Use of expanded and water-repellent corn for the manufacture of three-dimensional molded parts

Abstract

The invention relates to shaped parts produced from popcorn that has been previously hydrophobicized with a polymer. This allows for the production of very lightweight and flexible molded parts.

Description

Use of expanded and water-repellent corn for the manufacture of three-dimensional molded parts The present invention relates to the field of molded parts, such as those used for packaging, in the automotive industry (interior and exterior), as sound absorbers, for thermal insulation, or in the consumer goods industry. These molded parts must be easy to manufacture and lightweight, and preferably composed wholly or partially of renewable raw materials. Until now, these molded parts have been manufactured primarily from polypropylene, polyethylene, polyvinyl chloride, and polystyrene. In addition to positive properties such as low density, water-repellent surface, good processability, and low thermal conductivity, these molded parts from four plastic families also exhibit numerous negative characteristics. On the downside, the material is often very brittle and has very low chemical resistance and a very low softening temperature. Furthermore, products made with these plastics typically have a very low melting point, meaning the plastic melts at temperatures just above 100°C and drips out while burning. These droplets can ignite and contribute to the spread of fire. Flammability can be reduced by using suitable flame retardants, but these are often highly toxic. To date, brominated additives (polybrominated diphenyl ethers or hexabromocyclododecane), which are extremely harmful to the environment and human health, have frequently been used. Furthermore, these plastics are mostly manufactured from limited fossil raw materials, some of which are difficult to recycle. The increase in plastic waste on land and, especially, in the world's oceans is becoming a growing environmental problem with global repercussions. Incineration releases carbon dioxide, plastic particles enter the food chain, and decomposition releases pollutants. Organizations such as the EU and the UN point out that if the economy continues to grow and consumer behavior remains the same, the environmental problems associated with plastic will continue to increase. Due to these widely known health and environmental problems, the demand for alternatives has grown increasingly strong in recent times. Molded parts comprising expanded corn are known, among others, from documents DE 102006047279 A1, US 3511 899 A, US 3630 821 A and US 5300 333 A. Therefore, the objective is to provide alternative molded parts and procedures for their manufacture. This objective is achieved by means of a molded part according to claim 1. Accordingly, a molded part is proposed containing expanded corn that is substantially surrounded by polymer and an additional binder, wherein the sum proportion of polymer and binder is < 20% (w / w) with respect to the molded part, in which case the polymer is a water-repellent polymer. "Substantially" in the sense of the present invention means a proportion of > 95% (by weight), preferably > 97%, even more preferably > 99%. According to the present invention, therefore, the vast majority of the expanded corn is surrounded by polymer. Surprisingly, it has been found that in this way a large number of molded parts with good to excellent properties (including low thermal conductivity, excellent dimensional stability, excellent material absorption properties and low flammability) can be manufactured in many applications of the invention, which thus consists predominantly of renewable raw materials, namely, expanded corn. According to the invention, the molded part comprises both the polymer and the binder. According to a preferred embodiment, the molded part essentially comprises or consists of expanded corn, polymer, and binder. The term "expanded corn" within the meaning of the present invention includes in particular all materials that, like puffed corn (Zea mays, convar. Microsperma), burst when rapidly heated to high temperatures, optionally after suitable lubrication, rapidly evaporating the water present in the seed and thus converting the starch contained in the seed into a foam-like consistency. Such behavior is known, among others, in quinoa, amaranth, rice, and even wheat; materials based on these raw materials are also referred to as and explicitly include "expanded corn" within the meaning of the present invention. The term "expanded corn" is not intended to be limited to corn and was chosen in particular for reasons of simplicity, clarity, and legibility. Preferably, the combined proportion of polymer and binder is < 15% (w / w) of the molded part, even more preferably < 10% (w / w). A lower proportion of polymer and binder (when present) is advantageous, as this makes the molded part lighter and increases the proportion of renewable raw materials (e.g., expanded corn). According to a preferred embodiment, the expanded corn is used whole in the molded piece, i.e., the whole grains and / or seeds are expanded and the expanded corn is not chopped (crushed) or crumbled. According to an alternative and equally preferred embodiment, expanded corn produced from previously crushed starting materials (e.g., cracked corn kernels) is used. If necessary, the expanded granules can be crushed before being molded into pieces. Of course, the forms of embodiment in which both whole expanded corn and expanded corn treated according to the previous paragraph are used in the molded piece are also advantageous. According to the invention, the fat content of the expanded corn before processing is < 10 (weight) %. The "fat content" of expanded corn does not refer to the total fat content in the expanded corn, but rather to the fat content used to make the seed's epidermis water-repellent, leading to better trapping of the water contained in the seed. In many applications within the present invention, it has been found advantageous to keep this fat content as low as possible, as this facilitates further processing of the puffed corn. Preferably, the fat content is < 5% (by weight); according to a particularly preferred embodiment, no fat is added to change the consistency (conversion) ("inflated"). The expanded corn used to manufacture the three-dimensional molded parts is coated with a polymer after inflation. "Coated" means that the individual particles of expanded corn are surrounded and / or enveloped by the polymer, which is composed of synthetic and / or biological components. However, it is preferable that no general sticking occurs, or that it is minimal, so that, for example, the expanded corn after coating and before further processing is in the form of granules, i.e., pourable. The polymer coating the expanded corn is a water-repellent polymer. The preferred polymers are selected from the group comprising thermoplastics such as polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyacrylate, and thermoset plastics, particularly condensed aminoplastic resins.Furthermore, bio-based polymers such as polylactic acids (PLA), polyhydroxy acids such as polyhydroxybutyric acid, or cellulose derivatives are suitable for coating the surface of individual expanded corn granules. The polymer may also comprise any mixture of these. Preferably, the proportion of polymer in the molded part (in % by weight with respect to the weight of the molded part) is < 5%, preferably < 3%. According to a preferred embodiment of the invention, the molded part comprises another binder. In particular, the binders may preferably be thermoplastics, thermoset plastics, aminoplastics, phenolic plastics, isocyanates, proteins, tannins, starch, synthetic binders, or natural binders or mixtures of binders, such as, for example, urea-formaldehyde resin, melamine-formaldehyde resin, melamine-reinforced urea-formaldehyde resin, tannin-formaldehyde resin, phenol-formaldehyde resin, polymeric diphenylmethane diisocyanate, or mixtures thereof. Preferably, the proportion of binder in the molded part (in % by weight relative to the weight of the molded part) is < 10%, preferably < 5%. Preferably, the binder-to-polymer ratio (w / w) is > 1:1 to < 10:1. This has proven advantageous for many applications within the present invention. Preferably, the binder-to-polymer ratio (w / w) is > 1.5:1 to < 5:1. The present objective is also achieved by a procedure according to claim 9. Accordingly, a procedure for manufacturing the molded parts described above is proposed, comprising the steps of a) manufacturing expanded corn b) making the expanded corn manufactured in step a) water-repellent by means of a polymer, wherein the polymer is a water-repellent polymer c) treat subsequently as optional d) add binder e) manufacture the molded part f) optionally coat the surface of the molded part g) optionally laminate where the total proportion of polymer and binder is < 20% (w / w) with respect to the molded part. This procedure preferably refers to molded parts as described above; that is, the procedure is preferably a procedure for manufacturing the molded parts described above. The individual steps of the procedure are explained in more detail below, where any partial step can be combined with others as desired. a) To manufacture expanded corn Corn kernels can be expanded using various procedures. According to a preferred embodiment of the invention, the expanded corn used to manufacture the molded parts is produced by inflation. Depending on the application, unmodified grains may be used, or suitable seeds, such as feed corn kernels, may first be crushed, and the grain fragments then expanded by pressure and temperature according to the Bichsel process (WO 1999042005A1) in a defined procedure. Other methods for inflating starch-containing grains include, for example, hot plates, hot air machines, and microwave ovens. A preferred embodiment of the invention uses the so-called Cerex process of Cerex AG, CH-3368 Bleienbach. The process can be divided into three sections: a preheating element, a reactor, and an expansion chamber. First, the cracked cereal grains are heated uniformly to about 100°C in the preheating element. Then, the grain is treated with superheated steam in the reactor, and finally, the grain is introduced into an expansion chamber. Here, the expansion of the corn kernels (cracked corn pellets) is induced by reducing the pressure for a certain period of time. Finally, the inflated material is collected and separated from the uninflated components (Bichsel, n.d.). The conversion of cracked corn kernels into expanded corn pellets using the Cerex process is almost 100% in most applications; only less than 5% of the cracked kernels fail to inflate. Furthermore, before step b), the expanded corn can be re-shredded so that, according to a preferred embodiment of the invention, the procedure comprises a step a1) carried out between steps a) and b): a1) Shrinking the inflated expanded corn Step a1) can be performed using all current manufacturing techniques. b) Water repellency using polymer In step b), the expanded corn is waterproofed so that it is substantially surrounded by polymer at the end. This can preferably be done by mixing the expanded corn and spraying it with the polymer and / or precursor substances or a solution containing the polymer and / or precursor substances. Following waterproofing or coating, a water-repellent, transportable (e.g., pneumatically), and pourable expanded corn granule is preferably generated. According to a preferred embodiment of the invention, the polymer is selected such that, after waterproofing, it is possible to crosslink the coated expanded corn granules. c) Optional post-treatment According to a preferred embodiment of the invention, step b) is followed by post-treatment of the resulting water-repellent expanded corn. Preferably, it is heated to a temperature of > 60°C to < 150°C. This has proven advantageous in many applications, as the water-repellent properties of the resulting expanded corn granules can be further improved. d) Addition of binder Another binder is added. The binders used are, in particular, thermoplastics, thermoset plastics, aminoplastics, phenolic plastics, isocyanates, proteins, tannins, starch, synthetic or natural binders, or mixtures of binders such as, for example, urea-formaldehyde resin, melamine-formaldehyde resin, melamine-reinforced urea-formaldehyde resin, tannin-formaldehyde resin, phenol-formaldehyde resin, polymeric diphenylmethane diisocyanate, or mixtures thereof. Preferably, the proportion of binder in the molded part (in % by weight with respect to the weight of the molded part) is < 10%, preferably < 5%. The binder can be applied using any conventional mixing or flow procedure, for example, by spraying the granules into several mixing units. e) Manufacturing of the molded part The molded part is preferably manufactured from expanded corn granules at a slightly increased pressure and / or temperature. The preferred pressures are > 0.1 bar and < 10 bar, preferably < 5 bar, and more preferably < 2 bar. The preferred pressing times are > 0.5 s / mm of molded part and < 24 s / mm of molded part minute, preferably < 8 s / mm of molded part. According to an alternative and equally preferred embodiment, the molded part is manufactured using steam or dry steam curing. A temperature of > 50 °C and < 330 °C is preferably used, and even more preferably > 80 °C and < 140 °C. Dry steam is particularly preferred, in which case the dry steam is preferably generated from wet steam by means of a separator. Preferably, the temperature of the dry steam is between > 120 °C and < 220 °C, even more preferably > 160 °C and < 290 °C. Two techniques are preferably used to manufacture the molded part itself: (a) compression molding. This process is particularly preferred for slightly curved or flat components. Its main applications are typically in the automotive and packaging industries, where larger components with two-dimensional or three-dimensional structures are manufactured. At the start of the process, the molding compound—expanded corn surrounded by polymer—is placed in a cavity along with any additional binder and sealed by a pressure piston. The pressure causes the molding compound to take the shape specified by the mold. The molding compound in the cavity is heated under pressure and conductive heat transfer by electrical heating of the cavity or by steam (possibly dry steam). When thermoset plastics are used as polymers, temperature is typically used to influence the curing process; in the case of thermoplastics, it is used to melt the plastic. The finished part can then be removed from the mold and, if necessary, reworked, further processed, coated, or laminated (for example, with starch-based films or PU films). b) Use of automatic molding machines This technique typically uses special automatic molding machines that allow for higher pressures and / or temperatures. The first step involves pneumatically compressing the molding compound (i.e., expanded corn surrounded by polymer with a possible additional binder) and filling the closed, automatic molding machine with the compressed compound. Alternatively, the molding compound can also be introduced into the cavity under vacuum. Using temperature and pressure, the molding compound is brought to the desired curing temperature, for example, by steam (optionally dry steam), and thus, depending on the application, the polymer is fully cross-linked. The aforementioned media can flow through the molding compound: from one side, from alternating sides, or from all sides.Once the expanded corn fibers have been crosslinked or fused, the molded part is removed from the mold tool in the final step of the process. The molded parts can then be coated or laminated (e.g., with starch-based films, PU or PLA films, or flocking). f) Optional coating of the surface of the molded part Depending on the application, the surface of the molded part can also be coated, for example, with paint. Alternatively, the surface can be flocked; depending on the application, applying an additional impregnation layer may also be advantageous. g) Optional lamination Depending on the application, lamination can also be used as an alternative or as a complement. Common laminating agents such as lacquer, glue, or wax can be used. The molded parts according to the invention and / or the molded parts manufactured according to the process according to the invention can be used in a variety of applications, including (but not limited to): Packaging materials (e.g., refrigerators, protective packaging for household appliances, spice jars, etc.), car parts (e.g., headrests, sunshades, child seat shells, insulating mats for interior door panels and motorhome cabin linings), insulating materials (e.g., household appliances, tableware, sporting goods (e.g., yoga rolls, cushions), toys (e.g., dice, board games, puzzles), picture frames, gift baskets, composite acoustic moldings, motorhome parts, etc. The components mentioned above, as well as the claimed components to be used in accordance with the invention and described in the exemplary embodiments, are not subject to any special exceptional conditions as regards their size, shape, selection of materials and technical design, so that the selection criteria known in the field of application can be applied without restriction. Further details, features, and advantages of the object of the invention are set forth in the dependent claims and the following description of the associated drawings, which, by way of example, show several embodiments of the process according to the invention. In the drawings: Figures 1 to 3 schematically show the sequence of a manufacturing process for a molded part according to the invention in accordance with a first embodiment; and Fig. 4 schematically shows the sequence of a manufacturing procedure for a molded part according to the invention in accordance with a second embodiment. Figures 1 to 3 schematically show the sequence of a manufacturing process for a molded part according to the invention in a first embodiment. In this embodiment, in step 1 shown in Figure 1, a molding mass 10 consisting of expanded corn surrounded by a polymer with possibly additional binder is introduced into a cavity formed by two corresponding molding bodies 20 and 21. In step 2, shown in Figure 2, heating takes place so that the molded part 30 is formed under the influence of temperature (and pressure), which is then removed in step 3, shown in Figure 3. Figure 4 schematically shows the sequence of a manufacturing process for a molded part according to the invention in a second embodiment by means of an automatic molding machine. Here, the cavity formed by the two molding bodies 40 and 41 is first closed (step A), then the molding mass 10 is filled under pressure (step B). After heating under pressure (step C) and cooling (step D), the resulting molded part 30 can be removed. The invention is further explained with reference to examples that are purely illustrative and should not be considered limiting. The molded parts with different densities, manufactured as described above, were examined for their strength properties. The results are summarized in Table 1. Table 1: Mechanical-technological properties of molded parts made of expanded corn, coated with a polymeric layer of polypropylene (PP) or polyethylene (PE) as a function of apparent density A polypropylene-based polymer and a melamine-urea-formaldehyde (MUF) resin were used to manufacture flexible molded parts from expanded corn granules. In the first stage, the polypropylene was sprayed onto the expanded corn in a mixer at 2% (relative to the expanded corn). The material was then dried at approximately 105 °C. In the second step, the material was conveyed in a mixing unit and bonded with a MUF (66% solids content) at a dosage of 5% over the polymer-enriched expanded corn. The material was then introduced as a molding mass into the cavity, which was heated under pressure and heat transfer by conduction. The cavity was then sealed by a pressure piston. The pressure gave the molding mass the shape specified by the mold. In the final step, the finished, flexible molded part was removed from the mold.Table 2 shows the mechanical and technological properties of these flexible molded parts. Table 2: Mechanical and technological properties of molded parts made of expanded corn surrounded with a polymeric layer of polypropylene (Pp) or polyethylene (PE) and glued by MUF as a function of apparent density To manufacture molded parts from expanded corn granules using dry steam, the expanded corn granules were pretreated with a polymer (polyethylene) and urea-formaldehyde resin (UF, BASF Kaurit 350). First, 1.5% polyethylene was applied to the expanded corn granules. Next, the treated expanded corn granules received 66% urea-formaldehyde resin in the bonding unit. In the second step, the bonded material was conveyed to the cavity under a negative pressure (vacuum) of 2.5 bar and cured using dry steam. To generate dry steam, wet steam was passed through a separator, which removes approximately 98% of the original wet steam and converts it into approximately 99% dry steam. The temperature of the dry steam used here was > 100 °C. Depending on the thickness and apparent density of the molded part, different amounts of dry steam were passed through it for up to 90 seconds. The finished molded part was then removed from the cavity. Table 3 shows the mechanical and technological properties of the dry steam molded parts. Table 3: Mechanical-technological properties of molded parts joined with UF resin, with different densities and thicknesses after crosslinking by hot dry steam at approx. 150 °C The individual combinations of components and features of the above-mentioned embodiments are exemplary; the interchange and substitution of these teachings with other teachings contained in this publication with cited publications are also expressly contemplated. The skilled worker will recognize that variations, modifications, and other embodiments described herein may also be generated without departing from the spirit and scope of the invention. Accordingly, the foregoing description is illustrative and should not be considered limiting. The term "comprising" used in the claims does not exclude other components or steps. The indefinite article "a" does not exclude the meaning of a plural. The mere fact that certain measures are set forth in mutually different claims does not imply that a combination of these measures cannot be advantageously used.The scope of the invention is defined in the following claims and their equivalents.

Claims

1. A molded part containing expanded corn substantially surrounded by a polymer and another binder, wherein the combined proportion of polymer and binder is < 20% (w / w) of the molded part, wherein the polymer is a water-repellent polymer, and wherein the expanded corn has a particle size distribution in which the fat content of the expanded corn before processing is < 10% (w / w).

2. A molded part according to claim 1, wherein the combined proportion of polymer and binder is < 15% (w / w) of the molded part.

3. A molded part according to either claim 1 or 2, wherein the proportion of polymer in the molded part (in % by weight of the molded part) is < 5%.

4. Molded part according to any one of claims 1 to 3, wherein the proportion of binder in the molded part (in % by weight with respect to the weight of the molded part) is < 10%. 5.A molded part according to any one of claims 1 to 4, wherein the polymer is selected from the group containing polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyacrylate, condensed aminoplastic resins, polylactic acids (PLA), polyhydroxy acids, cellulose derivatives, or mixtures thereof.

6. A molded part according to any one of claims 1 to 5, wherein the binder is selected from urea-formaldehyde resin, melamine-formaldehyde resin, melamine-reinforced urea-formaldehyde resin, tannin-formaldehyde resin, phenol-formaldehyde resin, polymeric diphenylmethane diisocyanate, or mixtures thereof.

7. A molded part according to any one of claims 1 to 6, wherein the binder-to-polymer ratio is from >1:1 to <4:

1. 8.A method for manufacturing molded parts according to any one of claims 1 to 7, comprising the steps of: a) manufacturing expanded corn, wherein the expanded corn has a particle size distribution in which the fat content of the expanded corn before processing is < 10% (by weight); b) waterproofing the expanded corn manufactured in step a) using a polymer, wherein the polymer is a water-repellent polymer; c) optional post-treatment; d) addition of binder; e) manufacturing the molded part; f) optional coating the surface of the molded part; g) optional lamination, wherein the total proportion of polymer and binder is < 20% (w / w) of the molded part.

9. A method according to claim 8 for manufacturing molded parts according to any one of claims 1 to 7.

10. A method according to claim 8 or 9, wherein step c) is not optional and comprises heating to > 60°C to < 150°C. 11.A process according to any one of claims 8 to 10, wherein step e) is carried out at a pressure of >1 bar and <10 bar.

12. A process according to any one of claims 8 to 11, wherein step e) is carried out using steam curing or dry steam.

13. A process according to any one of claims 8 to 12, wherein step e) is carried out using dry steam. 14.Use of molded parts according to one of claims 1 to 7 and / or molded parts manufactured according to a process according to one of claims 8 to 13 for: - composite acoustic molded parts - packaging materials - refrigerators, - protective packaging for electrical appliances, - spice jars, - automotive parts, - parts for motorhomes, - headrests, - sunshades, - child seat shells, - insulating mats, - insulating materials (e.g., for electrical appliances), - tableware, - sporting goods, - yoga rolls, - cushions, - toys, - photo frames, - gift baskets.

Images