Heat sealing biaxially oriented film

(12) Patent Application

<td> (19) ^? (gr INTELLECTUAL PROPERTY</td><td> (11) Publication number: NZ 210331 A (41) Publication date: 05.12.1986 (⁵¹)lnt. Cl: B29C65/18; B29C65/30; B31B1/64;</td>

<td> (21) Application number: NZ19840210331 (22) Date of filing: 26.11.1984 (30) Priority: 19830561684 US 15.12.1983</td><td> (71) Applicant(s): JOHNSTON Ο B (72) Inventor(s): JOHNSTON Ο B</td>

(54) Title:

HEAT SEALING BIAXIALLY ORIENTED FILM

This PDF First Page has been artificially created from the NZ Bibliographic Data.

A selected segment of a web of at least two layers 12, 12' of biaxially oriented plastics film are heat sealed by pressing together the web layers and a selected segment 24 of the pressed web is heated above the bonding temperature of the plastics. At the same time adjacent web segments 26,28 are maintained below that temperature. The surfaces pressing the heated web segment have a lower surface friction than the surfaces pressing the adjacent web segment. The layers of the heated segment of the web are therefore unrestrained against shrinking during heating and are allowed to shrink back to their pre-oriented molecular configuration while the adjacent segment is restrained against movement. A hermetic bead seal 34,36 is thus formed betrween the web layers.

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Priority Date(s):

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Complete Specti'celion Filed:*2.4. (I'. S/t

Class:

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Publication Date:

P.O. Journal. No:

........έ 5 DEC '1986

.............

NEW ZEALAND

PATENTS ACT. J 953

No.:

Date: '

COMPLETE SPEC! FICATION

HEAT BONDING METHOD AND DEVICE θ l/W, ORIN BENJAMIN JOHNSTON, a citizen of the United States of

America, residing at 16480 North Hillcrest Court, Eden Prairie, Minnesota 55344, United States of America, hereby declare the invention for which I / wi pray that a patent may be granted to me/vK&amp;₍ and the method by which it is to be performed, to be particularly described in and by the following statement: 1

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^x HEAT BONDING METHOD AND DEVICE

BACKGROUND OF THE INVENTION

210391

This invention relates to heat bonding plastics films, and particularly to heat bonding biaxially oriented plastics films. Biaxially oriented plastics films are stretched in both 7 planar axes during manufacture to re-orient their molecuLar strucQ ture to increase tensile strength, toughness and flexibility, θ When the temperature of a biaxially oriented film is Increased above a given temperature, e.g. for heat bonding, the film shrinks to its pre-oriented molecular configuration, unless restrained.

To utilize biaxially oriented films, e.g. MYLAR polyester film, in heat-sealed articles, it has previously been known to laminate such films to a layer of a non-shrinking, easily heat sealable polymer, e.g. polyethylene. To heat seal Laminated l' * J films, e.g. in manufacture of the popular MYLAR novelty balloons, the polyethylene layers are placed in contact and the laminated films are locally heated to a temperature above the bonding temperature of the polyethylene, but below the Level at which the biaxially oriented film will shrink.

With the foregoing in mind, it is an object of the invention to provide an apparatus and process for producing a sealed article by directly heat bonding two or more layers of biaxially oriented polymeric film.

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2103η

It La anoCher object to join two or more layers of blaxlally oriented polymeric film by heat bonding to form a seal ^d between the layers, comprising a smooth, solid homogeneous piece of plastics having complete molecular interlocking between layers of film.

It is still another object of the invention to provide a bead seal superior to classical bar or edge seals used in the plastics film packing industry, by allowing the manufacturer to operate with higher production speeds while providing more reliable quality control, better hermetic seals and less scrap film.

Summary of the Invention

According to the Invention there is provided in an apparatus for heat sealing a selected segment of a web comprising at lease two layers of biaxially oriented plastics fiLm, the apparatus having means for pressing the web layers together, means for simultaneously heating the selected segment to above bonding temperature, means for maintaining an adjacent segment of the web below bonding temperature, and means for cooling the selected segment sufficiently quickly to avoid degradation of the plastics, the means for pressing including pressing surfaces for pressing contact with the web, the following improvement:

The pressing surfaces in contact with the selected segment of the web subjected to heating above bonding temperature have relatively lower surface friction than Che pressing surfaces

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1033 1, in cQntacC with che adjacent segment of Che web, whereby the heated segment of the web is physically unrestrained by the surfaces against shrinkage during heating and is al Lowed to shrink back to pre-oriented molecular configuration while the web in the adjacent segment is restrained against providing for formation of a hermetic bead of the web.

In preferred embodiments, a pair movement, thereby seal between the layers of hermetic bead seaLs is formed on opposite sides of the centerline of the selected segment subject to heating to above bonding temperature; the novel apparatus is adapted to subject a multiplicity of selected spaced apart segments of web simultaneously to bonding temperature, whereby a multiplicity of seals is simultaneously formed, preferably the heating to above spaced apart bead means for simuL15

Caneously subjecting the multiplicity of selected segments of web to heating to above bonding temperature are disposed and '1 arranged Co seal the web Co form a pouch having an opening to provide for placing an article therein, the apparatus being further adapted for sealing the opening of the pouch to enclose

Che article therein; and the pressing surfaces in contact with the selected segment of web subjected to heating above bonding temperature are treated selected from che group with a low friction substance preferabl^^^ of silicone lubricanCs and fluorocarbon⁴.

According Co another aspect of che invention, the method

I

210881 of heat sealing a selected segment of a web comprising at least

- two layers of biaxially oriented plastics film comprises pressing the layers of the web together, heating a selected segment of the web to above bonding temperature of the plastics, allowing the heated segment of the web while so pressed to shrink back θ to its pre-oriented molecular configuration while restraining an adjacent segment of the web against movement by pressing and maintaining the temperature thereof beLow bonding temperature, θ and cooling the heated segment sufficiently quickly to avoid degradation of the plastics, thereby permitting the formation of a he rmetic bead seal between Che Layers of the web.

A preferred method of this aspect of the invention comprises forming a pair of hermetic bead seals on opposite sides of Che centerline of the selected segment subject to heating lo to above bonding temperature; the method includes subjecting a multiplicity of selected spaced apart segments of the web simul- taneously to heating to above bonding temperature simultaneously to form a multlpliciy of spaced apart bead seals, and. prefer- ably, the method comprises simultaneously subjecting the multipli- city of selected segments of web to heating to above bonding temperature to seal the web to form a pouch having an opening, placing an article therein, and similarly sealing the pouch open- ing thereby enclosing the article therein.

Still another aspect of the invention comprises Che

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210831 heat sealed product resulting from heat sealing a selected segment of a web comprising at least two layers of selected biaxlally oriented plastics film by pressing the web layers together, heating the selected segment of the web to above bonding temperature of the plastics, allowing the heated segment of the web while so pressed to shrink back to ita pre-oriented molecular configuration while restraining an adjacent segment of the web against movement by pressing, and maintaining the temperature thereof below the bonding temperature, cooling the heated segment sufficiently quickly to avoid degradation of the plastics, thereby permitting the formation of a hermetic seal between the layers of the web.

Still further objects, features and advantages will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.

Brief Description of the Drawings

Fig. 1 is an end cross-section view showing somewhat schematically opposed diaphragms for heac bonding, e.g. a web formed of two layers of biaxlally oriented film;

Figs. 2A, 2B, 2C and 2D are end views showing, sequentially, the changes in sections of film during its subjection to heat bonding; and

Fig. 3 is a perspective view showing a web of plastic

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- 6 ·' ·Α» ·.

-V210331 sealed and separated transversely at measured intervals, into separate pouches open at the ends, while

Fig. 4 is a similar view showing a single pouch also sealed at one end along the film axis, and

Fig. 5 shows che pouch of Fig. 4 closed about an article and sealed on both sides and both ends.

Detailed Description of a Preferred Embodiment

Referring to Fig. 1, the opposed diaphragms 10, of identical construction, for heat sealing web 11 formed of two layers 12, 12’ of biaxlalLy oriented polymeric film, e.g. polyvinyl ldene chloride, are shown. As described more fully in my issued U.S. patents Nos. 3,964,958; 4,251,314; and 4,273,604, the diaphragms comprised bodies 14 of flexible material, e.g. silicone rubber, and, embedded therein, heater elements lo and heat conductor elements 18, 20. The surface layer 22 of diaphragms contacting the web 11 is also silicone rubber. In the bonding area 24, that closest to heater element 16, surface 22 is smooch with relatively lower friction. In areas 26, 28 adjacent bonding area 24 and more remote from heater element 16, the surface 22 is comprised of silicone rubber with particles of ded therein to create a sandpaper-like surface of higher friction.

The diaphragms are urged into pressured opposite sides of the web 11 by fluidic pressure, sand 30 embedrelatively contact with shown represent-

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210351

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atively by arrows 32.

Operation

Still referring to Fig. 1, two layers of film 12, 12'

-. 4 i in web 11 to be joined by heat bonding are placed together and

- i - - * ¹ positioned between Che opposed diaphragms 10, with the area to f

be bonded beneath bonding area 24 of surface 22. Fluidic pressure

32 is applied to the diaphragms Co bring Chem inCo pressured contact with the web 11. Heater element 16 is heated by passing an elecCric current through the element. The temperature of.

element 16 is maintained just below the bonding temperature, and increased during the bonding cycle by pulsing a high current through the element 16. Referring now also to Figs. 2A through

2D, the increased temperature in the bonding area 24 increases the temperature of web 11 above the bonding temperature to initi- ate bonding between the film layers 12, 12', as shown in Fig.

2A. The temperature at surface 22 outside the bonding area, in adjacent areas 26, 28 more remote from heater element 16, is maintained below the bonding temperature as heat conductors 18,

20 conduct away some of the heat generated by heater element

16. This is shown in Figs. 2A through 2D as the web 11 fails

Co bond away from area 24 close to the heater element.

Area 24 also has relatively lower friction which allows the web to contract to its pre-oriented state, while areas 26, are of higher surface friction which forces the web to remain

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Ln the oriented state, even in presence of slightly elevated tercperaCures.

Referring now to Fig. 28, the now bonded web 11 in area 24 under the effects of increased temperature has contracted from centerline A to initiate formation of bead seals 34, 36 at the end of unbonded sections of web 11, with a markedly narrowed section 38 lying on the centerline between the beads.

In Fig. 2C, the bead seals 34, 36 have separated at the centerline and contraction continues, the beads 34, 36 forming separately into homogeneous segments at the ends of web 11 with complete molecular interlocking between the plies.

In Fig. 2D, the seals have formed completely as solid smooth beads, with the film formerly in the bonding area now returned to its original pre-oriented state, with the film of both plies in a single, homogeneous mass. The actual final shape of the bead seals is controlled by tnolecuLar forces of the film being bonded, by the pressure, bonding temperature, bonding time, and time to cool the film below its flow temperature. For example, to form a generally cylindrical bead when joining two plies of blaxially oriented polyvinylidene chloride film SARAN sold by Dow Chemical Company, each 0.001 inch thick, a pressure of 60 psi is applied, with bonding temperature of 290°F, over 0.3 second, and a cooling time of 0.3 second to Lower the temperature below the flow point. A substantially homogeneous bead seal with

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molecular interlocking between the film plies was formed having approximate dimensions in the X and Y direction of 0.006 inch and 0.005 inch, respectively. A total cycle time for bonding and cooling of less than one second is possible for some biaxially thick (0.9508 millimeters).

I pressure, the fluid plas- i oriented plastics films up to 0.002 inch

As the seals are formed under tics fl ows together to form a completely integrated mass, which creates a hermetic seal as impervious to transmission of fluids,

i.e. gases or liquids, as the original film itself.

Referring now to Fig. 3, a dual web of biaxially oriented film is shown afcer heat bonding for plastics packaging

Six bead seals 40, 42, 44, the web to produce pouches

46, 48 and 50 are shown formed in

39, 43, 47 and 51, open at both ends as shown. Fig. 4 shows the result of a second operating cycle in which a bead seal 52 has been formed to provide the boctom seal of pouch 43. In Fig. 5, article 54 has been placed in the pouch and a final bead seal 56 formed completely hermetically closing the pouch. Of course, the first three sealing operations can be performed simultaneously followed by inserting the article and completing the final seal; and, indeed, all four operations can be done simultaneously utilizing the invention.

Alternate

Embodiments

Other embodiments are within the following claims.

For example, a number of sheets of biaxially oriented polymeric

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-2 10331

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1' jj film, e.g. three sheets or more, may be placed together to be

- t ' bonded together at the edge Ln a single, homogeneous bead seal.

Also, further to decrease the friction between the film and the l‘ diaphragm surface in the bonding area, the surface may be locally . coated with a fluorocarbon film, e.g. TEFLON (\' , sold by E.

! I . I. duPont de Nemoura Company, Inc. of Wilmington, Delaware, or ! the bonding area may be locally lubricated with silicone fluid.

I ¹ ί In the latter case, increasing the friction of the diaphragm surface outside of the bonding surface may be unnecessary.

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210381

WHAT l/Vs£ CLAIM IS: