WO2001014477A1

WO2001014477A1 - Method for latex-free cold sealing and compositions used therein

Info

Publication number: WO2001014477A1
Application number: PCT/US2000/023486
Authority: WO
Inventors: Christine Bentley; Nhan V. Le; Thomas Cusack
Original assignee: Croda Adhesives, Inc.
Priority date: 1999-08-26
Filing date: 2000-08-25
Publication date: 2001-03-01

Abstract

This invention is directed to a method for cold sealing a plurality of substrates, typically plastics, foil, paper or combinations thereof, utilizing a cold-sealable adhesive composition that is free of natural latexes ('natural latex-free'). The present invention is also directed to a natural latex-free, cold-sealable adhesive composition that as used therein comprising a latex polychloroprene in the range between about 40% to 100% by weight and a tackifier resin dispersion in the range of about 60% to 0% by weight. In another embodiment, the present invention is directed to a sealed package, wherein the package is sealed in accordance with the method and/or composition of the present invention. A cold seal adhesive composition of the present invention is particularly suitable for use in high-speed printing press and preferably by means of the forward gravure method.

Description

METHOD FOR LATEX-FREE COLD SEALING AND COMPOSITIONS USED THEREIN

BACKGROUND

A. Field of the Invention

This invention relates to a method for cold sealing a plurality of substrates, typically plastics, foil, paper or combinations thereof, utilizing a cold- sealable adhesive composition that is free of natural latexes ("natural latex-free").

The present invention is also directed to a natural latex-free, cold-sealable adhesive composition that is used therein. In another embodiment, the present invention is directed to a sealed package, wherein the package is sealed in accordance with the method and/or composition of the present invention. The method and compositions of the present invention are particularly useful in the food and medical packaging industries since they eliminate any potential risk for severe allergic reactions by persons who are allergic to natural latex, and who handle the cold-sealed packaging or its contents.

B. Background

Plastic, foil and paper structures are used as mono-webs or laminates in the food, medical and industrial packaging industries for the wrapping and protection of the vast majority of foodstuffs, medical products, and for the protection of general goods such as books and cassettes. The laminates may be formed from combinations of different plastics, plastics and metal foils, or plastics and paper. Typically, the goods to be sealed are wrapped in the above-described mono-web or laminate structures and then sealed by welding with heat and pressure, or by activating a heat- seal adhesive with heat and pressure, or by the application of pressure alone. The wrapping and sealing of confectionery is of special concern in the food packaging industry because the quality of the final product is affected by heat. This is particularly true for chocolate-based products. Thus, there is a need for a sealing process that does not require heat. High-speed wrapping facilities that rely on heat sealing present additional problems. The sealing machinery must cope with high throughputs. Moreover, the sealing machinery must first reach a suitable temperature and then maintain that temperature for a given throughput of wrapping material. This requires operator skill and a reliable temperature regulating system. Further, line breakdowns may cause heat sensitive food or medical products to remain stationary in close proximity to the heated sealing apparatus with consequent risk of heat damage. Thus, it is an object of the present invention to provide a sealing process that does not require strict temperature regulation and that does not cause heat damage to the product in the event of a line breakdown.

Heat sealing processes also present safety problems for operators. In changing the wrapping material, the operator must take great care to avoid coming into contact with heated surfaces. When wrapping material is inadvertently jammed over the heated surfaces, the operator must take additional care in removing the jam. The sealing machinery must be partly turned off to allow the heated surfaces to cool down sufficiently to safely allow the operator to remove the jam. Such incidents lead to decreased productivity and lower profits. Thus, it is an object of the present invention to provide a sealing process that does not expose operators to the risk of heat injuries. The traditional cold sealable adhesive composition avoids many of the problems associated with heat-sealing but has been found to present unacceptable health risks to a more-attuned food and health-care industry. In particular, the traditional cold-sealable adhesive composition is a colloid comprising natural rubber latex molecules dispersed in water containing a synthetic polymer of the acrylate family. For example, a typical composition is a dispersion of a synthetic polymer of styrene, acrylic acid and natural latex. The latex molecules interact with the synthetic polymer to produce a stable colloid. When the composition is applied to a suitable substrate such as SHD-film, plastic, paper or foil, it results in good bonding without excessive tackiness. Consequently reels of substrate coated with latex -based adhesive do not block when reeled up.

However, natural latex based adhesive formulations present numerous problems. Natural latex is extracted from tree sap collected from the rubber tree (Hevea brasiliensis). Sunshine, soil conditions, precipitation, wind shear, and plant disease all combine to ensure a high degree of unpredictability in the quality and quantity of the tree sap. Moreover, rubber tree plantations are frequently located in far flung locations and are reliant on poorly developed infrastructure. Natural phenomenon such as hurricanes, and man made disasters, such as wars, can also impact the supply of natural rubber latex. Consequently, the quality and availability of natural rubber latex can fluctuate dramatically.

Further, it has recently been determined that the proteins in tree sap of the rubber tree carry over into the latex produced therefrom and can cause severe allergic reactions, including death, in persons sensitive to these proteins. (Turjanmaa,

K., "Allergy To Natural Rubber Latex: A Growing Problem, " Ann Med (1994) 26(4):297-300, 297.) This is particularly a problem when foodstuff or disposable medical devices are packaged, using natural latex-based adhesives. In particular, the foodstuffs so packaged may contain minute amounts of the natural latex-based adhesive which is then ingested. In a person already sensitized to natural latex, even minute amounts of natural latex can lead to a cascade of events resulting in anaphylaxis and even death. Likewise, merely tearing open the packaging could be sufficient to release microscopic particles of the adhesive into the air which are then inhaled or which come into contact with the skin. In a sensitized person, the inhaled particles could lead to an anaphylactic reaction and possibly even death. Disposable medical products that are sealed in packaging using a natural latex-based adhesive would pose an even greater risk because they are usually administered to a person whose health has already been compromised. Accordingly, it is an object of the present invention to provide a cold seal, natural latex-free adhesive composition for use in the food packaging, health-care and other industries.

In response to the above needs, the adhesive industry has developed a cold seal, natural latex-free adhesive composition that is based on acrylic polymers and pressure sensitive technology. However, these acrylic based adhesive compositions have many shortcomings. For example, when these acrylic based adhesives are applied to a substrate to make a converted film, their inherently tacky nature causes blocking (i.e., sticking) when the converted film is wound up into reels. Also, due to the blocking, an undesirable noise results when the reels of converted film are unwound at packing stations. Thus, there is a need for a synthetic cold seal, natural latex-free adhesive formulation which is "tack-free" and which does not cause blocking or unacceptable noise during unwinding.

SUMMARY OF THE INVENTION

The present invention has multiple aspects. In its first aspect, it is directed to a method for packaging a product or foodstuff in a substrate by cold- sealing using an adhesive that eliminates the risk to a downstream user of an allergic reaction to natural latex. Typically, the product is a manufactured product, preferably, a disposable medical product. The method comprises: a) providing a substrate for packaging a medical product or foodstuff, the substrate being one or more layers of plastic, a foil, a paper product or a combination thereof; b) applying as a pattern or overall coating on the substrate

("coated substrate") a cold-seal, natural latex-free, tack- free adhesive composition, the composition comprising a dispersion of a synthetic latex polychloroprene homopolymer or a copolymer thereof with maleate, styrene-butadiene or acrylic acid, in the amount of 40% to 90% by weight, and a tackifier dispersion in the amount of 60% to 10% by weight; c) positioning within the pattern or on the coating of the "coated substrate" a product or foodstuff that is to be packaged; and d) enclosing the product or foodstuff in the coated substrate by causing opposing sides of the coated substrate or patterns of the adhesive thereon to contact one another, whereby the positioned product or foodstuff is packaged in a manner that eliminates the risk of an allergic response to natural latex in a downstream user that contacts the packaging or the product or the foodstuff that was packaged therein. In its second aspect, the present invention is directed to a cold- seal, natural latex-free, tack-free composition for use in the above described method, comprising an aqueous dispersion of a synthetic latex polychloroprene or a copolymer thereof in the amount of 40% to 90% by weight of the adhesive composition, and a tackifier dispersion in the amount of 60% to 10% by weight of the adhesive composition. The cold seal adhesive composition of the present invention may further include zinc oxide in the amount of 0% to 10% by weight, preferably about 0.1% to 0.2% by weight. In its third aspect, the present invention is directed to a packaged product that is packaged by the method and/or composition of the present invention to eliminate the risk of an allergic reaction in persons allergic to natural latex. In particular, the present invention is directed to a packaged medical product or foodstuff wherein the packaging eliminates the risk of causing an allergic reaction in a person sensitive to natural latex, the packaging comprising a substrate that is sealed by a cold-seal adhesive composition that is natural latex-free, the substrate being foil, plastic, a paper product or a combination thereof, the cold-seal adhesive composition comprising from 40% to 100% by weight of an aqueous dispersion of synthetic latex polychloroprene, and from 60% to 0% by weight of a tackifier dispersion. Thus, the various embodiments of the present invention provide a cold- sealed, natural latex-free packaged product that eliminates the risk of an anaphylactic reaction by persons that are allergic to natural latex.

DETAILED DESCRIPTION OF THE INVENTION As described above, the present invention has multiple aspects. In its first aspect, the present invention is directed to an improvement in the flow wrap packaging process wherein a product is positioned and packaged on a continuously flowing roll of substrate. In particular, the present invention is directed to a method for packaging a manufactured product (e.g., a disposable medical product) or foodstuff in a substrate using a cold-seal adhesive composition that eliminates the risk to a downstream user of an allergic reaction to natural latex, comprising: a) providing a substrate for packaging a manufactured product or foodstuff, the substrate being one or more layers of a plastic, a foil, a paper product or a combination thereof; b) applying as a pattern (e.g., opposing rows) or as an overall coating on the substrate (collectively "the coated substrate") a cold-seal, natural latex -free, tack-free adhesive composition, the composition comprising a dispersion of a synthetic latex polychloroprene homopolymer or a copolymer thereof with maleate, styrene- butadiene or acrylic acid, in the amount of 40% to 90% by weight, and a tackifier dispersion in the amount of 60% to 10% by weight; c) positioning within the pattern or on the coating of the coated substrate a product or foodstuff that is to be packaged; and d) enclosing the product or foodstuff in the coated substrate by causing opposing sides of the coated substrate or patterns of the adhesive thereon to contact one another, whereby the positioned product or foodstuff is packaged in a manner that eliminates the risk of an allergic response to natural latex in a downstream user that contacts the packaging or the product or the foodstuff therein.

In the above described method, the first step comprises "providing a substrate for packaging a product or foodstuff, the substrate being one or more layers of plastic, a foil, a paper product, a lacquer coated film, paper product or a combination thereof." In accordance with the above-described step, the substrate is either a single monolayer web or a plurality of layers, typically in the form of a laminate, wherein the laminate has two to four layers. On occasion, the substrate is a combination of a laminate and a monolayer, or two laminates. The substrates that are suitable for use in the present invention are commercially available as pre-rolled substrates that are ready for adhesive application and/or pπnting. One class of suitable plastic substrates includes oπented polypropylene (OPP), a plastic film capable of being sterilized. Examples of commercially available OPPs that are suitable for use in the method of the present invention include TRESPAPHAN SHD, which is a coextruded biaxially oπented polypropylene that is commercially available from Hoechst Trespaphan UK Ltd., Wiltshire England. TRESPAPHAN SHD is a laminate packaging film having four layers comprising m sequence an outer high gloss layer, an OPP layer, a white opaque voided OPP core, and an outer heat sealable layer. Other suitable OPP films that are suitable for use in the method of the present invention are commercially available from Mobil Plastics, under the tradename BICOR® MB 200, which is a monolayer biaxially oπented transparent OPP film, OPPalyte® MW 247, which is a biaxially oπented polypropylene film that is a tπ- layer laminate having a white opaque cavitated OPP core sandwiched between two white OPP skins; BICOR® MB 400, which is a tπ-laminate film compπsmg an OPP core sandwiched between two heat sealable skins, and which can also function as a monofilm; OPPalyte® MW 747, which is a biaxially oπented polypropylene film that is a tπ-layer laminate having a white opaque cavitated OPP core sandwiched between an acrylic coating on one side and a polyvinyhdme chloπde coating on the other, and OPPalyte® MW 647, which is a biaxially oπented polypropylene film that is a tπ- layer laminate having a super white opaque cavitated OPP core sandwiched between two acrylic coatings Other suitable films for use in the present invention are polyester films such as sold under the MELINEX® tradename by ICI Films. An example of such a film is MELINEX® 840 which is a polyethylene terephthalate film that is pretreated on one side to give improved adhesion of vacuum-deposited metals, notably aluminum.

The thickness of the above-descπbed substrates vanes with the application Since the Applicants' claimed method employs commercially available paper, foils, plastic films, or laminates to package known products, one skilled the art would know what thickness of paper, foils, film or laminate to use to package these known products. Typically, the plastic films that are employed as substrates in the present invention have a thickness in the range of 15-60 gauge, wherein a "gauge" is equivalent to .25 microns.

The second step of the above described method comprises applying as a pattern or as a coating on the substrate a cold-seal, natural latex-free, tack-free adhesive composition, the composition comprising 40% to 90% by weight of a synthetic latex polychloroprene dispersion or a copolymer thereof, and 60% to about 10% by weight of a tackifier dispersion. In one embodiment, the pattern of adhesive is applied as substantially parallel opposing rows on the substrate, with a sufficient space between the rows for positioning (and enclosing) the substrate therebetween. By the term "opposing rows" is meant substantially parallel rows of adhesive that when brought in contact with one another under pressure would adhere (i.e., cold- seal) to one another. In the above described method, the adhesive composition is applied to the substrate using conventional application techniques. Typically, the adhesive can be printed on the substrate using flexographic or gravure printing techniques, preferably using the forward gravure method. In a state-of-the-art packaging facility, there are normally multi-station presses in which adhesives, inks and lacquers are printed onto the substrate, which may be paper, plastic or foil, lacquer coated or uncoated, or a combination thereof.

The adhesive is applied directly to the substrate inn a pattern (e.g., rows) or as a coating in sufficient amount to give a dry coat weight of at least 1.5 g per square meter. The substrate is then passed through a drying tunnel normally zoned with increasing increments of temperature as the substrate passes through the tunnel. Once the adhesive has dried at the far end of the tunnel, the converted substrate is rewound onto another reel such that the adhesive printed face is against the opposite face of the substrate, which opposite face is either untreated homopolymer film, foil, paper or laminate or one that has been treated with a release lacquer. Because of the "tack-free" nature of the cold-seal adhesive composition, the roll that has been printed with adhesive may be unwound without blocking and without creating the large amount of noise that is produced by the tacky adhesives of the prior art as they are pulled away from the opposing unprinted face. The use and application of release lacquers is well known in the art. Suitable release lacquers are commercially available from major ink companies, such as Manders Liquid Inks, Ltd., Wrexham England, under the tradename PML 18510.

In yet another embodiment of the above described method, the face of the substrate that does not receive the adhesive composition is printed with various trademarks and trade dress to identify the manufacturer of the product to be packaged therein. To this printed face, one can optionally apply a coating of a release lacquer to further protect the printing thereon.

In a particularly preferred embodiment of the above-claimed method, the substrate is wide enough to accommodate a plurality of substantially parallel rows of adhesive composition, wherein the adhesive bearing substrate is ultimately cut into parallel rows of substrate, each having two opposing patterns or rows of the cold-seal, natural latex-free, tack-free adhesive composition of the present invention.

In the above described method, the cold-seal, natural latex-free, tack- free adhesive composition of the present invention comprises a dispersion of a synthetic latex polychloroprene or a copolymer thereof in the amount of 40% to 90% by weight of the adhesive composition (hereinafter "by weight"), and an aqueous tackifier dispersion in the amount of 60% to about 10% by weight. Preferably, the synthetic latex polychloroprene dispersion or a copolymer thereof comprises 60% to 90% by weight of the adhesive composition, more preferably about 65% to 80% by weight. A suitable synthetic latex polychloroprene dispersion for use in the present invention is commercially available from DuPont Dow Elastomers L.L.C. under the tradename NEOPRENE® 750.

The adhesive composition of the present invention may be supplemented by the addition of dispersions or emulsions (collectively "dispersions" herein) of synthetic polymers other than polymers of polychloroprene or polymers thereof that improve the adhesion of the adhesive composition of the invention to polyolefin-based films. These other synthetic polymers are based upon acrylic monomers, or copolymers of acrylics, or homopolymers or copolymers containing vinyl acetate or styrene-butadiene copolymers. The glass transition temperature ("Tg") of the polymers in the aqueous dispersion are preferably within the range of -

25 C to +20° C, but more preferably within the range of -15° C to +10° C. Suitable dispersions of acrylic polymers for use in the cold-seal method and composition of the present include those dispersions sold by S.C. Johnson Company, under the JONCRYL® trademark, such as JONCRYL® 8050 (Tg -8° C) and JONCRYL® 74 (Tg -16° C). JONCRYL® 8050 and JONCRYL® 74 each have molecular weights greater than 200,000 Daltons, percent nonvolatiles of 42% and 47% respectively, and pHs of 7.8 and 8.3 respectively.

Other acrylic-based polymer dispersions that are suitable for use in the present invention are commercially available from B.F. Goodrich Company under the tradename HYSTRETCH™, such as HYSTRETCH™ V-43, HYSTRETCH™ V-43 FDA, HYSTRETCH™ T-35 and HYSTRETCH™ 2742. The synthetic latex dispersions that are sold under the HYSTRETCH™ mark contain fully saturated elastomeric terpolymers of acrylamide, ethyl acrylate and N-methylol-acrylamide. A preferred acrylic dispersion is HYSTRETCH™ V-43FDA which is FDA approved for use with food and drugs. The properties of HYSTRETCH™ V-43FDA include a total solids of 50%, a particle size of about 0.2 microns, a glass transition temperature Tg of -43° C, and a pH of 8.5.

Yet other suitable acrylic-based polymer dispersions that are suitable for use in the present invention are Lucidene™ 606LS (Non-Volatiles (NV) = 47%, pH = 7-9, and Tg = 11° C) and Lucidene 605 (NV = 50%, pH = 7-9, and Tg -42° C), both of which are commercially available from Morton Poylmers, Hounslow Middlesex England; Neocryl™ 1052 (NV = 49%, pH = 8-9, and Tg = 0° C) and

Neocryl™ 1044 (NV = 47%, pH = 9-10, and Tg = 11° C); and Zinpol™ 352 (NV = 41%, pH = 8-9, and Tg = 0° C).

The cold-seal, natural latex-free, tack-free adhesive composition that is used in the above-described method contains a second component comprising a tackifier dispersion in the amount of 60% to about 10% by weight, preferably 15% to about 10% by weight. The tackifier dispersion is an aqueous dispersion of a tackifier resin that is rosin, rosin ester, a hydrocarbon, a terpene, or a terpene-phenolic. One or more of the functions of the tackifier dispersion is to provide better tack and adhesion, better low temperature performance, better adhesion to difficult surfaces and/or better bond strength. Tackifier dispersions are commercially available in high solids (50-62%) with small particle size (less than 10 microns). Examples of suitable tackifier dispersions include RD 257, and RD333M which are commercially available from Blueminster Ltd. Kent, England. Other suitable tackifier dispersions include an aqueous dispersion of the glycerol ester of hydrogenated rosin, such as commercially available for Hercules Chemical Specialties, Wilmington DE under the tradename STAYBELITE® Ester 10-55WKX, having about 55% solids and an average resin particle size of less than 1 ("<1") micron; a synthetic resin dispersion based upon a high softening-point resin, such as commercially available for Hercules Chemical Specialties, Wilmington DE under the tradename TACOLYN® 1100, having about 55% solids and an average resin particle size of less than 1 ("<1") micron; an anionic aqueous dispersion of the glycerol ester of hydrogenated rosin, such as commercially available for Hercules Chemical Specialties, Wilmington DE under the tradename

FLORAL® 85-55WKX, having about 55% solids and an average resin particle size of less than 1 ("<1") micron; and an anionic, aliphatic hydrocarbon resin dispersion, such as commercially available for Hercules Chemical Specialties, Wilmington DE under the tradename PICCOTAC® 95-55 WK, having about 55% solids and an average resin particle size of less than 1 ("<1") micron.

The third step of the claimed method recites positioning on the substrate, or between the opposing rows of adhesive, a product (typically, a manufactured product; preferably a disposable medical product) or a foodstuff that is to be packaged. In one embodiment, the opposing rows of adhesive are spaced sufficiently far apart to allow the medical product or foodstuff that is placed therebetween to be enclosed by the substrate when the opposing rows are folded over so as to contact one another. Almost any foodstuff or disposable medical product is capable of being packaged by the method of the present invention. Typical foodstuffs that are packaged by the method and composition of the present invention include those foodstuffs sold in small packages and those foodstuffs having components (e.g., chocolate) wherein the use of heat sealing would damage the food or its aesthetic appeal. Examples of such foodstuffs include cookies, crackers, candy bars, snack bars, meal bars, candies and confectionaries. Typical medical products that are packaged by the method and composition of the present invention include those items that are sterile and/or intended for a single use, such as a bandage, a suture kit, a wound dressing, a gauze pad, a trachea ("trach") tube, a naso-gastric tube, a catheter, or a medicament. A preferred substitute for packaging medical products is a coated paper.

The fourth step of the claimed method comprises enclosing the product (e.g., a disposable medical product) or a foodstuff in the coated substrate by causing the adhesive on opposite sides of the product (such as printed on opposing rows or as coated on the substrate) to contact one another under pressure, whereby the medical product or foodstuff that is positioned therebetween is packaged in a manner that eliminates the risk of an allergic response to natural latex in a downstream user who contacts the packaging or the medical product or the foodstuff therein. When the substrate is large relative to the product or foodstuff to be packaged or contains more than two opposing patterns, rows or coatings of adhesive, the substrate is cut before or after placement of the foodstuff or product thereon so as to provide a plurality of substrate strips, each having a pair of opposing adhesive patterns, rows or coatings thereon. Cross-sealing the substrate strips to isolate an individually packaged foodstuff or medical product along the rows is achieved by bringing the opposing cold seal surfaces together under pressure. The result is a foodstuff or a medical device or medicament that is packaged in a manner that would not cause an adverse allergic response in a person that is allergic to natural latex.

Thus, in its second aspect, the present invention is directed to a cold- seal natural latex -free, tack-free composition for use in the above described method, comprising an aqueous dispersion of a synthetic latex polychloroprene or a copolymer thereof in the amount of 40% to 90% by weight of the adhesive composition, and a tackifier dispersion in the amount of 60% to 10% by weight of the adhesive composition. The synthetic latex and the tackifier dispersion components of the cold- seal, natural latex-free, tack-free adhesive composition of the present invention are as already described above.

Optionally, the cold seal adhesive composition of the present invention may further include zinc oxide in the amount of 0% to 10% by weight, preferably about 0.1% to 0.2% by weight. To optimize smooth application on high-speed printing presses, the cold-seal adhesive composition may also contain antifoam agents, wetting agents and stabilizers (e.g., anti-oxidants and bactericides) that are well known to those in the adhesive formulation art. Example of suitable antifoam agents include Rhodoline DF™ 6681, a mineral oil antifoam that is commercially available from RHODJA, and BEVALOID™ 6681, a mixture of mineral oils and non-ionic surfactants that is commercially available from Rhone-Poulenc Chemicals, North Humberside, England. Examples of suitable surfactants include sodium dioctyl sulphosuccinate, which is commercially available under the tradename AEROSOL ⁺ OT™ as a 75% formulation in ethanol from Cytec Industries B.V., Ka Botlek- Rotterdam, Havens, the Netherlands; or nonionic surfactants, such as those based upon ethylene oxide, which are commercially available from Sigma Chemicals, St. Louis, MO under the BRLT™ tradename, such as Brij™ 35, BRIJ™ 52, 56, 58, 72, 76,

78, 92, 96 or 99, or under the TWEEN™ tradename, such as TWEEN™ 20, 40, 60 or 80, or from Air Products Co. or under the SURFYNOL™ tradename, such as SURFYNOL™ 420, 440, 465, and 485.

Examples of suitable antioxidants include those sold under the tradename WINGSTAY L™, which is commercially available from Goodyear,

Columbus OH; or Naugard XL-1™ which is commercially available from Uniroyal Chemicals, CT; or IRGANOX® 1076, which is octadecyl-3-(3,5-ditert-butyl-4- hydroxyphenyl)-propionate, and which is commercially available from Ciba; or Alkanox 240™, which is tris(2,4-ditert-butyl-phenyl)phosphite and which is commercially available from Great Lakes Chemical Corp. or TOPANOL OC™, a hindered phenol type antioxidant which is commercially available from I.C.I, and LOWINOX CPL, the butylated reaction product of p-cresol with dicyclopentadiene, which is commercially available from Anchor Chemical (UK) Ltd., Manchester, England. An example of a suitable bactericide for use in the adhesive composition of the present invention is isothiazolaine derivatives, such as 1,2- benzisothiazolin-3-one, which is commercially available under the tradename PROXEL from Zeneca Biocides, England.

In its third aspect, the present invention is directed to a packaged product that is packaged by the method and/or composition of the present invention, whereby the packaging eliminates the risk of an allergic reaction in persons allergic to natural latex. In particular, the present invention is directed to a packaged medical product or foodstuff wherein the packaging eliminates the risk of causing an allergic reaction in a person sensitive to natural latex, the packaging comprising a substrate that is sealed by a cold-seal adhesive composition that is tack-free and natural latex- free, the substrate being foil, plastic, a paper product or a combination thereof, the cold-sealed composition comprising from 40% to 90% by weight of an aqueous dispersion of synthetic latex polychloroprene, or copolymer thereof and from 60% to 0% by weight of a tackifier dispersion. In this aspect of the present invention, the medical product and the foodstuff being packaged is the same as that already described above. Likewise, the cold-seal adhesive composition of the above described package may be in any of the embodiments described above, including the addition of other polymeric dispersions, antifoam agents, wetting agents and stabilizers (e.g., anti-oxidants and bactericides).

Thus, the various embodiments of the present invention provide a natural latex-free packaging, and a method and a composition for producing the same that substantially reduces the risk of an anaphylactic reaction by persons that are allergic to natural latex.

To test the integrity of the adhesive bond that is formed by the cold- seal adhesive composition of the present invention, the substrate bearing the adhesive composition is cold-sealed at ambient temperature (i.e. room temperature) and at a pressure of about 40 psi (pounds per square inch) and a dwell time of around 0.5 seconds. The strength of the adhesive bond is preferably ascertained by pulling the joint apart in the jaws of a tensometer at a rate of 300 mm/min and at a peel angle of 90°. Bond strengths that exceed three Newton's per 25 mm² are acceptable with or without substrate destruction. While the exact nature of the tensometer is not critical, a Monsanto T10 Tensometer is a suitable tensometer.

In addition to assessing bond integrity, the product should be investigated for residual odor and taint to ensure that adequate drying has taken place in the converting process.

The following examples provide specific but non-limiting embodiments of the various aspects of the present invention: EXAMPLE 1

To a vertical kettle mixer fitted with an anchor stirrer was added 300 g of JONCRYL 74™, an acrylic emulsion of 47% non-volatiles, having a MW (i.e molecular weight) of greater than 200,000 Daltons and having a glass transition temperature ("Tg") of -8° C to -16° C. JONCRYL 74™ is commercially available from Specialty Chemicals Mijdrecht bv, a subsidiary of S.C. Johnson Co., Racme, WI. To the kettle mixer was then added with stirπng 10 g of a 20% solution of a nonyl phenyl ethoxylate of (having an ethylene oxide number of 30) 1 g of the biocide l,2-benzιsothιazohn-3-one, which is commercially available under the tradename

PROXEL BD20™ from Zeneca Biocides, and the pH was then raised to eleven by the addition of an ammonia solution of specific gravity (SG) 0.91. To this was added 700 g of a chloroprene dichlorobutadiene copolymer latex (NEOPRENE® 750), which is commercially available from DuPont Dow Elastomers LLC. To the reaction mixture was then added 2 g of IRGANOX 1520D™, a hindered phenol type antioxidant which is commercially available from Ciba-Geigy, Hawthorne, NY, and 3 g of Rhodoline DF 6681, a mineral oil antifoam that is commercially available from RHODJA. A suitable alternative antioxidant is butylated hydrocytoluene (BHT). Stirπng was continued for a further 15 minutes to ensure a homogenous mix. The viscosity of the resultant mix was measured at 25° C using a BS4 flow cup and found to be 37 seconds The nonvolatile percentage was found to be 50% by gravimetπc measurement The adhesive was then applied using a Meyer bar at a coat weight of approximately 3 gsm dry (gsm = gram/m²) to (TRESPAPHAN SHD™ film) a treated oπented polypropylene (OPP) film which is commercially available from Hoechst Trespaphan U.K., LTD., Wiltshire England. Seal strengths, which were measured by peeling at a 90° angle at a jaw separation rate of 300 mm/minute using a Monsanto T10 Tensometer, were found to give 4.5 Newtons (N) to 5 5 Newtons (N)/25mm with adhesive failure. EXAMPLE 2

To a vertical kettle mixer fitted with an anchor stirrer was added 268 g of JONCRYL 74™, an acrylic emulsion of 47% non-volatiles, having a MW of greater than 200,000 Daltons and having a Tg of -8° C to - 16° C. JONCRYL 74™ is commercially available from Specialty Chemicals Mijdrecht bv., a subsidiary of S.C. Johnson Co., Racine, WI. To this kettle mixer was added with stirring 10 g of a 20% solution of a nonyl phenyl ethoxylate of Example 1. Thereafter, to the reaction mixture was added 1 g of l,2-benzisothiazolin-3-one, a biocide, which is commercially available under the tradename PROXEL BD20™ from Zeneca

Biocides. The pH was then raised to eleven by the addition of an ammonia solution of specific gravity 0.91. To the reaction mixture was then added 625 g of a chloroprene dichlorobutadiene copolymer latex (NEOPRENE® 750). To the reaction mixture was added 2 g of 4,6-bis(octylthiomethyl)-o-cresol, a hindered phenol type antioxidant which is commercially available from Ciba Specialty Chemicals, under the tradename

IRGANOX 1520 D™, followed by 42 g of RD 257™, which is an aqueous dispersion of rosin ester that is commercially available from Blueminster Ltd., Kent U.K. The mixture was then diluted by the addition of 25 g of water, and followed by the addition of 3 g of Rhodoline DF6681, a mineral oil anti-foaming agent. Stirring was then continued for a further 15 minutes to ensure a homogenous mix.

The viscosity of the resultant mix was measured at 25° C using a BS4 flow cup and found to be 30 seconds, non-volatile percentage was found to be 47% and the pH found to be 11. The adhesive was then coated on to treated SHD film using a Meyer bar at a coat weight of approximately 3 g/m². Seal strengths were then measured by peeling at 90° at a jaw separation rate of 300mm/minute using a

Monsanto T10 Tensometer and found to give 5 N to 6 N/25mm ². Blocking tests were carried out at five tons pressure for twenty-four hours at 25° C against a variety of release lacquers with the following results (Table 1). TABLE 1

A pilot trial was then conducted on a commercial printing press using a selection of films commonly encountered in the industry and the following seal values were obtained (Table 2).

TABLE 2

EXAMPLE 3

To a vertical kettle mixer fitted with an anchor stirrer was added 165 g of JONCRYL 74™ an acrylic emulsion of 47% non-volatiles, having a MW greater than 200,000 Daltons and a Tg of -8° C to -16° C. To the kettle mixer was then added with stirring 10 g of a 20% solution of the nonyl phenyl ethoxylate of Example 1, 3 g of zinc oxide and 1 g of the biocide l,2-benzisothiazolin-3-one which is commercially available under the tradename PROXEL™ from Zeneca Biocides, and the pH was then raised to eleven by the addition of an ammonia solution of specific gravity 0.91. To this was added 761.5 g of a chloroprene dichlorobutadiene copolymer latex (NEOPRENE® 750), 1.5 g of IRGANOX 1520 D™ BHT a hindered phenol type antioxidant, which is commercially available from Ciba-Geigy, Hawthorne NY, and

50 g of a 55% solids dispersion of a hydrocarbon resin of softening point 100° C. An alternative antioxidant is BHT. To this were added 3 g of a mixture of antifoam of the acetylinic or acetylinic diol and mineral oil types and 2 g of surfactant. Stirring was then continued for a further 15 minutes to ensure a homogenous mix. The viscosity of the resultant mix was measured as 28 seconds with a BS4 cup at 25 °C and the pH determined as 11.

A pilot trial was then conducted on a commercial printing press and the adhesive applied to metalised polyester. Seal strengths were measured after sealing at ambient temperature and 40 psi using a crimped jaw. Seal values of between 7.5

N/25mm² and 7.8 N/25mm² were achieved prior to adhesive failure. Cling values were determined after blocking against untreated OPP at 40° C, and ten tons pressure for 24 hours, and found to be from 0.55 N/25mm² to 0.75 N/25mm².

EXAMPLE 4

(Validation of Cold-seal Adhesive for Paper Packaging of a Medical Product)

A vertical kettle stirrer fitted with an anchor stirrer with 810 g of a chloroprene dichlorobutadiene copolymer latex (NEOPRENE® 750). To this was added with stirring 40 g of a 20% solution of a nonyl phenyl ethoxylate of thirty moles of ethylene oxide, 14 g of a hindered phenol type antioxidant and 160g of an acrylic emulsion, having 47% non-volatiles with a molecular weight (MW) greater than 2000,000 and a Tg of -8° C. Then, 2 g of an anti-foam agent of the silica type and 1 g of a biocide of the benzyl thioxazilone type were added, along with 3 g of a 15% zinc oxide solution. Stirring was then continued for a further 15 minutes to insure a homogeneous mix.

The viscosity of the resultant mix was measured at 25° C and found to be 160 mPas, the non-volatile percentage was determined to be 48% and the pH was determined to be 10. The adhesive was then coated onto a 22 lb basis weight medical grade paper (a type typically used for medical packaging) using a meyer bar at a coat weight of approximately 2 grams per square meter (gsm). After sealing two coated ends at ambient temperature and 40 psi, seal strengths were then measured using a flat jaw by peeling at a 90° angle with a jaw separation of 300 g/25mm using a Monsanto T10 Tensometer and found to give a seal strength of 90 g/25mm. Accelerated storage tests were carried out by subjecting the sealed samples of paper to a temperature of 65.5° C for 8 weeks. The results of the tests showed no deterioration of the seal strengths.

To seal a medical product, the above-described adhesive composition is applied to opposing ends of a medical grade paper product at approximately 2 g per square meter. The medical product to be package is positioned on the medical grade paper between the applied adhesive. The opposing ends of the medical grade paper are sealed at by having their adhesive bearing faces brought into contact with one another at ambient temperature under pressure (about 40 psi).

Claims

What is claimed is:

1. A method for packaging a product or foodstuff in a substrate by cold-sealing using an adhesive that eliminates the risk to a downstream user of an allergic reaction to natural latex, comprising: a) providing a substrate for packaging a product or foodstuff using the flow wrap packaging process, the substrate being one or more layers of plastic, a foil, a paper product or a combination thereof; b) applying as a pattern or overall coating on said substrate a cold-sealable, natural latex-free, tack-free adhesive composition, said composition comprising a dispersion of a synthetic latex polychloroprene homopolymer or a copolymer thereof with maleate, styrene-butadiene or acrylic acid, at 40% to 90% by weight, and a tackifier dispersion at 60% to 10% by weight; c) positioning within the pattern or on said coating a product or foodstuff that is to be packaged; and d) enclosing said product or foodstuff in said substrate by causing opposing sides of the coated substrate or patterns of the adhesive to contact one another, whereby said positioned product or foodstuff is packaged in a manner that eliminates the risk of an allergic response to natural latex in a downstream user contacting said packaging or the product or the foodstuff that was packaged therein.

2. The method of claim 1, wherein said substrate is one or more layers of plastic.

3. The method of claim 2, wherein one of said layers of plastic is an oriented polypropylene.

4. The method of claim 1, wherein said adhesive composition comprises a synthetic latex polychloroprene dispersion or a copolymer thereof that is about 65% to 80% by weight.

5. The method of claim 4, wherein said adhesive composition comprises a tackifier dispersion that is about 15% to 5% by weight.

6. The method of claim 5, wherein said adhesive composition further comprises zinc oxide in the amount of about 0.1% to 0.2% by weight.

7. The method of claim 6, wherein said adhesive composition further comprises an effective amount of a wetting agent, an antifoam agent, a stabilizer or a combination thereof.

8. A packaged medical product or foodstuff wherein the packaging is at low risk of causing an allergic reaction in a person sensitive to natural latex, said packaging comprising a substrate that is sealed by a cold-seal adhesive composition that is natural latex-free, said substrate being foil, plastic, a paper product or a combination thereof, said cold-sealed composition comprising an aqueous dispersion of synthetic latex polychloroprene or a copolymer thereof in the amount of from 40% to 90% by weight, and a tackifier dispersion in the amount of 60% to 10% by weight.

9. The packaged product of claim 8, wherein the product is a medical product.

10. The packaged product of claim 9, wherein the medical product is disposable.

11. The packaged product of claim 10, wherein the disposable medical product is a bandage, a suture kit, a wound dressing, a gauze pad, or a medicament.

12. The packaged product of claim 11, wherein said disposable medical product is a bandage.

13. The packaged product of claim 8, wherein said product is a foodstuff.

14. The packaged product of claim 13, wherein said foodstuff is a candy bar, a snack bar, a meal bar or cookies.

15. The packaged product of claim 14, wherein said foodstuff is a candy bar.

16. The packaged product of claim 13, wherein said foodstuff is a confectionary.

17. A cold-seal, natural latex-free, tack-free adhesive composition comprising an aqueous dispersion of a synthetic latex polychloroprene or a copolymer thereof in the amount of 40% to 90% by weight, and a tackifier dispersion in the amount of 60% to 10% by weight.

18. The adhesive composition of claim 17, further comprising zinc oxide in the amount of 0% to 10% by weight.

19. The adhesive composition of claim 18, further comprising an effective amount of an anti-foam agent or a wetting agent.

20. The adhesive composition of claim 19, further comprising an effective amount of a stabilizer.

21. The adhesive composition of claim 20, wherein said aqueous dispersion of a synthetic latex polychloroprene or a copolymer thereof in the amount of 65% to 80% by weight.

22. The method of claim 1, wherein said product is a disposable medical product.

23. The method of claim 22, wherein said substrate is a coated paper.