CA1076733A - Polyurethane adhesive compositions and heat-activatable films thereof - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An heat activatable adhesive composition which, is a partially cured reaction product of a hydroxyl terminated poly-urethane polyester having a hydroxyl number no greater than about 15, a member containing at least difunctional active hydro-gen having an active hydrogen equivalent weight of at least about 27 and less than about 500, a component having available free isocyanate groups and a fourth component such as a chlorinated aliphatic hydrocarbon, a chlorinated aromatic hydrocarbon, or an alkylated polystyrene.

Description

:1076'~3 This invention relates to an improved polyurethane adhesive composition and more particularly to a dried, par-tially cured heat-activatable, preformed adhesive film of such an adhesive composition.
Coated abrasive belts are manufactured, in general, by adhesively joining together the free ends of strips of coated abrasive sheet material of a suitable length and width.
An adhesive composition found highly suitable for use in the manufacture of endless abrasive belts and meeting many of the above-disclosed requirements, is a polyurethane composi-tion. Such a composition involves as the essential components an isocyanate and an isocyanate reactive compound, i.e., a poly-functional active hydrogen containing component.
Polyurethane adhesive compositions, in general, must be used in a relatively short time after formulation and for that reason, among others, have not generally been accepted for use in certain industrial applications. Various means have been suggested whereby a composition of longer shelf or pot life would be provided, one of which is disclosed in United States Patent No. 3,637,359 for Coated Abrasive Belt Overlap Joint.
Therein, chlorinated aliphatic and aromatic hydrocarbons and alkylated polystyrene resins are disclosed for accompllshing this purpose.
Liquid adhesive compositions of glue and various --~ 25 resinous and rubbery like materials have long been used in the iO76~33 .
mallu~acture of abrasive belts. One disadvantage associated ~ith the use of a li~uid adhesive composition is that it, in general, requires a "dwell time" for, among other things, the removal of solvent, before joining-the ends together for joint formation. Curing of some adhesive materials to some degree before joining the adhesive coated surfaces together is absolute-ly necessary in order that an inordinate amount of time is not taken, e.g., for a press curing cycle and, most importantly, so that the adhesive material will have sufficient cohesive strength prior to pressing that it will not be squeezed out dur-ing pressing thus resulting in an adhesive starved joint area and therefore a joint with inferior bond strength. A further disadvantage associated with the use of a liquid composition results from the fact that to provide a layer of adhesive material sufficiently thick for provision of a bond of suitable ; strength, the adhesive must be applied in multiple coats because -application of a thicker layer by means of a more viscous composi-tion is not possible.
Rather than using a liquid adhesive composition in coated abrasive belt manufacture, Applicant has heretofore sug-gested the use of a preformed adhesive film. Such a preformed adhesive film for coated abrasive belt manufacture of somewhat similar composition is disclosed in United States Patent No.
3,770,555, which discloses an adhesive composition which is the partially cured reaction product, in dry film form, of~a com-ponent having available free isocyanate groups, a first active - ~hydrogen containing component having a hydroxyl number of from about 2 to 15 and a second active hydrogen containing component having an active hydrogen equivalent weight of from about 27 to less than about 500. Other prior art exemplary of the use of ~ ' , , ` ., , ~-~ , . - i preformed adhesive films are United States Patent Nos. 2,060,906;

2,778,169; 2,794,726; 3,406,053; and 3,449,280. As di~closed in these patents, adhesive films have been suggested for use in the bonding together of various lamina. The formation of endless coated abrasive belts is disclosed in, e.g., United States Patent Nos. 2,778,169 and 2,794,726.
Adhesive films used in the practice of this invention basically comprise the partially cured reaction product of a composition comprising in admixture: (1) a first active hydrogen containing component in the form of a hydroxyl terminated poly-urethane polyester having a hydroxyl number of from 2 to lS, (2) a second active hydrogen containing component containing at least difunctional active hydrogen and having an active hydrogen equivalent weight in the range ~rom about 27 to less than about 500 and preferably from 67 to 300, (3) a component having avail-able free isocyanate groups, and (4) a tackifier or reaction inhibitor such as a chlorinated aliphatic or aromatic hydrocarbon, or an alkylated polystyrene.
In particular the invention provides an adhesive com-position comprising in admixture:
(a) a hydroxy terminated polyurethane-polyester having a hydroxyl number of from about 2 to about 15;
(b) an active hydrogen component containing at least di-functional active hydrogen and having an active hydrogen equivalent weight in the range of from 27 to less than about 500;
(c) a component having available free isocyanate groups; and (d) a component selected from the group consisting of chlorinated aliphatic hydrocarbon, chlorinated aromatic hydro-carbon, alkylated polystyrene and mixtures thereof, said component being miscible with components (a), (b) and (c).

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1076'733 The invention will now be described by way of example, with reference to the drawings, in which:
Figure 1 is an end view of a roll of preformed adhesive film in accordance with the invention interwound with a release carrier;
Figure 2 is a sectional view showing two ends of abrasive material being joined together as in the formation of an endless abrasive belt having an overlap joint;
Figure 3 is a greatly enlarged view in section showing a strip of the adhesive film-release carrier assembly of Figure 1 laminated ~o a reinforcement; and Figure 4 is a partial sectional view showing the adhesive film-reinforcing fabric assembly in Figure 3, with the release carrier removed, used in the formation of a butt jointed abrasive belt.
In Figure 1, in accordance with one aspect of the invention, a roll 10 of dry, heat-activatable, at least partial-ly cured, preformed adhesive film 11 on release liner or carrier 12. Adhesive film 11 can be used as is in the joining together of various similar and dissimilar lamina.
In Figure 2, adhesive film 11 is shown being used to join together surfaces 13, 14 of the two free ends 15, 16 respec-tively, of a strip of abrasive material 17 to form a lap joint.
Abrasive material 17 comprises a backing member 18 and, on the front side thereof, abrasive grains 19 adhered to the backing member by means of an adhesive bond 20.
Abrasive strip 17 is cut to the desired width and length from a suitable coated abrasive sheet material. The free ends 15, 16 of the coated abrasive strip are cut at an angle of from 30 to 75 ~egrees, with respect to the lengthwise direction .' ' ` , ;, ~
. . ' . , ' '' , , ' .. ~ . , 1~)76733 of the strip of abrasive material. A preferred angle is 55 degrees.
In the formation of a lap joint (Figure Z) surfaces 13 and 14 are beveled by skiving and abrading respectively.
Thus, a narrow area is delimited adjacent each free end 15 and 16 of the abrasive strip 17 for application of adhesive film 11.
In general, in skiving the upper portion of end 15 it is prefer-red to remove substantially all the adhesive layer 20. A taper, as shown, of 2-3 mils is desired from the trailing edge of the skived area to the leading edge thereof. The lower surface 14 of end 16 can be back rubbed, wire brushed, sand blasted, or the like to provide an abraded surface area matching with the skived surface 13 on end 15. Sand blasting is preferred as a ~acking preparation for joining as this results in somewhat better joint performance.
After surface preparation, the free ends 15, 16 of strip 17 of coated abrasive material are superposed in overlap-ping manner, as shown and joined together, by the preformed adhesive film 11.
In some bonding applications, it will be preferred to - provide a reinforcement in combination with adhesive film 11 such as woven fabric 21 shown in Figure 3. An adhesive film-rein-. , ~
` forcement combination is used to advantage, for example, in the formation of an abrasive belt by butt joining. Such an abrasive belt is chown in Figure 4 of the drawing. Therein, abrasive ends 15, 16 are seen to be closely abutted together. Backing member 18 is back rubbed or the like, as before-described, in the area immediately adjacent free ends 15, 16 so that adhesive film 11 will contact the backing member rather than a coating material -30 applied to the backing member.

, , . , : , ' 107~i 733 - ~-As illustrated in Figure 4 the adhesive film 11 when subjected to pressure while heated, flows and fills up the joint line crevice as shown by reference numeral 22. Adhesive film 11 also flows into and partially penetrates reinfor~ing patch 21.
Hydroxyl terminated polyurethane polyesters are well known, and are prepared by reacting a molar excess of a hydroxyl terminated polyester with a suitable polyisocyanate. A hydroxyl terminated polyurethane polyester elastomer, as is deEired in the practice of this invention, is available commercially in solvent solution from United Shoe Machinery Corporation. One such a solution is identified as "Bostik" 7070 in their bulletin BA20, page 4. "Bostik" 7076 is comparable except that a mixture of acetone-toluene is used as the solvent rather than ethyl acetate.
The other active hydrogen containing member or component may, in general, be any compound containing at least difunctional active hydrogen in the form of -OH, -SH, -NH--and -NH2 so long as the àctive hydrogen equivalent weight of the compound is in the range from about 27 to less than about 500, preferably from about 67 to about 300. When one desires a somewhat longer adhesive film shelf-life, a higher equivalent welght member will be used. One of this type compound which may be used in the practice of the invention is "Thylon" D-406, a polyester-poly-urethane isocyanate blocked prepolymer available from Thiokol Chemicai Corporation. Another is "Unithane" 200, a polyether-polyurethane isocyanate blocked prepolymer, also available from the same manufacturer.
The isocyanate component utilized in the practice of the invention is not critical so long as it has available suf-ficient free isocyanate groups to react satisfactorily with the * Trade Mark ~2 ~ .
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~0'~6733 re~lctive hydroyens and thus cure the adhesive composition.
The particular diisocyanate or polyisocyanate used must be either soluble in the solvent used for the active hydrogen com-ponents or dissolved in a solvent compatible therewith. An iso-cyanate material meeting these requirements a product available commercially under the trade designation "Mondur" CB-75 from Mobay Chemical Company. This product, a polyurethane prepolymer in solution, is the reaction product of trimethylol propane and toluene diisocyanate.
A chlorinated aliphatic hydrocarbon which has been found quite satisfactory in the practice of the invention is "Paroil"
170 HV available commercially from Dover Chemical Company, Dover, Ohio. Incorpora~ion of this component into the adhesive composi-tion results in, it is believed, an abrasive belt joint~of unex-pectedly high resistance to flexural fatigue and improved adhesion over adhesive compositions not incorporating such a component.
Another chlorinated aliphatic hydrocarbon which produces an improved adhesive for belt joints is a material sold as "Unichlor"*
40 by the Neville Chemical Company; "Unichlor" 40 contains about 41.5% chlorine. Also suitable are alkylated polystyrenes such *
as the Piccolastics manufactured by Harwick Standard Chemical Company and the Arochlors (chlorinated aromatics) manufactured by Monsanto Company. Of importance also is the fact that these generally improved properties can be obtained at lower joining temperatures thereby making it possible to join abrasive materials incorporating backing members susceptible to heat degradation at ! higher joining temperatures.
Ultimate curing of the adhesive composition used in the manufacture of the adhesive film depends upon the number of free (-NCO) groups available in the adhesive composition and the * Trade Mark ~i .
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1(~76733 amour.t and particular combination o~ active hydrogen members used in the adhesive composition. A joint of satisfactory initial strength, as well as one of ultimate strength, will be obtained, where the hydroxyl terminated polyurethane elastomer is "Bostik" 7076, with from about 4.7 to about 12.5, preferably 4.8 to about 6.8 parts, "Thylon" D-406 and from about 4.4 to about 15 parts "Mondur" CB-75 per 100 parts "Bostik" 7076. Where the amount of "Thylon" D-406 is less than as above-indicated, curing is not sufficiently promoted to give a joint of the desired strength within the time desired. Use of greater amounts of "Thylon" D-406 results in a film too heat resistant to permit heat activation thereof at temperatures found most suitable for belt joint formation. The amount of "Paroil" 170 HV in the com-position can be from about 6.75% to about 41%, preferably 13.5 to 34% solids, per 100 parts solids in "Bostik" 7076.
Preformed adhesive film 11 may be manufactured from the adhesive composition according to any usual film forming techniques preferably those methods utilizing a release liner.
However, the adhesive film must remain heat-activatable at the joining temperatures found suitable in the manufacture of coated abrasive belts. By "heat-activatable" is meant the ~adhesive film will be merely softened and tackified. The extent of partial curing should provide sufficient cohesive strength in the adhesive film that it will not unduly flow, i.e., be squeezed out from and result in a starved joint, on application of heat and pressure during the joining cyale. In general, where higher joining temperatures are allowable, an adhesive film having a greater degree of partial cure can be used.
To provide adequate bond strength when used in a coated -30 abrasive belt joint, the adhesive film should be at least about _ g_ : ~ ' ' " ' 1.5 mils thick up to about 4 mils thickness.
The layer of adhesive composition may be dried and partially cured by any well known means. Partial cures have been found satisfactory which result in an adhesive film which can be heat activated at temperatures ranging from about 175F.
to about 375F. Above this temperature, damage can result to a coated abrasive backing member. Desirable partial cures can be obtained in general by heating an adhesive film for from about 10 to about 60 minutes at from about 300F. to about 250F.
The adhesive film-carrier comhination, after partial curing, can then be wound into rolls and slit, if desired, into rolls of lesser widths. The adhesive film composition continues curing (moisture from atmosphere, backing member, etc.) even at room temperature. However, the rate of curing is relatively slow and can be retarded even further by storing the rolls of adhesive film in sealed plastic bags, e.g., of polyethylene, at relatively low humidity and temperature. A desiccant such as anhydrous calcium sulfate is advantageously included in each bag.
Provided the adhesive film is stored in a dry atmosphere, e.g., about 0-5~ relative humidity (R.H.) at 5F. or less, the adhesive films can be used and satisfactory bonds achieved in belt joints even after a storage life of several months. Once the adhesive film is removed from these controlled conditions of low tempera-tures and humidity, however, it must be used generally in a matter of hours depending on atmospheric conditions. In the practice of the invention, when adhesive film 11 is to be used relatively immediately, it need not, of course, be packaged.
When an abrasive belt as disclosed in Figure 2 of the drawing is to be manufactured, a suitable width and length of - 30 abrasive material is provided and the ends 15, 16 of the abrasive --10-- ,i .
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Stli~ are prepared for belt formation, as before disclosed, according to usual techniques. An appropriate length of adhesive film-carrier combination 11, 12 is unwound from a roll 10 thereof, is applied to the skived surface 13 of the coated abrasive strip 17 which previously has been positioned a~ u~ual on the bottom bar of a platen press and, is then cut off.
Coated abrasive strip 17 with the partially cured, heat-activatable adhesive film 11 - release liner 12 thereon (adhesive film against skived surface) is then subjected to light pressure, e.g., about 388 lbs/in.2 while being heated by the bottom bar only te.g., about 240F.) for about 3 seconds. Thus, the adhesive film is heat activated, i.e., softened and tackified, in preparation to forming the belt joint. The pressure is then released, the upper bar retracted and the release liner removed from the activated adhesive film. End 16 of coated abrasive strip 17 is then overlapped as shown in Figure 2 with end 15 and the overlapped ends are then again subjected to heat and pressure as above-mentioned to initiate the joining operation. Joining is then completed by subjecting the superposed, overlapped coated abrasive ends to pressure while simultaneously heating from both sides. The pressure used in this portion of the joining cycle can be varied as desired, e.g., froM about 1000 lbs./in. to about 12000 lbs./in.2. In general, the time and temperature required to effect optimum initial joint strength whereby to obta-n suitable handling strength of the abrasive belt for any particular adhesive composition will, of course, vary with each particular adhesive composition. Satisfactory joints have been made, for example, by using joining temperatures within the range from about 175F. to about 375F., a preferred temperature range ~ 30 being about 240F. to about 335F; for from about 5 seconds to ; .. . .. . .
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iO76733 about 30 seconds, while pressing at from about 4300 lbs./in.2 to about 8600 lbs./in.2.
In a further aspect of the invention, adhesive film 11 can be provided in combination with a woven fabric 21 as shown in Figure 3 of the drawing. This is accomplished, in general, by laminating a strip of some suitable fabric, to an adhesive film as disclosed in this application. A highly preferred fabric is one made from yarn or roving of aromatic polyamide fiber.
Preferably, the woven fabric is pre-impregnated with some suitable adhesive composition and this adhesive composition is then dried or cured to an essentially tack-free condition prior to laminating with the heat-activatable adhesive film. The adhesive composition used for pre-impregnation can be of the same or different composition as the adhesive film. A highly desir-able combination with the polyurethane adhesive film of this in-vention is a nylon polyamide-epoxy saturant.
The adhesive film-release carrier combination can be laminated continuously or not, as desired, to the woven fabric ~trip and afterwards wound into rolls of suitable length. In this form, the adhesive film-reinforcing fabric assembly can be ` used immediately or packaged and stored as described previously for future use.
In manufacturing abutted abrasive belt joint as dis-closed in Figure 4, the backside of free ends 15, 16 are back rubbed or otherwise prepared as before described. The coated abrasive ends are abutted together and the reinforcing patch-adhesive film assembly of Figure 3 is positioned so as to bridge the abutted ends as shown in the drawing. The adhesive film directly contacts the backing member. Heat and pressure, depend--- 30 ing on the abrasive material being joined, is usually then :' ', . .' ' ' "~ ,, ` :' '' '' ~ :' . . .
.. . . .

, applied to the joint assembly - preferably in steps, e.g., a 15-second press at a low pressure, e.g., 194 psi, at 335F., preferably 240F - 275F. (bottom bar only) followed by at least one, sometimes two additional pressings, e.g., for from 20 secs., using a heated bar top and bottom. In the second pressing stage, the top bar and bottom bar are both heated to 240F. - 335F.
The pressure setting in these two final presses may be as high as 2 or 3 tons per inch of belt width. As a result of the application of heat and pressure, the adhesive intimately bonds the special reinforcing patch to both ends of the coated abrasive material. Thus, the reinforcing patch and adhesive, in combina-tion, provides a joint which offers advantageous resistance to failure because of forces and temperatures on the coated abrasive material in the grinding operation. The reinforcing patch must be sufficiently porous and so positioned in the completed joint that the adhesive will at least partially penetrate the weave (warp and fill yarns form interstices) of the patch to develop satisfactory adhesion~
The following examples, which are given for purposes - 20 of illustration only and are not intended to be limiting of the inventive concept, will more clearly illustrate the preferred embodiments of the invention.

An adhesive composition was prepared by mixing together the following components.
COMPONENTPARTS BY WEIGHT

(21~ solids in acetone -toluene solvent) 88.8 ~75% solids in ethyl ; acetate) 4-5 ' ' ' .

iO76733 COMPONENT PARTS BY WEIGHT
Thylon D- 4 0 6 (70% solids in methyl -ethyl ketone) 4.3 PAROIL 170 HV 2.4*
*10~ by weight based on total solids not including Paroil 170 HV.
Mixing was conducted at room temperature, Mondur CB-75, Thylon D-406 and Paroil 170 HV being added to Bostik 7076 10sequentially, a few minutes mixing occurring between each addi-tion. Mixing was continued for about an hour after adding the chlorinated aliphatic hydrocarbon to provide a homogenous mixture. ?
The above composition was coated onto a conventional silicone coated release carrier using a doctor blade with a 30 15mil gap setting. The wet adhesive layer was allowed to air dry for 30 minutes at room temperature, i.e., 70F. 50% Relative Humidity (R.H.). Afterwards, the adhesive coated carrier was heated at 225F. for 40 minutes to form a partially cured heat-activatable adhesive film 3.0 - 3.5 mils thick. The film is 20observed to have a slight degree of finger tack and is, of course, extremely tacky with respect to itself.
Prior to application of the coating to the release carrier, the adhesive composition was allowed to stand overnight so that entrapped air bubbles from mixing could escape.
The adhesive film-release carrier combination was slit into a plurality of strips 13/16 inches wide and wound into rolls of suitable length for use as hereinafter described.
A strip (6 in. x 24 in.) of 120 X RESINALL~ METALIT ~
abrasive cloth was prepared for formation of an endless abrasive belt. The abrasive surface of one free end of the abrasive strip - was skived thereby removing the abrasive material and the . . : ~

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1076~733 adhesive bond, leaving the upper portlon of the backing member exposed. The skived surface (3/8" x 7.5") was at an anyle of 55 degrees with respect to the lengthwise direction of the àbrasive strip and was slightly tapered, from trailing edge to leading edge thereof, at an angle of about 5 degrees with respect to the horizontal. The mating surface of the other end of the abrasive strip was back rubbed with an abra~ive belt, leaving the surface very slightly tapered and free of previously applied backsize.
A suitable length of the adhesive film-carrier combina-tion was cut at a length and of a shape complementary to theskived surface area. The heat-activatable adhesive film was then positioned directly on the skived surface (See Figure 2), the strip of abrasive material having been positioned previously on the bottom bar of a conventional platen-press.
The upper bar (platen) of the press was then brought into contact with the release liner, a pressure of about 386 psi. being exerted on the adhesive film-carrier combination and skived abrasive end. This pressure was held for a period of about

3 seconds while the film-abrasive material was being heated sole-ly by the bottom bar having a surface temperature of about 240F.
Thus, the adhesive film was softened and tackified in preparation for the subsequent joining operation.
Next, the pressure was released and the upper bar was withdrawn from contact with the release liner. The release liner was then removed from the heat activated, i.e., softened and tackified adhesive film. The bottom surface of the other end of the coated abrasive strip was then positioned in contact with the upper surface of the activated adhesive film.
The overlapped coated abrasive strip-adhesive film -30 assembly was then again pressed while being heated only by the .,- . , ' ' ' ' ' . ' ' ' ' ~076733 lo~ler bar. A pressure of 386 1bs./in.2 was maintained for 3 seconds (bar temperature 240F.~ after which it was released and the upper bar was slightly withdrawn. The coated abrasive strip-film adhesive assembly was then removed from this press and was positioned in a similar press. The upper bar therein was ~rought into contact with the overlapped portions of the coated abrasive strip. A precsure of 8600 lbs./in.2, was maintained while the assembly was heated by both bars for about 20 seconds (bar temperature 240F.). The pressure was then released and the thus produced abrasive belt was removed from the press. On visual examination, the abrasive belt was observed to have a joint thickness not substantially greater than the thickness of the coated abrasive material per se.
On subjecting belt joints thus manufactured and con-ditioned for at least 24 hours at 70F., 50% R.H. to severe and continuous flexing in the immediate area of the belt joint on a multi-head oscillating flex fatigue tester, belt joints according to the invention were found to have the flexes, as below indicat-ed, before failure occurred. A control differing only in that the adhesive film used did not contain chlorinated aliphatic hydrocarbons was evaluated after the same conditioning period.
In this test, a strip of coated abrasive material (1/2" x 18") including the joint is held under tension (32-34 lbs./in. width) and the abrasive material is moved back and forth at 200 cycles per minute in a 90 change in direction over a 1/4" diameter -roll. This test is particularly directed at producing delamina-tion failure in an abrasive joint.

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TEST DATA
EXAMPL FLEXES TO FAILURE
lA INVENTION3220 2 o lB INVENTION4460 56 lC INVENTION3620 370 lD CONTROL14412600 120900 lE CONTROL111660 10300 lF INVENTION35oo66oo 165 lG INVENTION1500 92 The above results in flex fatigue resistance using an adhesive film of the invention are believed quite surprising when compared to those obtained with an adhesive film composition omitting the Paroil 170 HV. Disregarding the extreme results at each end, an improvement of at least 140% is indicated.

Adhesive compositions were prepared, as before describ-ed, by mixing the following components together in the amounts indicated:
COMPONENT PAR ~
? 3 4_ 5_ 6 _ 7 (21% solids in acetoner toluene solvent)91.0 89.9 88.887.886.7 84.5 (75% solids in ethyl acetate) 4.6 4.53 4.54.4 4.4 4.25 THYLON D-406 4.4 4.35 4.34.2 4.2 4.10 PAROIL 170 HV -0- 1.22 2.43.6 4.7 6.88 ~ .
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COMPONENT PARTS BY WEIGHT
EXAMPLE

& By Weight 5Paroil Based on Total Solids Except Paroil -0- 5.0 10.0 15.0 20.0 30.0 After formulation, each composition was allowed to stand overnight so that entrapped air bubbles could escape.
These compositions of varying Paroil 170 HV amounts were each ; 10 then coated onto release carriers and partially cured as before described in Example 1. A control was prepared having no Paroil 170 HV added to the adhesive composition. The adhesive film-release carrier combinations were each then slit into strips 13/16 inches wide and wound into rolls.
The strips of adhesive film-release carrier combina-tion were laminated to 3/4 inch wide strips of bias cut (55) woven aromatic polyamide fabric, below described, by pressing the lamina together in superposed relationship for 3 seconds at 240F. The adhesive film was in contact with the fabric strip and was so positioned as to extend laterally an equal distance on each side thereof. These assemblies were then used in the manufacture of abrasive belt joints, as hereinafter disclosed.
; The reinforcing fabric, which is available from Stern and Stern Textiles, Inc., under the trade designation HT3 and `
weighs 3.62 ozs./sq. yd. (6.5 mils thick), was saturated, prior to laminating with the adhesive film, with a nylon-epoxy adhesive composition as follows:
PARTS BY
COMPONENT WEIGHT
ELVAMIDE 8061* 12.2 EPON 828** 4.1 METHANOL 68.6 - : . . ~ -.

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107~733 COMP~.~ENT PARTS BY WEIGHT
1,l,l-TRICHLOROETHANE 1~.~
TRIET~IYLENE TETRAMINE 0.5 *
*Elvamide 8061 is available commercially from E.I. DuPont de Nemours and Co. and is their trade name for an ethyl alcohol/-water mixture soluble nylon polyamide formed from the reaction of hexamethylene-diammonium adipate and hexamethylene-diammonium sebacate with caprolactam.
**Epon 828 is the trade name for an epoxy resin resulting from the condensation of epichlorohydrin with Bisphenol-A having an epoxide equivalent of 185-192 and is available from Shell Chemical Co.
After saturation, the impregnated fabric was heated for 4 hours at 250F. to cure the saturant (10% by weight dry pickup) and to provide a dry, tackfree, saturated woven fabric reinforcement for the adhesive film.
Two free ends of abrasive material tl20 X RESINAL ~ -METALITE~ cloth) which had been cut to matching 55 angles with respect to the longitudinal direction were abutted together and on a suitably cut portion of the above manufactured adhesive film, on the bottom pla'en of a conventional platen press in usual fashion for the formation of a butt joint. Each of the free ends had been prepared by sand blasting, according to usual techniques to remove any backsize material from the bonding area.
The adhesive film-woven fabric combination (carrier removed) was assembled with the butted coated abrasive ends in such a fashion that the warp yarns of the woven fabric strip extended approximately parallel to the edges of the coated abrasive material. This assembly (adhesive film against backsize coated abrasive material) was then subjected to a 15 second press * Trade Mark .""

`` 1076733 (bot~om platen only heated - 335F.) at 194 lbs./in.2 followed by a 20 second press at 4300 lbs./in.2, both platens heated to 335F.
On examining the abrasive material after the joining operation, the adhesive film was observed to have flowed into the joint line crevice. This is shown as 22 in Figure 4.
The joints thus formed, i.e., abrasive material incorporating such a joint, were then conditioned (4 days, 70F., 50% R.H.) and then evaluated for flex fatigue resistance on an oscillating belt joint tester. In this test a 1/2 inch wide specimen, 16 inches long including the joint, is held under tension (22 lbs.) and moved back and forth at 200 cycles per minute in a 90 change in direction over a 1/4" diameter roller.
The results are indicated below.
RESISTANCE TO FLEX FATIGUE

PROPERTY and AMOUNT EXAMPLE
CHLORINATED
HYDROCARBON 2 3 4 5 6 7 .

~ PAROIL
170 HV -0- 5.0 10.0 15.0 20.0 30.0 JOINT LIFE
PER CENT 100 294 450 350 520 *

FLEXES TO

*not tested - excessive blisters in joint area.
As indicated, by the ~ roved resist~nce to flex fatigue, the addition of Paroil 170 HV to the adhesive composition results in a joint much more resistant to delamination then one without this additive.

_ Additional dry film adhesive compositions were prepar-,~
ed as described in Example 1, utilizing the following components .
w~

in the quantities indicated.
ADHESIVE - WT. IN GRAMS
COMPONENT _ B C D E_ MONDUR CB-7517.8517.85 17.85 17.85 17.85 THYLON D-40617.4917.49 17.49 17.49 17.49 PAROIL 170 HV 9.75 UNICHLOR 40 9.75 AROCHLOR 5460 4.88 PICCOLASTIC A5 4.88 The resulting strips of adhesive film-release carrier combination were used to form lap jointed continuous abrasive belts as described in Example 1 and butted-reinforced jointed continuous abrasive belts as described in Examples 2-7. The belts were tested in the manner set out in Example 1 except that the flexing test was terminated when the number of flexes had reached 3000 with no belt failure. The other distincton, as compared to Examples 1-7, was that 60X RESINA~ ~ METALIT ~ was used as the abrasive material instead of the 120 X RESINAL ~
METALITE~ cloth of Examples1-7, the significance being that the coarser 60 grit material tends to be less flexible than the 120 material and hence generally will not survive as many flexes as the latter. The flexing test results were as follows:
EXAMPLEADHESIVE JOINT TYPEFLEXES TO FAILURE
8 A lap 1140 9 B " 700 C " 400 11 D " 400 ~30 12 E " 1020 ,'~' ' .-: :
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.
EX.~ ~`LEADHE_IVE JOINT TYPEFLEXES TO FAILIJRE
13 A reinforced-butt 3000*
14 s " 3000*
C " 3000*
16 D " 3000*
17 E " 3000*
*test stopped after 3000 flexes, with no evidence of joint failure From the foregoing data it can be seen that when the fourth component is Paroil 170 HV or Piccolastic A5 the most durable lap joints results, with the two Arochlors and the Unichlor producing good lap joints but joints substantially inferior to joints involving the former two materials. When the joints are reinforced-butt joints, all five materials produce extremely high durability joints.
The fourth component of the adhesive composition of the present invention i.e., component (d~ is preferably a liquid which is miscible in the mixture of the other three components.
However, the fourth component may be a solid but it too must be miscible in the other components of the adhesive system and must remain so when essentially all the solvents have been removed from the four component mixture. If the fourth component is a solid which precipitates out of the mixture when the solvents are removed, then it cannot perform its function and behaves as an organic filler. An example of a material that was inoperable was Chlorez 70, a solid chlorinated aliphatic hydrocarbon sold ~ by the Dover Chemical Company. This material was miscible in ; the other 3 components of the adhesive system, in the initial mixing because of the presence of the three solvents toluene, eth~l acetate and methylethyl ketone. However, when the 4 * Trade Mark B
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:1076733 component adhesive mixture was deposited on the release backing and partially cured, the solvents were evaporated and, it was believed, the Chlorez 70 precipitated out of the mixture. By contrast, two solid materials that produced excellent belt joints were Neoprene AC and Neoprene AD available from E. I. DuPont de Nemours & Co. These latter materials are film formers when deposited from a solvent as opposed to precipitating out of the solvent; as a result they remain miscible with the other three components of the instant adhesive composition after the solvents therein are removed.
From the above various examples and data" one can readily see that the inclusion of a chlorinated aliphatic or aromatic hydrocarbon, or an alkylated polystyrene component in the polyurethane adhesive composition in accordance with this invention provides a joint with high resistance to flexural fatigue, this being an indication also of high joint adhesion.
Moreover and this is an important feature of the invention, im-proved results are obtained with a wide variety of abrasive material.
While in Examples 2-7 butt joints are assembled and reinforced with a fabric patch, with the invention adhesive hav-ing been applied to the fabric after having been first formed on a release backing, this may not be the most expeditious method from a mass production point of view. Rather than forming the dry film adhesive on a release backing initially and then apply-ing it to the fabric, the dry film adhesive has been formed directly on the fabric, thus e~iminating a step in the assembly operation. This approach has proven to be a definite cost sav-ings over the method of Examples 2-7 when the invention was put into mass production.

* Trade Mark 107~733 Although the adhesive films of this invention are par-ticularly useful in the manufacture of coated abraslve belts, the invention is obviously not so limited. The adhesive films disclosed herein, reinforced or not, can be used in the laminat-S ing together of various similar or dissimilar materials, e.g.,metals such as aluminum and plastic lamina of various types, e.g., polyester films, as well as wood, cloth and paper lamina.

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Claims (16)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An adhesive composition comprising in admixture:
(a) a hydroxy terminated polyurethane-polyester having a hydroxyl number of from about 2 to about 15;
(b) an active hydrogen component containing at least difunctional active hydrogen and having an active hydrogen equivalent weight in the range of from 27 to less than about 500;
(c) a component having available free isocyanate groups;
and (d) a component selected from the group consisting of chlorinated aliphatic hydrocarbon, chlorinated aromatic hydro-carbon, alkylated polystyrene and mixtures thereof, said component being miscible with components (a), (b) and (c).

2. The adhesive composition of claim 1, wherein said (d) component is a chlorinated aliphatic hydrocarbon which is present in the composition in an amount up to about 30% by weight, based upon the weight of solids in the adhesive composition not includ-ing the aliphatic hydrocarbon.

3. The adhesive composition of claim 1, wherein said (d) component is a chlorinated aromatic hydrocarbon which is present in the composition in an amount up to about 30% by weight, based upon the weight of solids in the adhesive composition not includ-ing the aromatic hydrocarbon.

4. The adhesive composition of claim 1, wherein said (d) component is an alkylated polystyrene which is present in the composition in an amount up to about 30% by weight, based upon the weight of solids in the adhesive composition not including the alkylated polystyrene.

5. An adhesive film suitable for splicing together various lamina comprising the reaction product of the composition in claim 1 which has been at least partially cured but which can still be activated at a temperature suitable for splicing said lamina together.

6. A preformed adhesive film according to claim 5, in which said active hydrogen containing member has an active hydro-gen equivalent weight of from about 67 to about 300.

7. A preformed adhesive film according to claim 6, wherein said hydroxyl terminated polyurethane polyester is the reaction product of a diisocyanate and a hydroxyl terminated polyester of a dicarboxylic acid and a polyhydric alcohol.

8. A preformed adhesive film according to claim 7, wherein the dicarboxylic acid is adipic acid and the polyhydric alcohol is butylene glycol.

9. A preformed adhesive film according to claim 8, wherein said isocyanate component is an isocyanate terminated poly-urethane reaction product of a polyhydric alcohol and an iso-cyanate.

10. A preformed adhesive film according to claim 9, wherein said isocyanate terminated polyurethane is the reaction product of trimethylol propane and toluene diisocyanate.

11. A preformed adhesive film according to claim 1, wherein the chlorinated hydrocarbon contains 70 per cent combined chlorine.

12. An assembly for laminating various lamina together com-prising an adhesive film of the composition set forth in claim 5 and laminated thereto a woven reinforcing fabric.

13. An assembly as set forth in claim 12, wherein said reinforcing fabric is impregnated with a compatible adhesive material.

14. An assembly as set forth in claim 13, wherein said assembly is in roll form and is contained within a plastic bag containing a desiccant.

15. An assembly as set forth in claim 13, wherein said reinforcing fabric comprises yarns of an aromatic polyamide and the fabric is impregnated with a nylon polyamide-epoxy saturant.

16. Coated abrasive article comprising a backing member and having abrasive grain adhered thereto by an adhesive bond, said article having two ends thereof joined together by means of a layer of an adhesive composition which in its initial state is a preformed adhesive film according to claim 5.