The present invention relates to surface-coating compositions and to composite materials, each having enhanced resistance to corrosion and to ultra-violet degradation.

The present invention provides a method of protect¬ ing a substrate, which comprises applying to the said substrate, without addition of water, a water-free surface-coating composition which comprises at least 37.5% by weight (based on the total weight of the composition) of a cement as active filler, a film-former or binder, and a non-aqueous solvent or diluent, the particle size of the cement being not greater than 200 microns and the proportion by weight of cement being greater than the total proportion by weight of any other inorganic solids in the composition.

The invention also provides a surface-coating composition for use in the method.

The invention further provides a composite material comprising a fibre-reinforced plastics material an'ϊ at least 37.5% by weight (disregarding the fibre reinforce¬ ment) of a cement as active filler, the particle size of the cement being not greater than 200 microns.

It has been found that surface coatinσs formed from

surface-coating compositions according to the invention have enhanced resistance to corrosion and to ultra-violet degradation (demonstrated in ultra-violet accelerated weathering test equipment) . In particular, the coatings are resistant to corrosion caused by atmospheric oxygen and water/water vapour and to corrosion caused by water/water vapour and ion penetration, such as is prevalent in marine environments as a result of exposure to sea water. The enhanced corrosion-resistance is believed to stem from reduced oxygen-, water/water vapour and ion- permeability of the coating. Although the reason for the enhanced protective properties of coatings produced according to the invention is not fully under¬ stood, it is believed to be attributable to hydration of the cement filler within the surface layer applied to the substrate. Moreover, if the surface of the protective coating is damaged by abrasion or impact, subsequent contact with water or water vapour will result in hydration of newly-exposed cement filler, so that the protective coating is self-repairing.

A further important factor is believed to be the expansion of the cement on hydration, which will tend to seal some of the pores formed in the applied coating as a result of the evaporation of volatiles. Also, a varnish will normally swell as a result of water absorption, and that swelling will tend to increase the porosity of the material. In a coating formed from a composition of the

invention, on the other hand, it is believed that the expanded cement hydrate formed on exposure to water or water vapour will tend to force closure of a proportion of any pores that form in the varnish base as a result of hydration.

A coating according to the invention will in general provide effective corrosion resistance without the use of a sacrificial anode such as zinc, and the compositions of the invention are preferably free of such additives.

A composite plastics material of the invention has advantageous properties including the following: i) Reduced water-, air- and ion-permeability, believed to result from the formation of a relatively impermeable hydrate layer. Also, if the surface of the material is damaged by abrasion or impact, subsequent further contact with water or water vapour will result in hydration of newly-exposed cement filler, with consequent further protective layer formation, so that the material is effectively self-repairing, i) Reduced ultra-violet degradation, believed to arise as follows: after initial surface deterioration of the plastics material caused by ultra-violet irradiation, subsequent exposure to water or water- vapour will cause the plastics material to be at least partially shielded by the cement hydrate

formed.

On exposure to aqueous media, the cement filler expands to form an insoluble and relatively impermeable hydrate (having a lower density than the anhydrous filler) which establishes a protective layer or matrix which will tend to seal diffusion pathways and pores in the material, such as are commonly found in glass-fibre reinforced epoxy resins.

The plastics material may be a thermoplastic or ther osetting material.

Examples of thermoplastic materials which may be used include polyethylene, polypropylene, polycarbonates, polyvinylchlorde, polyesters, thermoplastic rubbers, copoly ers and polymer mixtures.

Examples of thermosetting materials which may be used include epoxy resins and unsaturated polyesters, and a particularly important application of the present proposal lies in improving the corrosion-resistance of glass fibre-reinforced epoxy resin compositions, which have hitherto suffered from water-permeability problems caused by the presence or development of a multiplicity of deep and complex leakage pathways.

Depending on the intended end use, the composite material will normally also include one or more conven¬ tional additives in addition to the active filler material: for example, pigments, processing aids (for example, lubricating aids), and reinforcing materials.

The cement may be incorporated in the plastics material using any of the techniques conventionally employed for the incorporation of fillers. Care must be taken to keep the materials dry once the cement is present to avoid undesirable pre-hydration and inactiva- tion of the active material by encapsulation. Water- cooling after hot mixing, however, is not entirely excluded because subsequent heating to 200°C or more (for example, in injection-moulding) may reverse up to about 80% of the hydration.

In principle, the cement could in certain cases be incorporated before or during polymerisation of the plastics material, but in order to avoid premature hydration it is then essential to avoid polymerisation processes which themselves generate significant amounts of water.

A composite plastics material of the invention can be processed using standard techniques (extrusion, injection-moulding, blow-moulding, or compression- moulding) into a wide range of shaped structural com¬ ponents (pipes, roof tiles, cladding, other building components etc.. ) In the case of a composite material of the invention in sheet form, the sheet may be part of a laminated arrangement, or may be non-laminated. Mention should be made in general of applications in which the composite material is in a form other than sheet form. For certain purposes, important forms of composite

material according to the invention include those in which the plastics material is other than polyethylene, is other than a polyolefin, or is other than a natural or synthetic rubber.

Preferably the fibre reinforcement comprises glass fibre. For present purposes, a fibre may be considered to be an thread-like structure of which the length is at least an order of magnitude greater than the diameter, possibly as much as two orders of magnitude greater, or even more.

The length of each fibre will in general be at least 5 cm, normally at least 7.5 cm and more especially at least 10 cm. Depending on the intended use of a fibre- reinforced composite material of the invention, the length of each fibre may also be 12.5 cm or above, for example, at least 15 cm, at least 20 cm, at least 25 cm, or at least 30 cm.

The cement filler in a composition or composite material of the invention may be any hydraulic cement, high alumina cement, white or black Portland cement, or a pozzolanic cement, and may be used alone or in admixture with one or more other materials of cementitious character including, for example, fly ash, volcanic ash, blast furnace slag, magnesium oxide or/ -alumina. Mixtures of cements may be used. Especially good results have been obtained using a calcium aluminate cement (such as that available from Lafarge). It is believed that

those results are attributable to the relatively high rate of hydration of such cements."'

The maximum particle size of the cement will in general be significantly less than 200 microns, advan¬ tageously less than 150 microns, preferably less than 100 microns, more especially less than 50 microns, in particular less than 25 microns.

The maximum particle size of any other inorganic solids in the surface-coating composition or composite material is also important, and will in general not exceed 200 microns, is advantageously less than 150 microns, preferably less than 100 microns, more especial¬ ly less than 50 microns, in particular less than 25 microns.

It is not essential for the maximum particle size of the cement, or its particle size distribution, to be the same as that of any other inorganic solids that may be present.

The surface area (BET) of the cement, giving an indication of its average particle size, may lie, for example, in the range of from 0.2-0.4 m ² /g, equivalent to an average particle diameter of approximately 5 to 10 microns.

It will be appreciated from the particle size criteria given above that a surface-coating composition or composite material according to the invention will be substantially free of mineral aggregates.

It is essential in the case of a surface-coating composition for the proportion by weight of cement to be greater than the total proportion by weight of any other inorganic solids, and that ratio by weight of cement : other inorganic solids preferably also exceeds 1:1 in the case of a composite material according to the invention. It is in general important for the cement to be the dominant inorganic component and the ratio by weight of cement : other inorganic solids is advantageously at least 2:1, preferably at least 3:1, more especially at least 4:1.

In the case of a composite material according to the invention, the proportion by weight of inorganic solids is to be calculated without including the fibre rein¬ forcement.

Disregarding any fibre reinforcement, the proportion by weight of inorganic solids other than cement in a surface-coating composition or composite material of the invention advantageously does not exceed 20%, pre erably does not exceed 15%, and more especially does not exceed 10%.

Advantageously, disregarding any fibre reinforce¬ ment, the proportion of the cement filler does not exceed 70% by weight, preferably does not exceed 60% by weight, and more especially does not exceed 55% by weight. A cement content in the range of from 40 to 50% by weight will be useful in many cases.

Disregarding any fibre reinforcement, the total content of cement filler and any other inorganic solids will advantageously not exceed 70% by weight, and will preferably not exceed 60% by weight, more especially 50% by weight.

Expressed on a dry solids basis, the proportion of cement filler in a surface-coating composition according to the invention will in general be at least 5-7.5% by weight higher than the corresponding proportion in the total composition including volatiles. Accordingly, a coating composition of the invention will in general contain at least 42.5% by weight of the cement filler, on a dry solids basis, advantageously at least 45% by weight and preferably at least 50% by weight.

In a composite material according to the invention, the proportion of volatile material will in general be significantly less than in a surface-coating composition (and may, for example, be of the order of 2% by weight). A surface-coating composition or composite material according to the invention may contain one or more pigments or other colouring agents, in a proportion which advantageously does not exceed 20% by weight (disregard¬ ing any fibre reinforcement) and preferably does not exceed 10% by weight. Proportions below 5% by weight have been found to be satisf ctory.

A pigment or colouring agent may be an organic or inorganic material, and may be any pigment or colouring

material suitable for use in plastics materials or in paint technology. A preferred class of pigments com¬ prises the titanium dioxide pigmen€is. * A titanium dioxide pigment may be used alone (in a proportion which may be in the range of from 3 to 10% by weight, preferably not exceeding 5% by weight) or in combination with one or more other pigments or colouring agents. In such a combination, the proportion of titanium dioxide will advantageously not exceed 10% by weight (based on the total composition or composite material), and the total proportion of any other pigment(s) or colouring agent(s) is likewise advantageously not greater than 10% by weight. Each of the said proportions preferably does not exceed 5% by weight.

Other pigments which may be mentioned include iron oxides, carbon blac , and organic pigments such as, for example, phthalocyanines, quinacridones, azo compounds and dioxazines.

A surface-coating composition of the invention may contain one or more additives customarily used in paint technology, which may for example be selected from thickeners, flow agents, matting agents, wetting agents, catalysts (driers or accelerators), anti-settling agents and anti-skinning agents or other inhibitors.

The term "drier" refers to a material which will catalyse the oxidative curing of drying oils or drying oil modified alkyd resins and which, when incorporated in

a varnish or paint, will accelerate the drying or curing process. Examples of suitable driers include salts of naphthenic acids or of Cg-C ₃₀ aliphatic acids. Preferred drier salts are those of cobalt and manganese, such as cobalt naphthenate or octoate. Compounds of calcium or lead may also be used.

The film-former or binder ^" in a surface-coating composition of the invention, and the solvent or diluent, may in general be any of those conventionally used in non-aqueous paints or varnishes. (The term "varnish" is used herein to denote a paint composition containing no pigment) .

It will be appreciated that, depending on the materials used, the film-former or binder may also act as a solvent or diluent, and that may in turn make it unnecessary to provide a separate ingredient for that purpose.

The surface-coating composition may in principle be so formulated that it dries by any of the processes customarily employed in paint technology, for example, so-called "lacquer drying" (drying by evaporation of solvent or diluent, with substantially no chemical reaction); oxidative drying (of, for instance, drying oils or other unsaturated materials, such as unsaturated polyesters); or drying by chemical reaction between ingredients of the composition (as in so-called "two- pack" systems) .

Examples of paint systems which may be mentioned include those based on alkyd resins (drying or non- drying, long-, medium- or short-oiled), boiled oils, stand oils, oleoresinous varnishes, and lacquers.

Mention should, also be made of epoxy-based coatings (for example, epoxy-ester resins, epoxy-alkyds, epoxy- phenolics) , polyurethane-based coatings, urea-formal¬ dehyde resins, melamine-formaldehyde resins, and acrylic resins.

Whilst a small amount of water can in principle be tolerated in a surface-coating composition of the invention (say, up to 1-2% by weight), it is considered essential that the composition should be substantially water-free prior to application, so as to avoid un¬ desirable pre-hydration and resultant inactivation of the cement filler. To avoid detracting from the enhanced protective properties obtainable according to the invention, it is important that there should be no significant hydration of the cement filler until the coating has been applied to the substrate surface.

In principle, the film-forming system may be such that the drying process involves a reaction which itself generates water as a by-product. Such a system may be acceptable provided that the resultant water content of the coating is not too high.

A surface-coating composition of the invention may be prepared by mixing of the various ingredients by

2/04297 - 13 -

standard techniques used in paint-technology, with the active cement filler being incorporated, in dry condi¬ tion, at any appropriate stage. Typically, the starting material will be any commercially available non-aqueous varnish and the cement and any other desired additives (pigment, drier, anti-skinning agent etc. ) will be mixed in thoroughly, normally with the addition of a non- aqueous solvent or diluent to produce a composition with adequate flow properties. As a further possibility, the varnish may already contain certain desired additives before the cement is incorporated.

Alternatively, the starting material may be a non- aqueous paint composition to which an appropriate proportion of the cement is then added, with addition of further solvent or diluent as necessary to obtain adequate flow properties.

The protective properties of surface-coating compositions according to the invention find application in a wide range of substrate materials, and for substrate products to be used in a wide range of environments. Thus, for example, the substrate material may be metal, wood, plastics or a building material, and the composi¬ tions may be used, for example, as external paints for domestic and industrial buildings; as a coating for cans, especially for beverages; as a protective coating for a wide range of marine structures such as oil rigs, vessels, dock and harbour installations, buoys and

underwater pipelines; and as a protective coating for pipes to be laid in aggressive soil conditions, for reinforcing steel rods in concrete, and for bridge structures. A further possible use comprises the protection of electronic circuit boards and other components.

The protective coating applied to a substrate in accordance with the invention may be the sole coating thereon, or there may be one or more additional coatings applied under and/or over the coating of the invention, for example, a priming layer may be applied directly to the substrate, and/or an outer decorative layer may be applied over the coating of the invention. In the latter case, the outer decorative layer will not itself provide protective properties equivalent to those of a coating according to the invention, but the underlying coating of the invention will still provide good protection. If desired, there may be an undercoat applied between a priming layer and the coating of the invention.

The following Examples illustrate the surface- coating compositions of the invention:

Example 1

% bv weight

Plastokyd sc-600 50.00

Cement 40.oδ Titanium dioxide 4.70

Bentone 34

(anti-settling aid) 0.30

Driers:

8% Cobalt naphthenate 0.30

33% Lead Siccatol 0.50

Methyl ethyl ketoxime 0.10

(anti-skinning aid)

White spirit 4.10

100.00

Notes on ingredients i) Plastokyd SC-600 (Croda Resins Ltd) is a silicone- modified orthophthalic alkyd resin, modified with soya bean oil and esterified with pentaerythritol. ii) Bentone 34 is an anti-settling aid available from Steetley Co. Ltd. iii) Lead Siccatol is available from Akzo Chemie UK Ltd.

Example 2

*Plastokyd 750 W/65 (Croda Resins Ltd) is a long oil length alkyd resin modified with low linolenic oil, esterified with pentaerythritol.

The- cement used in the compositions of Examples l and 2 may be, for instance, a black or white Portland cement or a high-alumina cement.

Example 3 - Determination of water uptake by various coatings

A) A series of different coatings according to the

invention, each 200 microns thick, were applied to both sides of 60 mesh nickel screen substrates (25 x 2 cm ² ) and the water absorption at 20°C, 100% relative humidity, of each sample coating was measured over a six-week period by weighing the samples at regular intervals. Each of the coating compositions according to the invention comprised 50% by weight of a cement in a varnish base, the specific formulation being as follows:

Plastokyd 750 W/65 8% cobalt naphthenate 33% lead siccatol

5% calcium siccatol Methyl ethyl ketoxime White spirit Cement

To provide a basis for comparison, similar tests were carried out on 60 mesh nickel screen substrates (25 x 2 cm ² ) bearing 200 micron coatings of various different compositions not containing cement according to the invention.

The results are summarised in the following table:

Table I

3 . 1

3 . 2

3.3 Varnish + Lafarge 1.3 0.024 cement

3.4 Neat varnish 9.3 0.116

3.5 varnish + 30% τio ₂ 7.1 0.120

3.6 White paint 7.6 0.130

It should be mentioned that whilst the water uptake and absorption of the comparison coatings (3.4-3.6) continued to increase significantly over the whole six- week period, the corresponding figures for the coatings of the invention (3.1-3.3) were not only substantially lower but also showed a significant levelling-σff after 20-30 days. It is believed that the levelling-off is attributable to the formation of impermeable cement hydrates caused by interaction between the cement filler and the water initially absorbed.

B) A similar series of experiments was conducted to those described under A), using the same coating compositions, except that the coated samples instead of being applied to nickel screen substrates, were cast onto polythene trays (each 58.09 cm ² ) and were immersed in water at 20°C instead of being exposed to water vapour at 100% relative

humidity.

The results for % water uptake and water absorption (g) after six weeks are summarised in the following table: •*—

Table 2

3.7 Varnish + black cement

3.8 Varnish + white cement

3.9 Varnish + Lafarge cement

3.10 Neat varnish

3.11 Varnish + 30% Tio ₂

3.12 White paint In the case of the coatings according to the invention (3.7-3.9), the same general levelling-off in water uptake and absorption after 20-30 days' immersion in water was observed as in the case of the samples exposed to water vapour at 100% relative humidity, and it is believed that the same protective mechanism (formation of impermeable cement hydrates) is responsible for the observed trend.

Example 4 - Determination of rate of oxygen diffusion through various coating films

200 micron sample films (13 mm diameter) were prepared from the same compositions as used in Example 3, by casting the compositions onto flat glass and then

carefully removing the cast film samples from the glass. Each sample was exposed to 100% relative humidity at 20°C for different times up to 40 days, and at the end of each exposure the sample was tested to determine the time taken for atmospheric.oxygen to diffuse through the film into a nitrogen-filled chamber. The time taken to reach 10 ppm oxygen was used as the standard in each case.

The results are shown in the following table, which gives for each sample the diffusion time to reach 10 ppm oxygen after 40 days' exposure of the sample film at 100% relative humidity and 20°C The table also gives the standard diffusion time (up to 10 ppm) for each dry sample before exposure to water vapour. Table 3

Diffusion time (min)

.1 Varnish + black cement

4.2 Varnish ^• + ^■ white cement

4.3 Varnish + Lafarge cement

4.4 Neat varnish

4.5 Varnish + 30% Tio ₂

4.6 White paint It will be seen that the standard diffusion times for the coatings according to the invention (4.1-4.3) were very much longer after 40 days' exposure than those of the comparison coatings (4.4-4.6). In addition, it should be noted that whereas the oxyggen permeability of

the comparison coatings increased following exposure to water vapour, (as a result of progressively increased porosity following swelling of the varnish base) that of the coatings of the invention showed a. significant decrease over the 40-day period. It is believed that the cement hydrates formed following moisture absorption will tend to block oxygen-permeable pores.

Example 4.1 - Rate of oxygen diffusion as a function of cement concentration in the coating composition

The procedure of Example 4 was repeated using coating compositions having basically the same formula¬ tion as in that Example but with varying cement content. As in Example 4, the standard diffusion time (up to 10 ppm oxygen in a nitrogen-filled chamber) was measured for each sample after 40 days' exposure to water vapour at 100% relative humidity and 20°C

The results are shown in Figure 1, from which t is evident that the standard oxygen diffusion time began to rise rapidly after 35-37.5% by weight cement concen¬ tration, falling off again about 50% by weight.

The symbols used in Figure 1 have the following meanings:

V = varnish base

BC = Black Portland cement

WC = White Portland cement

Laf = Lafarge high-alumina cement.

Example 5

Compositions according to the invention ( 50% cement

in a varnish base) were painted onto steel coupons (each l cm x 1.2 cm), 0.3 mm thick) at a loading of 45 mg/cm ² . Before the coatings were applied, ^" the" steel was polished with sandpaper, washed with distilled water and dried. The reverse side of each coupon was protected with a heavy coating of lacquer.

The coated samples were immersed in 3% NaCl solution at room temperature for different periods of time.

To provide a measure of the extent of corrosion, the short-circuit current (the so-called "corrosion" current) between the coated steel substrates as cathode and a zinc anode was measured at daily intervals. The zinc anode and the steel cathode were connected only when the short- circuit current was being measured.

In order to provide a basis for comparison, the test procedure of Example 5 was repeated using coatings comprising white gloss paint, varnish alone and a composition comprising varnish and a high surface-area silica.

The results are shown in the following Table (Table 4). The black cement was Blue Circle Portland Cement, and the white cement was a Lafarge aluminous cement "Secar 71". The varnish was u-v resistant yacht varnish supplied by International Paint. Each short-circuit current given was the average of four samples.

As can be seen from Table 4, there was little or no observed corrosion current in the case of the steel

samples protected by the cement-containing compositions of the invention. It should be noted that the eventual fall-off in the corrosion current in the case of the samples coated with gloss paint, varnish alone and the varnish/silica admixture was due to the fact that most of the steel had corroded away.

TABLE 4:

Example

The test procedure described in Example 5 was repeated using various coatings on the steel substrates, but, in order to provide a more stringent test, the steel samples were connected to the zinc anode continuously throughout the test period, and not merely at the time of measurement of the short-circuit current. The coatings were applied to a loading of 50 mg/σm ² and the steel samples were circular, with an area of approximately 4 sq. cm.

For the purpose of Example 6, the comparison experiments were carried out using uncoated steel samples and samples coated with white gloss paint, varnish alone, and with compositions comprising varnish/silica (30% silica by weight) and varnish/sand.

The results are shown in the following Table (Table 5) . Each short-circuit current given was the average of four samples. The markedly improved, corrosion-resistance of the cement-containing compositions of the invention is immediately evident.

TABLE 5

^~ Fβ Varnish wTϊ> Vfβand V silica V+WCB V4WC8 V+BOC ^"

Short-circuit current (μA)

DAY

Ul 1

^' i

W.P: gloss paint WCS: white alumina cement

V : varnish BOC: black portland cement

WCB: white portland eβnent

Example 7

Corrosion testing of a series of coated steel samples was carried out broadly as described in Example 6, except that a graphite anode was used instead of the zinc anode (to eliminate the formation of zinc hydroxide) and that a 6 volt battery was applied continuously across the electrodes in order to provide an accelerated- corrosion regime.

The coating compositions comprised varnish contain¬ ing varying proportions of white Portland cement. The results are shown in the following Table (Table 6), which gives the short-circuit current between the electrodes after times up to 94 hours.

The marked increase in corrosion-resistance obtained at cement concentrations of 37.5% by weight and above is clearly evident, as is the progressive decrease in corrosion-resistance at cement concentrations of 60% by weight and above. Each reading given was the average of three samples.

TABLE 6

Time (hours) 20 38 94

Short-circuit current (μA)

Example 8

A coating composition according to the invention (50% by weight Black Portland cement in varnish) was applied to both sides of a series of steel substrates (each having an area of approximately 2 cm ² ) and the coated substrates (loading: 100 mg/cm ² ) were exposed to ultra-violet radiation in an accelerated weathering tester. The procedure was based on the ASTM standard (sequential cycles comprising 4 hours incubation at 100% humidity, 50 ^* C, followed by 6 hours of ultra-violet irradiation at the same temperature) . After exposure for various periods the samples were subjected to an accel¬ erated short-circuit test by applying a 9-volt battery (Leclanche cell) across the coated substrate as anode and a graphite cathode, in 3% by weight NaCl. The time

taken for the short-circuit current to reach 1 mA was taken as the basis for comparison.

The results are given in the following Table (Table 7) , which also shows results for steel substrates coated with varnish alone and with varnish containing 30% silica.

TABLE 7

Varnish Varnish+ Varnish+ silica cement (7:3) (i:i)

Time (hours) to reach 1 mA

7.5 36

4.1 17

1.9 10.5

0.5 7.9

0.28 5.5

0.15 1.5 0.02 1.2

The corresponding improvement ratios for varnish/- silica and varnish/cement, each as compared with varnish alone, are given in the following Table (Table 8).

TABLE 8

Varnish+silica (7:3)/ Vamish+cement (1:1)/ Varnish Varnish

Improvement Ratios

6.92

6.54

16.15

30.38

68.75 150.00

Example 9

Table 9 summarises the results of accelerated corrosion testing of mild steel substrates (4.2 cm ² ) coated with cement/epoxy resin composite materials containing varying proportions of White Portland Cement. The loading in each case was 50 mg/cm ² , and the resin was Isopσn Fast Glass Resin. The accelerated corrosion testing was carried out as described in Example 7.

TABLE 9

Time (hours) 11 20 47

Short-circuit current (μA)

The general trend is clear from Table 9.