JP2938186B2 - Resealable packaging material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Flexible packaging materials comprising layers of a thermoplastic polymer are used to package a variety of articles, especially food products. For example, cereals, potato chips and other snack foods are packaged with such materials. The packages are formed on a packaging machine in which the packaging material is sealed to itself by heated sealing jaws. However, once the package is opened by pulling away one of its heat seals, usually at the top of the package, the heat seal cannot be resealed without the application of heat and pressure. The present invention provides a flexible packaging material that can be resealed by the application of pressure only in the area of the seal formed by the packaging machine.

The material of the present invention comprises a base layer, an adhesive layer adjacent to the base layer, and a skin layer covering the adhesive layer. When the seal formed by sealing the packaging material to itself is pulled apart, the adhesive is exposed at the surface of the sealing area, thus allowing the material to itself in the sealing area by the application of only hand pressure. The package is resealed so that the package can be reclosed.

The base layer may be made of any material commonly used for flexible packaging applications, such as plastic film, metal foil, paper or a combination thereof. The plastic film base layer may be a single layer or multiple layers, and may be stretched or unstretched. The film can be a polyamide, polyester, or olefin polymer or copolymer. Suitable base layers include poly (ethylene terephthalate) film, paper, oriented polypropylene film, and nonwoven materials.

As used herein, the term "sticky adhesive"
In the practice of the present invention, it refers to an adhesive that forms a resealable joint at room temperature by the application of only manual pressure. The reseal strength is preferably about 0.5 to 4 pounds per inch (0.1 to 0.7 kg / cm), and more preferably about 1 to 2 pounds per inch (0.18 to 0.36 kg).
/ cm). Such adhesives may include cold seals and tack lacquers. A cold seal is formed from an elastomeric aqueous latex emulsion. The tacky adhesive is preferably a pressure sensitive adhesive that is a blend of an elastomer and an adhesion promoter. The pressure sensitive adhesive is preferably about 40 to 80 percent thermoplastic elastomer,
20 to 60 percent of tackifier, and up to about 15 percent of other ingredients, such as fragrances and conventional additives,
For example, it consists of an antioxidant and an oil.

If the adhesive layer in the packaging material includes a fragrance, the fragrance is substantially encapsulated in the packaging material until the material is formed into a package and the package is opened. So it's not so noticeable. When the package is opened, the fragrance is dissipated, thus enhancing the appeal of the article in the package. Best results are obtained with an oil-based fragrance that is absorbed by the elastomer component of the adhesive.

Particularly suitable elastomers are the styrene-butadiene copolymer sold under the trademark Stereon by Firestone and the Kraton trademark by Shell Chemical Company.
And styrene copolymers such as the styrene-isoprene copolymer sold under Other suitable elastomers include polyurethanes and ethylene-vinyl acetate copolymers having a vinyl acetate content of about 18 percent or more.

The tackifier can be any tackifier commonly used with elastomers to make pressure sensitive adhesives. Suitable tackifiers are sold by Arizona Chemical Company under the trademark Zona
Includes terpene resins, such as those sold under tac, and petroleum hydrocarbon resins, such as those sold under the trademark Escorez by Exxon Chemical Company.

The pressure sensitive adhesive is preferably co-extrudable. The co-extrudability of a pressure sensitive adhesive can be enhanced by utilizing a thermoplastic elastomer having a low melt index and by increasing the proportion of the elastomer in the adhesive. The melt index of the adhesive is preferably less than 30, for coextrusion with conventional polyolefins,
More preferably, it is less than 10.

Pressure-sensitive adhesives, or other adhesives, other than extrusion,
It can also be applied to the substrate by methods such as adhesive lamination, gravure, flexon or silk screen printing, Meyer rod, spray coating or vacuum deposition. The adhesive is in the form of a 100% solid,
Alternatively, it can be applied by using water or a solvent as a vehicle.

Since the adhesive is only needed in the area where the package will be opened, the adhesive need only be applied in a superimposed manner only where it is needed. Similarly, the skin layer can be applied over the adhesive alone, such as by printing the adhesive layer and the skin layer sequentially on the base layer using a central contact pressure press. However, the skin layer may be similarly applied to other surface areas, including the entire surface of the packaging material.

Alternatively, the adhesive may be applied to the substrate by transferring it from a supporting medium. This technique is commonly used in the manufacture of metallized packaging materials to transfer a thin metal layer, such as a thin layer of metal produced by evaporation, from one substrate to another. You. The skin layer can also be transferred with an adhesive by this technique. Preferably, the support medium is paper coated with a silicone release agent. The paper substrate may be reused and may be an endless belt in a continuous process. When the paper supporting the adhesive layer is wound up, it is preferable that both sides are coated with a release agent to prevent blocking.

The thickness of the adhesive layer is preferably about 0.1 to 2.0.
Mill (2.5-51 microns), more preferably about 0.3
To 0.7 mils (7.6 to 18 microns).

The epidermal layer performs two important functions. First, it creates a coefficient of friction on the surface of the packaging material such that the packaging material can be processed in a conventional packaging machine. Second, when the seal is pulled apart, the skin layer breaks so that the adhesive is exposed at the surface of the seal. There are two mechanisms by which this can occur. In one mechanism (first mechanism), the skin layer is ruptured by shearing use of a sealing jaw in the packaging machine,
Thus, there is an adhesive at the interface where the packaging material is sealed to itself. The skin layer is preferably
Explodes over most of the area of the seal. This mechanism allows an initial seal to be made with the adhesive alone, thereby eliminating the need to apply heat to the sealing jaws. In another mechanism (second mechanism),
The skin layer is itself heat-sealed, preferably by using a planar sealing jaw, and ruptures until the skin layer reaches the adhesive layer when force is first applied to separate the heat seal. Until then, it has remained virtually intact. The skin layer then delaminates from the base layer to the end of the seal when additional force is applied. Delamination occurs between the skin layer and the adhesive layer, between the adhesive layer and the base layer, or preferably on the surface passing through the adhesive layer, and thus the seal area after the adhesive has been separated from the seal. On both surfaces. The latter type of delamination is facilitated by heating both sealing jaws as the heat seal is formed.

When the second mechanism is employed, the adhesive is a co-extrudable pressure-sensitive adhesive, which, along with the skin layer,
Preferably, it is coextruded with or onto the substrate. When the base layer is coextruded with the skin layer and the adhesive layer, a blown film coextrusion method or a cast film coextrusion method can be employed. The extrudate may include multiple layers of pressure sensitive adhesive.

The skin layer may be a layer of a thermoplastic film-forming polymer commonly used as a heat seal layer in packaging materials. The polymer preferably has a tensile strength such that, at the desired thickness of the skin layer, the heat seal is easily opened, preferably by a force of about 0.4 to 0.9 kg / cm. Also preferably, the polymer has a low elongation at break, preferably less than 400 percent. The polymer is
Preferably, it is a copolymer of ethylene and an ethylenically unsaturated comonomer selected from the group consisting of carboxylic acids and esters, salts and anhydrides of carboxylic acids.
Examples of such comonomer components include acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, methyl methacrylate, vinyl acetate, and maleic anhydride. Such copolymers are well-known commercial polymers commonly used to form heat seal layers in flexible packaging materials. Other polymers, such as polyolefins, may be blended with the copolymer in small amounts. Preferably, the copolymer is an ionomer.
The term ionomer is a film-forming copolymer of an olefin and an ethylenically unsaturated monocarboxylic acid, wherein at least 10% of the carboxylic acid groups have metal ions,
It preferably refers to those neutralized by zinc. Olefin has the formula RCH = CH _2, R is an alkyl group containing a carbon atom to which or eight hydrogen. The olefin is preferably ethylene. The carboxylic acid is preferably acrylic acid, methacrylic acid or methyl methacrylic acid. The proportion of olefin units in the ionomer is at least 50 mole percent, preferably at least 80 mole percent. Suitable ionomers are described in U.S. Patent No. 3,355,319 and have the trademark Surly.
Commercially available as n.

The skin layer is preferably relatively thin, and thinner than the heat seal layer of conventional packaging materials, and thus preferably breaks when the sealing jaws are applied or the seal is pulled apart. The thickness of the skin layer is preferably about 0.05 to 0.5 mil (1.3 to 13 microns), more preferably about 0.075 to 0.2 mil (1.9 to 5 microns).

If the first mechanism is employed, the skin layer will be in contact with any material that will produce the desired coefficient of friction and will be ruptured sufficiently by the sealing jaws so that the adhesive is present at the sealing interface. You may. In addition, the material may be finely divided solid particulates (dust), such as talc or starch particles. The particles can be applied to the adhesive layer by conventional methods, such as using an Oxydry ™ device.

The skin layer and the layer of pressure-sensitive adhesive can be coextruded together, generally by conventional coextrusion coating techniques, to form the packaging material of the present invention. Preferably, the components of the pressure sensitive adhesive are maintained under an inert atmosphere, such as nitrogen, to minimize oxidation at extrusion temperatures that causes decomposition and odor.

The packaging material may be sealed by the methods typically used to seal flexible packaging material in a packaging machine. If the first mechanism is employed, the packaging material is preferably sealed by a sealing jaw that shears the skin layer, as described in US Pat. No. 4,582,555. Shearing promotes rupture of the skin layer and exposure of the adhesive upon opening the seal. When the first mechanism is employed, the temperature of the sealing jaw is preferably lower than the melting point of the skin layer. In some embodiments, the jaws are at ambient temperature so that the material is effectively cold sealed rather than heat sealed. If a second mechanism is employed, the skin layer is heat sealed to itself at a conventional temperature of about 230 ° F (110 ° C). In either arrangement, the seal has sufficient joint strength to prevent the package from opening during normal handling. Preferably, the bond strength is at least about 2 pounds per inch (0.4 kg / cm). However, it is also preferred that the seal be easily opened by being pulled apart by hand, so that the bond strength is preferably less than about 5 pounds per inch (0.9 kg / cm).

Until the skin layer is broken, the coefficient of friction of the skin layer is determined by the material forming the skin layer. Thus, the materials of the present invention can be used in conventional packaging machines, such as molding, filling and sealing machines, in the same manner as conventional flexible packaging materials. Materials having a tacky adhesive on their surface could, of course, not be used in such machines, due to the high coefficient of friction of the adhesive. The ability of a packaging machine to use the packaging material is referred to in the art as machinability. The material of the present invention has good machinability. In a preferred embodiment, each surface of the material has a coefficient of friction for stainless steel of about 0.1 to 0.5, which is within a preferred range for machinability.

Example 1 A laminate was made by simultaneously extruding a skin layer and a pressure sensitive adhesive onto a base layer. The base layer was a poly (ethylene terephthalate) film (Dupont Myler) having a thickness of 12.2 microns. The skin layer extruded at 218 ° C
It consisted of polystyrene (Dow Styron625). About 163
The pressure sensitive adhesive extruded at 70 ° C is a 68% styrene-isoprene-styrene block copolymer (Shell Kr
aton D-1107), 30% aliphatic petroleum hydrocarbon resin (Exxon Escorez1310) and 2% phenolic antioxidant (Ciba Geigy Irganox 1010). The hydrocarbon resin was injected into the extruder barrel. The thickness of the polystyrene layer was about 0.1 mil (2.5 microns) and the thickness of the pressure sensitive adhesive layer was about 0.5 mil (12.7 microns). U.S. Patent No.
This was sealed against itself using a heat seal jaw as described in US Pat. No. 4,582,555 by applying a pressure of 80 psi (5.6 kg / cm) at a temperature of 110 ° F. for 2 seconds. A force of 3.3 pounds per inch (0.59 kg / cm) was required to open the heat seal. The opened heat seal was then resealed, opened again 20 times and resealed by applying a pressure of 14 psi (0.99 kg / sq cm) at room temperature within 0.1 seconds. The average reseal strength was 1.03 pounds per inch width (184 grams / cm).

This example illustrates that the packaging material of the present invention is particularly suitable for packaging cereal and snack foods as a package that can be easily resealed after each intermediate use.

Example 2 A laminate was made by applying a coat of a molten pressure sensitive adhesive onto a base layer, allowing the adhesive to cool, and then applying a coat of polyvinylidene chloride (PVDC) to the surface of the adhesive. . The coats were applied using a Meyer rod. The base layer was a 1 mil (25 micron) thick poly (ethylene terephthalate) film. Heat the pressure-sensitive adhesive to about 150 ° C and apply about 14
It was applied with a pound cord weight (23 grams per square meter). The pressure sensitive adhesive, commercially available from Findley Adhesives, has a viscosity at 150 ° C. of about 42,000 centipoise. PVDC was applied at a coat weight of about 4 pounds per series (7 g per square meter) and dried at about 93 ° C. The laminate was then sealed to itself using sealing jaws providing high shear. The jaws were heated to 71 ° C and 80 psi (5.6 kg / sq.
m) applied at pressure. Opening the seal required 3.2 pounds per inch (0.57 kg / cm) of force.
The opened seal was then resealed, opened 20 times and resealed by applying a pressure of 14 pis (0.99 kg / sq cm) at room temperature within 1 second. The average reseal strength was 0.53 pounds per inch (95 grams per cm).

This example illustrates the manufacture of a packaging material of the present invention employing a first mechanism. This material can be used to package packaged cereals and snack foods that can be easily resealed after each intermediate use.

Example 3 A laminate was made by co-extruding a skin layer and a pressure sensitive adhesive onto a high density polyethylene film having a thickness of 2 mils (51 microns). The skin layer extruded at 230 ° C. consisted of an ionomer commercially available from DuPont. Pressure sensitive adhesives extruded at 196 ° C. are commercially available from Findlay Adhesives. This adhesive has a viscosity at 177 ° C. of more than one million centipoise. The adhesive weighed 4 pounds per series (7 grams per square meter). The laminate was sealed to itself by applying a pressure of 40 psi (2.8 kg / cm) for 1 second using flat sealing jaws, one jaw at room temperature and the other at 116 ° C. Was. 2.4 pounds per inch (0.4 pounds per inch)
A force of 3 kg / cm) was required. The opened heat seal was then opened again 20 times and resealed by applying a pressure of 14 psi (0.99 kg / sq cm) at room temperature within 1 second. The average reseal strength was 1.03 pounds per inch (184 grams per cm).

This example illustrates the manufacture of a packaging material of the present invention employing a second mechanism. This material can be used to package cereal and snack foods in packages that can be easily resealed after each intermediate use.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Bower, William B. 94306, Palo Alto, Fane Street, California 462 (72) Inventor Yanidis, Apostle 94703, California, United States 94703, Berkeley, Virginia Street 1737 ( 56) References JP-A-1-167707 (JP, A) JP-A-61-14943 (JP, A) JP-A-61-83039 (JP, A) Full-open sho-59-32659 (JP, U) Full-open Sho 59-121368 (JP, U) Shogun 57-21703 (JP, Y2) US Patent 3,542,210 (US, A) US Patent 4,763,601 (US, A) (58) Fields investigated (Int. Cl. ⁶ , DB Name) B32B 1/00-35/00 B65D 65/40

Claims (20)

(57) [Claims] 1. A flexible packaging material comprising a base layer, a layer of pressure-sensitive adhesive adjacent to the base layer, and a skin layer covering the pressure-sensitive adhesive layer, wherein each surface of the packaging material comprises Has a coefficient of friction such that it can be machined in the machine; the material has an initial bond strength that is sealed against itself by the sealing jaws of the packaging machine and remains closed during normal handling. The package can be formed with a seal that can be easily peeled off by hand for opening; this skin layer breaks when the seal is peeled off, exposing the adhesive to the surface of the seal area, Flexible packaging material characterized in that the packaging material can be sealed against itself in the area of the seal by the application of only hand pressure to reclose the package. 2. The friction coefficient against stainless steel is about 0.1.
And the packaging material of claim 1 which is between 0.5 and 0.5. 3. The packaging material according to claim 1, wherein the adhesive comprises a fragrance. 4. The packaging material according to claim 1, wherein the pressure-sensitive adhesive is a pressure-sensitive adhesive. 5. The skin layer and the layer of pressure-sensitive adhesive are coextruded together, with or onto the base layer, and the skin layer is torn when the seal is pulled apart, down to the adhesive layer and then from the base layer. 5. The packaging material of claim 4, wherein the packaging material is broken by delamination, thereby exposing the pressure sensitive adhesive in the sealed area. 6. The packaging material of claim 5 wherein the pressure sensitive adhesive comprises about 40 to 80 percent of a thermoplastic elastomer and about 20 to 60 percent of a tackifier. 7. The packaging material according to claim 5, wherein the skin layer is a layer of a thermoplastic film-forming polymer capable of forming a heat seal when the jaws have a temperature of 230 ° F. (110 ° C.). 8. The method according to claim 7, wherein the skin layer comprises an ionomer.
Packaging material. 9. The packaging material of claim 7 wherein the heat seal has an initial bond strength of about 2 to 5 pounds per square inch (0.4 to 0.9 kg / cm). 10. The packaging material of claim 9 wherein the resealable bond formed by the pressure sensitive adhesive has a strength of about 0.5 to 4 pounds per inch (0.1 to 0.7 kg / cm). 11. The packaging material of claim 7 wherein the skin layer has a thickness of about 0.05 to 0.5 mil (1.3 to 13 microns). 12. The pressure-sensitive adhesive layer having a thickness of about 0.1 to 2.0.
12. The packaging material of claim 11, which is a mill (2.5 to 51 microns). 13. The packaging material of claim 1, wherein the skin layer is broken by the sealing jaws such that there is an adhesive at the interface where the packaging material is sealed to itself. 14. The packaging material according to claim 13, wherein the temperature of the sealing jaw is lower than the melting point of the substance forming the skin layer. 15. The packaging material of claim 13 wherein the seal has an initial bond strength of about 2 to 5 pounds per inch (0.4 to 0.9 kg / cm). 16. The packaging material of claim 15 wherein the strength of the resealable bond formed by the adhesive is from about 0.5 to 4 pounds per inch (0.1 to 0.7 kg / cm). 17. The packaging material according to claim 13, wherein the skin layer is composed of finely divided granules. 18. The packaging material of claim 17, wherein the particulate matter is talc or starch particles. 19. The method of forming a packaging material according to claim 13, comprising transferring a layer of adhesive from a support medium to a base layer. 20. The method of claim 19, wherein the skin layer is transferred to an adhesive-backed substrate and the support medium is a paper coated with a silicone release agent.