CA2260487A1 - Environmentally friendly autoxidisable film-forming alkyd polymer coating compositions - Google Patents

Abstract

An environmentally friendly autoxidisable filmforming alkyd polymer coating composition which comprises liquid carrier, autoxidation catalyst and autoxidisable alkyd film-forming polymer at least some of which is a polyester of a polycarboxylate and a polyol containing more than three hydroxyl groups at least some of which are esterified by autoxidisable hydrocarbylcarbonyl moieties characterised in that the polyol comprises an anhydroalditol.

Description

ENVIRONMENTALLY FRIENDLY 110~!OxIDI8A8LE FILM-FORMING
~~D BOLYMER COAT~!1f3 COMP08ITIONB
This invention relates to environmentally friendly autoxidisable film-forming alkyd polymer coating compositions such as paint, varnish or woodstain in' which the alkyd polymer contains a large proportion of material obtainable from renewable resources without any substantial degradation of properties as compared to conventional alkyd polymer coating compositions.
The invention especially relates to coating compositions suitable for application at ambient temperatures (e. g. 5 to 40~C) to architectural surfaces such as those found on buildings or their fittings or furnishings. The invention also relates to autoxidisable film-forming alkyd polymers suitable for use in the coating composition.
"Autoxidisable" is synonymous with "drying" or "air drying". A11 three terms mean that when a coating of the autoxidisable film-forming material is applied to a surface and exposed to air in the presence of an autoxidation catalyst (such as calcium, zirconium or cobalt octoate or naphthenate), the alkyd polymer will crosslink or "dry" to form a macromolecular film by oxidation involving the olefinic unsaturation which is found in alkyd polymers. The macromolecular film serves to protect the surface and to bind together any non-film-forming components of the coating composition such as pigments and extenders.
Alkyd polymers are amongst the oldest protective binder materials used in paints. The alkyd polymers generally used in coating compositions for architectural surfaces usually comprise high molecular weight dicarboxylate polymer chains having molecular weights in the range 200 to 200,000 with chains having molecular weights above 100,00o being important in assisting alkyd paints to dry quickly at ambient temperatures. This is particularly important if coatings applied in a thickness of from loo to 200 ~cm are to be able to dry without wrinkling. 1 ~cm is 10'6m.
Conventional alkyd polymers for use in paints suitable for application at ambient temperatures are dicarboxylates made by esterifying an aromatic dicarboxylic acid or its anhydride with a substituted polyol which is an alcohol or ether alcohol originally containing at least three alcoholic hydroxyl groups but nowadays containing more than three in order to obtain the amounts of higher molecular weight chains needed for quicker drying. At least two of these hydroxyl groups esterify pairs of dicarboxylic acid or anhydride molecules whilst most of the remainder are substituted by an autoxidisable hydrocarbylcarbonyl moiety, i.e.
O
II or RCO-R-C-where R is a partially olefinically unsaturated hydrocarbon chain (such as is found in linolenic acid) generally containing 9 to 29 (usually 16 or 18) carbon atoms. Typical autoxidisable hydrocarbylcarbonyl moieties include those derivable from autoxidisable natural oils such as linseed, cottonseed, corn, rapeseed, soya bean and tung oils and tall oil fatty acid. For this reason they are often called "oils" in the paint industry.
Typical of the dicarboxylic acids are isophthalic, succinic, adipic and sebacic acids whilst phthalic anhydride is typical of the anhydrides. Typical alcoholic polyols in commercial use are the alcohols and ether alcohols such as trimethylol propane, glycerol, pentaerythritol and di- and tripentaerythritol. Glycerol is of course obtainable from renewable resources, but it results in slow-drying alkyd polymers. The products obtained from a conventional process for making alkyd polymer are too complex to merit a simple chemical formula but it is probable that an alkyd dicarboxylate polymer made using isophthalic acid and substituted pentaerythritol would contain a predominant proportion of units as represented below R R
I I

.__.C02 / C02 C02 / C02 ~-_..
2 5 \ I C~ 02 \ I C02 I I
R R
with the possibility of chain branching to give higher molecular weights when more than two of the alcoholic hydroxy groups of a polyol react with the acid.

In the above formula represents -CH2_C_CH2~
1o CH2-and RC02- represents a hydrocarbylcarbonyloxy moiety made autoxidisable by the presence of olefinic unsaturation in the hydrocarbyl part of the moiety.
Esterification is usually performed until the acid value of the alkyd ester has fallen to below lOmgKOH/g of the ester. A typical modern alkyd polymer suitable for use in architectural paints can therefore in principle be described as a high molecular weight polymeric aromatic dicarboxylic ester of low acid value (e. g. below lOmgKOH/g of the ester) containing mainly divalent esterifying groups which are-polyols having more than three hydroxyl groups of which at least one is esterified by an autoxidisable hydrocarbylcarbonyl or "oil" moiety.
The oil components of commercial alkyd polymers have the advantage of being largely derivable from 3o agricultural products which are of course renewable sources. They are also easily biogradable when buried in landfill sites which is advantageous when large quantities of waste or surplus paint need to be discarded. However the polyols having more than three hydroxyl groups and the dicarboxylic acid components of commercially viable alkyd paints are still obtained from petrochemical feedstocks. European Patent Specification EP 0 668 305B mentions the possible use of polyols such as sorbitol, mannitol or glucose (page 2 line 52) which contain more than three hydroxyl groups and which are obtainable from renewable resources but attempts to use these in commercial alkyd manufacture result in highly discoloured polymers which can only be used in dark coloured paints.
The present invention seeks to provide an autoxidisable film-forming alkyd polymer coating composition wherein the alkyd polymer is a polyester of a polyol containing more than three hydroxyl groups which is obtainable from renewable resources but which does not have the same extent of disadvantage shown by alkyd polymers obtained from polyols such,as sorbitol, mannitol or glucose.
Accordingly this invention provides an environmentally friendly autoxidisable film-forming alkyd polymer coating composition which comprises liquid carrier, autoxidation catalyst (for example a calcium, cobalt or zirconium carboxylate) and autoxidisable film-forming alkyd/polymer at least some of which is a polyester of a polycarboxylate (preferably a dicarboxylate) and a polyol containing more than three hydroxyl groups at least some of which hydroxyl groups are esterified by autoxidisable hydrocarbylcarbonyl moieties characterised in that the polyol comprises an anhydroalditol, preferably a 2,5 anhydroalditol.
This invention also provides a process for preparing an autoxidisable film-forming alkyd polymer which comprises reacting an anhydroalditol mixture with a dicarboxylic acid or anhydride thereof in the presence of an autoxidisable natural oil, wherein the anhydroalditol mixture has been obtained by:
i) subjecting a starch hydrolysate obtained by hydrolysing a starch, ox a sugar, to heterogeneous catalytic hydrogenolysis to produce an alditol mixture, and ii) subjecting the alditol mixture to heterogeneous catalytic cyclodehydration to produce the anhydroalditol mixture.
This invention additionally provides a substrate comprising a coating of a cured coating composition as defined above .
The invention further provides the use of an anhydroalditol as a polyol component in an autoxidisable alkyd film-forming polymer.
The coating composition of the present invention does not discolour as much as coating compositions containing alkyd polymers obtained 'from polyols such 20 as sorbitol, mannitol, or glucose. The compositions may, for example, also dry as quickly as conventional alkyd coating compositions.

Examples of anydroalditols are H ~H HO OH
O t O ~"~"/ ~~ (:) HO .OH OH HO~ OH Hc>j UH
1,4 anhydro-sorbitol 2,5 anhydro-mannitol 2,5 anhydro-iditol The 2,5 isomers are preferred because they resist further dehydration to form dianhydroalditols which have only two hydroxyl groups.
The invention also provides an environmentally friendly autoxidisable film-forming alkyd polymer which is a polyester of a polycarboxylate (preferably a dicarboxylate) and a polyol containing more than three hydroxyl groups at least some of which are esterified by autoxidisable hydrocarbylcarbonyl moieties characterised in that the polyol comprises an anhydroalditol, preferably a 2,5 anhydroalditol.
The alkyd polymers of this invention can be used to make coating compositions having drying times and light colours comparable with those of conventional alkyd formulations. In particular, they can be used to make coating compositions containing about 15 wt%
rutile titanium dioxide which when applied to a standard white surface in a thickness of 100 ~m and allowed to dry completely, produce dried coats having an NCS greyness factor of less than 60 as defined by the Swedish Standard SS O1 91 03.
German patent application no. 19749202.9, herein -incorporated by reference, shows that anhydroalditols can be obtained economically from natural starches found in such agricultural crops as potato, wheat, barley, maize and rice or from sugars found in crops such as sugar cane or sugar beet. The first step, if a starch is used as a raw material, is to perform a conventional aqueous hydrolysis of the starch, preferably by means of an enzyme such as ~-amylase, whereupon there is produced a so-called aqueous starch l0 hydrolysate of uncertain composition. The starch hydrolysate, or the sugar, is next subjected to heterogeneous catalytic hydrogenolysis preferably using ruthenium supported on a large pore zeolite at l30 to 150~C and 5 to 20 Mpa (50 to 200 bar) hydrogen pressure. Hydrogenolysis produces an aqueous mixture of alditols including sorbitol. The aqueous alditol mixture is then subjected to heterogeneous catalytic cyclodehydration preferably using palladium supported on activated carbon at 250 to 300~C and 5 to 15 Mpa (50 to l50 bar) hydrogen pressure in the presence of an acidic catalyst such as a dispersed acidic zeolite of the H-Y or H-ZSMS types or alternatively a dissolved acid such as propionic acid. The dehydration gives a mixture of polyols, in which tetrols predominate, which comprises approximately:
1,4 - anhydrosorbitol - 30 wt%
2,5 - anhydroiditol - 25 wt%
2,5 - anhydromannitol - 18 wt%
The above mixture of anhydroalditols may be used directly as the polyol in a conventional condensation polymerisation for the production of alkyd polymers.
Alternatively, the mixture may be blended with conventional polyols (such as pentaerythritol or dipentaerythritol) to give minor variations in the properties of the alkyd polymer. For example, up to - g -60wt%, for example 15 to 60wt%, of the polyol may be conventional polyol. Yet a further variation comprises blending alkyd made according to this invention with totally conventional alkyd, for example an alkyd made using pentaerythritol as the polyol. Preferably such a blend comprises up to 60wt%, for example from 15 to 60wt%, of the conventional alkyd.
The alkyd polymers and blends according to this invention may be formulated into coating compositions by mixing with a liquid carrier and preferably one or more conventional non-film-forming materials of the type found in paints, varnishes and woodstains. Such materials include inorganic or organic pigments, dyes, extenders, thickeners, structuring agents, fungicides, anti-skinning agents, flow improvers and drying agents. The liquid carrier is preferably an organic solvent such as white spirit. However, it may also be an aqueous carrier containing the alkyd polymer in the form of an emulsion and a suitable surfactant as is well known in the art. Suitably in the latter case the alkyd polymer has an oil length of 30 to 80%, preferably 35 to 60%.
The coating compositions should preferably have a cone and plate viscosity at 25~C of at least 1 and preferably at least 1.5 poise (i.e. 0.1 and 0.15 Pa. s) to ensure that wet coatings have acceptable sag-resistance when applied to a vertical surface and preferably not more than l0 poise (lPa.s) so as to enable them to be applied by brush, pad or roller at ambient temperatures.
The viscosity of a coating composition comprising alkyd polymer dissolved in volatile organic solvent CA 02260487 1999-O1-28.

' increases as the concentration of the polymer increases. This places an upper limit on the amount of solid material (i.e. non-volatile material) which can be accommodated in the composition, if the composition is to remain easily applicable by brush.
It has been found that the rate of increase is slower for compositions according to this invention than it is for conventional compositions. Therefore, compositions according to the invention can, if desired, accommodate more solid materials (over 75wt%
and usually over 80wt%) which in turn means that they can contain less organic solvent. Less solvent is an environmental advantage because the solvent is lost to the atmosphere when the composition dries and it has been recently acknowledged that solvent from drying paints causes a significant proportion of modern atmospheric pollution. For the avoidance of doubt, it should be explained that the "solid", i.e. "non-volatile" material is the content of the liquid composition which remains to form a dried coat of the composition after a11 the volatile components of the liquid coating compositions have been lost by evaporation.
The following techniques may be used to measure molecular weights and drying times:
Molecular Weights:
The molecular weights of the various polymeric materials are determined by gel permeation chromatography. A 0.5wt% solution of material in tetrahydrofuran was passed at lml/min through cylindrical columns 300mm long by 20mm diameter packed with a gel available from Polymer Laboratories Limited of Church Streeton, England and known as "Mixture D".
The results obtained are calibrated against a polystyrene standard.
Drying Time Measurement:
The time taken for a freshly applied coating to become dry to touch is measured by a sand deposition procedure as follows:
A coating 100 ~Cm thick is applied at 20~C to a horizontal glass sheet. A hopper having a small outlet in its base is filled with sand which then trickles through the outlet. The hopper is caused to traverse the coating at a speed of 25.4mm/hour with sand trickling onto the coating. Initially the sand sticks to the coating which is still wet but as time passes, the coating dries and there comes a point when the sand ceases to stick to it. The time taken to reach this point is regarded as the touch dry time for the purposes of the specification. The point is easily detected by blowing the loose sand from the fully dried coating so as to leave a trail of stuck sand of a length from which the touch dry time is calculated by dividing the speed of traverse.
The invention is illustrated by the following Examples of which A is comparative and by the drawings of Figure 1 which is a graph of cone and plate viscosity at 25~C of a solution of alkyd polymer in white spirit versus the polymer content of the solution expressed as a weight percentage of the total weight of the solution.

Obtaining an Anhydroalditol Mixture:
An aqueous mixture of anhydroalditols was obtained from potato starch by first subjecting the starch to a conventional enzymatic hydrolysis using ~-amylase, which produced a solution consisting of 20wt% starch hydrolysate in water.
This aqueous starch hydrolysate was subjected to 5 hours of hydrogenolysis at l50~C and 5 to 20 Mpa (50 to 200 bar) pressure of hydrogen in the presence a ruthenium catalyst supported on a large pore zeolite of the Y type. 5wt% of catalyst (based on the weight of the starch hydrolysate) was used and the ruthenium made up iwt% of the weight of the supported catalyst. On completion of the process the supported catalyst was filtered off, whereupon an aqueous mixture of alditols was obtained. The water content of the mixture was adjusted by distillation to give an aqueous mixture containing 50wt% of alditols.
The alditols were then converted to anhydroalditols by adding, to the 5owt% aqueous mixture, 5wt% propionic acid as an acid catalyst and 1 wt% of a catalyst comprising palladium supported on activated carbon where the weight percentages of both catalysts are based on the weight of alditols present in the 50wt% aqueous mixture. The palladium made up lwt% of the supported catalyst.
The aqueous alditol and catalysts mixture was cyclodehydrated at 270~C and 7 Mpa (70 bar) hydrogen pressure to produce an anhydroalditol mixture which was found to contain:
29.6wt% - 1,4-anhydrosorbitol l7.lwt% - 2,5-anhydromannitol 25.7wt% - 2,5-anhydroiditol and 9.lwt% - 1,4,3,6-dianhydrosorbitol plus unidentified material.
Preparation of an Alkyd Polymer according to the l0 invention:
A 5 litre glass flask was fitted with a stirrer and a Dean and Stark reflux condenser operable so as to allow the escape of water from an azeotropic solvent. The flask was purged with nitrogen and then charged with:
Charge Parts by Weight Tall Oil fatty acid (TOFA) 693 Phthalic anhydride 208 Pentaerythritol 66 Anhydroalditol mixture obtained 204 as above Xylene azeotropic solvent 64 The contents of the flask were stirred and slowly heated to 230~C over a period of 36 hours.
Esterification occurred in which TOFA esterified in the main about 2 to 3 of the hydroxyl groups of anhydroalditols and about 3 of those of the pentaerythritol. The water produced was removed from the xylene via the separator. Esterification was continued at 230~C (adding extra xylene to cool as necessary) until the acid value of the contents had fallen to 9.8mg OH/g of solids content. The contents were then cooled to ambient temperature, thinned by adding 255g white spirit and then found to contain 75%
by weight of alkyd polymer.
Formulation of the Paint:
The following ingredients were added to a "Dispersomat" mixer at ambient temperature:
Ingredient Parts by Weight Alkyd polymer in white spirit 16 as above White Spirit 18 Rutile Titanium Dioxide 78 Clay extender 0.75 Polytetrafluoroethylene extender 0.45 The agitator blade of the mixer was operated at 1,500 rpm for 30 minutes.
Stirring was continued and the following further ingredients were added:
Ingredient Parts by Weight Alkyd polymer in white spirit 142 as above White Spirit 10 Calcium alkanoate drier 1.6 Cobalt alkanoate 0.7 Zirconium alkanoate drier 4.6 Antifoam and Anti-skin additives 1 White Spirit 17.9 Gentle stirring was resumed for 5 minutes and produced a paint having a viscosity of 0.27 Pa.s (1.7 poise) which therefore could be brushed onto an alkyd undercoat surface at 18~C as easily as conventional alkyd paint. The paint had a solids content of 69.2wt~.
Testing the paint.
A primed surface was prepared by priming a hardboard surface with "Dulux" Trade white alkyd wood primer (available from ICI Paints of Slough, England) and then allowing the primed surface to age at ambient temperatures for seven days.
A coating 100 ~m thick of the paint was applied to the primed surface using a block spreader and the surface was mounted vertically. No sagging of the coating was observed during the period of 30 minutes following application which is the time when sagging is most likely to occur.
A coating 100 ~cm thick was also subjected to the drying Time Measurement as described above. It was found to dry in two and a half hours.
A dried 100 E.cm thick coating was assessed for colour using a spectrophotometer. It was found to match closely the colour of the conventional pentaerythritol alkyd paint made according to Comparative Example A.
Testing the Viscosity of the Dissolved Alkyd Polymer:
A sample of the alkyd polymer solution prepared above was taken prior to thinning with the 255g of white spirit. The sample was further divided into smaller samples which were then thinned to different extents with white spirit so as to produce a series of solutions having different polymer concentrations and the cone and plate viscosity of each thinned solution was measured at 250~C and plotted as a graph of viscosity against concentration. The graph is shown as the curve for Alkyd 3 in Figure 1. The graph shows that solution can accommodate at least 80wt%
solids and even 85% before its viscosity begins to rise above 1 Pa.s (10 poise).
COMPARATIVE ERAMPLE A
Comparison with a Conventional Alkyd Paint:
A conventional alkyd polymer and paint were made according to Example 1 except that the whole of the anhydroalditol was replaced by pentaerythritol. The conventional paint obtained had a viscosity of 0.33 Pa.s (3.3 poise). A 100 ~cm coating of the conventional paint was subjected to the Drying Time measurement and found to dry in 2.5 hours. A dried 100 ,um coat of the paint was assessed for colour using a spectrophotometer and found to be very similar to that of Example 1.
Testing the Viscosity of the Dissolved Conventional Alkyd:
Solutions of the conventional alkyd polymer containing various amounts of alkyd polymer were made as in Example 1 and their cone and plate viscosities were measured at 25~C. The results are shown as the curve for Alkyd 1 in Figure 1 from which it will be seen that the viscosity increases to an unsatisfactory level of over 1 Pa.s (10 poise) well before the solids content reaches 75wt%.
.ERAMPLE 2 Dissolved alkyd polymer was made according to Example 1 except that 33wt% of the anhydroalditol mixture was replaced by pentaerythritol during the preparation of the alkyd polymer to provide a polymer in which the diol consists of 50wt% pentaerythritol and 50wt% of the anhydroalditol mixture. The amount of white spirit in the alkyd polymer solution was varied to produce alternative solutions as in Example 1 and the graph of cone and plate viscosity at 25~C against alkyd polymer content was plotted and is shown as the curve for Alkyd 2 in Figure 1. Figure 1 shows that the viscosity of the alkyd solution reaches 1 Pa.s (10 poise) at a solids content of about 77wt%.

Alternative Paint according to the invention:
An alternative alkyd polymer was made using an anhydroalditol mixture obtained from a mannitol starting material and containing 1,4-anhydrosorbitol 8.5wt%
2,5-anhydromannitol/iditol 59wt%
1,4,3,6 dianhydrosorbitol 0.5wt%
This mixture was used to make a paint as in Example 1 and the paint was tested in the same way. It was found to have a cone and plate viscosity of 3.2 poise (0.32Pa.s), to be as sag-resistant as the conventional paint of Comparative Example A, to have a drying time of 1; hours and a colour very similar to that of Comparative Example A.
Dissolved alkyd polymer was made according to Example 1 except that the weights used were as shown below and the preparation was carried out at 250~C.
Charge Parts by Weight Tall Oil fatty acid 693.45 Phthalic Anhydride 208.39 Anhydroalditol mixture 340.19 Xylene 40.79 The anhydroalditol mixture was the same as that obtained in the first part of Example 1. The final acid value of the polymer was 9.6 mg KOH/g and the corresponding paint had a viscosity of 0.32 Pa.s (3.2 poise) and a drying time of 3 hours.
COMPARATIVE EXAMPLE B
Dissolved alkyd polymer was made according to Example 1 except that the weights used were as shown below:
Charge Farts by Weight Tall Oil fatty acid 818.52 Phthalic Anhydride 213.04 Pentaerythritol 114.94 Sorbitol 209.61 Xylene 90.53 The final acid value of the polymer was 12.0 mg KOH/g and the corresponding paint had a drying time of 5.25 hours. The colour of the paint was poor (yellow) and when measured using a Lovibond colorimeter was found to be twice as yellow as the paint from Comparative Example A.

Claims (12)

1. An environmentally friendly autoxidisable film-forming alkyd polymer coating composition which comprises liquid carrier, autoxidation catalyst and autoxidisable alkyd film-forming polymer at least some of which is a polyester of a polycarboxylate and a polyol containing more than three hydroxyl groups at least some of which are esterified by autoxidisable hydrocarbylcarbonyl moieties characterised in that the polyol comprises an anhydroalditol.

2. A coating composition according to Claim 1 wherein the liquid carrier is an organic solvent.

3. A coating composition according to Claim 1 or 2 characterised in that the anhydroalditol is a 2,5-anhydroalditol.

4. A coating composition according to any one of the preceding Claims characterised in that up to 60wt% of the polyol used to make the alkyd polymer is pentaerythritol, dipentaerythritol or a mixture of the two.

5. A coating composition according to any one of the preceding Claims which when dry has an NCS greyness factor of less than 60.

6. A coating composition according to any one of the preceding Claims having a cone and plate viscosity at 25°C of from 0.1 to 1Pa.s (1 to 10 poise) characterised in that the composition contains at least 75wt% of solids.

7. A coating composition according to any one of the preceding Claims characterised in that the anhydroalditol is a mixture of anhydroalditols obtainable by hydrogenation and subsequently dehydration of a potato starch hydrolysate.

8. A process for preparing an autoxidisable film-forming alkyd polymer which comprises reacting a anhydroalditol mixture with a dicarboxylic acid or anhydride thereof in the presence of an autoxidisable natural oil, wherein the anhydroalditol mixture has been obtained by:
i) subjecting a starch hydrolysate obtained by hydrolysing a starch, or a sugar, to heterogeneous catalytic hydrogenolysis to produce an alditol mixture, and ii) subjecting the alditol mixture to heterogeneous catalytic cyclodehydration to produce the anhydroalditol mixture.

9. An environmentally friendly autoxidisable film-forming alkyd polymer as defined in any one of Claims 1, 3 or 4.

10. An autoxidisable film-forming alkyd polymer obtainable by the process defined in Claim 8.

11. A substrate comprising a coating of a cured coating composition as defined in any one of Claims 1 to 7.

12. Use of an anhydroalditol as a polyol component in an autoxidisable alkyd film-forming polymer.