GB1558555A

GB1558555A - Binders

Info

Publication number: GB1558555A
Application number: GB17032/78A
Authority: GB
Original assignee: Vianova Resins AG
Current assignee: Allnex Austria GmbH
Priority date: 1977-04-28
Filing date: 1978-04-28
Publication date: 1980-01-03
Also published as: DE2815823A1; AT348637B; IT1094538B; IT7822708A0; JPS53134897A; ATA298777A; FR2388840A1; ES469161A1; DE2815823B2

Description

(54) IMPROVEMENTS IN OR RELATING TO BINDERS (71) We, VIANOVA KUNSTHARZ AKTIENGESSELSCHAFT an Austrian Body Corporate of Altmannsdorferstrasse 104. A-1120 Vienna, Austria, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly describd in and by the following statement: This invention is concerned with improvements in or relating to the preparation of binders which may be used in the formulation of paints which deposit at the cathode when subjected to a process of electrodeposition.

In recent years a considerable research effort in the surface coatings industry has been devoted to the examination of water-soluble polymers in which the part of the inonizable group which is attached to the polymer is basic. Such polymers, in general, have basic nitrogen atoms attached to the backbone chain and are neutralised by means of low molecular weight acids.

When such polymers have been employed as binders in paints for application by electrodeposition it has been found that, while the resulting coated products possess generally good corrosion resistance they do, nevertheless, have attendant disadvantages. In use such polymers result in the liberation of free low molecular weight acids at the anode.

These acids are formed by the donation of protons to acidic ions at the anode. Moreover, traces of neutralised paint binder may be occluded in cavities of irregularly or complex shaped objects despite the usual rinsing operations and, on baking, such traces may liberate free acid.

Free acid liberated in this way can be harmful for several reasons. Thus their corrosive effect and the vapours that they give off are harmful to the painting and baking installations and their toxicity and irritant effect on the respiratory system are particularly disadvantageous.

In German Offenlegungsschrift 24 60 470 there is described a method of neutralising cathodic polymers with carbonic acid. The basic groups of the binder (in the form of tertiary amines) are protonised by a carbon dioxide sparge or by means of dry ice to yield an aqueous solution or dispersion. However the use of dry ice in the neutralisation process is not very practicable commercially and, in any event, the degree of dissociation of carbon dioxide is, in general, not sufficient to give a binder suitable for subsequent processing. The dispersions formed separate out after little more than 10 minutes of standing which, in our experience, is inadequate for practical purposes.

In US Patent Specification No. 3,962.165 there are described resin compositions which include quarternary ammonium salts formed by reaction of amine salts with polyglycidylethers of phenols and which are depositable at the cathode. The acids used for neutralisation have a dissociation constant of more than 1 x 10-5 and those listed are ones which give rise to the difficulties discussed above.

It is also known to form amine salts of carbon dioxide but these are only stable for a short time and decompose to their starting materials, particularly at elevated temperature.

Surprisingly, we have now discovered a way in which such-amine carbonates can be used in the preparation of water-soluble cationic binders. Since amines are weak bases and carbon dioxide is a weak acid, amine carbonates are relatively unstable compounds, especially at elevated temperature. Nevertheless we have found that such amine carbonates can be reacted with macromolecules possessing oxirane groups to form a product that is water-soluble without the need for any further neutralisation. In such a reaction there are formed quarternary ammonium carbonates which are attached to the macromolecule.

According to the present invention therefore there is provided a process for the preparation of a water-soluble cationic binder which comprises reacting a macromolecule having an average molecular weight of at least 300 and possessing at least one oxirane groups with an amine salt in amounts such that from 0.1 to 1 mole of amine nitrogen is employed per oxirane group wherein the amine salt is a carbonate or hydrogen carbonate of a tertiary aliphatic, cycloaliphatic or alkanoamine.

In the process according to the invention one is able to employ carbon dioxide as a neutralising agent and thereby secure the favourable properties regarding corrosion and environmental protection while the quarternisation considerably enhances the basicity of the nitrogen atoms which, in turn, results in the formation of stable carbon dioxide salts and stable solutions of the macromolecules in the aqueous medium. The advantages of using carbon dioxide as neutralising agent are realised to the full in the process of the invention.

Thus, excess neutralising agent may be discharged as gaseous carbon dioxide thereby preventing enrichment in the bath or a change in the parameters (for example the pH) of the paint bath. Hitherto it has been necessary to separate the anode and cathode sections of the bath by membranes but such separation may be omitted when using binders prepared by the process according to the invention.

During deposition the neutralising agent (CO.) is set free in gaseous form in the stoichiometric amounts to the binder coagulated in its basic form on to the object. The bath is therefore depleted of both of them (gaseous CO. and deposited solid material) to equal extents. Coating composition in the paint bath can be replenished as required with material fully neutralised with carbonic acid. The excellent solubility of the binder gives rise to a number of technical advantages. Morewover, when the paint that has not been rinsed off decomposes on curing, only carbonic acid evaporates off into the atmosphere.

Suitable amines for use in the formation of amine salts which may be employed in the process according to the invention include triethylamine, tripropylamine, tributylamine, N,N-diethylmethylamine, N,N-diethylbutylamine and N,N-diethylcyclohexylamine. Suitable akanol amines are N,N-dimethylethanolamine, N,N-diethylethanolamine, Nmethyldiethanolamine, triethanolamine, triisopropanolamine and Nhydroxyethylmorpholine. The amine is preferably a tertiary aliphatic or cycloaliphatic amine with alkanol groups.

The structural formula of the preferred film forming organic macromolecule possessing at least one oxirane group may be represented as follows:-

in which Y represents the bulk of the film forming macromolecular substance and R is hydrogen. an alkyl group or a macromolecular moiety Y. The average molecular weight of these film forming macro-molecules is at least 3()(i.

Suitable macromolecules for use in the process of the present invention are polyglycidyl ethers of polyphenols preferably bisphenol A, polyglycidylethers of novolak type linked phenols, and polyglycidylethers of polyphenols which, additionally. carry oxyalkylene groups and which are formed by reaction of alcohols carrying ether-type linked oxygen. for example ethylene glycol monoethylether, with epoxy groups, with catalytic action of tertiary emines.

Other useful macromolecules are copolymers carrying oxirane groups based on acrylic compounds, epoxidised natural oils and epoxidised diene oligomers.

The amine salts employed in the process according to the present invention may be prepared by contacting carbon dioxide. preferably under pressure, with a solution which contains per mole of amine nitrogen at least 1 mole of water. The following reaction equations apply: NR + H2O + CO2 - > NR:,H + CHQ 2NR3 + H2O + CO2 < (NRAH)2+ (CO.)- where R is alkyl. cycloalkyl or hvdroxvalkvl.

It is desirable to react the amine salts with the oxirane-group containing macromolecule immediately after the salt has been formed since its readiness to react tends to diminish on prolonged storage. This is presumably due to the instabilitv discussed above.

The ratios of the reaction components in the reaction of the amine salt with the macromolecule can be chosen from within a wide range. Normally, 1 mole of epoxy group is reacted with from 0.1 to 1.0 moles of amine nitrogen in the form of its amine salt. A preferred ratio is from 0.2 to 0.6 moles of amine salt per mole of epoxy group. The reaction is preferably effected at a temperature of from 20 to 100"C. The reaction may be carried out in the presence of inert solvents or in the absence of solvents. Frequently an exothermic reaction is observed and in some cases the reaction may with advantage be performed in a carbon dioxide atmosphere, particularly if elevated pressures are to be applied.

Since, with the preferred ratios for reaction between the amine salt and the other epoxy groups, not all oxirane groups are consumed, the remaining oxirane groups may be reacted with other components. For instance the oxirane groups may be reacted with aliphatic, cycloaliphatic or aromatic carboxylic acids such as octane or nonane carboxylic acid and isomers thereof; acrylic acid; methacrylic acid; itaconic acid; crotonic acid; sorbic acid; unsaturated oil fatty acids such as linseed oil fatty acid, soya oil fatty acid, dehydrated castor oil fatty acid, tall oil fatty acids and abietic acid; primaric acid; benzoic acid and p-t-butyl benzoic acid as well as semiesters of unsaturated dicarboxylic acids such as maleic acid. By using such compounds the degree of crosslinking and flexibility of the film may be enhanced. Small quantities of dicarboxylic acids may be coemployed to synthesize binders with high molecular weight. Adipic acid is quite suitable for this purpose.

The carboxylic acid and the oxirane groups may conveniently be reacted at 80 to 1500C, preferably with the catalytic action of bases and optionally in the presence of phenolic polymerisation inhibitors. In general an acid value of the reaction product of below 5 mg KOH/g is aimed at.

If desired a proportion of the oxirane groups may be reacted with the carboxylic acid prior to the reaction with the amine salt. This method is of advantage if temperatures of more then 90"C are to be used in the esterification.

With all reactions in which oxirane groups are opened, products carrying hydroxy groups result. These hydroxy groups may be reacted in various different ways so as to enhance the properties of the binder or the degree of crosslinking of coating compositions prepared therefrom. Such a reaction is for instance the reaction with unsaturated monoisocyanates or diisocyanates. Moreover, the products may be combined with phenol formaldehyde condensates to give certain properties. Preferred such condensates are resols of substituted phenols.

Coatings with particularly good corrosion resistance are obtained with a composition which besides the binder contains from 10 to 30% of a trishydroxymethylphenolallylether.

This and similar water-insoluble phenolic resins are best combined with the water dilutable binder carrying quarternary ammonium carbonate groups by partial condensation at 50 to 100"C. In order to obtain infinite solubility in water, in general a condensation time of from 0.5 to 5 hours is necessary.

We have found that the crosslinking capacity of basic binders is considerably enhanced by the presence of small quantities of acidic groups. Such groups preferably are carboxyl groups (-COOH) or sulfonic acid groups (-SO3H). The desired carboxy groups may be added in the form of polycarboxylic acid resins or advantageously, in the form of a resin-like zwitter ion. Such zwitter ions can be prepared from adducts of maleic anhydride to vegetable oils or synthetic polybutadiene oils which subsequently may be reacted with a primary-tertiary amine in varying proportions.

The binder, optionally in conjunction with phenolic resins and/or resin-like zwitter components, is used as clear coating composition or in the form of pigmented paints. The usual inorganic pigments and extenders such as iron oxides, titanium dioxide, lead silicate, carbon black, strontium chromate, aluminium silicate and talcum may be employed as well as organic pigments such as copper phthalocyanine. The coating compositions may contain further additives such as solvents, plasticisers. wetting agents, anti-foaming agents or antioxidising agents.

The following Examples illustrate the invention without limiting the scope of it. All parts and percentages are by weight.

Examples Preparation of amine carbonate A 89g of N,N-dimethylethanolamine and 18g of water are charged to an autoclave. After elimination of the air, a constant pressure of 12 atmospheres of carbon dioxide is maintained in the autoclave, with simultaneous stirring of the batch. After 2 hours the solution has gained 22g of weight. The finished amine carbonate has a syrup-like consistency.

Preparation of amine carbonate B 149g of triethanolamine and 54g of water are charged to an autoclave. After elimination of the air, a constant pressure of 12 atmospheres of carbon dioxide is maintained in the autoclave, with simultaneous stirring of the batch. After 3 hours the solution has gained 22g of weight. The finished amine carbonate has a syrup-like consistency.

Preparation of an unsaturated isocyanate (UMI) 174g of tolylene diisocyanate (isomer blend of about 80% of 2,4- and 20% of 2,6-diisocyanate), preventing access of moisture, are added dropwise over a period of 1 hour to 130g of hydroxyethylmethacrylate. The batch is then slowly heated to 700C and held at this temperature for 1 hour while stirring.

Preparation of the resin-like Zwitter ion (ZW) 400g of polybutadiene with a molecular weight of about 1400 and a microstructure of about 75% 1 ,4acids and about 25% 1,4-trans configuration are reacted at 2000C with 100g of maleic anhydride in the presence of 1.5g of a copper naphthenate solution (9%Cu) until the content of a free maleic anhydride has fallen to below 1%. The viscosity of a solution of 72g of adduct and 48g of ethylene glycol monoethylether acetate is about 70 s (DIN 53 211), the acid value is 200 mg KOH/g. At 1300C, 65g of N,N-diethylaminopropylamine are added over a period of 30 minutes and the reaction is carried on at 1800C until the total amine has reacted. After cooling to 1200C, 50g of diacetone alcohol are added. At 100"C, the esterification is carried out with 17g of methanol and 1.5g of triethylamine as catalyst, until the acid value remains constant. The batch is then diluted with 180g of ethylene glycol monoethylether to a solids content of 70%. The amine number is then about 50 mg KOH/g, the acid value 50 mg KOH/g. The batch is partially neutralised by the addition of 3.5g of lactic acid (80%) for each 100g of solids and further diluted with water to 30% resin solids.

Example I 470g of an epoxy resin based on bisphenol A with an epoxy equivalent of 425 - 525 are dissolved in 370g of ethylene glycol monoethylether acetate. At 80"C, 65g of amine carbonate A are added over a period of 30 minutes. After a further 30 minutes of reaction time at 850C the viscosity of the product has risen. A sample of the reaction mass is infinitely and clearly soluble in water.

Into an aqueous solution of the reaction mass with a solids content of about 10% and a pH-value of 8.8, a carbon anode and a steel cathode are immersed and wired to a direct current source. With a voltage of 50 Volt a film deposits on the cathode within 1 minute. It has good adhesion and can be rinsed with water. The coating cures at 200"C for 30 minutes to a film with excellent film properties. Deposition on more steel panels is repeated until the binder content of the deposition bath has fallen to 5% of solids. A new measurement of the pH-value gives an unchanged result of 8.8.

Example 2 950g of an epoxy resin based on bisphenol A with an epoxy equivalent of 900 to 1000 are dissolved in 240g of ethylene glycol monoethylether acetate. At 120cm a solution of 15g acrylic acid, 0.05g hydroquinone and 0.2g triethylamine is added. The acid value has fallen to 0.6 mg KOH/g after 3 hours of reaction time. The reaction mass is further diluted with 460g of ethylene glycol monoethylether acetate and cooled to 80 C. Over a period of 30 minutes 91g of amine carbonate A are added dropwise. After another hour at 85"C, a sample of the reaction mass is soluble in water. At 80 C, 174g ethylene glycol monoethylether acetate and 262g of unsaturated isocyanate (UMI) are added over a period of 30 minutes. The batch is reheated to 80"C and the enhancement of solubility of the total reaction mass in water is monitored. After 2 hours the product is clearly and infinitely soluble in water. The finished binder solution has a solids content of 60% and an amine number (DIN 53 176) of 47 mg KOH/g. The viscosity of a solution of 7 parts of the binder solution and 3 parts of ethylene glycol monobutylether is K (Gardner standard).

The binder solution is diluted with water to a solids content of 15%. The pH-value is 7.4.

In a manner analogous to that described in Example 1, steel panels are coated. After 30 minutes of cure at 1800C, smooth hard films with excellent quality and film thickness of 15 llm are obtained. A thus coated panel is scratch-marked with a steel needle and exposed to salt spray according to ASTM B 117-64. After 240 hours of exposure the rust has migrated about 1.5 mm under each side along the incision.

Example 3 480g of an epoxy resin based on bisphenol A with an epoxy equivalent of 425 to 525, 56g of dehydrated castor oil fatty acids and 0.05g of sodium carbonate are heated to 1500C. As soon as the acid value of the product has fallen to below 3 mg KOH/g, 170g of ethylene glycol monoethylether are added and the batch is cooled to 95"C. 155g of amine carbonate B are added over a period of 30 minutes; after another 30 minutes at 100"C an infinitely and clearly water soluble resin is obtained. At 80"C. 120g of a commercially available trishydroxymethylphenol allyl ether are added and a temperature of 80"C is maintained for a further 3 hours. During this period the water-solubility of the reaction product continuously improves to give a nearly clear solution. The resin is cooled to 50C and blended with 250g of a 30% solution of the resin-like zwitter ion (ZW). The finished binder has a solids content of about 70%.

145g of this binder are passed over a triple roll mill with 12g aluminium silicate pigment and 3g red iron oxide. The paste is blended in increments with 500g of water with intense stirring and is homogenized for 24 hours by stirring at about 20"C. The pH-value of the solution is 6.9.

In a manner analogous to that described in Example 1 steel panels as cathode are coated at a voltage of 150 Volt and rinsed with water then cured for 30 minutes at 1900C. The obtained coatings are flat and brown, smooth, hard and flexible and have a thickness of about 181rum. A thus coated panel is scratched with a steel needle and is sprayed with a salt solution according to ASTM-B 117-64. After 240 hours of testing the scratch is undermined at both sides with about 1 mm of rust.

Further steel panel cathodes are coated in the paint bath until the solids content of the batch has fallen from the original level of 17% to 12%. The obtained coatings show no change in appearance. At the end of the test the pH-value is measured and recorded as 6.8.

WHAT WE CLAIM IS: 1. A process for the preparation of a water-soluble cationic binder which comprises reacting a macromolecule having an average molecular weight of at least 300 and possessing at least one oxirane group with an amine salt in amounts such that from 0.1 to 1 mole of amine nitrogen is employed per oxirane group wherein the amine salt is a carbonate or hydrogen carbonate of a tertiary aliphatic, cycloaliphatic or alkanolamine.

2. A process as claimed in claim 1 wherein the reaction components are present in amounts such that from 0.2 to 0.6 moles of amine nitrogen is employed per oxirane group.

3. A process as claimed in claim 1 or claim 2 wherein the reaction is effected at a temperature of from 20 to IOO"C.

4. A process as claimed in any of the preceding claims wherein a proportion of the oxirane group(s) of the macromolecule are reacted with an oxirane reactive compound prior to reaction with the amine salt.

5. A process as claimed in any of the preceding claims wherein any oxirane group(s) remaining free after reaction with the amine salt are reacted with an oxirane reactive compound.

6. A process as claimed in claim 4 or claim 5 wherein the oxirane reactive compound is a carboxylic acid.

7. A process as claimed in any of the preceding claims wherein any hydroxy groups of the macromolecule are reacted with a hydroxy reactive compound prior to or after reaction with the amine salt.

8. A process as claimed in claim 7 wherein the hydroxy reactive compound is a mono-or diisocyanate.

9. A process as claimed in claim 1 substantially as described herein.

10. A process as claimed in claim 1 substantially as described herein with reference to the Examples.

11. A water-soluble cationic binder whenever prepared by a process as claimed in any of the preceding claims.

12. A binder as claimed in claim 11 in physical admixture or chemically combined with a phenol-formaldehyde condensate.

13. A binder as claimed in claim 11 or claim 12 in physical admixture or chemically combined with minor amounts of a film-forming macromolecule containing basic nitrogen groups and/or carboxy groups.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. continuously improves to give a nearly clear solution. The resin is cooled to 50C and blended with 250g of a 30% solution of the resin-like zwitter ion (ZW). The finished binder has a solids content of about 70%. 145g of this binder are passed over a triple roll mill with 12g aluminium silicate pigment and 3g red iron oxide. The paste is blended in increments with 500g of water with intense stirring and is homogenized for 24 hours by stirring at about 20"C. The pH-value of the solution is 6.9. In a manner analogous to that described in Example 1 steel panels as cathode are coated at a voltage of 150 Volt and rinsed with water then cured for 30 minutes at 1900C. The obtained coatings are flat and brown, smooth, hard and flexible and have a thickness of about 181rum. A thus coated panel is scratched with a steel needle and is sprayed with a salt solution according to ASTM-B 117-64. After 240 hours of testing the scratch is undermined at both sides with about 1 mm of rust. Further steel panel cathodes are coated in the paint bath until the solids content of the batch has fallen from the original level of 17% to 12%. The obtained coatings show no change in appearance. At the end of the test the pH-value is measured and recorded as 6.8. WHAT WE CLAIM IS:

1. A process for the preparation of a water-soluble cationic binder which comprises reacting a macromolecule having an average molecular weight of at least 300 and possessing at least one oxirane group with an amine salt in amounts such that from 0.1 to 1 mole of amine nitrogen is employed per oxirane group wherein the amine salt is a carbonate or hydrogen carbonate of a tertiary aliphatic, cycloaliphatic or alkanolamine.

9. A process as claimed in claim 1 substantially as described herein.