WO1999008859A1

WO1999008859A1 - Film containers

Info

Publication number: WO1999008859A1
Application number: PCT/EP1998/005048
Authority: WO
Inventors: Harri Rings; Hermann Onusseit
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1997-08-18
Filing date: 1998-08-08
Publication date: 1999-02-25
Also published as: AU9259798A; EP1005414A1; DE19834356A1

Abstract

The invention relates to a method for producing film containers. According to said method, at least two sections of film are glued together with adhesive in partial areas. At least one of said sections of film is sufficiently transparent to UV radiation at least in the glued area. The adhesive used is a hot-melt adhesive which can be set with UV-radiation. The inventive method is economical and the glued edges of the film containers demonstrate a good degree of heat resistance.

Description

Foil container

The invention relates to a method for producing film containers using hot-melt adhesive curable with UV rays, and to film containers that are produced using such an adhesive.

Substances, for example food or pharmaceuticals, are often filled into bag-like packaging for storage and in particular for protection against environmental influences. Such packagings generally have at least one "seam" at which either the sections of a two-layer folded film are connected to themselves at the edges or a section of a first film is connected to a section of a second film, for example circumferentially on three edges is. An opening remaining for filling the container can also be closed after the filling process. It is also possible to fill a first film provided with recesses for receiving the filling material and then to close the filled first film by applying a second film so that the filling material contained in the recesses is shielded from external influences.

Such packagings are often exposed to stresses, for example when filling the contents, during transport to the consumer or by the consumer himself. High demands are therefore made on the seams of the packagings in order to prevent the packaging contents from being released prematurely, possibly associated with their spoilage. A number of methods for producing seams between two foils are known from the prior art

A widely used method for edge fastening in the production of film containers is the fusion of the film sections by heat application. A disadvantage of this method is its duration, since the time taken to form a connection of the foils that is still permanent after cooling prevents a high throughput.

It is also known to connect sections of film by hot melt bonding. Here, a hot melt adhesive is applied in the molten state to a film section, this combination is brought into contact with another film section and then cooled. The connections obtainable in this way are permanent, but in some cases show a lack of heat resistance, since the hot-melt adhesive softens quickly at elevated temperature. This behavior can be problematic in particular if the film containers are filled with products at an elevated temperature or are stored at an elevated temperature.

US-A 4,849,040 describes a method for printing and for producing open pockets from thermoplastic films, in which a first film is printed on a first surface and is applied to a second surface with patterns of an electron-beam-curable adhesive, which to form the later seams of the bags. After congruent application of a second film on the surface provided with the adhesive, the two films are moved through a "curtain" of electron beams, whereby the adhesive hardens. Then the glued areas are cut out and you get open pockets on one side. The method described has the disadvantage that plants for generating Electron radiation require a high investment and also require extensive security measures, so that they are generally not profitable for smaller companies or companies with a low production capacity for film containers.

DE-A 29 13 676 relates to a method for producing composite films by means of solvent-free adhesives. Oligomeric or polymeric esters or ethers which contain both free isocyanate groups and free (meth) acrylate groups in the molecule are used as adhesives. The adhesive is applied to a carrier film and then irradiated with UV light in order to achieve an initially sufficient adhesive strength. The maximum of the adhesive strength only sets in after a few weeks.

It was therefore an object of the invention to provide a method for producing film containers which includes a very fast bonding process in order to enable the highest possible throughput of bonds per unit of time. Furthermore, it was an object of the invention to provide a method for producing film containers, which enables connections with high heat resistance. Another object of the invention was to provide a method for producing film containers, in which the adhesive reaches its full strength shortly after the adhesive process. Another object of the invention was to provide a process for the production of film containers, in which the film sections to be bonded are exposed to the lowest possible temperature increase during the heat seal bonding, and the bonds subsequently nevertheless have excellent heat resistance.

It has now been found that UV-curable hot melt adhesives solve the above-mentioned problems. The invention therefore relates to a method for producing film containers, in which at least two film sections are bonded to one another with adhesive in partial areas, at least one of the film sections being sufficiently transparent to UV rays at least in the area of the bond, and an adhesive by irradiation with UV radiation curable hot melt adhesive is used.

The adhesives used in the context of the invention are so-called hot melt adhesives. Hot melt adhesives are understood to be adhesives that are applied from the melt, i.e. at elevated temperatures of generally about 80 to about 180 ° C., and are solid again after cooling.

For the sake of simplicity, the hot melt adhesives are referred to in the following text as "adhesives", unless expressly stated otherwise.

In the context of the present invention, a “film container” is understood to mean a container whose walls consist at least partially of films and which contains at least one adhesive connection of two film sections.

In the context of the present invention, a “film” is understood to be a thin, flat, flexible, windable web made of a flexible material. For the implementation of the present invention, films can be used which only consist of a single layer and also films which, for. B. by partial or preferably at least in the area of the sections to be glued full-surface lamination by means of adhesives or as so-called extrusion laminates each from individual films of the same chemical composition or from films of different chemical composition have been combined with each other or with metal foils or with paper to form composite foils. The term "film" also includes coated or lacquered films. For the sake of simplicity, both single-layer or multilayer films consisting of only one material and the described composite films or laminates are referred to as "films" in the following text, unless expressly stated otherwise. The films in the sense of the invention also include those film structures which, for example for the purposes of thermal insulation or transport protection, generally have gas-filled cavities which are sealed off from the environment.

The films to be used in the context of the present invention have at least one surface which is at least predominantly formed by a synthetically producible polymer. The proportion of synthetically produced polymers preferably represents the predominant volume of the entire film.

In the context of the present invention, “synthetic polymers” are understood on the one hand to be the polymers produced by polymerization, condensation, polyaddition or other known polymer build-up reaction, but on the other hand naturally occurring polymers also count among the synthetic polymers which can be used in the context of the invention if they are in have been derivatized in a suitable manner, for example by polymer-analogous reaction. The first-mentioned group of synthetic polymers includes, for example, polyolefins, poly (meth) acrylates, polyesters, polyethers, polyamides, polyimides, polyurethanes, polyureas and the like. The group of naturally occurring polymers which have been derivatized in a suitable manner, for example by polymer-analogous reaction, includes in particular the cellulose and starch derivatives, for example alkyl celluloses, Carboxyalkyl celluloses or hydroxyalkyl celluloses or starches, but also esters such as cellulose acetate. The use of biodegradable polymer films is also possible and also provided within the scope of the present invention. The use of polyolefin films, in particular polyethylene or polypropylene films, is particularly preferred in the context of the present invention.

The films can be produced, for example, by casting, calendering or blow molding, the latter usually leading to so-called tubular or blown films. The films can be pretreated in any way, for example subjected to mono- or biaxial stretching or subjected to a surface treatment, for example a corona treatment. The foils can also have been coated or painted. The films can also contain property-modifying additives, for example plasticizers, antioxidants or UV stabilizers.

The film thickness can vary widely. For example, very thin foils can be used (which can also be referred to as films) as long as these foils fulfill the desired tear strength and stability for the intended purpose. As a rule, the lower limit for the film thickness is approximately 10 μm and the upper limit approximately 95 μm or approximately 80 μm. It is preferred if the film used in the process according to the invention has a minimum thickness of approximately 20 μm and a maximum thickness of approximately 50 μm.

According to the present invention, at least two film sections are glued together in partial areas with adhesive. The at least two film sections can originate from at least two physically separate, possibly different films. However, there are also different film sections Foil sections are referred to as they result, for example, from folding and superimposing a single foil or as can be seen, for example, in principle in the case of a foil tube in a top view.

The films which can be used in the context of the present invention can be in web form or in sheet form.

The at least two film sections which can be used in the context of the present invention are bonded to one another in parts with hot melt adhesives, so that, in contrast to composite films, there is no largely full-area lamination. For example, in the method according to the invention, a carrier film coated in some areas with adhesive and an inflow film are brought together, and then, if appropriate, H. if more than one film container is produced from two or more glued film sections, cut to the desired size. An example of such a method is described in the above-mentioned US Pat. No. 4,849,040.

A further preferred possibility for producing the film containers consists in folding a single film sheet or a single film web and gluing the film sections resulting from the folding to one another at least in partial areas, preferably at at least one edge area. If, for example, a film web is folded and the film sections thus created are glued to one another along the entire length of the film web, a film tube is formed which can subsequently be cut, for example, at right angles to the longitudinal axis of the film web and optionally glued in a further edge area.

In the context of the present invention, it is preferred if Position of the film container film webs are used. Therefore, in a preferred embodiment of the invention, the glued film sections are cut to a certain size after the gluing.

In the context of the present invention, a hot-melt adhesive that is curable by radiation and UV rays is used as the adhesive for bonding the at least two film sections at least in partial areas. The main component of an adhesive curable by radiation is at least one so-called photopolymer (photoreactive polymer). In the context of the present invention, photopolymers are understood to be polymers whose properties can be changed in a targeted manner under the influence of irradiation of a specific wavelength. Irradiation of the photopolymers triggers, for example, induced curing through crosslinking. After the crosslinking reaction, the aim is to increase the mechanical strength with improved heat resistance of the polymer. The crosslinking reaction can e.g. B. via CC multiple bonds of polymers after addition of bisfunctional reagents, for example bisazides. It can also proceed via photoreactive functional groups as substituents on the main polymer chain, for example via the cinnamic acid residue in poly (vinylcinnamates). Such postpolymerization or crosslinking reactions usually take place by light-induced initiation, which initiates a radical or ionic polymerization mechanism. In principle, all hot melt adhesives curable by irradiation with UV rays can be used within the scope of the present invention, provided that they at least temporarily firmly bond the materials to be bonded to one another. Examples of adhesives which are particularly suitable in the context of the present invention are those based on polyurethanes, polyacrylates or polymethacrylates and block copolymers based on styrene, butadiene, ethylene or vinyl acetate in various combinations known to those skilled in the art. In the context of the invention, preference is given to using adhesives based on polyacrylates or polymethacrylates.

While conventional adhesives (i.e. adhesives with the exception of the UV-curable hot melt adhesives) usually set either by physical processes or by a chemical reaction, adhesives which combine both setting processes are used in the context of the present invention. Particularly preferred in the context of the present invention are those adhesives which initially bring about a physical adhesion of the two film sections to be bonded and then harden at any later point in time by irradiation with UV rays and thus obtain increased strength, the UV-curable hotmelt adhesives. Acrylate hot-melt adhesives which can be crosslinked by irradiation with UV rays are very particularly suitable in the context of the present invention. On the one hand, these adhesives, as hotmelt adhesives, have the possibility of forming an adhesive connection by physical setting, and on the other hand the adhesive connection can subsequently be reinforced by chemical crosslinking at any later point in time. Instead of the hot melt adhesives, it is also possible, for example, to use hot melt adhesives which initially only form an adhesive bond with low load capacity and low heat resistance. For example, an adhesive connection that can be detached again by light heating and is therefore not yet finally fixed can be achieved, which is finally converted into a firmly adhering connection in a subsequent step by irradiation with UV rays.

In principle, in the context of the present invention, all hot melt adhesive systems in which at least some of the final ones are used can be used as hot melt adhesives curable by irradiation with UV rays Strength of the adhesive bond is caused by a chemical reaction in the adhesive triggered by irradiation with UV rays. In the case of such adhesive systems, the curing mechanism is generally based on the fact that the adhesives contain at least one polymer which, triggered by the radiation, can undergo a chain extension or crosslinking reaction. This presupposes that the polymer carries at least one functional group which, directly or indirectly as a result of the irradiation, undergoes one of the two reactions mentioned above. Such chain-extending reactions are usually triggered by ionic or radical mechanisms. While, for example, functional groups such as epoxy groups are accessible to a chain extension or crosslinking reaction by means of ionic mechanisms, the curing process of the adhesive is preferably triggered by free radical mechanisms in the context of the present invention. This means that the polymers used in the hot melt adhesive in the context of the present invention have at least one free-radically polymerizable, ethylenically unsaturated double bond. It is particularly preferred if the polymers used in the adhesive in the context of the present invention have at least two ethylenically unsaturated double bonds. In principle, all types of polymer which have sufficient initial tack after the film sections have been joined are suitable as polymers which carry these ethylenically unsaturated double bonds. Suitable polymer systems are polyesters, polyurethanes, polyamides, polyacrylates and / or polymethacrylates.

Corresponding polyesters can be prepared, for example, by reacting low molecular weight alcohols, in particular ethylene glycol, propylene glycol 1, 3, diethylene glycol, neopentyl glycol, hexane diol 1, 6, butane diol 1, 4, glycerol or trimethylol propane with caprolactones. Other suitable polyesters can be produced by polycondensation. So difunctional and / or trifunctional alcohols with a corresponding Amount of dicarboxylic acids and / or tricarboxylic acids or their reactive derivatives are condensed into polyesters. Suitable dicarboxylic acids for this are, for example, succinic acid and its higher homologues with up to 16 carbon atoms, furthermore unsaturated dicarboxylic acids such as maleic acid or fumaric acid and aromatic dicarboxylic acids, in particular the isomeric phthalic acids such as phthalic acid, isophthalic acid or terephthalic acid. Citric acid or trimellitic acid, for example, are suitable as tricarboxylic acids. In this case, ethylenically unsaturated, free-radically polymerizable groups are introduced into the polymer either by condensing in unsaturated carboxylic acids or by condensing in unsaturated di- or polyfunctional alcohols.

If di- or polyfunctional compounds containing ethylenically unsaturated double bonds are used in the production of the polyesters, the polymer chain contains the ethylenically unsaturated double bonds in a statistical distribution inside the chain and / or at the chain end. If the ethylenically unsaturated double bond is only to be present at the chain end, then, for example, ethylenically unsaturated, monofunctional acid or alcohol components can also be present in the course of the polymerization of the saturated acid and alcohol components. This defines an ethylenically unsaturated function at the chain end of the polymer chain. Optionally, the polyesters which can be used according to the invention can also carry the ethylenically unsaturated functionality as a side group to the main polymer chain.

Polyurethanes which contain ethylenically unsaturated double bonds can also be used as an adhesive in the context of the present invention. Polyurethanes can be obtained by reacting polyisocyanates with polyols. As a rule, difunctional polyester polyols or polyether polyols are used as polyols. As polyester polyols, which in the Usually have a molecular weight of about 500 to 10,000, for example the above-mentioned polyesters can be used, provided that they have at least one, preferably at least two, OH groups. The molecular weight of the polyester polyols is 100 to 5,000.

Polyether polyols can also be used as the alcohol component. Polyether polyols are understood to mean the reaction products of low molecular weight, polyfunctional alcohols with alkylene oxides having up to four carbon atoms. For example, the reaction products of ethylene glycol, propylene glycol, the isomeric butanediols or hexanediols with ethylene oxide, propylene oxide and / or butylene oxide are suitable for the purposes of the present invention. The reaction products of polyfunctional alcohols such as glycerol, trimethylolethane and / or trimethylolpropane, pentaerythritol or sugar alcohols with the alkylene oxides mentioned are also suitable for polyether polyol. Polyether polyols with a molecular weight of about 100 to 10,000, preferably of about 200 to 3,000, are particularly suitable. In the context of the present invention, polypropylene glycol with a molecular weight of approximately 400 to approximately 2500 is very particularly preferred. Also suitable are polyether polyols, such as are obtainable, for example, by the cationic polymerization of tetrahydrofuran.

The polyurethanes can contain the ethylenically unsaturated, free-radically polymerizable groups at the ends, at the chains (within the polymer chain) or at the sides (ie as a side group to the main polymer chain). The introduction of a terminal, ethylenically unsaturated double bond can, for example, by producing a polyurethane prepolymer with terminal isocyanate groups and further reacting the prepolymer with an ethylenically unsaturated monocarboxylic acid, preferably methacrylic acid, acrylic acid or an ethylenically unsaturated derivative of the latter Acids, or an ethylenically unsaturated alcohol. The polyurethanes which can be used in the context of the present invention can have, together with the terminal and / or chain-linked, ethylenically unsaturated double bonds or instead of these, lateral, ethylenically unsaturated double bonds.

In the context of the present invention, particular preference is given to the use of ethylenically unsaturated polyacrylates or polymethacrylates as hot-melt adhesives which harden by irradiation with UV rays (UV-hardening acrylate adhesives). Such polymers can be obtained, for example, by free-radical or ionic polymerization of acrylic acid and / or methacrylic acid derivatives and subsequent polymer-analogous functionalization of the polymer chain with ethylenically unsaturated compounds.

UV-curing acrylate adhesives are generally one-component products which consist of ethylenically unsaturated polyacrylic or polymethacrylic acid derivatives in a mixture with a photoinitiator. By irradiation with UV light with a wavelength of about 200 to about 400 nm, the molecule of the photoinitiator is usually cleaved or at least excited to form radicals. The radicals formed react with the ethylenically unsaturated double bonds of the polyacrylic or polymethacrylic acid derivatives and trigger free-radical polymerization. If the poly (meth) acrylates contain more than one ethylenically unsaturated double bond, a three-dimensional network is created. All Norrish-Type I fragmenting substances are suitable as photoinitiators. Examples include benzophenone, camphorquinone, quantacure (manufacturer: International Bio-Synthetics), Kayacure MBP (manufacturer Nippon Kayaku), Esacure BO (manufacturer: Fratelli Lamberti), Trigonal 14 (manufacturer: Akzo), Irgacure 651 (manufacturer: Ciba, below other names also available from BASF, Fratelli Lamberti and Kawaguchi), Darocur 1173 (manufacturer: Ciba) and / or Fi-4 (manufacturer: Eastman).

The photoinitiators can be mixed into the adhesive, i. that is, have freedom of movement within the scope of diffusion. However, it is also possible to use polymers in the adhesive which carry the photoinitiator as part of the polymer chain, in particular at the chain end or in a side chain. This concept is applicable to all polymer systems commonly used in adhesives, such as polyesters, polyurethanes and polyacrylates. An advantage of the covalently bound photoinitiators is that the products obtained after the irradiation are essentially free of migratable, low molecular weight components, for example unreacted photoinitiator molecules. This is particularly advantageous in the case of the increasingly important applications in the field of food packaging, since the aim is for such applications to have the lowest possible amount of migratable, low molecular weight components.

Polyurethanes which do not contain olefinically unsaturated double bonds are particularly preferably used in the process according to the invention.

This is of great advantage particularly in the case of hot melt adhesives, since their temperature resistance is much higher due to the lack of ethylenically unsaturated double bonds. Another advantage is that the products are less susceptible to discoloration due to the lack of double bonds and can be stored over a long period of time essentially without the addition of radical inhibitors. In this context, polyacrylic acid esters (polyacrylates) which have at least two different alcohol components in the polyacrylic acid esters are particularly advantageous. One of the alcohol components is usually an alkyl group, the other alcohol component is a photoinitiator, especially a suitably substituted benzophenone derivative. The photoinitiator can be introduced into the polymer molecule in any manner known to the person skilled in the art. For example, this can be done by a polymer-analogous reaction on the polyacrylate, but it is also possible to copolymerize an ethylenically unsaturated, free-radically polymerizable monomer equipped with a photoinitiator in the presence of further acrylic acid esters.

Without wishing to be bound by any particular theory, it is assumed that the crosslinking takes place via an insertion reaction of the irradiated benzophenone molecule, which is in the excited state, into the C-H bond of an alkyl radical in an adjacent polymer molecule. The low tendency to discoloration, the long shelf life and the low tendency towards subsequent embrittlement have an advantageous effect in this class of hot melt adhesives.

The commercial products Arconal® DS 3429 and DS 3458 (manufacturer: BASF AG, Ludwigshafen), for example, are particularly suitable for use in the process according to the invention.

In addition to the polymers described, the adhesive to be used according to the invention may also contain further additives. These include, for example, so-called tackifier resins, which increase the initial stickiness of the hot melt adhesives. In particular, these are modified natural resins, hydrocarbon resins, e.g. Acronal® 4 F, Acronal® A 150 F, Lutonal® M 40 (manufacturer: all BASF AG, Ludwigshafen), Staybelite Ester 10 or Foral 85 (manufacturer: all Hercules, Middelburg, NL).

The UV-curable adhesives are generally irradiated with light of a wavelength of approximately 280 nm to approximately 450 nm. The adhesives used in the process according to the invention are so-called hot melt adhesives. This means that they are processed at a temperature which is at least higher than room temperature. So far, the problem with the use of hot-melt adhesives for the seam bonding of film containers was that the requirements of the hot-melt adhesive for the formation of a durable and resilient, in particular a particularly heat-resistant, adhesive bond were opposed to the thermal properties of the plastic film to be bonded. In order to achieve the best possible heat resistance, the hot melt adhesive must have as high a melting range as possible, while a flexible plastic film generally has a relatively low softening point. This is particularly important in the storage of filled film containers and during the filling process itself, since the seam bonding of the film containers may have to be exposed to elevated temperatures in both processes, even for longer periods.

An advantage of the present invention is therefore also that the film containers have an excellent load-bearing capacity, even under thermal load, immediately after the seam bonding. This is particularly important with a view to avoiding stocks of empty film containers, which should be kept as low as possible for economic reasons.

In the process according to the invention, the hotmelt adhesives are generally applied at temperatures of about 70 to about 140 ° C. Depending on the material to be bonded, the hot melt adhesives are applied in an amount of approximately 1 g / m ² to approximately 100 g / m ² . Good results can be achieved, for example, with an application of about 10 to about 40 g / m ² . If only one UV lamp is used for the irradiation, then Depending on the material and the selected adhesive system, durable bonds with good heat resistance can be achieved, for example, with lamp outputs of approximately 80 to approximately 120 W at a throughput speed of approximately 20 m / min.

The invention thus also relates to a film container, at least having at least two film sections bonded to one another in a partial area by means of a hot-melt adhesive cured with UV rays. At least one of the bonded film sections in the film container according to the invention is preferably a polyolefin film section.

The invention is explained in more detail below with the aid of examples, which, however, do not represent any restriction.

Examples

A polypropylene film web was mechanically glued overlapping on the side edges to form a film tube. Acronal® DS 3458 (adhesive 1) was used as the UV-curable hot melt adhesive. For comparison, an adhesive was made with the non-UV-curable hot melt adhesive Q 8725 N (manufacturer: Henkel KGaA, Düsseldorf) (adhesive 2). The bonds were either not irradiated (Examples 1 and 5) or irradiated with increasing lamp power (Examples 2, 3 and 4). The maximum power of the lamp was 120 W. The peel values were then determined at different temperatures.

To determine the peel values, the bond was loosened at each end of 100 mm long, bonded film sections and one of the two resulting released film sections was fixed during the second film section was loaded with a weight of 30 g. Then the time until the respective, lengthwise complete, separation of the adhesive connection was measured.

The results of Examples 1 to 5 are shown in Table 1 below.

Table 1

Claims

PATENT CLAIMS

1. A process for the production of film containers, in which at least two film sections are glued to one another in partial areas with adhesive, at least one of the film sections being sufficiently transparent to UV rays at least in the area of the bond, and as an adhesive a curable by irradiation with UV rays Hot melt adhesive is used.

2. The method according to claim 1, characterized in that the glued film sections are cut to a certain size after the gluing.

3. The method according to claim 1 or 2, characterized in that at least one film section is a polyolefin film section.

4. The method according to any one of the preceding claims, characterized in that the adhesive is applied at a temperature of 70 to 140 ° C.

5. The method according to any one of the preceding claims, characterized in that the adhesive is exposed to radiation with UV radiation of a wavelength of 280 nm to 450 nm.

6. A film container, at least having at least two sections of film bonded to one another by a hot melt adhesive cured with UV rays.

7. A film container according to claim 6, characterized in that at least one of the glued film sections is a polyolefin film section.