Stock material or miscellaneous articles – Composite
Reexamination Certificate
1999-09-23
2001-08-28
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Composite
C428S500000, C428S689000, C428S696000, C428S702000, C428S704000, C428S921000
Reexamination Certificate
active
06280845
ABSTRACT:
TECHNICAL FIELD
This invention relates to flame retardant films, and more particularly, multilayer films having flame-retardant layers.
BACKGROUND OF THE INVENTION
Flame retardant films have been used in many applications where polymeric properties offer unique performance advantages over properties of other inherently flame retardant materials such as metal sheets and foils, and ceramics. Typically, the polymeric articles are either inherently flame retardant or rendered flame retardant by the addition of flame retardant additives. However, these approaches are limiting.
Polymer films made of inherently flame retardant polymers such as polyvinyl chloride (PVC) and polyimide (PI) usually have a limited range of properties. For example plasticizers are generally added to PVC to render it more readily processable, however plasticizer migration often adversely affects adhesion to subsequent surfaces. In addition, PVC generally has little elasticity and low to moderate tensile strength. Similarly, PI is difficult to process and more expensive than most common polymers.
Polymer films made of blends of polymer materials and flame retardant materials also have limited performance. While the range of polymer materials is broad, the concentration of flame retardant material is generally high enough to significantly adversely affect mechanical properties of the polymer material. In addition, the flame retardant materials often migrate to the film surfaces and adversely affect adhesion to subsequent surfaces.
Thus, there is a need for new flame retardant polymeric films and articles that have a broader range of mechanical mechanical properties and reduced surface fouling.
SUMMARY OF THE INVENTION
The present invention provides flame retardant films that not only have desirable mechanical properties and reduced surface fouling, but have improved flame retardant efficiency and/or reduced cost when compared with conventional flame retardant polymer films or articles. The present invention provides unified multilayer films of at least five film layers wherein at least one layer, preferably an internal layer, comprises a flame retardant film layer and at least one layer comprises a non-flame retardant film layer.
Preferably, multilayer films include layers that include a flame-retardant film alternating with layers that include a film that is not a flame retardant. In other preferred embodiments, multilayer films have layers of different flame retardant films. For example, the construction can include alternating layers of a first flame retardant film, a second flame retardant film and a non-flame retardant film.
One aspect of the present invention provides a multilayer film having a unified construction of at least 5, preferably 10, more preferably at least 13 substantially contiguous film layers wherein at least one layer (preferably one internal layer) comprises a flame retardant film layer and at least one layer comprises a non-flame retardant film layer.
Another aspect of the present invention provides a multilayer film having a unified construction; wherein the construction comprises at least 5, preferably 10, more preferably at least 13 substantially contiguous layers of organic polymeric material; the construction comprising layers comprising a flame retardant film alternating with layers comprising a film that is not flame retardant.
The present invention also provides a process of preparing a flame-retardant multilayer film. The process includes melt processing organic polymeric material to form a unified construction of at least 5 substantially contiguous film layers of organic polymeric material, wherein at least one internal layer of the organic polymeric material comprises a flame retardant film. Preferably, all the layers are simultaneously melt processed, and more preferably, all the layers are simultaneously coextruded.
A further aspect of the present invention provides a process of preparing a multilayer film, the process comprising melt processing organic polymeric material to form a unified construction of at least 5 substantially contiguous layers of organic polymeric material, the construction comprises film layers comprising a flame retardant film layer, alternating with non flame retardant film layers.
Herein, the following definitions are used:
“Unified” means that the layers are not designed to be separated or delaminated as would a tape in roll form.
“Flame retardant” means a characteristic of basic flammability has been reduced by some modification as measured by one of the accepted test methods such as the Horizontal Burn or Hanging Strip tests.
“Flame retardant additive” means a compound or mixture of compounds that when incorporated (either chemically or mechanically) into a polymer serves to slow or hinder the ignition or growth of fire.
“Flame retardant films” means polymeric films which are inherently flame retardant, or have been rendered flame retardant by means of a flame retardant additive.
“Melt processable” means polymers that are fluid or pumpable at the temperatures used to melt process the films (e.g., about 50° C. to about 300° C.), and do not significantly degrade or gel at the temperatures employed during melt processing.
“Pressure sensitive adhesive” means an adhesive that displays permanent and aggressive tackiness to a wide variety of substrates after applying only light pressure. It has a four-fold balance of adhesion, cohesion, stretchiness, and elasticity, and is normally tacky at use temperatures, which is typically room temperature (i.e., about 20° C. to about 30° C.).
“Melt viscosity” means the viscosity of molten material at the processing temperatures and shear rates employed.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention is directed to multilayer products in the form of films of organic polymeric material, wherein the films have at least one layer, preferably at least one internal layer that includes a flame retardant film layer and at least one layer comprises a non-flame retardant film layer. Each of the other layers may include a flame retardant film layer, or a film layer that is not a flame retardant. In certain preferred embodiments there are flame retardant film layers alternating with film layers that are not flame retardant. In other preferred embodiments there are alternating layers of a first flame retardant film layer, a second flame retardant film layer and a non-flame retardant film layer. The two outermost film layers may be flame retardant films, non-flame retardant films, or one of the outermost layers may include a flame retardant film layer and the other a film layer that is non flame retardant. Each layer of the construction is continuous and has a substantially contiguous relationship to the adjacent layers. Preferably, each layer is substantially uniform in thickness. The multiple layers in any one construction are “unified” into a single multilayer film such that the layers do not readily separate.
Flame retardant films used in the flame retardant film layer(s) include films which are inherently flame retardant, or have been rendered flame retardant by means of a flame retardant additive. Inherently flame retardant films are prepared from polymers, which due to their chemical structure either do not support combustion, or are self-extinguishing. These polymers often have increased stability at higher temperatures by incorporating stronger bonds (such as aromatic rings or inorganic bonds) in the backbone of the polymers or are highly halogenated. Examples of inherently flame retardant polymers include poly(vinyl chloride), poly(vinylidine chloride), polyimides, polybenzimidazoles, polyether ketones, polyphosphazenes, and polycarbonates. Useful inherently flame retardant films generally have a Limiting Oxygen Index (LOI) of at least 28% as determined by ASTM D-2863-91.
Useful flame retardant additives include halogenated organic compounds, organic phosphorus-containing compounds (such as organic phosphates), inorganic compounds and inherently flame retardant polymers. These additives are adde
Devens Douglas A.
Hoisington Mark A.
Kollaja Richard A.
Russell Patrise M.
3M Innovative Properties Company
Hess Bruce H.
Kokko Kent S.
Xu Ling
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