Polyolefin film, its use, and process for its production

Details Polyolefin film, its use, and process for its production Polyolefin film, its use, and process for its production

1999-05-21

2003-01-14

Tarazano, D. Lawrence (Department: 1773)

Stock material or miscellaneous articles

Composite

Of addition polymer from unsaturated monomers

C428S323000, C428S327000, C428S409000, C428S910000, C156S244230, C156S244240, C156S272600, C264S173150

Reexamination Certificate

active

06506500

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a polyolefin film having more than one layer and made from a base layer and from at least one outer layer. The invention further relates to the use of the film having more than one layer, and also to a process for its production.
2. Description of the Related Art
For particular applications, the packaging industry requires packaging materials with properties which cannot all be realized within a single film. Different types of film are therefore frequently combined to give a laminate. This lamination requires adhesives or adhesion promoters, which ensure that the laminated films have sufficiently firm adhesion to one another.
In addition, the resultant film laminate has to fulfill certain requirements, in particular, have combinations of properties which firstly are not possessed by individual films and secondly are difficult to achieve even in a laminate made from a variety of components.
Selection of suitable films for producing the laminate, together with finding the right adhesion promoter and cost-effective production pathways, are problems which constantly recur in the technical field of packaging materials.
A cost-effective process for producing laminates of this type is known as extrusion lamination. This process uses extrusion to apply a thin polyethylene layer to a film which has been produced previously in a separate process, and this film to which molten polyethylene has been applied is combined directly with another film. The molten polyethylene layer applied has something of the function of a tie layer between the two laminated films. This is a useful process, since polyethylene is a cost-effective tie layer and the polyethylene layer improves the mechanical properties of the laminate.
German Patent Application P 41 35 096.0 discloses polyolefin films having more than one layer and made from a polypropylene base layer and from an outer layer of an HDPE blend. This HDPE blend is composed of HDPE and co-and/or terpolymers of &agr;-olefins and, if desired, polypropylene. The outer layer of the film having more than one layer has minimal gloss and maximum haze, as a result of which the film takes on a characteristic matt appearance.
A biaxially oriented three-layer polyolefin film, sealable on both sides, is disclosed in U.S. Pat. No. 4,419,411. In these films, an additive combination of polysiloxane and silica has been incorporated into both sealable layers. The base layer consists essentially of polypropylene and comprises a small amount of monocarboxamide, which migrates to some extent from the base layer into the two sealable layers. The polyolefin film described having more than one layer is claimed to have a particularly low coefficient of friction.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a film which is suitable for extrusion lamination and can be printed on both sides and has a low coefficient of friction, where the values of the sliding and static coefficients of friction for one side do not differ substantially from one another. For the lamination, it is important that the film has good adhesion to a polyethylene layer applied by melt extrusion. Another important factor here is that these good adhesion properties should not be impaired by storage or aging of the laminate, i.e., after a certain storage time the bond strength of the laminate should be and preferably must be as good as immediately after its production.
It is also an object of the invention to provide methods of making and using said film.
In accordance with these objectives, there has been provided a biaxially oriented polyolefin film including a base layer comprising a propylene polymer and a fatty amide and an outer layer that comprises at least 80% by weight of a linear olefin polymer.
Further objects, features and advantages of the invention will become apparent from the detailed description that follows.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The outer layer including the linear olefin polymer is referred to below as outer layer D1. Outer layer D1 of the film having more than one layer comprises at least 80% by weight, preferably from 90 to 100% by weight, in particular from 95 to 98% by weight, of linear polyolefin (linear olefin polymer), based in each case on the weight of the outer layer.
Linear polyolefin which is suitable for the purpose of this invention is disclosed in U.S. Pat. No. 5,272,236, which is hereby incorporated by reference. U.S. Pat. No. 5,272,236 also discloses the process for preparation of such linear polyolefin. Amongst the linear polyolefin disclosed in U.S. Pat. No. 5,272,236 those linear polyolefin are preferred which comprise from 99.5 to 92% by weight of ethylene and from 0.5 to 8% by weight, preferably from 1 to 6% by weight, of octene units (C8). Preferably the octene units of said preferred linear polyolefins are incorporated into the ethylene-chain matrix in such a way that the linear olefin polymer has a particular type of long-chain branching. The preferred linear olefin polymer gives only one GPC peak maximum, the position of which depends on the molecular weight. In contrast, conventional C
2
-C
8
copolymers produced with Ziegler-Natta catalysts exhibit a double peak composed of absorption maxima for LDPE and HDPE.
The linear olefin polymer has particularly long-chain branching. The chain length of the branching is given by the formula
where R>6 carbon atoms for the linear polyolefin, preferably from 8 to 15 carbon atoms.
The C
2
-C
8
copolymers of the prior art have chains with shorter branching, in which the corresponding value would be R=6 carbon atoms.
In dynamic viscometer measurements, the high level of long-chain branching in the linear olefin polymer gives high pseudoplasticity at low shear rates with a marked fall-off at a shear rate of 100 l/s due to the lubricating effect of the high level of long-chain branching with respect to the C
2
-chain matrix. The crystallization interval, determined by DSC from the heating and cooling curve at a rate of temperature change of 20 K/min, is from 90 to 120° C., preferably from 100 to 110° C.
It has been found that the outer layer of linear polyolefin has excellent adhesion to an extrusion layer of polyethylene. Surprisingly, the addition of fatty amides to the base layer results in only insignificant impairment of this good adhesion. Adding fatty amides to the base layer therefore permits the coefficient of friction to be reduced in a manner known per se, and does not impair the excellent adhesion of the outer layer to polyethylene during extrusion lamination.
This is all the more surprising, since it has repeatedly been found in a wide variety of experiments with other outer layer materials, that good adhesion to the extrusion layer is only obtained if the film is free from fatty amides which reduce friction. When the linear polyolefin described above is selected as an outer layer, it becomes possible simultaneously to obtain firstly the low coefficient of friction by adding fatty amides and secondly good adhesion of this outer layer to polyethylene during extrusion coating.
In addition, it has been found that the linear polyolefin is also highly suitable for coextrusion with the polypropylene base layer and unexpectedly does not delaminate from the oriented polypropylene base layer during downstream processing. According to the present invention, a polymer has been found for outer layer D1 which on the one hand has the required high adhesion to the polyethylene layer and at the same time has good adhesion to the base layer, i.e., there is the required balance of bond strengths in addition to high strengths in an absolute sense. This balance is an additional important requirement which, in a finished bag pack made from the laminate, ensures that the bag comes apart at the interface intended, specifically in the sealable layer. An outer layer D1 which merely has one side with a high bond strength to the extrusion layer is unsuitable. In a composite of this type, when the

Affiliated with

Also associated with

Rating

Polyolefin film, its use, and process for its production does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Polyolefin film, its use, and process for its production, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polyolefin film, its use, and process for its production will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3006107