Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-03-22
2002-11-12
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C428S343000, C428S346000, C428S347000, C428S423500, C428S424800
Reexamination Certificate
active
06479576
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a deep-drawable composite film having a high degree of transparency and good UV-blocking properties. The film according to the invention is particularly suitable for the packaging of packed goods sensitive to UV-radiation (ultraviolet radiation), such as, for example, meat goods, which are presented to the purchaser in a transparent and protective packaging. The invention thus also relates to the use of the composite film for the packaging of foodstuffs.
BACKGROUND OF THE INVENTION
Many foodstuffs are subject to spoilage induced by UV-radiation. Photo-induced oxidative processes in meat goods can be mentioned by way of an example. This spoilage mechanism occurs, for example, in the case of storage in refrigerating counters where light sources which also emit light in the UV-spectrum are used for reasons of costs in many cases.
In this way, in the case of packaging materials which do not ensure UV-protection, the storage time in the counter, also referred to as shelf life in the following, can be considerably reduced. In such cases there is a need for packaging materials which counteract such shelf life reduction, i.e., films which exert an absorption effect in the ultraviolet radiation range.
Due to the easier application of the contents, covering packaging materials comprising a deep-drawn tray and a lid are generally used for meat goods. Both components must possess a high UV-barrier to protect the contents from photo-oxidative spoilage. The films must additionally be highly transparent to enable the consumer to view the offered product and permit the product to be presented as attractively as possible.
The tray film must also possess good drawability for the forming of the tray. Here deep-drawability is to be understood as the ability of a film to permanently assume a contoured shape under the effects of heat and mechanical force and pressure. A measure of the deep-drawability is given in association with the examples according to the invention and comparison examples.
The design of corresponding films according to the prior art will be described in the following. The following stipulations apply to these and all further explanations.
Symbols for plastics materials according to DIN 7728 and ISO 1043-1987(E) are used to describe the polymers contained in the individual layers unless indicated otherwise.
In the case of multi-layer constructions, the layer sequence is represented by a combination of the symbols of the polymers of the corresponding layers or symbols explained elsewhere, separated from one another by double oblique strokes. The side of the sealing layer is always the right side. Only a part of the total layer sequence constituting the construction may also be indicated. In such cases the side of the sealing layer again is always the right and layers or combinations of layers not indicated are represented by three dots, ( . . . ). Similar polymers can be differentiated from one another by numbering, for example in the form PE-LD-1//PE-LD-2//PE-LD-3. Mixtures of different polymers are represented by the symbol + and the combination of the components in brackets ( ). Optionally, additional indications of the percentage composition can also be given. Unless otherwise stated, these are always weight percentages relating to the total weight of the mixture. Thus, for example, the term . . . //PA//E/VOH// . . . //(PE-LD-1+PE-LLD)//d describes a construction with an unspecified outer layer or outer layer sequence, followed by a layer substantially consisting of polyamide, followed by a layer substantially consisting of ethylene/vinyl alcohol/copolymerisate (E/VOH), followed by an unspecified layer or layer sequence, followed by a layer comprising a mixture of a polyethylene of low density (PE-LD-1) bearing the number 1 and an ethylene/&agr;-olefin-copolymerisate (PE-LLD), and a layer following on the sealing side to be more precisely specified by d.
Layers which primarily serve to mechanically connect the layers adjoining them on both sides will be designated in the following by . . . //BA// . . . , where BA is an abbreviation for bonding agent. Typical polymers used as bonding agents will be described later in the specification.
The indication of melting points relates in the following to the value determined according to ASTM 3418 by DSC analysis (differential scanning calorimetry analysis).
The indication of melt flow rates (MFR) relates in the following to the value determined in accordance with DIN ISO 1133. If no further indications are given, the measuring condition in the form of temperature and bearing mass will be assumed as condition D in DIN ISO 1133 with a temperature of 190° C. and a bearing mass of 2.16 kg.
The density of the raw materials relates to the measuring method according to ISO 1183 (A).
The relevant prior art has long consisted of the use of composite films comprising a stabilising layer or layer sequence and a sealing layer which, in contact with a further sealing layer, facilitates an impervious packaging by bonding following melting.
Polyethylene or copolymerisates based on ethylene and other comonomers constitute preferred sealing materials due to the low melting point of these systems, in particular in the case of the packaging of heat-sensitive meat goods. Sealing media based on polypropylene or propylene-based copolymerisates are not suitable here due to the high sealing temperatures.
Films whose stabilising layer(s) consist(s) of polyamide are normally used for the packaging of perishable foodstuffs due to their balanced pattern of properties: deep-drawability, toughness and temperature-resistance. Polyamide 6 again is normally used for this purpose.
Constructions according to the prior art are described, for example, in “The Wiley Encyclopaedia of Packaging Technology” (pub. M. Bakker. D. Eckroth; John Wiley & Sons, 1986) and in “Nentwig” (Joachim Nentwig: Kunststoff-Folien, Carl Hanser Verlag 1994, Munich).
A UV radiation barrier can be achieved not only by the use of organic UV absorbers, but also by the use of solid fillers. However, so as not to impair the transparency of the films too greatly, the solid fillers must be present in adequately finely dispersed form, although the particles should not be too fine so as to comply with the required interaction with UV radiation.
The use of fine-particulate titanium dioxide (TiO
2
) is also known. Thus U.S. Pat. No. 5,391,609 discloses the use of nano-scale TiO
2
in the particle size range of 10 nm to 50 nm as additive for the acquisition of a UV barrier while retaining sufficiently good transparency. Particularly good results are achieved with TiO
2
in the particle size range of 18 nm to 40 nm. These systems are described in polypropylene and ethylene/propylene-copolymerisates.
In practice however, as stated above, polypropylene-based films prove distinctly inferior to polyamide in terms of puncture strength, and to ethylene-copolymerisates and polyethylene in terms of the commencement of sealing. In this respect the theory described in U.S. Pat. No. 5,391,609 cannot be utilized for the present requirement.
SUMMARY OF THE INVENTION
The objective was to make available a film which, in addition to good UV-absorption capability, also has a high degree of transparency and possesses good deep-drawability with good mechanical strength and can be sealed at low temperatures.
In accordance with the present invention, there is provided a multi-layer film comprising:
(a) at least one first layer (i) of polyamide;
(b) at least one second layer (ii) of polyethylene or an ethylene-copolymerisate containing fine-particulate titanium dioxide, a majority of the titanium dioxide particles having a diameter of between 5 and 30 nm;
(c) optionally at least one EVOH-containing third layer; and
(d) optionally at least one bonding layer,
wherein said multi-layer film has a value of from 5 to 200, as determined from the summation of the product of the following equation (I) for all second layers of said multi-layer film,
(A×B) E
Brandt Rainer
Eggers Holger
Norris McLaughlin & Marcus P.A.
Nutter Nathan M.
Ribar Travis B.
Wolff Walsfode AG
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