WO1989007077A1 - Film thermoretractable - Google Patents

Film thermoretractable Download PDF

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Publication number
WO1989007077A1
WO1989007077A1 PCT/US1988/000320 US8800320W WO8907077A1 WO 1989007077 A1 WO1989007077 A1 WO 1989007077A1 US 8800320 W US8800320 W US 8800320W WO 8907077 A1 WO8907077 A1 WO 8907077A1
Authority
WO
WIPO (PCT)
Prior art keywords
layer
tube
container
vinyl acetate
tubular unit
Prior art date
Application number
PCT/US1988/000320
Other languages
English (en)
Inventor
Joseph-Zu Sun
Original Assignee
Sun Joseph Zu
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sun Joseph Zu filed Critical Sun Joseph Zu
Publication of WO1989007077A1 publication Critical patent/WO1989007077A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/16—Layered products comprising a layer of synthetic resin specially treated, e.g. irradiated

Definitions

  • U.S. Patent No. 3,953,557 issued to Brax et al., discloses a sequential process of coating a PVDC middle layer and a thin outer EVA layer on to an extruded and subsequently irradiation crosslinked thick first inner EVA layer.
  • Brax et al empolyes the sequential coating process to avoid the irradiation of their PVDC layer, which degrades when subjected to high irradiation dosage. They use an electron beam device of 0.5 mev without voltage adjustment, thereby all three layers in their multilayered laminate would be penetrated resulting in a degraded PVDC layer when subjected to irradiation in integral.
  • the packaging film described in this patent does not possess a shipping abuse resistant outer layer which renders the film susceptible to loss of integrity through abrasion.
  • the cross linked first inner layer is hard to self-weld to reduce the effect of breakage by puncturing in the process of packaging.
  • the process of manufacturing the film of the prior art, heretofore identified is a coating process which is more expensive and energy consuming than a coextrusion process in that more dies are required and a large amount of plasticizer is necessary in its production. The latter step reduces the oxygen and water barriers of the inner Saran layer.
  • U.S. Patent No. 4,225,373, issued to Bieler et al. discloses a method to improve the high temperature seal strength of a container formed from Brax's tubular laminate by post irradiating the seal area induce crosslinking between the two layers that form the seal. Bieler's irradiation penetrates all three layers of the laminate to reach the interface. Hence, she has to limit the post irradiation to the seal area to avoid degradation of the saran middle barrier over the whole container.
  • Widiger et al. teach an EVA blend saran EVA blend laminate. Without significant crosslinking of any of the EVA blend layers, the film is conjuctured to have little heat strink properties and impact strength imperovement.
  • a novel container especially useful for packaging food stuffs and a process for manufacturing the same is provide which overcomes the disadvantages of the prior art.
  • the heat shrinkable container manufacturing process utilizes coextruding a middle tube of material having an oxygen transmission rate of less than 200 cc/m 2 , mil 24 hours at 23oC , between outer and inner tubes of an olefin or condensed copolymer.
  • the resultant coextrusion forms a multilayered tubular unit.
  • the outer tube and inner tube may comprise polymers of ethylene and vinyl acetate.
  • the outer layer would be formed to have a thickness in excess of either the middle or inner layers.
  • the middle tube may be formedof a copolymer of vinylidene chloride and vinyl chloride, i.e. commonly known as Saran, or a hydrolyzed EVA.
  • the tube may be flattened such that the outer layer is easily cross linked by irradiation. Such irradiation may be applied to one side of the flat tube and then by changing the direction of the flattened tube in a continuous process, reirradiating the back side of the same tube. It follows that the tube is reinflated, and heated in a conventional manner to biaxially orient or form the multilayered tubular unit to a desired size. The container is finally formed by sealing the inner tube to itself.
  • Another object of the present invention is to provide a container for food stuffs and a process for manufacturing the same which is easily formed into bags by sealing the inner layer upon itself upon the application of heat.
  • FIG. 1 is a sectional view of the laminate used for the container of the present invention.
  • FIG. 2 is a sectional view of the container of the present invention.
  • FIG. 3 is a perspective schematic of the irradiation step performed in the process of the present invention.
  • the invention as a whole is represented by refer ence character 10, which depicts a container which is especially useful for the storage and transportation of food stuffs.
  • Container 10 is generally formed by coextruding three concentric tubes, 12, 14, and 16, FIG. 1.
  • Tube 12 provides a first inner layer of an olefin polymer.
  • Tub 16 provides the third, outer layer utilizing an olefin polymer which has been cross linked to withstand shipping abuses, which will be hereinafter described.
  • Tube 14 forming the middle layer is constructed of a material having a low oxygen transmission rats, i.e. less than 200 cc/ m 2 , 24 hours at 23° C.
  • Saran or vinyliderie chloride polymers may be used for this purpose.
  • Saran is defined as a polymer made by polymerizing vinylidene chloride and vinyl chloride.
  • Other polymers may be employed to form the oxygen impermeable middle layer 14, such as the fluorocarbon polymers, and hydrolyzed EVA.
  • First layer 12 may possess a thickness ranging from 2 to 7 mils.
  • second middle layer 14 would possess a thickness ranging between 1 and 5 mils.
  • the third layer 16 is relatively thick in relation to firs and second layers 12 and 14, and might have a thickness ranging between 14 and 24 mils.
  • the inner layer 12 may have the composition of an ethylene-vinyl acetate copolymer with, a vinyl acetate weight of 4% to 30%.
  • the upper part of this range is generally considered to be a very high percentage of this component, such a combination produces a self welding characteristic whereby the inner layer 12 welds to itself under normal heat shrinking conditions.
  • Such self welding characteristic would remedy the problem occurring through puncture of the multi-ply film 10 by a bone. In other words, "ballooning-up" would be eliminated as a problem in packaging.
  • layer 12 welds to itself to form a seal along, seam 18.
  • application of a vacuum to the interior 20 of container 22 would bring layer 12 together everywhere except those areas interrupted by the food product 24 within interior 20 of container 22.
  • the subsequent application of heat during the heat shrinkage step would weld all areas where first layer 12 touches itself within container 22.
  • prior art containers which have a cross linked inner layer are not capable of performing this function.
  • outer layer 16 may itself be a coextrusion of olefin polymers, namely ethylene and vinyl acetate having 3.5% to 8.5% vinyl acetate as the outer layer, and a polymer of ethylene and vinyl acetate having 8.5% to 15% vinyl acetate by weight as an inner layer.
  • the outermost layer of outer layer 16 would function as a layer resistant to shipping abuse and heat seal burn-through while inner layer of outer layer 16 would be resistant to cold storage puncture.
  • middle tube 14 is coextruded between inner and outer layers 12 and 16 having the chemical components hereinabove described.
  • coextrusion is known in the art and will not be further described herein.
  • the tube is generally flattened after coextrusion and delivered to irradiation device 26, FIG. 3.
  • Irradiation device 26 delivers the proper amount of radiation to flatten tube 24 which travels over rollers 23, through pinch rollers 30, and over reversing roller 32. At this point flattened tube 24 is sent back to irradiation device 26 through pinch rollers 34 and to the next step in the process over roller 36.
  • the formed and cross-linked tube 24 is then reinflated and passed into a heating medium such as a hot water bath for biaxially orientation which is known in the art.
  • the prior art film's heating of the outer layer weakened the same.
  • the outer layer of the present invention being cross-linked is able to withstand substantially more heating than the inner layers 12 and 14, thus pinholing is substantially reduced, if not entirely eliminated.
  • the oxygen and water impermeable barrier layer 14 is not weakened by the biaxial orientation. Saran tends to crystallize upon the application of heat, however, relatively thick cross-linked layer 16 serves as a shield to prevent this phenomenon from occurring. Also, a lesser amount of Saran is required than in the prior art as a hedge against crystallization of the same.
  • the antiblocking agents such as starch, which are normally used in the processing of multilaminate films, are found only in layer 12, thus obviating the disadvantage of the use of such, agents, namely unacceptable appearance and a roughened surface which is unsuitable for printing. It may be apparent that the container of the present invention may use a larger amount of anti-blocking agents than in the prior art in this regard without affecting the sealing characteristics. On the other hand, less plasticizers are necessary in the coextrusion process described above as would be required in a coating process of the prior art.
  • the tube After orientation, the tube is expanded into a bubble, cooled, flattened, and wound up for storage.
  • the application of heat to the flattened tube causes sealing of the inner layer 12 to itself to form containers such as bags or coverings for food stuffs. Again, the application of heat would have little effect on the thick outer crosslinked layer 16.
  • a four inch tape was assembled by the process described above such that the outer layer 16 was formed from ethylene-vinyl acetate, 14 mils; middle layer 14 was formed from Saran, 2.0 mils; and the inner layer 12 was formed from ethylene-vinyl acetate, 4.5 mils.
  • the EVA copolymer used in inner layer 12 and outer layer 16 contained 3% to 5% vinyl acetate by weight and possessed a melt index of 0.25, A ⁇ TM method D 1238, condition E.
  • the Saran layer 14 was a 90% copolymer of vinylidene chloridevinyl chloride.
  • the Saran layer was plasticized with 4% linseed oil and stabilized with 1% organic tin type stabilizers.
  • the exiting extrudate temperature was measured at approximately 340° F.
  • the four inch tape was passed through the beam of a 25 MEV Energy Science ElectroCurtain accelerator.
  • the outer layer 16 received a dosage of 6.5 MR (megarads).
  • the flattened tape was passed through a water tank having a water temperature of 200° F.
  • Tube 24 was oriented into a sixteen inch diameter having a total thickness of 1.8 mils. The orientation bubble was stable and the appearance of the film was excellent.
  • the resulting film had a 32% free shrink in the transverse direction at 195° F, determined by ASTM method D 2732.
  • a four inch tube was again produced by the extruder conditions described in Example I.
  • the inner and outer layers 12 and 16 of tube 24 will form from ethylenevinyl acetate copolymer having a 9-1/2% vinyl acetate content, by weight, and a melt index of 0.7, ASTM method D 1238, condition E.
  • Tube 24 was flattened into a tape having a four inch width. Irradiation was performed as described in Example I to the dosage levels in the 3 to 6 MR range.
  • the orientation bubble was produced and biaxially orientation took place as described in Example I. Bags were made from the orientation tubing of this example by making a transverse heat seal across the web and severing the tubing parallel to and immediately behind the seal. Thus,. layer 12 was sealed to itself.
  • a multilayered tube 24 was produced by the same coextrusion process described above.
  • Outer layer 16 was itself a coextrusion of EVA 1, 4.5% vinyl acetate by weight 0.25 MI, NPE 481, produced by the Northern Chemical Company, EVA 1 was employed as the outermost layer of outer layer 16.
  • EVA 2 was used as the inner layer of outer layer 16 and con- tained 9-1/2% vinyl acetate by weight, 0.7 MI manufactured by Dupont De Nemours. The ratio of the EVA 1 to EVA 2 was approximately 1 : 3.
  • Irradiation, biaxial orientation, and bag production was performed in the same manner as described in Examples I and II.
  • the preferred method of cross-linking outer layer 16 is by irradiation, chemical cress-linking may also be employed.
  • Peroxides such as 2, 5, dimethyl-2, 5 di (t-butylperoxy) hexane as described in United States Patent No. 3,201,503. It should be noted that care must be taken in controlling the extruded temperature with chemical cross-linking in order to forestall premature cross-linking in the extruder barrel or in the die. Photosensitive cross-linking agents may also be incorporated such that upon the exposure to ultraviolet light, crosslinking takes place.
  • a coextrusion slot die may be used in conjunction with a tenter frame during the biaxial orientation step.

Landscapes

  • Laminated Bodies (AREA)

Abstract

Un nouveau procédé permet la fabrication d'un récipient obtenu par coextrusion d'un tube intermédiaire (14) en matière à faible vitesse de transmission d'oxygène, entre les tubes externe (16) et interne (12) de polymère d'oléfine, afin de former une unité tubulaire à couches multiples. Le tube externe (16) est réticulé et l'unité est orientée biaxialement pour prendre une taille voulue. On scelle le tube interne (12) à lui-même afin d'achever la formation du récipient (10) qui comprend une couche interne d'un polymère d'oléfine, une couche intermédiaire de matière ayant une faible perméabilité à l'oxygène, ainsi qu'une couche externe relativement résistante de polymère d'oléfine réticulé.
PCT/US1988/000320 1983-03-18 1988-02-05 Film thermoretractable WO1989007077A1 (fr)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US47670983A 1983-03-18 1983-03-18

Publications (1)

Publication Number Publication Date
WO1989007077A1 true WO1989007077A1 (fr) 1989-08-10

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US1988/000320 WO1989007077A1 (fr) 1983-03-18 1988-02-05 Film thermoretractable

Country Status (1)

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WO (1) WO1989007077A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1997013637A1 (fr) * 1995-10-11 1997-04-17 Tetra Laval Holdings & Finance S.A. Recipients en polyolefine munis d'une couche protectrice exterieure de polyethylene
WO1997019807A1 (fr) * 1995-11-30 1997-06-05 Borealis A/S Utilisation de materiaux polyolefiniques reticules dans des conduites de pression

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4048280A (en) * 1971-09-17 1977-09-13 Jury Gordeevich Borzyak Method of manufacturing electrotechnical articles
US4064296A (en) * 1975-10-02 1977-12-20 W. R. Grace & Co. Heat shrinkable multi-layer film of hydrolyzed ethylene vinyl acetate and a cross-linked olefin polymer
US4501780A (en) * 1982-12-15 1985-02-26 W. R. Grace & Co., Cryovac Div. Tubular film having sealing layer of propylene ethylene random copolymer
US4547433A (en) * 1981-11-11 1985-10-15 Kureha Kagaku Kogyo Kabushiki Kaisha Heat-shrinkable laminate film
US4714638A (en) * 1985-06-14 1987-12-22 Viskase Corporation Irradiated multilayer film for primal meat packaging

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4048280A (en) * 1971-09-17 1977-09-13 Jury Gordeevich Borzyak Method of manufacturing electrotechnical articles
US4064296A (en) * 1975-10-02 1977-12-20 W. R. Grace & Co. Heat shrinkable multi-layer film of hydrolyzed ethylene vinyl acetate and a cross-linked olefin polymer
US4547433A (en) * 1981-11-11 1985-10-15 Kureha Kagaku Kogyo Kabushiki Kaisha Heat-shrinkable laminate film
US4501780A (en) * 1982-12-15 1985-02-26 W. R. Grace & Co., Cryovac Div. Tubular film having sealing layer of propylene ethylene random copolymer
US4714638A (en) * 1985-06-14 1987-12-22 Viskase Corporation Irradiated multilayer film for primal meat packaging

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1997013637A1 (fr) * 1995-10-11 1997-04-17 Tetra Laval Holdings & Finance S.A. Recipients en polyolefine munis d'une couche protectrice exterieure de polyethylene
WO1997019807A1 (fr) * 1995-11-30 1997-06-05 Borealis A/S Utilisation de materiaux polyolefiniques reticules dans des conduites de pression
US6325959B1 (en) 1995-11-30 2001-12-04 Borealis A/S Use of cross-linked polyolefins material in pressure pipes

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