Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-08-09
2001-06-26
Nutter, Nathan M. (Department: 1711)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S402220, C428S402240, C428S403000
Reexamination Certificate
active
06251521
ABSTRACT:
FIELD OF THE INVENTION
The invention contemplates UV-absorbing compositions including latices, agglomerate particles, powders, films, coatings, multilayer articles, and other materials prepared from or containing the polymeric particles or derivatives thereof, and methods associated with the particles and compositions.
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. There is a further need to incorporate UVAs into chemical compositions that contain other materials with which the UVA may not be compatible, wherein the UVA becomes a relatively permanent component of the composition, and wherein the composition is relatively thermodynamically stable, to provide long-term protection from ultraviolet radiation.
SUMMARY OF THE INVENTION
The invention provides ultraviolet radiation-absorbing compositions including latices of core/shell particles wherein the core comprises a core polymer and a UVA, as well as multiphase polymeric compositions comprising a polymeric core phase and a polymeric shell phase, wherein the polymeric core phase includes ultraviolet absorber.
Preferred multiphase polymeric compositions comprising a core phase, a shell phase, and a phase of an additional polymeric material can exhibit improved thermodynamic stability and UVA retention, thereby exhibiting time-stable protection from ultraviolet radiation, with lasting physical and mechanical properties. This can be true even if the UVA is used in combination with an additional material that is not compatible with the UVA.
An exemplary composition is a latex comprising core/shell particles and a polymeric film-forming material, wherein the latex may be coated and dried to form a film, or which may be spray dried to form a powder which can be further processed. Such a latex can be formed into a film or coating e.g., by coating and drying, or, dried to form a powder, preferably spray-dried to form a powder comprising agglomerate particles which can be coated onto a substrate and fused to form a film or coating.
Multiphase polymeric compositions of the invention can comprise phase domains of a polymeric core phase, a polymeric shell phase, and a polymeric film-forming phase, wherein the morphology is such that the polymeric core phase does not substantially contact the polymeric film-forming phase, but both of these phases contact the polymeric shell phase, which separates the other two phases. It has been found that compositions having this preferred morphology, particularly if the core particle (or a component thereof) is not compatible with the polymeric film-forming material, can exhibit improved initial physical properties, which can be maintained with aging, as compared to chemical compositions containing chemically identical ingredients, in identical amounts, but exhibiting a different morphology. Such properties can include one or more of: flexibility, lasting protection from ultraviolet radiation due to reduced migration loss (e.g., bleeding or blooming) of the UVA (especially if the UVA is not chemically attached to the core polymer); thermodynamic stability; and improved resistance to water (e.g., reduced water sensitivity).
A particular advantage of this preferred morphology is that it allows the use of a core particle or a component thereof, e.g., a core polymer or a UVA, to be used in a composition that contains another material (e.g., a polymeric film-forming material) that is incompatible with the core particle or core particle component. If a core particle or its component is incompatible with a polymeric film-forming material, the shell material shields the core particle phase from the incompatible phase, thus preventing the consequences otherwise associated with including the core particle with an incompatible material, and thereby preferably achieving a thermodynamically stable composition.
Multiphase polymeric compositions having the described morphology can be prepared by various methods. For instance, such a multiphase composition can be prepared from a latex that includes polymeric particles having a core/shell structure, wherein the core comprises UVA, and particles of polymeric film-forming material. This can be accomplished by forming the latex into a film or coating, and allowing the latex to dry. Alternatively, such a multiphase composition can be prepared by spray-drying the latex to prepare a powder of agglomerate particles, powder coating the agglomerate particles, and fusing the coated powder.
An aspect of the invention relates to compositions comprising fluoropolymer and polymeric core/shell particles wherein the core comprises a UVA. The composition can be in the form of one or more of the following: a latex; an agglomerate particle of the core/shell particles fused to fluoropolymer particles; a powder comprising core/shell particles and fluoropolymer particles, or their agglomerates; a polymeric composition such as a multiphase polymeric composition, e.g., in the form of a film, coating, or multilayer article; or a product or composition derived from or containing any of these compositions. Such compositions can block or absorb ultraviolet radiation for any desired reason and can exhibit desirable cleanability properties, and desired mechanical or physical properties such as flexibility. The core/shell particles can be included in a composition to protect
Andrus, Jr. Milton H.
Eian Gilbert L.
Ludwig Bret W.
3M Innovative Properties Company
Nutter Nathan M.
Zillig Kimberly S.
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