Stock material or miscellaneous articles – Composite – Of polyester
Reexamination Certificate
2004-03-29
2004-11-09
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyester
C428S304400, C428S458000, C428S461000, C428S480000, C428S910000, C525S165000, C525S173000, C525S174000, C525S184000, C528S354000, C528S361000, C264S288800, C264S290200
Reexamination Certificate
active
06815079
ABSTRACT:
The present invention relates to an opaque, biaxially oriented PHC film which includes at least one layer comprising polymers based on hydroxy-carboxylic acids and a cycloolefin copolymer (COC). The invention furthermore relates to a process for the production of the PHC film and to the use thereof.
Opaque biaxially oriented films are known in the prior art. These films are distinguished by a glossy, mother-of-pearl-like appearance, which is desired for certain applications. In addition, films of this type have a reduced density, which enables the user to achieve increased yield.
The object of the present invention was to provide environmentally friendly packaging which firstly can be produced from renewable raw materials and secondly can be disposed of in an environmentally friendly manner. In addition, the film should have an opaque appearance and have a density of below 1.25 g/cm
3
.
The object is achieved by an opaque, biaxially oriented film having at least one layer whose characterizing features consist in that this layer comprises at least one polymer l made from at least one hydroxycarboxylic acid (PHC) and from 0.5 to 30% by weight, based on the layer, of a cycloolefin copolymer (COC) having a glass transition temperature in the range from 70 to 270° C.
For the purposes of the present invention, the term opaque, biaxially oriented PHC film is taken to mean a film which has a whiteness of at least 10%, preferably greater than 20%, and an opacity of greater than 20%, preferably greater than 25%. In general, the light transmission in accordance with ASTM-D 1003-77 of opaque films of this type is less than 95%, preferably less than 75%.
In order to achieve the desired appearance and the reduced density, the proportion of cycloolefin copolymers (COCs) in the base layer must be greater than 0.5% by weight, based on the weight of the base layer. If, on the other hand, the cycloolefin copolymer (COC) content is greater than 30%, the film cannot be disposed of in an environmentally friendly manner.
It is furthermore necessary for the glass transition temperature of the cycloolefin copolymer (COC) employed to be above 70° C. It has been found that the desired effects with respect to the density reduction of the film and with respect to the appearance of the film are not achieved with a COC having a glass transition temperature of below 70° C. On the other hand, if the glass transition temperature is below 70° C., the raw material mixture has poor processing properties (poor extrusion properties), the desired whiteness is no longer achieved, and the re grind employed results in a film which has an increased tendency towards yellowing. If, on the other hand, the glass transition temperature of the cycloolefin copolymer (COC) selected is above 270° C., the raw material mixture can no longer be homogeneously dispersed to an adequate extent in the extruder This results in a film having inhomogeneous properties.
In a preferred embodiment of the film according to the invention, the glass transition temperature of the COCs used is in the range from 90 to 250° C. and in a particularly preferred embodiment in the range from 110 to 220° C.
Surprisingly, it has been found that the addition of a cycloolefin copolymer (COC) in a PHC polymer matrix allows the production of an opaque, glossy film having reduced density.
The film according to the invention has a single-layer or multilayer structure. Single-layer embodiments are built up like the COC-containing layer described below. Multilayer embodiments have at least two layers and always include the COC-containing layer and at least one further layer, where the COC-containing layer can be the base layer, and, if desired, the interlayer or the top layer of the multilayer film can also be the COC-containing layer. In a preferred embodiment, the COC-containing layer forms the base layer of the film having at least one top layer, preferably having top layers on both sides, it being possible, if desired, for an interlayer(s) to be present on one or both sides.
In a further preferred embodiment, the COC-containing layer forms an interlayer of the multilayer film. Further embodiments with COC-containing interlayers have a five-layer structure and, in addition to an optionally COC-containing base layer, have COC-containing interlayers on both sides. In a further embodiment, the COC-containing layer can form a top layer on the base layer or interlayer. If desired, both top layers can be COC-containing. For the purposes of the present invention, the base layer is the layer which makes up more than from 30% to 100%, preferably from 50 to 90%, of the total film thickness and has the greatest layer thickness. The top layers are the layers which form the outer layers of the film. Interlayers are of course provided between the base layer and the top layers.
The COC-containing layer, which is, if desired, the single layer of the film according to the invention, comprises a polymer I made from at least one hydroxycarboxylic acid, at least one COC and optionally, further additives in effective amounts in each case. In general, this layer comprises at least from 50 to 99.5% by weight, preferably from 60 to 98% by weight, in particular from 70 to 98% by weight, of a polymer I made from at least one hydroxycarboxylic acid, based on the weight of the layer.
The base layer of the film comprises at least one polymer I made from at least one hydroxycarboxylic acid, referred to as PHC (polyhydroxycarboxylic acids) below, in general in an amount of from 50 to 99.5% by weight, preferably from 70 to 95% by weight. These are taken to mean homopolymers or copolymers built up from polymerized units of preferably aliphatic hydroxycarboxylic acids. Of the PHCs which are suitable for the present invention, polylactic acids are particularly suitable. These are referred to as PLA (polylactide acid) below Here too, the term is taken to mean both homopolymers built up only from lactic acid units and copolymers comprising predominantly lactic acid units (>50%) in combination with other aliphatic hydroxylactic acid units.
Suitable monomers of aliphatic polyhydroxycarboxylic acid (PHC) are, in particular, aliphatic mono-, di- or trihydroxycarboxylic acids and dimeric 35 cyclic esters thereof, of which lactic acid in its D or L form is preferred. A suitable PLA is, for example, polylactic acid from Cargill Dow (Nature-Works®). The preparation of polylactic acid is known from the prior art and is carried out via catalytic ring-opening polymerization of lactide (1,4-dioxane-3,6-dimethyl-2,5-dione), the dimeric cyclic ester of lactic acid, for which reason PLA is also frequently known as polylactide. The preparation of PLA has been described in the following publications: U.S. Pat. No. 5,208,297, U.S. Pat. No. 5,247,058 or U.S. Pat. No. 5,357,035.
Preference is given to polylactic acids built up exclusively from lactic acid units. Of these, particular preference is given to PLA homopolymers comprising 80-100% by weight of L-lactic acid units, corresponding to from 0 to 20% by weight of D-lactic acid units. In order to reduce the crystallinity, even higher concentrations of D-lactic acid units may also be present as comonomer. If desired, the polylactic acid may additionally comprise aliphatic hydroxycarboxylic acid units other than lactic acid as comonomer, for example glycolic acid units, 3-hydroxypropanoic acid units, 2,2-dimethyl-3-hydroxypropanoic acid units or higher homologues of the hydroxycarboxylic acids having up to 5 carbon atoms.
Preference is given to lactic acid polymers (PLAs) having a melting point of from 110 to 170° C., preferably from 125 to 165° C., and a melt flow index (measurement DIN 53 735 at a load of 2.16 N and 190° C.) of from 1 to 50 g/10 min, preferably from 1 to 30 g/10 min. The molecular weight of the PLA is in the range of from at least 10,000 to 500,000 (number average), preferably from 50,000 to 300,000 (number average). The glass transition temperature Tg is in the range from 40 to 100° C., preferably from 40 to 80° C.
In accordance with the inven
Busch Detlef D.
Hade Petra
Kochem Karl-Heinz
Rosenbaum Manfred
Rosenbaum Marlies
Chen Vivian
Connolly Bove & Lodge & Hutz LLP
Rosenbaum Manfred
Rosenbaum Marlies
Treofan Germany GmbH & Co. KG
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