Pipe-in-pipe homogenizer

Abstract

Preservative composition, including: at least 40% water by weight; a primary amino alcohol with a total of 2 to 6 carbon atoms in a proportion of 15 to 50 wt.%; at least one surfactant in a proportion exceeding its solubility at 23°C in the water-amino alcohol mixture; and a buffer component with a pKa value between 8 and 10.5.

Description

[0001] The present invention relates to a preservative composition, its manufacture and a device for its manufacture, as well as its use.

[0002] When storing aqueous dispersions such as wall paints, varnishes, etc., problems with microbial contamination, such as mold growth, can easily occur. It is known to add an isothiazolinone derivative to prevent this, for example, methylisothiazolinone (MIT), chloromethylisothiazolinone (CMIT), and / or benzisothiazolinone (BIT). For example, an antiseptic and antibacterial preservative composition based on alkylaminopropanediol, intended for cleaning products that come into contact with the skin, is known from European patent EP 4 364 567 A1. For the treatment of certain viral infections, a combination of polyacrylic acid and 2-amino-2-methylpropanol for prophylactic and / or therapeutic use is known from European patent EP 2 803 354 A1. Publication WO 2009 / 140061 A2 discloses an antimicrobial composition comprising a biocide of the above type and a primary amino alcohol.Publication WO 2011 / 069961 A1 discloses a calcium carbonate slurry containing a biocide and a primary monoalkanolamine, with a similar objective. However, more recent studies have shown that the biocides mentioned may be of concern or even harmful to health.

[0003] Therefore, there is a need for an alternative to prevent mold and generally preserve the aforementioned aqueous dispersions.

[0004] To this end, the present invention proposes a preservative composition according to claim 1, a manufacturing process according to claim 13, a device according to claim 14 and a use according to claim 16 or 18.

[0005] The inventors have found that the composition according to the invention inhibits the growth of molds, yeasts, bacteria, and other microbes in aqueous dispersions of the type mentioned above, even without the addition of a biocidal agent. Thus, the required composition, which is harmless to health and therefore does not require approval, has been found.

[0006] Another aspect of the manufacturing process for the composition includes a step of homogenization to a particle size in the range of 50 - 500 nm ("nanodisperse"), which ensures excellent efficacy and storage stability against creaming (over several months).

[0007] A third aspect of a device for producing the composition or for carrying out the above process includes a continuous flow reactor along with a high-performance homogenizer for exerting the shear forces required for nanodisperse emulsification.

[0008] Finally, a fourth aspect of the present invention involves the use of the aforementioned composition as a preservative additive to an aqueous dispersion. In particular, the composition acts as a microbial inhibitor, specifically as an inhibitor of the growth or reproduction of molds, yeasts, and bacteria. Furthermore, the aqueous dispersion is, in particular, a varnish or (wall) paint.

[0009] Without committing to a specific theory, the inventors assume that the particularly fine emulsion allows the amino alcohol to inhibit the metabolism of the microbes without itself having a biocidal effect. This has the advantageous side effect of not being allergenic. Furthermore, the pH value of the dispersion being preserved is stabilized, preventing creaming. Incidentally, the aqueous dispersions in question are predominantly more or less alkaline, exhibiting a pH value between 8 and 10.5.

[0010] The composition according to the invention is not effective as a biocide; that is, it does not actively reduce microbial counts by killing microbes, but merely prevents their proliferation in technical products. If the microbial load in these products is at a hygienically acceptable level (titer) before the application of the composition according to the invention, its addition ensures that no noticeable proliferation of harmful microbes occurs and that the technical product remains storable without a concerning microbial load, even without the use of biocides.

[0011] Embodiments of the invention are explained in more detail below with reference to the figures. These show: Fig. 1 a flowchart for the manufacturing process according to one aspect of the present invention; Fig. 2. A schematic block diagram of the manufacturing process; Fig. 3a, b schematically a device for carrying out the manufacturing process according to a further aspect of the present invention; and Fig. 4 the droplet size distribution density of an emulsion obtained according to the inventive method.

[0012] The composition according to the invention comprises, in addition to the main component water (40 wt.% or more, preferably more than 50 wt.%) and the primary amino alcohol (15–50 wt.%, preferably less than 40 wt.%) and the buffer component, a surfactant in a concentration that exceeds its solubility at 23°C in the water-amino alcohol mixture, so that it is not a clear solution but a nanodispersed emulsion. Nevertheless, this emulsion is stable against creaming for several months, even under storage conditions with temperature fluctuations within the usual range.

[0013] The nanodisperse emulsion is obtained by feeding a mixture of water, surfactant, and amino alcohol (optionally also the buffer component) through a continuous flow reactor at atmospheric pressure and a slightly elevated temperature of, for example, 25–35°C into a high-performance homogenizer, which operates at 3000–9000 rpm with a radial gap width of typically 100 µm, i.e., 2πr / mm·500s -1 up to 2πr / mm·1500s -1 Within a maximum of 1 minute of average flow time, a slightly cloudy but long-term stable emulsion is produced. Depending on the viscosity of the mixture, speeds of 1000–10000 rpm can be used. As with a rotational viscometer, the shear rate was divided by the gap width to obtain the shear rate, which, multiplied by the viscosity, yields the required shear stress. Typical radii for the inner rotor are 0.5 to 6.0 cm, depending on the desired throughput, resulting in a shear rate of 10000 s⁻¹.-1 up to 100,000 s -1 This results in... Of course, any number of such reactors can be arranged in parallel to provide a sufficient overall flow cross-section.

[0014] For application, the resulting nanoemulsion is added to the water-based dispersion to be preserved in an amount of at least 0.1% by mass, but typically 0.25–1.0% by mass. The buffer component ensures that the pH of the water-based dispersion does not decrease by more than 0.1 units.

[0015] Without a preservative, ubiquitous yeasts, molds, and / or bacteria that are already present multiply and gradually lower the pH of the medium through their metabolic products, which further promotes their growth and reproduction. The composition according to the invention inhibits this further multiplication and growth, thus stabilizing the pH.

[0016] It should be noted that a sample pre-contaminated with microbes remains microbiologically contaminated after the addition of the preservative composition according to the invention, but this contamination does not increase. In this respect, it is confirmed that the primary amino alcohol itself is not a biocide, but only a biostatic agent. In particular, the composition according to the invention itself does not contain a biocide.

[0017] The composition according to the invention contains, in addition to water, primary amino alcohol, and a buffer component, as well as optionally further excipients, at least one surfactant in a proportion in which it is no longer completely miscible with the main components (at 23°C). In embodiments, the composition therefore exhibits a certain turbidity, which can be measured nephelometrically (i.e., in scattered light) or turbidimetrically (i.e., in transmitted light) according to ISO 7027-1:2016. It is preferred if the turbidity at 23°C is at most 400 NTU (nephelometric turbidity units). The turbidity is due to the presence of surfactant micelles. When the composition is mixed into the dispersion to be preserved, the surfactant molecules aggregated in the micelles become surface-active and promote the action of the amino alcohol on microbes present there.From this perspective, it is preferable if the turbidity is not less than 50 NTU, as otherwise the surfactant content will be insufficient. Incidentally, this turbidity corresponds to a mass fraction of the surfactant used, depending on its composition, in the range of 1% to 10%, preferably 2.5% to 5%.

[0018] The composition according to the invention contains no or essentially no biocide, namely in particular less than 15 ppm MIT, less than 50 ppm CMIT and less than 500 ppm BIT.

[0019] The buffer component of the composition according to the invention includes, for example, 0.1 - 2% of a so-called good buffer, namely in particular one selected from the group consisting of 4-(2-hydroxyethyl)piperazine-1-propanesulfonic acid, glycinamide, N-(tri(hydroxymethyl)methyl)glycine, N,N-bis(2-hydroxyethyl)glycine and [tris(hydroxymethyl)methylamino]propanesulfonic acid, since these have a high pKa value compared to other good buffers.

[0020] Non-ionic surfactants such as polyalkylene glycol ethers, sorbitan fatty acid esters, alkyl polyglucosides, or fatty alcohol ethoxylates have proven particularly effective. Zwitterionic surfactants such as betaines (e.g., cocamidopropyl betaine) or sultaines (e.g., cocamidopropyl hydroxysultaine) have also proven suitable.

[0021] In preferred embodiments, the compositions according to the invention may contain further additives and excipients, including so-called superhydrophobic substances, e.g., n-hexadecane or another alkane with 9-24 carbon atoms, in a small amount of, e.g., 0.05-0.1 wt%, to prevent Ostwald ripening, and hydrogen-bonding agents such as urea derivatives and amino acid derivatives. Without committing to a specific theory, the inventors assume that these substances form supramolecular buffer systems that trap any metabolic products of microbes and thus inhibit their proliferation.

[0022] Due to the high shear rate resulting from the reactor geometry and operating mode, extensive disaggregation occurs rapidly in the homogenizer, forming a nearly monodisperse emulsion with droplet sizes between 50 and 500 nm. This (nano- or mini-)emulsion is also exceptionally stable during storage. Unlike, for example, the coaxial reactor known from DT 2024714, the gap between the two cylinders is not divided into sections, and the components to be mixed are fed directly into the gap from the end face. Also unlike, for example, the coaxial hollow-vessel stirrer known from DE 40 18 780 A1, its outer circumference is cylindrical and not polygonal-prismatic.Furthermore, the opposing cylindrical surfaces are essentially smooth, so that the sum of their Rz values ​​(peak-to-valley roughnesses) is smaller than the nominal gap width, in stark contrast to the coaxial mixer known from GB 2 118 058 A with macroscopic depressions in the cylindrical surfaces and a rotational speed that is more than an order of magnitude lower with the same rotor diameter, as well as a mass throughput that is more than an order of magnitude greater.

[0023] The Fig. Figure 1 shows a flowchart with steps S1 (introducing the components into the homogenizer), S2 (homogenizing the mixture) to S3 (discharging the emulsion), along with an optional first step S0 for pre-mixing some or all components. Fig. Figure 2 shows in more detail which components are combined and how they are then added to the homogenizer. This illustration is only an example and can be modified in many ways. However, it is advisable to first combine the superhydrophobic surfactant (if present) with the second surfactant, which has a lower hydrophilicity (HLB), and then dissolve it in water with the first surfactant, which has a higher HLB (solution 1). Conversely, readily water-soluble excipients such as urea and amino acid derivatives should first be dissolved in water (solution 2) and only then added to the homogenizer, in parallel with the amino alcohol. If using an amino alcohol that is solid at room temperature, it can first be mixed with a little water (or obtained as a 90% solution) to liquefy it and only then added.In this example, the reactor / mixer is depicted as a two-stage system, where the reactor can be a stirred tank; however, this is not a limiting factor, and the reactor / mixer can be an integral unit. The components can be introduced into the reactor individually, or the lines can be combined. Naturally, each line can be equipped with a metering valve and a flow meter. The flow through the reactor / mixer can be automatic (by hydrostatic pressure) or by means of a pump. The pump can be controllable. A central control system is advantageous, which controls the valves and pump(s). For preheating purposes, the first reactor section (at the top) can be... Fig. 2) heated and / or the second homogenizer part (below in Fig. 2) be designed to be coolable.

[0024] In Fig. 3a is schematically a longitudinal and in Fig.Figure 3b shows a cross-section (along line B--B) of a mixer 1 (homogenizer) according to the invention, in which an inner rotor cylinder 3, driven by a motor 5 and heated as required, rotates concentrically in an outer stator hollow cylinder 7, which in turn is optionally equipped with a cooling jacket 9. The individual and / or premixed composition components are fed directly into the gap 11 between the two cylinders 3 and 7, e.g., by means of a (diaphragm) pump and valves (not shown). The finished emulsion is drawn off at the opposite end face of the homogenizer 1. In variations thereof, the inner cylinder 3 can also be cooled and / or the outer cylinder 7 heated. The gap width w is typically a few tens of micrometers to one millimeter, and the diameter of the annular gap a few millimeters to several tens of millimeters.It is readily conceivable and often practical to arrange, for example, 7, 19, or 37 such homogenizers together as a (e.g., symmetrical) bundle to increase the total cross-sectional area and thus the throughput. In such a case, cooling (or, if necessary, heating or thermostatic control) can be achieved externally via a common fluid in a vessel, as in a tube bundle reactor. The inner rotor cylinder can be hollow and / or coated on its exterior. Its circumferential surface can be polished or pickled to the specified roughness.

[0025] The primary amino alcohol can, in particular, have 2 carbon atoms (e.g., monoethanolamine), 3 carbon atoms (e.g., N-methylethanolamine), 4 carbon atoms (e.g., diethanolamine or dimethyl-2-hydroxyethylamine), 5 carbon atoms (e.g., N-methyldiethanolamine), or 6 carbon atoms (e.g., triethanolamine). In these cases, the amino alcohol is a 1,2-amino alcohol (β-amino alcohol), which is preferred but not mandatory. The amine can be a primary (e.g., monoethanolamine or dimethyl-2-hydroxyethylamine), secondary (e.g., diethanolamine or N-methylethanolamine), or tertiary amine (e.g., N-methyldiethanolamine or triethanolamine). Among these, primary amines are preferred. Dimethyl-2-hydroxyethylamine (or 2-methyl-2-aminopropanol-1) is particularly preferred.

[0026] The material flow in the mixer is helical overall due to shear forces, but ideally turbulent to achieve intensive mixing and homogenization. Depending on the components used, preheating can be helpful. During mixing, the temperature rises due to internal losses, so heat should be dissipated (both temporally and spatially) towards the end of the process. For the example mixer geometry, a rotational speed of up to 8000 rpm is usually sufficient. The Reynolds number is then, for example, between 1900 and 2050, depending on the viscosity, thus just below the critical Reynolds number (Prof. Dr. Björn Hof, 2011). An ultrasonic transducer can be used to support homogenization. With an annular gap circumference of approximately 16 cm and a gap width of 0.1 mm, the cross-sectional area of ​​the mixing chamber is 16 mm². 2 , and with an exemplary volume flow rate of 0.8 ml / s = 800 mm 3The axial flow rate is 800 / 16 mm / s, or 50 mm / s. This applies to a typical mixer volume of approximately 10,000 mm³. 3 (10 ml) This volume is exchanged within approximately 12.5 s mean residence time. The resulting emulsion typically exhibits a monodisperse droplet size distribution. In one example, the mode D m approximately 250 nm, the width of the distribution ΔD approximately 50 nm, and the ratio ΔD / D m Therefore, 20%. Here, ΔD represents the width of the distribution density peak at half height (FWHM, full width at half maximum). Even higher throughput rates of up to, for example, 4000 mm² 3 However, / s are possible, with correspondingly shorter dwell times (down to about 2.5 s) in the mixer.

[0027] The term "derivatives" of urea and amino acids refers to compounds in which single atoms or groups of atoms have been exchanged. This includes alkylations (e.g., single or double methylation) at the amine nitrogen atom, esterification (of the amino acid), and similar modifications, including dimers, even in combination. Specifically, this includes urea derivatives with single or double substitutions at the nitrogen atom, such as N-methylurea, N,N'-dimethylurea, or N-(2,5-dioxo-4-imidazolidinyl)urea (allantoin), as well as esterified amino acid derivatives or, for example, [(aminoacetyl)amino]acetic acid (glycylglycine). However, triple or multiple substitutions or the exchange of nitrogen or oxygen atoms for other atoms (S) or groups of atoms are not included.

[0028] In summary, the invention provides a preservative composition comprising a primary amino alcohol with a total of 2 to 6 carbon atoms, at least one surfactant, water, and a buffer component with a pKa value between 8 and 10.5. A device for producing the composition has an inner rotor cylinder and an outer stator cylinder configured to rotate relative to each other and to guide the mixture axially through a gap between the two cylinders in order to generate an emulsion under the influence of a shear force. This emulsion, or the composition thus produced with preferably > 50% water, is used as a preservative additive to an aqueous dispersion with a target pH value of 8 to 10.5. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] EP 4 364 567 A1

[0002] EP 2 803 354 A1

[0002] WO 2009 / 140061 A2

[0002] WO 2011 / 069961 A1

[0002] DE 40 18 780 A1

[0022] GB 2 118 058 A

[0022]

Claims

[1] Preservative composition, comprising: at least 40% water by weight; a primary amino alcohol with a total of 2 to 6 carbon atoms in a proportion of 15 to 50 wt.%; at least one surfactant in a proportion exceeding its solubility at 23°C in the water-amino alcohol mixture; and a buffer component with a pKa value between 8 and 10.

5. [2] Preservative composition according to claim 1, wherein the composition is essentially free of biocides. [3] Preservative composition according to claim 1 or 2, wherein the primary amino alcohol is a β-amino alcohol such as triethanolamine, diethanolamine, monoethanolamine, N-methyldiethanolamine, N-methylethanolamine or, particularly preferably, dimethyl-2-hydroxyethylamine. [4] Preservative composition according to any one of claims 1 to 3, wherein the surfactant is a non-ionic or zwitterionic surfactant. [5] Preservative composition according to claim 4, wherein the surfactant comprises one or more selected from the group consisting of polyalkylene glycol ethers, sorbitan fatty acid esters, alkyl polyglucoside, fatty alcohol ethoxylate, betaine such as cocamidopropyl betaine and sultaine such as cocamidopropyl hydroxysultaine. [6] Preservative composition according to claim 4 or 5, wherein the surfactant is a combination of at least one surfactant with a higher HLB value and at least one surfactant with a lower HLB value. [7] Preservative composition according to any one of claims 1 to 6, further comprising a superhydrophobe, in particular an n-alkane having 9 to 24 carbon atoms, especially preferably n-hexadecane. [8] Preservative composition according to any one of claims 1 to 7, further comprising a multifunctional component comprising at least one amino group and at least one secondary hydroxy or carbonyl group and having a molecular mass of preferably up to 150 atomic mass units, wherein the carbonyl group is in particular bonded directly or via 1 carbon atom to the at least one amino group. [9] Preservative composition according to claim 8, wherein the multifunctional component is a urea derivative or an amino acid derivative. [10] Preservative composition according to any one of claims 1 to 9, wherein the buffer component comprises one or more from the group of Good buffers, in particular selected from the group consisting of 4-(2-Hydroxyethyl)piperazine-1-propanesulfonic acid, N-(Tri(hydroxymethyl)methyl)glycine, [Tris(hydroxymethyl)methylamino]propanesulfonic acid, glycinamide and N,N-Bis(2-hydroxyethyl)glycine. [11] Preservative composition according to any one of claims 1 to 10, wherein the composition is a miniemulsion or nanoemulsion. [12] Preservative composition according to claim 11, wherein the emulsion has a turbidity of 50 NTU or more and 400 NTU or less when measured nephelometrically according to ISO 7027-1:2016. [13] Method for producing the preservative composition according to claim 11 or 12, comprising mixing at least the amino alcohol, the surfactant and the water in a continuous flow reactor under increased pressure and / or increased temperature and homogenizing the mixture under shear force to obtain a miniemulsion or nanoemulsion. [14] Apparatus for producing the preservative composition of any one of claims 1 to 12 according to the method of claim 13, comprising a coaxial homogenizing mixer and a continuous flow reactor upstream of or integrated with the latter, wherein the mixer has an inner rotor cylinder and an outer stator cylinder and is configured to guide the mixture in a substantially axial direction through a gap between the two cylinders rotating against each other, wherein the sum of the Rz values ​​of the cylinder surfaces facing each other is smaller than the nominal gap width, so that the mixture is subjected to a shear force by the rotation of the inner rotor cylinder. [15] Device according to claim 14, further comprising a cooling jacket for the outer stator cylinder and / or a heater for the inner rotor cylinder. [16] Use of the device according to claim 14 or 15, wherein the absolute circumferential speed of the inner rotor cylinder relative to the outer stator cylinder, measured at the outer surface of the rotor, divided by the radial width of the gap between the rotor cylinder and the stator cylinder, during operation of the device is between 40000 and 80000 s -1 amounts. [17] Use of the device according to claim 16 or in the method according to claim 13, wherein the Reynolds number is in the range of 800 to 3200. [18] Use of the preservative composition of any one of claims 1 to 12, or of the preservative composition produced according to claim 13 or by means of the apparatus according to claims 14 to 16, as a preservative additive to an aqueous dispersion with a target pH of 8 to 10.

5. [19] Use according to claim 18, comprising inhibiting the growth of ubiquitous microbes such as molds, yeasts and / or bacteria. [20] Use according to claim 18 or 19, wherein the aqueous dispersion is a varnish, a paint or wall paint, an adhesive or a binder. [21] Use according to any one of claims 18 to 20, comprising the addition of the preservative composition in a proportion of 0.1 to 1.0 vol% of the volume of the aqueous dispersion.

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