WO2017048169A1

WO2017048169A1 - Process for producing a water dispersible, air drying coating binder

Info

Publication number: WO2017048169A1
Application number: PCT/SE2016/000046
Authority: WO
Inventors: Ramakrishnan Subramanian; Bhushan SAINDANE; Saurabh KUSURKAR; Kent Sorensen
Original assignee: Perstorp Ab
Priority date: 2015-09-17
Filing date: 2016-09-07
Publication date: 2017-03-23

Abstract

The present invention refers to a process for producing a water dispersible, air drying coating binder comprising the following steps: a) producing an alkyd by reacting at least one unsaturated fatty acid and/or at least one corresponding triglyceride, at least one polyol and at least one polycarboxylic acid b) reacting the product obtained in a) by adding at least one hydroxyfunctional carboxylic acid and at least one polyisocyanate to produce a polyurethane c) chain extending the polyurethane obtained in b) by adding at least one polyol The present invention also refers to a coating composition produced by neutralising the acid groups of a coating binder produced by said process and dispersing said neutralised coating binder in water.

Description

Process for producing a water dispersible, air drying coating binder

FIELD OF THE INVENTION

The present invention refers to a process for producing a water dispersible, air drying coating binder comprising the following steps: a) producing an alkyd by reacting at least one unsaturated fatty acid and/or at least one corresponding triglyceride, at least one polyol and at least one polycarboxylic acid b) reacting the product obtained in a) by adding at least one hydroxyfunctional

carboxylic acid and at least one polyisocyanate to produce a polyurethane

c) chain extending the polyurethane obtained in b) by adding at least one polyol.

The present invention also refers to a coating composition produced by neutralising the acid groups of a coating binder produced by said process and dispersing said neutralised coating binder in water.

BACKGROUND OF THE INVENTION

Polyurethanes are a very broad group of polymers differing widely in composition and properties. These compounds are characterised by having urethane groups -NH-CO-O- formed by polyaddition of hydroxyfunctional compounds, typically diols, triols or polyols, to the -NCO groups of di-, tri-, or polyfunctional isocyanates.

Owing to the strong demands for low-pollution chemical industry, organic solvent-based polyurethanes are increasingly being restricted. The consciousness toward environmental care and the efforts of governmental organizations are limiting the amount of volatile organic compounds (VOCs) released in the atmosphere, forcing the development of new

environmentally friendly water-based products. Coatings with no or limited amount of solvent are needed, also for improving the working environment for painters. Aqueous dispersions of polyurethanes are well known in production of coating compositions. They may be used for protective or decorative coating, optionally in combination with additives like dyes, pigments, matting agents and the like. Polyurethanes exhibit many desirable properties, such as good chemical resistance, water resistance, solvent resistance, toughness, abrasion resistance and durability.

Air drying polyurethane dispersions are typically prepared using autoxidatively drying alkyd resins having terminal hydroxyl groups being reactive toward polyisocyanates. Alkyd resins are polyesters which have been modified by the addition of for instance fatty acids and/or corresponding triglycerides. The term "alkyd" or "alkyd resin" was coined to define the reaction product of polyalcohols and polycarboxylic acids, in other words, polyesters.

However, its definition has been narrowed to include only those polyesters comprising, in addition to polyalcohols and polycarboxylic acids, monobasic acids, usually long-chain fatty acids, or corresponding triglycerides. The inclusion of the fatty acid/triglyceride confers a tendency to form flexible coatings.

Air drying polyurethane dispersions modified with fatty acids and/or corresponding triglycerides represent a synergistic combination of air drying alkyd resins and polyurethanes, thus combining the excellent property profiles of both polymer types.

Chain extension is a chemical procedure commonly used for raising the molecular weight of polymers. An increased molecular weight of the polymer will improve the mechanical properties of a coating based on that polymer.

Chain extension can for example be performed by adding an amine to the polymer. However, low molecular weight amines, such as ethylene diamine, are toxic, and some are easily absorbed through the skin. It is therefore desirable to use as little as possible of these chemicals and instead use other molecules than amines for the chain extension process. In the process according to the present invention, a polyol is used for the chain extension step.

To conclude, the present invention discloses a new process for producing a water dispersible, air drying coating binder. The coating binder disclosed is based on an alkyd which is reacted with a hydroxyfunctional carboxylic acid and a polyisocyanate to form a polyurethane and chain extended with a polyol. Disclosed is also a coating composition produced by neutralising the acid groups of a coating binder produced by the process according to the invention and dispersing said neutralised coating binder in water.

Coating compositions of the present invention have shown good hardness and very good drying properties. This, together with the dispersibility in water and the amine-free chain extension step makes coating compositions of the present invention an excellent choice for, for example, outdoor paints.

DETAILED DESCRIPTION OF THE INVENTION

In the context of the present invention, "poly" is defined as two or more. "Air drying" means autoxidatively drying in the context of the present invention.

carboxylic acid and at least one polyisocyanate to produce a polyurethane

c) chain extending the polyurethane obtained in b) by adding at least one polyol

The first step of the process according to the invention is to produce an alkyd, according to methods well known in the art. At least one unsaturated fatty acid, at least one polyol and at least one polycarboxylic acid are charged together in a suitable reaction vessel, optionally together with an azeotropic solvent, like for example xylene. The temperature is raised to about 200-260 °C and an esterification reaction takes place between the unsaturated fatty acid, the polyol and the polycarboxylic acid. Alternatively, at least one triglyceride may be transesterified with at least one polyol and thereafter esterified with at least one

polycarboxylic acid, optionally at least one polyol and optionally at least one unsaturated fatty acid. Said unsaturated fatty acid is preferably chosen from the group consisting of soybean fatty acid, linseed fatty acid, tall oil fatty acid, safflor fatty acid and/or sunflower fatty acid, but also fatty acids like for example linoleic acid, linolenic acid, palmitic acid, ricinoleic acid and/or dehydrated castor oil fatty acid can be used or, as mentioned above, a corresponding triglyceride.

Polyols used in the alkyd syntheses step include, but is not limited to, linear or branched aliphatic, cycloaliphatic or aromatic polyalcohols, polyester polyalcohols and polyether polyalcohols, such as but not limited to alkylene glycols, poly(alkylene) glycols, polycarbonate polyols, dihydroxyalkyl-l ,3-dioxanes, di(hydroxyalkyl)furans, di(hydroxyalkyl)tetrahydrofurans, 2-alkyl- 1,3 -propanediols, 2,2-dialkyl-l,3-propanediols, 2- hydroxyalkyl- 1 ,3 -propanediols, 2,2-dihydroxyalkyl- 1 ,3 -propanediols, 2-alkyl-2- hydroxyalkyl- 1,3 -propanediols, as well as polyalkoxylated, such as a polymethoxylated, polyethoxylated and/or polypropoxylated, and dimeric, trimeric and polymeric species of said polyols. Further polyols include dendritic polyester and/or polyether polyalcohols. Said polyols can suitably be exemplified by ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4- butylene glycol, 1,3-butylene glycol, neopentyl glycol, 2-butyl-2-ethyl- 1 ,3-propanediol, 5,5- dihydroxymethyl- 1 ,3 -dioxane, di(hydroxymethyl)furan, di(hydroxymethyl)tetrahydrofuran, pentaerythritol spiroglycol (2,4,8, 10-tetraoxaspiro[5.5]undecane-3,9-diethanol), isosorbide, isomannide, isoidide, glycerol, di-glycerol, trimethylolethane, trimethylolpropane, trimethylolbutane, di-trimethylolethane, di-trimethylolpropane, di-trimethylolbutane, pentarerythritol, di-pentaerythritol, tri-pentaerythritol, anhydroennea-heptitol, sorbitol, mannitol, glycerol mono(meth)allyl ether, di-glycerol di(meth)allyl ether, trimethylolethane mono(meth)allyl ether, trimethylolpropane mono(meth)allyl ether, trimethylolbutane mono(meth)allyl ether, pentaerythritol mono(meth)allyl ether, pentaerythritol di(meth)allyl ether, di-trimethylolethane mono(meth)allyl ether, di-trimethylolethane di(meth)allyl ether, di-trimethylolpropane mono(meth)allyl ether, di-trimethylolpropane di(meth)allyl ether, di- trimethylolbutane mono(meth)allyl ether, and/or di-trimethylolbutane di(meth)allyl ether, as well as by polyalkoxylated species of a said polyol.

Preferred polyols are pentaerythritol, di-pentaerythritol, trimethylolethane,

trimethylolpropane, trimethylolbutane, di-trimethylolethane, di-trimethylolpropane, di- trimethylolbutane, neopentylglycol, glycerol and /or di-glycerol. Polycarboxylic acids that can be used in the alkyd syntheses include aliphatic, cycloaliphatic or aromatic polycarboxylic acids and corresponding anhydrides, alkyl esters and halides, such as but not limited to o-phthalic acid, isophthalic acid, terephthalic acid, 1,2- cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4- cyclohexanedicarboxylic acid, tetrahydrophthalic acid, hexahydrophthalic acid, maleic anhydride, fumaric acid, adipic acid, azelaic acid, succinic acid, sebacic acid, furandicarboxylic acid, tetrahydrofurandicarboxylic acid, trimelletic acid, itaconic acid, citraconic acid, pyromelletic acid and/or, when applicable, their corresponding anhydrides .

Specially preferred polycarboxylic acids are phthalic acid, isophthalic acid, maleic anhydride, azelaic acid, adipic acid, tetrahydrophthalic acid, hexahydrophthalic acid, furanedicarboxylic acid, itaconic acid, succinic acid and/or, when applicable, their corresponding anhydrides.

The alkyd resin prepared in a) has a hydroxyl number between 30-220 mg KOH/g, preferably between 60-120 mg KOH/g. The acid number is below 10 mg KOH/g and preferably below 5 mg KOH/g.

The alkyd produced in step a) is reacted with at least one hydroxyfunctional carboxylic acid and at least one polyisocyanate, to produce a polyurethane in step b). The alkyd and the hydroxyfunctional carboxylic acid are charged together with a suitable solvent, like for example ketones like methylethylketone, acetone or N-Methyl-2-pyrrolidone. The polyisocyanate is added and the mixture is heated to about 60-100 °C. A catalyst, for example dibutyl tin dilaurate, can be added together with the polyisocyanate at a concentration of 0.01- 0.1%, calculated on prepolymer.

Suitable hydroxyfunctional carboxylic acids include, but are not limited to, dimethylolpropionic acid, dimethylolbutyric acid, trihydroxymethylacetic acid, 2,2- dihydroxymethylvaleric acid, tartaric acid, dihydroxymalonic acid, dihydroxybenzoic acid and/or hydroxypivalic acid.

According to a preferred embodiment of the invention, the hydroxyfunctional carboxylic acid is dimethylolpropionic acid. The polyisocyanate used in step b) can be for example toluene diisocyanate, diphenyl methane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, tetramethylxylene diisocyanate, dicyclohexyl methane diisocyanate, furan diisocyanate, tetrahydrofuran diisocyanate, cyclohexylene diisocyanate, xylene diisocyanate, naphthalene diisocyanate, phenylene diisocyanate, nonane triisocyanate and/or triphenyl methane tnisocyanate. Further suitable isocyanate based components include isocyanurates, biurets and allophanates.

According to a preferred embodiment of the invention, the polyisocyanate used in step b) is isophorone diisocyanate.

In order to increase the molecular weight (and thereby improve the mechanical properties of the resulting coating), the polyurethane produced in step b) is chain extended in step c) by addition of a suitable polyol at a temperature of about 60-100°C. Examples of suitable polyols for the chain extension step are ethyleneglycol, 1,2-propanediol, 1,3 -propanediol, 1,4-butylene glycol, 1,3-butylene glycol, neopentyl glycol, 2-butyl-2-ethyl-l,3-propanediol, 1 ,6-hexanediol and/or cyclohexanedimethanol.

According to a preferred embodiment of the present invention, the polyol used in step c) is neopentylglycol, ethyleneglycol and/or 2-butyl-2-ethyl-l,3-propanediol. According to a more preferred embodiment of the present invention, the polyol used in step c) is ethyleneglycol.

In order to disperse the coating binder produced by the process according to the invention in water, the carboxylic groups of the product produced in step c) need to be neutralised.

The present invention also refers to a coating composition produced by neutralising the acid groups of a coating binder produced by the process according to the invention and dispersing said neutralised coating binder in water.

According to a preferred embodiment of the present invention, the acid groups of the coating binder are neutralised by addition of a volatile (at ambient conditions) tertiary amine, such as triethylamine. However, the neutralisation can also be made by adding for example ammonia, sodium hydroxide, potassium hydroxide and/or lithium hydroxide. According to one embodiment of the present invention, the coating composition additionally comprises additives like dyes, pigments, matting agents, fillers, flow and/or levelling additives and the like.

According to one embodiment of the present invention, a drier is added to the coating binder, before it is being neutralised and dispersed in water. Said drier can for example be derived from ions of cobalt, manganese, zirconium, calcium and/or iron.

Coating compositions according to the present invention may be used for protective or decorative coating on various substrates like for example metal, wood, plastic and/or paper.

EMBODIMENT EXAMPLES

The present invention is further explained with reference to the enclosed Embodiment Examples, which are to be construed as illustrative and not limiting in any way.

Example 1 illustrates the invention and refers to synthesis of an alkyd from soy bean fatty acid (SOFA), pentaerythritol and phthalic anhydride.

Example 2 illustrates the invention and refers to preparation of an alkyd polyurethane dispersion chain extended with ethyleneglycol.

Example 3 illustrates the invention and refers to preparation of an alkyd polyurethane dispersion chain extended with neopentylglycol.

Example 4 illustrates the invention and refers to preparation of an alkyd polyurethane dispersion chain extended with 2-butyl-2-ethyl-l,3-propanediol.

Example 5 shows some evaluation data for the alkyd polyurethane dispersions produced in Examples 2-4. EXAMPLE 1: Synthesis of Alkyd Polyol-Long oil SOFA

81.46 parts per weight of soybean fatty acid (SOFA), 18.57 parts per weight of pentaerythritol and 5.92 parts per weight phthalic anhydride were charged together with xylene into a reaction vessel equipped with an agitator, a Dean-Stark separator and nitrogen inlet. The temperature was initially raised to 105°C. The temperature was then raised to 180°C, reflux was applied and the temperature was kept for one hour. The temperature was then raised to 224°C during a two hour period, kept at that temperature for 35 min, where after the heating was turned off. The resulting alkyd polyol-long oil SOFA had an acid number of 1.97 mg KOH/g, an OH-value of 98.1 mg KOH/g and a viscosity of 400 mPas (Brookfield) @23°C Sp 03/6 rpm.

EXAMPLE 2: Coating binder chain extended with Ethyleneglycol (MEG), neutralised and dispersed in water

17.06 parts per weight of the alkyd polyol prepared in Example 1 , 2.68 parts per weight dimethylolpropionic acid and 9.90 parts per weight of N-Methyl-2-pyrrolidone were charged into a reaction vessel equipped with an agitator, a Dean-Stark separator and nitrogen inlet, and the temperature was raised to 50°C. 1 1.57 parts per weight of isophorone diisocyanate (IPDI) was added during 15 min. Dibutyl tin dilaurate catalyst was added as 0.04% on prepolymer and the reaction solution was slowly heated to 80°C. The reaction was continued at 80°C until the NCO-content was 3.16%. The prepolymer was chain extended by addition of 1.26 parts per weight of ethyleneglycol and the reaction was continued until the NCO-content was 0.52%. 1.72 parts per weight of triethylamine was added to neutralise the acid groups. The prepolymer was dispersed into 55.81 parts per weight of water. The resulting dispersion was yellowish translucent, had a viscosity of 94 mPas (Brookfield) @23°C Sp 01 , a solid content (105°C /3h) of 35.21 % and a pH-value of 7.41. EXAMPLE 3: Coating binder chain extended with Neopentylglycol (Neo), neutralised and dispersed in water

16.92 parts per weight of the alkyd polyol prepared in Example 1 , 2.66 parts per weight of dimethylolpropionic acid and 9.82 parts per weight of N-Methyl-2-pyrrolidone were charged into a reaction vessel, equipped with an agitator, a Dean-Stark separator and nitrogen inlet, and heated to 50°C. 1 1.47 parts per weight of IPDI was added during 15 min. Dibutyl tin dilaurate catalyst was added as 0.04% on prepolymer and the reaction solution was slowly heated to 80°C. The reaction was continued at 80°C until the NCO-content was 3.54%. The prepolymer was chain-extended by addition of 2.08 parts per weight of neopentylglycol and the reaction was continued until the NCO-content was 1.12%. 1.71 parts per weight of triethylamine was added to neutralise the acid groups. The prepolymer was dispersed into 55.34 parts per weight of water. The resulting dispersion was white translucent and had a viscosity of 27 mPas (Brookfield) @23°C Sp 01, a solid content (105°C /3h) of 35.12% and a pH -value of 7.3.

EXAMPLE 4: Coating binder chain extended with 2-butyl-2-ethyl-l,3-propanediol (BEPD), neutralised and dispersed in water

16.57 parts per weight of the alkyd polyol prepared in Example 1, 2.60 parts per weight of dimethylolpropionic acid and 9.62 parts per weight of N-Methyl-2-pyrrolidone were charged into a reaction vessel, equipped with an agitator, a Dean-Stark separator and nitrogen inlet, and heated to 50°C. 1 1.23 parts per weight of IPDI was added during 15 min. Dibutyl tin dilaurate catalyst was added as 0.04% on prepolymer and the reaction solution was slowly heated to 80°C. The reaction was continued at 80°C until the NCO-content was 3.16 %. The prepolymer was chain-extended by addition of 4.1 1 parts per weight of 2-butyl-2-ethyl-l,3- propanediol (BEPD) and the reaction was continued until the NCO-content was 0.58 %. 1.67 parts per weight of triethylamine was added to neutralise the acid groups. The prepolymer was dispersed into 54.20 parts per weight of water. The resulting dispersion was yellowish translucent, had a viscosity of 98 mPas (Brookfield) @23°C Sp 01 , a solid content (105°C /3h) of 35.12% and a pH- value of 7.4. EXAMPLE 5: Evaluation data

The alkyd polyurethane dispersions produced in Examples 2, 3 and 4 were evaluated in coating compositions. Drying agent Oxycoat was used (1% on polyurethane dispersion).

Hardness

Konig hardness, dry film thickness 35-40 microns at 23°C & RH 55-65% was measured after 1 day for the alkyd polyurethane dispersions produced in Examples 2, 3 and 4. The results are shown in Table 1.

Table I.

Drying properties

Drying properties (dry film thickness 25 microns) were measured for the alkyd polyurethane dispersion chain extended with ethyl eneglycol (Ex 2). The results are shown in Table 2 below.

Table 2.

Claims

1) A process for producing a water dispersible, air drying coating binder comprising the

following steps:

a) producing an alkyd by reacting at least one unsaturated fatty acid and/or at least one corresponding triglyceride, at least one polyol and at least one polycarboxylic acid b) reacting the product obtained in a) by adding at least one hydroxyfunctional

carboxylic acid and at least one polyisocyanate to produce a polyurethane

2) A process according to claim 1 , characterized in that the unsaturated fatty acid in a) is selected from the group consisting of soybean fatty acid, linseed fatty acid, tall oil fatty acid, safflor fatty acid, dehydrated castor oil fatty acid and/or sunflower fatty acid.

3) A process according to claim 1 or 2, characterized in that the polyol in a) is selected from the group consisting of pentaerythritol, di-pentaerythritol, trimethylolethane,

trimethylolpropane, trimethylolbutane, di-trimethylolethane, di-trimethylolpropane, di- trimethylolbutane, neopentylglycol, glycerol and /or di-glycerol.

4) A process according to any of the claims 1-3, characterized in that the polycarboxylic acid in a) is selected from the group consisting of phthalic acid, isophthalic acid, maleic anhydride, azelaic acid, adipic acid, tetrahydrophthalic acid, hexahydrophthalic acid, furanedicarboxylic acid and/or, when applicable, their corresponding anhydrides.

5) A process according to any of the claims 1-4, characterized in that the hydroxyfunctional carboxylic acid in b) is selected from the group consisting of dimethylolpropionic acid, dimethylolbutyric acid, trihydroxymethylacetic acid, dihydroxymethylvaleric acid, dihydroxypropionic acid, tartaric acid, dihydroxymalonic acid, dihydroxybenzoic acid, and/or hydroxypivalic acid. 6) A process according to any of the claims 1-5, characterized in that the hydroxyfunctional carboxylic acid in b) is dimethylolpropionic acid.

7) A process according to any of the claims 1-6, characterized in that the polyisocyanate in b) is selected from the group consisting of toluene diisocyanate, diphenyl methane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, tetramethylxylene diisocyanate, dicyclohexyl methane diisocyanate, furan diisocyanate, tetrahydrofuran diisocyanate, cyclohexylene diisocyanate, xylene diisocyanate, naphthalene diisocyanate, phenylene diisocyanate, nonane triisocyanate and/or triphenyl methane triisocyanate.

8) A process according to any of the claims 1 -7, characterized in that the polyol in c) is ethyleneglycol, 1,2-propanediol, 1,3 -propanediol, 1,4-butylene glycol, 1,3-butylene glycol, neopentyl glycol and/or 2-butyl-2-ethyl-l,3-propanediol.

9) A process according to any of the claims 1-8, characterized in that the polyol in c) is ethyleneglycol, neopentylglycol and/or 2-butyl-2-ethyl-l,3-propanediol.

10) A coating composition produced by neutralising the acid groups of a coating binder

produced by the process according to any of the claims 1-9 and dispersing said neutralised coating binder in water.

11) A coating composition according to claim 10, characterized in that the acid groups of the coating binder are neutralised by addition of a volatile tertiary amine.

12) A coating composition according to claim 1 1, characterized in that said volatile tertiary amine is triethylamine.

13) A coating composition according to any of the claims 10-12, characterized in that said coating composition additionally comprises additives like dyes, pigments, matting agents, fillers, flow and/or levelling additives and the like.