CA1089814A - Mating adhesive bands for serially arranged coplanar fasteners - Google Patents

Abstract

A B S T R A C T

Mating adhesive tapes are provided for serially arranged coplanar fasteners having cylindrical shanks bonded together by tapes adhered to the fasteners wherein the tapes are prepared from a blend of a polyolefin plastic with an elastomer; the adherence of the tapes being such that each tape portion and fastener may be driven together into the work piece.

Description

1(?89814 This invention relates to the bonding of rod-shaped fastener element~, such as nails or staple6, and more particularly to the bonding of such fasteners with specially formulated adherent polyolefin copolymer.
This application is a dlvision of Canadian application serial number 194,599 filed March 11th, 1974 and consequently claims only certain features of the invention fully disclosed below.
Automatic nailers, especially those which are actuated pneumati-cally, are a relatively new innovstion in the bullding industry. But they are flnding wide acceptance and it 18 contemplated that the market will io grow qulte rapldly.
These automatlc nallers require nails which are held together in a prearranged configuratlon 80 that they may be conveniently fed into the nailer itself and can be "processet" properly within the nailer. The pre-arranged configuration in a specific aspect is referred to as a nail stack.
The concept is quite analogous to cartridges held in a belt which are fed into a heavy caliber machine gun. Thus, by "processed" it is meant that the nalls ln the stack have to move cleanly ln the chamber and lnto firing po8itlon. The device used to feed the stack is a spring loaded arrange-ment.

Most nail stacks presently available utilizé a hot-melt adhesive which bridges the interstices between ad~oining nails in the stack. Paper strlps are placed on one or even both sldes of the stack. Such strlps are requlred ln order to increase the rigidity of the nail stack but these strips also contrlbute towards lmproved appearance.

~ Nail ~tacks prepared accordlng to these techniques of the art `~ suffer from several ma~or dlsadvantages. Some o these include:
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1 ~i) when exposed to low temperatures, whlch are 2 common to building activity which takes place

3 outside, the adhesives undergo brittle fail-

4 ures when dropped or during loading and cause -extensive stack breakage;
6 (ii) the same adhesives will also tend to break 7 away from the nail during the firing process 8 with sufficient velocity to constitute a safe-9 ty problem, to say nothing of the additional -clean-up problems;
11 (iii) very often a portion of paper strip, with an 12 area exceeding that of the nail head, will be 13 caught by the nail and pinned underneath the 14 nail head, requiring additional manpower to lS remove it prior to the finishing steps of 16 plastering, etc.
17 Thus, a potentially enormous and significant auto-18 matic fastening industry is waiting poised at the threshold 19 or ma~or significance. Any improvements that can be effected upon the unsolved disadvantages attendant upon the presently 21 available nail stack itself will accelerate that growth.
22 Furthermore, an additional related problem i8 in the area of staples which are used either in automatic dis-2~ pensers or hand-operated dispensers for a wide variety of uses.
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~ 26 These are conventionally bonded together into a .,.
.~, , 27 fastener article having a plurality of rod elements rigidly 28 bonded to each other in an adjacent planar, parallel rela-29~ tion8hip- Usually, in order to bond, the wires are cleaned ln a solvent bath, dried, and exposed to an adhesive tank.
31~ ~ Conventionally, nitrocellulose is used as the ad-. ~
32 ~hesive to bond the rod or wire elements of a staple fastener 1(~85~8~4 1 article. This is not a particularly effective adhesive.
2 Moreover, it is applied from a solvent/nitrocellulose solu-3 tion. The solvent is removed by passing the wires through a 4 series of electrical heaters (ovens) since the solvent is not recovered (recycled) but vented to the atmosphere. This 6 presents a difficult problem of complying with increasingly 7 stringent solvent emission standards promulgated by various 8 governmental regulatory agencies.
9 The invention comprises a fastener article of manufacture, which is an assemblage of rod-shaped, fastener 11 elements suitable for use in automatic dispensing devlces l2 for dispensing fastener elements such as nails or staples.
13 These elements are held properly together in a prearranged 14 configuration by virtue of a specifically defined adhesive polyolefinic composition.
l6 In the drawings:
17 Fig. l shows an enlarged view of a typical portion 18 of fastener elements, e.g. nails comprising the article of 19 manufacture of the invention;
Fig. 2 shows a cross-sectional view of the article 21 of Fig. l taken across 2-2;
22 Fig. 3 shows a fastener element of the invention 23 embedded in two pieces of wood which it is joining together;
24 and Fig. 4 is a photograph of an actual embodiment of 26 the invention.
27 It has been discovered and forms the substantial 28 conceptual basis of this invention, that a novel, unobvious 29 and highly useful fastener article of manufacture can be pre-~ pared according to the invention. In essence, fastener art-31 icles arranged and constructed in specific configurations 3~ and held together with specifically defined bonding agents . . . . . .. ...

r-8~4 1 and techniques comprise the sub~ect matter of the invention.
2 In particular, the novel fastener articles of the 3 invention are a plurality of individual fastening elements, 4 e.g. nails, rods or staples especially adapted to be driven -into a substrate material by automatic driving means such as 6 pneumatic actuated automatic nailers.
7 These elements are firmly held in a specific and 8 prearranged structure and relationship to form the fastener 9 article by means of certain adhesive, binders comprising a ma~or portion of C2 to C8 polyolefin graft copolymers used 11 as tapes, film or powder. These latter are referred to gen-12 erally as adhesives.
13 When used herein the term copolymer is intended to 14 include polymers with two or more monomers.
In one preferred aspect the binder, when used as a 16 tape, comprises a ma~or portion of C2~C3 polyolefin copoly-17 mer ~trip l mil to 40 mils, preferably 5 mils to 30 mils, 18 and most preferably 6 mils to 20 mils thlck, having a width 19 sufficient to cover from 5 to 75, preferably 20 to 60, and most preferably 30 to 40~ of the length of the fastener ele-21 ments, e.g. nail shanks.
22 It is most desirable and therefore preferred that 23 the tape covers both sides of the fastener article, e.g.
24 nail stack.
The polyolefin copolymer is preferably grafted 26 rather than randomly copolymerized (but not limited to grafts) 27 with certain reactive compounds as described herein. The 28 adhesive component, e.g. graft, content will be from about 29 0.12 to 20, preferably l to lO and most preferably 2.0 to 8 weight percent of the total polymer.
31 Preferably this adhesive component of the composi-32 tion, e.g. graft portion, will comprise the class of unsatu-1C~898~
1 rated mono- and di-carboxylic-containing acids (C3-C m) with 2 preferably_at least one olefinic unsaturation and will ln-3 clude anhydrides, salts, esters, ethers, amides, nitriles, 4 thiols, thio acids, glycidyl, cyano, hydroxy, glycol, and s other substituted derivatives from acids.
6 Preferred examples of such acids, anhydrides, and 7 derlvatives thereof include maleic acid, fumaric acid, himlc 8 acid, itaconic acid, citraconic acid, acrylic acid, glycidyl 9 acrylate, methacrylic acid, glycidyl methacrylate, cyanoacry-late, hydroxymethacrylate, acrylic polyethers, acrylic anhy-11 drides, sodium acrylate, calcium acrylate, magnesium acryl-l2 ate- Substituted styrenes, acrylonitrile, vinyl halides, 13 acrylate esters, dimethyl aminoethyl acrylate, vinyl pyri-dines, vinyl pyrrilidone, vinyl ether copolymers, maleic anhydride-styrene copolymers, acrylamide, strained ring l6 diels-alder adducts such as ethylidene norbornene and the 17 like are other unsaturated grafting monomers which can be 18 usefully employed.
19 ~crylic acid and glycidyl acrylate are especially preferred species of monomeric grafting agent.
21 Although random copolymer~ and grafted copolymer~ can be 22 prepared utillzing any known technique in the art, a particularly pre-23 ferred technique for preparing the preferred grafted copolymer binders 24 of the invention is that described in Italian Patent 953~632 granted August 1~, 1973 in the name of R.A. Ste~nkamp and T.J. Grall.
26 It wIll be recognized that a wide variety of poly-; - 27 olefin copolymer materials will be suitable so long as they 28 will adhere well to the individual fastener elements, e.g.
29 rods, i.e. nails. Nevertheless, certain physical criteria defining especially preferred polyolefins will be described.
31 Such polyolefins will produce fastener articles of outstand-32 ing commercial value.
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1 Among these is the prerequisite that the tape be 2 made to have adequate toughness or flexural strength, e.g.
3 an ASTM D790 secant flexural modulus (p.s.i. x 105) of 1.8 4 to 0.5, preferably 1.5 to 0.5, and most preferably 1.20 to o.6. The D790 test gives an indication of the flexibility 6 of the adhesive binders.
7 The preferred material will have an ASTM D256, 8 Izo~ ioom temperature impact strength in foot/pounds per g inch of notch of o.6 to DNB*, preferably 1.3 to DNB, and most preferably 1.5 to DNB. Over the temperature range of 11 -40 to 150 F, preferably -20 to 130 F., and most prefera-l2 bly -10 to 110 F. the unnotched Izod impact values range 13 from 6 to DNB. The D256 test indicates the resistance of 14 the binder material to shattering at low temperatures.
The other important criteria is the ASTM D638 ten-l6 sile strength measured in psi, which is 6,ooo to1,500, pre-17 ferably 4,000 to 1,700 and most preferably 3,000 to 1,800. - -18 Furthermore, the adhesion values should be on the 19 order of at least 3 and can be up to 60, preferably at least 10 and can be up to 30, at least and most preferably 20 21 pound~ per inch (of width), e.g. so that the grafted binder ad-22 heres to the fastener, i.e. nall, as :i8 is being nailed and 23 even after nailing. This is to ensure that no polymeric mat-2~ erial is forced off the surface of the nail. Thus the use of the inventive article eliminates accumulations under and 26 extending beyond a nail head.
27 For nail stacks, a very crude and practical test 28 is to drop a nail stack fastener article of the invention, 2~ such as that in Figure 4, with about 30-40 nails in it, from a height of about four feet. The binder composition is con-31 sidered to perform satisfactorily if no catastrophic break-32 * DNB S Does Not Break 1~858~4 1 age occurs.
2 ~urthermore, the polymeric tape material should 3 not shatter and spray tape fragments as the individual fast-4 ener elements of the fastener article are actually driven in-to various materials for fastening purposes.
6 Specifically, in terms of nails, the nail itself 7 must penetrate the material to be nailed, carry the grafted 8 tape with it and at the same time the tape-to-nail adhesion 9 must be tenacious enough not to separate during the actual automatic nailing step.
11 Not only are the fastener articles of manufacture I2 of the invention possessed of outstanding utility for use in j~
; 13 automatic fastener dispensers, the invention also provides 14 an extremely important process advantage of greater ease of manufacturing the assembly of fastener elements comprising t 16 the fastener articles~ than had been possible in the prior e 17 art.
; 18 Thus, a grafted polyolefin tape meeting the physi-19 cal and other criteria set forth herein which is c~pable of being strongly adhered to the surface of the nail or other 21 fastener element can be applied to fastener elements in at 22 least two extremely convenient ways.
23 One of these is that the nails are assembled in 24 their prearranged configuration. The tape is placed on the surface of the nails and the entire assembly is sub~ected to 26 sufficient heat either by heating the nails or by placing 27 the assembly in an oven so that the tape is able to soften 28 and flow enough to adhere tenaciously to the surface of the 29~ nail after solidification.
This also preferably permits some of the tape 31 material to flow into the interstices between the ad~acent 32 nails in the assembly. Such flow contributes toward maximiz-:' ~ - 8 -.

1 ing the surface area of nail adhered to binder, e.g. tape.
2 The exact ~onditions will vary somewhat depending on the 3 particular fastener elements to which the tape is being fix-4 ed and the exact composition of the tape.
Alternatively, the tape itself can be extruded 6 directly while the fastener elements are held in a ~ig or 7 other device in their prearranged conflguration. The soft, 8 extruded tape will be laid down over the fastener element, 9 e.g. nail surfaces, and will tenaciously adhere to these surfaces upon cooling. The nails can be preheated to a pre-11 determined temperature so that the extruded tape is not l2 initially cooled too rapidly to develop proper adhesion.
13 Quenching a molten tape after a heat soak of a few minutes 14 on the fastener element develops maximum adhesion values, but it is not necessary, less than maximum adhesion values l6 are perfectly adequate for the purposes of this invention.
17 Although polyolefin copolymer tapes as described 18 above are the preferred means for adhering fastener elements 19 together to form the fastener articles of the inv~ntion, other techniques of utilizing the copolymer are available 21 and can be used to form novel fastener articles.
22 One approach which can be used is to coat the in-23 dividual fastener elements with a thin partial or complete 24 coating of the adhesive polyolefinic copolymer. The coating can be accomplished with solution, extrusion or powder tech-26 niques.
27 The coated elements are then placed into then pre-28 arranged configuration proximi*ies by any convenient means 29 as-described, such as a ~lg, subjected to sufficient heat to L
cause flow of the coating and cooled passively or actively 31 to obtain fastenér articles.
32 The elements can also be placed in their pre-!

,~, g 1 arranged configuration, coated with a polyolefin copolymer 2 powder either electrostatically or in a fluid bed, heated to 3 cause flow of the coating and cooled passively or actively 4 to obtain a fastener article.
Although the technique described in the paragraph 6 immediately above can be used for nail stac~ fastener arti-7 cles, it is especially preferred when the fastener article 8 i8 to be a planar configuration of staples for staple guns.
~ Although the articles and techniques of this in-vention generically encompass both staple configurations and 11 nail stacks, there are enough differences in specifics to l2 ~ustify discussion of a particular techni~ue which is espe-13 cially well adapted for forming staple fastener articles.
14 Staple fastener articles with good dispensing prop-erties can most conveniently be prepared by first arranging l6 a laxge number of staple elements in a touching, ad~acent, 17 parallel, planar relationship. Subsequently, a film or 18 binder (as described herein) is placed over the staples.
t9 Heat is applied either by heating in an oven, or directly heating the staples sufficient to cause the film to 21 soften and flow. Upon cooling, the staples are held in the 22 prearranged configuration by the adhesive quality of the fllm.
23 Alternatively, the film can be melt-extruded 24 directly on the heated staples or other fastener element. A
tape can be used in the same manner.
26 It is also to be noted that for many fastening 27 applicat~ons the functional binder copolymer material used 28 on a fastener element will also adhere to the surface of the 2~ materials it penetrates because of the interaction of the binder~s functional groups, e.g. carboxy with the functional 31 nature of the host material, i.e. wood, steel, etc. See 32 Figure 3.
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1 In the Figures, Fig. 1 shows partial fastener 2 article 10-(nail stack) with Nails 12 and the adhesive 3 polyolefin tape 14 of the example bonded to the nails and 4 holding them in their prearranged configuration.
Fig. 2 is a cross-section view of Figure 1 taken 6 across 2-2.
7 Fig. 3 shows two pieces of wood held together by a 8 fastener element (nail) from the nail stack.
9 Fig. 4 is a photograph of a section of an actual nail stack article according to a preferred embodiment of 11 this invention. Note that the nails are cliphead nails.
12 The especially preferred compositions used in the 13 articles of the invention will contain portions of plastic 14 and elastomer as set forth in TABLE I below.
TABLE I
16 RangesPlastic Elastomer 17 Isotactic polypropylene*, Ethylene, propylene, 18 or high density PE copolymer, or butyl or 19 polyisobutylene, or other compatible elas-21 tomers 22 General 30 to 90 wt. % 70 to 10 wt.
23 Preferred 40 to 80 wt. % 60 to 20 wt. %
24 Most Pre-ferred _ 50 to 70 wt. % 30 to 50 wt. %
26 * (including thermoplastic impact grades and block copoly-27 mer impact grades.) that can be used without additional 28 additives.
29 It will be noted that the preferred compositions of the invention comprise a sizeable elastomeric component.
31 This plays an important role in the rheology of the adhesive 32 binder as well as the level of adhesion strength.

1 The elastomer EPR or EPDM copolymers will contaln 2 from 20 to ~5, preferably 40 to 80, and most preferably 50 3 to 80 weight percent of ethylene. Generally it is preferred 4 that they have a high crystalline component, e.g. high green strength. The type and quantity of elastomer is not criti-6 cal, so long as the final composition has the specified pro-7 portions.
8 Blends of ethylene polymers and propylene polymers 9 can also be used as the plastic component. They will com-prise from 50 to 90 weight percent polypropylene and 50 to 11 10 weight percent polyethylene, preferably 50 to 85 weight l2 percent polypropylene and 15 to 50 weight percent polyethyl-13 ene, and most preferably 60 to 75 weight percent polypropyl-14 ene and 40 to 25 weight percent polyethylene. The polyethyl-1s ene component can be either high density or low density.
I6 The grafted or copolymer portion of these polymers 17 will preferably be acrylic acid or glycidyl acrylate and will 18 be present in quantities of 0.2 up to 20 weight percent as 19 de~cribed above. While the polymers can be grafted directly to the desired level, it is often convenient to graft a poly-21 mer to a relatively high level and then blend it with un-22 grafted polymer to arrive at the particular desired level.
23 This is particularly useful when relatlvely low graft levels 24 are required.
Although the adhesive binder compositions de-26 scribed herein will adhere extremely well to all ferrous 27 metals and most nonferrous metals, special subgenus composi-28 tions within the scope of the generally described binder com-29 positions are necessary to achieve necessary adhesion to copper and copper-containing alloys.
31 The binder composition that must be used to effect-32 ively bond copper fastener elements or any other copper item _ 12 -1 or copper-containing alloy for that matter is as follows:
2 G~nerally, it has been found that blends of 60 3 to 97, preferably 80 to 95, and most preferably 85 to 90 4 weight percent of a low density polyethylene blended with a balance of butyl rubber or polyisobutylene and then 6 grafted with from about 0.02 to 20, preferably 0.l to l0, 7 and most preferably 0.2 to 8 weight percent of acrylic 8 acid or glycidyl acrylate will adhere well to copper or 9 copper alloy substrates. Glycidyl acrylate grafts to poly-propylene containing a small ethylene polymer component are particularly outstanding for achieving maximum copper l2 adhesion.
13 In formulating the adhesive binders of the inven-14 tion, it was found that there was a delicate balance or trade-off between full-contact of binder with fastener l6 elements and melt-strength. The final composition must 17 be 8atisfactory in both regards.
B Melt-strength is important since the binder will 19 often be applied under kinetic conditions, when it is molten. And it must have the ability to hang together 21 when being stressed and moved while molten.
22 On the other hand effectiveness of adhesion de-23 pends on maximum contact of the binder with fastener ele-2~ ments. Therefore, the binder must flow to some extent while molten to achieve best results.
26 A rough measure of these characteristics can be 27 obtained by measuring either melt index (MI) or melt flow 28 rate (MFR3, which for the purposes of this discussion will 29 be considered interchangeable and will be referred to as MF~.
31 Generally, the novel adhesive binder of the inven-32 tion should have an MFR of about l to 30, preferably S to 20 1 and most preferably 8 to 12.
2 _When elastomer is blended into a given plastic, 3 the resul~ing MFR will tend to be lower than the MFR of the 4 starting plastic. Therefore, generally, a plastic is fab-ricated (by peroxide break-down for instance) with a higher 6 MFR than is desired in the final composition.
7 A wide variety of elastomers can be used for 8 blending with the plastic. These are largely amorphous 9 materials which provide additional flexibility to absorb the shock of impact, particularly at low temperatures when the 11 plastic component approaches or exceeds its glass transition l2 temperature.
13 Generally, the elastomers are selected because of 14 convenience in blending with the plastics, particularly when only extruder mixing is available. Also, the saturated l6 elastomers, or low unsaturated elastomers (ERR, EPDM) are 17 usually preferred over the highly unsaturated elastomers, 18 e-g natural rubber, polybutylene, etc.
19 The invention is further illustrated by the follow-ing examples.
21 Example 1 22 In a preferred embodiment, the fastener article of 23 Fig. 4 comprising a plurality of nails held in a flexible, 24 pre-arranged configuration was prepared by the following technique.
26 The nails were placed in a jig in the prearranged 27 configuration. A strip of grafted polyolefin tape 3/8"
28 wide, 6 mils thick, consisting of 60 weight percent h~gh 2~ molecular weight isotactic polypropylene having an MFR of between 1-22 and 40 weight percent ethylene-propylene elast-31 omer (EMD-492, obtained from Exxon Chemical Co. U.S.A.), 32 both of which were grafted with 4 weight percent of acrylic .

r lt~ 3~4 1 acid, to result in a grafted adhesive composition having an 2 MFR of - lQ, was used to hold the nails in the proper config-3 uration. The polyolefin tape had a ASTM D638 tensile strength 4 of 2000 psi ft/lb/in of Notch, a ASTM D790 secant flexural modulus of 75,000 psi and a notched Izod ASTM D256 room tem-6 perature impact of 1.7 ft/lbs/inch.
7 The tape was placed over the nails which were in 8 the same configuration as illustrated in Fig. 1. The nails 9 with the tape on top were heated to a temperature of 425 F.
for a time of 3 minutes. Simultaneously an identical tape 11 was applied to the opposite side of the nail configuratlon l2 utilizing the same adhesion process conditions.
13 The resulting article was allowed to cool to room 14 temperature. Adhesion of the tape to the nails was tested.
Adhesion strengths of 15-30 lbs/in width were measured.
l6 The resulting nail stack article, after passing 17 the drop test, was tested in a pneumatic automatic nailer 18 manufactured by the Paslode Division of Signode Corporation.
19 The test results indicated that the nails performed ext~emely well in the pneumatic nailer. The results were far superior 21 to those obtained using nail stacks bonded together with con-22 ventional adhesive techniques.
23 Example 2 24 The technique of Example 1 is repeated, except that the na~ls are replaced with glass-fiber reinforced thermo-26 plastic rods which are to be used as fastening elements.
27 Example 3 28 Example 1 is repeated except that the steel nails 29 are replaced with aluminum rods which are to be used as fas-tening elements.
31 Example 4 32 Example 1 is repeated except that the steel nails 1 are replaced with copper wires and the tape is low density 2 ethylene polymer containing lO wt. % of butyl rubber, the 3 total composition grafted with 3 wt. % of acrylic acid.
4 Example 5 S A staple article according to the invention is pre-6 pared by arranging wire staple elements in an adjacent, 7 touching, planar relationship. The elements while heated to 8 a temperature exceeding that of the binder are covered with 9 a thin film (about 3 mils) of the binder of ~xample l.
Example 6 11 Example 5 is repeated except that the elements are l2 covered with a fine powder prepared fromlthe binder of Example l-14 It is to be noted that the specific embodiments described above are for nail-stack fastener articles in l6 which clip-head nails are the fastener elements.
17 Other types of nails can also be used in nail-18 stacks with suitable ad~ustments for the particular type of t 19 na$1. For instance drywall nails have a full-head as opposed to the half-head of a clip-head nail. Therefore, they, of 21 necessityJ are placed further apart in the stack.
22 Preferably, when tapes are used for dry-wall nail 23 stacks, they are notched, marked, or indented in the approxi-24 mate mlddle of the span between each nail. This is so that L
the tape breaks in such a manner that each nail carrles with 26 it no more than its share of the tape binder. t L

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE
IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A strip of fasteners for use in a rapid-acting fastener driving apparatus, comprising: a plurality of metal fasteners having elongated cylin-drical shanks disposed in close generally parallel relationship to define a gap between adjacent shanks, and carrier means for connecting said fasteners to form said strip, said carrier means including a plurality of single-component, metal-adherent plastic envelopes extending about a major portion of each half of said-shanks and having the properties of an adhesive bond without requiring a separate adhesive, each of said envelopes being of uniform thickness and having a pair of opposed portions each adhering respectively to opposite sections of the circumference of each shank during the entire driving action including entry into the workpiece, the carrier means between said envelopes extending into said adjacent gaps and defining therein between the envelope portions adhered to adjacent shanks recessed portions directed inwardly toward similar recessed portions between envelope portions secured to the opposite portions of the shanks, the bonding properties of the carrier means being such that the resistance to shear at the interface between the carrier and shank is greater than the shear resistance of the carrier material in the gap between two adjacent fasteners and greater than the resistance of the workpiece encountered when the fastener and carrier material penetrate same, thereby securing said fasteners together into said fastener strip while permitting each respective envelope and fastener to be easily and cleanly sheared and driven into said workpiece, wherein said metal-adherent plastic is an ethylene-propylene terpolymer.