WO2019197234A1

WO2019197234A1 - Oxygen scavenging aqueous lamination adhesive composition

Info

Publication number: WO2019197234A1
Application number: PCT/EP2019/058363
Authority: WO
Inventors: Maria SANTIAGO GALARZA; Raphael Dabbous
Original assignee: Basf Se
Priority date: 2018-04-13
Filing date: 2019-04-03
Publication date: 2019-10-17
Also published as: EP3775084A1

Abstract

A description is given of an oxygen scavenging aqueous lamination adhesive composition comprising (I) at least one lamination adhesive polymer dispersed or dissolved in an aqueous medium; (II) at least one photosensitizer compound; and (III) optionally at least one additive different from (I) and (II).Described are also laminates made by using said composition, for example for making film-to-film laminates, film-to paper laminates and packaging materials, in particular food packaging.

Description

Oxygen scavenging aqueous lamination adhesive composition

Description

The invention relates to an oxygen scavenging aqueous lamination adhesive composition corn- prising a lamination adhesive polymer dispersed or dissolved in an aqueous medium, a photo- sensitizer compound and optionally further additives. Described are also laminates made by using said composition, for example for making film-to-film or film-to-paper laminates and pack- aging materials, in particular food packaging.

It is known that many oxygen sensitive products, including food products such as meat and cheese, smoked and processed luncheon meats, as well as non-food products such as elec- tronic components, pharmaceuticals or medical products deteriorate in the presence of oxygen. For example, the color and the flavor of foods can be adversely affected or the oxidation of li- pids within the food product can result in the development of rancidity. Several techniques have been developed in the packaging industry to limit oxygen sensitive packaged materials to oxy- gen exposure. Such techniques include the use of barrier material with low permeability to oxy- gen as part of the packaging; the inclusion of items capable of consuming oxygen other than the packaging material (e.g. through the use of sachets with material capable of reacting with oxy- gen); the creation of a reduced oxygen environment within the package (e.g. modified atmos- phere packaging - MAP- and vacuum packaging); or the inclusion of an oxygen scavenger as a part of the packaging article.

The use of oxygen scavenger materials for packaging applications for providing an extension of shelf-life of the packaged good is also known. Their implementation helps to reduce the availa- ble oxygen remaining within the packaging headspace, aiming to retard off-reactions which can lead to losses of food, due to enzymatic or microbiological activity causing food spoilage. The scavenging reaction has either a chemical or enzymatic route. The most common carriers of the scavenging system can be a sachet inside the food packaging or a layer with incorporated scavenging material within a system of layers of a multilayer film packaging.

The use of scavenging materials other than in sachets can for example be found on lids and closures, on labels and between the layers of a laminated or coextruded packaging.

The introduction of scavenging materials into a laminate is desired not only to reduce the risk of accidentally fouling of the foodstuff, but also to decrease the complexity of the converting pro- cess; help to compensate for defects within the film, such as pinholes with a diameter less than 10 pm; to provide a passive oxygen barrier with an extra buffer in the form of an active barrier counteracting against temporary loss of barrier properties (retort shock); and to work as a fallback system against flexural stress, e.g. of barrier materials based on AIOx or SiOx which are very brittle barrier materials. Most of the oxygen scavenging systems currently available on the market comprise either a polymer that binds oxygen or comprise systems based on iron ions. Oxygen scavenging sys- tems based on iron ions provide off-color and are activated by moisture. This is a drawback for certain types of food products due to the loss of visual and sensory properties. Likewise, it leads to issues along the packaging conveyor line in the metal detector area, as well as constrains the compatibility of such packaging application for microwaveable foodstuff. In addition to that, iron can react with humidity before being placed in the packaging or in the multilayer film, which leads to a detrimental premature consumption of iron.

Various oxygen absorptive packagings or oxygen scavenging materials for thermoplastics, mainly comprising metal based systems, in particular iron based systems, are described in EP 2 965 906 A1 , JP 5605121 B2, EP3078604 A1 , JP 4590823 B2, WO 2009/080586, WO 201 1/067196, WO 99/47596, WO 201 1/067196. A multi-layer package comprising an interme- diate layer containing an oxygen-absorbing adhesive resin is described in JP2016-013868. Thus, while a variety of approaches to maintaining or reducing oxygen levels in packaged items are known, there remains a need for improved oxygen-scavenging compositions and packaging materials utilizing the same.

Following market trends as well as regulatory trends towards lightweight packaging, i.e. lower environmental impact by elimination of aluminum, recyclability and shelf life extension, the aim of this invention is to develop scavenging systems suitable for laminates made with water-based lamination adhesives in order to extend the shelf life of oxygen-sensitive packaged foodstuff, to further decrease the complexity of a multifilm laminate by eliminating one step in the converting process, and to achieve reduction or elimination of material.

A further aim of the invention is to provide a system with an advanced on-demand activation trigger mechanism, ensuring a long shelf life of the laminate with a high oxygen scavenging per- formance starting the oxygen scavenging activity only upon activation and not unnecessarily earlier than needed. In the case of oxygen scavenging materials having no on-demand activa- tion, the concentration of the oxygen scavenging material needs to be high enough in order to guarantee high oxygen scavenging activity along the whole converting process and a long shelf life of the food packed.

It has now been found that the use of photosensitizer compounds in aqueous lamination adhe- sive compositions can be effectively activated on demand, e.g. by UV-irradiation to provide packaging with enhanced resistance of packed items, e.g. food products, against oxygen attack for longer shelf life of the packed items.

Thus the present invention relates to an oxygen scavenging aqueous lamination adhesive corn- position comprising

(I) at least one lamination adhesive polymer dispersed or dissolved in an aqueous medium;

(II) at least one photosensitizer compound; and (III) optionally at least one additive different from (I) and (II).

Oxygen scavenging materials help to remove or decrease the level of oxygen in a package.

In the following the term„(meth)acryl...“ and similar terms may be used as abbreviations for „acryl... or methacryl...“. In the term Cx-alkyl(meth)acrylate and similar terms x means the num- ber of C-atoms in the alkyl group.

Glass transition temperature Tg is measured by Differential Scanning Calorimetry (ASTM D 3418-08, "midpoint temperature”, heating rate 20 °C/min). The Tg of a polymerizate is the Tg from evaluation of the second heating curve.

Lamination adhesives are preferably not self-adhesive and non-tacky. Not self-adhesive adhe- sives are adhesives which in contrast to pressure-sensitive adhesives have no or only very low tack at room temperature and which are typically applied by using pressure and/or elevated temperatures. The tack measured as Loop Tack is preferably lower than 1 ,7 N / 25 mm (adhe- sive applied in an amount of 20 pm on a 12 pm polyethylene terephthalate film, measured on steel at room temperature (20 °C) and at a removing speed of 300 mm/min).

A photosensitizer is a molecule that produces a chemical change in another molecule in a pho- tochemical process, thus acting as photochemical catalyst. Photosensitizers generally act by absorbing ultraviolet or visible region of electromagnetic radiation and transferring absorbed energy to adjacent molecules which have different light absorption characteristics and which can chemically react after the energy transfer from the photosensitizer. Photosensitizers usually have large de-localized pi-systems, which lower the energy of HOMO orbitals. Absorption of light might be able to ionize the molecule or to produce free radicals and to initiate oxygen scavenging reactions after activation by light.

The concentration of the photosensitizer compound in the aqueous lamination adhesive compo- sition is preferably at least 0.05 wt.%, e.g. from 0.05 wt % to 15 wt %, more preferably from 0.1 wt % to 8 wt %, based on the amount of the lamination adhesive polymer. Photosensitizers can be monomeric, oligomeric or polymeric. Preferred photosensitizer compounds are monomeric or oligomeric. The photosensitizer may be water-soluble or water-insoluble.

Suitable photosensitizer compounds are for example carbonyl compounds. Suitable photosensi- tizer compounds can be selected from the group consisting of alpha-hydroxyketones (in particu- lar 1-aryl-2-hydroxy ketones), phenylglycoxylates, acyl phosphine oxides (in particular phenyl benzoyl phosphine oxides), phenyl benzoyl phosphinates, aminoketones, benzophenone corn- pounds, anthraquinone compounds, benzildimethylketals, and onium salts. Preferred onium salts are for example diaryliodonium salts and triarylsulfonium salts. Also preferred are alpha- hydroxyketones and acyl phosphine oxides. Exemplary photosensitizers suitable for use in the practice of this invention are 2,3-hexanedione, diacetyl acetophenone, benzoin and benzoin ethers such as the methyl, ethyl, propyl or butyl ethers of benzoin, 2,2-diethoxyacetophenone, 2,2-dimethoxyacetophenone, benzophenone or a benzophenone salt, and phenyl-(1-hydroxy- cyclohexyl)ketone. Preferred photosensitizers (II) are selected from the group consisting of 1- aryl-2-hydroxy ketones and benzoyl phenylphosphinates. More preferred photosensitizer corn- pounds (II) are selected from the group consisting of 2-hydroxy-2-methyl-1 -phenyl-propan-1 - one, 2-hydroxy-1 -{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1 -one and 1 -[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1 -propane-1 -one).

The aqueous lamination adhesive composition comprises at least one lamination adhesive pol- ymer dispersed or dissolved in an aqueous medium. The adhesive polymers are present in the adhesive compositions preferably in amounts of from 15 to 75 wt.-%, more preferably from 20 to 70 wt.-%. or from 30 to 60 wt.-% or from 40 to 55 wt.-%. The adhesive polymers may be pol- ymers obtainable by free radical polymerization of ethylenically unsaturated compounds (mon- omers) or may be polymers obtainable by polycondensation of suitable monomers, such as pol- yurethanes, for example. Preferred dispersion adhesives are aqueous dispersions of poly(meth)acrylates or aqueous dispersions of polyurethanes.

The monomers are preferably selected such that the glass transition temperature of the lamina- tion adhesive polymer is in the range from -40°C to +15°C, more particularly from -35°C to +10°C or from -10 to +10 °C. By a controlled variation of the nature and amount of the mono- mers it is possible for the skilled person to prepare adhesive polymer compositions whose pol- ymers have a glass transition temperature within the desired range. The glass transition tem- perature is determined by differential scanning calorimetry (ASTM D 3418-08, midpoint temper- ature). The glass transition temperature of the polymer in the polymer dispersion is the glass transition temperature obtained on evaluation of the second heating curve (heating rate

20°C/min).

Suitable adhesive polymers are more particularly poly(meth)acrylates, ethylene/vinyl acetate copolymer, polyurethanes, polyamide resins, saturated polyesters, polyolefins, styrene/buta- diene block copolymers, styrene/isoprene block copolymers and polyimides. Most preferred are poly(meth)acrylates and polyurethanes.

Suitable lamination adhesive polymers are for example polymers prepared by free radical polymerization of monomers comprising at least 60 wt.-%, or at least 80 wt.-%, more preferably at least 90 wt.-%, based on the total amount of monomers, of at least one monomer (principal monomer) selected from the group consisting of alkyl acrylates with 1 to 20 C-atoms in the alkyl group, alkyl methacrylates with 1 to 20 C-atoms in the alkyl group, vinyl esters of carboxylic ac- ids with up to 20 C-atoms, vinyl aromates with up to 20 C-atoms, ethylenically unsaturated ni- triles, vinyl halides, vinyl ethers of alcohols with 1 to 10 C atoms, aliphatic hydrocarbons with 2 to 8 C atoms and one or two ethylenic double bonds, Preferred lamination adhesive polymers are for example polymers prepared by free radical polymerization of monomers comprising

a) at least 60 wt.-%, or at least 80 wt.-%, more preferably at least 90 wt.-%, based on the total amount of monomers, of at least one monomer selected from the group consisting of alkyl acrylates with 1 to 20 C-atoms in the alkyl group, alkyl methacrylates with 1 to 20 C-atoms in the alkyl group, vinyl esters of carboxylic acids with up to 20 C-atoms, vinyl aromates with up to 20 C-atoms, ethylenically unsaturated nitriles, vinyl halides, vinyl ethers of alcohols with 1 to 10 C atoms, aliphatic hydrocarbons with 2 to 8 C atoms and one or two ethylenic double bonds,

b) at least 0.1 wt.-%, based on the total amount of monomers, of at least one monomer with at least one acid group, preferably selected from acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, vinyl acetic acid, vinyl lactic acid, vinyl sulfonic acid, styrene sulfonic acid, acrylamido methylpropane sulfonic acid, sulfopropyl acrylate, sulfopro- pyl methacrylate,

c) optional at least one further monomer different from monomers a) and b).

Preferred adhesive polymers are (meth)acrylate polymers and vinyl acetate polymers. The (meth)acrylate polymers are formed from at least one (meth)acrylate monomer, which may be copolymerized with further monomers. The vinyl acetate polymers are formed from at least one vinyl acetate monomer, which may be copolymerized with further monomers; ethylene/vinyl ace- tate copolymer is an example. Suitable monomers are, for example, (meth) acrylic acid alkyl esters having a C1-C10 alkyl radical, such as methyl methacrylate, methyl acrylate, n-butyl acry- late, ethyl acrylate, and 2-ethylhexyl acrylate. In particular, mixtures of the (meth)acrylic acid alkyl esters are also suitable. Vinyl esters of carboxylic acids having 1 to 20 C atoms are, for example, vinyl laurate, vinyl stearate, vinyl propionate, Versatic acid vinyl esters, and vinyl ace- tate. Vinylaromatic compounds contemplated include vinyltoluene, a- and p-methylstyrene, a-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene, and - preferably - styrene. Examples of ni- triles are acrylonitrile and methacrylonitrile. The vinyl halides are chlorine-, fluorine- or bromine- substituted, ethylenically unsaturated compounds, preferably vinyl chloride and vinylidene chlo- ride. Examples of vinyl ethers include vinyl methyl ether and vinyl isobutyl ether. Preferred vinyl ethers are those of alcohols comprising 1 to 4 C atoms. Suitable hydrocarbons having 4 to 8 C atoms and two olefinic double bonds are, for example, butadiene, isoprene, and chloroprene. Hydrocarbons having 2 to 4 C atoms are, for example, ethylene, propylene or butene. Preferred principal monomers are C1 to C10 alkyl acrylates and C1 to C10 alkyl methacrylates, more particu- larly C1 to Cs alkyl acrylates and methacrylates, and vinylaromatics, more particularly styrene, and mixtures thereof. Especially preferred are methyl acrylate, methyl methacrylate, ethyl acry- late, n-butyl acrylate, n-hexyl acrylate, octyl acrylate, and 2-ethylhexyl acrylate, styrene, and also mixtures of these monomers.

As well as the principal monomers, the adhesive polymer may comprise further monomers, ex- amples being acid monomers, monomers containing hydroxyl groups, more particularly C1-C10- hydroxyalkyl (meth)acrylates, or (meth)acrylamide. Further monomers also include phenyloxy- ethylglycol mono(meth)acrylate, glycidyl (meth)acrylate, aminoalkyl (meth)acrylates such as, for example, 2-aminoethyl (meth)acrylate. Alkyl groups have preferably from 1 to 20 C atoms.

Other further monomers include crosslinking monomers. The further monomers are used gen- erally in minor amounts; their fraction in total is preferably below 10 wt.-%, more particularly below 5 wt.-%.

Preferred adhesive polymers of the adhesive composition are acrylate or methacrylate polymers which are formed not only of acrylic ester and/or methacrylic ester monomers but also of mon- omers having acid groups. The monomers having acid groups are present preferably at not less than 0.1 wt.-%, e.g. 0.1 wt.-% to 15 wt.-%, preferably in amounts of 0.1 wt.-% to 5 wt.-%, more preferably 0.2 wt.-% to 4 wt.-%, very preferably 0.5 wt.-% to 3 wt.-%, based on the total amount of monomers. Examples of monomers having acid groups are monomers having carboxylic, sulfonic or phosphonic acid groups. Carboxylic acid groups are preferred. Examples include acrylic acid, methacrylic acid, itaconic acid, maleic acid or fumaric acid. The acid groups may be present in the form of their salts.

The radically polymerized adhesive polymers are preferably prepared by emulsion polymeriza- tion.

Another type of preferred lamination adhesive polymers are polyurethanes. The polyurethanes are preferably made from

a) at least one diisocyanate,

b) at least one diol, of which

b1 ) 10 to 100 mol-%, based on the total amount of diols(b), have a molecular weight of from 500 to 5000 g/mol, and

b2) 0 to 90 mol-%, based on the total amount of diols(b), have a molecular weight of from

60 to 500 g/mol,

c) at least one monomer different from monomers (a) and (b) having at least one isocyanate group or at least one group reactive with isocyanate groups and which additionally has at least one hydrophilic group or at least one potentially hydrophilic group, and

d) optionally at least one monomer different from monomers (a) to (c) having at least two reac- tive groups selected from alcoholic hydroxy groups, primary or secondary amino groups and isocyanate groups, and

e) optionally at least one monofunctional monomer different from monomers (a) to (d) having one reactive group selected from alcoholic hydroxy groups, primary or secondary amino groups and isocyanate groups.

The polyurethane is preferably synthesized from at least 40 wt.-%, more preferably at least 60 wt.-%, and very preferably at least 80 wt.-% of diisocyanates and at least one diol selected from polyetherdiols and polyesterdiols.

Suitable diisocyanates a) are organic diisocyanates, for example selected from diisocyanates of the formula X(NCO)2, where X is a noncyclic aliphatic hydrocarbon radical having 4 to 15 car- bon atoms, a cycloaliphatic hydrocarbon radical having 6 to 15 carbon atoms, an aromatic hy- drocarbon radical having 6 to 15 carbon atoms, or an araliphatic hydrocarbon radical having 7 to 15 carbon atoms.

Preferred diisocyanates a) are selected from tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), dodecamethylene diisocyanate, 1 ,4-diisocyanatocyclohexane, 5-isocyanato- 1-(isocyanatomethyl)-1 ,3,3-trimethylcyclohexane (IPDI), 2,2-bis(4-isocyanatocyclohexyl)propane, trimethylhexane diisocyanate, 1 ,4-diisocyanatobenzene, 2,4-diisocyanatotoluene, 2,6-diisocya- natotoluene (TDI), 4,4’-diisocyanatodiphenylmethane, 2,4’-diisocyanatodiphenylmethane, p-xylylene diisocyanate, tetramethylxylylene diisocyanate (TMXDI), the isomers of bis(4-isocya- natocyclohexyl)methane (HMDI) such as the trans/trans, the cis/cis, and the cis/trans isomers, and also mixtures consisting of these compounds. Diisocyanates of this kind are available commercially.

With particular preference the diisocyanate a) is selected from the group consisting of hexa- methylene diisocyanate, 5-isocyanato-1-(isocyanatomethyl)-1 ,3,3-trimethylcyclohexane,

2,6-diisocyanatotoluene, and tetramethylxylylene diisocyanate, or a mixture thereof.

Preferred mixtures of these diisocyanates are in particular the mixtures of the respective struc- tural isomers of diisocyanatotoluene and of diisocyanatodiphenylmethane, particularly suitability being possessed by the mixture of 80 mol% 2,4-diisocyanatotoluene and 20 mol% 2,6-diisocya- natotoluene. Also particularly advantageous are the mixtures of aromatic isocyanates such as 2,4-diisocyanatotoluene and/or 2,6-diisocyanatotoluene with aliphatic or cycloaliphatic isocya- nates such as hexamethylene diisocyanate or IPDI, with the preferred mixing ratio of the ali- phatic to aromatic isocyanates being 4 : 1 to 1 : 4.

Isocyanate compounds used to synthesize the polyurethanes, in addition to those mentioned above, also include isocyanates which in addition to the free isocyanate groups carry further, blocked isocyanate groups, e.g., uretdione groups.

The diol compounds b) preferably have a number-average molar weight of 500 to 5000 g/mol, preferably of 1000 to 3000 g/mol. The molecular weight in question is the number-average mo- lar weight Mn. Mn is obtained by determining the number of end groups (OH number). The diol compounds b) preferably comprise no ionic group or group which can be converted into an ionic group.

The diol compounds b1 ) may be polyester diols. Preference is given to using polyester diols obtained by reacting dihydric alcohols with dibasic carboxylic acids. Instead of the free dicar- boxylic acids it is also possible to use the corresponding dicarboxylic anhydrides or correspond- ing dicarboxylic esters of lower alcohols (alcohols having 1 to 4 C atoms) or mixtures thereof for preparing the polyester diols. The dicarboxylic acids can be aliphatic, cycloaliphatic, araliphatic, aromatic or heterocyclic and can, if appropriate, be substituted, by halogen atoms for example, and/or unsaturated. Exam- pies thereof include the following: suberic acid, azelaic acid, phthalic acid, isophthalic acid, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlo- rophthalic anhydride, endomethylenetetrahydrophthalic anhydride, glutaric anhydride, maleic acid, maleic anhydride, fumaric acid, and dimeric fatty acids. Preferred dicarboxylic acids are those of the general formula HOOC-(CH2)_y-COOH, where y is a number from 1 to 20, preferably an even number from 2 to 20, examples being succinic acid, adipic acid, sebacic acid, and do- decanedicarboxylic acid. Adipic acid is particularly preferred.

Examples of suitable alkanediols include ethylene glycol, propane-1 ,2-diol, propane-1 ,3-diol, butane-1 ,3-diol, pentane-1 ,5-diol, neopentyl glycol, bis(hydroxymethyl)cyclohexanes such as 1 ,4-bis(hydroxymethyl)cyclohexane, 2-methylpropane-1 ,3-diol, methylpentanediols, and also diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, dibutylene glycol, and polybutylene glycols. Preferred dialcohols are those of the general formula HO-(CH2)_x-OH, where x is a number from 1 to 20, preferably an even number from 2 to 20. Examples thereof are ethylene glycol, butane-1 ,4-diol, hexane-1 ,6-diol, octane-1 ,8-diol, dodecane-1 ,12-diol, and neopentyl glycol. Butane-1 ,4-diol and hexane-1 ,6-diol are particularly preferred.

The diol compounds b1 ) may be polycarbonatediols, such as may be obtained, for example, by reacting phosgene with an excess of the low molecular weight alcohols specified as synthesis components for the polyesterpolyols.

The diol compounds b1 ) may be lactone-based polyesterdiols, which are homopolymers or co- polymers of lactones, preferably hydroxy-terminated adducts of lactones with suitable difunc- tional starter molecules. Preferred lactones are those derived from compounds of the general formula HO-(CH2)_z-COOH, where z is a number from 1 to 20 and where one hydrogen atom of a methylene unit may also be substituted by a Ci to C₄ alkyl radical. Examples are s-capro- lactone, b-propiolactone, g-butyrolactone and/or methyl-s-caprolactone, and mixtures thereof. Examples of suitable starter components are the low molecular weight dihydric alcohols speci- fied above as a synthesis component for the polyesterpolyols. The corresponding polymers of e-caprolactone are particularly preferred. Lower polyesterdiols or polyetherdiols as well can be used as starters for preparing the lactone polymers. Instead of the polymers of lactones it is also possible to use the corresponding chemically equivalent polycondensates of the hydroxy- carboxylic acids corresponding to the lactones.

The diol compounds b1 ) may be polyether diols. Polyetherdiols are obtainable in particular by polymerizing ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, styrene oxide or epichlorohydrin with itself, in the presence of BF3 for example, or by subjecting these corn- pounds, if appropriate in a mixture or in succession, to addition reaction with starter components containing reactive hydrogen atoms, such as alcohols or amines, examples being water, eth- ylene glycol, propane-1 ,2-diol, propane-1 ,3-diol, 2,2-bis(4-hydroxyphenyl)propane, and aniline. Particular preference is given to polypropylene oxide and polytetrahydrofuran, preferably with a molecular weight of from 240 to 5000, and in particular of from 500 to 4500. The polyether diols are obtainable in particular by polymerization of propylene oxide or tetrahydrofuran with itself, in the presence of BF₃, for example, or by addition reaction of these compounds, optionally in a mixture or in succession, with starter components containing reactive hydrogen atoms, such as alcohols or amines, examples being water, ethylene glycol, propane-1 ,2-diol, propane-1 ,3-diol, 2,2-bis(4-hydroxyphenyl)propane, or aniline. A suitable polytetrahydrofuran has, for example, a number-average molecular weight of 240 to 5000 g/mol or of 500 to 5000 g/mol or of 500 to 4500 g/mol.

Compounds subsumed under b1) include only those polyetherdiols composed to an extent of less than 20 wt.-% of ethylene oxide. Polyetherdiols with at least 20 wt.-% are hydrophilic poly- etherdiols, which are counted as monomers c).

It may also be possible to use polyhydroxyolefins, preferably those having 2 terminal hydroxyl groups, e.g., a,w-dihydroxypolybutadiene, a,w-dihydroxypolymethacrylic esters or a,oo-di- hydroxypolyacrylic esters, as monomers (b1 ). Such compounds are known for example from EP-A 622 378. Further suitable polyols are polyacetals, polysiloxanes, and alkyd resins.

The polyurethane is preferably formed from at least 50 wt.-%, more preferably at least 85 wt.-%, very preferably at least 95 wt.-% or of 100 wt.-%, based on all the dihydroxy compounds, of the polyester diols or polyether diols b1 ). Use may also be made of mixtures of the aforementioned polyester diols and polyether diols. Preferred dihydroxy compounds b1 ) are the polyesterdiols specified above. Particularly preferred are adipic acid-butanediol polyesters and adipic acid- hexanediol polyesters.

The hardness and the elasticity modulus of the polyurethanes can be increased by using as diols (b) not only the diols (b1 ) but also low molecular weight diols (b2) having a molecular weight of from about 60 to 500, preferably from 62 to 200 g/mol. Monomers (b2) used are in particular the synthesis components of the short-chain alkanediols specified for preparing poly- esterpolyols, preference being given to unbranched diols having 2 to 12 carbon atoms and an even number of carbon atoms, and also to pentane-1 ,5-diol and neopentyl glycol.

Examples of suitable diols b2) include ethylene glycol, propane-1 ,2-diol, propane-1 ,3-diol, bu- tane-1 ,3-diol, pentane-1 ,5-diol, neopentyl glycol, bis(hydroxymethyl)cyclohexanes such as 1 ,4-bis(hydroxymethyl)cyclohexane, 2-methylpropane-1 ,3-diol, methylpentanediols, and also diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, dibutylene glycol, and polybutylene glycols. Preferred diols b2) are those of the general formula HO-(CH2)_x-OH, where x is a number from 1 to 20, preferably an even number from 2 to 20. Examples thereof are ethylene glycol, butane-1 ,4-diol, hexane-1 ,6-diol, octane-1 ,8-diol, dodecane-1 ,12-diol, and neopentyl glycol. In order to make the polyurethanes dispersible in water they comprise as synthesis components at least one monomer (c) different from monomers (a) and (b) which carry at least one isocya- nate group or at least one group reactive toward isocyanate groups and, furthermore, at least one hydrophilic group or a group which can be converted into a hydrophilic group. In the text below; the term“hydrophilic groups or potentially hydrophilic groups” is abbreviated to“(poten- tially) hydrophilic groups”. The (potentially) hydrophilic groups react with isocyanates at a sub- stantially slower rate than do the functional groups of the monomers used to synthesize the pol- ymer main chain. The fraction of the components having (potentially) hydrophilic groups among the total quantity of components (a), (b), (c), (d), and (e) is generally such that the molar amount of the (potentially) hydrophilic groups, based on the amount by weight of all monomers (a) to (e), is from 30 to 1000, preferably from 50 to 500, and more preferably from 80 to 300 mmol/kg. The (potentially) hydrophilic groups can be nonionic or, preferably, (potentially) ionic hydrophilic groups.

Particularly suitable nonionic hydrophilic groups are polyethylene glycol ethers composed of preferably from 5 to 100, more preferably from 10 to 80 repeating ethylene oxide units. The amount of polyethylene oxide units is generally from 0 to 10 wt.-%, preferably from 0 to 6 wt.-%, based on the amount by weight of all monomers (a) to (e). Preferred monomers containing nonionic hydrophilic groups are polyethylene oxide diols containing at least 20% by weight of ethylene oxide, polyethylene oxide monools, and the reaction products of a polyethylene glycol and a diisocyanate which carry a terminally etherified polyethylene glycol radical. Diisocyanates of this kind and processes for preparing them are specified in patents US-A 3,905,929 and US- A 3,920,598.

Ionic hydrophilic groups are, in particular, anionic groups such as the sulfonate, the carboxylate, and the phosphate group in the form of their alkali metal salts or ammonium salts, and also cat- ionic groups such as ammonium groups, especially protonated tertiary amino groups or quater- nary ammonium groups. Potentially ionic hydrophilic groups are, in particular, those which can be converted into the abovementioned ionic hydrophilic groups by simple neutralization, hydrol- ysis or quaternization reactions, in other words, for example, carboxylic acid groups or tertiary amino groups.

Of particular practical importance as (potentially) cationic monomers (c) are, in particular, mon- omers containing tertiary amino groups, examples being tris(hydroxyalkyl)amines, N,N’-bis- (hydroxyalkyl)alkylamines, N-hydroxyalkyldialkylamines, tris(aminoalkyl)amines, N,N’-bis(amino- alkyl)alkylamines, and N-aminoalkyldialkylamines, the alkyl radicals and alkanediyl units of these tertiary amines consisting independently of one another of 1 to 6 carbon atoms. Also suit- able are polyethers containing tertiary nitrogen atoms and preferably two terminal hydroxyl groups, such as are obtainable in a conventional manner, for example, by alkoxylating amines containing two hydrogen atoms attached to amine nitrogen, such as methylamine, aniline or N,N’-dimethylhydrazine. Polyethers of this kind generally have a molar weight of between 500 and 6000 g/mol. These tertiary amines are converted into the ammonium salts either with acids, preferably strong mineral acids such as phosphoric acid, sulfuric acid, hydrohalic acids, or strong organic acids, or by reaction with suitable quaternizing agents such as Ci to C₆ alkyl hal- ides or benzyl halides, e.g., bromides or chlorides.

Suitable monomers having (potentially) anionic groups normally include aliphatic, cycloaliphatic, araliphatic or aromatic carboxylic acids and sulfonic acids which carry at least one alcoholic hydroxyl group or at least one primary or secondary amino group. Preference is given to dihy- droxyalkylcarboxylic acids, especially those having 3 to 10 carbon atoms, such as are also de- scribed in US-A 3,412,054. Particular preference is given to compounds of the general formula (d )

R³

HO-R — R-OH (^)

COOH

in which R¹ and R² are a Ci to C₄ alkanediyl (unit) and R³ is a Ci to C₄ alkyl (unit), and especially to dimethylolpropionic acid (DMPA). Also suitable are corresponding dihydroxysulfonic acids and dihydroxyphosphonic acids such as 2,3-dihydroxypropanephosphonic acid.

Otherwise suitable are dihydroxyl compounds having a molecular weight of more than 500 to 10 000 g/mol and at least 2 carboxylate groups, which are known from DE-A 39 1 1 827. They are obtainable by reacting dihydroxyl compounds with tetracarboxylic dianhydrides such as pyro- mellitic dianhydride or cyclopentanetetracarboxylic dianhydride in a molar ratio of from 2 : 1 to 1 .05 : 1 in a polyaddition reaction. Particularly suitable dihydroxyl compounds are the mono- mers (b2) cited as chain extenders and also the diols (b1 ).

Suitable monomers (c) containing amino groups reactive toward isocyanates include aminocar- boxylic acids such as lysine, b-alanine or the adducts of aliphatic diprimary diamines with a,b- unsaturated carboxylic or sulfonic acids that are specified in DE-A 20 34 479.

Such compounds are for example of formula H2N-R⁴-NH-R⁵-X (c₂)

where R⁴ and R⁵ independently of one another are a Ci to Ce alkanediyl unit, preferably eth- ylene, and X is COOH or SO₃H.

Particularly preferred compounds of the formula (c2) are N-(2-aminoethyl)-2-aminoethane carb- oxylic acid and also N-(2-aminoethyl)-2-aminoethanesulfonic acid and the corresponding alkali metal salts, with Na being a particularly preferred counterion.

Also particularly preferred are the adducts of the abovementioned aliphatic diprimary diamines with 2-acrylamido-2-methylpropanesulfonic acid, as described for example in DE-B 1 954 090.

Where monomers with potentially ionic groups are used, their conversion into the ionic form may take place before, during or, preferably, after the isocyanate polyaddition, since the ionic monomers are frequently difficult to dissolve in the reaction mixture. Examples of neutralizing agents include ammonia, NaOH, triethanolamine (TEA), triisopropylamine (TIPA) or morpholine, or its derivatives. The sulfonate or carboxylate groups are particularly preferably in the form of their salts with an alkali metal ion or ammonium ion as counterion.

The polyurethane comprises preferably anionic groups, especially sulfonate groups, and with particular preference carboxylate groups.

The monomers (d), which are different from the monomers (a) to (c) may serve for crosslinking or chain extension. They comprise nonphenolic alcohols with a functionality of more than 2, amines having 2 or more primary and/or secondary amino groups, and compounds which as well as one or more alcoholic hydroxyl groups carry one or more primary and/or secondary ami- no groups. Alcohols having a functionality of more than 2, which may be used in order to set a certain degree of branching or crosslinking, include for example trimethylolpropane, glycerol, or sugars. Also suitable are monoalcohols which as well as the hydroxyl group carry a further iso- cyanate-reactive group, such as monoalcohols having one or more primary and/or secondary amino groups, monoethanolamine for example. Polyamines having 2 or more primary and/or secondary amino groups are used especially when the chain extension and/or crosslinking is to take place in the presence of water, since amines generally react more quickly than alcohols or water with isocyanates. This is frequently necessary when the desire is for aqueous dispersions of crosslinked polyurethanes or polyurethanes having a high molar weight. In such cases the approach taken is to prepare prepolymers with isocyanate groups, to disperse them rapidly in water, and then to subject them to chain extension or crosslinking by adding compounds having two or more isocyanate-reactive amino groups. Amines suitable for this purpose are generally polyfunctional amines of the molar weight range from 32 to 500 g/mol, preferably from 60 to 300 g/mol, which contain at least two amino groups selected from the group consisting of primary and secondary amino groups. Examples of such amines are diamines such as diaminoethane, diaminopropanes, diaminobutanes, diaminohexanes, piperazine, 2,5-dimethylpiperazine, ami- no-3-aminomethyl-3,5,5-trimethylcyclohexane (isophoronediamine, I PDA), 4,4’-diaminodicyclo- hexylmethane, 1 ,4-diaminocyclohexane, aminoethylethanolamine, hydrazine, hydrazine hydrate or triamines such as diethylenetriamine or 1 ,8-diamino-4-aminomethyloctane. The amines can also be used in blocked form, e.g., in the form of the corresponding ketimines (see for example CA-A 1 129 128), ketazines (cf. e.g. US-A 4,269,748) or amine salts (see US-A 4,292,226). Ox- azolidines as well, as used for example in US-A 4,192,937, represent blocked polyamines which can be used for the preparation of the polyurethanes of the invention, for chain extension of the prepolymers. Where blocked polyamines of this kind are used they are generally mixed with the prepolymers in the absence of water and this mixture is then mixed with the dispersion water or with a portion of the dispersion water, so that the corresponding polyamines are liberated by hydrolysis. It is preferred to use mixtures of diamines and triamines, more preferably mixtures of isophoronediamine (IPDA) and diethylenetriamine (DETA).

The polyurethanes comprise preferably from 1 to 30 mol%, more preferably from 4 to 25 mol%, based on the total amount of components (b) and (d), of a polyamine having at least 2 isocya- nate-reactive amino groups as monomer (d). For the same purpose it is also possible to use, as monomers (d), isocyanates having a functionality of more than two. Examples of standard commercial compounds are the isocyanurate or the biuret of hexamethylene diisocyanate.

Monofunctional monomers (e) comprise monoisocyanates, monoalcohols, and mono-primary and -secondary amines. Their fraction is generally not more than 10 mol%, based on the total molar amount of the monomers. These monofunctional compounds customarily carry further functional groups such as olefinic groups or carbonyl groups and serve to introduce into the polyurethane functional groups which facilitate the dispersing and/or the crosslinking or further polymer-analogous reaction of the polyurethane. Monomers suitable for this purpose include those such as isopropenyl-a,a-dimethylbenzyl isocyanate (TMI) and esters of acrylic or meth- acrylic acid such as hydroxyethyl acrylate or hydroxyethyl methacrylate.

Within the field of polyurethane chemistry it is general knowledge how the molecular weight of polyurethanes can be adjusted by selecting the proportions of the mutually reactive monomers and also the arithmetic mean of the number of reactive functional groups per molecule.

Components (a) to (e) and their respective molar amounts are normally chosen so that the ratio A : B, where

A is the molar amount of isocyanate groups and

B is the sum of the molar amount of the hydroxyl groups and the molar amount of the func- tional groups which are able to react with isocyanates in an addition reaction,

is from 0.5:1 to 2:1 , preferably from 0.8:1 to 1.5, more preferably from 0.9:1 to 1.2:1. With very particular preference the ratio A:B is as close as possible to 1 :1.

The monomers (a) to (e) employed carry on average usually from 1.5 to 2.5, preferably from 1.9 to 2.1 , more preferably 2.0 isocyanate groups and/or functional groups which are able to react with isocyanates in an addition reaction.

The polyaddition of components (a) to (e) for preparing the polyurethane takes place preferably at reaction temperatures of up to 180°C, preferably up to 150°C, under atmospheric pressure or under the autogenous pressure. The preparation of polyurethanes, and of aqueous polyure- thane dispersions, is known to the skilled worker.

The polyurethanes preferably have a K value of 20 to 60, measured in N,N-dimethylformamide (DMF) at 21 °C. The K value is a relative viscosity number, which is determined in analogy to DIN 53 726 at 25°. It comprises the flow rate of a 1 weight% strength solution of the polyure- thane in DMF, relative to the flow rate of pure DMF, and characterizes the average molecular weight of the polyurethane.

The oxygen scavenging aqueous lamination adhesive composition optionally comprises at least one additive (III) different from (I) and (II). The additive (III) is preferably selected from the group consisting of sulfites, carboxylic acid salts, vitamin A derivatives, vitamin C derivatives, phos- phites, nitrites and nitrates, preferably selected from the group consisting of bisulfites, ascorbate salts and nitrite salts. Preferably the at least one additive (III) is selected from the group consist- ing of vitamine A acetate and metal salts such as the metal salts of metabisulfite, the metal salts of ascorbic acid or metal salt nitrites, wherein the metal salts are preferably alkaline metal salts or alkaline earth metal salts, most preferably the sodium salts.

Preferred combinations of photosensitizers (II) with additives (III) are compositions comprising at least one photosensitizer (II) selected from the group consisting of 1-aryl-2-hydroxy ketones and benzoyl phenylphosphinates and at least one additive (III) selected from the group consist- ing of vitamine A acetate and metal salts such as the metal salts of metabisulfite, the metal salts of ascorbic acid or metal salt nitrites, wherein the metal salts are preferably alkaline metal salts or alkaline earth metal salts.

The weight ratio of metal salt additive (III) to photosensitizer (II) is preferably from 1 to 50, pref- erably 2 to 10 parts by weight of metal salt additive (III) per part by weight of photosensitizer (II).

The weight ratio of vitamin A acetate to photosensitizer (II) is preferably from 0,1 to 10, prefera- bly 0,5 to 2 parts by eight of vitamin A acetate per part by weight of photosensitizer (II).

The adhesive composition of the invention is aqueous and contains preferably no or only minor amounts of organic solvents, in particular no or only minor amounts of organic solvents with boiling points under 100 °C. Organic solvents are present in an amount of preferably less than 5 weight-%, more preferably from 0 to less than 4 weight-%, more preferred from 0 to less than 2 weight-%, based on the total weight of the aqueous composition.

The lamination adhesive may be employed as a one-component composition, i.e. without addi- tional crosslinking agents or as a two-component composition including at least one crosslinking agent such as for example isocyanate crosslinkers. A one-component composition is a compo- sition contained in a single package. A two-component composition is a composition wherein a second component, which is reactive with a first component, is packaged in a separate package and combined with the separate first composition shortly before use.

The lamination adhesive polymer preferably does not contain UV-crosslinkable groups.

The lamination adhesive composition preferably does not contain a tetrazol compound. The lamination adhesive composition preferably does not contain an UV-polymerizable compound.

The lamination adhesive composition preferably does not contain transition metals or transition metal ions, in particular no iron or iron ions.

The present invention also provides a laminate made by using a lamination adhesive composi- tion as described above. The laminate is preferably a film-to-film laminate or a film-to-paper lam- inate. The laminate preferably comprises at least on substrate selected from the group consist- ing of polyethylene terephthalate, polypropylene, preferably cast polypropylene or biaxially ori ented polypropylene, polyamide, polyethylene, polylactide, aluminum, cellulose film, paper, pol- yacetate and poly(butylene adipate-co-terephthalate), wherein the polymeric substrates can be corona-treated, plasma-treated, metallized or coated with vapor deposition barrier coatings.

The laminate according to the invention can comprise additionally at least one passive oxygen barrier layer. Preferred passive oxygen barrier layers are ethylene/vinyl alcohol copolymer (EVOH), polyvinylidene chloride (PVDC), polyamide or aluminum foil.

The present invention also provides a process for making laminates, in particular film-to-film laminates (composite films) or film-to-paper laminates, i.e. for the bonding of substrates of large surface area, more particularly for the production of composite films using suitable lamination adhesives including adhesive polymers which may be formulated with typical auxiliaries. The method of making a film-to-film or a film-to-paper laminate, comprises the steps of

(i) coating a first film substrate or paper with a composition according to the invention described herein,

(ii) adhering a second film substrate to the first film substrate or to paper, or adhering the paper to a film substrate and

(lii) activating oxygen-scavenging functionality by irradiating the coated substrate,

wherein the activating step can take place before or after the adhering step.

The coated substrate can be irradiated before or after drying. Preferred light sources are UV- lamps or LED lamps. Activation of the oxygen-scavenging functionality is preferably done by irradiating with light from a mercury lamp with approximate energy distribution of 8-20% in the UV-C domain, 5-10% in the UV-B domain and 3-10% in the UV-A domain, in proportion to the total electrical power. Alternatively, mercury lamps doped with gallium-indium, iron or lead, as well as LED lamps, can be used. The intensity is preferably adjusted in a way to provide enough irradiation in the part of the energy spectrum where the photosensitizer absorbs the incident energy.

A special benefit of the invention is that the activation of the oxygen scavenging functionality can be done on demand at various time points in time along the packaging value chain accord- ing to the needs of the goods or foodstuff, for example at the lamination process, shortly before or after filling the package with goods, or during the tracking or dispatching process.

The oxygen scavenging performance of the scavenging composition and the rate of the oxygen uptake can be easily steered and adjusted by the activation energy and exposure time.

The oxygen scavenging performance of the scavenging composition and the rate of the oxygen uptake can also be easily steered and adjusted by choosing a suitable substrate that receives the activation energy wherein the substrate has a suitable refraction index. In the process for producing composite films, at least two films are bonded with one another using a lamination adhesive. Examples of typical auxiliaries include wetting agents, surfactants, thickeners, protective colloids, light stabilizers, biocides, defoamers, tackifiers, filler, dyes, pig- ments, coloring agents, crosslinker, plasticizer, etc. The amount of auxiliaries is preferably from 0,05 to 10 or from 0,1 to 5 parts by weight based on 100 parts by weight of adhesive polymer (solids).

In the process for producing laminates the lamination adhesive is applied to the large-surface- area substrates to be bonded (such as polymer films), preferably with an adhesive layer thick ness (dry) of 0.1 to 50 g/m², more preferably 1 to 25 g/m², by means, for example, of knife coat- ing, spreading, etc. Typical coating techniques may be employed, examples being roller coat- ing, reverse roller coating, gravure roller coating, reverse gravure roller coating, brush coating, rod coating, spray coating, air brush coating, meniscus coating, curtain coating or dip coating. After a short time for the water of the dispersion or organic solvents to evaporate (preferably after 1 to 60 seconds), the coated substrate may then be laminated with a second substrate, the temperature can be, for example, 20 to 200°C, preferably 20 to 100°C, and the pressure can be, for example, 100 to 3000 kN/m², preferably 300 to 2000 kN/m².

At least one of the films may be metalized or printed either on the side that is coated with adhe- sive or on the side opposite to the adhesive. The film substrates can be transparent or opaque. Examples of suitable substrates include polymer films, more particularly thermoplastic polyole- fines (TPO) such as polyethylene (PE), oriented polypropylene (OPP), bi-oriented polypropyl- ene (BOPP), unoriented polypropylene (cast polypropylene, CPP), polyamide (PA), polyester (preferably polyethylene terephthalate (PET)), polylactide (PLA), poly(butylene adipate-co- terephthalate) (PBAT), polyacetate, ethylene/vinyl acetate copolymers (EVA), ASA (acrylni- tril/styrene/acryl acid ester copolymers), PUR (polyurethane), polyvinylchloride (PVC), prefera- bly soft-PVC, poly(meth)acrylates, polycarbonates or their alloys, cellophane, polymer films (va- por-)coated with metal, e.g., with aluminum (metalized films for short), or metal foils, of tin or aluminum, for example.

Preferred substrates are PET, polypropylene, PA, PE, OPP, BOPP, PBAT, PLA, aluminum foil, and metalized or vapor deposition barrier coatings with SiOx or AIOx layers.

The stated films and foils may be bonded with one another or with a foil or film of a different type for example polymer films with metal foils; different polymer films with one another; etc.

The stated foils and films may also, for example, be printed with printing inks.

A preferred composite film produced using a lamination adhesive, the material of a first film be- ing selected from OPP, BOPP, CPP, PE, PET, PBAT, PLA and PA, and the material of a sec- ond film being selected from OPP, BOPP, CPP, PE, PET, PBAT, PLA and PA, paper and metal foil. In one embodiment of the invention, the first film and/or the second film is metalized or printed on the respective side coated with the polymer dispersion of the invention. The thick ness of the substrate films may be, for example, from 5 to 100 pm, preferably from 5 to 40 pm.

Surface treatment of the film substrates prior to coating with a polymer dispersion of the inven- tion is not absolutely necessary. Better results, however, may be obtained if the surface of the film substrates is modified prior to coating. In this case it is possible to employ typical surface treatments, an example being corona treatment, for the purpose of intensifying the adhesion effect. The corona treatment or other surface treatments are carried out to the extent required for sufficient wettability with the coating composition. Typically, corona treatment of approxi- mately 10 watts per square meter per minute is sufficient for this purpose. The corona treatment can take place over one pass or several passes. Alternatively or additionally it is also possible, optionally, to use primers or tie coats between film substrate and adhesive coating. Further- more, other, additional functional layers may be present on the composite films, examples being barrier layers, print layers, color layers or varnish layers, or protective layers. These functional layers may be located externally, i.e., on the side of the film substrate facing away from the ad- hesive-coated side, or internally, between film substrate and adhesive layer.

The present invention also provides the use of an adhesive composition as described herein for making film-to-film or film-to-paper laminates and the use of an adhesive composition as de- scribed herein in packaging, preferably in food packaging.

The oxygen scavenging functionality is of special interest in the area of modified atmosphere packaging (MAP; CO2, N2) allowing to customize the speed, concentration of the scavenging composition and the combination of the different substrates used. The final products can be any type of products used in packaging applications, in particular any type of plastic product for food packaging applications, which needs enhanced oxygen scavenger activities. For example, the invention may be used to manufacture mono- or multilayer plastic films, sheets, laminates, bags, bottles, cups, pouches, plastic utensils, blister packages, boxes, package wrapping, cap- sules. The articles may be manufactured by any process available to those of ordinary skill in the art, but not limited to, extrusion, extrusion blowing, film casting, film blowing, calendaring, injection molding, blow molding, compression molding, thermoforming, spinning, blow extrusion and rotational casting.

The main benefits of the invention are:

• that the performance of the oxygen scavenging composition and the rate of the oxygen up- take can be easily steered by adjusting the concentration of photosensitizer incorporated in- to the aqueous adhesive dispersion causing no or only very low coloration issues (e.g. yel- lowing) or any other alteration of the optical properties (transparency, haze), in comparison to typical prior art metal based (in particular iron based) oxygen scavenging compositions;

• that the amount of passive oxygen barrier materials (e.g. aluminum foil, EVOH, PA, PVDC and others) can be reduced for achieving a desired oxygen protection effect, due to the ox ygen scavenging functionality of the aqueous dispersion adhesive; • that the oxygen scavenging functionality can be easily activated on demand by irradiating a laminate according to the invention with a suitable light source.

Examples

The following examples illustrate the invention without limiting the scope thereof. All per- centages and parts are by weight, unless stated otherwise.

Materials:

Epotal® CF 605 aqueous dispersion of a lamination adhesive copolymer

based on acrylic ester and styrene; 45-47% solids

Epotal® CF 300x aqueous dispersion of a lamination adhesive copolymer

based on acrylic ester and methacrylic ester; about 45% solids

Darocur® 1173 photosensitizer; 2-hydroxy-2-methyl-1 -phenyl-1 -propanone

Irgacure® 127 photosensitizer; 2-Hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)- benzyl]-phenyl}-2-methyl-propane-1-one

Irgacure® 2959 photosensitizer; 1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl- propane-1-one

Irgacure® TPO-L photosensitizer; 2,4,6-trimethylbenzoylphenyl phosphinate

Basonat® LR 9056 polyisocyanate based on isocyanurated hexamethylene diisocyanate;

NCO content 17.5-18.5%; crosslinker for polymer dispersions containing reactive OH groups

Measurement of oxygen scavenging activity of an adhesive polymer film

An aqueous lamination adhesive composition containing light activatable oxygen scavenging material is poured onto a thermoplastic film carrier, let dry and activated with a mercury UV lamp. The dry specimen can be removed from the film carrier or left onto the film carrier or the laminate, cut to a known quantity, weighed, and placed in a glass bottle of known volume in ml, equipped with an oxygen sensor, and hermetically closed. The amount of oxygen scavenged by the test samples is determined from the change in the oxygen concentration in the head space of the glass container. The glass containers with test samples are stored at 23°C. At known time intervals, as indicated in the below corresponding tables, the oxygen concentration is measured with an optical fluorescence 02 Analyzer (0pTech®-02 P of Mocon GmbH) by applying the OpTech O2 apparatus onto the bottle at the position of the sensor. The oxygen concentration has an initial value close to 21 %, which is the typical oxygen concentration in air, and then de- creases over time due to the scavenging action of the additives incorporated into the adhesive composition. The measurements are typically performed up to several days. Knowing the bottle volume in ml and the concentration of the additives in the adhesive composition, the quantity of scavenged oxygen (ml O2) scavenged per g scavenger can be determined according to the fol- lowing equation:

Scavenged oxygen (ml/g) = {(% 0₂)i - (% 0₂)_f} ^* 0.01 ^* Vj / ( W_F ^* 0.01 ^*C_S) where:

(% 0₂), Initial oxygen concentration in the glass container (%);

(% 0₂)_f Oxygen concentration in the glass container at time of test (%)

0.01 : Conversion factor

V_j! Free air volume of the glass container (ml)

W_F: Weight of test material placed into the glass container (g), i.e. weight of the adhesive, ei- ther removed from the film carrier or left onto the film carrier or the laminate

Cs: Concentration of oxygen scavenger in the test material (%)

Example 1 - 2

100 ml of aqueous dispersion adhesive Epotal® CF 605 was mixed by manual stirring during 5 minutes at an approximate speed of 100 rpm with 10.2 g of a scavenging composition based on 10 g of sodium metabisulfite (example 1 ) or sodium ascorbate (example 2) and 0.2 g of photo- sensitizer Darocur® 1173. 300 pm of the mix was applied on a siliconized surface and dried for 24 h in a climatized cabinet under vacuum and 25°C, yielding a 150 pm of dry film. The dried film was activated with a UV-Mercury lamp at 4-5 m/min at 80 W/cm or 1200 mJ/cm². In order to measure the scavenging activity, 5g of each sample was introduced into a 100 ml glass and the headspace oxygen concentration was measured with a Mocon OpTech 02 P Optical Fluores- cence analyzer for several days. The results show an effective oxygen scavenging activity and almost oxygen exhaustion as of the 10^th day.

Table 1 : Oxygen scavenging activity of examples 1-2, headspace oxygen concentration in %

Examples 3-4: film-to-film laminates made with one component adhesives

100 ml of aqueous dispersion adhesive Epotal® CF 605 was mixed with a Skandex machine during 10 minutes at an approximate speed of 100 rpm with 2 g of a scavenging composition based on photosensitizer Darocur® 1173. In order to make a 2-substrate component laminate, 24 pm of the mix was applied on a PET film yielding a 12 pm of dry film, after being subject of corona pretreatment at a low energy of approximate 15 W/m. The applied mix was dried for 2 h in a climatized cabinet under vacuum and 80°C. After drying, a second film (BOPP film of ap- proximate 20 pm) was also corona pretreated under the same conditions and placed on top of the coated first film, thus finalizing the laminate. In order to activate the oxygen scavenging ac- tivity, the laminate was exposed to a UV-Mercury lamp at 4-5 m/min and at 80 W/cm or 1200 mJ/cm² either after application of the adhesive composition and before drying (example 3) or after application of the adhesive composition and after drying (example 4). In order to measure the scavenging activity, the equivalent of 60.5 cm² cut in small stripes of each sample was in- troduced into a 100 ml glass and the oxygen headspace concentration was measured with a Mocon OpTech 02 P Optical Fluorescence analyzer for several days. General structure of the laminates:

PET film about 175 pm 11 dried lamination adhesive film about 1 1-20mhΊ 11 BOPP film about 20pm

Example 5 (comparative): oxygen scavenging film material made by extrusion

As comparison ShelfPlus® 0₂ 2400 (Albis GmbH) was taken. It is a commercial oxygen scav- enger material consisting of a masterbatch containing 50% polyethylene, 25% iron and 25% salts. This masterbatch was incorporated at a level of 10% into low density polyethylene by ex- trusion and films were then produced by extrusion cast film. The oxygen scavenging perfor- mance of the films were then prepared and measured as described above.

Table 2: Oxygen scavenging activity of examples 3-5, amount of scavenged oxygen

in ml/g scavenger

Examples 6-7: film-to-film laminates made with two-component adhesives

100 ml of aqueous dispersion adhesive Epotal® CF 605 was mixed with a Skandex machine during 5 minutes at an approximate speed of 100 rpm with 10 g of sodium nitrite (example7) or 12 g of a scavenging composition based on 10 g of sodium nitrite and 2 g of photosensitizer Irgacure® 127 example 6). Irgacure® 127 can be substituted by photosensitizer Irgacure®

2959. Sodium nitrite can be substituted by sodium metabisulfite or by sodium ascorbate. After the initial mix, 5 ml of a second component was added to the mix. The second component Ba- sonat® LR 9056 is a crosslinking material and comprises a polyfunctional isocyanate. In order to make a 2-substrate component laminate, 24 pm of the mix was applied on a PET film yielding a 12 pm of dry film after being subject of corona pretreatment at a low energy of approximate 15 W/m. The applied mix was dried for 2 h in a climatized cabinet under vacuum and 80°C. After drying, the second film of the laminate, a BOPP film of approximate 20 pm was also corona pre- treated under the same conditions and placed on top, thus finalizing the laminate. In order to activate the oxygen scavenging activity, the laminate was exposed to a UV-Mercury lamp at 4-5 m/min at 80 W/cm or 1200 mJ/cm². In order to measure the oxygen scavenging activity, the equivalent of 60.5 cm² was cut in small stripes and each sample was introduced into a 100 ml glass and the headspace oxygen concentration was measured with a Mocon OpTech 02 P Op- tical Fluorescence analyzer for several days. Table 3: Oxygen scavenging activity of examples 5-7, amount of scavenged oxygen in ml/g scavenger

Examples 8-12: film-to-film laminates made with one component adhesives

100 ml of aqueous dispersion adhesive Epotal® CF 300x was mixed with a Skandex machine during 10 minutes at an approximate speed of 100 rpm with scavenging compositions as de- scribed in table 4 based on photosensitizers Irgacure 127, Irgacure 2959 or Irgacure TPO-L. In order to make a 2-substrate component laminate, 20 pm of the mix was applied on a PET film yielding a 10 pm of dry film after being subject of corona pretreatment at a low energy of ap- proximate 15 W/m. The applied mix was dried for 2 h in a climatized cabinet under vacuum and 80°C. After drying, the second film of the laminate, a BOPP film, of approximate 20 pm was also corona pretreated under the same conditions and placed on top, thus finalizing the laminate. In order to activate the oxygen scavenging activity, the laminate was exposed to a UV-Mercury lamp at 4-5 m/min and at 80 W/cm or 1200 mJ/cm². In order to measure the scavenging activity, the equivalent of 60.5 cm² was cut in small stripes and each sample was introduced into a 100 ml glass. The oxygen headspace concentration was measured with a Mocon OpTech 02 P Op- tical Fluorescence analyzer for several days. Table 4: Oxygen scavenging activity of examples 8-12 and 5, amount of scavenged oxygen in ml/g scavenger

Claims

Claims:

1. An oxygen scavenging aqueous lamination adhesive composition comprising

(II) at least one photosensitizer compound; and

(III) optionally one or more additives different from (I) and (II).

2. Composition according to the preceding claim, wherein the concentration of the photosensi- tizer compound is from 0.05 wt % to 15 wt %, preferably from 0.1 wt % to 8 wt %, based on the amount of the lamination adhesive polymer.

3. Composition according to any of the preceding claims, wherein the photosensitizer corn- pound (II) is monomeric or oligomeric and selected from the group consisting of alpha- hydroxyketones, phenylglycoxylates, acyl phosphine oxides, phenyl benzoyl phosphinates, aminoketones, benzophenone compounds, anthraquinone compounds, benzildimethyl- ketals, and onium salts, preferably diaryliodonium salts, triarylsulfonium salts, alpha- hydroxyketones and acyl phosphine oxides.

4. Composition according to any of the preceding claims, wherein the photosensitizer corn- pound (II) is selected from the group consisting of 2-hydroxy-2-methyl-1 -phenyl-propan-1 - one, 2-hydroxy-1 -{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1 - one and 1 -[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1 -propane-1 -one).

5. Composition according to any of the preceding claims, wherein the lamination adhesive polymer (I) has a glass transition temperature of from -40 to +15 °C, preferably from -10 to +10 °C, measured by differential scanning calorimetry with a heating rate of 20° C/min and is selected from the group consisting of polyurethanes and polymers prepared by free radi- cal polymerization of ethylenically unsaturated, radically polymerizable monomers.

6. Composition according to any of the preceding claims, wherein the lamination adhesive polymer (I) is prepared by free radical polymerization of monomers comprising

a) at least 60 wt%, based on the total amount of monomers, of at least one monomer se- lected from the group consisting of alkyl acrylates with 1 to 20 C-atoms in the alkyl group, alkyl methacrylates with 1 to 20 C-atoms in the alkyl group, vinyl esters of car- boxylic acids with up to 20 C-atoms, vinyl aromates with up to 20 C-atoms, vinyl halides, vinyl ethers of alcohols with 1 to 10 C atoms, aliphatic hydrocarbons with 2 to 8 C atoms and one or two ethylenic double bonds,

b) at least 0.1 wt%, based on the total amount of monomers, of at least one monomer with at least one acid group, preferably selected from acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, vinyl acetic acid, vinyl lactic acid, vinyl sul- tonic acid, styrene sulfonic acid, acrylamido methylpropane sulfonic acid, sulfopropyl acrylate, sulfopropyl methacrylate,

c) optional at least one further monomer different from monomers a) and b).

7. Composition according to any of claims 1 to 5, wherein the lamination adhesive polymer (I) is a polyurethane made from

a) at least one diisocyanate,

b) at least one diol, of which

b2) 0 to 90 mol-%, based on the total amount of diols(b), have a molecular weight of from 60 to 500 g/mol,

c) at least one monomer different from monomers (a) and (b) having at least one isocya- nate group or at least one group reactive with isocyanate groups and which additionally has at least one hydrophilic group or at least one potentially hydrophilic group, and d) optionally at least one monomer different from monomers (a) to (c) having at least two reactive groups selected from alcoholic hydroxy groups, primary or secondary amino groups and isocyanate groups, and

e) optionally at least one monofunctional monomer different from monomers (a) to (d) having one reactive group selected from alcoholic hydroxy groups, primary or second- ary amino groups and isocyanate groups.

8. Composition according to any of the preceding claims, wherein the additive (III) is selected from the group consisting of sulfites, carboxylic acid salts, vitamin A derivatives, vitamin C derivatives, phosphites, and nitrites, preferably selected from the group consisting of bisul fites, ascorbates and nitrite salts.

9. Composition according to any of the preceding claims, wherein the lamination adhesive polymer does not contain UV-crosslinkable groups and/or wherein the composition does not contain a tetrazol compound or an UV-polymerizable compound.

10. Composition according to any of the preceding claims, wherein the composition does not contain transition metals or transition metal ions.

1 1. A laminate made by using a composition according to any of the preceding claims.

12. A laminate according to the preceding claim, wherein the laminate is a film-to-film laminate or a film-to-paper laminate; and wherein the laminate comprises at least one substrate se- lected from the group consisting of polyethylene terephthalate, polypropylene, wherein pre- ferred polypropylene is cast polypropylene or biaxially oriented polypropylene, polyamide, polyethylene, polylactide, aluminum, cellulose film, paper, polyacetate and poly(butylene adipate-co-terephthalate), wherein the polymeric substrates can be corona-treated, plasma- treated, metallized or coated with vapor deposition barrier coatings.

13. A laminate according to any of claims 1 1 to 12, wherein the laminate additionally comprises at least one passive oxygen barrier layer, preferably at least one layer of ethylene/vinyl al- cohol copolymer, polyvinylidene chloride, polyamide or aluminum foil.

14. Use of a composition according to any of claims 1 to 10 for making film-to-film or film-to- paper laminates; or in packaging, preferably in food packaging.

15. Method of making a film-to-film or film-to-paper laminate, comprising the steps of

(i) coating a first film substrate or paper with a composition according to any of claims 1 to

10,

(iii) activating oxygen-scavenging functionality by irradiating the coated substrate, wherein the activating step can take place before or after the adhering step.

16. Method according to the preceding claim, wherein the coated substrate is irradiated with a UV-lamp or with a LED lamp before or after drying of the aqueous lamination adhesive composition.