Polar-modified corn waxes, and esterification or saponification products thereof

Abstract

The invention relates to polar-modified corn waxes and esterified or saponified derivatives thereof, to the production thereof, and to the use thereof for coatings and as plastic processing aids.

Description

[0001] Polar-modified maize waxes and their esterification or saponification products

[0002] The invention relates to a light-colored, polar-modified corn wax, a process for producing these oxidation products of corn wax, and their use for agricultural or forestry purposes, as an additive in plastics processing, in personal care products, in printing inks, and / or in paints and coatings. Also related are saponified and esterified polar-modified corn waxes produced by the saponification or esterification of the polar-modified corn wax according to the invention.

[0003] The composition of corn wax was first described by Shriner et al. (Shriner et al. "The composition of corn wax", JACS, 1927 (49), 1290-1294).

[0004] In a recent publication, Kang et al. analyze the physicochemical properties of corn wax and compare them to those of other waxes (Kang, B, Liu, Y, Yang, R, Liang, S. Composition and physicochemical properties of corn wax. J Am Oil Chem Soc. 2023; 100(10): 783-790 https: / / doi.org / 10.1002 / aocs.12717). According to their findings, corn wax esters have longer chain lengths than other natural waxes such as rice wax, sunflower wax, or candelilla wax. The acid value of crude corn wax is below 2 mg KOH / g, as the proportion of free fatty acids in the wax is very low.

[0005] In addition to wax esters and free fatty acids, natural wax, including corn wax, contains other components such as phospholipids and steryl esters. Further variable components of corn wax, considered to be present in trace amounts, include unspecified dark substances, squalene, and the so-called gum content. These components typically result in product quality that varies in color and usability and is difficult to reproduce consistently.

[0006] Refining processes, such as classic hydrogen peroxide bleaching, reduce the dark substances in natural wax, and the acid value may increase slightly, but it still largely corresponds to that of the original wax. In corn wax, it does not exceed 8 mg KOH / g. Hydrogen peroxide-bleached natural waxes are yellowish and their ester content largely corresponds to that of the original wax. Hydrogen peroxide-bleached types are predominantly offered on the market as defatted and refined natural waxes; however, because the bleached minor components remain in the product, they also exhibit fluctuating product quality.

[0007] The applications for natural waxes are diverse. Waxes are used in polishes, coatings, printing inks and / or varnishes, as well as for agricultural and forestry purposes. A large proportion is used as processing aids in plastics processing. There, the waxes serve as degassing, leveling, lubricating, demolding, and / or dispersing agents for plastics and must withstand the high temperatures used to melt the plastic. The waxes remain in the plastic. Accordingly, waxes particularly suitable for plastics processing are those that exhibit the highest possible thermal stability, minimal coloration, low viscosity, and a low dropping point, and which ideally can be produced as sustainably as possible. Furthermore, natural waxes can be used in coatings, such as those used in the agricultural and food sectors.Examples include coatings for fruit, seeds, sweets, and fertilizers.

[0008] However, raw and bleached natural waxes are only partially suitable for such purposes, as they exhibit the fluctuating product quality described above and, due to their chemical properties, are not suitable or only conditionally suitable for the described applications. For this reason, oxidation processes for natural waxes have been developed that bleach the waxes, remove interfering components, and change the polarity of the waxes to adapt them to the respective application.

[0009] The oxidation of fossil and non-fossil natural waxes with chromic acid has been known since the beginning of the 20th century and has been carried out industrially using fossil montan waxes since 1927 in the still-operated "Gersthofen process." Besides fossil montan wax, renewable natural waxes such as carnauba wax and candelilla wax can also be oxidized using these chromic acid-based processes. A process for the chromic acid oxidation of carnauba wax is described in DE-A 10231886. Natural carnauba waxes (grease gray, type 4; medium yellow, prima yellow, and flor, types 3 to 1) and raw montan wax (black) are distinctly dark in color. Oxidation with chromic acid leads to lighter wax products.

[0010] Oxidation products of rice bran wax and their derivatives are known from EP-A 2909273 from 2015, as well as from EP-A 3808819 and EP-A 3808820 from 2019. They are produced by oxidation with chromic acid. This allows the production of acid waxes over a wide acid number range. These can then be partially or fully saponified with a basic metal salt, or esterified with a mono- or polyvalent alcohol.

[0011] Chromic acid-based oxidation products of maize wax and their esterification products are described in WO-A 2022 207517. These are also light in color, but harder and more brittle than air-oxidized maize waxes, which reduces their potential uses for fruit, seed, and fertilizer coatings. Furthermore, they exhibit moderate thermostability, depending on the acid value.

[0012] The oxidation of rice or corn wax with chromic acid essentially results in the cleavage of the wax esters and a / ns / ftj oxidation of the resulting wax alcohols to wax acids. The acid number is a measure of the content of free wax acids. Typical conversions of such oxidations range from 10% to 90% with respect to the ester groups. Natural waxes bleached in this way, in addition to the desired lightening, have a higher saponification number and acid number than unbleached waxes, although the increase in saponification number is almost always less than that in acid number. Only at very low acid numbers is the increase in saponification number greater than that in acid number.

[0013] Oxidation with chromic acid is problematic from an ecological perspective, as it produces large quantities of Cr(III) compounds as a byproduct. These compounds are either used in the controversial chrome tanning process or require energy-intensive electrochemical recycling. To avoid these problematic salts, it is desirable to provide a product manufactured via an alternative oxidation process that offers excellent brightness, stable product quality, and properties suitable for the respective application, while minimizing environmental impact.

[0014] German patent DE-A 25 46 791 discloses the production of natural waxes for carbon wax papers, wherein the natural waxes are treated with atmospheric oxygen. This type of treatment does not increase the acid number of the natural wax and thus does not result in any polar modification. Additionally, the treatment raises the dropping point of the wax, indicating that some low-melting minor components are driven off with the gas stream during this process. However, this type of refining only slightly improved the brightness. For the use of carbon papers, the brightness of a wax is of secondary importance, as dark colors, especially black, are preferred.

[0015] WO-A 2017 108 542 discloses the oxidation of rice wax with atmospheric oxygen. The described polar-modified rice waxes exhibit yellowness indices greater than 50 and are therefore poorly suited as processing aids in light-colored, colorless, or transparent plastics, as they cause undesirable discoloration. Discoloration caused by an additive is also undesirable in coating compositions and the corresponding varnishes. Thermostability is irrelevant for the described applications, as the focus is primarily on the production of dispersions.

[0016] There is therefore a great need for sustainably produced natural waxes and their derivatives that exhibit good thermal stability, low viscosity, good sliding properties, and low inherent color, for use in applications such as plastics processing or coatings. Furthermore, demolding aids and coating additives based on derivatives of such waxes are also desirable. Surprisingly, it has now been found that light-colored, air-oxidized corn waxes with variable polarity (hereinafter referred to as polar-modified corn wax (O)) and their derivatives can be produced efficiently and exhibit significantly improved properties compared to known air-oxidized waxes, such as rice bran wax, as they are harder and more thermally stable.

[0017] They also offer certain advantages compared to corn wax oxidized with chromium-sulfuric acid. The polar-modified corn waxes are somewhat softer, which is reflected in the lower needle penetration value. Thus, the polar-modified corn waxes, oxidized with oxygen, achieve a hardness range that, especially in combination with their light color, could not be reached with either conventional air-oxidized or chromium-sulfuric acid-oxidized natural waxes. Natural waxes that are softer than chromium-sulfuric acid-oxidized products, but still exhibit greater hardness than conventional air-oxidized natural waxes, are better suited as a base material for sustainable, biodegradable coatings, such as fruit and seed coatings, because their flexibility allows them to form a continuous film more easily.

[0018] The invention therefore relates to a polar-modified maize wax (O) that can be produced by oxidation with an oxygen-containing gas and that has a needle penetration number (NPZ), measured according to DIN 51579, greater than 5, preferably between 7 and 35, particularly preferably between 8 and 20, wherein the acid number and the saponification number of the maize wax (E) are increased by the oxidation.

[0019] The polar-modified maize wax (O) is preferably characterized in that the oxidation with an oxygen-containing gas causes an increase in the saponification number which exceeds the increase in the acid number by at least a factor of 1.3, preferably by at least a factor of 1.5, particularly preferably by at least a factor of 1.7.

[0020] Furthermore, the polar-modified corn wax (O) has an IFZ measured according to DIN 6162 of less than 35, preferably less than 20, particularly preferably less than 15, because polar-modified waxes with such an iodine colour number are particularly suitable for light-colored or transparent plastics and coatings.

[0021] Preferably the Yellowness Index (Yl), measured according to ASTM E 313 - 20, which describes the yellow coloration of a substance, is less than 70, preferably less than 50, particularly preferably less than 40.

[0022] Preferably, the polar-modified maize wax (O) is characterized in that it has a dropping point between 50 and 80 °C, preferably between 60 and 78 °C, as measured according to ISO 2176.

[0023] Preferably the acid number of the polar-modified maize wax (O) (according to ISO 21 14) is greater than 3 mg KOH / g, preferably greater than 4 mg KOH / g, particularly preferably greater than 8 mg KOH / g and most preferably greater than 10 mg KOH / g.

[0024] For use as a plastic additive, the polar-modified corn wax (O) preferably has an acid value (according to ISO 21 14) of 3–140 mg KOH / g, preferably between 4 and 80 mg KOH / g, particularly preferably between 8 and 60 mg KOH / g, and most preferably between 10 and 40 mg KOH / g. Polar-modified corn waxes according to the invention, which have low acid values, are particularly suitable as processing aids in the plastics industry because they exhibit high thermal stability and high hardness, expressed by a low needle penetration number.

[0025] Preferably, the polar-modified maize wax (O), which is used as a processing aid, has a saponification number (according to ISO 3681) between 90 and 285 mg KOH / g, preferably between 100 and 180 mg KOH / g, particularly preferably between 100 and 150 mg KOH / g.

[0026] For use in coating compositions, polar-modified corn wax (O) with higher acid values ​​between 20 and 140 mg KOH / g is preferred. Particularly preferred in this application is a polar-modified corn wax (O) with an acid value between 25 and 110 mg KOH / g, particularly preferably between 35 and 90 mg KOH / g, and most preferably between 45 and 80 mg KOH / g, because polar-modified corn waxes in this acid value range exhibit medium hardness and a relatively low iodine color value (IFV) and are therefore well-suited for coatings. Due to their sustainable and biodegradable raw material source, they are particularly suitable for coatings on fruit, confectionery, and seeds.

[0027] Preferably, the polar-modified corn wax (O) used in coating compositions has a saponification number (according to ISO 3681) between 110 and 285 mg KOH / g, preferably between 120 and 230 mg KOH / g, and particularly preferably between 125 and 170 mg KOH / g.

[0028] A further object of the invention is a process for producing a polar-modified corn wax, comprising the steps of: i) providing a native or refined corn wax (MW); ii) providing an oxygen-containing gas; iii) carrying out the oxidation of the corn wax (MW) by reacting the corn wax (MW) with air or oxygen while stirring to obtain a polar-modified corn wax (O); iv) stopping the reaction once the desired acid number has been reached, wherein the acid number and saponification number of the corn wax (E) are increased by the oxidation, and wherein the polar-modified corn wax (O) has an NPZ, measured according to DIN 51579, greater than 5, preferably between 7 and 20, particularly preferably between 8 and 16, and wherein in step (iii) of the process the oxidation is carried out at a temperature between 100 and 170°C, preferably at a temperature between 135 and 155°C.

[0029] Preferably, between 150 and 250 liters of oxygen-containing gas are passed through per hour during step iii) of the process.

[0030] Preferably, the oxidation in step iii) of the process is carried out for a period of at least 30 minutes, preferably for a period of 1 to 25 hours, particularly preferably for 2 to 10 hours, and most preferably for 3 to 9 hours. Preferably, a stirring speed of between 100 and 1000 rpm, more preferably between 300 and 900 rpm, and particularly preferably between 600 and 800 rpm is used in step iii) of the process.

[0031] A further aspect of the invention is an esterified polar-modified corn wax (E) produced by esterification or reaction of the polar-modified corn wax (O) described above with an alcohol. Preferred alcohols are polyhydric alcohols, for example ethylene glycol, butylene glycol, glycerol, diglycerol, trimethylolpropane, pentaerythritol, or sorbitol, etc. In the esterification, a weight ratio of alcohol to polar-modified corn wax (O) of 1:200 to 1:5 is preferably chosen, more preferably 1:150 to 1:10, and most preferably 1:120 to 1:20.

[0032] In addition to being based on renewable raw materials and using a chromium-free oxidation process, the esterified products are preferably characterized by good thermal stability, measured according to DIN 51006 (2005), with a mass loss of less than 20%, preferably less than 15%, until a temperature of 300 °C (heating rate: 5 °C / min) is reached.

[0033] Preferably, the esterified products have an acid number of less than 40 mg KOH / g, particularly preferably less than 30 mg KOH / g, and most preferably less than 20 mg KOH / g.

[0034] A further aspect of the invention is a saponified polar-modified corn wax (V) produced by saponifying the polar-modified corn wax (O) described above or the esterified polar-modified corn wax (E) described above with a basic metal salt selected from the group consisting of metal hydroxides (e.g., NaOH, KOH, Ca(OH)₂, and Zn(OH)₂, etc.), metal oxides (e.g., CaO, etc.), metal carbonates (e.g., Na₂CO₃, CaCO₃, etc.), or aqueous alkalis (such as NaOH, KOH, etc.). Alkali metal hydroxides and / or alkaline earth metal hydroxides, in particular NaOH, KOH, and / or Ca(OH)₂, are preferred. Ca(OH)₂ is particularly preferred. In the saponification process, a weight ratio of basic metal salt to polar-modified maize wax (O) of 1 :100 to 1 :5 is preferably chosen, particularly preferably 1 :75 to 1 :10, and most preferably a ratio of 1 :60 to 1 :20.

[0035] Corresponding general manufacturing instructions for the saponification of waxes can be found, for example, in EP1010728. Preferably, the saponified products are characterized, in addition to being based on renewable raw materials, by particularly good thermal stability up to a temperature of 300 °C, measured according to DIN 51006 (2005), with a mass loss up to a temperature of 300 °C (heating rate: 5 °C / min) of less than 25 wt.%, preferably less than 20 wt.%. Preferably, the saponified products have an acid number of less than 40 mg KOH / g, particularly preferably less than 30 mg KOH / g, and most preferably less than 25 mg KOH / g.

[0036] Preferably, the saponified products are characterized by a particularly good long-term thermostability value, measured according to DIN 51006 (2005), which is determined after a temperature of 300 °C (heating rate: 5 °C / min) has been reached and then maintained at 300 °C for 30 min. Here, the mass loss is less than 50 wt.%, preferably less than 40 wt.%, and most preferably less than 30 wt.%.

[0037] The invention also relates to the use of the polar-modified corn wax (O) or the saponified polar-modified corn wax (V) or the esterified polar-modified corn wax (E) according to the invention for agricultural or forestry purposes, as an additive in plastics processing, in care products, in printing inks and / or in varnishes.

[0038] In a preferred use, the polar-modified corn wax (O) according to the invention, in particular the polar-modified corn wax (O) which has an acid number, measured according to ISO 2114, between 3 and 140 mg KOH / g, preferably between 4 and 80 mg KOH / g, particularly preferably between 8 and 60 mg KOH / g, most preferably between 10 and 40 mg KOH / g, and / or a saponification number, measured according to ISO 3681, between 90 and 285 mg KOH / g, preferably between 100 and 180 mg KOH / g, particularly preferably between 100 and 150 mg KOH / g, or the saponified or esterified polar-modified corn wax ((V) or (E)) according to the invention, is used as a degassing, leveling, lubricating and / or dispersing aid for plastics.

[0039] In another preferred use, the polar-modified maize wax (O) according to the invention, which has an acid number, measured according to ISO 2114, between 20 and 140 mg KOH / g, preferably between 25 and 110 mg KOH / g, particularly preferably between 35 and 90 mg KOH / g, most preferably between 45 and 80 mg KOH / g and / or a saponification number, measured according to ISO 3681, between 110 and 285 mg KOH / g, preferably between 120 and 230 mg KOH / g, particularly preferably between 125 and 170 mg KOH / g, is used as a coating additive, preferably as a coating additive for agricultural and food coatings.

[0040] Another aspect of the invention is the use of maize wax (MW) to produce a polar-modified natural wax by oxidation with air or oxygen.

[0041] Substance characterization

[0042] The standard methods listed in Table 1 are used to determine the characteristic values ​​of natural and synthetic waxes and the characteristic values ​​of printing inks, varnishes, and coatings. They are used to characterize the polar-modified maize wax according to the invention, its starting materials, and the reference substances.

[0043] Table 1: Overview of methods

[0044] To further characterize the polar-modified maize waxes (O) according to the invention, the chain length distributions of their components are determined by gas chromatography. Wax acids and wax alcohols with carbon chain lengths between C6 and C36 served as reference substances.

[0045] Wax esters with C44 to C58 were synthesized by combining the model substances. To identify the peaks in the gas chromatograms of the maize waxes, a defined amount of each component was added to a wax sample, and a significant increase in the area of ​​the corresponding peak was observed. The measurement conditions are shown in Table 2.

[0046] Table 2

[0047] Two different corn waxes (MW 1 and MW 2) and two rice bran waxes (RBW 1 and RBW 2), both in their raw and refined states, were used as raw materials. The properties of the corn waxes and rice bran waxes in their raw and refined states are shown in Table 3.

[0048] The rice bran waxes were chosen such that their acid values, saponification values ​​and oil contents have values ​​that lie between those of the corn waxes used.

[0049] Table 3 (Methods, abbreviations and units in Table 1)

[0050] 'Comparative example'

[0051] Examples 1-8: Modification of waxes by oxidation with air

[0052] 500 g of one of the waxes listed in Table 1 was melted in a glass vessel equipped with a stirrer and internal thermometer. While stirring at a speed of 750 rpm, an airflow of 200 liters per hour was introduced at a temperature of 85 °C or 145 °C at atmospheric pressure. Samples were taken at appropriate intervals and their acid number determined. Once the desired value was reached, the molten wax was poured out.

[0053] Table 4

[0054] Examples 1 to 6 show that polar-modified maize waxes (O) according to the invention could be produced which are light in color, possess good thermostability, and exhibit adequate hardness. Comparative Examples 7* to 9* do not meet at least one of these requirements.

[0055] The chain length distributions of the components of the polar-modified maize wax from Example 4 were analyzed using gas chromatography and are shown in Fig. 1 and Fig. 2.

[0056] Examples 10 to 12: Saponification of polar-modified maize waxes

[0057] In a 1 L reaction vessel equipped with a stirrer, temperature sensor, dropping funnel, and reflux condenser, the polar-modified maize waxes according to the invention from Examples 3 and 4 are melted under a nitrogen atmosphere and mixed with the amount of Ca(OH)2 specified in Table 5. The reaction mixture is stirred until the specified acid value is reached, and then the reaction mixture is pressure-filtered while still hot.

[0058] Table 5

[0059] Examples 9 to 11 show that by saponification of the polar-modified maize waxes with Ca(OH)2, saponified products with low acid numbers of less than or equal to 20 mg KOH / g can be produced, which are particularly suitable for applications requiring high thermostability.

[0060] Examples 13 to 16: Esterification of the polar-modified maize waxes. In a 1 L reaction vessel equipped with a stirrer, temperature sensor, dropping funnel, and reflux condenser, the polar-modified maize waxes according to the invention from Examples 3 and 4 are melted under a nitrogen atmosphere and mixed with the amount of alcohol specified in Table 6 and 0.4 g of methanesulfonic acid. The reaction mixture is stirred until the specified acid number is reached, the water formed is distilled off, and then the reaction mixture is pressure-filtered while hot. Table 6

[0061] Examples 12 to 15 show that products with low acid numbers less than 20 mg KOH / g can be easily produced by esterifying polar-modified maize waxes with ethylene glycol, glycerol or pentaerythritol, which are particularly suitable for applications requiring high thermostability.

Claims

Patent claims 1. Polar-modified maize wax (O) producible by oxidation with an oxygen-containing gas, wherein the acid number and the saponification number of the maize wax (MW) are increased by the oxidation and wherein the polar-modified maize wax (O) has a needle penetration number (NPZ), measured according to DIN 51579, greater than 5, preferably between 7 and 35, particularly preferably between 8 and 20.

2. Polar-modified maize wax (O) according to claim 1, characterized in that the increase in saponification value, measured according to ISO 3681 (2019), exceeds the increase in acid value, measured according to ISO 2114 (2002), by at least a factor of 1.3, preferably by at least a factor of 1.5, particularly preferably by at least a factor of 1.

7.

3. Polar-modified corn wax (O) according to claim 1 or 2, characterized in that it has an iodine colour number (IFZ) measured according to DIN 6162 of less than 35, preferably less than 20, particularly preferably less than 15.

4. Polar-modified maize wax (O) according to at least one of the preceding claims, characterized in that it has a Yellowness Index (Yl), measured according to ASTM E 313-20, less than 70, preferably less than 50, particularly preferably less than 40.

5. Polar-modified maize wax (O) according to one or more of the preceding claims, characterized in that it has an acid number, measured according to ISO 2114 (2002), between 3 - 140 mg KOH / g, preferably between 4 and 80 mg KOH / g, particularly preferably between 8 and 60 mg KOH / g, most preferably between 10 and 40 mg KOH / g.

6. Polar-modified corn wax (O) according to one or more of claims 1-4, characterized in that it has an acid number, measured according to ISO 21 14 (2002), between 20 - 140 mg KOH / g, preferably between 25 and 110 mg KOH / g, particularly preferably between 35 and 90 mg KOH / g, most preferably between 45 and 80 mg KOH / g.

7. A process for producing a polar-modified maize wax (O) according to at least one of the preceding claims, comprising the steps of: i) providing a maize wax (MW), ii) providing an oxygen-containing gas; iü) carrying out the oxidation of the maize wax (MW) by reacting the maize wax (MW) with air or oxygen while stirring to obtain a polar-modified maize wax (O); iv) stopping the reaction once the desired acid number has been reached. wherein the acid number and the saponification number of the maize wax (E) are increased by oxidation and wherein the polar-modified maize wax (O) has an NPZ, measured according to DIN 51579, greater than 5, preferably between 7 and 35, particularly preferably between 8 and 20, and wherein in step (iii) of the process the oxidation is carried out at a temperature between 100 and 170°C, preferably at a temperature between 135 and 155°C.

8. Method according to claim 7, wherein during step iii) between 150 and 250 liters of oxygen-containing gas are passed through per hour.

9. Method according to one or more of claims 7 to 8, wherein the oxidation in step iii) is carried out over a period of at least 30 minutes, preferably over a period of 1 to 25 hours, particularly preferably from 2 to 10 hours, most preferably from 3 to 9 hours.

10. Method according to one or more of claims 7 to 9, wherein the stirring speed in step iii) is between 100 and 1000 rpm, preferably between 300 and 900 rpm, particularly preferably between 600 and 800 rpm. 1 1. Esterified polar-modified maize wax (E) obtainable by reacting the maize wax oxidate (O) according to at least one of claims 1 to 6 with an alcohol, preferably a polyhydric alcohol, particularly preferably with ethylene glycol, butylene glycol, glycerin, diglycerin, trimethylolpropane, pentaerythritol or sorbitol.

12. Saponified polar-modified maize wax (V) obtainable by saponifying the polar-modified maize wax (O) according to at least one of claims 1 to 6 or the esterified polar-modified maize wax (E) according to claim 1 with a basic metal salt, a metal oxide, a metal carbonate or with an aqueous alkali, preferably with an alkali metal hydroxide and / or alkaline earth metal hydroxide, particularly preferably with Ca(OH)2.

13. Use of the polar-modified corn wax (O) according to at least one of claims 1 to 6, the saponified polar-modified corn wax (V) according to claim 12 or the esterified polar-modified corn wax (E) according to claim 1 for agricultural or forestry purposes, as an additive in plastics processing, in care products, in printing inks and / or in varnishes.

14. Use of the polar-modified corn wax (O) according to claim 5 or the saponified polar-modified corn wax (V) according to claim 12 as a degassing, leveling, lubricating and / or dispersing agent for plastics.

15. Use of the polar-modified corn wax (O) according to claim 6 as an additive in coatings, in particular as an additive in agricultural and food coatings.

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