GB2121061A - Water resistant coating compositions - Google Patents

Abstract

A coating composition especially for use on roofs and walls to provide new surfaces thereon or to repair damaged or leaking surfaces comprises an aqueous emulsion polymer and a drying oil. The polymer may be an acrylic or styrene modified acrylic polymer or a blend thereof and the drying oil may be a vegetable drying oil, preferably dehydrated castor oil. The composition may include driers, emulsifiers and insolubilizing agents.

Description

SPECIFICATION Coating compositions This invention relates to coating compositions and especially to compositions which may be applied to roofs or walls to provide new surfaces thereon or to repair damaged or leaking surfaces. The practice of applying hot bitumen to roofs has been known for many years.

However, this material is not particularly easy to handle, it involves the risk of fire and in time becomes brittle and cracks. Further coats become necessary and a layer of bitumen on the roof builds up might be too heavy.

Bitumen emulsions have also been used. These are easier to apply but are highly brittle and prone to cracking.

High polymers have also been used for some considerable time. Initially polymers such as neoprene were used in solutions having a low solids content. Very thin films were applied and it was necessary to apply five or six coats in order to produce a satisfactory coating, the application of these polymers being highly labour intensive.

Subsequently polymer emulsions, containing no solvents, were used. These could be applied in thicker layers, perhaps of the order of .088 to .01 inch (the thickness of a dry coat) per application. Initially styrene butadiene rubber (SBR), which was carboxylated, was used. Such an emulsion dries quickly but is very unstable in the can. The resultant coating has poor resistance to weathering, due to the unsaturated nature of the butadiene.

Subsequently acrylic emulsions and styrene acrylic emulsions were used. Acrylic emulsions are very slow drying but have good resistance to weathering. Styrene acrylic emulsions dry more quickly although they do not dry as fast as the SBR emulsion. They do not have as good resistance to weathering as the pure acrylic emulsion but nonetheless they are better in this respect than SBR emulsions. The styrene acrylic emulsions have good stability in the can. They may comprise a blend of an acrylic polymer modified with a styrene acrylic copolymer or alternatively a pure styrene acrylic copolymer. Alternatively a solventless two pack system may be provided, the components being mixed together prior to application. However, such a system is very expensive if used for large roof areas.

According to the present invention there is provided a coating composition comprising an aqueous emulsion polymer and a drying oil.

Preferably the composition includes a drier to accelerate the polymerisation of the drying oil.

Preferably the composition includes one or more emulsifiers to improve the stability of the composition in the can.

Preferably the composition includes one or more film insolubilisers to improve the resistance of the coating to water and other solvents.

The present invention also provides a method of coating a surface to protect or repair the surface, the method comprising applying to the surface a composition in accordance with the invention.

A composition in accordance with the present invention dries quickly, has good weathering resistance and good stability in the can. As far as drying time is concerned, the composition quickly becomes "touch dry" and, perhaps more importantly, has a considerably improved water resistance time when compared with conventional compositions. The latter is important because it is the measure of the time taken for applied compositions to reach the state where it will not be washed of by, for instance, a shower of rain.

A composition in accordance with the present invention can be applied as a thick film, for instance, a film having a dry thickness in the region of 250ym per coat.

A composition in accordance with the present invention has good adhesion to most substrates and, where necessary, adhesion can be improved by the use of a priming or conditioning solution.

The aqueous emulsion polymer is preferably a styrene butadiene polymer, an ethylene vinyl acetate polymer, a pure acrylic or a styrene modified acrylic polymer, or a blend of these polymers, especially a blend of the pure acrylic and styrene modified acrylic polymers. Most preferably the aqueous emulsion copolymer is a styrene modified acrylic polymer.

The drying and tensile properties of the compositon are affected by the degree of styrene modification and it is preferred that the amount of styrene in the styrene modified acrylic copolymer be between 42 and 50% by weight of the total solid polymer. A particularly preferred amount of styrene is of the order of 46% by weight.

Preferably the styrene acrylic copolymer is present in the composition of the invention in an amount of from 40 to 50% weight of the total solid polymer.

The drying oil is preferably a vegetable drying oil. Examples of drying oils which may be used include linseed oil, tung oil, dehydrated castor oil, as well as derivatives of those oils, may also be used. A preferred drying oil is dehydrated castor oil.

The particular drying oil and the amount of the drying oil in the composition affects the touch dry time and the time taken for the composition to become water resistant. A particularly preferred oul is dehydrated castor oil having a viscosity of from 25 to 35 poise.

Preferably the dehydrated castor oil is present in an amount of from 1 5 to 50% by weight of solid polymer in the aqueous polymer emulsion.

The above-mentioned dehydrated castor oil having a viscosity within the above-stated limits, employing a specific level of polymerisation, provides a particularly preferred compromise between minimum and maximum overcoating times (the period following the application of a layer of the composition to a surface during which a further layer can be applied) and the extensibility of the film.

The drier is preferably a soluble metal drier such as an organo-metallic compound, for instance, cobalt or lead octoate or a non-metallic material such as 2-ethylhexoate or naphthenate. When such driers are included the film sets to a gel structure more rapidly and as a result the drying characteristics of the aqeuous emulsion polymers are improved. In addition the final dry film has good flexibility, adhesion and colour retention.

A preferred drier is a combination of cobalt octoate and lead octoate which is present in the composition in an amount such that there is 0.01-0.07%, more preferably about 0.05%, cobalt metal by weight based on the total weight of oil. Preferably the amount of cobalt (as the metal) in the combination is about 6% and the amount of lead (as the metal) is about 24%.

In order to improve the blending together of the polymer and the drying oil to provide a stable medium and to reduce problems associated with stability and separation of the composition, it is desirable to include in the composition one or more emulsifiers.

Preferred emulsifiers are sorbitan esters. More preferably the emulsifier is a blend of sorbitan esters and polyethoxylated derivatives of such esters. Particularly preferred are the monoesters and their polyethoxylated derivatives. General formulae for the sorbitan monoesters and the polyethoxylated derivatives are as follows:

where R is the alkyl group of the relevant fatty acid and X plus Y plus Z is the total number of moles of ethylene oxide per mole of sorbitan ester.

A particularly preferred sorbitan mono ester is sorbitan monooleate such as that sold by Croda Chemicals under the name CRILL 4. This material has a hydrophilic-lyophilic balance (HLB) of 4.3. Although such a sorbitan mono ester is an efficient water in oil emulsifier, its use for an oil in water system is improved by combining it with a polyethyoxylated sorbitan ester. A particularly preferred ethoxylated material is polyethyoxylated sorbitan monooleate, for instance, CRILLET 4 produced by Croda Chemicals and having a POE value of 20 and an HLB value of 15.

Preferably the sorbitan ester blend is present in the composition in an amount of from 1 to 5% by weight of the drying oil.

The inclusion in the composition of insolubilisers or insolubilising agents assists the insolubilising of aqueous polymer following application to the surface. A preferred insolubiliser is ammonium zirconium carbonate. This material has proved an excellent insolubiliser for styrene acrylic emulsions improving resistance to water and other solvents. Preferably the ammonium zirconium carbonate is present in an amount such that there is 2 to 4 weight percent ZrO2 based on the weight of solid polymer present in the composition.

Preferably the composition includes pigments and/or extenders in order to provide colour to the composition and preferably also to impart some additional strength to the composition.

Preferably also a fibrous material is included in the composition to provide an additional reinforcing effect. A preferred fibrous material is a nylon flock of such dimensions as to be readily incorporated into the composition without making the application of the composition more difficult.

The amount of pigment and/or extender used in the composition affects the weathering, flexibility and tensile properties of the applied composition. Preferably the pigment volume concentration (PVC) is from 20 to 55% of the total non-volatile volume in the composition.

Preferably the PVC should be in the region of 25%.

A composition in accordance with the present invention may additionally include antifoam, wetting and biocidal agents in order to assist the manufacturing process and achieve satisfactory "in can" storage and film protection against bacteria and fungi.

A composition in accordance with the present invention is a one component composition having a storage life of many months or even years. On application to a surface, such as a roof surface, the material dries initially by evaporation of water from the film followed by insolubility of the styrene acrylic polymer and the drying of the dehydrated castor oil.

An example of a composition in accordance with the present invention will now be given.

The composition has the following constituents, the quantites indicated being parts by weight: A. Styrene acrylic copolymer (50% solids, 46% Styrene) 43.58 B. Pigment dispersing aid 0.22 C. Water softening agent 0.12 D. Emulsion stabiliser 0.13 E. Antifoam 0.21 F. Biocide 0.24 G. Ammonium hydroxide 25% 0.27 H. Ammonium zirconium carbonate 4.36 I. Pigments/extenders 28.59 J. Nylon flock 0.29 K. Plasticizer 2.20 L. Coalescent 1.30 M. Dehydrated castor oil (25 to 30 poise) 6.54 N. Sorbitan monooleate (HLB 4.3) 0.08 O. Polyethoxylated sorbitan monooleate (POE 20, HLB 15) 0.08 P. Metaliic driers 0.18 Q. Water 9.74 R. Thickening agent 1 1.33 S. Butyl glycol 0.27 T.Thickening agent 11 0.27 100.00 Referring to certain of the above-mentioned components of the composition: H-The ammonium zirconium carbonate used may be the material sold as BACOTE 20 by Magnesium Elektron Limited.

I-The pigments/extenders may be a blend of appropriate materials including titanium dioxide, black iron oxide, calcium carbonate, yellow iron oxide, silicon dioxide, red iron oxide and zinc oxide. The particular materials chosen will depend on the desired colour and properties of the composition.

P-The metallic driers used were 0.05 parts by weight of the cobalt salt of 2-ethylhexoic acid (having 6% cobalt) and 0.13 parts by weight of the lead salt 3-ethylhexoic acid.

R-Thickening agent I was an invert polyacrylate emulsion sold as VISCALEX PL 30 by Allied Colloids.

T-Thickening agent Il was a non-ionic polyurethane thickener sold as BORCHIGEL DP40 by Borchers.

The composition has a viscosity of 2.2 poise, a density of 1.27 g/cm-3, a touch dry time and water resistant time at 20'C and 46% RH of 25 minutes and 50 minutes respectively. The composition was easily applied by brush to give a smooth, even film of up to 250 Lm dry film thickness without sagging. The percentage elongation of a dry film after 1000 hours accelerated weathering in accordance with B53900 part F3 was 110%.

The composition was prepared in the following manner:1. Components A to J were mixed together in a high speed disperser such as a MASTERMIX or TORRANCE disperser.

2. Separately components K to P were mixed together using an ordinary stirrer and allowed to stand to ensure that the driers are given an induction period, the result of which is that the drying time on application of the final composition is reduced. Following this induction period these components are then dispersed with components A to J on a high speed mixer.

3. The water and Thickener I are then added to the high speed mixer.

4. After the mixture in the mixer becomes homogeneous the butyl glycol and thickener ll are added.

As a result of this method of preparation a homogeneous composition is prepared.

Variations in the above composition have been investigated as is illustrated in the following Examples.

EXAMPLE 1 The effect of varying the level of the styrene modification in the polymer was determined using the following compositions: I The polymer component was a pure acrylic polymer and the vegetable drying oil was dehydrated castor oil having a viscosityof 3.0-3.5 poise.

II The polymer component was an acrylic with a styrene modification of 42% based on the weight of solid polymer and the vegetable drying oil was as Formulation I.

III The polymer component was an acrylic with a styrene modification of 46% based on the total weight of polymer and the vegetable drying oil was as Formulation I.

Test pieces of free films of each formulation were prepared and subjected to artificial weathering according to B53900 Part F3 equipment for periods up to 500 hours and then tested for percentage elongation at break using a NENE Tensometer in accordance with B52782:F3-301 D.

The following results were obtained: ELONGATION AT BREAK FORMULATION INITIAL 100 HOURS 500 HOURS 100% 200% 180% II 225% 170% 150% lil 275% 150% 150% Accordingly, the effect of increasing the styrene modification is to increase the percentage elongation initially but on weathering a more marked reduction is observed.

EXAMPLE 2 Formulation I to Ill were tested for touch dry time and time to achieve water resistance. Test coatings were applied to glass plate at a dry film thickness of 0.01 inch, the drying conditions being 19"C and 48% RH.

WATER RESISTANT FORMULATION TOUCH DRY AFTER 50 mins. 110 mins.

II 30 mins. 80 mins.

III 25 mins. 52 mins.

Accordingly, the increasing levels of styrene give more rapid drying and water resistant times. It may well be that although Formulation I has the highest elongation, the preference would be for an emulsion polymer with a shorter drying time, for example, Formulation Ill with 46% styrene based on the total weight of polymer.

EXAMPLE 3 The efficacy of the drying oil is demonstrated by comparing the water resistance time of formulation Ill with that of formulation IIIA in which the dehydrated castor oil is replaced by a conventional plasticiser, di-butylphthalate, which imparts no inherent drying properties.

FORMULATION WATER RESISTANT AFTER lil 52 mins.

lIlA 90 mins.

EXAMPLE 4 The position was varied by using different vegetable oils to determine the effect on drying time. The following formulation based on variations of Formulation Ill, were prepared: III See Example 1 IV Natural tung oil V High stand linseed oil VI 50:50 blend of natural tung oil and dehydrated castor oil.

The following results were obtained on test coatings from these formulations, the drying conditions being 20"C and 48% RH: % ELONGATION AT BREAK WATER RESISTANT AFTER 500 HRS FORMULATION TIME INITIAL WEATHERING lil 50 275 125 IV 50 130 90 V 75 150 125 VI 50 130 100 It can be seen that considerable variations in the various properties resulted from changes in drying oil and dehydrated castor oil and high stand linseed oil give particularly good results. In terms of water resistant time, however, formulations III, IV and VI are preferred. In terms of extensibility on weathering, however, formulations Ill and V are preferred. A particularly preferred formulation, in terms of overall performance, is formulation Ill.

EXAMPLE 5 An important feature of a multicoat roofing system of the type with which this invention is concerned is that a particular layer should be receptive to overcoating for a reasonable period of time. The formulations of Example 4 were compared for maximum overcoating periods: FORMULATION MAX OVERCOATING TIME (HOURS) lil 48 IV < 24 V 168 VI 24 Here it can be seen that the preferred formulation is Formulation V.

EXAMPLE 6 In order to establish the effect of a change of polymerisation of the dehydrated castor oil on the maximum overcoating time, various formulations were prepared in which the dehydrated castor oil (DCO) had differing viscosities. In the following formulations, Formulation III was varied by changing the polymerisation of dehydrated castor oil as indicated by the viscosity as follows: VII Viscosity 1 0-1 5 poise.

VIII Viscosity 20-30 poise.

IX Viscosity 40-50 poise.

The following results were obtained: MAXIMUM OVERCOATING TIME % ELONGATION AT BREAK AT 20"C AND 46% RH INITIAL 500 HR lil 48 hours 275 125 VII 48 hours 300 120 VIII 168 hours 275 110 IX 168 hours 225 70 A maximum overcoating period of 168 hours is not unreasonable, and since the percentage elongation after weathering decreased with increasing polymerisation it is preferred to use oils having a viscosity no greater than 40 to 50 poise. A preferred oil had a viscosity in the range 20 to 30 poise.

EXAMPLE 7 The effect of variation of the level of pigment volume concentration (PVC) was determined by varying Formulation III although maintaining a ratio blend of pigments/extenders throughout, as follows: X PVC 20% Xl PVC 25% XII PVC 33% XIII PVC 45% XIV PVC 55% The percentage of elongation was determined by testing free films of the materials after suitable periods of accelerated weathering. The results are given below: FORMULATION INITIAL 100 HOURS 500 HOURS 1000 HOURS X 766% 410% 300% 210% XI 275% - 110% 100% XII 150% 60% 40% XIII 25% - XIV 20% - A percentage elongation below 100% was regarded as a failure. It is considered that 1000 hours accelerated weathering in the tests used was approximately equivalent to two years natural exposure. Preferably the PVC is no greater than 25%.

Claims (11)

1. A coating composition comprising an aqueous emulsion polymer and a drying oil.

2. A coating composition as claimed in claim 1 wherein the polymer is selected from the group consisting of a styrene butadiene polymer, an ethylene vinyl acetate polymer, a pure acrylic and a styrene modified acrylic polymer, and a blend of these polymers.

3. A coating composition according to claim 1 or claim 2 wherein the polymer is a blend of pure acrylic and styrene modified acrylic polymers.

4. A coating composition according to any of the preceding claims where the polymer includes a styrene modified acrylic polymer present in an amount of from 40 to 50% by weight of the total solid polymer.

5. A coating composition according to any of the preceding claims wherein the drying oil is a vegetable drying oil.

6. A coating composition according to any of the preceding claims wherein the drying oil is dehydrated castor oil.

7. A coating composition according to any of the preceding claims wherein the drying oil is dehydrated castor oil present in an amount of from 15 to 50% by weight of solid polymer in the aqueous polymer emulsion.

8. A coating composition according to any of the preceding claims wherein the composition includes a drier and an emulsifier.

9. A coating compostion according to any of the preceding claims wherein the composition includes, as insolubilising agent, ammomium zirconium carbonate.

10. A coating composition for application to roofs and walls comprising an aqueous emulsion polymer including a styrene modified acrylic polymer, dehydrated castor oil, a drier comprising cobalt octoate and lead octoate and an emulsifier blend of sorbitan esters.

11. A coating composition according to claim 1 and substantially as described herein.

1 2. A coating composition substantially as described in any of the specific examples.

1 3. A method of providing a new surface on a roof or wall or repairing a damaged or leaking roof or wall surface, the method comprising applying to the surface a coating composition as claimed in any of the preceding claims.