Polyolefine materials with improved adhesivity

Details Polyolefine materials with improved adhesivity Polyolefine materials with improved adhesivity

1998-11-20

2003-06-24

Zalukaeva, Tatyana (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S088000, C526S204000, C526S217000, C526S259000, C526S260000, C524S095000, C524S099000, C524S102000, C524S103000, C524S141000, C524S171000, C524S186000, C524S243000, C525S265000, C525S274000, C525S281000

Reexamination Certificate

active

06583250

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to polyolefins having improved bondability, for example by cyanoacrylate adhesives, through the incorporation of polymerization initiators, more particularly sterically hindered bases, such as diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,5-diazabicyclo[4.3.0]non-5-ene (DBN). The present invention also relates to a process for improving the bondability of polyolefins, for example by incorporation of polymerization initiators in the polyolefin compound during extrusion or injection.
BACKGROUND OF THE INVENTION
Whereas plastics based on polyolefins, such as polyethylene or polypropylene, are now widely used in the manufacture of utility goods by virtue of their favorable price and their excellent material properties, their processing behavior is generally characterized by a deficiency which has already been the subject of numerous studies. The low polarity of the macromolecules, which generally consist solely of hydrocarbons, results in a material surface with little surface energy.
It is known that moldings and films of plastics, more particularly plastics belonging to the above-mentioned group of polyolefins with a non-polar surface, do not readily lend themselves to protective, decorative or informative surface modifications, for example in the form of lacquering, bonding or printing. To accommodate surface modifications such as these, the particular molding generally has to be subjected to one or more pretreatment steps which normally lead to a modification of its surface structure. These include, for example, the pretreatment of the particular plastic, more particularly polyethylene or polypropylene, with chlorinated polyolefins. Pretreatments such as these are expensive, involve a separate production step and increase the production costs of the end product.
In order for example to increase the adhesion of conventional polyurethane coatings to polyolefin materials, the surfaces of the moldings are oxidatively polarized by plasma treatment. Depending on the geometry of the moldings, however, this form of surface treatment is not always successful because irregularly shaped moldings in particular are difficult to expose to a uniform plasma concentration which leads to uneven surface modification. This in turn results in lacquer films of irregular structure which, besides an unsatisfactory appearance, generally lack stability and, accordingly, do not meet the quality requirements which the workpiece is expected to satisfy.
Further efforts to improve the surface polarity of polyolefins have been made. For example, attempts have been made to graft polypropylene with unsaturated carboxylic acids or anhydrides. To this end, efforts have been made to produce initiator sites for radical polymerization on the polymer chain by peroxides so that the acids or anhydrides could then be grafted on at those sites. However, only a limited number of polar groups could be introduced into the polypropylene in this way because the oxidative modification of the polymer chain resulted in dramatic losses in regard to the stability of the workpiece.
To improve the surface properties of polyolefins, EP-A1 311 723 proposes incorporating a modified polypropylene resin grafted with unsaturated dicarboxylic acids in the polyolefin.
In particular, the class of so-called “instant adhesives” (hereinafter also referred to in short as adhesives) so attractive to the consumer have not yet been considered for use in conjunction with polyolefins because the adhesive—which generally consists mainly of cyanoacrylate monomers—on the one hand showed inadequate adhesion and, on the other hand, was slow to cure.
&agr;-Cyanoacrylate adhesives have acquired increasing significance in recent years in the field of industrial adhesives. Apart from the fact that they can largely be formulated as one-component solventless adhesives, &agr;-cyanoacrylate adhesives have an unusual curing rate of—in some cases—just a few seconds. Depending on their formulation, the low-viscosity adhesives are able to fill narrow gaps and thus provide for whole-surface bonding between various substrates. However, adhesive bonding such as this presupposes that the surface of the materials to be joined makes polymerization initiators available in sufficient numbers to initiate curing of the adhesive. In general, substrates with a polar surface contain molecule residues with free electron pairs and/or water molecules which are capable of initiating polymerization of the adhesive. In the absence of these initiators, the adhesive is unable to cure and to form a durable bond between the substrates. Attempts have been made to overcome this disadvantage by using so-called primers, i.e. by applying coupling agents to the surface of the polyolefin.
Thus, DE-A1 43 16 585, for example, describes a process for improving the adhesion properties of polyolefins with respect to water-based dispersion adhesives by application of an aqueous copolymer dispersion based on vinyl acetate and ethylene to the surface of the polyolefin.
In its preamble, DD-PS 50 947 discloses that efforts to modify the surface properties of polyolefins by incorporation of relatively low molecular weight additives, such as fatty acid amides or condensation products of alkylene oxides and fatty alcohols, had resulted in permanently reduced deteriorations in the mechanical properties of the materials thus joined.
DE-A1 40 17 801 describes the use of imidazoline derivatives in primers which are applied to the surface of polyolefins to improve their adhesion properties.
WO 88/10289 proposes the use of sterically hindered bases, such as diazabicyclo(5.4.0)undec-7-ene (DBU) for example, for priming the surface of polyolefins and materials produced from them.
Unfortunately, the efforts described in the foregoing to modify the surface of polyolefins have a number of disadvantages which, hitherto, appeared irreversible. Either the plastics could not be durably bonded by cyanoacrylate adhesives with their particularly favorable performance properties and their durable mechanical bonds or the process for improving surface properties to be additionally integrated in the production process added enormously to the cost of the material and could not be conveniently applied.
SUMMARY OF THE INVENTION
The problem addressed by the present invention was to provide polyolefins of which the surface would be modified in such a way that so-called “instant adhesives”, generally based predominantly on cyanoacrylate monomers, could be used to bond the polyolefins to various substrates. In particular, this effect would be achieved without adversely affecting the mechanical properties of the polyolefin. To this end, it would be desirable or even necessary for the surface modification to affect only the surface of the workpiece and those layers lying immediately beneath its surface and to cause no adverse changes to the inner structure.
Another problem addressed by the present invention was to provide a process for the production of such polyolefins.
The problem addressed by the invention has surprisingly been solved by the addition of one or more additives capable of initiating curing of the adhesive to the polyolefin during its extrusion or injection, i.e. during its processing to the final molding. The additives affect the mechanical properties of the polyolefin to only a limited extent, if at all, and remain storage-stable in the plastic for relatively long periods. The polymerization initiators suitable for incorporation in the polyolefins are readily miscible therewith, but on the other hand have a polarity which enables polymerization of the adhesive monomers to be initiated.
Accordingly, the present invention relates to polyolefin compositions having improved bonding behavior which are obtainable by mixing at least 0.001% by weight, based on the polyolefin, of one or more polymerization initiators with the polyolefin at temperatures above its glass transition temperature, characterized in that the polymerization initiators are capable of initiatin

Affiliated with

Also associated with

Rating

Polyolefine materials with improved adhesivity does not yet have a rating. At this time, there are no reviews or comments for this patent.

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

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3144334