Method for recovering metal from composite materials of metal and resin compositions

Abstract

The objective is to provide a method for recovering metal from a composite material of metal and resin composition without causing corrosion by solvents or reducing corrosion resistance. [Solution] A method for recovering metal from a composite material of a metal and a resin composition, wherein the resin composition is separated from the composite material by immersing the composite material in a solvent, and the solvent is a linear carbonate solvent, an alkylamide solvent, or a mixture thereof.

Description

Technical Field

[0001] The present invention relates to a method for separating and recovering metal from various products made of a composite material of a metal such as a magnesium alloy or an aluminum alloy and a resin composition.

Background Art

[0002] Magnesium alloys and aluminum alloys are widely used in vehicle parts, electrical and electronic parts, etc. because they are lightweight and have high specific strength. When recovering and recycling the metal from such products, mechanical separation and recovery, a recovery method in which the resin composition is expanded or peeled off by immersing in water or a solvent and heating, a method of burning the resin composition to recover the metal, etc. can be considered.

[0003] However, in the mechanical separation and recovery method, it is difficult to completely remove the resin composition, and in the method of immersing in water or a solvent and heating, there is a high risk of corrosion of metals such as magnesium alloys and aluminum alloys. In addition, in the method by combustion, if the carbon remaining after combustion is mixed into the metal such as a magnesium alloy, there is a risk of deterioration of corrosion resistance and an environmental load due to the generated gas becomes a problem.

[0004] For example, Patent Document 1 discloses a method for cleaning a core metal for a steering wheel in which a resin composition is mechanically peeled off in advance from a magnesium alloy steering wheel covered with a crosslinked polyurethane resin composition, and then laser light is irradiated to decompose the crosslinked polyurethane. However, it is difficult to irradiate laser light uniformly to a steering wheel having a complex shape, and it is also necessary to wash the crosslinked polyurethane decomposed and liquefied by the laser light.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] The present invention aims to provide a method for recovering metal from a composite material of a metal and a resin composition without causing corrosion by a solvent or reducing its corrosion resistance. [Means for solving the problem]

[0007] The present invention relates to a method for recovering metal from a composite material of a metal and a resin composition, wherein the resin composition is separated from the composite material by immersing the composite material in a solvent, and the solvent is characterized in that it is either a linear carbonate solvent or an alkylamide solvent, or a mixture thereof.

[0008] Here, the linear carbonate solvent may be a phosphate ester, which, like the linear carbonate solvent, has a dipole moment, but this is canceled out, resulting in low viscosity. In the present invention, the metal is not particularly limited as long as it is compounded with the resin composition, and may be a metal such as iron or copper, but it is preferable to apply it to magnesium alloys or aluminum alloys, which have been considered difficult to recycle horizontally due to the tendency for impurities to be mixed in.

[0009] In the present invention, the resin composition is preferably either a polyurethane resin composition having a urethane bond [-O-(C=O)-NH-] which has a chemical structure similar to that of a linear carbonate solvent or an alkylamide solvent, or a polycarbonate resin composition having a carbonate ester bond [-O-(C=O)-O-]. These resin compositions have high affinity for linear carbonate solvents and alkylamide solvents, and the solvents penetrate them easily.

[0010] Although the chain-like carbonate solvent has a dipole moment, these cancel each other out, resulting in small intermolecular forces and low viscosity, making it easy to penetrate urethane resin compositions (hereinafter referred to as urethane resins), etc. Therefore, it is presumed that mixing an alkylamide solvent with a relatively high dielectric constant with a linear carbonate solvent facilitates penetration into the urethane resin, and that the synergistic effect with the swelling effect of the alkylamide solvent further improves the release properties of the resin composition.

[0011] Examples of linear carbonate solvents include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). Examples of phosphate esters that have a dipole moment but whose viscosity is low due to the cancellation of this dipole moment, and can be used as an alternative solvent, include trimethyl phosphate and triethyl phosphate. Examples of alkylamide solvents include dimethylacetamide (DMAc) and N,N-dimethylformamide (DMF). Among these, a mixed solvent of dimethyl carbonate (DMC) and dimethyl acetamide (DMAc) is preferred.

[0012] The inventors conducted verification experiments using three solvents: DMAc, DMF, and DMC. The structural formulas of these solvents are shown below. TIFF2026063628000002.tif48166TIFF2026063628000003.tif42166TIFF2026063628000004.tif32166

[0013] The metals used in this invention include various metals and their alloys, but aluminum alloys and magnesium alloys, which have been known to be prone to impurities and difficult to recycle horizontally, are particularly well-suited. Examples of magnesium alloys include Mg-Al-Mn alloys such as AM50 (AM50B) and AM60 (AM60B), which have high toughness and are used in automotive steering wheels, Mg-Al-Zn alloys such as AZ91 and AZ31, which have excellent corrosion resistance and castability, as well as Mg-Zn-Zr alloys such as ZK61 and ZK60, and Mg-rare earth element alloys. Examples of aluminum alloys include various cast and wrought materials.

Advantages of the Invention

[0014] In the present invention, by simply immersing a composite material in which a metal is coated with a resin composition in one of a chain carbonate solvent or an alkylamide solvent or a mixed solvent thereof at room temperature, the coated resin can be peeled off from the metal. Particularly, in the case of a magnesium alloy, its corrosion and deterioration of corrosion resistance can be suppressed. In the present invention, peeling can be promoted by combining immersion in the above solvent with a physical impact such as ultrasonic vibration. As a result, horizontal recycling of scrap materials into structural materials and the like becomes possible. Further, the solvent can be separated and recovered and reused.

Brief Description of the Drawings

[0015] [Figure 1] An example of the steering wheel used for evaluation is shown. [Figure 2] The appearance results by the immersion test are shown. [Figure 3] The test method is shown. [Figure 4] The peeling depth of the single solvent is shown. [Figure 5] The peeling depth of the mixed solvent is shown. [Figure 6] The measurement results of the mixed solvent of DMAc and DMC are shown. [Figure 7] The spreading distance of the solvent is shown. [Figure 8] The peeling test results using an ultrasonic cleaner are shown. [Figure 9] (a) shows the tensile strength and (b) shows the elongation. [Figure 10] The corrosion resistance is shown.

Modes for Carrying Out the Invention

[0016] An example of a recovery test of a magnesium alloy as the recovery of a metal from the composite material according to the present invention will be described below. We conducted tests and evaluations using scrap material in which a polyurethane resin composition (urethane resin) was applied by injection molding to a steering wheel base material of a vehicle cast using AM-type tough magnesium alloy (AM50A, AM60B, etc.) as the core metal, and the results are described below. Figure 1(a) shows the appearance of the steering wheel, and a test piece was cut from a product recovered as scrap material. Figure 1(b) shows a test piece cut from scrap material, which is a composite material of Mg alloy and urethane resin (foamed polyurethane resin).

[0017] First, as a preliminary test, as shown in Figure 1(b), a 20 mm long test piece was cut from the steering wheel and immersed in 12 ml of solvent at room temperature for 24 hours. The results of the visual observation after immersion are shown in Figure 2. In DMAc and DMF, separation of the urethane resin was observed, and in DMC, some separation of the urethane resin was observed. In ethanol and xylene, the material appeared moist, but it remained fixed to the mandrel.

[0018] Next, I will explain the peeling depth test that was conducted. As shown in Figure 3, test pieces cut from the steering wheel to a length of 20 mm as described above were immersed in 12 ml of each solvent for 24 hours. The peelable portion was removed using tweezers or the like, and the length of the peel in the depth direction that could be removed was defined as the peeling depth and evaluated. Figure 4 shows the results of exfoliation depth measurements using DMAc, DMF, and DMC as individual solvents, while Figure 5 shows the results of exfoliation depth measurements using a mixed solvent. Figure 6 shows the results of n=3 tests, where the mixed solvent ratio of DMAc and DMC was varied. As shown in Figures 3 and 4, DMC alone exhibited poor peelability, but a mixed solvent of DMC with DMAc or DMF showed high peelability. Furthermore, it was observed that the material exhibits exfoliating properties even in a mixed solvent of DMAc and DMF. The results in Figure 6 show that while DMAc alone exhibits peelability, adding 25-75 Vol% of DMC to DMAc improves performance.

[0019] To confirm the mixing action of DMC, the following experiment was conducted. A test specimen measuring 5 mm thick, 10 mm wide, and 50 mm long was cut from foamed polyurethane resin (hereinafter referred to as urethane resin). The test specimen was placed vertically, and the lower 2 mm end was immersed in each solvent. The solvent's elution distance was measured after 90 minutes. The results are shown in Figure 7. These results suggest that DMC exhibits excellent penetration into urethane resin, and in addition, the swelling effect of DMAc and DMF improves its peelability. Although the test piece cut from the steering wheel and immersed in DMC-only solvent for 24 hours could not be easily peeled off with tweezers, etc., it had peeled slightly as shown in Figure 2. Therefore, a peeling test was performed using an ultrasonic cleaner, which will be explained below. Figure 8 shows the test method and its results. The steering wheel portion shown in Figure 1(a) was cut out, and in this case, a test piece was used in which both the outside and inside of the Mg alloy were coated with urethane resin. As shown in Figure 8(a), the test piece was immersed in a container containing DMC, stirred for 2 hours at a solvent temperature of 15°C using a magnetic stirrer at a rotation speed of 300 rpm, and then left immersed for 24 hours. The results are shown in Figure 8(b). The outer urethane resin of the Mg alloy core peeled off and detached, but the inner urethane resin remained firmly attached to the core. Next, the test piece with urethane resin remaining inside the core was subjected to an ultrasonic cleaning machine for 1 hour, as shown in Figure 8(c), and then immersed in DMC for 24 hours. The results are shown in Figure 8(d). The urethane resin on the inside of the core metal is also peeling off. This revealed that applying physical impact, such as ultrasonic cleaning, makes it even easier to detach the resin composition from the metal.

[0020] Next, using a mixed solvent of 25%DMAc-75%DMC, test specimens were prepared using Mg alloy recovered from the steering wheel via thixomolding, a type of high-pressure casting method, and their physical properties were evaluated. The methods for producing and evaluating recycled materials are as follows: The recovered Mg alloy was melted in a SUS430 crucible to produce cutting ingots, which were then used for chipping. Subsequently, iron-based impurities were removed by magnetic separation, and the resulting fine powder was classified and removed. The thixomolding machine has a clamping force of 2.8 MN, a cylinder bore diameter of 51 mm, and mold cavity dimensions of 2 mm thickness x 100 mm width x 150 mm length. The molding conditions were as follows: mold temperature set to 523K, cylinder temperature set to 893K for the slurry reservoir, and maximum screw injection speed of 3.2 m / s. For comparison, a flat plate was also formed using virgin material chips of the same composition under similar conditions. The mechanical properties were determined by dividing a flat plate into five sections along its length, with a parallel section width of 12.5 mm, a gauge length of 50 mm, and an initial strain rate of 1 × 10⁻⁶. -2 The tensile strength, tensile strength, and elongation at break were evaluated in a tensile test at room temperature using the 0.2% proof stress, tensile strength, and elongation at break parameters. Corrosion resistance was evaluated based on the rating number after 24 hours of salt spraying, and the corrosion rate calculated by dividing the weight loss after washing away corrosion products by the exposed surface area and the test time.

[0021] The evaluation results are shown in Figures 9 and 10. "Virgin" material refers to an ingot of Mg alloy used in casting, while "Recycled" material refers to recycled Mg alloy recovered using the Mg alloy recovery method according to the present invention. In terms of tensile strength (Figure 9(a)), elongation (Figure 9(b)), RN (corrosion resistance rating No.) (Figure 10), and corrosion rate, the material exhibited physical properties equivalent to or better than those of virgin material, demonstrating that the recycling method according to the present invention enables horizontal recycling of Mg alloys.

Claims

1. A method for recovering metal from a composite material of a metal and a resin composition, The resin composition is peeled off the composite material by immersing it in a solvent. A method for recovering metals, characterized in that the solvent is either a linear carbonate solvent or an alkylamide solvent, or a mixture thereof.

2. The method for recovering metal according to claim 1, characterized in that the chain-like carbonate solvent has a dipole moment as a substitute solvent, but this is canceled out, resulting in a phosphate ester with low viscosity.

3. The method for recovering a metal according to claim 1, characterized in that the chain-like carbonate solvent is dimethyl carbonate and the alkylamide solvent is dimethylacetamide.

4. The method for recovering metal according to any one of claims 1 to 3, characterized in that the resin composition is either a polyurethane resin composition having a urethane bond [-O-(C=O)-NH-] which has a chemical structure similar to that of a linear carbonate solvent or an alkylamide solvent, or a polycarbonate resin composition having a carbonate ester bond [-O-(C=O)-O-].

5. The method for recovering a metal according to any one of claims 1 to 3, characterized in that the aforementioned metal is a magnesium alloy or an aluminum alloy.

Images