Polymer for improving the removal of printing inks from polymer substrates

Abstract

The invention relates to polymers that are soluble in alkaline solution and / or in polar solvents, but are poorly soluble in water, and to printing inks containing these polymers.

Description

[0001] Polymer for improving the removal of printing inks from polymer substrates

[0002] Field of the invention

[0003] The invention relates to polymers for improving the removal of printing inks from polymer substrates.

[0004] Prior art

[0005] Increasing impact on the environment means that the level of recycling of discarded articles and packaging needs to be improved so as to be able to reuse the recyclables present therein.

[0006] This is especially true of plastic articles. Plastics, i.e. synthetic polymers such as polyethylene (PE), polypropylene (PP) or polyethylene terephthalate (PET) or polyamide (PA), are extremely efficient for flexible packaging. This advantage has however led to excessive use of plastic packaging, with high use of fossil raw materials. Without efficient recycling, the environmental impact already observed, such as pollution of the seas, will continue to increase. This also increases the health risk from microplastics, which enter the environment in an uncontrolled manner. Even when plastic waste is collected, problems still arise: Some of it may re-enter the environment from overcrowded landfill sites, or it is incinerated and results in further CO2 emissions, which are driving global warming. For example, in Germany, in 2021 , over 53% of plastic waste was utilized for energy (Conversio study 2022, https: / / www.bvse.de / dateien2020 / 2-PDF / 01-Nachrichten / 03-

[0007] Kunststoff / 2022 / Kurzfassunq Stoffstrombild 2021 13102022 1 .pdf). In some regions, such as the EU, regulations have been introduced that prescribe specific quotas for recycling and the use of recyclates for new products and packaging. In addition, many major brand owners have, regardless of regulations, committed to increasing the proportion of recycled material in their products.

[0008] There is consequently a need for efficient recycling concepts for plastic material.

[0009] Whereas for PET bottles there sometimes exist closed recycling chains, as is the case in Germany, flexible PE and PP packaging in particular is mainly incinerated or sent to landfill, but at the same time accounts for up to 40% of plastic waste, depending on the country. It is accordingly an important source of raw materials of the future.

[0010] As well as the colouring of plastics, an important obstacle to providing high-quality plastic recyclates is the incomplete removal of printing ink in the recycling process. Of particular importance here are solventcontaining nitrocellulose printing inks, NC printing inks for short, which are inexpensive and used mainly for printing on flexible packaging. If these NC printing inks are not removed completely during the recycling process, this results in discoloured recyclates of lower quality that also lead to the development of odours, release of toxic gases and blistering during extrusion of moulded parts manufactured therefrom.

[0011] Consequently, when recycling printed plastic articles such as flexible packaging it is advisable to remove printing inks as completely as possible in order to obtain high-quality recyclates. In this context, EP3932642 describes a primer composition for the delamination and deinking, i.e. the removal of printing ink, of a printed substrate, wherein the primer composition comprises a binder component that has a polymer backbone with hydroxy and / or carboxy groups, thus making the priming coat soluble in an alkaline aqueous medium.

[0012] Disadvantages here are that, for deinking, a primer must be applied using an additional printing unit and that the primer is poorly accessible for attack by the alkaline medium. WO2021165081 (A1) describes a largely analogous approach, but the deinking additionally requires elevated temperatures of 60-85°C, which is energy- and cost-intensive.

[0013] JP3232742U describes a recyclable nonwoven tote bag that is screen-printed with water-based flexo printing ink doped with polyvinyl alcohol and has a screen-printed ink layer that can be removed with warm alkaline water. Disadvantages are that this process is slow and represents a niche process for printing on flexible packaging that is important only in regional markets.

[0014] WO2021081288 describes a special solution for printed shrink sleeves for PET bottles and containers, the ink of which normally dissolves during the alkaline wash in the recycling process and discolours the PET flakes. To prevent this, an ink is proposed that is stable to alkaline washes and remains on the shrink sleeves.

[0015] Disadvantages are that these shrink sleeves cannot be deinked and recycled and that this approach is not a solution for the flexible PE and PP packaging in widespread use.

[0016] W09509206 describes an ink composition for offset printing that is stable and insoluble at alkaline pH during the printing process and can therefore print lithographically, but is soluble or washable when using an aqueous wash solution with an acidic pH. This is used to clean the blanket cylinder after a print job has been completed. However, this approach cannot be transposed to deinking in flexo printing, since the printing ink must be stable on packaging materials in the neutral as well as slightly acidic and alkaline range.

[0017] US2021395425 describes a radiation-curing composition that is alkali-soluble and comprises a carboxylated acrylate, a urethane acrylate, a monomer and a photoinitiator and can be applied in the flexo printing process. Disadvantages are the high costs and the limitation to radiation-curing printing inks, which are not widely used for printing on packaging.

[0018] WO2023278440 describes a process for recycling plastic material from a container comprising the plastic material and a water-based ink that had been applied either directly to the container or to a label attached to the container, wherein the plastic material is not coloured or contaminated by the water-based ink during recycling. What is characteristic is that the ink is not soluble, but can be detached in solid particles. The polymer used comprises a self-crosslinking polyurethane-based acrylate copolymer. The alkali used is an aqueous solution of 1% by weight to 3% by weight of NaOH and / or nonionic surfactant at 70°C to 95°C, typically from 80°C to 90°C. A disadvantage here is that the process is optimized only for PET containers and PET containers having PETG heat-shrink sleeves and, in particular, very high temperatures and long residence times in the alkali are required.

[0019] US 6 147 041 describes a removable ink composition that is used for printing on plastic containers and plastic films and can be removed and decolorized by treating the ink composition with a dilute aqueous alkali solution, and also a process for removing the ink composition from parts printed with the ink composition. US 6 147 041 describes an ink composition comprising (A) a urethane resin and a cellulose resin and (B) a mixture comprising styrene-acrylic acid copolymers, styrene-maleic acid resins, rosin- maleic acid resins and phenolic resins, wherein the composition is resistant to water, but is detachable from the substrate through an aqueous alkali solution. A disadvantage here is that solubility was observed only with 3% aqueous sodium hydroxide solution and at very high temperatures of between 80 and 90°C.

[0020] WO2023150251 describes a process for recycling plastic material from an article comprising the plastic material and a UV-curing ink applied either directly to the article or directly to a label attached to the article, the process comprising: a) providing a plastic article having a surface on which a UV-curing ink has been directly printed without the use of an intermediate layer, or on a label attached to the product on which a UV-curing ink has been directly printed without the use of an intermediate layer; wherein the UV- curing ink comprises one or more dyes that are resistant to dissolution in alkali, and wherein the one or more colorants and the UV-curing ink are removable in the form of solid particles that are not soluble in a hot alkali wash; b) immersing the plastic article or plastic article plus label in a hot corrosive wash to remove the inks in the form of a particulate precipitate that is essentially insoluble in the corrosive wash, in order to provide an uncoloured plastic article and an uncoloured label; c) separating the uncoloured plastic article or plastic article plus label from the ink precipitate and the hot alkali wash; wherein the hot alkali is an aqueous solution of 1% by weight to 3% by weight of NaOH and / or nonionic surfactant at 70°C to 95°C, for example from 80°C to 90°C; and wherein the plastic material is not soiled or contaminated by the UV-curing ink during recycling.

[0021] Disadvantages here are the high temperatures of the alkaline solution and the higher costs of the UV- crosslinking printing inks.

[0022] WO 2021 / 081288 discloses ink compositions that do not contaminate and discolour plastic materials when they are removed by a hot alkali wash solution during recycling, since the inks do not dissolve in the hot alkali wash solution, but form a solid or precipitate. The solid or precipitate can then be easily separated from the recycled plastic and the wash solution, for example by filtration. The ink compositions in WO 2021 / 081288 comprise: (a) a resin selected from the group consisting of: polyvinyl chloridepolyvinyl acetate copolymer, semi-aliphatic polyurethane, polymethyl methacrylate copolymer, isobutyl methacrylate copolymer, cellulose-based resins, styrene-maleic anhydride copolymer and combinations thereof; (b) an organic solvent; and (c) a colorant resistant to dissolution in a hot alkali.

[0023] Disadvantages here are primarily the high temperatures of the alkaline solution.

[0024] JP 2001-131484 discloses the presence of a separation layer on the surface of a substrate on the separation layer of which the ink is printed. The separation layer comprises a polymer or copolymer containing 10-60% by weight of a carboxyl group that becomes water-swellable or water-soluble through at least one neutralization treatment. During neutralization, the carboxyl groups are converted into the respective carboxylate groups, as a result of which the releasing layer becomes water-soluble. The separation layer and the ink applied thereto are then removed from the surface of the substrate.

[0025] A disadvantage here is that a separation layer must first be applied using an additional printing unit or a separate process step.

[0026] Object

[0027] The object of the invention is to significantly improve and / or speed up the removal of printing ink from printed PET, PA and polyolefin packaging, especially from PE and PP packaging and in particular from PE and PP films, in the recycling process through washing under mild conditions and thus to improve, speed up, simplify or permit the production of high-quality PET, PE and PP recyclates that are uncontaminated by printing inks and to permit an energy-efficient recycling process through lower process temperatures during the removal of printing ink.

[0028] Achievement

[0029] According to the invention, the deinking process is improved by virtue of the printing ink having an altered composition and consequently being easier to remove.

[0030] Surprisingly, it was found that the use of suitable polymers as an additive allows printing inks to be removed more readily from the substrate under alkaline conditions even at 35°C, which helps foster an energy-efficient recycling process.

[0031] The object was achieved through polymers that have good solubility both in aqueous alkaline solutions and in polar solvents commonplace in the printing ink industry.

[0032] It was found that these polymers are soluble in aqueous sodium hydroxide solution, preferably 1-2% by weight, even at temperatures of between 15 and 35°C, and are therefore particularly suitable.

[0033] It was found that the polymers of the invention can be used as an additive in printing inks for printing on common polymer substrates, especially on polyethylene terephthalate (PET) and polyethylene (PE) and polypropylene (PP), polyamide (PA), without adversely affecting the performance properties thereof, but improve the deinkability of the printing ink and thus make it possible, when applying the print, to avoid using additional intermediate layers to improve the deinkability of the printing ink.

[0034] The polymers are provided as a polymeric additive for printing inks, in particular for NC flexo and gravure printing inks. The polymers of the invention are employed as a polymeric additive in pigmented and unpigmented formulations and products capable of application in flexo and gravure printing, in nitrocellulose-containing or nitrocellulose-free printing inks, deinking formulations and systems.

[0035] The polymers of the invention contain:

[0036] 0-30% by weight of hydroxyethyl methacrylate,

[0037] 5-16% by weight, more preferably 10-14% by weight, of methyl methacrylate,

[0038] 30-60% by weight, more preferably 45-55% by weight, of n-butyl methacrylate,

[0039] 15-30% by weight, more preferably 20-25% by weight, of methacrylic acid and

[0040] 10-20% by weight, more preferably 13-17% by weight, of n-butyl acrylate particularly based on 100% by weight of the polymer.

[0041] Further preference is given to polymers of the invention containing:

[0042] 20-50% by weight, more preferably 40-44% by weight, of n-butyl methacrylate,

[0043] 15-30% by weight, more preferably 21-25% by weight, of methacrylic acid,

[0044] 10-20% by weight, more preferably 13-17% by weight, of n-butyl acrylate and

[0045] 10-25% by weight, more preferably 18-22% by weight, of hydroxyethyl methacrylate 0-20% by weight of methyl methacrylate.

[0046] The average molecular weight Mw of the polymers of the invention is between 10 000-60 000 g / mol, preferably between 15 000-25 000 g / mol, measured by DIN 55672-1.

[0047] Mw stands for weight-average molecular weight and Mnstands for number-average molecular weight. The molecular weights Mw and Mnare determined by GPC [gel permeation chromatography] as described in DIN 55 672-1 . Specifically, GPC was performed at 35°C. THF was used as mobile phase with a flow rate of 1 mL / min and one SDV Guard column (50 x 7.5 mm, precolumn) and four SDV columns (300 x 7.5 mm) were used as the stationary phase. Detection was performed by means of an Rl detector. The datasets were evaluated using WinGPC software (Polymer Standards Service, Mainz) and polystyrene calibration with Mark-Howink transformation to PMMA.

[0048] The polymers of the invention are soluble in alkaline solutions, preferably in aqueous sodium hydroxide solution, and at the same time in polar solvents selected from the group of alcohols, preferably ethanol, isopropanol and 1-ethoxy-2-propanol, and esters, preferably ethyl acetate, and mixtures thereof.

[0049] The alkaline solutions are selected from the group of aqueous solutions of alkali hydroxides, preferably aqueous sodium hydroxide solutions, lime water and aqueous potassium hydroxide solutions. Preference is given to using 1-10% by weight solutions, preferably 1-2% by weight solutions.

[0050] The present invention also relates to a process for removing printing inks, NC flexo printing inks and gravure printing inks comprising inventive polymers, comprising the steps:

[0051] - detaching the printing ink in aqueous alkaline solution without the addition of further auxiliaries to the wash solution

[0052] - at temperatures of between 15 and 35°C. Surprisingly, it was found that the polymers of the invention have very good solubility even in cold aqueous solutions of the alkali hydroxides, preferably in 2% by weight aqueous sodium hydroxide solution, at 20-40°C, preferably at 25-35°C, but also have very good solubility in aqueous sodium hydroxide solution at elevated temperatures, for example at 70-90°C. However, in cold water, preferably 20-35°C, and particularly surprisingly also in hot water, preferably 50-85°C, the polymers of the invention are insoluble and stable for at least 24 hours.

[0053] The good solubility of the polymers of the invention in the abovementioned polar solvents and mixtures thereof permits the simple incorporation of the polymers as cobinders or additives in printing inks, especially in flexo and gravure printing inks, that are suitable for printing on plastics such as polyethylene terephthalate (PET), high-density polyethylene (HDPE), polypropylene (PP), polyamide (PA), cast polypropylene (CPP), and are especially suitable for printing on flexible plastics such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), oriented polypropylene (OPP) and biaxially oriented polypropylene (BOPP).

[0054] After printing on plastics, printing inks that contain this polymeric additive have the characteristic features of high stability or fastness to neutral cold water, preferably 0-20°C, and to neutral hot water, even at 50- 85°C, and of good detachability of the printing ink in alkaline solutions. This ensures broad suitability for the use of correspondingly printed packaging, including for deep-freeze uses.

[0055] The printing ink of the invention can in alkaline solutions be rapidly and completely detached from printed plastics and printed packaging, in particular from flexible packaging constituents. This is an essential prerequisite in order for a suitable recycling process to be able to produce clean, ink-free recyclates from packaging plastics in a purity sufficiently high for use as a raw material for new, high-quality plastic products.

[0056] The removal of the printing ink in alkaline solution can be further accelerated by adding ionic and nonionic surfactants and dispersing additives.

[0057] Also the removal of the printing ink in alkaline solution can be further accelerated by adding one or more auxiliaries, to the wash solution, selected from the group of detergents and stabilizers, surfactants or wetting agents, emulsifiers or macro-emulsifiers, defoamers or combinations thereof.

[0058] The process for producing the polymers of the invention involves providing a mixture A containing water, stabilizers and emulsifiers.

[0059] The stabilizers are selected from the group of water-soluble polymers, with very particular preference given to polyvinyl alcohols such as Mowiol 18 / 88 from Sigma Aldrich, Germany.

[0060] The emulsifiers used are selected from the group of anionic emulsifiers (sodium alkyl sulfonates), with very particular preference given to the emulsifier E30-40 (Leuna Tenside GmbH, Germany) In addition, a monomer mixture B is provided. The monomers here are selected from the group of acrylates and methacrylates, preferably n-butyl methacrylate, n-butyl acrylate, hydroxyethyl methacrylate and methacrylic acid and optionally methyl methacrylate.

[0061] This mixture is mixed with chain-transfer agents, preferably 2-ethylhexyl thioglycolate and n-dodecyl mercaptan, and initiators, preferably tert-amyl peroxy-2-ethylhexanoate, usually at room temperature. To set the average molecular weight Mw of the polymers of the invention at between 10 000- 60 000 g / mol, 0.5-4% by weight, preferably 2-3.8% by weight, of chain-transfer agents are employed.

[0062] After the addition of monomer mixture B to mixture A, the reaction solution undergoes reaction at temperatures of between 75°C and 85°C. The temperature is maintained until the exothermic reaction has largely ended. The temperature is then raised to 85°C to 95°C for 30-100 min to ensure conversion is as complete as possible. The mixture is then cooled to 25°C to 35°C and the polymer obtained filtered off and washed. The polymer obtained is then dried at 50°C to 60°C.

[0063] A further advantage of the invention is that the particles of printing ink detached under alkaline conditions can be precipitated by lowering the pH through acidification with e.g. HCI, forming larger agglomerates that can be separated particularly easily by mechanical means, whereas particles of printing ink detached by detergents such as ionic or nonionic surfactants form stabilized and more finely divided dispersions that are difficult to remove by filtration, even after altering the pH.

[0064] The particles of printing ink detached under alkaline conditions comprising the polymers of the invention are preferably brought to precipitation and agglomeration through acidification of the solution. This can be done using acids selected from the group of organic and inorganic acids, preferably hydrochloric acid. In particular, 1-5% by weight aqueous acids are used.

[0065] Flocculants can optionally be added to the aqueous mixture.

[0066] To speed up the precipitation process, the aqueous mixture can be heated and / or stirred.

[0067] The precipitated material can be removed using standard separation methods for solid / liquid separation. The separation is preferably carried out continuously by means of filtration, centrifugation or separation by gravity, for example flotation and sedimentation.

[0068] Also claimed are printing inks comprising the polymethyl (meth)acrylate-based polymers of the invention. Preference is given to nitrocellulose-containing pigmented and unpigmented printing inks comprising the polymers of the invention capable of application in flexo and gravure printing.

[0069] Also claimed are NC flexo printing inks and gravure printing inks comprising these polymers of the invention.

[0070] Nitrocellulose-containing printing inks are understood as meaning in particular solvent-containing systems consisting of low alcohols and esters of same as well as other potential solvents having a, nitrocellulose, optionally a further polymer from the class of polyurethanes, polyamides, polyacrylates and polyesters, optionally adhesion-improving additives from the class of ketone resins, titanates, zirconates, slip additives of a silicone-containing or silicone-free nature (for example oleic acid amides), waxes and suitable pigments (inter alia organic pigments from the class of azo pigments, perylene pigments, quinacridone pigments, diketopyrrololpyrrole pigments, dioxazine pigments, isoindoline pigments or inthanthone pigments, and also inter alia inorganic pigments such as carbon blacks, titanium dioxides calcium carbonates or barium sulfates).

[0071] Printing inks comprising the polymers of the invention can be produced by prior art processes. These processes are comprehensively described in Organic Coatings - Science and Technology (4th Edition) from Frank N Jones, Mark E. Nichols, Socrates Peter Pappas, published in 2017 by John Wiley & Sons.

[0072] Claimed in particular is the use of polymers of the invention in printing inks, nitrocellulose printing inks for the packaging industry, in particular for printing flexible packaging based on polyolefin films and / or polycondensate films such as polyethylene terephthalate (PET), high-density polyethylene (HDPE), polypropylene (PP), cast polypropylene (CPP), polyamide (PA) and in particular for printing on flexible plastics such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), oriented polypropylene (OPP) and biaxially oriented polypropylene (BOPP).

[0073] Also claimed is the use of polymers of the invention in solvent-containing, pigmented and unpigmented systems for printing on packaging.

[0074] A preferred use of polymers of the invention is in nitrocellulose-containing pigmented and unpigmented formulations and products capable of application in flexo and gravure printing, in order to facilitate deinking.

[0075] The following polymers were produced and their suitability for achieving the object tested:

[0076] Production of polymers

[0077] The polymers were in each case produced as described below using the stabilizer Mowiol 18 / 88 (from Sigma Aldrich, Germany) and the emulsifier E30-40, a mixture of glyceryl monostearate and glyceryl monolaurate (from Leuna Tenside GmbH, Germany). Comparative example 1 : Polymer 1

[0078] A jacketed vessel fitted with thermostats, reflux condenser, paddle stirrer and internal thermometer was initially charged with 1393.74 g of deionized water, 4.86 g of stabilizer and 0.14175 g of emulsifier and the mixture was stirred at 50°C. In parallel therewith, a mixture of 90 g of methyl methacrylate, 135 g of n- butyl methacrylate, 135 g of methacrylic acid, 90 g of ethyl triglycol methacrylate, 8.55 g of 2-ethylhexyl thioglycolate and 4.025 g of tert-amyl peroxy-2-ethylhexanoate was weighed out in a beaker and mixed with a magnetic stirrer at room temperature for 15 min. This monomer mixture is then transferred via a funnel to the glass reactor within 2 min. The water-monomer mixture is now heated to the reaction temperature of 80°C. This temperature is maintained until the exothermic reaction has ended. Heating is then continued at 90°C for 90 min. The mixture is then cooled to 30°C and the polymer filtered off and washed.

[0079] The polymer is dried overnight in a paint drying cabinet at 60°C.

[0080] Comparative example 2: Polymer 2

[0081] A jacketed vessel fitted with thermostats, reflux condenser, paddle stirrer and internal thermometer was initially charged with 1393.74 g of deionized water, 4.86 g of stabilizer and 0.14175 g of emulsifier and the mixture was stirred at 50°C. In parallel therewith, a mixture of 135 g of hydroxyethyl methacrylate, 112.5 g of n-butyl methacrylate, 103.5 g of methacrylic acid, 99 g of n-butyl acrylate, 8.55 g of 2-ethylhexyl thioglycolate, 4.5 g of n-dodecyl mercaptan and 2.025 g of tert-amyl peroxy-2-ethylhexanoate was weighed out in a beaker and mixed with a magnetic stirrer at room temperature for 15 min. This monomer mixture is then transferred via a funnel to the glass reactor within 2 min. The water-monomer mixture is now heated to the reaction temperature of 80°C. This temperature is maintained until the exothermic reaction has ended. Heating is then continued at 90°C for 90 min. The mixture is then cooled to 30°C and the polymer filtered off and washed.

[0082] The polymer is dried overnight in a paint drying cabinet at 60°C.

[0083] Example 3: Polymer 3

[0084] A jacketed vessel fitted with thermostats, reflux condenser, paddle stirrer and internal thermometer was initially charged with 1040.5 g of deionized water, 4.5 g of stabilizer and 0.132 g of emulsifier and the mixture was stirred at 50°C. In parallel therewith, a mixture of 160 g of hydroxyethyl methacrylate, 336 g of n-butyl methacrylate, 184 g of methacrylic acid, 120 g of n-butyl acrylate, 15.2 g of 2-ethylhexyl thioglycolate, 8 g of n-dodecyl mercaptan and 3.6 g of tert-amyl peroxy-2-ethylhexanoate was weighed out in a beaker and mixed with a magnetic stirrer at room temperature for 15 min. This monomer mixture is then transferred via a funnel to the glass reactor within 2 min. The water-monomer mixture is now heated to the reaction temperature of 80°C. This temperature is maintained until the exothermic reaction has ended. Heating is then continued at 90°C for 90 min. The mixture is then cooled to 30°C and the polymer filtered off and washed. The polymer is dried overnight in a paint drying cabinet at 60°C.

[0085] Comparative example 4: Polymer 4

[0086] A jacketed vessel fitted with thermostats, reflux condenser, paddle stirrer and internal thermometer was initially charged with 1040.5 g of deionized water, 4.5 g of stabilizer and 0.132 g of emulsifier and the mixture was stirred at 50°C. In parallel therewith, a mixture of 160 g of hydroxyethyl methacrylate, 216 g of ethyl methacrylate, 184 g of methacrylic acid, 240 g of n-butyl acrylate, 15.2 g of 2-ethylhexyl thioglycolate, 8 g of n-dodecyl mercaptan and 3.6 g of tert-amyl peroxy-2-ethylhexanoate was weighed out in a beaker and mixed with a magnetic stirrer at room temperature for 15 min. This monomer mixture is then transferred via a funnel to the glass reactor within 2 min. The water-monomer mixture is now heated to the reaction temperature of 80°C. This temperature is maintained until the exothermic reaction has ended. Heating is then continued at 90°C for 90 min. The mixture is then cooled to 30°C and the polymer filtered off and washed.

[0087] The polymer is dried overnight in a paint drying cabinet at 60°C.

[0088] Example 5: Polymer 5

[0089] A jacketed vessel fitted with thermostats, reflux condenser, paddle stirrer and internal thermometer was initially charged with 1040.5 g of deionized water, 4.5 g of stabilizer and 0.132 g of emulsifier and the mixture was stirred at 50°C. In parallel therewith, a mixture of 96 g of methyl methacrylate, 400 g of n- butyl methacrylate, 184 g of methacrylic acid, 120 g of n-butyl acrylate, 15.2 g of 2-ethylhexyl thioglycolate, 8 g of n-dodecyl mercaptan and 3.6 g of tert-amyl peroxy-2-ethylhexanoate was weighed out in a beaker and mixed with a magnetic stirrer at room temperature for 15 min. This monomer mixture is then transferred via a funnel to the glass reactor within 2 min. The water-monomer mixture is now heated to the reaction temperature of 80°C. This temperature is maintained until the exothermic reaction has ended. Heating is then continued at 90°C for 90 min. The mixture is then cooled to 30°C and the polymer filtered off and washed.

[0090] The polymer is dried overnight in a paint drying cabinet at 60°C.

[0091] Comparative example 6: Polymer 6

[0092] A jacketed vessel fitted with thermostats, reflux condenser, paddle stirrer and internal thermometer was initially charged with 1393.74 g of deionized water, 4.86 g of stabilizer and 0.14175 g of emulsifier and the mixture was stirred at 50°C. In parallel therewith, a mixture of 90 g of methyl methacrylate, 180 g of n- butyl acrylate, 135 g of methacrylic acid, 45 g of ethyl triglycol methacrylate, 8.55 g of 2-ethylhexyl thioglycolate, 4.5 g of n-dodecyl mercaptan and 4.5 g of tert-amyl peroxy-2-ethylhexanoate was weighed out in a beaker and mixed with a magnetic stirrer at room temperature for 15 min. This monomer mixture is then transferred via a funnel to the glass reactor within 2 min. The water-monomer mixture is now heated to the reaction temperature of 80°C. This temperature is maintained until the exothermic reaction has ended. Heating is then continued at 90°C for 90 min. The mixture is then cooled to 30°C and the polymer filtered off and washed.

[0093] The polymer is dried overnight in a paint drying cabinet at 60°C.

[0094] Example 7: Polymer 7

[0095] A jacketed vessel fitted with thermostats, reflux condenser, paddle stirrer and internal thermometer was initially charged with 2996.64 g of deionized water, 12.96 g of stabilizer and 0.38016 g of emulsifier and the mixture was stirred at 50°C. In parallel therewith, a mixture of 230.4 g of methyl methacrylate, 960 g of n-butyl methacrylate, 441 .6 g of methacrylic acid, 288 g of n-butyl acrylate, 15.36 g of 2-ethylhexyl thioglycolate and 8.64 g of tert-amyl peroxy-2-ethylhexanoate was weighed out in a beaker and mixed with a magnetic stirrer at room temperature for 15 min. This monomer mixture is then transferred via a funnel to the glass reactor within 2 min. The water-monomer mixture is now heated to the reaction temperature of 80°C. This temperature is maintained until the exothermic reaction has ended. Heating is then continued at 90°C for 90 min. The mixture is then cooled to 30°C and the polymer filtered off and washed.

[0096] The polymer is dried overnight in a paint drying cabinet at 60°C.

[0097] Solubility of the polymers

[0098] The polymers of the invention should be soluble in aqueous sodium hydroxide solution but insoluble in water, in order that corresponding printing inks are likewise stable to water and have a broad range of applications. The stability to 80°C hot water over 24 h was accordingly tested. The solubility in water, aqueous sodium hydroxide solution, alcohols, ethyl acetate and a mixture of ethyl acetate and ethanol was tested by weighing 0.2 g of polymer into 9.8 g of solvent at room temperature and stirring at 35°C for 15 min. The resulting samples were assessed with the naked eye. A residue-free clear solution after 15 min was graded as “+++”; a completely insoluble sample as “ — ”. Polymers 3 and 5, which largely met the solubility requirements, were investigated in respect of their suitability for use in printing inks in further tests as a constituent in a base formulation of a nitrocellulose printing ink for flexo and gravure printing processes.

[0099] Production and performance testing of nitrocellulose printing inks

[0100] First of all, solutions of polymer 3 (P3) and polymer 5 (P5) were produced.

[0101] This was done by dissolving 5 g of the respective polymer in 95 g of a 1 :1 mixture of ethyl acetate and ethanol with stirring at room temperature. For the production of the printing ink premix, an NC blend (NC 2450 in ethanol from Siegwerk having a solids content of approx. 20% by weight) was initially charged under the dissolver. The recipe constituents (see table below) were added in the stated order with moderate stirring. The mixture was then produced by operating the dissolver at 1000 rpm for 2 minutes. The amounts used in the polymer solutions were calculated such that the premixes and the printing inks produced therefrom were produced with a concentration of 10% by weight, 15% by weight, and 20% by weight of polymer content based on the dry solids content of the nitrocellulose solution.

[0102] To measure the influence of the polymers on the viscosity of the printing inks, the premixes were used without colour solids. The reference used was the premix VM-0, which consisted of one part of NC 2450 blend in ethanol and one part of a 1 :1 mixture of ethanol and ethyl acetate, but did not contain any polymer or any pigment.

[0103] For better evaluability of squeegee applications and proofs in respect of transparency, adhesion and seal strength, blue-coloured printing inks were produced from the respective premixes. This was done by adding 5% by weight of the non-alkali-soluble blue pigment concentrate PB 15:3 of the Siegwerk NC 23 colour series (wax-free) to the premixes and incorporating with a SpeedMixer for 2 min at 3000 rpm.

[0104] First, the viscosity of the premixes compared to reference VM-0 was investigated:

[0105] By adding the pigment concentrate PB 15:3, the blue-coloured printing inks DF 3-10, DF 3-15, DF 3-20 and DF 5-20 were produced from the premixes with the polymer of the invention as described above. Similarly, the blue-coloured reference printing inks DF-Ref1 and later DF-Ref2 were produced from reference VM-0 by adding the pigment; these do not contain any polymer to be tested and served for comparison purposes.

[0106] The printing ink properties were evaluated after applying the printing inks on 100 pm biaxially stretched PET films, 50 pm biaxially stretched PP (BOPP) films and 40 pm LDPE films and drying. The BOPP and LDPE films underwent a prior corona surface pretreatment. The resulting surface pretreatment was

[0107] ~41 dyn.

[0108] The printing inks were applied to the LDPE films using an Erichsen printing proofer with double 8 wedge plates with 60 lines / cm and densities of 100-95-90-90-80-75-70-60%. The drawdowns on PET and BOPP films were produced using a 6 pm spiral bar coater.

[0109] The following performance results were measured for the resulting printing inks:

[0110] Key: +++ = very good; ++ = good; + = satisfactory; 0 = not measured

[0111] Evaluation of the performance tests

[0112] The addition of polymer 3 to the base printing ink has no adverse effects on the viscosity or on the investigated performance properties; only when the content of polymer 3 in the solid printing ink is at least 20% by weight does the visually evaluated transparency of the drawdowns on PET decrease somewhat as a consequence of the limited solubility of polymer 3.

[0113] The addition of 20% by weight of polymer 5 to the printing ink has no adverse effects on the viscosity.

[0114] The transparency, colour adhesion and seal stability were likewise not adversely affected by the addition of polymer 5 to the tested PET, HDPE and BOPP films (see table).

[0115] After storage at room temperature for several weeks, the optical and performance of the printed areas and drawdowns are unchanged; they showed no differences when the above measurements were repeated.

[0116] The printing inks DF 3-10, DF 3-15, DF 3-20 and DF 5-20 and the films printed therewith accordingly qualify for further deinking tests.

[0117] Rate of detachment of printing ink from printed films in aqueous sodium hydroxide solution Procedure

[0118] The LDPE films printed in blue on their surface with the printing inks to be investigated and the BOPP and PET drawdowns coated in blue on their surface were cut into squares measuring approx. 1 .5 x 1.5 cm.

[0119] The procedure for measuring the rate of detachment was as follows:

[0120] 5 squares in 15 ml of NaOH (2% by weight) were used per measurement; the aqueous sodium hydroxide solution was thermally equilibrated at 35°C and stirred at 350 rpm with a magnetic stirrer bar. For each printing ink sample, the measurement series was continued until complete removal of printing ink from the film could be observed. Samples were taken after 15 min, 30 min and thereafter at intervals of 10 min until complete removal of printing ink from the film could be observed. They were assessed visually on a white Teflon plate under neutral white LED illumination compared to the unprinted film.

[0121] In some cases, additional strips of the sample were suspended in the stirred aqueous sodium hydroxide solution and removed at the stated times and wiped once with a weighted (50 g) laboratory tissue and likewise visually assessed.

[0122] An assessment of “completely removed” was awarded when at least 4 of the 5 squares no longer showed any visual traces of printing ink.

[0123] The removal of the printing ink from the samples was visually assessed on a five-point scale compared to the unprinted film. Key: +++ = completely; ++ = mostly; + = predominantly; - = partially; - = hardly or not decolorized at all. Results

[0124] In order also to assess the removal of the printing ink quantitatively, the recently published DIN SPEC 51496:2024-02 was employed. This recommends in chapter 8.1 the measurement of the colour difference delta E between an unprinted and a printed, completely deinked film. This method was used to investigate the removal of printing ink DF 5-20 from the LDPE film after stirring for 40 min in 2% by weight NaOH compared to the unprinted film. The triplicate determination of the reference and sample resulted in an average delta E of 1 .03. In accordance with DIN SPEC 51496 (chapter 9), the sample is therefore considered to be deinkable, since delta E is < 3.0.

[0125] When surfactants are additionally used in the alkaline solution (2% by weight NaOH), the time to complete removal of the printing ink can be shortened further:

[0126] When 0.5% by weight of the nonionic surfactant TEGO® Cycle WA 111 is added, the time to complete removal of printing ink DF 5-20 from the LDPE film is shortened from 40 min to 15 min, and to 10 min when adding 0.2% by weight of the cationic surfactant cetyltrimethylammonium chloride (CTAC).

[0127] However, if the detached particles of printing ink are to be subsequently removed from the wash solution using mechanical separation methods, it is advantageous to dispense with the addition of surfactants, since surfactants result in smaller, better stabilized printing ink particles in the wash solution that are less readily filtered or centrifuged off either A) at alkaline pH or B) after precipitation at acidic pH. Thus, the median particle size D50 (measured with Horiba LA 950 V2 according to DIN / ISO 13320) in the alkaline surfactant-free wash solution after detachment of the ink DF 5-20 from the LDPE film is 147 pm. However, the median particle size D50 of the CTAC-containing alkaline wash solution after detachment of ink DF 5-20 from the LDPE film is 117 pm.

[0128] A) In accordance with these findings, it is not possible to remove the particles of blue printing ink from the alkaline wash solution with added surfactant using a laboratory fluted filter paper (Macherey- Nagel, type MN 605); a strongly blue-coloured, turbid filtrate is obtained.

[0129] If, on the other hand, the surfactant-free alkaline solution is filtered through the above laboratory filter paper, a clear filtrate that is only slightly blue-coloured is obtained.

[0130] B) Acidifying the CTAC-containing alkaline wash solution to pH 5 with hydrochloric acid after detachment of ink DF 5-20 from the LDPE film and then filtering it through the laboratory fluted filter paper (Macherey-Nagel, type MN 605) results in a blue-coloured, slightly turbid filtrate.

[0131] Acidifying the CTAC-free alkaline wash solution to pH 5 with hydrochloric acid after detachment of ink DF 5-20 from the LDPE film and then filtering it through the laboratory fluted filter paper results in a completely colourless and clear filtrate.

[0132] Lowering the pH to within the acid range results in protonation of the acid groups of the polymers of the invention, which are present in ionic form in alkaline conditions; this causes a decrease in the solubility of the polymers or of the printing inks containing the polymers and onset of particle growth and precipitation, particularly when surfactants are absent.

[0133] Thus, after detachment from the polymer film, the printing inks containing the polymers of the invention can be completely removed particularly easily by mechanical separation methods such as filtration, and the wash water reused.

[0134] Evaluation of the rate of detachment of the printing ink from the investigated films

[0135] The progress of the detachment of printing inks DF 3-10, DF 3-15, DF 3-20 and DF 5-20 was investigated more closely on LDPE. As can be seen, with increasing content of polymer 3, the rate of detachment increases compared to the reference DF-Ref1 and in the case of DF 3-20 with 20% polymer is now only 40 min instead of 80 min.

[0136] The progress of printing ink removal was likewise determined for polymer 5 on LDPE with 20% by weight of polymer 5: With 20% by weight of polymer 5 in the printing ink, the time to complete removal of the printing ink can likewise be halved from 80 to 40 min.

[0137] The tests were then extended to BOPP and PET films, but with only the time to complete removal determined: As can be seen, the rate of detachment can be significantly shortened on the BOPP, PET and LDPE films investigated, both with polymer 3 and with polymer 5 as printing ink additive.

[0138] The additional evaluation of deinking quality according to DIN SPEC 51496 carried out on the DF 5-20 sample confirms the complete removal of the printing ink after 40 min and the validity of the optical evaluation.

[0139] The present invention is also characterized by the following items:

[0140] 1. Polymethyl (meth)acrylate-based polymers, characterized in that they are soluble in aqueous alkaline solution and in polar solvents. 2. Polymethyl (meth)acrylate-based polymers according to Claim 1 , characterized in that they are soluble in aqueous sodium hydroxide solution at temperatures of between 20 and 35°C.

[0141] 3. Polymethyl (meth)acrylate-based polymers according to Claim 1 , characterized in that the polar solvents are selected from the group of alcohols, preferably ethanol, isopropanol and 1-ethoxy-2- propanol, and esters, such as ethyl acetate, and mixtures thereof.

[0142] 4. Polymethyl (meth)acrylate-based polymers according to Claim 1 , characterized in that they are insoluble and stable in water at temperatures of between 50 and 85°C.

[0143] 5. Polymethyl (meth)acrylate-based polymers according to Claim 1 , characterized in that the polymer contains:

[0144] 0-20% by weight of methyl methacrylate,

[0145] 1-65% by weight of n-butyl methacrylate,

[0146] 1-35% by weight of methacrylic acid,

[0147] 0-30% by weight of n-butyl acrylate,

[0148] 0-30% by weight of hydroxyethyl methacrylate.

[0149] 6. Polymethyl (meth)acrylate-based polymers according to Claim 5, characterized in that the polymer contains:

[0150] 5-16% by weight of methyl methacrylate,

[0151] 30-60% by weight of n-butyl methacrylate,

[0152] 15-30% by weight of methacrylic acid, 10-20% by weight of n-butyl acrylate.

[0153] 7. Polymethyl (meth)acrylate-based polymers according to Claim 5, characterized in that the polymer contains:

[0154] 20-50% by weight of n-butyl methacrylate,

[0155] 15-30% by weight of methacrylic acid,

[0156] 10-20% by weight of n-butyl acrylate,

[0157] 10-25% by weight of hydroxyethyl methacrylate.

[0158] 8. Polymethyl (meth)acrylate-based polymers according to Claim 1 , characterized in that the average molecular weight Mw of the polymers is between 10 000-60 000 g / mol, preferably between 15 DOO- 25 000 g / mol.

[0159] 9. Process for producing polymers according to Claim 1 , characterized in that

[0160] - a mixture A: an aqueous solution containing stabilizers and emulsifiers, is initially charged and heated to 40°C to 60°C,

[0161] - a monomer mixture B containing n-butyl methacrylate, methacrylic acid, n-butyl acrylate, hydroxyethyl methacrylate and optionally methyl methacrylate is added,

[0162] - 0.5-4% by weight, preferably 2-3.8% by weight, of chain-transfer agents and initiators are added and the reaction solution obtained is mixed, - the reaction solution undergoes reaction at temperatures of between 75°C and 85°C,

[0163] - on completion of the reaction, the reaction solution is stirred further at 85°C to 95°C for 30 min to 100 min,

[0164] - the reaction solution is cooled to 25°C to 35°C, filtered off and washed,

[0165] - the polymer obtained is dried at 50°C to 60°C.

[0166] 10 Printing inks, NC flexo printing inks and gravure printing inks comprising polymethyl (methacrylate- based polymers according to at least one of Claims 1 to 8.

[0167] 11. Printing inks, NC flexo printing inks and gravure printing inks comprising polymethyl (methacrylate- based polymers according to Claim 10, characterized in that they are detachable in aqueous alkaline solution without the addition of further auxiliaries to the wash solution.

[0168] 12. Printing inks, NC flexo printing inks and gravure printing inks comprising polymethyl (methacrylate- based polymers according to Claim 10, characterized in that they are detachable in aqueous alkaline solution at temperatures of between 15 and 35°C without the addition of further auxiliaries to the wash solution.

[0169] 13. Printing inks, NC flexo printing inks and gravure printing inks comprising polymethyl (methacrylate- based polymers according to Claim 10, characterized in that they are detachable in alkaline solution with the addition of one or more auxiliaries, to the wash solution, selected from the group of detergents and stabilizers, surfactants or wetting agents, emulsifiers or macro-emulsifiers, defoamers or combinations thereof.

[0170] 14. Printing inks comprising polymethyl (meth)acrylate-based polymers according to Claim 13, characterized in that they are detachable in alkaline solution, particularly with the addition of nonionic surfactants such as TEGO Cycle WA 111 and cationic surfactants such as cetyltrimethylammonium chloride to the wash solution.

[0171] 15. Use of polymethyl (meth)acrylate-based polymers according to Claim 1 in printing inks, NC flexo printing inks and gravure printing inks according to Claim 10 for the packaging industry, in particular for printing on flexible packaging based on polyolefin films and / or polycondensate films such as polyethylene terephthalate (PET), high-density polyethylene (HDPE), polypropylene (PP), cast polypropylene (CPP), and in particular for printing on flexible plastics such as low-density polyethylene (LDPE), linear low- density polyethylene (LLDPE), oriented polypropylene (OPP) and biaxially oriented polypropylene (BOPP).

[0172] 16. Use of polymethyl (meth)acrylate-based polymers according to Claim 1 in nitrocellulose-containing or nitrocellulose-free pigmented and unpigmented formulations and products capable of application in flexo and gravure printing, deinking formulations and systems.

Claims

Claims1. Polymers containing:0-30% by weight of hydroxyethyl methacrylate5-16% by weight of methyl methacrylate,30-60% by weight of n-butyl methacrylate,15-30% by weight of methacrylic acid,10-20% by weight of n-butyl acrylate.

2. Polymers, containing:20-50% by weight of n-butyl methacrylate,15-30% by weight of methacrylic acid,10-20% by weight of n-butyl acrylate,10-25% by weight of hydroxyethyl methacrylate0-20% by weight of methyl methacrylate.

3. Polymers according to Claims 1 and 2, characterized in that the average molecular weight Mw of the polymers is between 10 000-60 000 g / mol, preferably between 15 000-25 000 g / mol, measured by DIN 55672-1.

4. Process for producing polymers according to any one of the preceding claims, characterized in that- a mixture A: an aqueous solution containing stabilizers and emulsifiers, is initially charged and heated to 40°C to 60°C,- a monomer mixture B containing n-butyl methacrylate, methacrylic acid, n-butyl acrylate, hydroxyethyl methacrylate and optionally methyl methacrylate is added,- 0.5-4% by weight, preferably 2-3.8% by weight, of chain-transfer agents and initiators are added and the reaction solution obtained is mixed,- the reaction solution undergoes reaction at temperatures of between 75°C and 85°C,- on completion of the reaction, the reaction solution is stirred further at 85°C to 95°C for 30 min to 100 min,- the reaction solution is cooled to 25°C to 35°C, filtered off and washed,- the polymer obtained is dried at 50°C to 60°C.

5. Printing inks, NC flexo printing inks and gravure printing inks comprising polymers according to at least one of claims 1 to 3.

6. Process for removing printing inks, NC flexo printing inks and gravure printing inks comprising polymers according to at least one of claims 1 to 3, comprising the steps:- detaching in aqueous alkaline solution without the addition of further auxiliaries to the wash solution- at temperatures of between 15 and 35°C.

7. Process for removing printing inks, NC flexo printing inks and gravure printing inks according to claim 6 comprising polymers according to at least one of claims 1 to 3, comprising the step- detaching in alkaline solution with the addition of one or more auxiliaries, to the wash solution, selected from the group of detergents and stabilizers, surfactants or wetting agents, emulsifiers or macro-emulsifiers, defoamers or combinations thereof.

8. Use of polymers according to at least one of claims 1 to 3 in printing inks, NC flexo printing inks and gravure printing inks according to Claim 10 for the packaging industry, in particular for printing on flexible packaging based on polyolefin films and / or polycondensate films such as polyethylene terephthalate (PET), high-density polyethylene (HDPE), polypropylene (PP), cast polypropylene (CPP), and in particular for printing on flexible plastics such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), oriented polypropylene (OPP) and biaxially oriented polypropylene (BOPP).

9. Use of polymers according to at least one of claims 1 to 3 in nitrocellulose-containing or nitrocellulose-free pigmented and unpigmented formulations and products capable of application in flexo and gravure printing, deinking formulations and systems.

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