Primers polyolefin

Primers for cyanoacrylate adhesives, chlorinated polyolefin primers... 

Cyanoacrylate adhesives cure by anionic polymerization. This reaction is catalyzed by weak bases (such as water), so the adhesives are generally stabilized by the inclusion of a weak acid in the formulation. While adhesion of cyanoacrylates to bare metals and many polymers is excellent, bonding to polyolefins requires a surface modifying primer. Solutions of chlorinated polyolefin oligomers, fran-sition metal complexes, and organic bases such as tertiary amines can greatly enhance cyanoacrylate adhesion to these surfaces [72]. The solvent is a critical component of these primers, as solvent swelling of the surface facilitates inter-... 

Fig. 11. Effect of polyolefin primers on bond strength of ethyl cyanoacrylate to plastics. All assemblies tested in accordance with ASTM D 4501 (block shear method). ETFE = ethylene tetrafluoroethylene copolymer LDPE = low-density polyethylene PFA = polyper-fluoroalkoxycthylene PBT = polybutylene terephthalate, PMP = polymethylpentene PPS = polyphenylene sulfide PP = polypropylene PS = polystyrene PTFE = polytetrafluoroethylene PU = polyurethane. From ref. [73].

Adhesion of paints and adhesives to TPOs is especially problematical due to the aliphatic nature of the substrate material. In Europe, plasma and corona treatment is employed to render these surfaces wettable and obtain strong adhesion by adhesives and paints in automotive manufacture. In the United States, however, primers based on solvent-borne chlorinated polyolefin oligomers (CPOs) have become the treatment of choice for these substrate materials. The VOC emissions from these primers are considerable (as in all solvent-borne adhesives), but the less... 

Low surface energy substrates, such as polyethylene or polypropylene, are generally difficult to bond with adhesives. However, cyanoacrylate-based adhesives can be effectively utilized to bond polyolefins with the use of the proper primer/activa-tor on the surface. Primer materials include tertiary aliphatic and aromatic amines, trialkyl ammonium carboxylate salts, tetraalkyl ammonium salts, phosphines, and organometallic compounds, which are initiators for alkyl cyanoacrylate polymerization [33-36]. The primer is applied as a dilute solution to the polyolefin surface, solvent is allowed to evaporate, and the specimens are assembled with a small amount of the adhesive. With the use of primers, adhesive strength can be so strong that substrate failure occurs during the course of the shear tests, as shown in Fig. 11. 

The mechanism by which the primers are thought to work is relatively straightforward. The primer first diffuses into the polyolefin surface, and subsequently becomes entangled in the polyolefin. The primer molecule can then act as an anchor in the substrate surface for the adhesive polymer, which forms after the primer initiates polymerization of the alkyl cyanoacrylate monomer [37]. 

This difference in reactivity between the different classes of amines explains the difference in the primer performance on polyolefin substrates with ethyl cyanoacrylate-based adhesives [37J. Since primary and secondary amines form low molecular weight species, a weak boundary layer would form first, instead of high molecular weight polymer. Also, the polymer, which does ultimately form, has a lower molecular weight, which would lower adhesives strength [8,9]. 

Accelerates peroxide and air-based cures (e.g., polyester SMC/BMC) adhesion promoter and primer for organic substrates Adhesion promoter for printing inks on treated polyolefin films Comparable to organosilanes at lower cost Adhesion promoters and primers for treated polyolefins... 

Sometimes primers can take the place of surface treatments. Two examples are with porous substrates and with certain plastic substrates. With weak porous substrates, such as wood, cement, or porous stone, the primer can be formulated to penetrate and bind weakly adhering material to provide a new, tightly anchored surface for the adhesive. Chlorinated polyolefin primers will increase the adhesion of coatings and adhesives to polypropylene and to thermoplastic olefins. The chlorine atoms in the outer surface of the primer increase surface energy and enhance adhesion of adhesives, sealants, and paints. 

Chlorinated polyolefin Paint, adhesives, Thin, uniform Application in organic Chlorine atoms in primer increase polarity... 

To obtain a usable adhesive bond with polyolefins, the surface must be treated. A number of surface preparation methods, including flame, chemical, plasma, and primer treatments, are in use. Figure 16.4 illustrates the epoxy adhesive strength improvements that can be made by using various prebond surface treatments to change the critical surface tension of polyethylene. 

Plastic types are variable, ranging from flexible to rigid and from thermoplastic to thermoset. Because of these variations, the type of coating applied to them also varies, depending on cure response, solvent sensitivity, and modulus. The type of coating also depends upon the end use of the coated plastic. For example, topcoats can be applied directly to the plastic without the use of a conductive primer if two-toning or blackout areas are not part of the styling latitude. Adhesion promoters also are often utilized if a particularly difficult-to-adhere-to plastic is encountered (i.e., polypropylenes or thermoplastic polyolefins (TPOs), a blend of elastomer and olefin). 

Modern electron processors offer high speed (high dose-rate) curing of low viscosity liquid coatings so that surface modification of films becomes practicable. A process has been developed for grafting vinyl monomers to polyolefin film surfaces with the aid of functional silane primers using electron initiated polymerization. 

The monomer chosen for this demonstration was acrylonitrile. It Is compatible with the hydrolyzed vinyl benzyl amine silane primer In methanol, and will polymerize and copolymerize with moderate doses of electron beam energy. This study was designated to demonstrate the effectiveness of the new process In radiation grafting of acrylonitrile onto polyolefin films. 

Sections of these coated films were examined by x-ray dispersive spectroscopy (EDX) which showed that the slloxane was confined strictly at the film surface with no significant migration Into the polyolefin. These results Illustrate that the exceptional adhesion which has been achieved with the use of the slloxane primer Is most likely the result of grafting of the primer to the surface. 

One of the slloxane polymers used as a primer on the surface of polyolefin films has demonstrated barrier properties toward oxygen, oil, and flavors comparable with the best known barrier polymers. 

Hydroxybenzamines of the general formula have been claimed to improve the adhesion of a wide range of coatings to zinc and cadmium and other metallic substrates when used as either pretreatment primers or additives [63]. Ethylenically unsaturated hydroxy-functional amines have been claimed to improve the adhesion of water-based systems [64], and amines have been examined as adhesion promoters for aromatic isocyanate cured adhesives on glass and other substrates [65]. Primary aliphatic amines are claimed to improve the bondability of polyolefines [66] and an oxyethylated polyethylene... 

Polyolefin bonding has been advanced using cyanoacrylates through the use of surface primers. These primers promote adhesion to untreated polyethylene (PE), polypropylene (PP), and EPDM rubber. Table 7 shows comparison bonds using standard industrial-grade cyanoacrylates. 

Chem. Descrip. Chlorinated polyolefin Uses Primer tor polyethylene coatings ingred. 

Chem. Descrip. Calcium carbonate (99%) high purity CAS 471-34-1 EINECS/ELINCS 207-439-9 Uses Opacifier reinforcing hiding power of plastics (PVC, PU, polyester, polyolefins), emulsion paints, primers, powd. coatings, paper/board adhesives... 

Chem. Descrip. Coated calcium carbonate CAS 471-34-1 EINECS/ELINCS 207-439-9 Uses Filler in plastics (PVCplastisols, automotive underseals, polyolefin moldings and film), paints (matte paints, primers, anticorrosion paints) Features Very low absorp. inc. load ability in masterbatches Properties Wh. microctyst. rhombohedral powd. fineness 24% < 2 p dens. 2.7 g/cm bulk dens. 1.4 g/cm (packed) oil absorp. 13/100 g powd. brightness 96% ref. index 1.59 pH 9 hardness (Mohs) 3 Micro-Cel T-38 [Celite]... 

Chem. Descrip. High purity Montana talc Chem. Analysis SiO (60%), MgO (33%), AEO, (1%), moisture (0.5%) CAS 14807-96-6 EINECS/ELINCS 238-877-9 Uses Filler for solv.- and water-based paints/coatings, semigloss paints, primers, OEM/specialty areas, and polyolefins Properties Powd. 2.4 p median particle size trace on 325 mesh fineness (Hegman) 5.5 sp.gr. 2.8 dens. 34 Ib/fC (lapped) bulk dens. 12.5 Ib/fC bulking value 23.3 Ib/gal oil absorp. 39 gH 00 g brightness 90 pH 8.8... 

Uses Filler for coatings (architectural, traffic, powd., primers), polyester BMC, PVC plastics and plastlsols, polyolefin films, adhesives and sealants, and rubber compds. 

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