1 3,458,392 United States Patent ' O ICC Patented July 29, 1969

1 2 yl styrene or ring alkylated styrenes may also be utilized 3,458,392 because the presence of the additional hydrocarbon TEAR SEAL BONDED POLYSTYRENE-SARAN groups does not affect the adhesive behavior of the basic LAMINATE polystyrene molecule. Charles J. Kremer, Brookhaven, Walter E. F. Lewis, Media, and Aaron Robert Gilden, Philadelphia, The saran polymers which may be utilized in the prac Pa., assignors to The Atlantic Re?ning Company, tice of this invention include homopolymers of vinylidene Philadelphia, Pa., a corporation of Pennsylvania chloride and copolymers of vinylidene chloride having a N0 Drawing. Filed Mar. 18, 1965, Ser. No. 440,943 minor amount of a comonomer such as vinyl acetate, Int. Cl. B3211 27/30, 27/08 vinyl chloride, acrylonitrile, etc. US. Cl. 161-245 4 Claims 10 If heat is to ‘be applied during lamination, it is desira ble to utilize a saran sheet which has had prior heat treat ment to prevent excessive shrinkage. Such a sheet is com ABSTRACT OF THE DISCLOSURE mercially'known as “pre-shrunk” saran. Tear seal bonded laminates comprising (a) a poly The adhesive is prepared by combining from about 25 styrene sheet having deposited on at least one side there 15 to about 50 weight percent wood rosin with from about of an adhesive coating consisting essentially of from 75 to about 50 weight percent of the low molecular weight about 25 to about 50 weight percent wood rosin and from polystyrene. A particularly preferred composition con about 75 to about 50 weight percent of a liquid poly tains from about 30 to about 35 weight percent wood styrene having a molecular weight ranging from about rosin and from about 70 to about 65 weight percent of 300 to about 1500, and (b) a polyvinylidene chloride 20 the low molecular weight polystyrene. When combining sheet in contact with said adhesive coating. These lami the wood rosin and polystyrene, it is desirable to apply nates have utility in the packaging ?eld especially for heat to the mixture to promote dissolution. Mix tem~ food packaging. peratures in the range of 140°-l60° F. will su?‘ice. It is usually desirable to lower the viscosity of the ad 25 hesive composition in order to obtain a uniform coating This invention relates to an adhesive for bonding poly on the polystyrene sheet. This may be accomplished by vinylidene chloride and polystyrene. More particularly, heating the composition or by adding a solvent such as this invention relates to a low molecular weight poly a light petroleum solvent until the desired viscosity is styrene-wood rosin composition which provides a tear obtained. seal bond between polyvinylidene chloride and poly 30 EXAMPLE I styrene sheets. Polystyrene has a high degree of water vapor trans An adhesive composition was prepared by dissolving mission. Therefore, in applications such as food packag- 32 grams of wood rosin in 68 grams of a 150° F. poly ing, requiring low water vapor transmission, it must be styrene having a molecular weight of approximately 1000. backed with a vapor impervious ?lm or sheet. The term 35 This adhesive composition was then deposited as an 0.1 “sheet” as used in this speci?cation includes thin sheets mil coating on a polystyrene sheet immediately after the commonly referred to as ?lms. Sheets made from poly ‘sheet emerged from the extruder die. The sheet tem vinylidene chloride, generically known as saran, have low perature was approximately 300° F. A 10 mil pre-shrunk moisture vapor transmission and may be used as protec saran ?lm was contacted with the adhesive coating and tive barriers for polystyrene sheets. However, it has been 40 the resulting laminate cooled to room temperature. The di?icult to obtain a strong, permanent bond between the laminate bond had a tear seal value of 400 grams per saran and polystyrene sheets. Epoxidized polymers have inch. The adhesive composition also prevented blistering been utilized as the adhesive but their high cost prohibits and shrinking of the saran ?lm and did not impair the their use in many applications. Furthermore, these ad gloss characteristics imparted by the saran. hesive coatings are opaque, thus destroying the gloss char 45 The term “wood rosin” as used throughout this speci acteristics imparted by the saran. ?cation includes the modi?ed and unmodi?ed forms of It has been found that a composition containing low wood rosin well-known to those skilled in the art. Com molecular weight polystyrene and wood rosin is an ex mon examples of the modi?ed forms include hydro cellent economical adhesive for bonding saran and poly genated, disproportionated and polymerized wood rosins. styrene sheets. 50 The laminates of this invention are particularly suited Therefore, it is an object of this invention to provide for food packaging applications. For example, contain an economical adhesive for bonding saran with poly ers made from heavier gauge laminates are outstanding styrene. for food storage, and thin ?lm laminates provide a clear, It is a further object of this invention to provide poly glossy, waterproof food wrap. styrene-saran laminates which have tear seal bonds. 55 We claim: The low molecular polystyrene resins which are uti 1. A tear seal bonded laminate comprising lized in the practice of this invention are viscous liquids (a) a polystyrene sheet having deposited on at least at ambient temperatures and have molecular weights‘ one side thereof an adhesive coating consisting essen ranging from about 300 to about 1500. A polystyrene tially of from about 25 to about 50 weight percent resin having a molecular weight ranging from about 800 60 wood rosin and from about 75 to about 50 weight to about 1500 is preferred. These styrene resins are com— percent of a liquid polystyrene having a molecular mercially available under the trademark Piccolastic. weight ranging from about 300 to about 1500, and (Pennsylvania Industrial Chemical Co.). Polymers made (b) a polyvinylidene chloride sheet in contact with from substituted homologs of styrene such as alpha meth said adhesive coating. 8,458,392 3 4 2. A tear seal bonded laminate accogliling to claim 1 FOREIGN PATENTS wherein the liquid p0 ystyrene in the a esive composi- . . tion has a molecular weight ranging from about 800 to 375’320 6/1932 Great Bmam‘ about1500- OTHER REFERENCES 3. A tear seal bonded laminate according to claim 1 5 _ . wherein the adhesive composition consists essentially of Plccolastlc Resins Catalog (Page 13), Published by from about 30 to about 35 weight percent wood rosin, Pennsylvania Industrial chemical Corp‘! February, 1962 and from about 70 to about 65 percent liquid polystyrene. 4. A tear seal 'bonded laminate according to claim 3 ROBERT F. BURNETT, Primary Examiner wherein the liquid polystyrene has a molecular weight ranging from about 800“, about 15m 1 0 LINDA M. CARLIN, Assistant. Exammer. References Cited US. Cl. X.R. UNITED STATES PATENTS 15 99_171; 106-239; 156-334; 161-254; 260-27, 669 2,271,093 1/1942 Pier et a1.