Laminated film

Details Laminated film Laminated film

1999-03-25

2002-04-09

Thibodeau, Paul (Department: 1773)

Stock material or miscellaneous articles

Composite

Of metal

C428S457000, C428S464000

Reexamination Certificate

active

06368721

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a laminated film which is used in packaging of dry foods or medicines, etc.
BACKGROUND OF THE INVENTION
Dry foods, for example, snacks such as potato chips, sweet stuffs such as biscuits, rice crackers and chocolate, and powder soup, when having absorbed moisture, exhibit poor palatability at the eating thereof. In particular, dry foods containing much oil, such as potato chips, when exposed to oxygen gas, has their oil component denatured. Therefore, it is commonly required that the packaging materials for these dry foods have excellent moistureproofing and oxygen gas barrier properties. Further, stricter requirements are imposed on the packaging materials for medicines because of the need to prevent the denaturation thereof by moisture absorption or gas. As a typical example of these packaging materials, use is made of a laminated film formed by extrusion lamination which consists of a surface substrate layer composed of, for example, a polyamide resin, a polyethylene terephthalate resin or paper, a polyethylene layer composed principally of a high-pressure-processed low-density polyethylene and a sealant layer composed of an aluminum foil or an acid copolymer such as ethylene/methacrylic acid copolymer (EMAA) or an ionomer.
The acid copolymer such as EMAA or an ionomer has the property of being excellent in adherence to aluminum foils, not possessed by the conventional high-pressure-processed low-density polyethylene, so that it is often employed in the above use. However, the acid copolymer is expensive and has an odor problem. Furthermore, when the acid copolymer is employed in the production of the above laminated film by extrusion lamination, satisfactory purging is required in the resin change to another such as the high-pressure-processed low-density polyethylene to thereby cause a problem of much resin loss.
For solving the above problems of the prior art, the inventors have selected the use of a linear low-density polyethylene (M-LLDPE) prepared with the use of a metallocene olefin polymerization catalyst, in place of the acid copolymer such as EMAA or an ionomer, as the sealant resin and have studied the adherence of M-LLDPE layer to aluminum foil and the heat sealing properties of M-LLDPE layers. Taking into account that, in actual packaging, the bond strength between sealant layers is occasionally regarded as being more important than the bond strength between sealant layer and aluminum layer, the inventors have found a laminated film which has a desirable balance of heat sealing properties and aluminum bond strength, thus, has an excellent quality as a dry food packaging material. The present invention has been completed on the basis of this finding.
OBJECT OF THE INVENTION
The object of the present invention is to provide a laminated film formed by extrusion lamination, which comprises an aluminum layer composed of an aluminum foil or an aluminum vapor deposition film and a linear low-density polyethylene layer prepared with the use of a metallocene olefin polymerization catalyst, thereby having a desirable balance of aluminum bond strength and heat sealing properties of linear low-density polyethylene layers, and further to provide a laminated film of multilayer structure having at least three layers including these.
SUMMARY OF THE INVENTION
The laminated film of the present invention comprises at least an aluminum layer (A) and, superimposed on one side thereof by extrusion lamination, a linear low-density polyethylene layer (B), this linear low-density polyethylene layer (B) prepared with the use of a metallocene olefin polymerization catalyst and having (i) a density (d; measured in accordance with ASTM D 1505) of 0.895 to 0.930 g/cm
3
and (ii) a melt flow rate (MFR; measured at 190° C. under a load of 2.16 kg in accordance with ASTM D 1238) of 0.1 to 100 g/10 min,
wherein the linear low-density polyethylene layer (B) at its surface exhibits an oxygen concentration of linear low-density polyethylene per se ranging from 1.0 to 1.4 atomic %.
In the laminated film of the present invention, a substrate layer (C) may further be superimposed on the opposite side of the aluminum layer (A) remote from the linear low-density polyethylene layer (B).
Also, in the laminated film of the present invention, a polyethylene layer (D) and a substrate layer (C) in this order may further be superimposed on the opposite side of the aluminum layer (A) remote from the linear low-density polyethylene layer (B).
Moreover, in the laminated film of the present invention, a first polyethylene layer (D) and a substrate layer (C) in this order may further be superimposed on the opposite side of the aluminum layer (A) remote from the linear low-density polyethylene layer (B) and a second polyethylene layer (D) may further be superimposed on the linear low-density polyethylene layer (B).
Still moreover, in the laminated film of the present invention, a first substrate layer (C), a polyethylene layer (D) and a second substrate layer (C) in this order may further be superimposed on the opposite side of the aluminum layer (A) remote from the linear low-density polyethylene layer (B).
When a linear low-density polyethylene having a desirable balance of melt tension and fluidity and having an excellent moldability is needed as one for go use in the formation of the linear low-density polyethylene layer (B), preferred use is made of a copolymer of ethylene and an &agr;-olefin which is:
a copolymer of ethylene and an &agr;-olefin having 4 to 20 carbon atoms having:
(i) a density (d) ranging from 0.895 to 0.930 g/cm
3
;
(ii) a melt flow rate (MFR), measured at 190° C. under a load of 2.16 kg, ranging from 0.1 to 100 g/10 min;
(iii) a melt flow rate (MFR, g/10 min) and a melt tension (MT, g) measured at 190° C., which satisfy the relationship:
MT>
2.0
×MFR
−0.84
;
(iv) a fluidity index (FI, 1/sec) defined as a shearing rate exhibited when the shearing stress of molten polymer at 190° C. has reached 2.4×10
6
dyne/cm
2
, the fluidity index and the melt flow rate (MFR, g/10 min) satisfying the relationship:
FI>
75
×MFR;
(v) a n-decane soluble content (W, wt. %) measured at 23° C., the n-decane soluble content and the density (d, g/cm
3
) satisfying the relationship:
when
MFR<
10 g/10 min,
W<
80×exp(−100(
d−
0.88))+0.1,
 and
when
MFR≦
10 g/10 min,
W<
80×(
MFR−
9)
0.26
×exp(−100(
d−
0.88))+0.1;
 and
(vi) a temperature exhibited at the maximum peak of endothermic curve obtained by a differential scanning calorimeter (Tm, ° C.), the temperature and the density (d, g/cm
3
) satisfying the relationship:
Tm<
400
d−
250.
DETAILED DESCRIPTION OF THE INVENTION
The laminated film of the present invention will be described in detail below.
The laminated film of the present invention comprises at least an aluminum layer (A) and a linear low-density polyethylene layer (B) prepared with the use of a metallocene olefin polymerization catalyst. Furthermore, the laminated film of the present invention may have a multilayer structure of at least three layers which, in addition to the aluminum layer (A) and linear low-density polyethylene layer (B), include a substrate layer (C) and a polyethylene layer (D).
Aluminum Layer (A)
An aluminum foil or an aluminum vapor deposition film is mainly employed as a material for use in the formation of the aluminum layer (A).
The thickness of the aluminum foil is generally in the range of 6 to 15 &mgr;m.
The type of substrate for use in the aluminum vapor deposition film is basically not particularly limited as long as it is a material possessing film forming capability. For example, use can be made of any polymer, paper or cellophane.
This polymer can be selected, for example, from among:
olefin polymers such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, ethylene/vinyl acetate copolymer, ethylene/acrylic ester copolymer, ethylene/vinyl alcohol copolymer, ionomers, po

Affiliated with

Also associated with

Rating

Laminated film does not yet have a rating. At this time, there are no reviews or comments for this patent.

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

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2827155