sign in sign up
<<
Home , Magnesium sulfate

3,394,024 United States Patent 0 "ice Patented July 23, 1968

1 2 from about 1 to about 25 milligrams of the -soluble 3,394,024 and the alkali metal salt (total). ANTIFOGGING CELLOPHANE Daniel K. Owens, Bon Air, Va., assignor to E. I. du Pout A convenient way of applying the improved antifog de Nemours and Company, Wilmington, DeL, a cor composition to the surface of a ?lm is to pass the ?lm poration of Delaware through an of the composition and re N0 Drawing. Filed Apr. 8, 1965, Ser. No. 446,728 move excess solution from the ?lm by passing it through 8 Claims. (Cl. 117-76) a set of squeeze rolls. The ?lm is thereafter dried. In the preferred embodiment of this invention the water soluble metal salt and the alkali metal salt of the aliphatic ABSTRACT OF THE DISCLOSURE 10 ‘hydrocarbon are employed in substantially equal A plastic ?lm coated with an antifogging composition molar quantities. A preferred alkali metal aliphatic hydro comprising a water-soluble salt of an carbon sulfate is sodium lauryl sulfate and a preferred and a hydrocarbon sulfate wetting agent. water-soluble metal salt is sulfate. A preferred ?lm is a vinylidene chloride copolymer coated regenerated 15 cellulose ?lm. Although the antifog composition of this invention is This invention relates to plastic ?lms and antifogging especially useful for the after~sizing of vinylidene chloride agents therefor. copolymer coated regenerated cellulose ?lms, and particu In the development of transparent Wrapping ?lms for larly for such coatings applied from a solvent system, packaging a variety of products a number of require 20 these compositions can also be used for the sizing of ?lms ments must be met. To be used successfully on automatic that have been coated with aqueous dispersions of vinyli packaging machinery the ?lm must have adequate slip dene chloride copolymers and including such base ?lms as and should be free of blocking tendencies and should be regenerated cellulose as well as the various thermoplastic readily heat scalable so that packages can be readily polyester base ?lms such as those of polyethylene tereph formed. For the wrapping of foodstuffs which are of rela 25 thalate, and polyole?n ?lms such as polypropylene and tively high moisture content an additional requirement polyethylene as well as various copolymer ?lms of the is that moisture from the packaged product should not polyole?ns, polymers of the haloole?ns such as poly deposit upon the interior surface of the ?lm package in vinyl chloride and polyvinyl ?uoride. These antifog com minute droplets or as a fog. This tendency of moisture positions can also be used on various ?lms that are not to deposit in the form of a fog on the interior surface 30 coated such as melt extruded ?lms of the polyole?ns and of the package reduces transparency and greatly inter the polyhaloole?ns such as polyethylene, polypropylene, feres with the effective display of the particular packaged polyvinyl chloride, polyvinyl fluoride and polyester ?lms article. such as those made from polyethylene terephthalate and One approach to this problem is to incorporate on the various copolyesters of this general type. surface of the packaging ?lm a small amount of a wetting 35 With respect to the alkali metal aliphatic hydrocarbon agent in the form of a continuous uniform layer which sulfate, other alkali metals, lithium, , rubidium functions to provide more effective wetting of the surface and cesium can be used in place of sodium. Representa or spreading of the moisture on the surface in the form of tive hydrocarbonyl radicals include octyl, decyl, dodecyl a layer rather than in the form of small droplets or fog. (lauryl), tetradecyl, hexadecyl and octadecyl as vwell as A difficulty incurred in this approach is that when the 40 the corresponding ole?nically unsaturated radicals and wetting agent is applied to the surface in an amount suf~ branched chain radicals. ?cient to act as an effective antifog agent the ‘heat seala In addition to the water-soluble salts, mentioned above, bility of the treated surface is adversely affected. Another others that can be used include magnesium acetate, zinc dif?culty lies in the fact that most wetting agents are not acetate, magnesium bromide, calcium bromide, calcium powerful enough to wet the ?lm uniformly and the ?lm 45 acetate as well as corresponding salts of other Group II exhibit-s fogging in patches. In some cases, combinations metals such as beryllium, strontium, cadmium, barium of different wetting agents have provided effective anti and mercury. It is important that the salt be water-soluble, fogging performance but an undesired side effect was a having a in water of at least 5% by weight at tendency for the ?lm to block rather easily in addition 25° C. to giving di?iculty in heat sealing. The primary advantage of this new sizing agent is that It is therefore an object of this invention to provide it provides a ready means for making heat scalable trans a ?lm which is readily heat scalable, which has good slip parent ?lms which will run well on automatic packaging and non-blocking properties, and which remains trans machines and will remain transparent even in the pres parent and is non~fogging when in contact with moist ence of high moisture containing products such as food atmospheres. A more speci?c object is to provide a vinyli products which are packaged in transparent ?lms. An dene chloride coated regenerated cellulose ?lm which is added advantage is that a more uniform non-fogging readily heat sealable, which has good slip and blocking characteristic can be realized at lower concentration levels properties, and which is non-fogging when used for the for the wetting agent than has been here before possible. packaging of moist objects or articles. Other objects will Thus, more effective antifogging characteristics are real appear from the description which follows. 60 ized at lower cost which is most important in large scale According to the present invention, there is provided a commercial manufacturing operations. useful coating composition comprising about 10 to 90 This invention will be more clearly understood by ref mol percent of a water-soluble nitrate, acetate, halide or erence to the following examples. These examples illus sulfate salt of a Group II metal and about 90 to 10 mol trate speci?c embodiments of the present invention and percent of an alkali metal salt of an aliphatic hydro 65 should not be construed to limit the invention in any way. carbon sulfate wherein the hydrocarbon group contains 8 through 18 carbon atoms. Example 1 This composition is applied in aqueous solution to the A ?lm was made by coating on a regenerated cellulose surface of a transparent heat sealable plastic ?lm in an ?lm a coating composition of a copolymer of 92 parts of amount to provide per square meter of the ?lm surface 70 vinylidene chloride, 2 parts of methyl methacrylate, 6 3,394,024 parts of acrylonitrile and 0.5 part of itaconic acid in a was substituted for the of that ex toluene/tetrahydrofuran coating solvent. The ?lm was ample, with similarly satisfactory results. thereafter passed through an aqueous solution of essen Example 4 tially equal molar portions of magnesium sulfate and sodium lauryl sulfate (0.15% by weight sodium lauryl Cl Example 1 was repeated except that sulfate and 0.13% by weight MgSO4-7H2O) and the ?lm was substituted for the magnesium sulfate of that ex was thereafter dried. The dried ?lm bearing approxi ample, with similarly satisfactory results. mately 3 milligrams of magnesium sulfate () Example 5 and 7 milligrams of sodium lauryl sulfate per square Example 1 was repeated except that calcium nitrate meter of ?lm surface had good ?lm slip as indicated by a ll) ?lm to ?lm coefficient of friction of 0.20 and ?lm to metal was substituted for the magnesiumsulfate of that example, coe?icient of friction of 0.15 and the ?lm showed no evi with similarly satisfactory results. ' dence of blocking. It was sealed to itself on a Simplex ADDITIONAL EXEMPLIFICATION bag machine to give excellent heat seals at temperatures To practice this invention using other Water-soluble as low as 100° C. A portion of the ?lm was formed into a bag, a head salts, other alkali metal salts of aliphatic hydrocarbon of lettuce was inserted in the bag, and the opening was , and/or other plastic ?lms, merely substitute such thereafter sealed and the package was refrigerated at 40° materials for the corresponding materials of the fore F. There was no indication of fogging on the interior going examples. ‘ V of the bag. The invention claimed is: In a control experiment a second sample of regenerated 1. A transparent heat sealable plastic ?lm having on cellulose ?lm having the same vinylidene chloride co~ at least one surface a coating composition consisting es polymer coating was passed through an aqueous solution sentially of about 10 to 90 mol percent of a water-soluble containing only sodium lauryl sulfate (0.50% by weight) salt selected from the group consisting of a nitrate, ace and there was produced a sized ?lm bearing on the sur tate, halide and sulfate of a Group II metal and about face 16 milligrams per square meter of ?lm surface. 90 to 10 mol perecnt of an alkali metal salt of an aliphatic The ?lm also had very good slip and was non-block hydrocarbon sulfate wherein the hydrocarbon group con ing but fogged in several discrete areas because of non tains 8 through 18 carbon atoms, said coating being in uniform wetting when submitted to a test similar an amount to provide per square meter of the ?lm sur face from about 1 to about 25 milligrams of said Water to that described above wherein a wet product such as - lettuce was packaged and then refrigerated. It Was also soluble salt and said alkali metal salt. found that this sized ?lm did not heat seal well. Poor 2. A ?lm as in claim 1 wherein said water-soluble salt seals were obtained on the Simplex bag machine at tem is magnesium sulfate. 3. A ?lm as in claim 1 wherein said water-soluble salt peratures as high as 130° C. and the ?lms could be sealed in only a relatively narrow range. is . In still another control experiment, another sample 4. A ?lm as in claim 1 wherein said Water-soluble salt of the same coated ?lm was drawn through an aqueous is . solution containing only magnesium sulfate. The solution 5. A ?lm as in claim 1 wherein said water-soluble salt did not wet the ?lm and it emerged essentially dry. No is calcium chloride. 6. A ?lm as in claim 1 wherein said water-soluble salt magnesium sulfate could be detected on the film surface 1170 and it fogged badly in the aforementioned test with a is calcium nitrate. moist product. 7. A film as in claim 1 wherein said alkali metal salt In a further set of control experiments sodium chlo is sodium lauryl sulfate. ride and were separately substituted for 8. A ?lm as in claim 1 wherein said ?lm is a vinylidene magnesium sulfate as in Example 1. These materials were chloride copolymer coated regenerated cellulose ?lm. not effective and fogging results paralleled those of the References Cited ?rst control. Example 2 UNITED STATES PATENTS 2,434,683 1/1948 Whitby et a1. ____ 252—16l XR Example 1 was repeated except that magnesium chlo 2,776,212 10/1956 Grifo ______252,——161 ride was substituted for the magnesium sulfate of that 2,835,595 5/1958 Salatiello ______99-174 example, with similarly satisfactory results. 3,222,191 12/1965 Steiner et al. ______99—174 Example 3 JAMES A. SEIDLECK, Primary Examiner. 55 Example 1 was repeated except that magnesium nitrate L. HAYES, Assistant Examiner.