FR2469436A1 - Alkyd-urethane paints contg. molybdenum di:sulphide or ferric oxide - used esp. for coating solar collectors, have excellent IR absorption properties - Google Patents

Abstract

Paint compsn. comprises a mixt. of (by wt. on total compsn.) 60-70%, esp. 6% MoS2 or Fe2O3 and 30-40%, esp. 35% of at least one alkyd-urethane. The latter is pref. comprised of 20-25% (20%) of at least one urethane and 10-15% (15%) of at least one alkyd, and is in the form of a matt colourless emulsion. The compsn. may also contain at least 20% of a diluent such as white spirit, trichloroethylene, turpentine oil, etc. The paints have excellent infra red absorption properties and are useful (esp. in layers at least 8 microns thick) for coating the front panels of solar collectors. The paints have a high performance, low cost and high heat resistance.

Description

 The subject of the invention is a paint based on molybdenum disulphide or ferric oxide and the solar collectors coated with said paint.

 The technical sector considered is that of paints and varnishes, more particularly those that capture infrared radiation and that of energy recuperators, especially solar.

It is known that an opaque paint, or a varnish, transparent or colorless, consists essentially of a binder, basic substance giving rise to a film covering the surface to be painted, possibly to make the binder fluid, of a solvent, which evaporates, and possibly additives such as pigment, charge additives ... adding or reinforcing properties to the paint.

We already know that many improvements to current paints have been made in recent years, in particular to facilitate application. Speed up drying, increase mechanical resistance to corrosion or even diversify the aesthetic appearance of the film. obtained after application.

 Are known in particular paints based on alkyds, polyester resins modified with oil offering a great diversity of use, being able to react with. many products. Numerous modifications of the alkyds have been studied, and in particular that made in the presence of isocyanates: alkyd urethanes are then obtained, which are used in particular in the composition of printing inks and paints.

 Solar collectors are also known whose face exposed to the sun is covered with a coating intended to capture the sun's rays. This coating must also resist the destructive action of the external environment and that of the rays, in particular UV rays.

We looked for a new paint with new properties, the application of which to the sensors provides a solution to the corrosion of the external front face of the sensor with a new ability to capture the I.R.

To achieve this objective, the paint according to the invention contains the following constituents, the percentages of which are indicated by weight of constituent relative to the total weight of said paint.
- between 60 and 70, preferably 65% of a first constituent taken from the following group: MoS2, Fe203;
- between 30 and 40%, preferably 35% of a second constituent comprising at least one urethane alkyd.

Preferably, the first constituent is an anhydrous powder, to allow better homogeneity in the alkyd-urethanes; and thus to obtain a perfect mixture and a product with uniform properties over the entire surface of the film.

said alkyd urethanes are prepared from alkyds and urethanes, in the following respective proportions
- between 20 and 25% of at least one urethane,
- between 10 and 15% of at least one alkyd.

 In one embodiment, the second constituent further comprises the usual components of a varnish associated with said alkyd-urethanes and is thus presented in the form of a matt and colorless emulsion.

 In view of its use, the paint must be diluted in at least 20% of a diluent preferably taken from the following group. : said spirit, trichlorethylene, turpentine the percentage being expressed by weight of diluent relative to the weight of said paint before dilution.

 In an application of this paint, a solar collector has a face exposed to the sun, coated with a layer of paint having the aforementioned composition.

 In a particular embodiment, a sensor is planar and said layer of paint is at least 8 11, that is to say of sufficient thickness to capture calories and protect the front face of said sensor.

 In a preferred embodiment, there is close to said front face and parallel thereto a window, the distance between them being at most 8mm and preferably between 3 and 5mm.

This measure allows, in addition to protection, in particular to avoid refractive phenomena, detrimental to the good results of the device.

 The result of the invention is a new product consisting of a paint based on MoS2 or Fe2O3 and an application to solar collectors of this paint.

 The main advantages of the invention are to provide a coating having the new property of capturing calories during solar radiation and of withstanding very high temperatures, of the order of 500 "C, caused by the heating of the front of the sensor under the sun.

 Another advantage is the low cost price of such a paint, the thickness of the layer being moreover minimal and sufficient for satisfactory results.

 The improvement of a solar collector by this application therefore does not bring a marked increase in its cost.

 An application of the invention is the manufacture of solar collectors.

Other characteristics and advantages of the invention will be better understood on reading the description which follows, accompanied by the appended drawings, where
- The single figure is a section through a solar collector bearing the paint according to the invention.

 The percentages indicated in the present description refer to the weight of the constituent relative to the total weight of the composition.

The main characteristic of the paint according to the invention is that it contains a constituent capable of capturing the calories coming from solar radiation striking a body coated with said paint.

 This constituent is taken from the following group: molybdenum disulphide and ferric oxide. This constituent is used in the state of purity supplied on the market. It is preferably taken in the form of an anhydrous powder.

In addition, a constituent is added to give the paint resistance to the destructive action of UV rays and to prevent rapid cracking and shaving of the film.

alkyde
Cette réaction donne des produits plus résistants à l'eau et à l'abras ion.For this purpose, we take at least one alkydeùrethanne. We know that this second constituent comes from alkyds and isocyanates (urethanes) according to the following reaction
RNCO + HO - alkyd y

alkyd
This reaction produces products that are more resistant to water and abrasion.

 the second constituent is preferably produced in the form of a varnish containing alkyd-urethanes accompanied by the solvents and any dyes or pigments that are usual and known by the manufacturers of paints and varnishes. It then appears as an emulsion, preferably matt and colorless. Once diluted, it is easy to spread, dries quickly and the resulting film resists aging without cutting or chipping.

Such a paint is prepared by gradually mixing the powder of the first constituent into the second constituent, with stirring. This gives a product of bluish gray color too consistent to be spread as is. Before use, it must be made fluid to allow application in a very thin layer of the order delO p, in the application below, non-limiting example, more generally with a thickness of between 8 and 12p.

 When it is desired to use the paint thus formed, it is mixed with a diluent suitable for compositions based on alkyd-urethanes. White spirit, trichlorethylene, essence of terebenthine are preferably used, for example at at least 20% thinner.

The composition of the paint according to the invention is as follows
- between 60 and 70% of molybdenum disulphide or ferric oxide;
between 30 and 40% of at least one alkyd-urethane.

In a preferred embodiment example, a painting of composition is taken below
- 65 Z of pure MoS2 or Fe2O3,
- 20 Z of urethanes,
- 15% of alkyds.

 This paint withstands a very high temperature, such as 450 "C.

A composition at 60 Z of the first constituent captures less well than solar radiation: in full sun and mistral, a flat collector, whose face exposed to the sun is covered with a film of 10 of this composition, rises at most to 900C, whereas, all other things being equal, a sensor for which we have taken a paint at 65% vajusqu a + 1450C,
A 700C paint of MoS2 or Fe2O3 is more fragile than the previous ones and requires more protection. It may, in the long run, crack or take off in shreds.

We will describe below a particular embodiment in an application of said paint
This, offering the property of capturing the sun's rays with good capacity, can be applied to the front face of a sensor exposed to the sun.

 Bringing the usual advantage of protecting this surface from external aggressions, it also adds the advantage of improving the results of such a sensor, without considerably increasing the price. Such an application applies to a sensor of any type. We have chosen, here, to show an embodiment of a solar collector-plane.

 According to one embodiment, shown in section in the single figure, the sensor consists of a housing 1 comprising a bottom la comprising longitudinal grooves lb of a trapezoidal cross section and side walls le, so that the housing is generally rectangular in shape and is open at the top.

On this housing 1 is disposed a plate 2 which completely closes the opening of the housing 1. This plate can be produced either from a galvanized steel plate, or from a stainless steel plate.

 This plate has a front face exposed to the sun 2a, a rear face 2b. The face exposed to the sun 2a is coated with a layer of paint according to the invention, the rear face 2b is brought into contact with a coil 3, placed in the housing 1 and embedded in an insulator 4, for example wool glass or vermiculite or any other insulator capable of withstanding a temperature of at least 1500C.

 In the coil 3 circulates a heat transfer fluid such as water or a gas, which fluid rises in temperature under the effect of the sun's rays.

 Above the plate 2 and close to the latter, a window 5 is arranged. The latter is parallel to the said plate and is at a distance therefrom of at most 8 mm, preferably between 3 and 5 mm. . This window is embedded in a frame made of L-shaped iron, which frame is fixed to the housing 1.

The sensor further comprises a strut 7 adjustable in length to allow the orientation of the sensor. This strut 7 is articulated on the grooved bottom of the housing and is intended to be pricked into the ground.

The sensor may comprise, at its part located on the ground side, two or more feet 8 that are tapered to be poked into the ground.

 We thus capture the maximum of radiation by achieving an excellent "black body" and avoiding refractive phenomena harmful to the proper functioning of the device.

 In a particular embodiment, take a standard glass pane, preferably of a bronze green tint and thickness 3mm, a plate or stainless steel / galvanized 5 / 10mm thick, covered with a layer of paint. îOr on its front side, a coil filled with water of inside-outside diameters 10-12mm and glass wool placed at the rear of the coil to a minimum depth of 45mm or maximum of 100mm, the rear 7 of the sensor being castellated as shown in the figure.

This coil is connected to a water reserve which is brought to a higher temperature according to atmospheric conditions. This reserve constitutes a mode of supply of hot water which can go as far as replacing the traditional water heater and constituting an auxiliary heating of the rooms of an apartment.
We tested the planar sensor as specified in the particular embodiment above and obtained the following results
90 C # # 130 C on 08/30/1979 +130 C at 6 p.m. when the weather is nice
90 C # # 130 C on 19.09.1979
# 145 C full sun and mistral on 09.21.1979
4115 C on 25.09.1979, by mistral force 8, outside temperature
lower = + 170C = the boiler water is at 88 "C.

 Of course, such a sensor could have air heat transfer fluid, for example, which would allow heating by hot forced air, lthiver, and could be used for air conditioning in summer by annexing a refrigerant exchanger of known type. .

 Of course, without departing from the scope of the invention, the paint and the solar collectors which have just been described could be replaced by the Man of the art by paints and solar collectors fulfilling the same function.

Claims (11)

1 - Painting characterized in that it contains the following constituents, of which the percentages are indicated by weight of constituent relative to weight  total of said painting  - between 60 and 70%, preferably 65% of a first constituent taken  in the following group: MoS2, Fe203;  - between 30 and 40%, preferably 35%, of a second constituent com  carrying at least one urethane alkyd. 2 - Painting according to claim 1, characterized in that said first  constituent is in the state of anhydrous powder. - between 10 and 15% of at least one alkyd. - between 20 and 25% of at least one urethane,  killing related to the total weight of said painting  taken in the following proportions, expressed in weight of consti  that said alkyd urethanes are prepared from the following components 3 -Paint according to any one of claims 1, 2, characterized in 4 - Paint according to any one of claims 1 to 3, characterized in  that said second constituent further comprises the usual components  of a varnish associated with said alkyd-ure-thanneset that it comes under the form of a matt and colorless emulsion. 5 - Paint according to any one of claims 1 to 4, ready for sound  application on the support to be covered, characterized in that it comprises  in addition at least 20% of a diluent preferably taken from the group  next: white spirit, trichlorethylene, turpentine essence,  percentage being expressed by weight of diluent relative to the weight of said paint before dilution. 6 - Solar collector characterized in that it has a face exposed to the sun  covered with a layer of paint comprising the following constituents  - between 60 and 70 X, preferably 65 Z of a first constituent taken  in the following group: MoS2, Fe203;  - between 30 and 40 X, preferably 35%, of a second constituent com  carrying at least one urethane alkyd. 7 - solar collector according to claim 6, composed of a plate having  a front face exposed to the sun and a rear face, of heat transfer fluid, disposed against said rear face, and an insulator separating said fluid  and said rear face of the external environment, characterized in that said  front side is covered with said paint. 8 - Sensor according to any one of claims 6, 7, characterized in that  that said layer of paint has an average thickness between 8 and 12p. 9 - Sensor according to any one of claims 7, 8, characterized in that that it further comprises a window disposed parallel to said face before and in front of it, at a distance from it of at most 8mm,  and preferably between 3mm and 5mm. 10- Sensor according to any one of claims 7 to 9, characterized in  what said insulator is taken from the group of insulating products and re  resistant to a temperature of at least 1500C, preferably wool glass, vermiculite. 11- Absorber element for a solar collector according to any one of the reven dications 6 to 10, characterized in that it has a face intended to be exposed to the sun coated with said paint.