Coating material with reflective properties in two wavelength ranges and absorbent properties in a third wavelength range

Abstract

The invention relates to a coating material having reflective properties in two wavelength ranges and absorbing properties in a third wavelength range, which can also obtain energy from the near-infrared range of the sunlight spectrum in the case of optically perceptible light colors without re-emitting it in the thermal radiation range in the usual way. The essence of the invention is the following: to a binder having a transparency of more than 40%, preferably more than 60% in the wavelength ranges of 0.38-0.75 ?m and 5-100 ?m, but at least in the ranges of 0.4-0.7 ?m and 10-50 ?m, whose refractive index n in the aforementioned wavelength ranges is below 2.0, preferably below 1.7, and particularly preferably 1.5, are added a) in an amount of 2-30% by weight, based on the wet weight of the coating material, of plate-shaped first particles, which have a thickness of less than 10 ?m, preferably less than 5 ?m, and which have a surface area (length x width) of more than 100 ?m2, preferably more than 2500 ?m2,and particularly preferably greater than 10,000 µm2, and their reflectivity R in the 5-100 µm wavelength range of thermal radiation, but at least in the 10-50 µm wavelength range, is greater than 40%, preferably greater than 60%; and which are b) at least partially coated by second particles which only show a transparency of more than 40%, preferably more than 60% in the visible range of solar radiation in the wavelength range of 0.38-0.75 μm, but at least 0.4-0.7 μm, and in the thermal range of 5-100 μm, but at least 10-50 μm, but have the highest possible absorption of more than 20%, preferably more than 40% in the near infrared range of the solar spectrum in the wavelength range of 0.8-2.5 μm, at least 1.0-2.0 μm, and which have a refractive index in the visible range of solar radiation in the wavelength range of 0.38-0.75 μm, but at least 0.4-0.7 μm, greater than of the binder; and in addition to the higher refractive index of the second particles, the size of the second particles is chosen such thatthat optimal backscattering and thus reflective effects occur in the visible range of solar radiation. à,

Description

The invention relates to a coating material with reflective properties in two wavelength ranges and absorbing properties in a third wavelength range. Known coating materials, such as wall paints used on the interior surfaces of houses, consist of binders, pigments and various additives. In most cases, white wall paints are preferred in order to make the most of light reflection. In addition to the reflection of the light walls in the room, it would also be desirable in winter if the heat radiation emanating from the objects in the room, the internal walls of the house and the people staying in the room were reflected by the inner sides of the outer walls. At a temperature of 20 °C, the inner wall of a house: It emits Μ=ε·σ·Τ4=397 Wm-2 heat energy. Here, ε is the surface emission rate, σ is the Stefan Boltzmann constant, whose value is 5.67 x 10~8, and T is the surface temperature in Kelvin. According to Wien's law, the wavelength corresponding to this temperature is 9.89 pm, which is in the thermal infrared range. This means that the wall radiates with a radiation character according to Planck, with a radiation maximum of 9.89 pm. Only 5% of this heat radiation is reflected from the inner side of the opposite external wall, as the coating materials used in houses strongly absorb heat radiation in the wavelength range of 5-100 pm. The remaining 95% goes outside due to the heat conduction of the wall and is lost to the room. In the case of winter sunshine, due to the low position of the sun at this time of the year, the solar radiation can reach an internal wall through, for example, a south-facing window of the house, and according to the reflective properties of the wall color, the solar radiation will be absorbed in the spectral range of 0.3-2.5 pm, and accordingly converted into heat transforms. Conventional wall paints naturally use pigments that also reflect in the near-infrared range of 0.8-2.5 pm after the visible range of the sunlight spectrum, and therefore reflect most of the sunlight's energy in this wavelength range, like the "white" color in the visible in range. In addition, the pigments and binders in conventional paints have broad absorption bands in the thermal infrared range, i.e. the range of thermal radiation. thus, 95% of the heat that could have been obtained from the sun's radiation is immediately released in the form of heat radiation. Although this heat is available to the room, the room is only warm when the sun is shining. Due to the low energy output in the near-infrared range, and especially the 95% immediate surface radiation of heat, it is not possible to store energy gains for the coming night. A similar thing applies to the outer sides of the house walls. Optically perceptible white and light wall paints are predominantly used, mostly for the sake of aesthetic appearance. Since the pigments applied to interior surfaces are similar, these paints also have a high reflectance in the near-infrared spectrum of sunlight. As in the case of wall paints applied internally, the reflection of wall paints applied externally in the thermal infrared range, i.e. in the range of heat radiation, is low. Due to the wide absorption bands in this wavelength range of the commonly used binders and pigments, 95% of what could have been converted from sunlight into heat in the wall paint is re-radiated. The task of the present invention is that the direct and diffuse solar radiation available even in winter positively influences the heat balance of a house in a simple way, while leaving the aesthetic aspects of the color of the house walls, such as the light shade, in the usual way. According to the invention, this task was solved with a coating material with reflective properties in two wavelength ranges and absorbing properties in a third wavelength range, which is characterized by the fact that for a binder with a transparency of more than 40%, preferably more than 60%, the 0.38- In the wavelength ranges of 0.75 pm and 5-100 pm, but at least in the ranges of 0.4-0.7 pm and 10-50 pm, whose refractive index n is below 2.0 in the aforementioned wavelength ranges , is preferably below 1.7, and particularly preferably 1.5, added to seam a) plate-shaped first particles in an amount of 2-30% of the wet weight of the coating material, the thickness of which is less than 10 pm, preferably less than 5 pm, and whose surface area (length x width) is more than 100 pm2, preferably more than 2500 pm2 , and particularly preferably greater than 10,000 pm2, and their reflectivity R in the wavelength range of 5-100 pm of thermal radiation, but at least in the wavelength range of 10-50 pm is greater than 40%, preferably greater than 60%; and which b) they are at least partially covered by second particles that are only in the visible range of solar radiation in the wavelength range of 0.38-0.75 pm, but at least in the range of 0.4-0.7 pm, and thermal radiation 5-100 pm, but at least in the range of 10-50 pm, they show transparency greater than 40%, preferably more than 60%, whereas in the near-infrared range of the sun's spectrum, 0.8-2.5 pm, but at least 1, In the 0-2.0 pm range, they have the highest possible absorption, exceeding 20%, preferably more than 40%, and whose refractive index of the visible range of solar radiation is 0.38-0.75 pm, but at least 0 in its wavelength range of .4-0.7 pm, it is greater than that of the binder; and in addition to the higher refractive index of the second particles, the size of the second particles is chosen in such a way that an optimal backscattering and thus reflective effect occurs in the visible range of the sun's radiation. The invention therefore relates to a coating material that can be endowed with reflective properties in the visible range of 0.4-0.7 pm and absorbing properties in the near-infrared range of 0.75-2.5 pm. The one beyond that is 3-100 pm HU 222 371 BI in the thermal infrared range, especially in the 5-50 pm range, i.e. in the wavelength range in which surfaces with a temperature of 0-30 °C have their radiation maximum, has a high degree of reflection with a small amount of absorption. This means that the coating material has little heat emission in this wavelength range. In addition, for the production of white and light coating materials in the visible range, we choose pigments that are transparent in the visible range and have a higher refractive index than the binder, thus resulting in greater backscattering in the visible range, thus making them white and light. The selected pigments absorb more or less in the near-infrared range of 0.75-2.5 pm, in the thermal infrared range, especially in the 5-50 pm range, the pigments are again predominantly transparent, so they will hardly absorb thermal radiation. In order to better distinguish them from other additives, these pigments are called second particles in the rest of the description. Between 5-50 pm, in order to achieve reflection in the thermal infrared range, plate pigments are added to the binder, whose reflectivity (R) according to the formula R(n-l)2+k2(n+l)2+k2 is greater than 40%, especially greater than 60 %. In the formula, n is the refractive index of the pigment and k is the absorption coefficient. For the sake of clarity, these pigments are called first particles in the rest of the description. The reflectance of these pigments is broad-band, which means that they reflect in both the visible, near-infrared and thermal infrared regions. In addition, we only want the reflective property in the thermal infrared range, they should be invisible in the visible range if possible. This can be achieved on the one hand by layering the second particles directly onto the first particles, or by layering them loosely in the binder. It also seems advantageous to choose the sheet size of the first particles as large as possible, as they contribute less to the graying of the color sensation. In the near-infrared range of 0.75-2.5 pm, i.e. beyond the visible wavelength range, the desired absorption of the binder is caused on the one hand by the second particles themselves, and on the other hand by additional particles used to color the binder. Additional particles were selected to be spectrally selective in the visible region and reflect only discrete colors such as red, green, or blue, have high absorption in the near-infrared region, and high transparency in the thermal infrared region to the reflection of the first particles in this range is preferably only slightly disturbed. The selection of the binder in which the above-mentioned pigments are dispersed depends on the surface to be treated. Basically, however, the binder must show high transparency in the visible and thermal infrared ranges, so that the backscattering and reflective effect of the coating material becomes possible in these wavelength ranges. It is preferred that the binder has absorption bands in the near-infrared region. For wall surfaces, dispersion binders are proven due to their ventilation properties. Mixtures of polyethylene-based dispersions and mixtures of polyethylene oxides containing a small amount of acrylic dispersion are particularly suitable for the binder according to the invention. For metal surfaces, such as metal window frames for interior and exterior use, but also for metal facades and metal structures, such as conservatories, solvent-containing binders are more suitable, such as cyclorubber and hydrated hydrocarbon resins, where the latter are preferably used only in interior spaces. An advantageous further development of the inventive idea consists in selecting the first particles from the group of metals, such as aluminum, copper, silver, gold, nickel, zinc, iron; from metal alloys such as stainless steel, brass, bronze; from the group of semiconductors, such as silicon, germanium; from the group of doped semiconductors, such as doped silicon. An advantageous development of the inventive idea consists in making the first particles electrically conductive and coating the first particle layer with an additional electrically conductive thin layer to increase the chemical resistance and gloss level. Another advantageous development of the inventive idea is that the first particles have electrical conductivity and that they are coated with an electrically non-conductive thin layer to form a color. Another advantageous development of the inventive idea is characterized in that the first particles consist of an electrically non-conductive material, such as plastic plates or mica plates, which are coated with an electrically conductive layer, such as doped tin oxide, indium tin oxide, or antimony they are coated with tin oxide. A further advantageous development of the inventive idea consists in selecting the second particles from the group of the following materials: metal sulphides, such as lead sulphide and zinc sulphide; metal selenides such as zinc selenide; chlorides such as sodium and potassium chloride; fluorides such as calcium fluoride, lithium fluoride, barium fluoride and sodium fluoride; antimonides such as indium antimonide; metal oxides such as magnesium oxide, antimony oxide and zinc oxide; of barium titanate; of barium ferrite; from pure calcium sulfate - CaSO4, from precipitated barium sulfate, from a crystal mixture of barium sulfate with zinc sulfide, like lithopone. Another advantageous development of the inventive idea is that the additional particles, if they are selected from the group of inorganic color pigments, are metal oxides, such as iron3 HU 222 371 Β1 oxides, especially transparent iron, red and yellow oxides such as BASF's sicotrans formulation, but also Bayer's α-iron oxides, iron oxide black pigments such as pigment black 11, chromium -oxides such as chromium oxide green, lead oxides such as minium, molybdenum oxides, metal oxide mixtures and iron blue pigments such as Degussa's vossen blue, which is microcrystalline Fe(II), It is based on Fe(III) cyanide complexes and, if they are selected from the group of organic dye pigments, disazo pigments, indigo pigments, especially thioindigo derivatives, such as 7,7'-dichlorothioindigo, phthalocyanines. Another advantageous development of the inventive idea is that the binder is a solvent-containing binder, an aqueous varnish, or an aqueous dispersion, and a cyclorubber, chlorine rubber, butyl rubber, hydrocarbon resin, α-methylstyrene-acrylonitrile copolymers, polyesterimide, butyl acrylic acid -ester-based acrylate resin, polyacrylic acid ester, especially polyacrylic butyl ester, polyethylene-based thin dispersion, polyethylene oxide-based thin dispersion, ethylene-acrylic acid copolymer-based thin dispersion, methacrylate-based, acrylate / styrene-based thin dispersion, vinyl-pyrrolidone-vinyl -acetate copolymers, atactic polyisopropyl acrylate, poly(vinyl pyrrolidone), or a mixture of the dispersions and varnishes mentioned above. In the following, the subject of the invention will be elucidated in more detail based on examples and in the context of experiments. Example 1 The effect of the coating material according to the invention is demonstrated on an interior wall located opposite a south-facing window. We use a dispersion mixture consisting of the following components: 200 g polyethylene dispersion with 40% solids 200 g polyethylene oxide with 40% solids g acrylic dispersion with 40% solids g antifoam g thickener 240 g of water 200 g of zinc sulfide 200 g zinc oxide g chromium oxide green g plate aluminum bronze The mixture resulted in a yellow-green, light wall paint, which we used to paint part of the wall. After the paint had dried, we measured the surface temperatures in the untreated and painted areas of the wall after exposure to sunlight. Despite the conduction of heat in the wall, the part of the wall painted with the paint according to the invention was 15 °C warmer than the other part. Example 2 The above experiment was also carried out with a recipe changed compared to Example 1. We used Bayer's α-iron oxide red instead of chromium oxide green and doped silicon particles instead of aluminum bronze. The color of the mixture was light with a slightly red tone. After exposure to sunlight, a temperature increase of 12 °C was measured compared to the untreated wall section. Example 3 We painted the inside of an exterior wall with the paint according to the second example. At night, we were able to determine with a thermal imaging camera that less heat escapes from the house in this location. Example 4 During a further experiment, the zinc sulfide and zinc oxide pigments used as second particles were replaced with the same amount of lithopone on a south-facing exterior wall of the house. The acrylic content of the mixture was slightly increased. For the reflection in the thermal infrared range, zinc flakes with a surface area of ​​10,000 pm2 were added as the first particles. It did not change the shade of the mixture and resulted in a light, refracted white color. The part of the wall painted with the paint according to the invention was 11 °C higher in temperature than the untreated part. Example 5 A small amount of calcium sulfate and barium ferrite was added to the same amount of mixture. In the near-infrared range of the sunlight spectrum, the absorption could thus be clearly increased, although the color effect in the optically perceptible range was almost white. At night, it was observed with a thermal imaging camera that the parts of the house that were painted with the paint according to the invention radiated significantly less heat than the untreated areas. Example 6 The aluminum frame of one of the two south-facing windows was painted on the outside with cyclorubber-based lacquer, which, in addition to second particles based on zinc oxide, contained a small amount of iron oxide black pigments as additional particles, and stainless steel flakes as first particles, as well as a softener that transmits infrared light. The inside of the window frames was painted with a hydrated hydrocarbon resin-based varnish. As second particles we used litho point, as first particles we used silver-coated nickel flake, and as additional particles we used transparent iron oxide to create the tone of the color. During the day, energy gains could be channeled into the interior, predominantly from the near-infrared range of the sunlight spectrum. At night, with the help of a thermal imaging camera, it was possible to observe that the window frames treated with the coating material according to the invention radiated less heat to the outside compared to the untreated ones. In the following, currently known solutions within the scope of the invention are described: US 4,916,014 describes a coating material that has reflective properties in two wavelength ranges. However, its disadvantage, in view of the tasks related to the present invention, is that in addition to a high degree of reflection in the range of visible light, it must also reflect in the near-infrared range of the sunlight spectrum in order to prevent the heating of buildings painted with it. HU 222 371 Bl DE 1 227 594 discloses an infrared-reflective, fire-resistant protective layer that has strong reflective properties, at least in the near-infrared wavelength range. However, its disadvantage, in view of the tasks related to the present invention, is that this layer reflects in the near-infrared range, but due to the selected materials, it absorbs above a wavelength of 10 pm in the thermal infrared range, and thus has an emitting effect.

Claims

PATENT CLAIMS 1. A coating material having reflective properties in two wavelength ranges and absorbing properties in a third wavelength range, characterized in that a) it has a binder having a transparency of more than 40% in the wavelength ranges of 0.38-0.75 and 10.0-50.0 pm and a refractive index n of less than 2.0 in the same wavelength ranges; and b) it has 20.0-30.0 wt.% of plate-shaped first particles, calculated on the wet weight of the coating material, which have a thickness of less than 10 pm, a surface area (length x width) of more than 100.0 pm and a reflectivity R of more than 40% in the wavelength range of 10.0-50.0 pm;and c) the first particles are at least partially overlapped by second particles whose transparency exceeds 40% only in the wavelength range of 0.4-0.7 pm and 10.0-50.0 pm, but whose absorption is greater than 20% in the wavelength range of 1.0-2.0 pm and whose refractive index in the wavelength range of 0.4-0.7 pm exceeds the refractive index of the binder; and the size of the second particles is selected in a way that ensures optimal backscattering and thus reflective effect in the wavelength range of 0.4-0.7 pm.; 2. The coating material according to claim 1, characterized in that the transparency of the binder is greater than 60% in the wavelength range of 0.4-0.7 pm and 10.0-50.0 pm.

3. The coating material according to claim 1, characterized in that the transparency of the binder in the wavelength range of 0.38-0.75 pm and 5.0-100.0 pm exceeds 40%.

4. The coating material according to claim 2, characterized in that the transparency of the binder in the wavelength range of 0.38-0.75 pm and 5.0-100.0 pm exceeds 60%.

5. The coating material according to claim 1, characterized in that the refractive index n of the binder is less than 1.7 in the wavelength ranges of 0.4-0.7 and 10.0-50.0 pm.

6. The coating material of claim 5, wherein the refractive index is about 1.

5.

7. The coating material of claim 1, wherein the thickness of the plate-shaped first particles is less than 5.0 µm.

8. The coating material according to claim 1, characterized in that the surface area (length x width) of the plate-shaped first particles is greater than 2500 pm2.

9. The coating material according to claim 8, characterized in that the surface area (length x width) of the plate-shaped first particles is greater than 10,000 pm2.

10. The coating material according to claim 1, characterized in that the plate-shaped first particles have a reflectivity R exceeding 40% in the wavelength range of 5.0-100.0 pm.

11. The coating material according to claim 1, characterized in that the plate-shaped first particles have a reflectivity R exceeding 60% in the wavelength range of 10.0-50.0 pm.

12. The coating material according to claim 10, characterized in that the plate-shaped first particles have a reflectivity R exceeding 60% in the wavelength range of 5.0-100.0 pm.

13. The coating material of claim 1, characterized in that it has second particles having a transparency greater than 40% in the wavelength range of 0.38-0.75 pm and 5.0-100.0 pm.

14. The coating material of claim 1, characterized in that it has second particles having a transparency greater than 60% in the wavelength range of 0.38-0.75 pm and 10.0-50.0 pm.

15. The coating material according to claim 13, characterized in that the transparency of the second particles in the wavelength range of 0.38-0.75 pm and 10.0-100.0 pm exceeds 60%.

16. The coating material of claim 1, characterized in that it has second particles having an absorption of greater than 40% in the wavelength range of 1.0 pm to 2.0 pm.

17. The coating material of claim 1, characterized in that it has second particles having an absorption exceeding 20% ​​in the wavelength range of 0.8 pm to 2.5 pm.

18. The coating material according to claim 16, characterized in that it has second particles whose absorption in the wavelength range of 0.8-2.5 pm exceeds 40%.

19. The coating material of claim 1, characterized in that it has second particles whose refractive index in the wavelength range of 0.38-0.75 pm is greater than the refractive index of the binder.

20. The coating material of claim 1, characterized in that d) it comprises additional particles whose transparency in the wavelength range of 10.0-50.0 pm exceeds 40%; whose selective reflection properties in the wavelength range of 0.4-0.7 pm are present in discrete regions of visible light; and whose absorption in the wavelength range of 1.0-2.0 pm exceeds 20%.

21. The coating material according to claim 20, characterized in that the transparency of said further particles in the wavelength range of 5.0-100.0 pm exceeds 40%. HU 222 371 BI 22. The coating material of claim 20, wherein the transparency of said further particles in the wavelength range of 10.0-50.0 pm is greater than 60%.

23. The coating material according to claim 21, characterized in that the transparency of said further particles in the wavelength range of 5.0-100.0 pm exceeds 60%.

24. The coating material of claim 20, wherein said further particles have selective reflective properties in discrete regions of visible light in the wavelength range of 0.38-0.75 pm.

25. The coating material according to claim 20, characterized in that said further particles have an absorption exceeding 20% ​​in the wavelength range of 0.8-2.5 pm.

26. The coating material of claim 20, wherein said further particles have an absorption in the wavelength range of 1.0-2.0 pm exceeding 40%.

27. The coating material according to claim 25, characterized in that said further particles have an absorption exceeding 40% in the wavelength range of 0.8-2.5 pm.

28. The coating material of claim 1, wherein the second particles are added directly to the binder.

29. The coating material of claim 1, wherein the second particles are applied to the first particles.

30. The coating material of claim 1, wherein the first particles are selected from the group of elements comprising aluminum, copper, silver, gold, nickel, zinc, iron, silicon, germanium, or mixtures or alloys thereof.

31. The coating material of claim 1, wherein the first particles are electrically conductive; and are coated with an additional electrically conductive thin layer to increase chemical resistance and gloss.

32. The coating material of claim 2, wherein the first particles are electrically conductive; and are coated with an additional electrically conductive thin layer to increase chemical resistance and gloss.

33. The coating material of claim 28, wherein the first particles are electrically conductive; and are coated with a further electrically conductive thin layer to increase chemical resistance and gloss.

34. The coating material of claim 29, wherein the first particles are electrically conductive; and are coated with an additional electrically conductive thin layer to increase chemical resistance and gloss.

35. The coating material of claim 30, wherein the first particles are electrically conductive; and are coated with an additional electrically conductive thin layer to increase chemical resistance and gloss.

36. The coating material of claim 1, wherein the first particles are electrically conductive and are coated with a thin, electrically non-conductive layer to provide color.

37. The coating material of claim 2, wherein the first particles are electrically conductive and are coated with a thin, electrically non-conductive layer to provide color.

38. The coating material of claim 28, wherein the first particles are electrically conductive and are coated with a thin, electrically non-conductive layer to provide color.

39. The coating material of claim 29, wherein the first particles are electrically conductive and are coated with a thin, electrically non-conductive layer to provide color.

40. The coating material of claim 30, wherein the first particles are electrically conductive and are coated with a thin, electrically non-conductive layer to provide color.

41. The coating material of claim 1, wherein the first particles are of an electrically non-conductive material provided with an electrically conductive coating.

42. The coating material of claim 2, wherein the first particles are of an electrically non-conductive material provided with an electrically conductive coating.

43. The coating material of claim 28, wherein the first particles are of an electrically non-conductive material provided with an electrically conductive coating.

44. The coating material of claim 29, wherein the first particles are of an electrically non-conductive material provided with an electrically conductive coating.

45. The coating material of claim 30, wherein the first particles are of an electrically non-conductive material provided with an electrically conductive coating.

46. ​​The coating material according to claim 1, characterized in that the second particles are selected from the group of the following materials: metal sulfides, metal selenides, chlorides of metals belonging to main group I; fluorides of metals belonging to main group I; fluorides of metals belonging to main group II, antimonides, metal oxides, barium titanate; barium ferrite, pure calcium sulfate CaSO4, precipitated barium sulfate, barium sulfate crystals mixed with zinc sulfide. HU 222 371 Bl 47. The coating material of claim 2, wherein the second particles are selected from the group consisting of: metal sulfides, metal selenides, chlorides of metals in Group I; fluorides of metals in Group I; fluorides of metals in Group II, antimonides, metal oxides, barium titanate; barium ferrite, pure calcium sulfate CaSO4, precipitated barium sulfate, barium sulfate crystals mixed with zinc sulfide.

48. The coating material of claim 28, wherein the second particles are selected from the group consisting of: metal sulfides, metal selenides, chlorides of metals in Group I; fluorides of metals in Group I; fluorides of metals in Group II, antimonides, metal oxides, barium titanate; barium ferrite, pure calcium sulfate CaSO4, precipitated barium sulfate, barium sulfate crystals mixed with zinc sulfide.

49. The coating material of claim 20, wherein the additional particles are inorganic colored metal oxide pigments selected from the group consisting of transparent iron oxides, red iron oxides, yellow iron oxides, α-iron oxides, iron oxide black pigments, green chromium oxide, red lead oxide, molybdenum oxides, mixed metal oxides, and iron blue pigments based on microcrystalline FE(II), FE(III) cyanide complexes.

50. The coating material of claim 20, wherein the additional particles are selected from the group consisting of disazo pigments, indigo pigments, thioindigo pigments, and phthalocyanine.

51. The coating material of claim 1, characterized in that it has a solvent-containing binder selected from the group consisting of cyclized rubber, chlororubber, butyl rubber, hydrocarbon resin, α-methylstyrene-acrylonitrile copolymer, polyester amide polymer, and butyl acrylate-based acrylic resin.

52. The coating material of claim 1, wherein the binder is an aqueous solution or dispersion selected from the group consisting of polyethylene, polyethylene oxide, ethylene-acrylic acid copolymers, methacrylate polymers, acrylate-styrene polymers, vinyl-pyrrolidine-vinyl acetate copolymers, atactic polyisopropyl acrylate polymers, poly(vinyl pyrrolidone) polymers, and mixtures thereof.