Jufiy 6, 1948.
`
`W. KELLGREN ETAL
`
`2,444,444
`
`ADHESIVE SHEETS AND METHOD OF MAKING
`
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`CLIO USA
`EXHIBIT 1009
`PAGE 000001
`
`PAGE 000001
`
`CLIO USA
`
`EXHIBIT 1009
`
`
`
`
`
`
`
`
`
`
`

`

`Patented July 6,1948
`
`2.. 444.830
`
`UNITED STATES PATENT OFFICE
`
`2.444,830
`ADHESIVE SHEET AND METHOD
`OF MAKING -
`
`Waldo Kellgren, St. Paul, Hubert J. Tierney,
`Mahtomedi, and Richard Gurley Drew, St.
`Paul, Minn., assignors to Minnesota Mining &
`Manufacturing Company, St. Paul, Minn., a
`corporation of Delaware
`
`Application April 4, 1938, Serial No. 199,942
`20 Claims.
`(Cl. 154—136)
`
`.
`1
`This invention relates to pressure-sensitivie
`adhesive sheets, conveniently in the form of tapes,
`characterized by having a flexible film or non-
`flbrous sheet backing. and a unified thin flexible
`paper reinforcing sheet which is coated on both
`sides with pressure-sensitive adhesive and firmly
`laminated to the backing to form a permanently
`unitary product which is thin, flexible and strong.
`This tape possesses the attractive and desir-
`able qualities of ordinary film-backed adhesive
`tapes but
`is stronger, having greater tensile
`strength and resistance to tear. It may be rolled
`or stacked without the use of a slip sheet and
`unrolled or removed without splitting or delam-
`ination and without offsetting of adhesive upon
`the back of the adjacent tape from which it is
`separated. It may be applied to various surfaces
`for sealing purposes and removed in condition
`for reuse and without leaving a. residue of ad-
`hesive upon the surface, although character-
`ized by an aggressive adhesiveness permitting of
`good adherence.
`Adhesive tapes prepared in accordance with
`this invention are of general utility and may
`be made to serve as removable and reusable
`packaging tape, can-sealing. tape, tape to replace
`viscose coverings on bottles, ceramic tape, elec-
`trical tape, repair tape, tape for making labels
`and index tabs, frost shield tape, etc., and in gen-
`eral may be applied to any analogous purpose
`for which a wrapping, covering, sealing. joining
`or splicing pressure-sensitive adhesive tape is
`desired.
`.
`Adhesive tapes may be prepared which are
`transparent or semi-transparent, so that they
`may be applied without concealing the coloring
`or markings of the surface to which applied.
`‘ Coloring material in dye or pigment form may be
`incorporated in the adhesive or in the backing.
`When a transparent backing is used, it may be
`printed in reverse, on the face which carries
`the adhesive and prior to coating, to provide an
`adhesive sheet with the printing visible through
`and protected by the backing.
`The adhesive is “normally tacky and pressure-
`sensitive,” by which it is meant that under ordi-
`nary atmospheric conditions the adhesive is stably
`in a candition such that it does not need to be
`activated by solvents or heat or otherwise pre—
`pared in order to secure good- adherence to sur->
`faces against which the adhesive tape may be
`pressed, to result in an aggressive adhesive bond-
`ing to the surface which resists separation there-
`from except by a lame greater than the pressure
`necessary to obtain adhesion. Furthermore, a
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`“non-offsetting” adhesive layer is provided, mean-
`ing that the adhesive is possessed of such coher—
`ence in relation to adhesiveness and is so firmly '
`united to the backing and to the reinforcing sheet
`that the adhesive sheet or tape may be stacked or
`rolled upon itself without offsetting of adhesive
`upon separation or unwinding for use, and may
`be separated in a condition for reuse from sur-
`faces (not possessing special chemical amnity
`for the adhesive), to which it may have been
`temporarily applied, without offsetting of ad-
`hesive material. Hence the term “non-oilsetting"
`designates an important physical or chemico~
`physical prOperty or characteristic of the ad-
`hesive.
`By a “unified” paper reinforcing sheet, it is
`meant that the paper is impregnated with a
`material which binds or welds the fibres to-
`gether, so that the paper will not split or the
`fibres pull loose under the force exerted by the ’
`normally tacky and pressure-sensitive adhesive
`coating when the product is unwound from rolls
`or removed from surfaces to which temporarily
`applied—that is, a fibre unity is present which
`prevents the unity of the reinforcing sheet from
`being destroyed by the pull of the adhesive. The
`unified sheet, because of
`the increased fibre
`unity, has an increased tensile strength and re-
`sistance to tear.
`The paper may be unified by impregnation with
`the normally tacky and pressure-sensitive ad-
`hesive itself, so that this material both unifies
`and coats the reinforcing sheet, making it pes-
`sible to unify and doub1e~coat the sheet in a
`single operation. Or the paper may be unified .
`with a diiierent composition, which will not ren-
`der the sheet stiff and for which the pressure-
`sensitive adhesive material has a strong amnity,
`and then be subsequently coated with the pres-
`sure-sensitive adhesive. Or the reinforcing paper
`may be partly unified by the pressure-sensitive
`adhesive penetrating into it from one or both
`sides and partly unified by another unifying
`impregnant.
`In any case, there is not a mere
`superficial penetration by a coating material but
`a thorough saturation or impregnation to produce
`a truly unified paper.‘
`The normally tacky and pressure-sensitive ad—
`hesive of this tape serves not only to provide an
`exposed adhesive surface, but the inner coating
`thereof on the back side of the reinforcing sheet
`serves to unite or bond the latter to the film
`backing.
`It is preferred, especially when the
`faceside of the film backing, which carries the
`adhesive, is of a smooth lustrous non-porous na-
`
`PAGE 000002
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`PAGE 000002
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`

`

`2,444,330
`
`3
`ture, to provide an interposed primer coating in
`order to secure greater anchorage of the inner
`adhesive coating to the backing and fully guard
`against subsequent delamination of the adhesive
`sheet.
`The backing isof the flexible film type, that
`is, it is a thin flexible non-fibrous sheet which
`may be transparent. translucent or opaque, and
`is characterized by a smooth dense non—porous
`surface which may be. and preferably is, lustrous
`or glossy. Representative backings are lustrous
`non-fibrous cellulosic films such as films of re—
`generated cellulose (normal Cellophane), cellu~
`lose esters (as cellulose nitrate. cellulose acetate
`and cellulose aceto-butyrate), cellulose ethers
`(as ethyl cellulose and benzyl cellulose), and
`Cellophane which has been waterproofed or mois-
`tureproofed on one or both sides by a lacquer or
`resin coating which is firmly bonded; all of which
`film materials may and generally do contain
`plasticizers to inCrease flexibility and suppleness.
`Other illustrative backings are films of rubber
`hydrochloride, chlorinated rubber, synthetic res~
`ins, and metallic films such as foil made of alu-
`minum, tin, copper or zinc and alloys thereof, etc.
`When Cel‘ophane is used, a preferred thickness
`is “300 point” (0.88 mil), but where extreme thin-
`ness and flexibility of the adhesive tape is not
`so important, Cellophane of “450 point” (1.25
`mils) or “600 point" (1.75 mils) may be used,
`for example.
`An undesirable characteristic of such thin
`non-fibrous films is lack of strength (i. e., a low
`internal cohesiVeness in one or. both directions)
`which is manifested in any given case by one or
`more of such attributes as low tensile strength,
`brittleness
`(either
`initially or after aging),
`tendency to crack on flexing, tendency to easily
`tear, and tendency of adhesive coatings to ofiset
`upon unwinding of adhesive tape from rolls or
`removal from surfaces. An object of this inven—
`tion is to use such a backing, because of its de-
`sirable characteristics, and yet to overcome the
`lack of strength, but without making the tape as
`a whole undesirably thick, still, or unattractive,
`or' have a tendency to delaminate when unwound
`from rolls or removed from surfaces to which
`temporarily affixed, or have a tendency to unduly
`curl, buckle Or warp because of lack of elastic
`equilibrium between its constituent parts.
`The paper reinforcing sheet should be thin,
`flexible, of open texture so as to be highly porous,
`and should be tough and strong. We prefer to
`employ a thin sheet of long-fibred rope paper of
`open texture. Rope paper is made from hemp
`fibres and-is quite tough and strong even when
`thin and open textured.
`Such paper is exemplified by “Troya Tissue,”
`made of purified Manila hemp fibres. The fibres
`range from 1/; to 1/2 inch in length and mostly
`run in a direction lengthwise of the web, which
`is advantageous in that when adhesive tapes are
`made with the fibres of the reinforcing sheet run-
`ning lengthwise, there will be a greater length-
`wise tensile strength and resistance to crosswise
`tear than would otherwise be possible. Paper of
`2 mil thickness, for example, weighs 14 lbs. per
`ream (i. e., 480 sheets 24 in. by 36 in., or the
`equivalent, weighs 14 lbs.) ; and has a lengthwise
`tensile strength of 161/2 lbs. per inch width and a
`crosswise tensile strength of 2 lbs. Paper of 11/2
`mil
`thickness weighs 12 lbs. per ream, has a
`lengthwise tensile strength of 16 lbs. and a cross-
`wise tens‘ilestrength of 2 lbs. The high porosity
`is indicated by the fact that 10 thicknesses of
`
`4
`either the 2 mil or 11/2 mil paper require only 5
`seconds to pass 400 cc. of air through a 1%; inch
`diameter opening on the Gurley densometer
`(original model, ‘No. 4100). The high porosity
`may also be indicated by the statement that for
`the. 2 mil paper it is 5 to 25 times greater than
`that of absorbent paper towelling, comparing
`equal test thicknesses. This brings up the point
`that porosity and absorptiveness are not synony-
`mous. Porosity is required in order that the uni-
`fying impregnant may adequately penetrate be-
`tween the fibres.
`The paper thickness to be used for present pur-
`posesis preferably 1 to 4 mils, and we ordinarily
`use a thickness of 11/2 or 2 mils, which permits of
`a high degree of flexibility in the finished ad-
`hesive sheet and for greater transparenCy when
`the latter is desired.
`Another example of rope paper is “Dextilose,”
`in which the fibres are also of hemp, but which
`differs in that the paper has substantially the
`same lengthwise and crosswise tensile strength
`and tear resistance.
`'
`The invention is illustrated by the following
`embodiments.
`In the accompanying drawing:
`Fig. 1 is a diagrammatic magnified section of
`an adhesive sheet showing the constituent parts;
`Fig. 2 is a diagrammatic representation show-
`ing a continuous method of making such adhesive
`sheeting; and
`Fig. 3 shows a method of presaturating the re-
`inforcing paper.
`Referring to Fig. 1, there is shown the combi-
`nation of a film backing l; impregnated and uni-
`fied paper reinforcing sheet 2 which is coated on
`both sides with normally tacky and pressure-
`sensitive adhesive forming outer adhesive coating
`3 and inner adhesive coating 4; and primer coat-
`ing 5 interposed between the inner adhesive
`coating and the backing; forming a permanently
`unitary adhesive sheet.
`For purposes of illustration, the approximate
`thicknesses of the various layers or films will be
`given for a representative embodiment of the in-
`vention, viz: film backing (1) of “300 point” nor~
`mal Cellophane—0.9 mil, unified Troya Tissue
`paper reinforcing sheet (2)—2 mils, outer and in-
`ner adhesive coatings (3 and 4)-—0.9 mil, primer
`coating (5)—-0.1 mil. Thus the total thickness of
`the adhesive sheet is about 5 mils (0.005 inch).
`The thicknesses may of course be varied some-
`what, but we prefer to employ a combination
`yielding an adhesive sheet having a thickness
`of not over about 8 mils, in order to secure a high
`degree of flexibility and to avoid a sheet differ-
`ing greatly in thickness from ordinary adhesive
`sheets which do not have a reinforcing sheet
`component.
`Referring to Fig. 2, the paper, in the form of
`a continuous web from a supply roll, is double-
`coated and impregnated by passing through a
`bath In of adhesive solution; the paper passing
`over and rearwardly under roller H (located
`above the solution), thence into the bath and
`under roll or rod l2, thence upwardly out of the
`bath (to allow air to escape from the web) and
`over roll l3, thence down into the bath and under
`roll it in a forward direction so that it moves
`horizontally through the bath to stationary rolls
`l5 and IS, which form an exit orifice and are
`spaced to secure the desired thickness of coating.
`A suitable diameter for these orifice rolls is 8
`inches.
`The wet, coated and impregnated paper web
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`PAGE 000003
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`,
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`12,444,880
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`5
`then passes through a drying oven ll, for sol-
`vent
`removal, moving horizontally forward,
`through an upper duct maintained at a temper-
`ature of about
`ISO-160° F., until substantially
`dry. then down over rollers i8 and It and back
`through a lower duct maintained at a temper-
`ature of about 140—150° F., to complete the dry-
`ing. and thence out of the oven and down over
`roller 20, which may be a drum cooled by cir-
`culationof water through the interior. While
`“dry," the web is tacky and pressure-sensitive on
`both faces owing to the nature of the adhesive.
`It passes down under roller 2i and then up over
`roll 22, which'is'one of a pair of horizontally
`positioned squeeze rolls 2.2 and 23, and then meets
`the primed backing flhn and passes with it down
`between the rolls.
`The Cellophane fllm backing i is taken from a
`supply roll as a web of slightly greater width than
`the paper web, and passes between a pair of horie
`zontal, vertically positioned coating rolls 26 and
`25, the former of which is lowermost and dips
`into a bath 29 of primer coating composition.
`thereby becoming coated on the lower face with a
`thin film of the composition. The coated Cello-
`phane. then passes up and over roller 26 and is
`drawn to squeeze roll 23, the coated face being
`uppermost, and the distance of travel being great
`enough so that the primer coating will have be-
`come substantially dried by evaporation of the
`solvent before reaching the squeeze roll.
`The paper, coated on both sides with tacky and
`pressure-sensitive adhesive, and the primed Cel-
`lophane, meet as they pass down between squeeze
`rolls 22 and .23, and are firmly pressed together,
`the adhesive becoming firmly united to the primer
`coating of the Cellophane because of their mu-
`tual affinity, so that a permanently unitary ad-
`hesive sheet results. The squeeze rolls are set
`so that sumcient pressure will be exerted to in-x
`sure squeezing out air from between the two webs
`as they come together, and to insure adequate
`bonding together to prevent delamination in sub-
`sequent normal use.
`The resultant adhesive sheet passes over driven
`pull drum 27!, which contacts the adhesive side
`and which serves to draw the adhesive sheet
`from the squeeze rolls and to draw the sheet-ma-
`terials clear through the various treatments with-i
`out
`intermediate driving means being needed.
`and is then wound up in a temporary roll al,‘
`a temporary liner being wound in. This roll
`is subsequently unwound and the adhesive sheet
`slit and wound into rolls of desired» width.
`-
`The above-described method of combining the
`coated paper and the primed backing is greatly»
`preferred to any method in which the adhesive
`or primer, or both, have not been substantially
`dried prior to lamination.
`if the latter is the
`case, volatile solvent will be trapped between the
`paper and the backing and will form bubbles or
`pockets which not only mar the appearance but
`weaken the bond.
`Referring now to Fig. 3, there is shown an»
`optional pretreatment of the paper before it en:-
`ters the above-described adhesive bath it. The
`paper web passes over roller til and then down
`at an angle into bath at of saturating solution,
`so that both sides will be“ exposed to the solution:
`passes under roller 32 (which dips into the solu-:
`tion) and then back up between roller 32 and
`overlying roller 33, which is spaced so as to re-
`move excess solution from the surface of the
`paper; and then passes over roller 3% and names
`to roller ii and down into bath It.
`In passing
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`between rollers at and Ii, which are suitably
`spaced. the volatile vehicle of the saturating solu-
`tion is permitted to evaporate: and this may be
`facilitated,
`if desired by providing heating
`means.
`This pretreatment may constitute a preliminary
`unification with pressure-sensitive adhesive solu-
`tion of the same kind that is used as bath Ill, but
`is more dilute so as to be less viscous, making for
`a more complete penetration of adhesive solids into
`the middle interior of the paper—an expedient
`which is desirable when dealing with paper of
`greater thickness and density than can be easily
`unified by impregnation in the concentrated solu-
`tion alone. The bath may be comprised of the
`cencentrated solution. as illustrated in examples
`hereafter set forth, thinned by adding a greater
`amount of solvent. Thus in Example 1, the
`ratio of solvent to rubber, by weight,'is about 5
`to 1, and this may be increased to 15-30 to 1
`for the pre-saturation bath.
`The pretreatment may, however, be for the
`purpose of unifying the paper with a compositiou
`which is relatively non-tacky and which would
`not be suitable for- the adhesive coatings, but
`which is effective ln'unifying the fibres of the
`paper, and which should be of a kind toward
`which the adhesive proper has a strong affinity,
`so that the subsequently applied adhesive coat-'
`ings will be firmly anchored. This unifying com-
`position is dispersed in a volatile liquid vehicle in»
`a proportion permitting the impregnant solids to
`thoroughly saturate and unify the paper, and the
`resultant solution is used as bath 3!. An ex-
`ample of a suitable composition is set forth here-
`after under the heading “Separate unifying com—
`position.”
`In the following examples of compositions,
`given for purposes of illustration rather than lim-
`itation. all parts are by weight.
`
`Primer composition
`Parts
`Selected tube reclaim rubber_________________ 90
`Latex crepe rubber_________________________ 1i)
`Whiting _--_ _____a-_-_____-_____--___-_____'_ to
`Wood rosin_____________________________ 140
`
`Heptane (volatile solvent) _____________ 360—450
`The wood resin is preferably the “FF” grade
`or, even more preferably, a heat—treated wood
`rosin known as “Solros” wood rosin.
`The reclaim rubber, latex and whiting (which
`serves as a reinforcing pigment and is optional)
`are compounded together on the ordinary type of
`rubber mill and milled for 30-40 minutes. This
`milled base is then transferred to a heavy duty
`internal mixer (such as 2. Baker Perkins Mogul
`type mixer) and mixed for 1-2 hours with 10—20
`lbs. steam pressure in the heating jacket. The
`rosin is then added and mixing is continued for
`another hour. The jacket steam is then turned
`off and the mass cooled. The solvent, preferably
`heptane, but substitutable by other volatile rub-
`ber solvents as benzol, naphtha and high-test
`gasoline, is then added and mixing is continued
`until the whole mass is homogeneous, generally
`requiring about
`1/2 hour. The resulting primer
`composition or solution 'is then ready for appli—
`cation to the backing.
`In this method of compounding. the reclaim
`rubber becomes plasticized by the mechanical
`working in the presence of heat and air, and is
`further plasticized by the rosin which is thor-
`oughly incorporated therewith.
`While raw rubber may be employed in place
`
`'
`
`PAGE 000004
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`PAGE 000004
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`

`

`9,444,330
`
`7
`of reclaim rubber (which is in a partially vul-
`canized state), the latter is much to be preferred
`because it makes for a primer coating having
`a greater bonding action. due to the higher ad-
`hesion value of the reclaim rubber resulting from
`the heating cycle and amount of break down ex-
`perienced in the reclaiming process. This is ob-
`tained without sacrifice or firmness or coherency
`of the primer coating. due to the high cohesive-
`ness of the reclaim rubber resulting from its prior
`vulcanization.
`If raw rubber were subjected to
`the same treatment, it would have softness and
`stickiness but would lack adequate cohesiveness.
`Instead of using reclaim rubber, a fresh partially
`vulcanized rubber may be employed.
`The whiting employed in the primer serves as
`a reinforcing pigment, imparting greater cohe—
`siveness and firmness. It does not prevent trans-
`parency, for the primer coating is quite thin.
`Adhesive Example 1
`
`Parts
`
`Latex crepe_____________________________ 132
`Zinc oxide______________________________ 165
`Blue pigment mixture____________________
`39.5
`No. 10 wood rosin________________________
`72.5
`“Flectol B” (antioxidant) _____________ ___
`1.5
`Heptane (volatile solvent) ________________ 750
`The blue pigment mixture is exemplified by
`“Du Pont rubber blue YD." a milled mixture of
`equal parts latex crepe and .'dry blue pigment.
`This may be'omltted.
`The latex crepe, zinc oxide» and pigment mix-
`ture are milled on a rubber mill for about 10
`minutes, at a temperature of ‘about 140—150“ E,
`and the resulting base is cut into small pieces.
`The rosin is dissolved in an equal amount of
`the solvent and the “Fiectol B" is likewise dis-
`solved in a portion of the solvent. The balance
`of the solvent (to make a total of 750 parts) is
`placed in a suitable churn and the solutions of
`rosin and "Flectol B." and the milled base, are
`added. The mixture is mixed until homogeneous,
`involving mixing for about 40 hours at a tempera-
`ture of about 70—100" F.
`The indicated heptane may be substituted for
`by another volatile rubber solvent such as benzol
`or naphtha. It will be understood that the pro-
`portion of solvent may be varied to produce the
`desired viscosity of the adhesive composition,
`which in any case should be sufficiently low to
`insure thorough saturation of the paper reinforc-
`ing sheet. The amount of hydrocarbon solvent
`required may be reduced by incorporating alcohol
`as a viscosity-reducer, which may be denatured
`ethyl alcohol (for example containing 5 volumes
`of methyl alcohol or ethyl acetate per 100 vol-
`umes of 190 proof ethyl alcohol) or may be methyl
`alcohol, and which may be used in amount equal
`to 10 to 20% of the hydrocarbon solvent.
`In the above example “Flectol B" (a liquid con-
`densation product of acetone. and aniline) is used
`as an antioxidant to improve the rubber aging
`qualities. other suitable antioxidants or age-
`resisters are: “Flectol H” (a solid condensation
`product of acetone and aniline), “Soiux” (p-hy-
`droxy--N—phenylmorpholine),
`“Agerite Resin”
`(aldol-alpha-naphthylamine reaction product).
`“Antox.” beta-naphthol, “Agerite Alba" and
`“Agerite White." Those which are soluble in the
`rubber solvent may be added directly, otherwise
`they may be milled into the rubber during the
`initial milling.
`Instead of wood rosin. a synthetic tack-produc-
`ing resin may be used, such as cumarone resin.
`
`L
`
`The coloring pigment serves also as a reinforc-
`ing pigment.” does the zinc oxide, giving greater
`cohesiveness (firmness) to the adhesive coating.
`These pigments may be omitted or reduced in
`order to produce transparent adhesive coatings.
`and a transparent, semi-transparent or translu-
`cent adhesive tape product. By omitting all pig-
`ment material and employing a Troya Tissue
`sheet of 1 or 1% mils thickness. a transparent
`tape will be obtained. The adhesive impregnant
`with which the paper is saturated serves to trans
`parentize it.
`~
`.
`When a coloring pigment is employed. in com
`junction with a transparent backing such as
`a film of Cellophane, the adhesive tape appears
`to have a glossy colored back, which renders it
`very attractive.
`'
`The above rubber-resin type of adhesive for-ms
`adhesive coatings which are not only normally
`tacky and pressure-sensitive, and non-offsetting,
`but which are water-insoluble, non-hygroscopic
`and moistureproof.
`Using the above formula to impregnate and
`double-coat Troya Tissue as shown in Fig. 2
`and accompanying description,
`to produce a
`thoroughly unified paper having .an adhesive
`coating on each side which is about 0.9 mil thick,»
`the weight of adhesive solids is indicated by the
`following illustrative data: a 4 in. by 6 in. piece
`of 1 1/2 mil thickness paper weighs 5.2 grains before
`treatment and takes up approximately 26—30
`grains of adhesive; and a similar piece of 2 mil
`paper.
`initially weighing 5.8 grains,
`takes 1",
`approximately 28-32 grains of adhesive.
`Adhesive Example 2
`
`Parts
`200
`Isobutylene polymer “medium”__________
`200
`Isobutylene polymer “low"_______________
`80
`Soft cumarone resin_____________________
`Heptane-___.._-_-______________.'. ________ 1,600 ’
`The isobutylene polymers are resinous mate-
`rials,
`the one designated “medium” having a-
`molecular weight of approximately 80,000 and
`the one designated “low” a molecular weight of
`approximately 14,000.
`The ingredients are
`placed in a churn and mixed until homogeneous.
`The cumarone resin acts as a tack-producer,
`as does the lower isobutylene polymer. The latter
`may be omitted and the stated proportion of
`cumarone resin retained or increased, and the
`cumarone resin may be substitutedi‘or by wood
`rosin or other tack-producing resin.
`This composition forms particularly clear and
`transparent pressure-sensitive adhesive coatings
`and is quite effective in transparentizing the
`paper reinforcing sheet. However, a coloring
`pigment may be incorporated in producing col-
`ored adhesive tape. as illustrated by the following:
`Adhesive Example 3
`
`10
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`15
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`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Parts
`Isobutylene polymer “medium”____________ 1
`Zinc oxide _______________________________ 0.5
`Para toluidine red________________________ 0.2
`Wood rosin ______________________________ 0.5
`Hydrogenated methyl abietate_____________ 0.2
`Heptane _________________________________ 7
`The isobutylene polymer, zinc oxide and col-
`oring ingredient (illustrated by para toluidine
`red) are first milled on a rubber mill until a uni-
`form plastic composition is secured. This plastic
`mass is then cut to pieces and placed in a suit-
`able churn with the balance of the ingredients
`75 and churned until a homogeneous solution ls
`
`70
`
`PAGE 000005
`
`PAGE 000005
`
`

`

`2,444,830 ,
`
`9
`formed. The wood rosin, which is used in amount
`less than the. isobutylene polymer, serves as a
`tack-producing agent, so that normally tacky
`and pressure-sensitive adhesive coatings will be.
`formed.
`The hydrogenated methyl abietate
`serves as a plasticizer and may be omitted.
`Separate unifying composition
`
`Parts
`Latex crepe _____________________________ 100
`Zinc oxide ______________________________ 100
`Rosin ___________________________________ 160
`Beta-naphthol (antioxidant) _____________
`1
`Oleum spirits (volatile solvent) ____________ 200
`The rubber and zinc oxide are milled on an
`ordinary rubber mill for 30 minutes, at about
`150—160° F., and then taken oiT in sheet form and
`placed in an internal mixer (such as 8. 'Baker
`Perkins Mogul mixer),
`the heating jacket of
`which carries steam at 40 lbs. pressure, and which
`has previously been allowed to warm up. A small
`proportion of the rosin (say 10—25%)
`is added
`to make for lubrication and a lower pOWer re-
`quirement, and the mass is mixed for about 8—10
`hours, or until reduced to a semi-fluid consist-
`ency. This mastication destroys the nerve of
`the rubber and makes possible a proper impreg-
`nation, the mechanical working in the presence
`of heat and air plasticizing the rubber. The
`rosin may be omitted from this stage of com-
`pounding, but with an increase in the power re-
`quirement; and an even greater proportion, or
`all, of the rosin may be added, but with an in-
`crease in the time required for breaking down
`the nerve of the rubber.
`If all the rosin is added
`at the beginning, about 24 hours mixing will be
`required.
`The balance of the rosin is added, care being
`taken to add slowly to avoid excessive foaming
`caused by the water evolved from the reaction
`between the rosin and the zinc oxide, and mixing,
`is continuedfor another hour. The beta-naph-
`thol is added, and the steam is turned oil and
`cooling water introduced into the heating jacket
`of the mixer. The oleum spirits is then added
`with continued mixing for half an hour, or until
`the mixture is homogeneous. The resultant im—
`pregnating composition is then ready for use.
`The rubber
`is preferably latex crepe, but
`smoked sheets or reclaimed rubber may be used.
`Reclaimed rubber is less desirable because of its
`partial degree of vulcanization, which resists
`breaking down to reduce the viscosity. Since
`reclaimed rubber ordinarily contains zinc oxide,
`a reduction may be made in the added zinc oxide,
`or the latter may be omitted.
`‘
`The zinc oxide functions both as a reinforc-
`ing pigment and as hardening agent for the rosin,
`part of it reacting with the rosin to saponify the
`latter, forming zinc abietate. Other basic oxides
`may be used as hardening agents in place of or
`in conjunction with zinc oxide to form water-
`insoluble resinates. Thus a small amount of
`lime (preferably hydrated lime), for example 1
`part in the above formula, may be employed, or
`a small amount of magnesia,
`Inert fillers, pref-
`erably in the nature of reinforcing pigments,
`may be substituted for part of the zinc oxide.
`The filler or pigment should have a particle size,
`following mastication, which is fine enough to
`penetrate into the backing. Thus clay, whiting,
`and lamp black may be used for this purpose.
`The rosin may be gum rosin or wood rosin,
`and may be substituted for in whole or in part
`by equivalent synthetic or natural resins which
`
`10
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`15
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`20
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`25
`
`30
`
`10
`blend with rubber. Thus,.for example, a part
`of the rosin in the above formula may be replaced
`by ester gum or“ copal resin. While it is pre-
`ferred to harden the rosin in situ during the com-
`pounding, it may be hardened in advance by
`treatment with zinc oxide, etc.
`The oleum spirits is a petroleum hydrocarbon ,
`- solvent of medium volatility, and may be sub-
`stituted for-by other volatile hydrocarbon sol-
`vents such as benzol, heptane, naphtha and gas-
`oline.
`The preferred range of composition in the
`above formula is as follows per 100 parts of rub-
`ber: 75—125 parts of zinc oxide and 140—180 parts
`of rosin. The solvent ratio should preferably be
`substantially as- indicated, although some varia-
`tion may be desired depending on the proportions
`of other ingredients and the degree of breakdown
`of the rubber; and in some cases a more dilute
`composition may be desired if it is intended to
`only partly unify the paper in the pretreatment
`bath.
`-
`The foregoing unifying composition provides
`a relatively non-tacky, water-insoluble and non-
`hygroscopic impregnant for the paper and one to
`which rubber or resin-containing adhesive coat-
`ings will firmly anchor.
`What we claim is as follows:
`1. As a new article of manufacture, a laminated ~~
`pressure-sensitive adhesive tape substantially
`transparent to reflected light when mounted upon
`a surface, which comprises a pliable, non-fibrous,
`transparent backing; and an integral multi-layer
`adhesive coat attached thereto, said coat com-
`prising a first layer of a substantially transparent,
`pressure-sensitive, adhesive composition; a thin,
`unsized, unfilled, porous paper overlying said first
`layer; and a second layer of a substantially trans-
`parent, pressure-sensitive. adhesive composition
`overlying said paper; said adhesive compositions
`impregnating said paper from both sides and hold-
`ing said paper
`in suspension therein as a
`strengthening bond to form therewith an inte-
`gral, multi-layer adhesive coat, thereby provid-
`ing a laminated adhesive tape having an