3,413,246 United States Patent Office Patented Nov. 26, 1968

1. 2 or a substituted styrene. The cyclic hydro 3,413,246 carbon component may consist of a single cyclic mono PRESSURE-SENSITIVE ADHESVE COMPOS hydrocarbon, such as dipentene, , ox TIONS BASED ON CYCLICTERPENE-STY. , 6-pinene, a carene, or a phellandrene; a mixture RENE COPOLYMERS Henry P. Weymann and Yun Jen, Pensacola, Fla., as of cyclic monoterpene hydrocarbons; or a mixture of one signors to Tenneco Chemicals, Inc., a corporation of or more cyclic monoterpene hydrocarbons with an acyclic Delaware terpene, such as allo-ocimene, and/or with terpene oligo No Drawing. Filed Aug. 26, 1965, Ser. No. 482,922 mers. The useful comonomers include styrene, alkyl 17 Claims. (C. 260-4) styrenes having fewer than 13 carbon atoms, alkenyl O styrenes having fewer than 13 carbon atoms, chloro styrenes, and mixtures thereof. Illustrative of these sub ABSTRACT OF THE DISCLOSURE stituted styrenes are cy-methylstyrene, ox-butylstyrene, o,2- Pressure-sensitive adhesive compositions that have an dimethylstyrene, ethylstyrene, divinylstyrene, ox-chloro excellent combination of tackiness, cohesive strength, ad styrene, 3-chlorostyrene, and the like. hesive strength, and other valuable properties comprise a 5 A preferred group of terpene copolymers for use as rubbery elastomer and a terpene copolymer. Particularly tackifiers for adhesive compositions are those prepared advantageous results have been obtained using composi from dipentene or 6-pinene and styrene. Another pre tions that contain styrene-butadiene rubber and/or natural ferred group of terpene copolymers includes those pre rubber as the elastomer and a dipentene-styrene co pared by polymerizing a mixture of comonomers compris 20 ing (a) a-pinene, turpentine, or a mixture of polymer as the tackifier. which is obtained by the pyrolysis of turpentine and which contains approximately 40 to 60 percent of dipentene, 25 to 40 percent of allo-ocimene, and 15 to 25 percent This invention relates to adhesive compositions. More of terpene oligomers and (b) divinylbenzene. The mix particularly it relates to normally tacky, pressure-sensitive 25 ture of monomers may also contain styrene or an alkyl adhesive compositions suitable for coating flexible and styrene. elastic backing materials to form pressure-sensitive ad These terpene copolymers, which have softening points hesive tapes. in the range of approximately 15° C. to 150 C., are Pressure-sensitive adhesive compositions which are use soluble in a wide variety of aliphatic, cycloaliphatic, and ful as adhesive coatings on tapes, strips, and sheets of 30 aromatic hydrocarbon solvents and are compatible with paper, fabric, cellulose acetate, polyvinyl chloride, and and with the synthetic rubbers that are other backing materials generally comprise a polymeric ordinarily used in the preparation of adhesive composi cohesive agent in combination with a compatible, thermo tions. plastic resinous material which serves as the adhesion The terpene copolymers may be prepared by any suit and tack-imparting component. able and convenient procedure. For example, a mixture For a composition to be useful as a pressure-sensitive of the comonomers can be polymerized in the presence adhesive it must have a proper balance between its ad of an acid polymerization catalyst, Such as aluminum hesive strength, its cohesive strength, and its tackiness. chloride or boron trifluoride, at a temperature in the Many materials have been recommended for use as tacki range of approximately 60° C. to 150° C. to form fiers in pressure-sensitive adhesive compositions, but none 40 resinous products having the desired properties. In most has proven to be entirely satisfactory in imparting the cases approximately 0.2 part to 20 parts by Weight of required adhesien and tackiness to the cohesive agents a terpene or a mixture of terpenes is used per part by that are ordinarily used in these compositions. Some of weight of the styrene component, according to the physi the materials which alone appear to be suitable as tacki 45 cal and adhesive properties desired. Copolymers of par fier materials are unsatisfactory for use in these composi ticular value as tackifiers for pressure-sensitive adhesive tions because they adversely affect the cohesion of the compositions that contain styrene-butadiene elastomers adhesive, they impart color to it, or they lower its resist result when approximately equal weights of the comono ance to oxidation, to heat, and to acids and alkalies. mers are used. Others are incompatible with the synthetic rubbers that 50 The cohesive agent that is used in the pressure-sensitive are used as the cohesive agent and do not impart the adhesive compositions of this invention may be natural necessary tackiness to compositions containing synthetic rubber, a synthetic elastomer, or a mixture of these elas rubber alone or in combination with natural rubber. tomers. Among the useful synthetic elastomers are polym In accordance with this invention, it has been discovered erized isomonoolefins, such as polyisobutylene rubber; that when certain terpene copolymers are employed as polymerized dienes and substituted dienes, such as poly the tackifier in combination with polymeric cohesive butadiene rubber, polyisoprene rubber, polymethylisoprene agents, the resulting pressure-sensitive adhesive composi rubber, polymethylpentadiene rubber; polymers of vinyl tions exhibit a highly satisfactory balance of tackiness, co substituted compounds, such as polyvinyl ethers and poly hesive strength, adhesive strength, and other properties. acrylates; binary and higher copolymers such as styrene The terpene copolymers that have been found to be 60 butadiene (SBR), butadiene-acrylonitrile, styrene-buta valuable as tackifiers for pressure-sensitive adhesive com diene-acrylonitrile, ethylene-propylene-ethylene dimeth positions are the thermoplastic resinous products obtained acrylate rubbers; and mixtures thereof. The invention is of by polymerizing a mixture of monomers comprising a particular value in the preparation of pressure-sensitive cyclic monoterpene hydrocarbon component and styrene adhesive compositions containing styrene-butadiene rub 3,413,246 3 ber alone or in combination with natural rubber inasmuch TABLE I as no tackifier has previously been known which will impart desired combination of tackiness, adhesion, and Copolymer Composition of Ball and Gardner other properties of these elastomers. Ex, No. monomer mixture ring color The amount of the terpene copolymer that is incorpa 5 (parts) Perce, softening (50% solids rated in the adhesive coposition is largely dependent upon yield oint in mineral the choice of copolymer and rubber elastomer and upon C.) spirits) I-A.---- 250 dipentene, 250 styrene. 95.4 87 3-4 the properties desired in the adhesive composition. Ap I-B-...--- 375 dipentene, 125 styrene 93. 6 O -2 proximately 20 parts to 200 parts by weight of the terpene I-C----- 125 dipentene, 375 styrene. 82.2 83 9 copolymer is generally used per 100 parts by weight of ----- 250 g-pinene, 250 styrene.-- 88.0 9. 5 O I-E.---- 250A3-carene, 250 styrene.-- 70.2 73 8-9 the elastomer, with particularly satisfactory results being I-F----- 250 dipentene, 250 76.6 63 2-3 cy-methylstyrene. obtained when 50 parts to 125 parts by weight of the I-G---- 450 dipentene, 50 76, 6 5. 5 copolymer is used per 100 parts by weight of the elasto divinylbenzene. I-H...-- 475 turpentine, 25 4.8 3 2-3 mer. Since the terpene copolymer is ordinarily less eXpen divinylbenzene. sive than the elastomer, there is a financial advantage in I-I----- 475 mixture containing 7.8 3 3. 50% dipentene, 30% using as much copolymer as possible. The upper limit of allo-ocimene and 20% the copolymer to elastomer ratio is often determined by terpene oligomers; 25 divinylbenzene. the physical state of the mixture; many copolymers will IJ----- 225 cy-pinene, 225 styrene, 75,0 98.5 at concentrations above those giving maximum adhesives 50 divinylbenzene, -K---- 225 a-pinene, 225 at 50 82.5 properties impart resinous rather than rubbery character 20 methylstyrene, 50 istics to the blend. divinylbenzene. The pressure-sensitive adhesive compositions of this in vention may contain the terpene copolymer as their sole Example 2 tackifier, or they may contain other tackifiers in combina A copolymer was prepared by the following procedure: tion therewith. Examples of other tackifiers that may be 25 used in combination with the terpene copolymers are To a mixture of 250 parts of toluene, 250 parts of petro rosin, hydrogenated rosin, disproportionated rosin, esters leum naphtha (boiling range 110-152 C.; KB value of rosin and hydrogenated rosin, terpene homopolymers, 34-36), and 25 parts of boron trifluoride etherate at petroleum hydrocarbon resins, and the like. -10° C. was added a mixture of 250 parts of d-limonene In addition to the elastomer and the terpene copolymer, 30 and 250 parts of styrene over a period of three hours. The the adhesive compositions may contain plasticizers, sta mixture was stirred at -10° C. for 30 minutes after the bilizers, solvents, fillers, pigments, dyes, curing agents, and addition of the monomers had been completed. The reac the like in the amounts ordinarily employed for these tion mixture was washed with four 500 part portions of purposes. water and then steam distilled at 220-230 C. to separate Any of the methods ordinarily used for the preparation the volatile materials from the resinous residue. There of products of this type can be used in the preparation of was obtained an 85.8% yield of a d-limonene-styrene the adhesive composition of this invention. For example, copolymer that had a Ball and Ring Softening Point of the rubbery elastomer can be mixed with the tackifier and 55° C. and a Gardner color (50% solids in mineral spir other ingredients, if any, and the resulting mixture dis its) of 2. solved in a hydrocarbon solvent, such as toluene, Xylene, 40 Example 3 mineral spirits, or cyclohexane, or the blend can be pre A series of pressure-Sensitive adhesive tapes were pre pared for use as a dry mix, as an aqueous dispersion, or pared using the following elastomers: natural rubber as an emulsion. Tapes can be prepared from dispersions, (pale crepe, milled to a Mooney viscosity of 48.5, MS/4, emulsions, or solutions by spreading the liquid film on Suit 212 F.) polyisoprene (Natsyn 2200, milled slightly), able backing materials, drying the now-layered product, and styrene-butadiene rubber (GRS 1502, milled slightly). optionally adding another layer, e.g., release paper, on top The tackifier used was a dipentene-styrene copolymer of the adhesive layer, and cutting the composition to the which was prepared from equal weights of the monomers desired widths. Essentially the same finishing procedures by the procedure described in Example 1 and which had a can be used when the blend is applied dry as a melt at Ball and Ring Melting Point of 100° C. For comparative higher temperatures; in this case, no solvent or water 50 purposes, similar series of adhesive compositions were removal is necessary. prepared that contained as tackifier either a terpene homo The invention is further illustrated by the examples that polymer that had a Ball and Ring Melting Point of 100 follow. In these examples all parts and percentages are C. (Nirez 1100) or a styrene homopolymer that had a parts by weight and percentages by weight unless other Ball and Ring Melting Point of 100° C. (Piccotex 100). wise specified. 55 Each of the three tackifiers was mixed with each of the Example 1 three elastomers at tackifier to rubber ratios of 25, 50, 75, 100, and 125 parts per 100 parts. The mixtures were A series of copolymers was prepared by the following dissolved in toluene to form solutions having viscosities procedure: To a mixture of 250 parts of toluene, 250 of approximately 5000 centipoises. These solutions were parts of petroleum naphtha (boiling range 110-152 C.; 60 applied to films of unprimed Mylar, one mill gage, at a KB value 34-36), and 25 parts of anhydrous aluminum wet thickness that yielded dry adhesive films of one chloride at 40° C. was added 500 parts of a monomer mix ounce per Square yard coating weight. Strips of pressure ture containing a terpene component and styrene or a Sensitive adhesive tapes which were cut from these coated substituted styrene over a period of one hour. The mix films were evaluated by the following procedures: Hold ture was stirred for one hour at 40 C. after the addition 65 Value (shear strength or the rate of cold flow of the of the monomers had been completed. Then 25 parts of adhesive under continuous stress). calcium hydroxide and 25 parts of decolorizing earth A half-inch strip of tape was attached to a half-inch (Filtrol 20) were added, and the mixture was heated to by half-inch bar to provide a contact area of one half-inch 140° C. with removal of sufficient lower-boiling solvent Square. The bar was then positioned so that the adhered to maintain reflux at that temperature. The mixture was 70 tape was 20 from the vertical with the adhered portion on heated at its reflux temperature for 16 hours and then the underside of the bar and the free end hanging down. A filtered. The filtrate was steam-distilled at 220-230 C. 400 gram Weight was suspended from the free end of the to remove the volatile materials from the resinous residue. tape. The time in minutes that the tape supported the The composition and properties of the copolymers are weight is recorded as the “Hold.” Adhesion Value (the given in Table I. 75 force required to peel tape from a clean dry surface). 3,413,246 5 6 This procedure is described in detail in Federal Speci The terms and expressions which have been employed fication UU-P-31, Method 100. It measures the force, in are used as terms of description and not of limitation, ounces per inch width of tape, required to peel the tape and there is no intention in the use of such terms and from a polished stainless steel panel at a rate of twelve expressions of excluding any equivalents of the features inches per minute with the tape doubled back on itself at shown and described or portions thereof, but it is recog an angle of 180°. nized that various modifications are possible within the Tack Value: Tack was measured by determining the scope of the invention claimed. distance in inches that a 3.0 gram, 3/8-inch diameter steel What is claimed is: ball rolled on a horizontal pressure-sensitive tape after 1. A pressure-sensitive adhesive composition compris being given momentum equivalent to a four-inch drop. O ing a rubbery elastomer selected from the group consist To convert this measurement to one which increases in ing of natural rubber, styrene-butadiene rubber, poly numerical value with increase in tack, it was divided into , and mixtures thereof and 50 parts to 125 parts four (the number of inches dropped) and the quotient by weight per 100 parts by weight of said elastomer of multiplied by 10. a tackifier, said tackifier comprising a copolymer of a In each case the styrene homopolymer was incompati 5 cyclic monoterpene hydrocarbon component and a comon ble with the rubbery elastomer and imparted no tack to omer selected from the group consisting of styrene it. alkylstyrenes having fewer than 13 carbon atoms, alkenyl The properties of the adhesive compositions containing styrenes having fewer than 13 carbon atoms, and mix a dipentene-styrene copolymer as tackifier and of com tures thereof, said copolymer containing approximately parative compositions containing a terpene homopolymer 20 0.2 part to 20 parts by weight of units derived from said as tackifier are set forth in Tables II, III, and IV. terpene per part by weight of units derived from said TABLE II-PROPERTIES OF PRESSURESENSTIVE AD. COOOle. HESIVES CONTAINING STYRENE-BUTADIENERUBBER 2. A pressure-sensitive adhesive composition accord AS THE ELASTONER ing to claim 1 wherein the terpene component of the Tape Tackifier PR Holid Adhesive Tack 25 copolymer is dipentene. No. value value value 3. A pressure-sensitive adhesive composition according II-a------25 O 2 6 to claim 1 wherein the terpene component of the co b------50 O 2 6 C------Dipentene-styrene 75 28 4. polymer is c-pinene. d-- copolymer------100 O 2 2 4. A pressure-sensitive adhesive composition according 25 53 25 O 40 O 30 to claim 1 wherein the terpene component of the co 50 O 32 O polymer is g-pinene. --Terpene Homopoly- 75 O 3. ------ner (Nirez, 100). OO O 4. O 5. A pressure-sensitive adhesive composition accord j------25 O 1. O ing to claim 1 wherein the comonomer is styrene. Parts of tackifier per 100 parts of elastomer. 6. A pressure-sensitive adhesive composition accord 35 ing to claim 1 wherein the rubbery elastomer comprises TABLE III-PROPERTIES OF PRESSURE SENSTIVE AD styrene-butadiene rubber. HESWES CONTAINING NATURAL RUBBER AS THE 7. A pressure-sensitive adhesive composition compris ELASTOMER ing a rubbery elastomer and 50 parts to 125 parts by Takifier PEIR Hod Adhesive Tack waitue vaue walue weight per 100 parts by weight of said elastomer of a 40 tackifier, said tackifier comprising a copolymer of a 25 O 9 50 50 6 33 cyclic monoterpene hydrocarbon component and divinyl Dipentene-styrene 75 1,000 19 17 benzene, said copolymer containing approximately 0.2 copolymer------100 1,000 32 125 2,100 47 O part to 20 parts by weight of units derived from said 25 O O 19 terpene component per part by weight of units derived - - - - - 50 O 6 22 h----- Terpene Ionopoly- 75 O 1. 3. 45 from divinylbenzene. i------Imer (Nirez 1100). 00 510 29 17 8. A pressure-sensitive adhesive composition accord i------125 650 45 O ing to claim 7 wherein the terpene component of the Parts of tackifier per 100 parts of eastoner. copolymer comprises dipentene. 9. A pressure-sensitive adhesive composition accord TABLE W-PROPERTIES OF PRESSURE SENSTIVE AD ing to claim 7 wherein the terpene component of the FEE's CONTAINING POLYISOPRENE AS THE ELAS 50 copolymer comprises a-pinene. Tap Tacklifier PR Hold Adhesive Tack 10. A pressure-sensitive adhesive composition accord No. walue walue walue ing to claim 7 wherein the terpene component of the 25 2 20 copolymer is turpentine. 50 O 4. 45 11. A pressure-sensitive adhesive composition accord 75 0 26 37 55 00 50 46 O ing to claim 7 wherein the terpene component of the 125 100 60 O copolymer is a mixture of terpenes containing approxi 25 O 3 23 50 O 12 50 mately 40 to 60 percent of dipentene, 25 to 40 percent Terpene Honopoly- 75 0. 26 4. of allo-ocimene, and 15 to 25 percent of terpene oligo ner (Nirez. 1100). 100 O 40 19 S. 25 O 54 O 60 12. Pressure-sensitive adhesive tape comprising back Parts of tackifier per 100 parts of elastomer. ing material and a tacky adhesive coating composition From the data in Tables II, III, and IV, it will be seen thereon, said coating composition comprising a rubbery that the dipentene-styrene copolymer is an excellent tacki elastomer selected from the group consisting of natural fier for styrene-butadiene rubber as is shown by the in 65 rubber, styrene-butadiene rubber, polyisoprene, and mix crease in adhesion with increased resin concentration and tures thereof and 20 parts to 200 parts by weight per by the development of tack. In polyisoprene and in 100 parts by weight of said elastomer of a tackifier, said natural rubber compositions, the dipentene-styrene co tackifier comprising a copolymer of a cyclic monoterpene polymer was also more effective as a tackifier than the hydrocarbon component and a comonomer selected from terpene homopolymer. the group consisting of styrene, alkylstyrenes having fewer Each of the other terpene copolymers disclosed herein 70 than 13 carbon atoms, alkenylstyrenes having fewer than may also be used to impart tack and adhesion to pressure 13 carbon atoms, and mixtures thereof, said copolymer sensitive adhesive compositions that contain a natural containing approximately 0.2 part to 20 parts by weight rubber or synthetic rubber as the polymeric cohesive of said terpene component per part by weight of said agent. 75 COOOc. 3,413,246 7 8 13. Pressure-sensitive adhesive tape comprising back and 15 to 25 percent of terpene oligomers and (b) ing material and a tacky adhesive coating composition divinylbenzene. thereon, said coating composition comprising a rubbery 16. Pressure-sensitive adhesive tape according to claim elastomer selected from the group consisting of natural 13 wherein the tackifier is a copolymer obtained by rubber, styrene-butadiene rubber, polyisoprene, and mix 5 polymerizing a mixture of monomers comprising a-pinene tures thereof and 50 parts to 125 parts by weight per and divinylbenzene. 100 parts by weight of said elastomer of a tackifier, said 17. Pressure-sensitive adhesive tape according to claim tackifier comprising a copolymer of a cyclic monoterpene 13 wherein the elastomer comprises styrene-butadiene hydrocarbon component and a comonomer selected from rubber. the group consisting of styrene, alkylstyrenes having O References Cited fewer than 13 carbon atoms, alkenylstyrenes having fewer UNITED STATES PATENTS than 13 carbon atoms, and mixtures, thereof, said co polymer containing approximately 0.2 part of 20 parts 2,349,210 5/1944 Traylor ------'-man m ram 260-86 by weight of said terpene component per part by weight 2,368,767 2/1945 Moore ------260-8 of said comonomer. 2,383,084 8/1945 Rummelsburg ------260-86 14. Pressure-sensitive adhesive tape according to claim 2,383,399 8/1945 Lindquist ------260-78 13 wherein the tackifier is a dipentene-styrene copolymer. 2,439,343 4/1948 Kropa ------260-86 15. Pressure-sensitive adhesive tape according to claim 2,648,614 8/1953 Martin et al. ------260-4 13 wherein the tackifier is a copolymer obtained by 3,058,930 11/1962 Samour ------260-4 polymerizing a mixture of monomers comprising (a) a 20 mixture of terpenes containing approximately 40 to 60 MURRAYTILLMAN, Primary Examiner. percent of dipentene, 25 to 40 percent of allo-ocimene, M. J. TULLY, Assistant Examiner.