Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-06-13
2003-03-18
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S071000
Reexamination Certificate
active
06534592
ABSTRACT:
BACKGROUND
This invention relates to compositions which can be used as capstock as well as in other applications. These compositions are especially useful for extruding into articles and for application to structural plastics such as poly(vinyl chloride) to prepare composites. The invention also extends to methods for manufacturing such extruded articles and to composites produced therefrom.
Poly(vinyl chloride) resin (hereafter “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 causes 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. However, the resulting improvements to weatherability do not to meet the 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 “capstock”. The capstock generally is much thinner than the substrate plastic, typically being about 10 to about 25% of the total thickness of the composite (i.e. the capstock and substrate plastic).
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 affect adversely 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 described in European Patent Application EP-A-473,379 which is incorporated herein by reference for its teaching of capstock compositions. This publication discloses a 20 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. Moreover, the compositions according to this invention have a high gloss and therefore are not appropriate for certain applications (e.g., PVC siding and profile) in which a high gloss appearance is undesirable. Although this publication suggests that appearance can be controlled by the addition of flatting or matting agents, the addition of such components undesirably increases the cost and complexity of preparing capstock materials having reduced gloss.
Thus there is a need for a cost-effective, weatherable, capstock material having a high impact strength and adequate color retention, which also has a reduced, preferably low, gloss.
We have now discovered such a capstock composition that is capable of providing the requisite impact strength, high color retention, and reduced gloss without requiring additional PVC or flatting agents. This composition contains a particular combination of “high rubber core” and “medium rubber core” acrylic-based “core/shell” polymers.
We have also discovered that processing the newly discovered capstock compositions in a plastics forming device (i.e., an extruder), wherein the metering and melt temperatures are carefully controlled, provides a capstock having the requisite impact strength, high color retention, and reduced gloss without the addition of PVC or flatting agents.
Therefore, an object of the present invention is to provide a capstock composition having a particular combination of “high rubber core” and “medium rubber core” acrylic-based “core/shell” polymers capable of providing the requisite impact strength, high color retention, and reduced gloss without the addition of PVC or flatting agents.
A further object is to provide a process for preparing a capstock capable of providing the requisite impact strength, high color retention, and reduced gloss without the addition of PVC or flatting agents.
Another object of the invention is to provide a synthetic resin composite having a first layer of a reduced-gloss, weatherable, impact-resistant capstock composition and a second substrate layer of a thermoplastic resin.
These and other objects, as will become apparent from the following disclosure, are achieved by the present invention.
STATEMENT OF THE INVENTION
In the present invention, the problem of providing a weatherable, impact resistant capstock having low gloss is solved generally by providing a particular combination of “high rubber core” and “medium rubber core” acrylic-based “core/shell” polymers having high impact strength, high color retention, and reduced gloss.
Thus, in a first aspect of the present invention is provided a capstock composition including:
(A) from 70 to 99 parts by weight of a first core/shell polymer including
(i) from 30 to 70 parts by weight of a core polymer including
(a) from 45 to 99.9 parts by weight of units derived from at least one C1-C8 alkyl acrylate monomer,
(b) from 0 to 50 parts by weight of units derived from at least one ethylenically unsaturated copolymerizable monomer different from the at least one C1-C8 alkyl acrylate monomer, and
(c) from 0.1 to 5 parts by weight of units derived from at least one crosslinker or graftlinker, and
(ii) from 30 to 70 parts by weight of a shell polymer grafted to the core polymer (A)(i) including
(a) from 80 to 99 parts by weight of units derived from at least one C1-C8 alkyl methacrylate monomer, and
(b) from 1 to 20 parts by weight of units derived from at least one ethylenically unsaturated copolymerizable monomer different from the at least one C1-C8 alkyl methacrylate monomer; and
(B) from 1 to 30 parts by weight of a second core/shell polymer including
(i) from 70 to 92 parts by weight of a core polymer including
(a) from 50 to 99.9 parts by weight of units derived from at least one C1-C8 alkyl acrylate monomer,
(b) from 0 to 45 parts by weight of units derived from at least one ethylenically unsaturated copolymerizable monomer different from the at least one C1-C8 alkyl acrylate monomer, and
(c) from 0.1 to 5 parts by weight of units derived from at least one crosslinker or graftlinker; and
(ii) from 8 to 30 parts by weight of a shell polymer grafted to the core polymer (B)(i) including
(a) from 50 to 100 parts by weight of units derived from at least one C1-C8 alkyl methacrylate monomer, and
(b) from 0 to 50 parts by weight of units derived from at least one ethylenically unsaturated copolymerizable monome
Chou Chuen-Shyong
Neglia Katerina Dukes
Szamborski Eugene Carl
Mullis Jeffrey
Rohm and Haas Company
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