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
2000-12-20
2002-07-09
Nutter, Nathan M. (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...
C525S216000, C525S240000, C525S241000
Reexamination Certificate
active
06417276
ABSTRACT:
FIELD OF THE INVENTION
This invention generally concerns a polymer film suitable for use as a carrier layer in a thermoformable or membrane-pressable heat transfer foil. This invention particularly concerns such a film made from a blend and/or composite structure containing an ethylene/styrene interpolymer (ESI) and a polymer formed from at least one vinyl or vinylidene aromatic monomer, at least one hindered aliphatic vinyl or vinylidene monomer or both. This invention more particularly concerns such a film wherein the blend also includes a homopolymer or interpolymer of aliphatic alpha-olefins (&agr;-olefins) having from 2 to 20 carbon atoms (C
2-20
) and, optionally, a monomer containing a polar group. This invention still more particularly concerns such films, both as a monolayer and as a component of a multi-layer film structure.
BACKGROUND OF THE INVENTION
Heat transfer films or foils for thermal imprinting of a substrate typically include a carrier layer that is temporarily or removably bonded to one or more layers that are transferred to the substrate. The number of layers transferred to the substrate varies depending on chosen applications. A transfer foil often contains a carrier layer, a release or separating layer temporarily bonded to the carrier layer, one or more protective coating layers permanently bonded to a side of the release layer other than the side adjacent the carrier layer, a pigmented or dye containing layer permanently bonded to the protective layer, and an adhesive layer permanently bonded to a surface of the dye layer other than that which bonds to the protective coating layer to bond the transferred layers to the substrate. Skilled artisans recognize that the release layer may, in some applications, also function as a protective layer. Skilled artisans also recognize that “permanent”, as used herein implies a much greater bonding duration than a material that readily peels away from a substrate. Nonetheless, use of scrapers or other implements may effect a mechanical destruction of one or more of the layers transferred to the substrate.
In practice, one places a heat transfer foil against a substrate, applies heat through the foil, under pressure, to transfer dye or pigment layer(s) to the substrate, and then removes the carrier layer for further handling or disposal as appropriate. When using heat transfer foils to imprint wood products, such as ready-to-assemble furniture, one often includes at least one scratch resistant coating to protect the dye or pigment layer(s). Heat transfer foils also provide a decorative pattern, such as a wood grain pattern, to other substrates such as countertops, walls, siding, automobile surfaces, wood profiles and edge banding, glass, metal or plastic substrates.
Conventional heat transfer films or foils readily transfer an image, dye or pigment onto a flat, two dimensional surface or substrate. These conventional foils may encounter difficulty when the substrate takes on a three dimensional character, as in the case of a wood panel with multiple contours, uneven surfaces or both. The difficulty may range from inadequate thermoformability as evidenced by failure to conform to all of the contours to bubbling or wrinkling of transferred layers or distortion of the transferred image, die or pigment. Heat transfer foils based upon polyvinyl chloride (PVC) or polyvinyl alcohol (PVOH) typically have satisfactory thermoformability but raise other problems or concerns. One or both of environmental concerns and migration of low molecular weight plasticizers drive(s) efforts to replace PVC films. PVC films are also limited to lower draw ratios during membrane pressing operations, which limits contour design options of a 3-dimensional panel. While PVOH films meet many performance constraints, they do so at an economically unattractive cost. In addition, PVOH films tend to be moisture sensitive or even water-soluble, at least to some degree. On a practical level, this translates to concerns about film dimensional stability and leads to use of controlled atmosphere processing in order to achieve and maintain consistent coating and printing performance. A continuing need exists for a heat transfer foil that has good thermoformability with none of the environmental concerns of PVC or cost and performance concerns of PVOH, especially for use in the furniture industry. Heat transfer foils based upon polyethylene terephthalate do not have satisfactory thermoformability and therefore tend to be limited to applications on flat two-dimensional surfaces.
A first aspect of the invention is a thermoformable polymer film, the film being used as a heat transfer foil carrier layer and comprising a blend of a first polymer that is a substantially random interpolymer comprising in polymerized form i) one or more of ethylene and an &agr;-olefin monomer and ii) one or more vinyl or vinylidene aromatic monomers and/or one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, and optionally iii) other polymerizable ethylenically unsaturated monomer(s) and a second polymer comprising in polymerized form a) one or more vinyl or vinylidene aromatic monomers, or b) one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, or c) a combination of a) and b).
In a related aspect, the blend of the first and second polymers further comprises a third polymer. The third polymer is selected from a polypropylene homopolymer, an interpolymer of propylene and one or more of ethylene or a C
4-8
(&agr;-olefin monomer or both, or a polymer that comprises in polymerized form x) one or more of ethylene and a C
3-20
aliphatic &agr;-olefin or y) one or more ethylene and a C
3-20
&agr;-olefin that contains at least one polar group. The third polymer is preferably polypropylene homopolymer or a propylene interpolymer.
A second aspect of the invention is a thermoformable film-forming polymer blend composition comprising a blend of a first polymer that is a substantially random interpolymer comprising in polymerized form, i) one or more of ethylene and an &agr;-olefin monomer and ii) one or more vinyl or vinylidene aromatic monomers and/or one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, and optionally iii) other polymerizable ethylenically unsaturated monomer(s), a second polymer comprising in polymerized form a) one or more vinyl or vinylidene aromatic monomers, or b) one or more sterically hindered, aliphatic or cycloaliphatic vinyl or vinylidene monomers, or c) a combination of a) and b), and a third polymer. The third polymer is selected from a polypropylene homopolymer, an interpolymer of propylene and one or more of ethylene or a C
4-8
&agr;-olefin monomer or both, or a polymer that comprises in polymerized form, x) one or more of ethylene and a C
3-20
aliphatic &agr;-olefin or y) one or more of ethylene and a C
3-20
&agr;-olefin that contains at least one polar group. The third polymer is preferably polypropylene homopolymer or a propylene interpolymer.
DESCRIPTION OF PREFERRED EMBODIMENTS
A blend of at least one first polymer or interpolymer and at least one second polymer or interpolymer forms a thermoformable film suitable for use as a carrier layer for heat transfer foil. The blend desirably includes at least one third polymer or interpolymer.
The first polymer is a substantially random interpolymer comprising in polymerized form, i) one or more of ethylene and an &agr;-olefin monomer and ii) one or more vinyl or vinylidene aromatic monomers and/or one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, and optionally iii) other polymerizable ethylenically unsaturated monomer(s).
The second polymer comprises in polymerized form a) one or more vinyl or vinylidene aromatic monomers, or b) one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, or c) a combination of a) and b).
The third polymer is selected from a polypropylene homopolymer, an interpolymer of propylene and one or more o
Dollinger Susan E.
Dubensky Ellen M.
McGee Robert L.
Read Michael D.
Van Volkenburgh William R.
Nutter Nathan M.
The Dow Chemical Company
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