FR2497214A1 - SHEET MATERIAL AND PACKAGE COMPRISING DETACHABLE CLOSING ZONES, MADE FROM SAID MATERIAL - Google Patents

Abstract

THE LAYER FOR HOT WELDING IS A MIXTURE OF ETHYLENE-VINYL ALCOHOL (OR EVOH) COPOLYMER AND A NORMALLY THERMOSCELLABLE POLYMER. AREAS OPPOSITE TO SUCH A LAYER FORM DETACHABLE HOT WELDINGS. WHEN THE EVOH IS PRESENT IN A QUANTITY BETWEEN 50 AND 80 BY WEIGHT IN THIS SEALING LAYER, IT FULFILLS A SECOND IMPORTANT FUNCTION IN THE PACKAGING CONSTITUTING AN EFFICIENT BARRIER TO THE TRANSMISSION OF GASEOUS OXYGEN THROUGH THE CLOSURE OF PACKAGING.

Description

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  The present invention relates to a perfect packaging

  heat sealed and made from a sheet material of the ethylene-vinyl alcohol copolymer type (also designated below by the abbreviation EVOH), preferably as a barrier to the transmission of gaseous oxygen. A widely used packaging method provided by the invention,

  uses a multi-layer sheet material of the invention

  tion placed around the product and heat sealed to wrap it.

  According to one aspect concerning the structure of the packaging

  In addition, it is often desirable to provide a sealed packaging structure with flanges and means allowing the packaging to be opened without seriously damaging the packaging structure. It is further desirable to provide an easy means for opening the package, not only for reasons of convenience, but also for better

  control of packaging and contents in the event of opening.

  Thus the packaging should open gently and avoid rough or jerky handling of the opening device, so that the contents do not spill when opening. Concurrently and in particular in packages which require a high degree of protection against gas diffusion inside the package, conventional opening systems such as slits, perforations and other lines of weakness are unacceptable because of the weakening or penetration of the barrier material by the imposed rupture line, necessary for the realization

of the opening system.

  In the packaging technique, special polymeric materials have been developed in a heat-sealable layer inside the packaging, forming hot welds having a high solidity, said hot welds being able to be subsequently separated (peeled off). ) for the opening

of the packaging.

  According to another aspect concerning the preferred structure of the package, it is often desirable to provide a significant barrier against the transmission of

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  oxygen through the packaging material. It is known that a packaging material comprising a continuous layer

  EVOH provides an excellent barrier against oxygen.

  Traditional heat-sealable packaging structures containing EVOH are sensitive to the penetration of oxygen through the packaging structure

  at the places of the joint, since the materials suitable

  heat sealers provide poor protection

  tion against the penetration of oxygen.

  1O The main object of the invention is a heat-sealable multilayer sheet material, in which the layer of sheet material constituting one of its surfaces

  comprises a mixture a) of 15% to 80% of ethylene copolymer-

  vinyl alcohol and b) from 20% to 85% of a normally heat-sealable polymer, the minimum heat-seal temperature of the normally heat-sealable polymer being at least about 31 ° C. lower than the minimum heat-seal temperature at

  ethylene-vinyl alcohol copolymer.

  A preferred sheet material comprises a blend of a) 50% to 80% EVOH and b) 20% to 50% of the normally heat sealable polymer. In the sheet material, the normally heat-sealable polymer in question is

  preferably chosen from an ionomer, an ethylene-

  acrylic acid, an ethylene-methacrylic acid copolymer, an ethylene-vinyl acetate copolymer and a polyethylene

  low density (also referred to below as LDPE).

  The subject of the invention is also a heat-sealable package comprising upper and lower panels of multi-layer sheet material heat welded to one another, face to face, when the package is completely

  formed and sealed. The layers of the upper and lower panels

  which are arranged face to face and constitute the

  Opposite sides of the formed and sealed package are composed of the above-mentioned mixture of a) 15% to 80% of ethylene-vinyl alcohol copolymer and b) 20% to 85% of the normally heat-sealable polymer. When using the preferred sheet material having 50% to 80% EVOH in the

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  mixed layer, the packaging is relatively impermeable to the passage of oxygen through the heat seals. The

  heat seals between the opposing layers are detachable.

  Another subject of the invention is the heat sealed and fully closed package.

  The invention will be further illustrated without being any-

  ment limited by the description below made with reference

  in the accompanying drawings, in which: - Fig. 1 is an enlarged section of a typical multi-layer packaging structure based on a sheet material constituting an oxygen barrier of the prior art. Fig. 2 is an enlarged section of a typical multi-layer packaging structure based on a material

  sheet constituting an oxygen barrier in accordance with the invention

  tion. - Fig. 3 is a resized section of the sheet material of FIG. 2, folded in the form of a package and showing the layers of hot weld close together in

weld areas.

  - Fig. 4 is a perspective view of a package formed by heat sealing with one side of the package open

  and available for filling with a product.

  - Fig. 5 is a perspective view of a package

filled and welded.

  - Fig. 6 is an enlarged section along 6-6 of the

  figure 5 and scaled up for a better illustration

  tion. Referring to Figure 2, a sheet material 10 is made up of three layers 12, 14 and 16. The layer

  external 12 is composed of a mixture of ethylene copolymer-

  vinyl alcohol and ethylene-vinyl acetate copolymer.

  The outer layer 16 is made of low density polyethylene. Intermediate layer 14 is polyethylene modified by polar carbonyl groups and serves as an adhesive between the two

outer layers 12 and 14.

  We transform the sheet material 10 into a

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  flexible, pocket-like packaging by folding the sheet material so that two layers 12 of the sheet material 10 are facing each other. FIG. 3 shows the position face to face and exaggerates the proximity of the layers 12 vis-à-vis in the heat seal zone. Heat seals are made along an area where the two layers of sheet material are located to form a packaging structure having an upper panel 19 and a lower panel 21 as shown in Figures 3 and 6. After the filling the packaging with the product 24, additional welding is carried out by the layers 12 to perfect the closure and the sealing of the packaging

as shown in figure 5.

  Suitable ethylene-vinyl alcohol copolymers

  for this use are commercially available. Such a copoly-

  suitable mother sold by the company Kuraray, Japan, under the brand "EP-F" has 32% to 36% of ethylene, a molecular weight of 29,500, a glass transition temperature TG of 691C and a melting point of 1801C . Another suitable commercially available copolymer has about 29% ethylene, a molecular weight of 22,000, a TG of 651C and a melting point of 1851C. Yet another polymer

  suitable has about 40% ethylene, a molecular weight

  laire of 26,000, a TG of 691C and a melting point of 1640C. The film structures and packaging shown in the following tables can be produced using

  these ethylene-vinyl alcohol copolymer resins available

commercially.

  The first important function of the ethylene-vinyl alcohol copolymers used according to the invention is to provide detachable hot solders. To ensure the ease of separation of the heat welds, the EVOH must be present in the mixed layer of the heat seal at a rate of at least about 15% by weight without exceeding about 80% by weight. At least 80% of the

  vinyl component is in the form of hydrolyzed alcohol.

  The EVOH copolymer, when it constitutes at least 50% by

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  weight of the mixed layer, fulfills a second important function in the package by also providing an effective barrier to the transmission of gaseous oxygen through the closure of the package. To perform this function, the EVOH copolymer contains at least 50% by weight of the vinyl component and preferably has at least

  % of this vinyl component, present in the hydro-

lysed or alcohol.

  The layer 12 of this structure is the component which can fulfill the essential double role as a barrier against the transmission of oxygen and as a layer of

  heat seal capable of forming detachable heat welds.

  Detachable welds are defined as welds between facing surfaces of the sheet material, the force required to separate the facing layers from each other being less than the force required to the tearing of one of the layers lying face to face when the package is opened. When opening the package, the unwelded portions of the opposite sides of the sealed sheet material are gripped and separated. When the weld is detachable, the areas facing the sheet material separate at the location of the weld. If, on the other hand, the weld is not detachable, the areas facing the sheet material do not separate at the location of the weld. The sheet material tends to give way internally, frequently under the effect of the tearing force between the weld and the point of application of the force and the packaging cannot

to be open.

  Although the sealing layer 12 may comprise an amount of EVOH as low as 15% for obtaining the detachable welding properties, it comprises, in order to fulfill this preferred dual function as a barrier to the transmission of oxygen gas, a mixture 1) of at least

  % to about 80% ethylene vinyl alcohol and 2) approx.

  ron 20% to about 50% of a normally thermoscel polymer-

  lable. In the illustrated embodiments, the normally heat-sealable polymer has a minimum temperature

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  heat seal, T min., at least about 31C lower than T min. EVOH as measured by ASTM M-463. The normally heat sealable polymer can be a homopolymer, a copolymer or a mixture thereof. By way of illustration of suitable heat-sealable polymers, mention may be made of polyethylene, polypropylene, an ethylene-propylene copolymer, an ethylene-vinyl acetate copolymer,

  an ethylene-acrylic acid copolymer, an ethylene-

  lene-methacrylic acid and a lonomer.

  For the preparation of the layer 12 mixture, solid ethylene vinyl alcohol pellets are mixed

  physically with solid pellets of normal polymer-

  heat sealable selected. The physically mixed pellets are then extruded in a conventional plastic extruder by forming a sheet of plastic film. The mixture is preferably extruded during a co-extrusion operation. The most economically produced multi-layer structure

by this process.

  The physical production of the inventive packaging

  tion can be carried out by any of the conventional techniques for manufacturing packaging with heat seal. In a preferred method, the material

  sheet 10 is folded back on itself to form respective-

  ment the upper and lower panels 19 and 21 of the packaging, the layer 12 being inside the fold as shown in Figure 3. Then using conventional heat sealing devices to achieve

  welds on all three sides of what constitutes final-

  a rectangular package with four sides. The packaging is shown at this stage of manufacture in FIG. 4 with the three welded sides designated by 18. After filling the packaging with the product, the fourth final side 20 is closed by heat sealing. The complete packaging is as shown in FIG. 5. In the finished packaging, the facing layers 12 are hot-welded to each other as shown in the figure

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  6. The part-22 of the outer edges of the opposite layers 12 preferably remains non-welded as shown in the figure

  6. These unwelded edges are conveniently gripped by the user.

  sator for opening the package by stretching.

  The following examples illustrate the invention without

in no way limit it.

EXAMPLE 1

  Ethylene vinyl alcohol copolymer pellets

  that the brand "EP-F" were physically mixed with ethylene vinyl acetate pellets 3130, available from DuPont Company, with a view to producing a mixture of 60% by weight of EVOH and 40% EVA. This mixture was co-extruded with "Plexar" described in US Patents 4,087,587 and 4,087,588 and available from Chemplex Company and with low density polyethylene in order to obtain a three-layer structure with a. middle layer of "Plexar". The mixture containing EVOH and low density polyethylene were arranged in the form

  of outer layers on the opposite sides of the "Plexar".

  The mixture layers of EVOH, "Plexar" and polyethylene had thicknesses of 7.6, 7.6 and .6 microns respectively for a total film thickness of 55.8

  microns. The resulting multi-layer structure has been trans-

  formed in a rectangular packaging of 20.3 x 40.6 cm on

  a vertical forming, filling and welding machine

  wedge, model 8000, manufactured by MIRAPAK Company, Houston, Texas, the EVOH mixture layer being on the inside of the package at the temperatures of the solder jaws. The peel strengths of the resulting welds were measured according to ASTM-D-882 on a machine

  Instron with a head speed of 32.3 cm per minute.

  The averages of the peel strengths were as indicated in Table I below and represent a separation of the layers opposite the EVOH mixture at the places of the weld rather than an internal rupture of the multi-sheet material. layers or one of its layers.

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TABLE 1

  Jaw temperature Resistance to solder coat 880C 240 g / 2.54 cm 990C 850 g / 2.54 cm 1100C 500 g / 2.54 cm

EXAMPLES 2 TO 12

  Additional structures have been made identically and have been tried. The structures and the means of their peel strengths, in grams per 2.54 cm, are given in Table 2. For ease of comparison, the peel strengths of Example 1 are given in Table 2. The oxygen permeability figures are also given for Examples 6 and 7. The oxygen permeability figures were not determined for Examples 1 to 5 and 8 to 12 but are assumed to be shown so realistic by Examples 6 and 7 as well as by Examples 13 to 15 below. Number

example

Mixed

EVOH Thermo-polymer

  EP-F%%%%%%%%%%%% cellable *%%%%%%%%%%%%

TABLE 2

  Resistance of 88oC to peeling at welding jaw temperature 99oC C Oxygen permeability cm3'-ml m2 day NM NM NM NM NM 0.15 0.46 NM NM NM NM NM * 3120 = EVA, 7.5% ethylene 3165 = EVA, 18% ethylene 3130 = EVA, 12% ethylene 1650 = EVA, a zinc ionomer 1707 = a sodium ionomer 455 = an ethylene-acrylic acid copolymer NM = not measured r%) 4-% 0 N) 9

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  It will be emphasized that the present invention provides the user with a certain number of advantages when it results in a packaging structure, in comparison with the structures of the prior art comprising EVOH as a separation layer, as in the figure 1. An advantage is simplicity due to the number of layers required in this new structure. As shown in Figure 1, the typical structure of the prior art comprises at least five layers. These layers are, as in Figure 1, from top to bottom: polypropylene / Plexar / EVOH / Plexar / EVA (sealing). The EVOH layer is included within the structure and has layers of special adhesive on both sides. The complete five-layer structure has a layer of sealant on the face of one adhesive layer and usually has a protective outer layer on the face of the other adhesive layer. In other words, the prior art comprises five-layer structures with a three-layer core containing EVOH and adhesive bonding layers and external and internal layers on the external faces of the adhesive layers. To realize

  this structure, it is necessary to have a team-

  rather complex five-layer co-extrusion. To perform the adhesive function, two layers of adhesive must

  be extruded during co-extrusion. Furthermore, the co-

  extrusion of a five-layer structure results in the formation

  of waste related to the complexity of the structure to be extruded.

  The fact of providing the layer containing the EVOH on the external face of the film as in the invention, leads to a much simpler structure. It is sufficient for one face of the layer containing the EVOH to contain adhesive to bond it to the rest of the structure, which removes an adhesive layer. Since the layer containing the EVOH is on the outside of the film and can fulfill both the heat sealing and barrier functions, the separate barrier layer can optionally be removed. As a variant, it can be considered by comparison that the layer of pure EVOH is removed. According to either consideration, the resulting structure with it 2497214

  deleting two layers has only three layers.

  It should be noted that matter is not really eliminated

  of the physical structure to make the comparison above

  above but rather that certain materials are removed from the

  description of the structure based on sheet material.

  This simpler three-layer structure offers several sources of savings. First, the use of expensive adhesive material is reduced from two layers to one. Second, the coextrusion process can be implemented on three-layer equipment that is less expensive than five-layer equipment. Third, the likely amount of waste produced when making a three-layer structure is less than that produced

  for the more complex five-layer structure.

  Although the oxygen barrier accompanying the structures, comprising oxygen barrier material only in the mixed sealing layer, is slightly lower than the barrier of a layer composed of 100% EVOH, for many applications the barrier that strengthens the layer

  at 100% EVOH is significantly higher than what is necessary

  even if the thickness of this layer is reduced to

  minimum to the degree authorized by known equipment.

  This is how the reduced barrier provided by the layer

  joint sealing is usually quite satisfactory

  health when the EVOH content is at least 50% by weight.

  Within the listed mixing range, the barrier can be specifically selected according to the protection required. Thus, the packaging of Example 1 has an oxygen permeability of 3.3 x 10 -3 cm '/ day as measured on an Oxtran 1050 device at 331C with a relative humidity of O%. The Oxtran 1050 is a test device available from Modern Controls Incorporated, Minneapolis, Minnesota. A package of the same size made from the sheet material of the prior art of identical thickness according to the structure of FIG. 1 and comprising a layer of 100% EVOH with a thickness of 7.6 microns, has permeability of

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  3 x 103 cm '/ day. Another similar prior art package having a 7.6 micron oxygen barrier

  composed of "Saran" has a permeability of 5.1 cm '/ day.

EXAMPLES 13-15

  A multi-layer structure is produced by co-extrusion of a multi-layer film consisting of LDPE / LDPE / mixture. LDPE is a low density polyethylene supplied by Chemplex Company under the designation 3024. The mixed layer is composed of EVOH EP-F mixed with EVA 3130 in three ratios. The oxygen permeability of the structure based on the resulting sheet material is

indicated in table 3.

TABLE 3 *

  Example NO Mixing ratio Permeability to EVOH / EVA oxygen cm3! 25 microns m2 / day

13 80/20 0.6

14 65/35 0.9

50/50 1.2

  100% EVOH control 0.003 100% SARAN control 15.0 * 7.6 micron barrier layer Table 3 provides an indication of the flexibility of use provided by the invention for adapting the oxygen barrier, within wide limits, the protection needs of the wrapped product. It shows that the oxygen permeability can be adjusted by adjusting the percentage of EVOH in the mixed layer. It can also be adjusted by changing the thickness of the layer. Such flexibility is economically very advantageous because it allows the user to derive maximum benefit from the use of the most expensive component of the

  sheet material - 1'EVOH - while benefiting directly -

  ment of its dual function to the degree to which it is used.

  In this unusual case where we are looking

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  a higher barrier than that provided by the% EVOH layer, the craftsman would usually have applied a thicker layer of EVOH. By taking advantage of the present invention, the craftsman now has the possibility of taking the detachable seal into account when calculating the barrier. For example, the presence as a sealing layer of a 7.6 micron layer of the mixture with an amount as low as 50% EVOH in a structure such as that

  in Figure 1, reduces permeability by an additional 12%

  mainly by reducing the passage of oxygen through the heat seals. We can thus make the choice by adjusting the thickness of one or the other or of the two layers containing the EVOH and by adjusting if necessary the

EVOH content of the mixed layer.

  In the previous illustrations, the invention has been described with three and four layer structures made entirely of polymeric materials. It is known in the packaging technique to produce composite structures comprising metallic and / or cellulosic layers. The structures of the present invention

  are fully compatible with these composite structures.

  In composite structures or in 100% polymeric structures, the invention is very suitable for packaging structures comprising layers of packaging material in addition to those which have been the subject of the discussion. For applications not indicated of the invention,

  sheet materials on opposite sides of the inter-

  hot welded face may be different from the point of view of the structure. This embodiment may find application, for example, when one of the sheet materials fulfills the function of a shaped container and the other acts as a detachable cover. In such an application, it is entirely possible that the two sheet materials

  dissimilar have substantially different stiffnesses

  annuities and have other physical dissimilarities.

  The process for preparing the mixture exposed above

  vant by mixing of pellets is only illustrative because other methods of mixing polymeric materials can

  be used and are commonly known.

  Thus the invention provides an improved sheet material for packaging and packaging structures obtained therefrom. Although the invention is described in conjunction with the structures illustrated, there is no question of limiting the invention to such structures. The scope of the invention must be appreciated by

  the above general definitions, in the light of the indica-

tions and parameters mentioned.

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Claims (10)

  1. A thermoscel- multi-layer sheet material   lable, the layer of which constitutes one of its faces comprises   a mixture a) of approximately 15% to 80% of ethylene copolymer-   vinyl alcohol and b) from about 20 to 85% of a normally heat-sealable polymer, the minimum heat seal temperature of said normally heat-sealable polymer being at least 3 C lower than the minimum heat seal temperature at   hot of said ethylene-vinyl alcohol copolymer.   2. A heat-sealable package, characterized in that it comprises upper and lower panels of a multi-layer sheet material, heat-welded to one another and face to face, when the package is fully formed and sealed; in that the layers opposite said   upper and lower panels, constituting the facing faces-   with respect to the formed and sealed packaging, are composed of a mixture a) of approximately 15% to 80% of ethylene-alcohol copolymer   vinyl and b) from about 20% to 85% of a normal polymer-   heat sealable, the minimum heat seal temperature of said heat sealable polymer being at least 3 C lower than the minimum heat seal temperature of said ethylene vinyl alcohol; and in that the heat seals   between said facing layers are detachable.   3. A heat-sealed package, characterized in that it comprises upper and lower panels of a multi-layer sheet material heat-welded to one another, face to face; in that the facing layers of said upper and lower panels constituting the facing faces are composed of a mixture a) of approximately 15% to 80% of ethylene-vinyl aleool copolymer and b) of about 20% to 85% of a normally heat-sealable polymer, the minimum temperature for heat sealing said polymer   heat sealable being at least 3 C lower than the temperature   minimum heat-weld strip of said ethylene vinyl alcohol; and in that the heat welds between said   facing layers are detachable.   4. Sheet material according to claim 1, -16 22 497 214   characterized in that the mixture comprises a) 50% to 80% of ethylene vinyl alcohol and b) 20% to 50% of said polymer normally heat sealable. -   5. Sheet material according to one of claims   1 and 4, characterized in that said normally heat-sealable polymer is an ionomer, an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, an ethylene-vinyl acetate copolymer or a low density polyethylene, and, in particular, a lonomer or a copolymer ethylene vinyl acetate.   6. Packaging according to one of claims 2 or 3,   characterized in that the sheet material is such that   defined in one of claims 4 or 5.   7. Packaging according to any one of the claims.   2, 3 or 6, characterized in that the opposite panels   are of substantially identical construction.   8. Packaging according to any one of the claims   2, 3 or 6, characterized in that the opposite panels are of different construction.   9. Packaging according to any one of the claims.   tions 2, 3 or 6y characterized in that the upper panels   and lower have different stiffnesses.   10. A heat-sealable package, said package, once closed and sealed, being relatively impermeable to the passage of oxygen through the heat seals, said package being characterized in that it comprises upper and lower panels made of a material made of multi-layer sheet which are welded to each other, face to face, when the packaging is fully formed and sealed, in that the layers of each of said upper and lower panels constituting the opposite faces of the formed and sealed packaging are   composed of a mixture a) of 50% to 80% of ethylene copolymer-   vinyl alcohol and b) from 20% to 50% of normally heat-sealable polymer, the minimum heat-sealing temperature of said normally heat-sealable polymer being at least 31C lower than the minimum heat-seal temperature said ethylene vinyl alcohol.