Weathering resistance of polymeric materials

Details Weathering resistance of polymeric materials Weathering resistance of polymeric materials

2002-02-28

2004-02-10

Harlan, Robert D. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S222000, C525S224000, C524S401000, C524S409000, C524S436000, C524S437000, C526S319000, C526S343000, C526S344000

Reexamination Certificate

active

06689840

ABSTRACT:

This invention relates to polymeric materials having improved weathering resistance. Particularly, although not exclusively, the invention relates to polymeric materials which include a halogen-containing polymer and, especially, to polymeric materials which include both a halogen-containing polymer and an acrylic polymer.
Halogen-containing polymers, for example, polyvinyl chloride (PVC) are relatively cheap and readily available materials. They have been used outdoors in buildings and glazing. However, the weatherability, for example the light stability of halogen-containing polymers is poor, leading to relatively short lifetimes particularly in pigmented formulations.
Acrylic materials are used in a variety of applications, for example buildings, including glazing, automotive lights, instrument dials, light diffusers, lenses, medical diagnostic devices, signs, bath/sanitary ware, because of their toughness, weatherability, appearance and stability characteristics. They may be used as capstock material to provide a coating layer over a substrate thermoplastic material and hence impart the advantageous properties of acrylic compounds to the underlying thermoplastic material. One example of the use of acrylic materials as capstocks is described in U.S. Pat. No. 5,318,737 in which suitable acrylic compositions for coextrusion with acrylonitrile-butadiene-styrene (ABS) are described for a variety of end-uses.
In many application areas the retention of beneficial properties following exposure to sunlight etc is important. Acrylic materials themselves generally have exceptional weathering performance and when formulated correctly can be used to impart these properties to underlying plastics materials. Blends of PVC and acrylic materials may be attractive in some situations. For example, compared to unmodified acrylics, acrylics modified by addition of PVC may be cheaper, have increased toughness, exhibit reduced flammability and have desireable melt-flow properties. However, whilst the weathering performance of an acrylic/PVC blend is generally improved compared to the PVC alone, the addition of PVC to acrylics reduces the weathering performance compared to unmodified acrylics. Thus, an acrylics/PVC blend may exhibit unacceptable colour stability, degradation in appearance and mechanical properties following exposure to sunlight or in weathering tests. In fact, unmodified pigmented acrylic/PVC blends behave similarly to PVC itself in that they begin to lighten (“chalk”) after several thousands hours accelerated weathering exposure in both xeno and QUV A machines. The “chalking” phenomenon is well known to those skilled in the art of PVC material formulation and generally manifests itself as a lightening in material colour, which is measured as a positive “&Dgr;L” in weathering testing. For unmodified pigmented acrylic/PVC blends the time that this “chalking” occurs is dependent upon the amount of PVC present in the blend, but even at concentrations of <20% w/w PVC a noticeable colour shift (&Dgr;E) occurs after 6000 hours exposure.
It is an object of the present invention to address the above-described problems.
According to a first aspect of the invention, there is provided a polymeric material comprising a halogen-containing polymer which contains between 5 to 70% by wt of halogen and 0.1 to 25% by wt of an inorganic hydroxide of zinc, magnesium, molybdenum, antimony, aluminium, tin, copper, manganese, cobalt or iron.
According to a second aspect, there is provided a method of manufacturing a polymeric material which comprises a halogen-containing polymer which contains between 5 to 70% by wt of halogen and 0.1 to 25% by wt of an inorganic hydroxide of zinc, magnesium, molybdenum, antimony, aluminium, tin, copper, manganese, cobalt or iron, the method comprising melt blending, preferably by extrusion, preferably between 150° C. to 250° C., said halogen-containing polymer and said inorganic hydroxide.
According to a third aspect, there is provided the use of an inorganic hydroxide of zinc, magnesium, molybdenum, antimony, aluminium, tin copper, manganese, cobalt or iron in a polymeric material comprising a halogen-containing polymer which contains between 5 to 70% by wt of halogen for improving the weathering resistance of said halogen-containing polymer, especially their colour stability.
The halogen-containing polymer is preferably a chlorine-containing polymer. The only halogen in said polymer is preferably chlorine. Said polymer may be a polyvinylchloride, polyvinyldichloride, polyvinylidene chloride, chlorinated PVC or chlorinated polyolefin. Said polymer is preferably chosen from a polymer or copolymer of vinyl chloride or vinylidene chloride. A particularly preferred halogen-containing polymer is polyvinyl chloride (PVC). The halogen containing polymer may contain other materials, as known to those skilled in the art, for example pigments, fillers, impact modifiers, lubricants, UV stabilisers, thermal stabilisers and viscosity modifiers. Said halogen containing polymer suitably includes at least 75% by wt of polymer, preferably at least 80% by wt, more preferably at least 90% by wt, especially at least 95% by wt of polymer. Said halogen containing polymer may consist essentially of polymer, especially PVC.
Suitably, the halogen containing polymer, preferably in the absence of any fillers or other ingredients (e.g. thermal stabilisers or viscosity modifiers), includes at least 10% by wt, preferably at least 20% by wt, more preferably at least 30% by wt, especially at least 40% by wt and most preferably at least 45% by wt of halogen, especially chlorine. The halogen containing polymer, preferably in the absence of said aforementioned ingredients, preferably includes less than 70% by wt, preferably less than 60% by wt, especially less than 57% by wt halogen, especially chlorine. Preferably, said halogen containing polymer includes no halogen other than chlorine.
Said polymeric material may include at least 0.5% by wt, suitably at least 0.75% by wt, preferably at least 1% by wt, especially at least 2% by wt, of said inorganic hydroxide. Said polymeric material may include 20% by wt or less, suitably 15% by wt or less, preferably 10% by wt or less of said inorganic hydroxide.
Said inorganic hydroxide may be selected from aluminium hydroxide, zinc hydroxide, iron hydroxide, magnesium hydroxide and tin hydroxide. Said inorganic hydroxide could be antimony hydroxide. Preferably said inorganic hydroxide is selected from magnesium hydroxide, antimony hydroxide, zinc hydroxide and aluminium hydroxide and, of the aforesaid, magnesium hydroxide, antimony hydroxide and zinc hydroxide are preferred. Preferably, said inorganic hydroxide comprises magnesium hydroxide. Preferably, said inorganic hydroxide does not include a material which comprises or consists of aluminium hydroxide. Said inorganic hydroxide may include more than one inorganic hydroxide. However, said inorganic hydroxide preferably consists essentially of magnesium hydroxide.
The weight average particle diameter of particles of said inorganic composition is suitably less than 250 &mgr;m, preferably less than 100 &mgr;m, more preferably less than 50 &mgr;m, especially less than 10 &mgr;m, suitably so that the material can have a high surface gloss. In some cases, the diameter may be smaller, for example less than 0.1 &mgr;m or below. In this case, the particles may be sufficiently small so that they do not scatter light when incorporated into the acrylic material and, accordingly, clear acrylic materials may be made.
Said polymeric material may include an acrylic polymer. Said acrylic polymer may comprise a homopolymer or a copolymer (which term includes polymers that have more than two different repeat units) of an alkyl(alk)acrylate or a copolymer comprising acrylonitrile, especially a copolymer which includes styrene and acrylonitrile, optionally in combination with other material (especially polymeric material).
Where said acrylic polymer is an alkyl(alk)acrylate, it is preferably a homo or copolymer of at least one

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