GB1572728A

GB1572728A - Structural units comprising vinylchloride polymers

Info

Publication number: GB1572728A
Application number: GB5422/77A
Authority: GB
Original assignee: Dynamit Nobel AG
Current assignee: Dynamit Nobel AG
Priority date: 1976-02-11
Filing date: 1977-02-09
Publication date: 1980-08-06
Also published as: SE431992B; FR2340973A1; BE851286A; IT1082700B; DE2605325B2; CH626818A5; IE44864L; DK57277A; NO770445L; CA1094897A; NL7701411A; SE7701488L; FR2340973B1; ES455801A1; DE2605325A1; ATA86377A; JPS52112634A; IE44864B1

Abstract

PVC surfaces with a covering layer of polymethyl acrylate or a copolymer thereof applied thereto in a strongly adhesive manner and containing colour pigments and UV stabilisers are additionally protected against the effects of sunlight. To this end, the covering layer is formed in such a way that it does not absorb IR radiation. IR-reflecting pigments and/or dyes in the covering layer or in the PVC layer reflect the IR radiation on incidence. The addition of UV stabilisers additionally makes the covering layer virtually opaque to UV. Warming and degradation by sunlight are thereby avoided, which is particularly important for external building components, such as window frames, etc..

Description

(54) STRUCTURAL UNITS COMPRISING VINYLCHLORIDE POLYMERS (71) We, DYNAMIT NOBEL AKTIENGESELLSCHAFT a German Company of 521 Troisdorf bez Koln, Postfach 1209, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to structural units comprising a portion formed from a vinyl chloride polymer having a surface layer of a methyl methacrylate polymer.

The poor resistance of PVC to weathering is attributable to the fact that the PVC molecules break down with elimination of HCl to form conjugated double bonds. This degradation process is initated by the effects of light and thermal energy. As a result of degradation, the PVC, which is basically neutral in colour, changes colour from yellow through brown to black. At the same time, the mechanical properties of the PVC are affected by degradation. In particular its impact strength and elongation are reduced to a considerable extent.

It is known that PVC can be stabilised by means of a stabiliser, for example a dibutyl tin maleate or lead phosphite or a barium/cadmium complex, which retards the degradation process.

UV-absorbers may also be used to protect against degradation, but unfortunately they are extremely expensive and are only effective when present in a relatively high concentration. Further, even in cases where a UV-absorber is present in large quantities in the upper boundary layer of the PVC, the PVC molecules remain unprotected over large areas because it is not possible, with the UV-absorber added, to obtain a complete covering of a non-translucent layer. In addition, UV-absorbers have a higher vapour pressure than the PVC and, over a period of time, can escape or may be degraded by other chemical reactions. Even in cases where the PVC compositions are pigmented, the PVC molecules at the surface boundary layer remain unprotected despite high concentrations of pigment.

Since the incorporation of any additive generally has an adverse effect upon the mechanical properties of PVC and since, in addition, a PVC surface directly exposed to weathering cannot be made completely weatherproof, the only known alternative is to coat the PVC surface.

German Offenlegungsschrift No. 22 46 497 describes plastics profiles with improved resistance to light and weathering, in which a layer of a polymethyl methacrylate or a copolymer thereof is firmly applied by co-extrusion to at least a part of the periphery of the profiles, preferably in a thickness of from 0.1 to lmm.

According to German Offenlegungsschrift No. 17 59 931, too, the appearance, resistance to weathering and colour stability of profiles of plastics are said to be improved by the provision of a surface layer which is heavily enriched with a high-quality pigment and/or contains a high concentration of a UV-stabiliser. More particularly, it is said to be possible inter alia through the choice of the material used for the surface layer, to protect the high polymers of the core layer against decomposition and to ensure that high polymers containing a double bond age to a reduced extent under the effects of heat, light and oxygen. Polymerisable monomers are said to be protected against undesirable polymerisation. There is no indication in Offenlegungsschrift No. 17 59 931 of what materials to use for the surface layer in order to achieve this objective.

The translucent surface layers mentioned in this Offenlegungsschrift, which are pigmented with light or translucent pigments, are definitely unsuitable because they do not prevent light from entering. On the other hand, the expert is given no indication as to what non-translucent materials could be used to achieve this objective.

Although a surface layer of polymethyl methacrylate or a copolymer thereof, as disclosed in German Offenlegungsschrift No. 22 46 497, is itself resistant to weathering, it does not afford the underlying PVC any protection against the effects of sunlight because it still allows short-wave UV-light through, even in a fairly considerable layer thickness of from about 0.2 to 0.3 mm.

German Offenlegungsschrift No. 22 47 980 describes a process for producing coloured structural components for external use in building construction, for example window frames and facing panels, from a thermoplastic plastics material such as PVC, for example by extrusion, deep-drawing or injection moulding. In the process the thermoplastic moulding composition is pigmented before the final moulding operation with a pigment having a high absorption for visible light coupled with high reflectance in the infrared region, in order to prevent excessive heating of the structural components, as a result of their colour, under the effect of sunlight.In this way, it is possible, especially in the case of structural components coloured in fairly dark shades, to ensure that they are not overheated by the effects of sunlight, thereby avoiding the release of internal stresses at elevated temperatures, in the case of PVC temperatures of 60"C upwards.

Unfortunately, in the process disclosed, the PVC surface itself is still not protected against degradation by sunlight.

According to the present invention, there is provided a structural unit comprising (a) a first portion formed from a vinyl chloride copolymer containing pigment for colouration, and (b) a second portion, in the form of a surface layer on the first portion, comprising (i) a methyl methacrylate polymer and (ii) a UV absorber and/or a UV stabiliser; the surface layer being transparent or containing pigment for colouration, the first portion and/or the second portion being substantially a non-absorber or infra-red radiation, and the first portion and/or the second portion containing a material which is reflective to infra-red radiation.

In a preferred embodiment of the invention, the surface layer is covered with a pigment system which has a high reflection of visible light of the desired colour, a low permeability to ultra-violet radiation and a high permeability to infra-red radiation, and the surface layer contains an infra-red reflecting pigment or pigment system or dye.

The present invention thus provides structural units, suitable for, external use, of a PVC-based thermoplastic plastics wherein the PVC-surface is protected against weathering and decomposition and, at the same time, the danger of coloured structural units, especially relatively dark-coloured structural units, being heated by sunlight is reduced. Structural units according to the invention comprise a first portion formed from a vinyl chloride polymer, for example PVC, to which, in order to protect the PVC surface against the effects of sunlight, is applied a second portion in the form of a surface layer of a polymethyl methacrylate or copolymer thereof contaming a coloured pigment and UV-stabiliser or UV-absorber.

The surface layer substantially does not absorb incident IR-radiation, which IR-radiation is reflected either from the surface of the methyl methacrylate polymer layer (by means of the presence in the polymer layer of an IR-reflecting pigment and/or dye) or from the vinyl chloride polymer portion (by means of the presence therein of an IR-reflecting pigment and/or dye). The surface layer portion is made substantially impermeable to UV-light by the incorporation of a UV-stabiliser or UV-absorber in the polymer material thereof.

Structural units according to the invention, which may be formed in a single process step, thus afford protection for the vinyl chloride polymer portion against weathering and decomposition and, at the same time, the temperature stability of the structural unit especially in regard to undesirable heating by sunlight, is improved by the special reflective pigmenting of the surface layer and/or the PVC-layer.

Figures 4 and 5 of the accompanying drawings illustrate the invention. In these Figures there is shown a structural unit comprising a polymethylmethacrylate applied to a PVC-portion 2, for example by co-extrusion. In the unit of Figure 4, the surface layer 1 is coloured with a pigment in such a way that infra-red rays of sunlight 3 are reflected at the surface of the surface layer 1, as indicated by the dashed arrow 4.

This reflection of the IR-rays at the surface of the surface layer prevents the PVC portion, especially if it is dark in colour, from being heated up through the surface layer At the same time, the surface layer physically protects the surface of the PVC-portion. In the example of Figure 4, the colour of the PVC-portion 2, i.e. the pigment with which it is coloured, is unimportant.

In the unit of Figure 5, the surface layer 1 is permeable to the IR-rays so that, according to the invention, the IR-rays, after passing through the surface layer, have to be reflected at the surface 5 of the PVC-portion, as indicated by the dashed arrow 4. In the unit of Figure 5, therefore, it is necessary in accordance with the invention for the PVC portion 2 to be coloured with a pigment, pigment system or dye which contains such a large amount of an IR-reflecting colouring agent that the incident IR-rays are reflected.

In this case, too the surface layer 1 performs the additional function of protecting the surface of the PVC portion against weathering and UV-radiation.

Thus from a basis of a weatherproof surface layer of a polymethyl methacrylate or copolymer thereof, the underlying vinylchloride polymer surface is generally protected against the effects of sunlight in one embodiment of the invention by virtue of the fact that the surface layer is opaquely pigmented with a pigment system, which shows extremely high reflection both in the spectral region of the required colour and in the IR-region, coupled with extremely low transmission in the UV-region, to such an extent that it substantially does not allow through any rays in the wavelengths and quantities which are damaging to PVC.By virtue of the invention, it has been possible for the first time to provide a PVC surface with complete protection by means of a surface layer coupled with resistance to weathering and reduced heating, limits being imposed on the pigments used insofar as not every pigment is suitable for use in accordance with the invention. Accordingly, the disadvantages which still attend the individual solutions according to the prior art are generally eliminated by the present invention, enabling PVC to be used as a plastics material for external application in building construction, especially in areas where considerable fluctuations in temperature and prolonged periods of sunshine are encountered as, for example, in tropical and sub-tropical countries.Hitherto in such regions known coated and uncoated plastics profiles and structural components of PVC could not be used because they were unable in the long term to withstand the effects of weather. A pigment system based on the light, more especially opaque white, colouring, of a polymethyl methacrylate applied to a PVC portion with the properties defined above also provides PVC with resistance to weathering in tropical climates.

By contrast, for climatic regions, such as central and northern Europe, it is possible also to weatherproof PVC portions with dark-coloured surface layers, such as grey, brown, green, blue or anthracite, in which case a similarly coloured PVC portion may also be provided.

The necessary quantity of pigment is governed on the one hand by the required colour and on the other hand by the layer thickness of the surface layer. Since the surface layer material is currently much more expensive than PVC, it is desirable on economic grounds not to make the surface layer too thick, the surface polymer layer preferably being applied in a thickness of from 0.5 to 1 mm. With the same quantity of pigment per unit area, a much higher concentration, but substantially the same coverage, will be obtained for a surface layer thickness of 0.5 mm than for a surface layer thickness of 1 mm.

In the case of dark shades, in order to reduce the considerable heating of the surface layer and, hence, of the underlying vinyl chloride polymer layer as well, it is preferred that at least one component of the organic or inorganic pigment used is IR-reflecting black or coloured pigment, i.e.

a pigment with a high remission in the infrared region. Thus according to the invention no predominantly IR-absorbing pigments are used for relatively dark pigments.

Coloured pigment, including UV-absorber, is preferably added in a total quantity of about 0.5 to 20% by weight, based on 100%by weight of the surface layer polymer material. It is further preferred that at least 0.1% by weight of this proportion of coloured pigment consists of IR-reflecting pigment, based on the total quantity of coloured pigment.

It is also preferred to use as pigmenting agent for determining the colour of the structural units, a pigment which has an inherently high IR-reflectance. The ability to reflect IR radiation is a physical property possessed by a number of coloured pigments, which ability can be determined by measurement. In this connection, reference is made for example to the antimony black pigments and antraquinone black pigments, phthalocyanines, and also to titanium dioxide, nickel titanium yellow and cadmium red. Mixed colours can be produced by means of corresponding pigment mixtures.

Other suitable IR-reflecting colouring agents are, for example, lead chromate, molybdate red, molybdate orange, chromium oxide green, antimony sulphide, cadmium sulphoselenide, cadmium sulphide, anthraquinone dark blue pigments, and monoazo pigments.

The second portion of the structural unit, comprising a methyl methacrylate polymer, may be made substantially impermeable to UV radiation by virtue of the presence therein of a UV absorber or stabiliser.

Suitable UV-absorbers are, for example, benzophenones and benztriazoles, preferably in quantities of from 0.2 to 0.5% by weight, based on the surface layer composition as a whole. In selecting the UV absorber, allowance must be made for their compatibility with the methyl methacrylate polymer and for a favourable vapour pressure so that the UV-absorber is largely prevented from escaping under the effects of temperature stressing as a result of weathering.

Structural units according to the invention are useful in building construction for thermoplastic profiles which are made for example in the form of hollow profiles and are used as, for example, window frames or door frames. One such profile is shown in cross-section in Figure 6 of the accompanying drawings. The multicompartment hollow profile consists of rigid PVC 2. That face of the hollow profile which is exposed to the weather is firmly affixed to a surface layer 1 of polymethyl methacrylate (PMMA) by co-extrusion. The protection of the PVC-portion 2 against the effects of sunlight and weather is described in the following Examples, which illustrate the invention.

EXAMPLE 1 A rigid PVC multi-compartment hollow profile for window frames, with a wall thickness of about 3 mm, was co-extruded with a surface layer of a polymethyl methacrylate having a molecular weight of 170,000. The layer had a thickness of 0.5 mm and a width of 70 mm. The PMMA surface layer was coloured on opaque white by virtue of a 0.51% by weight content of titanium dioxide, based on the total surface layer composition.

Prolonged weathering of this profile in the open air did not cause any damage to the PVC surface below the PMMA layer, neither did Weatherometer measurements reveal any deterioration either in the surface layer or in the under-lying PVC portion.

This Example embodies the process according to the invention as described with reference to Figure 4. That is, the surface layer 1 performs both the function of UV-absorption and also the function of IR-reflection. The following Example 2 is similarly effective with IR-reflecting anthraquinone black pigments.

EXAMPLE 2 An article was prepared as in Example 1 but having a surface layer coloured by virtue of a content of 2% by weight of anthraquinone black and 0.5%by weight of a benzophenone as UV-absorber, based on the surface layer composition. In this case, too, weathering in the open air did not cause any damage.

EXAMPLE 3 The same article as in Example 1, formed from a PVC starting compound which had been coloured an opaque white with titanium dioxide, had a surface layer pigmented with 2% by weight of titanium dioxide and 0.5% by weight of a benztriazole as UV-absorber.

These percentages by weight were based on the total surface layer composition.

In this case, the product obtained, consisting essentially of PVC, was weatherproof under tropical conditions on its coated side.

The product, which was a combination of the embodiments according to Figures 4 and 5, satisfied the stringent requirements of the tripical climate. In addition, the PVC-layer was coloured in such a way that it was also able to reflect IR-radiation.

The invention is further illustrated by the other figures of the accompanying drawings, these being graPhs showing the variation of the degree of reflectance of different pigments with the wavelength of the incident light.

Figure 1 shows a typical reflectance curve of a red-tinged black pigment having high reflectance in the IR-region, which pigment may be used in units according to the invention.

By contrast, Figure 2 shows the typical reflectance curve of an anthracite-coloured pigment finish obtained by using a non-IRreflecting black pigment, namely pigmentgrade carbon black. A pigment such as this is not suitable for use in units of the invention.

Figure 3 shows the reflectance curve of a pigment system suitable for structural units according to the invention, the curve illustrated being a typical transmission curve of a mixture of a red-tinged black pigment having high IR-reflectance and a UV-absorber of the benztriazole type.

As already explained with reference to Figure 4 and 5, at least one of the two portions has to be formed in such a way that it always reflects IR-radiation. For the case illustrated in Figure 4, the surface layer is formed in such a way that it reflects IR-radiation, i.e. is opaquely coloured in one colour and the necessary pigment and/or dye is either completely or at least partly IR-reflecting pigment or IR-reflecting dye.

For the embodiment illustrated in Figure 5, the vinyl chloride polymer portion is formed in such a way that it is able to reflect IR-radiation at its surface; in other words that portion is coloured with a corresponding colouring mixture consisting at least partly of IR-reflecting pigment or IR-reflecting dye.

In this case, the surface layer may be totally permeable to IR-radiation or may even reflect some of the IR-radiation, but it should not contain any dye or pigment which absorb IR-radiation. On the basis of the teaching according to the invention, it is possible to adopt the two variants illustrated in Figures 4 and 5 and to produce a correspondingly weatherproof structural unit based on, for example, PVC itself.

The reflectance curves shown in Figures 1 and 3 correspond in principle to the embodiments illustrated in Figure 4. Figure 7 shows a reflectance curve which works on the principle of Figure 5. In Figure 7, the reflectance curve of the surface layer is shown as la. It represents a relatively dark colour although coloured with normal pigments, i.e. without IR-reflection.

-absorbers are additionally provided which is shown by the trend of the reflectance curve la in the UV-region. In this case, the PVC layer is coloured in such a way that its reflectance curve shows a strong IR-reflection. As is apparent from curve 2a, this result may be achieved for example with an opaque white colouring based on titanium dioxide. The sum of the two curves la and 2a gives curve 5a which is measured as a total reflectance curve of all the incident light.

WHAT WE CLAIM IS: 1. A structural unit comprising (a) a first portion formed from a vinyl chloride copolymer containing pigment for colouration, and (b) a second portion, in the form of a surface layer on the first portion, comprising (i) a methyl methacrylate polymer and (ii) a UV absorber and/or a UV stabiliser; the surface layer being transparent or containing pigment for colouration, the first portion and/or the second portion being substantially a non-absorber of infra-red radiation, and the first portion and/or the second portion containing a material which is reflective to infra-red radiation.

2. A structural unit according to claim 1, wherein the surface layer is covered with a pigment system which has a high reflection of visible light of the desired colour, a low permeability to ultra-violet radiation and a high permeability to infra-red radiation, and the surface layer contains an infra-red reflecting pigment or pigment system or dye.

3. A structural unit according to claim 2, wherein the pigment system includes a colour or colour mixture comprising organic and/or inorganic coloured pigment, and wherein at least one component of the pigment system is an infra-red reflecting black or coloured pigment.

4. A structural unit according to any of the preceding claims, wherein a total of 0.5 to 20% of coloured pigment, including ultraviolet absorber, is present in the surface layer, based on the weight of the surface layer composition.

5. A structural unit according to claim 4, wherein the coloured pigment comprises at least 0.1% by weight of an infra-red reflecting pigment, based on the total weight of coloured pigment.

6. A structural unit according to any of the preceding claims, wherein at least one component of the covering mixture of the colour for the surface layer or the first portion consists of an infra-red reflecting organic dye.

7. A structural unit according to any of the preceding claims, wherein the infra-red reflecting colouring agent comrises lead chromate, molybdate red, molybdate orange, chromium oxide green, antimony sulphide, cadmium sulphoselenide, cadmium sulphide, an anthraquinone black pigment, an anthraquinone dark blue pigment, a monoazo pigment or a phthalocyanine.

8. A structural unit according to claim 1, substantially as hereinbefore described in any of the Examples.

9. A structural unit according to claim 1, substantially as hereinbefore described with reference to the accompanying drawings.

10. A structural unit according to any of the preceding claims, the unit being a window frame.

11. A structural unit according to any of claims 1 to 9, the unit being a door frame.

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**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. reflectance curve of the surface layer is shown as la. It represents a relatively dark colour although coloured with normal pigments, i.e. without IR-reflection. -absorbers are additionally provided which is shown by the trend of the reflectance curve la in the UV-region. In this case, the PVC layer is coloured in such a way that its reflectance curve shows a strong IR-reflection. As is apparent from curve 2a, this result may be achieved for example with an opaque white colouring based on titanium dioxide. The sum of the two curves la and 2a gives curve 5a which is measured as a total reflectance curve of all the incident light. WHAT WE CLAIM IS:

1. A structural unit comprising (a) a first portion formed from a vinyl chloride copolymer containing pigment for colouration, and (b) a second portion, in the form of a surface layer on the first portion, comprising (i) a methyl methacrylate polymer and (ii) a UV absorber and/or a UV stabiliser; the surface layer being transparent or containing pigment for colouration, the first portion and/or the second portion being substantially a non-absorber of infra-red radiation, and the first portion and/or the second portion containing a material which is reflective to infra-red radiation.

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