CH626818A5 - Process for the protection of PVC surfaces against the effects of sunlight - Google Patents

Description

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PATENT CLAIMS

1. A process for protecting PVC surfaces against the effects of sunlight with a top layer of a polymethyl methacrylate or copolymer thereof, which is applied to the PVC surface with colored pigments and UV stabilizers or UV absorbers, characterized in that the top layer has no IR Radiation is absorbed and the IR radiation either by an appropriate pigmentation using IR-reflecting pigments and / or dyes of the top layer when it strikes it, or by a corresponding pigmentation by means of IR-reflecting pigments and / or dyes of the PVC layer when it hits it this is reflected and the top layer is made almost UV-impermeable by the addition of UV stabilizers or UV absorbers.

2. The method according to claim 1, characterized in that the top layer with a pigment system that has the highest possible reflection in the spectral range of the desired color and in the IR range and the lowest possible transmission in the UV range, so It is dyed in a broad opaque way that it does not transmit any rays in the wavelengths or quantities harmful to PVC.

3. The method according to claim 1, characterized in that the cover layer with a pigment system that has the highest possible reflection in the spectral range of the desired color and in the UV range the lowest possible transmission and in the IR range a high transmission and the PVC Layer is colored with IR-reflecting pigments or pigment systems or dyes.

4. The method according to claim 1, characterized in that of the organic and / or inorganic color pigments of a color or color mixture at least one component consists of an IR-reflecting black or color pigments.

5. The method according to claim 1 or 2, characterized in that a total of 0.5 to 20 percent by weight of color pigments including UV absorbers are added to the top layer, based on 100 percent by weight of top layer composition.

6. The method according to claim 3, characterized in that at least 0.1 weight percent IR pigments, based on the total amount of color pigment, are used.

7. The method according to any one of claims 1 to 6, characterized in that of the color mixture of a color for the cover layer or the PVC layer, at least one component consists of an IR-reflecting organic dye.

8. The method according to any one of claims 1 to 7, characterized in that one or more of the following substances lead chromate, molybdate red, molybdate orange, chromium oxide green, antimony sulfide, cadmium sulfoselenide, cadminium sulfide, anthraquinone black pigments, anthraquinone as IR-reflecting colorants Dark blue pigments, monoazo pigments, phthalocyanines can be used.

The subject matter of the invention relates to a method for protecting PVC surfaces against the effects of sunlight with a top layer made of a polymethyl methacrylate or copolymer thereof and applied to the PVC surface with colored pigments and UV stabilizers.

The poor weather resistance of PVC is due to the fact that the PVC molecules crack with the release of HCl to form conjugated double formations. This degradation is triggered by the light and thermal energy. As a result of the degradation, the color-neutral PVC changes color from yellow to brownish to black. At the same time, the degradation changes the mechanical properties, i. H. in particular, the impact resistance and elongation of the PVC decrease sharply. It is known that the PVC by means of stabilizers, e.g. Dibutyltin maleate or lead phosphite or barium / cadmium complexes, can be stabilized in order to delay the described degradation. You can also add UV absorbers. However, the latter are very expensive and can only work if there is a sufficiently high concentration. Nevertheless, even if a large amount of UV absorbers is added to the upper boundary layer of PVC, the PVC molecules will remain unprotected in large areas, since an opaque opaque layer cannot be achieved with the added UV absorber. In addition, the UV absorber has a higher vapor pressure than the PVC and can escape over time or be broken down by other chemical reactions. Even with pigmentation of the PVC masses, the PVC molecules at the surface boundary layer remain unprotected with high pigmentation.

Since the addition of all auxiliaries generally worsens the mechanical properties of PVC and, moreover, absolute weather resistance of a PVC surface exposed to direct weathering cannot be achieved, the known auxiliary means of coating the PVC surface remains as a further route.

German laid-open specification 2 246 497 describes plastic profiles with improved light and weather resistance, in which a layer of a polymethyl methacrylate or a copolymer thereof, preferably in a thickness of 0.1 to 1 mm, is applied adherently by coextrusion on at least part of the circumference . In this way, the profile surface is refined and the excellent properties, in particular of the polymethyl methacrylate, such as high brilliance, easy coloring and high luminosity and purity of the colors, are transferred to the coated profile. UV absorbers can also be added to these cover layers.

According to German Offenlegungsschrift 1 759 931, the appearance, weather resistance and color fastness of profiles made of plastics are also to be improved by providing a cover layer which is highly enriched with high-quality pigments and / or has a high concentration of UV stabilizers. Here u. a. The choice of material for the top layer means that the high polymers of the core layer are protected from decomposition or that high polymers with double bonds are less exposed to aging due to heat and light or oxygen. Polymerizable monomers should be prevented from undesired polymerization. The materials of the cover layer that are suitable at all for solving this task are not specified in the published patent application 1,759,931. The translucent cover layers permitted according to this laid-open specification, which are colored lightly or translucently, are certainly not suitable, since they do not prevent the incidence of light. The person skilled in the art does not disclose which opaque materials could solve the problem.

The object of the invention does not go the way proposed in German Offenlegungsschrift 1 759 931 to choose an opaque material for the coating, but to use a colorless and transparent material that is known to be distinguished by good optical properties and high weather resistance, namely polymethyl methacrylate or a copolymer thereof.

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Such a cover layer is also used for plastic profiles according to German Offenlegungsschrift 2 246 497. The top layer made of polymethyl methacrylate or a copolymer of it is itself weather-resistant, but does not offer the underlying PVC surface protection against the effects of sunlight, since it still allows short-wave UV radiation to pass through even with a relatively thick top layer of about 0.2 to 0.3 mm . The arbitrary coloring of the top layer made of polymethyl methacrylate, as specified, for example, in German Offenlegungsschrift 2 246 497, does not offer any reliable protection of the PVC surface against the effects of sunlight, since not every type and amount of pigmentation fulfills the task underlying the present application solves.

In addition, from German published patent application 2 247 980 there is still a method for producing colored components for outdoor use in construction, such as Window profile frames, facade panels or the like., Made of a thermoplastic, preferably PVC, for example by extrusion, deep-drawing or injection molding, have become known in which, in order to prevent the components from overheating as a result of their coloring due to the sun's radiation, the thermoplastic molding composition before the final shaping using pigments with a high absorption of visible light and high reflectance in the infrared range. In this way, especially in the case of components colored with darker shades, the result is that they do not heat up too much due to solar radiation and thus the triggering of the residual stresses at elevated temperatures, in the case of PVC at temperatures from 60 ° C. upwards, is avoided. In this known method and the products produced afterwards, however, the PVC surface itself is not yet protected against attacks by solar radiation.

Based on the state of the art, the object of the application is to design components for outdoor use from thermoplastic based on PVC in such a way that the PVC surface is protected against any weather attack and decomposition and at the same time the risk of heating up colored components, in particular darker components, is reduced by solar radiation. The starting point is in particular components made of PVC. To protect the PVC surface against the effects of sunlight, a top layer of a polymethyl methacrylate or copolymer thereof is applied to the PVC surface and provided with color pigments and UV stabilizers or UV absorbers. The process according to the invention is characterized in that the top layer does not absorb any IR radiation and the IR radiation either by appropriate pigmentation using IR-reflecting pigments and / or dyes of the top layer when it hits it or by appropriate pigmentation using IR reflecting pigments and / or dyes of the PVC layer is reflected when it strikes it and the top layer is made almost UV-impermeable by the addition of UV stabilizers or UV absorbers. These measures protect the PVC from weathering and decomposition in a first process step, in particular through the formation of the cover layer, and at the same time through further measures regarding the special pigmentation of the cover layer and / or the PVC layer, the temperature efficiency of the object, e.g. of the component, especially with regard to the undesirable heating caused by the effects of sunlight. The principle of the invention is shown schematically in FIGS. 4 and 5. The cover layer 1 made of PMMA is applied to the PVC layer 2, for example by coextrusion. In the example according to FIG. 4, the cover layer 1 is color pigmented in such a way that the infrared radiation from sunlight 3 is reflected or remitted on the surface of the cover layer 1, as the arrow 4 indicates. This reflection of the IR radiation on the surface of the cover layer avoids heating of the component, in particular in the case of darker colors on the cover layer. At the same time, the top layer protects the PVC surface. In the example according to FIG. 4, it does not matter which color the PVC layer 2 has or which pigments it is colored with. In the exemplary embodiment according to FIG. 5, the cover layer 1 is transparent to the IR radiation, which must then be reflected on the surface 5 of the PVC layer after passing through the cover layer, as the arrow 4 marks. In the exemplary embodiment according to FIG. 5, it is therefore necessary in the sense of the invention that the PVC layer 2 is colored with pigments or pigment systems or dyes which contain such a large proportion of colorants that reflect infrared radiation that the incident IR radiation reflects or can be remitted. Here, too, the cover layer 1 then additionally takes on the task of further protecting the PVC surface from weathering and UV radiation.

Starting from a weather-resistant, but colorless and transparent cover layer made of a polymethyl methacrylate or copolymer thereof, according to a preferred embodiment of the invention, the protection of the underlying PVC surface against the effects of sunlight is achieved by covering the cover layer with a pigment system that is in the spectral range of the desired hue and in the IR range each have the highest possible reflection and the lowest possible transmission in the UV range, so that the color is opaque so that it does not transmit any rays in the wavelengths or quantities harmful to PVC. Through these measures in combination, a complete protection of a PVC surface is guaranteed for the first time by a cover layer with simultaneous weather resistance and reduced heating, with any pigmentation being limited, since not every pigment is suitable for use in the sense of the invention. This eliminates for the first time all the disadvantages that are still attached to the individual solutions known from the state of the art, and enables the use of PVC as a plastic for outdoor construction, in particular for landscapes in which high temperature changes and high levels of sunshine occur . Here, for example, the tropical and subtropical countries are thought of, in which all previously known coated and uncoated plastic profiles and components made of PVC could not be used, since they could not cope with weathering in the long run. A pigment system, which is based on a light, especially opaque, white coloring of the PMMA coating of the PVC surface, also guarantees the tropicalized weather resistance for PVC.

For climatic areas such as Central and Northern Europe, on the other hand, it is possible to use PVC surfaces even in darker colored cover layers such as gray, brown, green, blue, anthracite, weather-resistant, whereby a similarly colored PVC surface can also be provided.

The required amount of pigments depends on the one hand on the desired color and on the other hand on the layer thickness of the top layer. Since the top layer material is much more expensive than PVC at the current state, one will endeavor for economic reasons not to make the top layer too thick, whereby one will advantageously work in top layer thicknesses between 0.5 and 1 mm. With the same amount of pigments per unit area you will

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of course with the lower cover layer thickness of 0.5 mm a much higher concentration, but achieve approximately the same coverage as with a cover layer thickness of 1 mm. In order to reduce the strong heating of the cover layer and thus also the PVC layer underneath, which is caused in particular by dark colors, a further development of the method known from DE-OS 2 247 980 proposes the organic or inorganic color pigments of a color or Color mixture to use at least one component as IR-reflecting black or color pigments, which therefore have a high reflectance in the infrared range.

This means that predominantly IR-absorbing pigments are not used for darker color pigments. Based on 100% by weight of top layer mass, e.g. a total of about 0.5 to 20% by weight of color pigments, including UV absorber, were added. Of this proportion, color pigments are useful e.g. at least 0.1 wt .-% IR pigments, based on the total amount of color pigment provided.

Otherwise, the invention shows the way to increase the proportion of IR-reflecting pigments in the coloring from the light, white to the dark, black colors or to use those IR-reflecting pigments that have a higher IR reflection than comparatively have other IR-reflecting pigments. The ability to reflect IR is a physical property of a number of color pigments that can be determined by measurement. For example, the antimony black pigments or anthraquinone black pigments, phthalocyanines, but also titanium dioxide or nickel titanium yellow, cadmium red may be mentioned. Mixed colors can be produced using appropriate pigment mixtures.

Further suitable IR-reflecting colorants can be found, for example, in lead chromate, molybdate red, molybdate orange, chromium oxide green, antimony sulfide, cadmium sulfoselonide, cadmium sulfide, anthraquinone dark blue pigments, mono noazo pigments.

Suitable UV absorbers are, for example, benzophenones and benzotriazoles, preferably 0.2 to 0.5% by weight, based on the total top layer mass. When selecting the UV absorber, compatibility with PMMA must be taken into account and a favorable steam throughput must be available so that the escape from temperature exposure is prevented by weathering.

The method according to the invention is used, for example, in construction for thermoplastic profiles, which are designed, for example, as hollow profiles and the like for window frames, door frames. be used. Such a profile is shown in cross section in FIG. 6. The multi-chambered hollow profile is made of hard PVC 2. The side of this hollow profile facing the weathering side is bonded to the top layer 1 made of PMMA by coextrusion. The protection of PVC profile 2 against sunlight and weathering is explained using the examples below:

example 1

A multi-chamber hollow profile for window frames made of hard PVC with a wall thickness of about 3 mm is coextruded with a cover layer made of a polymethyl methacrylate with a molecular weight of 170,000 and a layer thickness of 0.5 mm and a layer width of along the visible side of the hollow profile 70 mm. The PMMA top layer was colored opaque white with 0.51% by weight of titanium dioxide, based on the total top layer mass.

Exposure to this profile over a longer period of time did not result in any damage to the

Layer of PVC surface, even measurements in the thermometer show no impairment of either the top layer or the underlying PVC surface.

This example 1 corresponds to the method explained in FIG. 4 with its effect. Here, the top layer 1 takes on both the task of UV absorption and the task of reflecting the IR radiation. Example 2 listed below with IR-reflecting anthraquinone black pigments also works in the same way.

10th

Example 2

In the case of an article as in Example 1, the cover layer was colored with 2% by weight of antrachinone black and 0.5% by weight of benzophenone as UV absorber, the% by weight being based on the cover layer mass.

Here too, outdoor weathering shows no damage.

Example 3

20 In the case of an article as explained in Example 1, the PVC base material of which was also colored in opaque white with titanium dioxide, the cover layer was colored with 2% by weight of titanium dioxide and 0.5% by weight of UV absorber of a benzotriazole type. The% by weight relate to the total top layer mass. In this way, a weatherproof product made of essentially PVC is obtained on the coated side.

To further explain the invention, three diagrams are attached in which the reflectance of various pigments is plotted as a function of the wavelength of the light. The first diagram, see FIG. 1, shows a typical reflectance curve of a red-tinged black pigment with a high reflectance in the IR range, which is used for the method according to the invention. In contrast, FIG. 2 35 shows a typical reflectance curve of an anthracite-colored pigmentation using a non-IR-reflecting black pigment, namely color black. Such a pigment is not suitable for the invention.

This example is a combination of the versions 40 according to FIGS. 4 and 5, whereby it meets the high requirements in the tropics and in addition the PVC layer is colored in such a way that it can also reflect IR radiation if necessary.

3 shows a reflectance curve of a pigment system in the sense of the method according to the invention, the curve shown representing a typical transmission curve of a mixture of a red-tinged black pigment with high IR reflectance and a UV absorber of the benzotriazole type.

As already explained above with reference to FIGS. 4 and 5, it is necessary to design one of the two layers in such a way that it reflects the IR radiation in any case. For the intended case according to Fig. 4, the cover layer is to be designed so that it reflects the IR radiation, i.e. in each case it must be opaque in one shade and the pigments and / or dyes required for this must either be wholly or at least partly IR pigments or IR dyes. 5, it is necessary to design the PVC layer so that it can reflect the IR radiation on the surface, i.e. the PVC layer is to be colored with a corresponding color mixture of at least a portion of IR pigments or IR dyes. In this case, the cover layer can be completely transparent to the IR radiation, it can also reflect part of the IR radiation, but it must not contain any dyes or color pigments that absorb the IR radiation. With the teaching given according to the invention, it is possible, according to the two variants shown in FIGS. 4 and 5

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procedure and to create a weather-resistant component based on PVC.

The reflectance curves shown in FIGS. 1 and 3 correspond in principle to the exemplary embodiments according to FIG. 4. A remission curve is shown in the further FIG. 7, which works on the principle of FIG. 5. The top layer is shown in Fig. 7 with the reflectance curve la, it represents a darker color, which, however, with normal pigments, i.e. without IR reflection, is colored. In addition, UV absorbers are provided, which is noticeable in the course of the remission curve la in the UV range. In this case, the PVC layer is colored so that its reflectance curve has a strong IR reflection. As can be seen from curve 2a, this can be done, for example, with an opaque white coloring based on titanium dioxide. The sum of the two curves la and 2a then results in curve 5a, which is measured as the total remission curve of the entire light.

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5 sheets of drawings