for chemical substances. Polymers, several naturally occurring products etc. have been exempted from REACH.

Apart from the regulatory aspects, adhesion of coatings on steel appears to be very difficult. Whereas commercially many adhesion promoters for aluminum are available, proven adhesion promoters for steel are very hard to find. Small variations in the steel composition can lead to substantially different bonding strengths, possibly resulting in loss of adhesion.

Invention

Surprisingly, Applicant found that excellent adhesion of coating compositions can be achieved upon adding a compound comprising the following structure:

X and Y can be independently selected from hydrogen, alkyl, aryl, substituted alkyls, substituted aryls, polar functional groups, such as alcohol, mercapto, nitro, amines, primary amides, secondary amides, ketones, aldehydes, epoxy phosphate esters, sulphates, carboxylic acids, phosphonic acids, phosphinic acids, sulphonic acids and sulphinic acids. One of the substituents X or Y must be a carboxylic acid, phosphonic acid, phosphinic acid, sulphonic acid and sulphinic acid or its corresponding ionic form (either metal salts or neutralized with an alkaline, such as an amino compound). The substitution on the aromatic ring can be ortho, meta or para. Higher substituted benzene molecules are also available and can meet also the criteria for adhesion promotion. W and Z can be independently selected from hydrogen, alkyl, aryl, substituted alkyls, substituted aryls, polycylic aromatics, substituted polycyclic aromatics, polar functional groups, such as alcohol, mercapto, nitro, amines, primary amides, secondary amides, ketones, aldehydes, epoxy phosphate esters, sulphates, carboxylic acids, phosphonic acids, phosphinic acids, sulphonic acids and sulphinic acids.

Next to benzene, the aromatic moiety can also be selected from naphthalene, anthracene, phenanthrene and structure homologues, possibly containing higher degree of substitution.

Typical candidates meeting these criteria are hydroxyl benzoic acids, such as salicylic acid, condensated with an aldehyde, preferably formaldehyde. These products combine the properties of both forming an ionic bonding with a metal surface, an aromatic structure for stabilization/complexation and a hydroxyl functionality to react with a cross linker, such as aminoplasts. As the molecules have a high density of active bonding sites, they show superior adhesion.

As the products according to the invention are polymers, they have been exempted from REACH regulations. Both salicylic acid and formaldehyde comply with the FDA (21CFR175.300) and EFSA (EU directive, No 10/2011) lists for direct food contact. It must be noted that formaldehyde is under suspicion, but no free formaldehyde will be present in the final cured coatings.

Coatings comprising an adhesion promoter according to the invention showed excellent adhesion in several 1K stoving coating systems, such as polyester/aminoplast, alkyd resin/aminoplast and polyol/aminoplast. The adhesion on steel was found to be surprisingly well.

Apart from the adhesion promotion, the compounds showed catalytic inhibition of the oxidative radical-induced degradation of polymers susceptible to oxy radical-induced attack/decomposition, e.g. polyethylene, polypropylene, homo-, co- and terpolymers as well as functionalized polymers. This is in line with another invention recently filed by the Applicant, showing an inhibitor to prevent oxidative radical degradation via a benzylic hydrogen abstraction mechanism, effective in an amount of less than 1% (w/w) based on the solid weight of the total polymer resin. The inhibitor comprises a conjugated benzyl moiety. The aromatic moiety can be selected from benzene, naphthalene, anthracene or phenanthrene.

Next to adhesion promotion and catalytic inhibition of radical induced degradation, several coating compositions showed high chemical and physical resistance especially towards wet adhesion.

Those skilled-in-the-art understand that the polyacidic (carboxylic, sulphonic, sulphinic, phosphonic or phosphinic) products according to the invention also may be applied in many other areas, such as stabilization of hardness in water treatment systems, corrosion inhibition of metals, concrete superplasticizer, chelating agent, wetting agent etc.

Background

Good adhesion is difficult to achieve. Adhesion is a surface phenomenon and is related to physical forces and chemical reactions/interactions at the interface. The highest molecular bonding strengths are primary bonds, wz. ionic (150-250 kcal/mole), covalent (15-170 kcal/mole) and metallic (27-83 kcal/mole). Secondary bonds, such as hydrogen bonds (<12 kcal/mole) and Van der Waals bonds (<10 kcal/mole) are much weaker.

Metal surfaces are usually alkaline in nature, especially in relation to active bonding sites, due to oxidation. Consequently, acidic products (low pKa) will show a higher reactivity on these surfaces.

One of the most powerful coating adhesion promoters to date for aluminum is an epoxy phosphate ester of bisphenol A, commercialized by DSM under the brand name Uradil DD79. Its excellent performance is assigned to the formation of strong ionic bonds (phosphate-metal), the aromatic character (stability and complexing properties) as well as the polymeric structure (introducing high molecular mass, flexibility etc.). A new adhesion promoter has to contain all these properties.

It is evident the mechanism of adhesion under wet conditions differs from dry adhesion. It must be noted that adhesion is more critical under wet conditions: Adhesion loss is very eminent under steam condition, even more under pasteurization condition, mostly under retort sterilization condition. During retort sterilization, high pressure and high temperature steam migrates through the coating, breaking the weakest bonds at the metal-polymer surface. Epoxy phosphate ester adhesion promoters show excellent adhesion up to pasteurization conditions, yet tend to loose adhesion under retort-sterilization conditions. It is obvious that a new adhesion promoter preferably remains its function under retort-sterilization.

Recently, Applicant has reported excellent performance of coating compositions, comprising alkylated polyamine and a substituted phenol, preferably salicylic acid (WO2012/177121 and WO2012/177122). The special characteristics in terms of stability and performance are attributed by the chemical structure of salicylic acid, wherein intramolecular exchange of protons can take place in a six membered ring structure. The dry adhesion properties of these compositions were found to be excellent. However, adhesion failure has been observed under wet conditions.

Salicylic acid can be condensated with formaldehyde in different molar ratios to form polymers in a very straightforward process (US 4,245,083). The resulting products have been claimed to be suitable as fixing agent for dye stuffs in paper printing. These compounds as well as many similar products have been extensively studied, but have never been recognized nor reported as adhesion promoters.

Condensation products of formaldehyde and phenol sulphonic acids have been reported as well, e.g. US 4,457,874. These compounds can be applied as dispersing agent in hydraulic cement, mortar, concrete or the like. Formaldehyde condensates of naphthalene sulphonic acids are widely applied as wetting and dispersing agent.

Phenol condensates with aldehydes have been extensively described in the literature e.g. US 4,026,867. The resulting products are generally known as phenoplasts. In principle, each phenolic compound can be polymerized in the presence of a proper aldehyde.

Typical starting molecules which meet the criteria for adhesion promotion are salicylic acid, 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, resorcylic acids (dihydroxy benzoic acids), gallic acid (trihydroxy benzoic acid), hydroxyl phthalic acids, dihydroxyl dicarboxylic benzenes, cashew nut shell liquid, aminobenzoic acid, lignosulphonates, phenol sulphonic acid, 4-hydroxyl sulphonic acid, 4-hydroxybenzylphosphonic acid, or mixtures thereof.

Apart from formaldehyde, also other aldehydes can be applied to obtain condensation products according to the invention, e.g. glyoxal (US 6,379,800), propionaldehyde (4,154,769), butyraldehyde (US 2,176,951) or furfural (US 2,745,816). Sometimes mixtures of aldehydes have been applied as well.

It is obvious for those skilled-in-the-art that upon varying the aromatic compounds and/or the aldehydes a wide range of molecules can be prepared, capable of promoting adhesion. The molecular weight and the amount of active bonding sites present can be also tuned by adjusting the reaction conditions, monomers or monomer mixtures selection, and molar ratios.

Examples

Formaldehyde salicylic acid condensation products have been synthesized according to the procedure described in US 4,245,083. After reaction, the polymer has been dissolved in butylglycol and neutralized with dimethylaminoethanol and diluted with water.

The formaldehyde salicylic acid condensate has been admixed (5% as solid on total amount of resin) with standard thermal curable coating system and tested on both aluminum and steel panels. The standard coating system contains: 10.0 g Cymel 3745, 1.0 g 1,6-hexanediol, 3.0 g butylglycol, 0.14 1-butanol and 0.03 g Cycat 500. After thermal curing (200 °C, 3 minutes), cross cuts have been made in the panels and pasteurized for one hour at 90 °C. Adhesion has been tested with Scotch 3M tape (ASTM D3359).

The experiments show that the components according the invention showed excellent adhesion in various concentrations on both aluminum and steel.

Claims

A coating or resin composition that is substantially free of bisphenol A with excellent surface adhesion, comprising a compound in an effective amount of less than 10% w / w based on the resin, having the following structure:

X and Y may be independently selected from hydrogen, alkyl, aryl, substituted alkyl groups, substituted aryl groups, polar functional groups such as alcohol, mercapto, amines, amides, ketones, aldehydes, carboxylic acids, phosphonic acids, phosphinic acids, sulfonic acids, and sulfinic acids. W and Z can be independently selected from hydrogen, alkyl, aryl, substituted alkyl groups, substituted aryl groups, polycyllic aromatic groups, substituted polycyclic aromatic groups, polar functional groups such as alcohol, amines, ketones, aldehydes, carboxylic acids, phosphonic acids, phosphinic acids, sulfonic acids and sulfinic acids.

The composition of claim 1, wherein the aromatic group is selected from benzene, naphthalene, anthracene, phenanthrene, or structural homologues, which may contain higher degrees of substitution.

A composition according to claim 1 or 2, wherein one of the substituents X or Y is a carboxylic acid, hydroxyl group, phosphonic acid, phosphinic acid, sulfonic acid and sulfinic acid or the corresponding ionic form thereof (either metal salts or neutralized with an alkali, such as an amino compound) .

A composition according to any one of claims 1-3, wherein one of the substituents X or Y is a hydroxyl group or carboxylic acid or the corresponding ionic form thereof.

A composition according to any one of claims 1-4, wherein one of the substituents X or Y is a carboxylic acid or the corresponding ionic form thereof.

The composition of any one of claims 1-5, wherein the aromatic groups are coupled via aldehyde condensation.

The composition of any one of claims 1-6, wherein the aldehyde is selected from formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, glyoxal or furfural.

A composition according to any one of claims 1-7, wherein the aldehyde is condensed with a hydroxyl benzoic acid, dihydroxyl benzoic acid, trihydroxyl benzoic acid, hydroxyl dicarboxyl benzene or dihydroxyl dicarboxyl benzene.

The composition of any one of claims 1-8, wherein the hydroxy benzoic acid is salicylic acid.

The composition according to any one of claims 1 to 9, wherein the starting materials comply with FDA (21CFR175.300) and EFSA (EU directive no. 10/2011) arrangements for direct contact with food.

The composition of any one of claims 1 to 10, wherein the adhesion promoter is mixed with a resin system, preferably polyester / aminoplast resin, polyol / aminoplast resin, polyacrylate / aminoplast or alkyd resin / aminoplast.

The composition of any one of claims 1 to 11, wherein the resin blend further comprises pigments, dyes, fillers, waxes, solvents, neutralizers, stabilizers, flow additives, slip additives, rheology enhancers, or mixtures thereof.

The composition of any one of claims 1 to 12, wherein the treated surface is a metal, preferably aluminum or steel.

A method for obtaining a coating with excellent wet adhesion properties for a wide range of surfaces, such as aluminum and steel, by applying a composition according to one or more of claims 1-13, wherein curing takes place between 0 and 300 ° C , preferably between 50 and 250 ° C and even more preferably between 140 and 220 ° C.