Stock material or miscellaneous articles – Structurally defined web or sheet – Physical dimension specified
Reexamination Certificate
2001-09-13
2004-01-27
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Physical dimension specified
C428S520000, C428S522000, C525S244000, C525S268000, C525S309000
Reexamination Certificate
active
06682809
ABSTRACT:
The present invention relates to: a method of preparing a capstock layer that includes a comb copolymer; a method of preparing a multi-layered polymeric composite, one layer of which is a capstock layer; and a capstock layer and a multi-layered polymeric composite formed, respectively, thereby.
The thermoplastic polymer, poly(vinyl chloride) (“PVC”) has a combination of properties which make it particularly suitable for use as a structural material. In applications in which impact strength of the structural plastic is important, the PVC can be formulated with impact-modifier resins which improve the impact strength of the resulting composition. Such high impact-strength PVC compositions can be readily extruded or otherwise formed into a variety of articles which have excellent impact strength, toughness and other desired mechanical and chemical properties; for example as siding for buildings, shutters, technical profiles for window and door frames, rain carrying systems (e.g., gutters and downspouts), and fencings.
Such PVC compositions however have relatively poor weatherability characteristics, particularly poor color retention in darker grade colors such as browns and blues. The color is imparted to the PVC composition, for instance, by the use of colorants such as pigments or dyes, but exposure to sunlight causes unappealing changes in the colors. Such unappealing changes are more severe for darker than for light colors. Poor weatherability characteristics also cause reduction in impact strength leading to embrittlement and cracking and/or mechanical failure of the articles prepared from such compositions. Thus, there is a need for improving the weathering characteristics of such materials.
One remedy has been to incorporate stabilizing additives into the PVC composition, for example UV absorbers, thermal stabilizers and titanium dioxide light scatterer. However, the resulting improvements to weatherability are still not sufficient to meet the new, stricter industry-wide standards (Vinyl Siding Institute, January 1999, adopting ASTM D3679 performance specifications).
Another attempted remedy has been to apply another resinous material over the PVC to provide a surface that can withstand sunlight and other environmental conditions. Such a surfacing material is called a “capstock”. The capstock layer generally is much thinner than the thermoplastic substrate layer, typically being about 5 to about 25% of the total thickness of the composite (i.e. the capstock layer and substrate layer).
A suitable capstock material must possess a certain combination of processing properties and other physical, chemical, and aesthetic properties, including exceptional weathering characteristics such as excellent color retention and high impact strength. Moreover, the capstock also must not adversely affect those properties which make PVC such a widely used building material. In particular, the capstock compositions that are particularly aesthetically desirable do not have a shiny appearance but rather have a flat, or reduced gloss appearance.
Various types of polymer-based compositions have been disclosed for use as capstock, including PVC-based compositions and acrylic resin based compositions. A number of these polymer-based compositions are disclosed in European Patent Application EP-A-473,379. This publication discloses a capstock composition containing a blend of PVC resin and an acrylic copolymer. We have found, however, that the presence of PVC in capstock compositions such as those disclosed in EP-A-473,379 results in reduced weatherability and high gloss.
EP-A-1,061,100 discloses a capstock composition that contains a particular combination of “high rubber core” and “medium rubber core” acrylic-based “core/shell” polymers and is capable of providing the requisite impact strength, high color retention, and reduced gloss without requiring additional PVC or flatting agents. Unfortunately, this approach is a macroscopic blend approach requiring a processing blend step which is undesirable from an economic point of view. Moreover, because the macroscopic blend approach produces macroscopic domains having sizes on the order of the wavelength of visible light, physical stressing of the capstock layer can be very deleterious to the appearance of the capstock layer, and to the appearance of the composite as a whole. Physical stressing by, for example, bending, creasing, or impact events caused pronounced whitening (so called “stress whitening”) at the point of stress.
Thus there is a need for a cost-effective, weatherable, capstock material having a high impact strength, adequate color retention, and resistance to crease or stress whitening.
We have, surprisingly, found that the comb copolymer of the present invention can be melt processed to form a capstock melt layer that can be contacted with a substrate melt layer to form a multi-layered polymeric composite in which the capstock layer displays superior weatherability, impact resistance, other mechanical properties, and stress whitening resistance, and which is capable of protecting the substrate layer from damage associated with weathering and other environmental stress, including impact events.
One aspect of the present invention relates to a composition comprising a comb copolymer:
wherein said comb copolymer comprises a backbone and at least one graft segment; and
wherein:
(i) said graft segment and said backbone are in a weight ratio from 30:70 to 60:40;
(ii) said backbone is immiscible with said graft segment at room temperature;
(iii) said backbone has a glass transition temperature of −65° C. to 10° C.; and
(iv) said graft segment has a glass transition temperature of 60 to 180° C.
A second aspect of the present invention relates to a process comprising the steps of:
(a) forming a capstock composition;
(b) feeding said capstock composition into an extruder comprising a feed section and a metering section;
(c) metering and melting said capstock composition to form a capstock melt;
(d) forming said capstock melt into a capstock melt layer;
(e) extruding said capstock melt layer; and
(f) cooling said capstock melt layer to form a solid capstock layer;
wherein said capstock composition comprises a comb copolymer comprising a backbone and at least one graft segment; and wherein:
(i) said graft segment and said backbone are in a weight ratio from 30:70 to 60:40;
(ii) said backbone is immiscible with said graft segment at room temperature;
(iii) said backbone has a glass transition temperature of −65° C. to 10° C.; and
(iv) said graft segment has a glass transition temperature of 60 to 180° C.
A third aspect of the present invention relates to a coextrusion process comprising the steps of:
(A) forming a capstock melt layer by a process comprising the steps of:
(a) forming a capstock composition;
(b) feeding said capstock composition into a first extruder comprising a feed section and a metering section;
(c) metering and melting said capstock composition to form a capstock melt;
(d) forming said capstock melt into a capstock melt layer; and
(e) extruding said capstock melt layer;
wherein said capstock composition comprises a comb copolymer comprising
a backbone and at least one graft segment; and wherein:
(i) said graft segment and said backbone are in a weight ratio from 30:70 to 60:40;
(ii) said backbone is immiscible with said graft segment at room temperature;
(iii) said backbone has a glass transition temperature of −65° C. to 10° C.; and
(iv) said graft segment has a glass transition temperature of 60 to 180° C.
(B) forming a substrate melt layer by a process comprising the steps of:
(a) forming a substrate composition;
(b) feeding said substrate composition into a second extruder comprising a feed section and a metering section;
(c) metering and melting said substrate composition to form a substrate melt;
(d) forming said substrate melt into a substrate melt layer;
(e) extruding said substrate melt layer; and
wherein said substrate composition comprises a thermoplastic polymer;
(C) causing said capstock melt layer
Clikeman Richard R.
Nakarani D. S.
Rohm and Haas Company
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