Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-08-09
2001-11-06
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S407000
Reexamination Certificate
active
06312807
ABSTRACT:
FIELD OF THE INVENTION
The invention contemplates polymeric particles having a core/shell structure, wherein the core comprises ultraviolet absorber.
BACKGROUND
Ultraviolet radiation (UV) can cause degradation of certain materials if exposed. Chemical materials known as ultraviolet absorbers, or UVAs, can be used to protect materials from the damaging effects of UV radiation. A UVA can be incorporated into a material to protect that material from UV radiation, or, a composition that contains UVA can be applied to a UV-sensitive substrate to protect the substrate.
Protective coating compositions, sometimes referred to as “topcoats,” can be applied to outdoor-durable materials such as signs based on flexible substrates and optionally having applied graphics, where the coating functions to inhibit dirt buildup or dirt penetration, as a barrier to water, to prevent plasticizers or other ingredients from migrating out of the substrate, or to allow ease of cleaning. A topcoat can include polymeric materials (e.g., a fluoropolymer to provide dirt resistance or cleanability), as well as stabilizers to protect the topcoat or the substrate from degradation, e.g., due to UV radiation. Degradation may involve yellowing, embrittlement, or loss of clarity, gloss, or water resistance.
Unfortunately, while it can be desirable to incorporate a UVA into a protective coating, UVAs can cause some difficult problems. One problem is the relative impermanence of UVAs in many chemical compositions. Non-reactive UVAs can be included in a chemical composition as a dispersed compound, not chemically attached to any other component. These UVAs can be lost from a composition by volatilization during processing (e.g., drying), or by otherwise migrating to the surface of a composition followed by removal as dust or wash off. Loss of the UVA leaves the composition and its substrate less protected from ultraviolet radiation, allowing UV radiation to degrade the composition or substrate. One imperfect remedy to this problem is to include larger amounts of UVA in a composition.
A further problem with UVAs is that they can be incompatible with different polymeric materials (e.g., fluoropolymers). This incompatibility can lead to instability (e.g., thermodynamic instability) or water sensitivity of the composition, which can cause a loss of physical or optical properties, including loss of clarity or increased fogginess. Incompatibility can also cause increased or accelerated loss of UVA by migration, bleeding, or blooming.
Attempts to incorporate UVAs into chemical compositions such as topcoats have been met with a variety of frustrating results, especially when the composition includes an ingredient that is incompatible with the UVA, as are many fluoropolymers. There is a general need to identify ultraviolet absorbing materials and compositions and also, to identify materials that can be used to prepare UV-absorbing compositions such as films and coatings.
SUMMARY OF THE INVENTION
The invention provides ultraviolet radiation absorbing polymeric particles, wherein the particles have a core/shell structure, and wherein the polymeric core phase includes ultraviolet absorber.
An aspect of the invention relates to polymeric particles having a core/shell structure, wherein the core comprises an ultraviolet absorber and a core polymer and the core polymer is prepared from core monomers including ethyl acrylate. Preferably the core monomers further include methyl methacrylate, and the core polymer can optionally be crosslinked. The UVA may be chemically incorporated into or otherwise attached to the core polymer, or the UVA may be dispersed within the core polymer.
As used herein, the following terms shall be given the recited meanings:
The term “thermoplastic” means materials that soften or flow upon exposure to heat and/or pressure. Thermoplastic is contrasted with “thermoset,” which describes materials that react irreversibly upon heating so that subsequent applications of heat and pressure do not cause them to soften or flow.
“(Meth)acrylate” means either acrylate or methacrylate.
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Eian Gilbert L.
Ludwig Bret W.
3M Innovative Properties Company
Le Hoa T.
Zillig Kimberly S.
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