Polypropylene laminates and process for the production thereof

A multi layer laminate containing a layer of a polypropylene material permanently bonded to an imine primed substrate is disclosed. This laminate contains a layer that is a blend of maleated high molecular weight polypropylene/low density polyethylene and a second layer that is substrate, such as nylon, that is primed with an imine primer such as polyethyleneimine.

FIELD OF THE INVENTION 
The present invention relates to laminates and the process for their 
production. The laminates have a layer of polypropylene containing 
material bonded to a substrate such as a non polar substrate. More 
particularly, the present invention relates to a method of producing 
laminates by extrusion coating a layer, a blend of a maleated 
polypropylene and a low density polyethylene, onto a substrate layer 
primed with an imine primer. 
BACKGROUND OF THE INVENTION 
Multi layered compositions such as permanently bonded laminates are very 
useful. These multi layered laminates take advantage of the good 
properties of each of the individual layers of the laminate. Laminates 
having good strength, good solvent resistance, good grease resistance and 
low gas permeability are very desirable and could be formed from a strong 
layer, a layer that is solvent or grease resistant and a layer that has 
low gas permeability giving the resulting laminate the desirable overall 
properties. These laminates have uses in packaging applications such as 
the packaging of grease covered metallic parts. 
Many laminates that are made of independent layers that are destructively 
bonded together are well known and are generally made of porous substrates 
and a bonded polymer coating such as a layer of polyethylene bonded to a 
substrate such as paper. However, laminates using a non porous substrate 
such as metal foil or nylon do not generally form permanent bonded layers 
that are destructive when separated. Thus, these non porous substrates 
must be primed with some sort of primer to allow permanent bonding of the 
polymer to the substrate. Polyethylenes are permanently bonded to non 
porous substrates if the substrate is primed with a polyethylene imine 
primer. Whereas polymers of propylene cannot be bonded to these non porous 
substrates without the use of a very unique primer, a chlorinated 
polypropylene primer. The polypropylene layer in a laminate adds the 
advantages of excellent grease and solvent resistance to the laminates, 
however, producing these polypropylene laminates is expensive due to the 
cost of the chlorinated polypropylene primer. Additionally, chlorine 
containing materials are undesirable due to the tendency of forming 
hydrochloric acid which is very corrosive. 
Thus, it would be very desirable to be able to produce inexpensive 
laminates containing a layer of polypropylene without the use of a 
chlorinated polypropylene primer. 
SUMMARY OF THE INVENTION 
The process of the present invention for producing an inseparably bonded 
polypropylene melt extrusion laminate comprises extruding onto an imine 
primed substrate a layer of a maleated high molecular weight 
polypropylene/low density polyethylene blend. 
The present invention further comprises an article of manufacture that is a 
destructively bonded melt extrusion laminate comprised of 
(1) a first layer of a blend of maleated high molecular weight 
polypropylene/low density polyethylene; and 
(2) a second layer of a substrate primed with an imine primer.

DETAILED DESCRIPTION OF THE INVENTION 
Applicants have unexpectedly discovered that maleated high molecular weight 
polypropylene compositions can be inseparably or destructively bonded to 
non porous substrates primed with imine primer. Prior to the present 
invention, laminates containing a layer of polypropylene on a non porous 
substrate were simply not known without the use of a chlorinated 
polypropylene primer. The laminated film of the present invention has 
excellent toughness as well as excellent barrier properties against 
grease, oil, and corrosion, and can be used in various applications such 
as wrap applications for metal parts (machine parts). 
The process of the present invention entails extruding under extrusion 
coating conditions, a layer that is a blend of maleated high molecular 
weight polypropylene/low density polyethylene onto a substrate that is 
primed with an imine primer. 
The substrate can be any number of substrates, porous, and non porous, but 
is preferably selected from non porous non reactive substrates. By non 
reactive it is meant that the unprimed substrate generally does not accept 
the maleated high molecular weight polypropylene/low density polyethylene 
blend to form a destructive bond, either chemically, by polar interaction, 
or mechanically. By non porous it is meant that a substrate does not have 
pores sufficient to significantly increase the bonding of the coating to 
the unprimed substrate. Although porous substrates can be used, non porous 
substrates are preferred since adhesion to these substrates is most 
improved by the present invention. The non porous substrates are 
preferably selected from polymers of polycarbonate, polyesters, nylons, 
and metallic foils such as aluminum foil, with nylons and metallic foils 
being more preferred. 
The imine primer used to coat the substrate in the present invention is 
preferably a polyethyleneimine primer such as Mica A-131-X manufactured by 
Mica Corporation, USA. It is expected that other polyethyleneimines will 
function well as primer in this application but Mica A-131-X is the most 
preferred polyethylene imine primer. 
The substrate can be primed with the imine primer by any conventional 
method of priming such as those methods used for priming substrates with 
water based primers. An example of a suitable method of priming the 
substrate is by spraying. 
The substrate is preferably primed well in advance of being subjected to 
the extrusion coating or extrusion lamination process. The substrate is 
preferably coated with a solution containing the imine primer followed by 
drying the substrate. This solution is preferably an aqueous solution 
containing very little volatile organics. This solution preferably 
contains between about 3-5 volume % polyethyleneimine and 95-97 volume % 
water. 
An example of the extrusion lamination process of the present invention is 
illustrated in FIG. 1. In this extrusion coating process 1 is the extruded 
blend layer of maleated high molecular weight polypropylene/low density 
polyethylene blend, 2 is the imine coated non porous substrate such as 
nylon film that is laminated to one side of the maleated high molecular 
weight polypropylene/low density polyethylene blend layer, and 3 is a 
third layer of an olefin polymer such as a polypropylene or polyethylene 
based polymer film or sheet that is laminated with blend layer 1 to non 
porous substrate 2 resulting in the laminated film 4. The extrusion die 
that extrudes the layer of maleated high molecular weight 
polypropylene/low density polyethylene blend is at 5. The large chilled 
roll that cools the laminated film is at 6 whereas 7, 8, and 9 are rolls 
that aid in pressing and advancing the film. 
The extrusion coating process of the present invention is preferably 
conducted at a temperature between 425.degree. F. and 525.degree. F. at a 
line speed of 200 feet per minute or faster, and at a throughput rate of 5 
to 10 pounds per hour per inch of die width with 10 pounds per hour per 
inch being most preferred. 
Any amount of maleated high molecular weight polypropylene would improve 
the grease resistance of a film, and would improve the adhesion compared 
to a corresponding amount of non maleated polypropylene. However, the 
maleated high molecular weight polypropylene/low density polyethylene 
blend preferably contains at least 10 weight % maleated high molecular 
weight polypropylene more preferably at least 30 weight with at least 50 
weight % being most preferred. The lower amounts of polypropylene in the 
blend would impart less of the grease and solvent resistant properties to 
the layer, and the adhesion of these low polypropylene blends is not as 
dramatically improved by the present invention. Therefore the higher 
amounts of polypropylene are more preferred. 
The maleated high molecular weight polypropylene/low density polyethylene 
blend requires some amount of low density polyethylene to be able to be 
extrusion coated and preferably contains at least 5 weight % low density 
polyethylene and no more than 95 weight % maleated high molecular weight 
polypropylene. At least 5% low density polyethylene imparts adequate 
extrusion coating capabilities to the blend, however 10-20 weight % low 
density polyethylene provides better extrusion coating properties. The 
overall balance of adequate extrusion coating properties and grease 
resistance are at a most preferred concentration of about 90 weight % 
maleated high molecular weight polypropylene and about 10 weight % low 
density polyethylene. 
The maleated high molecular weight polypropylene used in the blend of the 
present invention is generally prepared by taking maleated high molecular 
weight polypropylene that has been prepared by a conventional process as 
illustrated in U.S. Pat. Nos. 3,862,266 and 3,862,265. The maleated high 
molecular weight polypropylene of the blend is preferably maleated to 
about 0.1-2 weight % maleic anhydride, more preferably about 0.2-1 weight 
% with about 0.5 weight % maleic anhydride being most preferred. Although 
the adhesion of the blend is improved by incorporating any amount of 
maleic anhydride into the high molecular weight polypropylene, at 
concentrations less than about 0.1 weight % maleic anhydride, the high 
molecular weight polypropylene does not have an adequate acid number to 
render the resulting blend destructively bondable to imine prime 
substrates, whereas amounts much over 2 weight % do not provide any 
substantial increase in bonding. The maleated high molecular weight 
polypropylene preferably has an acid number between 1 and 8, more 
preferably between 2 and 6 with an acid number of about 4 being most 
preferred. 
The high molecular weight polypropylene can be a homopolymer or copolymer 
containing up to 5 weight % of other monomers without interfering with the 
overall properties of the polypropylene. The high molecular weight 
polypropylene preferably has a flow rate between 1 and 20 decigrams per 
minute at 230.degree. C. more preferably between 2 and 10 decigrams per 
minute at 230.degree. C. with flow rates between 2 and 5 being most 
preferred. A flow rate above 20 will produce maleated high molecular 
weight polypropylenes with flow rates above 70 which means that these 
maleated high molecular weight polypropylenes are too fluid and do not 
have a desirable melt strength. Whereas a flow rate below 2 will produce 
maleated high molecular weight polypropylenes with flow rates below 40 
which means that the maleated high molecular weight polypropylenes do not 
process well. Thus the maleated high molecular weight polypropylene 
preferably has a flow rate between about 40 and 70 decigrams/min at 
230.degree. C. preferably between about 50 and 60 decigrams/min with a 
flow rate of about 55 decigrams/min being most preferred. 
The low density polyethylene used in the blend of the present invention 
preferably has a poly-dispersity index between 3 and 15. The 
poly-dispersity index is the ratio of the weight average molecular weight 
to the number average molecular weight. This poly-dispersity index for the 
low density polyethylene is more preferably between about 5 and 10 with 
about 7 being most preferred. A low density polyethylene with a 
poly-dispersity index below about 3 exhibits excessive edge weaving during 
extrusion coating/lamination, whereas a low density polyethylene with a 
poly dispersity index above about 15 exhibits extrudate tear off during 
extrusion coating/lamination. 
The low density polyethylene also preferably has a with a melt index 
between about 1 and 10 decigrams/min at 190.degree. C., more preferably 
between about 3 and 7 decigrams preferred. A low density polyethylene with 
a melt index below about 1 does not blend well with maleated 
polypropylenes due to a viscosity mismatch, whereas a low density 
polyethylene with a melt index above about 10 is less preferred since it 
does not provide sufficient melt strength needed for this process. 
The maleated high molecular weight polypropylene/low density polyethylene 
blend of the present invention can have other conventional additives 
incorporated into the blend by conventional methods. Suitable additives 
include, for example, Irganox 1010 antioxidant. 
The blend of the present invention can be blended by any conventional 
process such as tumble blending. 
Corrosion inhibitors are presently added to some polyethylenes at about 
0.5% by weight to be made into film for use in laminations for protecting 
metal parts from oxidation and corrosion. Examples of corrosion-resistant 
polyethylene films are marketed by Northern Instruments Corporation, Lino 
Lakes, Minn., U.S.A., as "Zerust" Films. Such films can be used in 
combination with a film of the maleated high molecular weight 
polypropylene/low density polyethylene blend of this invention to form 
laminated structures with the two films destructively bonded together. 
Corrosion inhibitors at about 0.5% by weight could also be added to 
polypropylene films and laminated with a film of the blend of the present 
invention to form a destructively bonded laminate of the two films. 
Corrosion inhibitors at about 0.5% by weight can also be added directly to 
the maleated high molecular weight polypropylene/low density polyethylene 
blend of this invention for direct extrusion coating onto a substrate or 
for extrusion lamination of a multi layer structure. 
The destructively bonded melt extrusion laminate produced according to the 
present invention comprises: 
(1) a first layer of a blend of maleated high molecular weight 
polypropylene/low density polyethylene; and 
(2) a second layer of a substrate primed with an imine primer. 
The article manufactured is preferably a coextrusion that contains a third 
layer comprised of an olefin polymer that is coated on said first layer, 
said first layer being between said second layer, and said third layer. 
The layer of maleated high molecular weight polypropylene/low density 
polyethylene blend that is extruded in contact with the imine primed non 
reactive substrate preferably has a thickness between about 0.2 and 30 
mils (0.005-0.76 mm) more preferably between about 0.5 and 5 mils 
(0.0127-0.127 mm) with a thickness of about 1-2 mils (0.025-0.05 mm) being 
most preferred. About 1-2 mils is most preferred because it offers 
adequate grease proofness to a laminated structure. 
The following examples are meant to illustrate the present invention but 
are not intended to limit the reasonable scope thereof. 
EXAMPLES 
The following procedures were used to evaluate the examples: 
The bond was manually tested to determine if it was destructive, which 
means that the layers could not be separated without destroying the 
lamination. 
EXAMPLE 1 
Preparation of Maleated Polypropylene. A crystalline polypropylene mixture 
containing 49 parts by weight (pbw) Tenite polypropylene 423S from Eastman 
Chemical Company (ECC), 49 pbw Tenite polypropylene 424S from ECC, 1 pbw 
peroxide, and 1 pbw maleic anhydride was tumble blended in a drum and 
charged into an extruder with the following extruder conditions: 
Barrel Temperatures: 190.degree. C.-240.degree. C. 
Die Temperature: 240.degree. C.-250.degree. C. 
Melt Pressure: 40-100 psi 
Extruder Screw Speed: 125 rpm 
Feed Rate: 10 pound/hour 
Vacuum(vent): 2 mm Hg 
Residence time: 80-120 second 
The extruded product was pelletized and analyzed to have a melt flow rate 
of 50 dg per minute at 230.degree. C. and an acid number of 5.0 mg KOH per 
gram. 
EXAMPLE 2 
The maleated polypropylene from Example 1 (89.85 pbw), 10 pbw Tenite 1550p 
polyethylene from ECC having a melt index of 3.5 dg per minute, and 0.15 
pbw antioxidant were tumble blended and fed into a twin-screw extruder and 
pelletized under the same operating conditions as in Example 1. This 
extruded product was then extruded between a 0.6 mil unprimed nylon film 
(BCF "Curphane" from Bemis Corporation, U.S.A.) and a 2 mil polyethylene 
film containing 0.5% wt. Zerust corrosion inhibitor as shown in FIG. 1 and 
illustrated in Run 1, FIG. 2. 
Barrel temperature: 450.degree. F. 
Melt Temperature: 465.degree. F. 
Line Speed: 200 f/min 
Film Thickness: 0.001 in 
Substrate: nylon film 
No bond was formed between the extruded product and the nylon film, 
however, a good destructive bond was formed between the 
polyethylene/Zerust film and the extruded product. 
EXAMPLE 3 
This example was conducted essentially identical to Run 1 in Example 2 
above except that, prior to being coated with the extruded product, the 
nylon film was coated with a commercial aqueous polyethyleneimine primer 
(MICA A-131-X from MICA Corporation) as shown in Run 2, FIG. 2. Good 
destructive bonds were obtained from the extruded product with both the 
primed nylon film and polyethylene/Zerust film. 
EXAMPLE 4 
The blend from Example 2 was extruded onto a polyethyleneimine primed metal 
foil substrate as shown in Run 3, FIG. 3. A good destructive bond was 
formed between the extruded product and the primed foil. 
EXAMPLE 5 
This example was conducted according to Example 4 except that a maleated 
polypropylene was not included in the extruded blend. The extruded blend 
(Tenite 4G7DP) contained 80 wt. % Tenite 427S polypropylene and 20 wt. % 
Tenite 1550p polyethylene and is illustrated in Run 4, FIG. 2. No 
destructive bond was formed between the extruded layer of the nonmaleated 
polypropylene/low density polyethylene blend and the foil even with the 
presence of the polyethylene imine primer on the foil substrate. 
The invention has been described in detail with particular reference to 
preferred embodiments thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention.