US 3330720 A
Description (OCR text may contain errors)
July 11, 1967 E 1. STEVENS ETAL 3,330,720
CLOSURE LINER Filed May 18, 1965 INVENTORS falaz/ARUJ ZEz/f/v GOPDO/v Con//v United States Patent O 3,330,720 CLOSURE LNER Edward J. Stevens, Lake Elmo, and Gordon C. Brown, St.
Paul, Minn., assignors to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware Filed May 18, 1965, Ser. No. 456,628 6 Claims. (Cl. 161-162) This invention relates to closure liners that incorporate an innerseal. More particularly the invention relates t closure liners and innerseals that provide a secure, neatly sealed container and that expedite container filling and capping processes.
The use of innerseals-a separable facing part of a closure liner which is adhered over the container orifice and remains on the container when the cap with the rest of the liner is removed-has grown in popularity in recent years. In addition to providing added protection against contamination and against moisture changes during storage of the container, innerseals, since still adhered to the container after removal of the container closure, evidence the lack of tampering with the container or its contents. Containers sealed with innerseals have been found to have superior marketing appeal.
Nevertheless, the use of innerseals has been inhibited by difficulties in .forming a bond between the innerseal and container. In a conventional packaging process, the container lip is wet with a liquid adhesive immediately prior to capping the container with a closure lined by a liner that includes an innerseal. But in using this procedure, as a result of inability to wholly control the application of liquid adhesive, the -contents of a percentage of the containers being processed have been contaminated, a problem of special concern in the packaging of food and drugs, which are products otherwise quite adapted to the use of innerseals. Beside contamination of the container contents, the containers are made unsightly, process line interruptions are necessary, and there are added maintenance expenses with the capping machinery.
The innerseal of the closure liner of the present invention is adhered to the container top simply by pressure and accordingly eliminates the use of liquid adhesive. The surface of the innerseal that contacts the container top carries a pressure-activated adhesive that is non-tacky except for a short period of time during the capping operation, and then only in an area where it is pressed against the container lip. Accordingly, the liner is readily handled during storage and processing and the contents of the container never become adhered to the innerseal. Various degrees of adhesiveness can be provided including an aggressive adhesion such that the innerseal tears during removal.
In general, a closure liner of this invention includes a resilient, compressible backing to which is weakly adhered a sheet of innerseal membrane having on the exposed surface the previously noted layer of pressureactivated adhesive. This adhesive layer comprises a normally non-tacky matrix material in which are dispersed small pressure-rupturable capsules containing a fluid additive that combines with the matrix material to make it tacky. When a closure lined with a liner of this invention is rst tightened on a container in the capping operation, the capsules are ruptured in the area pressed against the container lip as a result of the compressive forces arising there. The liuid additive migrates out of the ruptured capsules and combines with the matrix material making it tacky whereby the innerseal is bonded to the container.
In a specific embodiment of the invention the adhesive layer comprises a film of a thermoplastic polymer that the bottle lip.
3533,72@ Patented July 11, 1967 is' plasticizable at room temperature and in which are d1spersed lcapsules containing a plasticizer or solvent for the polymer. Upon rupture of the capsules and migration of the plasticizer, the polymeric film layer is softened and becomes tacky.
In the drawings,
FIGURE 1 is an enlarged semi-diagrammatic view of a closure liner sheet construction of this invention;
FIGURE 2 is a screw cap in section and a spaced liner of this invention in elevation;
FIGURES 3 and 4 show a jar to which a screw cap having a liner of this invention is applied; FIGURE 3 is a vertical section with the screw cap in place; FIG- URE 4 shows the jar covered by the innerseal after removal of the screw cap.
The principal thickness and main body of the sheet construction 10 shown in FIGURE l is a resilient, compressible backing 11. Typically a form of pulpboard or newsboard having a thickness between 20 and 55 mils, the backing 11 absorbs sealing pressures and provides conformation to the irregularities of the top surface of Further, after the consumer ultimately removes the innerseal to obtain the containers contents, the backing, which remains in the closure when the closure is removed, continues to seal the container when the closure is replaced. A coating of wax 12 increases the impermeability of the member 11. As an alternative, the impermeability of the backing can also be improved with a lamination of metal foil or impermeable hlm to it, and instead of newsboard, the backing can be a resilient plastic film.
A variety of sheet materials are used as the innerseal membrane 13, depending principally on cost and the need for impermeability. Glassine is a common material but metal foils, which give the best vapor barrier, plastic films, other kinds of paper and impregnated paper, and combinations of such materials are also used. Any weak adhesive can be used to adhere the innerseal membrane 13 to the backing 11, but the already present wax coating 12 is inexpensive and adapted to the purpose.
The pressure-activated adhesive 14 is applied on one surface of the innerseal membrane typically as a thin non-tacky Iilrn of a thermoplastic polymer that becomes tacky when softened. Throughout this film is a dispersion of capsules which contain a softener or plasticizer for the particular polymer chosen. The capsule-containing film is normally coated on the innerseal from a liquid mixture prepared by adding capsules either in a dry powderlike form or in an aqueous slurry to an aqueous dispersion of the polymer. Because of the need to apply the capsule-containing mixture without pressure, Meyer bar and air-knife coating procedures are preferred.
Polymers can be chosen to provide different degrees of adhesion. In some cases it is desired that the innerseal, though tightly adhered to the container top, be smoothly removable without tearing. In other cases, to more fully evidence lack of tampering, it is desired that the innerseal tear as it is pulled from the container, leaving fibers on the container lip. For that situation a polymer and innerseal membrane sheet material having an appropriate [adhesive strength and cohesive strength respectively are chosen. In general, the minimum adhesion between the innerseal and container top that will satisfactorily retain the innerseal on the container when the cap is removed and that will provide a satisfactory resistance when the consumer peels the innerseal from the container has been measured as about 3A pounds/inch of width when the innerseal is pulled back from the surface to which it' is adhered at an angle of and at a rate of 12 inches per minute.
Polyvinyl acetate has been found to be a preferred polymer because it provides good adhesion and is also odor-free and non-toxic, making it especially useful in food and drug packaging. It may conveniently be applied by simple coating procedures and is readily plasticized. Alternatives to polyvinyl acetate and its copolymers include acrylates, polystyrene, polyvinylidene chloride, polyvinyl chloride, and their copolymers, polyvinyl alcohol, ethyl cellulose, cellulose acetate and cellulose nitrate. Rubber polymers in combination with an encapsulated tackiiier may also be used. Further, capsules with aqueous fills incorporated in a water-activated ladhesive or glue binder are useful. Capsules may also contain materials adhesive themselves.
Plasticizers or solvents are chosen on the basis of their compatability with the polymer that is to form the matrix, and, in addition, in food and drug packaging, plasticizers are chosen on the `basis of their purity and lack of odor. For polyvinyl acetate, diethyl phthalate has been found to be especially useful. Other plasticizers that might be used for polyvinyl acetate and 1its copolymers are diamyl phthalate, dibutyl phthalate, triethylene glycol di-2-ethylbutyrate, polyester plasticizer (such as Hercoflex 900), methyl phthalyl ethyl glycollate, tricresyl phosphate, and triphenyl phosphate. Plasticizers useful with other polymers include derivatives of adipic, benzoic, phthalic, sebacic, citric and phosphoric acids, glycol and :biphenyl compounds.
The pressure-rupturable capsules, which comprise thin, self-supporting, polymeric shells around particles of the desired liquid agent, are readily available and may be formed with a wide variety of aqueous or organic liquid lills. Many processes of capsule formation are known to art, as for example, the process described in the U.S. patent to Green, No. 2,800,457 or the process described in the U.S. patent to Raley, No. 2,766,478, or other known processes. Tough, useful capsules having good storage and handling characteristics have 'been found to be those having aminoplast polymer shell walls around nely divided particles of the liquid additive. Such capsules may be made by the procedure described in the copending U.S. patent application of G. W. Matson, Ser. No. 175,394, tiled Feb. 26, 1962, no abandoned.
In practicing this invention, capsules are preferred that have a diameter between about 50 and 170 microns. Capsules that are smaller than about 50 microns in diameter have been found to comprise too large a proportion of shell wall as compared to plasticizer to make their use ecient. Capsules larger than about 170 microns on the other hand have been found to be too easily ruptured during production of the liners and in processing land storage of nished liners. In addition, a liquid mixture containing large capsules is not conveniently coated with conventional coating apparatus. Within the broad preferred range, the best results are obtained when about 70 percent of the capsules are between about 90 and 120 microns.
Normally about 50 to 95 weight percent of a capsule is liquid ll. The capsules are added to the polymer in an iamount such that they will suiciently soften the polymer to provide adhesion while not plasticizing the polymer to such an extent that the polymer becomes stringy and loses its tack. With polyvinyl acetate, about 5 to 45 weight percent of the solids content of the adhesive mixture should comprise urea-formaldehyde capsules of diethyl phthalate.
Some rupture of capsules is expected and permissible. If care is taken in the mixing and coating processes, about l0 percent of the capsules may be expected to rupture during production of the liners. Another percent of the capsules maybe ruptured during winding and storage of the liner stock after its production, and in the further punching of liners from the liner stock.
In the usual practice of the present invention, a continuous web of a laminate sheet construction including a sheet of waxed resilient backing material such as waxed pulpboard to which a sheet of innerseal membrane material has been adhered by heating the wax, is coated on the exposed innerseal surface with the liquid capsule-containing mixture described above. After coating, the web is passed through an oven where the material coated is dried. The coating may vary in thickness, but it has been found that a coating of polyvinyl acetate having a thickness such that after drying it has a weight of about 1/2 to 11/2 grams/ 24 square inches is useful.
The finished liner stock is wound in rolls and supplied to packagers. To prevent the minor degree of blocking that may develop in the roll, a wax emulsion may be included in the adhesive coating in an amount comprising about 0.5-5 weight percent of the solids content of the coating mixture. As an alternative to supplying a coated laminate of backing and innerseal, a continuous web of innerseal stock separate from a backing may be coated and later adhered to a backing either `by the liner manufacturer or the Packager. Since heat is required to melt the wax in adhering the innerseal to the backing, it is somewhat preferred to coat after the innerscal and backing have been laminated. In some cases the innerseal and backing may not be adhered but be stamped into the cl-osure as separate parts.
In the packaging process, liners are punched from the stock int-o a container closure 4in the manner illustrated in FIGURE 2 with la liner 17 and screw cap 15. The container closure is then applied to the container. As the closure is tightened onto the container, as shown with the cap 15 and container 16 in FIGURE 3, the capsules are ruptured and the adhesive activated. In the case of polyvinyl acetate, after about 8 to 24 hours on the container, the polymeric lm layer has set up with full adhesion to the container lip.
The liner 17 should be of a size such that it fits frictionally within the closure. Then, when the closure is turned off the container, the backing 11 of the liner will turn with the closure, breaking the wax bond between it and the innerseal which remains fixed in place on the container as shown in FIGURE 4. As a further assistance in separating the backing and innerseal, the closure may be formed with an annular ridge as shown at 18 in FIG- URES 2, 3 and 4 of the drawings. The liner is punched into the closure past the ridge 18 and when the closure is removed from the container, the projecting ridge abuts the liner. The innerseal, adhered to the container, easily exes past the ridge, but the stiff backing is lifted away from the innerseal overcoming the relatively weak resistance of the wax bond.
The invention is further illustrated by the following examples.
EXAMPLE I An adhesive formulation was mixed using 40 parts of a 55 weight percent solids water emulsion of a low molecular weight copolymer of polyvinyl acetate and a maleate (Gelva TS 7l, manufactured by the Schawinigan Resins Corporation); 10 parts of urea-formaldehyde capsules having a diameter of nominally microns (70 percent of the capsules being between 90 and 120 microns) and containing diethyl phthalate in an amount comprising about 70 percent by weight of the capsules; and 10 parts water. This mixture was coated using a Meyer bar apparatus on a laminate of two-ply 47 pound glassine and 35 mil waxed pulpboard. The coated laminate was then passed through an oven having a temperature of about F. The coating, when dry, had a weight of 12 to 16 grains per 24 square inches. Liners were punched from the thus prepared stock into 4S mm. screw caps, and the caps tightened onto bottles with a torque of 30-inch pounds. When the caps were unscrewed after 24 hours, the glassine innerseal remained adhered to the bottle lip and could not be removed without tearmg it.
EXAMPLE n An adhesive mixture was prepared by dissolving 100 parts by weight of a copolymer of vinyl chloride and vinyl acetate having an average molecular weight of approximately 10,000 and including 85-88 percent vinyl chloride (Vinylite resin VYHH) in 300 parts of a 2:1 mixture of methyl ethyl ketone and toluene; adding parts of triethylene glycol di-Z-ethyl butyrate plasticizer (Flexal 3GH) and then adding 30 parts of urea-formaldehyde capsules having a diameter of nominally 100 microns (70 percent of the capsules being between 90 and 120 microns) and containing diethyl phthalate in an amount comprising about 70 percent by weight of the capsules. This mixture was coated on aluminum foil and dried. The coated foil was then pressed against glass for 24 hours at 250 pounds/square inch in a room having a temperature of 80 F. When foil was stripped from the glass at the rate of 12 inches/minute and at an angle of 165, a force of 2 pounds/ inch of width was required.
What is claimed is:
1. A sheet construction for use as a closure liner that may be adhered by pressure to a container over the container orifice comprising a resilient compressible backing to which is weakly adhered an innerseal membrane sheet having on the exposed surface a normally non-tacky selfsustaining continuous layer of thermoplastic polymer which is plasticizable at room temperature and becomes tacky when plasticized, small pressure-mpturable capsules containing plasticizer for the polymer being dispersed in said layer whereby when the innerseal surface of the liner is pressed against a container lip the polymer is made tacky in the area of pressure and the liner is adhered to the container.
2. A sheet construction for use as a closure liner that may be adhered by pressure to a container over the container orifice comprising a resilient compressible backing that is between about and 55 mils in thickness and carries on one surface a layer of wax, and an innerseal membrane sheet weakly adhered to the backing by the wax layer and having on the exposed surface a normally non-tacky layer of polymeric material based on polyvinyl acetate, small pressure-rupturable capsules between about 50 and 170 microns in diameter and containing a plasticizer for polyvinyl acetate being dispersed in said layer whereby when the innerseal surface of the liner is pressed against a container lip the polyvinyl acetate is made tacky in the area of pressure and the liner is adhered to the container.
3. The sheet construction of claim 2 in which the pressure-rupturable capsules comprise an aminoplast shell filled with diethyl phthalate.
4. A sheet construction for use as a closure liner that may be adhered by pressure to a container over the container orifice comprising a resilient compressible backing to which is weakly adhered an innerseal membrane sheet having on the exposed surface a normally nontacky continuous self-sustaining polymeric layer which is plasticizable at room temperature and becomes tacky when plasticized, small pressure-rupturable capsules containing a substantially nonvolatile plasticizer for the polymer being dispersed in said layer whereby when the innerseal surface of the liner is pressed against a container lip the polymeric layer is made tacky in the area of pressure and the liner is adhered to the container.
5. A sheet construction adapted for use as an innerseal in combination with a resilient compressible backing to complete a closure liner that may be adhered by pressure to a container over the container orifice, said sheet construction comprising a thin sheet having on one surface a normally non-tacky continuous self-sustaining polymeric layer which is plasticizable at room temperature and becomes tacky when plasticized, and small pressure-rupturable capsules containing a plasticizer for the polymer dispersed in said layer whereby when the polymeric layer is pressed and the capsules ruptured said layer is made tacky in the area of capsule rupture.
6. A sheet construction adapted for use as an innerseal in combination with a resilient compressible backing to complete a closure liner that may be adhered by pressure to a container over the container orifice comprising a thin sheet having on one surface a normally nontacky continuous self-sustaining polymeric layer which is plasticizable at room temperature and becomes tacky when plasticized, and small pressure-rupturable capsules containing a plasticizer for the polymer dispersed in said layer whereby when the polymeric layer is pressed against a container lip said layer is made tacky in the area of pressure and the sheet construction is adhered to the container.
References Cited UNITED STATES PATENTS JOSEPH R. LECLAIR, Primary Examiner.