A thin film type release agent for magnesium alloy finish machining and a preparation method and application thereof

Abstract

This invention discloses a thin-film release agent for manufacturing thin magnesium alloy parts, its preparation method, and its application, belonging to the field of release agents. The preparation steps are as follows: Raw materials are prepared according to the following mass percentages: 5%-20% organosilicon, 10%-30% modified wax, 1%-10% emulsifier, 1%-10% dispersant, 1%-10% lubricant, and the balance water. Water is heated, and then the emulsifier and dispersant are added. The pH is adjusted using a buffer solution, and the mixture is stirred until completely dissolved. The modified wax and lubricant are slowly added, and the mixture is homogenized and emulsified. After cooling, organosilicon is slowly added dropwise, stirred evenly, and cooled to room temperature to obtain the release agent. This invention utilizes the synergistic effect of specific polysiloxane-polyether copolymers, plant-based synthetic esters, and inorganic nanoparticles to form a uniform, ultra-thin organic-inorganic hybrid composite film on the surface of a high-temperature mold. This effectively overcomes the high-temperature Leidenfrost effect, meets the release requirements of thin-walled magnesium alloy parts and long-holding pressure conditions in extrusion casting, ensures the yield of subsequent T6 heat treatment, and fully complies with national environmental protection requirements for ultra-low VOC emissions.

Description

Technical Field

[0001] This invention relates to the field of mold release agents, and more specifically to a thin-film mold release agent for manufacturing thin magnesium alloy parts, its preparation method, and its application. Background Technology

[0002] Magnesium alloy thin parts have advantages such as low density, high specific strength, good thermal and electrical conductivity, electromagnetic shielding and easy recyclability. They are widely used in 3C electronics, automotive lightweighting, aerospace and defense, medical devices, rail transportation and new energy fields. They can be used to manufacture precision structural parts, lightweight components and functional support parts in various fields, fully meeting the core needs of lightweighting, precision and energy saving.

[0003] In the process of forming thin magnesium alloy parts, a release agent needs to be sprayed in the mold. The release agent forms a uniform isolation and lubrication film on the surface of the mold cavity to prevent sticking, reduce friction, ensure the integrity of the thin part forming and the surface finish, and at the same time assist in cooling and protecting the mold to extend the service life of the mold. However, in the existing technology, when producing thin-walled parts with a thickness of less than 1.0 mm, the release agent has obvious bottlenecks. (1) Film uniformity problem: The film thickness formed by traditional spray-type release agents fluctuates greatly (usually 3-8 μm). It is easy to accumulate or insufficiently cover in the small mold flow channels, resulting in incomplete filling of parts, flow marks or shrinkage marks on the surface and other defects, which seriously affect the dimensional accuracy and appearance consistency of the product. (2) Poor controllability of lubrication: The lubricity of traditional release agents usually depends on adjusting the solid content or changing the base material (such as more wax or more silicone oil). This is a macroscopic, indirect and feedback-lagging process, that is, it can only change the general category of the formula and cannot finely adjust the molecular structure of the interface. Lubricity is the result, but it lacks direct design points. After adjusting the formula, it is necessary to verify the effect through multiple actual die casting tests, which is costly and time-consuming. (3) Insufficient high temperature resistance: The semi-solid molding temperature of magnesium alloy is relatively high (usually 580-620℃). The organic components in ordinary release agents are very easy to decompose and carbonize at this temperature, forming scale, which not only reduces the release effect, but also contaminates the mold and product, increases the frequency of downtime for cleaning, and reduces production efficiency.

[0004] Therefore, developing a release agent suitable for thin-walled magnesium alloy parts with a thickness of less than 1.0 mm is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a thin-film release agent for manufacturing thin magnesium alloy parts, its preparation method, and its application. The release agent can form an ultra-thin, uniform, and high-temperature resistant protective film on the mold surface, and its lubricity can be precisely optimized by actively controlling its contact angle with the molten magnesium alloy. At the same time, by utilizing its low surface energy characteristics and excellent thermal stability, it fundamentally solves industry problems such as mold sticking, insufficient filling, and surface defects in the molding of thin-walled parts.

[0006] To achieve the above objectives, the present invention provides a method for preparing a thin-film release agent for manufacturing thin magnesium alloy parts, comprising the following preparation steps:

[0007] S1. Prepare the raw materials according to the following mass percentages: 5%-20% organosilicon, 10%-30% modified wax, 1%-10% emulsifier, 1%-10% dispersant, 1%-10% lubricant, and water as the balance.

[0008] S2, after heating water, add emulsifier and dispersant, adjust pH with buffer solution, and stir at a constant speed until completely dissolved; then slowly add modified wax and lubricant, and homogenize emulsify using a high-shear emulsifier; cool down, slowly add organosilicon, stir evenly, and then cool to room temperature to obtain the film-type release agent for making magnesium alloy thin parts.

[0009] Preferably, the organosilicon in step S1 is a polysiloxane-polyether copolymer with a weight-average molecular weight of 5000-15000. The ratio of dimethylsiloxane segments to polyether-modified siloxane segments in the main molecular chain is approximately 30-80:5-20, and the molar ratio of ethylene oxide to propylene oxide in the polyether side chain segments is 1-3:1.

[0010] Preferably, the modified wax in step S1 is a macromolecular plant-based synthetic ester that has undergone deep chemical modification, selected from one or more of pentaerythritol tetrastearate, pentaerythritol tetrabenzyl ester, neopentyl glycol diisostearate, trimellitic acid tristearate, and trimellitic acid tribenzyl ester.

[0011] Preferably, the emulsifier in step S1 is an environmentally friendly surfactant, selected from one or more of modified polysaccharides, polypeptide derivatives, or amino acid-based surfactants.

[0012] Preferably, the dispersant in step S1 is a polycarboxylate, selected from one or more of sodium polyacrylate, sodium polymethacrylate, ammonium polyacrylate, and potassium polyacrylate.

[0013] Preferably, the lubricant in step S1 is a high-performance inorganic nanoparticle selected from one or more of ultrafine, highly crystalline nano-sized mica powder, surface silane coupling agent modified layered silicate, and ultrafine hexagonal boron nitride.

[0014] Preferably, in step S2, the water is heated to 60-70°C; the buffer solution is any one of 2-amino-2-methyl-1-propanol / hydrochloric acid buffer, 2-diethylaminoethanol / hydrochloric acid buffer, and triethanolamine / hydrochloric acid buffer; the pH is adjusted to 9.0-10.5; the homogenization emulsification speed is 3000-5000 rpm and the time is 15-30 min; and the temperature is lowered to 35-40°C.

[0015] Secondly, the present invention also provides a uniform film-type release agent for use in the manufacture of magnesium alloy thin parts as described above.

[0016] In addition, the present invention also provides the application of the uniform film-type release agent used in the production of magnesium alloy thin parts as described above in the molding of magnesium alloy semi-solid thin-walled parts. The specific steps are as follows: diluting the release agent with pure water at a mass ratio of 1:80 to 1:120; using an automated micro-spraying system, performing atomized spraying on the surface of a high-temperature mold with a local hot spot temperature of 200°C to 400°C; controlling the spraying pressure at 0.4 to 0.6 MPa, instantly self-assembling and unfolding, and blowing air to dry and cure into a film.

[0017] In summary, this invention provides a thin-film release agent for manufacturing thin magnesium alloy parts, its preparation method, and its application. Compared with the prior art, the advantages of this invention are as follows:

[0018] (1) The present invention can form an extremely thin and uniform release film layer on the surface of the mold, with its thickness controlled in the range of 0.1μm-2.0μm, and even further in the range of 0.3μm-1.0μm, which is much lower than the film layer formed by traditional release agents (3-8μm).

[0019] (2) This invention differs from the traditional trial-and-error formulation development model. Instead, it achieves active lubrication design by precisely controlling the contact angle. A polysiloxane-polyether copolymer with a specific chain length is used as a key additive. By directionally arranging its molecules at the interface, the interfacial tension between the release film and the magnesium alloy melt is precisely changed, thereby achieving active control of the contact angle.

[0020] The moderate weight-average molecular weight of the polysiloxane-polyether copolymer ensures that the molecular chains are flexible, regular, and orderly arranged, which is conducive to forming a low surface energy interface on the magnesium alloy surface and effectively improving the contact angle. The dimethylsiloxane chain segments, which account for a dominant proportion in the molecular backbone, have excellent low surface energy characteristics, and the outward orientation of the side methyl groups can significantly weaken the interfacial polarity and continuously increase the contact angle. The appropriate ratio of polyether-modified siloxane chain energy can achieve stable anchoring of molecules on the metal surface, assist in the regular orientation of molecules, and help maintain a high contact angle. The propylene oxide in the side chain polyether segments has a hydrophobic structure and steric hindrance effect, which can restrain the excessive spread of the liquid film and stabilize and improve the contact angle. Combined with a reasonable ratio of ethylene oxide, it can synergistically optimize the interfacial arrangement configuration, further enhance the surface hydrophobic effect, and achieve a significant increase in the overall contact angle, which is conducive to forming an ultra-thin and dense release film layer and optimizing the release performance.

[0021] The performance of the mold release agent is quantified, requiring that the contact angle between the treated mold surface and the molten magnesium alloy simulation liquid (such as tin-bismuth alloy) be stable at ≥110°, preferably within the range of 115°-135°. This quantitative indicator provides a reliable guarantee for the consistency of product quality.

[0022] (3) To achieve excellent anti-sticking effect, the present invention uses a polysiloxane-polyether copolymer to construct a uniform and dense protective layer. The combination of low surface energy characteristics and suitable contact angle significantly reduces the demolding force and fundamentally solves the problem of high-temperature sticking of magnesium alloys.

[0023] (4) To ensure the stability of the release agent in the high-temperature environment of semi-solid molding of magnesium alloys, this invention introduces thermogravimetric analysis as a key screening and verification tool: after the release agent dries into a film, under nitrogen or air atmosphere, at a heating rate of 10℃ / min, its initial decomposition temperature is not lower than 350℃, and the residual carbon rate at 600℃ is less than 5%. This strict standard ensures that the release agent decomposes very little when encountering high-temperature magnesium alloy melt, fundamentally reducing scale buildup and gas pollution. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1: Preparation of Organosilicon

[0026] 78.0 g of octamethylcyclotetrasiloxane, 21.2 g of tetramethyltetrasiloxane, and 1.2 g of tetramethyldihydrodisiloxane were added to a dry three-necked flask. The mixture was stirred and heated to 100 °C under nitrogen protection. 0.22 g of potassium hydroxide was added, and the reaction was carried out at 100 °C for 6 h to complete the ring-opening polymerization reaction, yielding hydrogen-containing polydimethylsiloxane with side chains. The temperature was lowered to 85 °C, and 22.1 g of allyl polyether (EO:PO = 2:1, molecular weight 300) was added. 2.3 mL of chloroplatinic acid-isopropanol catalyst solution (1000 ppm) was added dropwise, and the reaction was maintained at 85 °C for 5 h to complete the hydrosilylation reaction. Low-boiling substances were removed by vacuum distillation at 110 °C and 0.08 MPa. After cooling, the polysiloxane-polyether copolymer was obtained, which is the organosilicon.

[0027] The obtained polysiloxane-polyether copolymer has a weight-average molecular weight of approximately 10,000, and the ratio of dimethylsiloxane segments to polyether-modified siloxane segments in the main molecular chain is approximately 55:15. Furthermore, the molar ratio of ethylene oxide to propylene oxide in the polyether side chain segments is 2:1.

[0028] Example 2: Preparation of release agent

[0029] S1. Take 50g of polysiloxane-polyether copolymer (organosilicon), 100g of pentaerythritol tetrastearate (modified wax), 20g of modified polysaccharide surfactant sodium octenyl succinate starch (emulsifier), 10g of sodium polyacrylate (dispersant), 20g of ultrafine high crystallinity nano-mica powder (lubricant), and 800g of water prepared in Example 1 for later use.

[0030] S2, heat water to 65℃, add modified polysaccharide surfactant sodium octenyl succinate starch and sodium polyacrylate, adjust the pH to 9.5 using 2-amino-2-methyl-1-propanol / hydrochloric acid buffer, and stir at a constant speed until completely dissolved; then slowly add pentaerythritol tetrastearate and ultrafine high-crystallinity nano-mica powder, and homogenize and emulsify using a high-shear emulsifier at 4000 rpm for 20 min; cool to 35℃, slowly add polysiloxane-polyether copolymer, stir evenly, and then cool to room temperature to obtain the film-type release agent for making magnesium alloy thin parts.

[0031] Example 3: Preparation of release agent

[0032] S1. Take 120g of polysiloxane-polyether copolymer (organosilicon), 200g of trimellitic acid tristearate (modified wax), 50g of modified polysaccharide surfactant sodium octenyl succinate starch (emulsifier), 30g of sodium polymethacrylate (dispersant), 50g of ultrafine hexagonal boron nitride (lubricant), and 550g of water prepared in Example 1 for later use.

[0033] S2, heat water to 65℃, add modified polysaccharide surfactant sodium octenyl succinate and sodium polymethacrylate, adjust the pH to 10.4 using 2-amino-2-methyl-1-propanol / hydrochloric acid buffer, and stir at a constant speed until completely dissolved; then slowly add trimellitic acid tristearate and ultrafine hexagonal boron nitride, and homogenize and emulsify using a high-shear emulsifier at 4000 rpm for 20 min; cool to 35℃, slowly add polysiloxane-polyether copolymer, stir evenly, and then cool to room temperature to obtain the film-type release agent for making magnesium alloy thin parts.

[0034] Example 4: Preparation of release agent

[0035] S1. Take 200g of polysiloxane-polyether copolymer (organosilicon), 300g of neopentyl glycol diisostearate (modified wax), 80g of sodium cocoyl glutamate (emulsifier) ​​(a polypeptide derivative surfactant), 50g of sodium polymethacrylate (dispersant), 70g of surface silane coupling agent modified layered silicate (lubricant) and 300g of water prepared in Example 1 for later use.

[0036] S2, heat water to 65℃, add sodium cocoyl glutamate and sodium polymethacrylate, which are peptide derivative surfactants, and adjust the pH to 10.0 using 2-amino-2-methyl-1-propanol / hydrochloric acid buffer. Stir at a constant speed until completely dissolved. Then slowly add neopentyl glycol diisostearate and surface silane coupling agent modified layered silicate, and homogenize and emulsify using a high-shear emulsifier at 4000 rpm for 20 min. Cool to 35℃, slowly add polysiloxane-polyether copolymer, stir evenly, and then cool to room temperature to obtain the film-type release agent for making magnesium alloy thin parts.

[0037] Comparative Example 1

[0038] S1. Take 100g of pentaerythritol tetrastearate (modified wax), 20g of modified polysaccharide surfactant sodium octenyl succinate starch (emulsifier), 10g of sodium polyacrylate (dispersant), 20g of ultrafine high crystallinity nano-grade mica powder (lubricant), and 850g of water for later use.

[0039] S2, heat water to 65℃, add modified polysaccharide surfactant sodium octenyl succinate starch and sodium polyacrylate, adjust the pH to 9.5 using 2-amino-2-methyl-1-propanol / hydrochloric acid buffer, and stir at a constant speed until completely dissolved; then slowly add pentaerythritol tetrastearate and ultrafine high-crystallinity nano-mica powder, and homogenize and emulsify using a high-shear emulsifier at 4000 rpm for 20 min; cool to 35℃, slowly add polysiloxane-polyether copolymer, stir evenly, and then cool to room temperature to obtain the film-type release agent for making magnesium alloy thin parts.

[0040] Comparative Example 2

[0041] S1. Take 50g of the polysiloxane-polyether copolymer (organosilicon) prepared in Example 1, 20g of the modified polysaccharide surfactant sodium octenyl succinate starch (emulsifier), 10g of sodium polyacrylate (dispersant), 20g of ultrafine high crystallinity nano-grade mica powder (lubricant), and 900g of water for later use.

[0042] S2, heat water to 65℃, add modified polysaccharide surfactant sodium octenyl succinate starch and sodium polyacrylate, adjust the pH to 9.5 using 2-amino-2-methyl-1-propanol / hydrochloric acid buffer, and stir at a constant speed until completely dissolved; then slowly add pentaerythritol tetrastearate and ultrafine high-crystallinity nano-mica powder, and homogenize and emulsify using a high-shear emulsifier at 4000 rpm for 20 min; cool to 35℃, slowly add polysiloxane-polyether copolymer, stir evenly, and then cool to room temperature to obtain the film-type release agent for making magnesium alloy thin parts.

[0043] Comparative Example 3

[0044] The traditional formula is used: 20% paraffin-based mineral oil, 10% dimethyl silicone oil, 5% nonylphenol polyoxyethylene ether (NPE), 10% isopropanol, 0.5% hexamethylenetetramine, and the balance water. The mixture is prepared by conventional mixing and stirring.

[0045] Performance testing

[0046] The release agents prepared in Examples 2-4 and Comparative Examples 1-3 were diluted with pure water at a ratio of 1:100 and then subjected to actual machine testing on an 800T horizontal extrusion casting machine (the test parts were thin-walled parts with a thickness of <1.0mm and locally thick-walled parts). The test data of various performance items are shown in the table below:

[0047] Film layer thickness (μm) 0.8 0.3 0.4 2.5 2.9 3.5-8.0 Mold surface contact angle 115° 132° 135° 68° 123° 85° TGA initial decomposition temperature 360℃ 390℃ 410℃ 345℃ 275℃ 220℃ 600℃ residual carbon ratio 1.2% 2.5% 3.8% 2.8% 13.2% 18.5% T6 heat treatment blister ratio 0% 0% 0% 2.5% 0% 12% Extrusion filling completeness 99.5% 100% 99.8% 94.3% 89.4% 85% Casting surface roughness Ra (μm) 0.82 0.58 0.68 1.30 1.75 2.42 Mold continuous production 50-mold carbon deposition adhesion grade Slight Very slight Very slight Slight Moderately severe Severe

[0048] The data in the table show that the release agent prepared in this invention has a smaller film thickness and less fluctuation compared to release agents prepared by traditional methods; a larger surface contact angle; a higher initial TGA decomposition temperature; a lower residual carbon rate at 600℃; a 0% foaming rate after T6 heat treatment; extremely high extrusion filling integrity; no flow marks; and the resulting magnesium alloy thin parts have a small surface roughness. Furthermore, after 50 consecutive molds, virtually no carbon buildup is produced. Therefore, it is far superior to release agents prepared by traditional methods.

[0049] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a thin-film release agent for manufacturing thin magnesium alloy parts, characterized in that, The preparation steps include the following: S1. Prepare the raw materials according to the following mass percentages: 5%-20% organosilicon, 10%-30% modified wax, 1%-10% emulsifier, 1%-10% dispersant, 1%-10% lubricant, and water as the balance. S2, after heating water, add emulsifier and dispersant, adjust pH with buffer solution, and stir at a constant speed until completely dissolved; then slowly add modified wax and lubricant, and homogenize emulsify using a high-shear emulsifier; cool down, slowly add organosilicon, stir evenly, and then cool to room temperature to obtain the film-type release agent for making magnesium alloy thin parts.

2. The preparation method according to claim 1, characterized in that, The organosilicon mentioned in step S1 is a polysiloxane-polyether copolymer with a weight-average molecular weight of 5000-15000. The ratio of dimethylsiloxane segments to polyether-modified siloxane segments in the main molecular chain is approximately 30-80:5-20, and the molar ratio of ethylene oxide to propylene oxide in the polyether side chain segments is 1-3:

1.

3. The preparation method according to claim 1, characterized in that, The modified wax mentioned in step S1 is a macromolecular plant-based synthetic ester that has undergone deep chemical modification, selected from one or more of pentaerythritol tetrastearate, pentaerythritol tetrabenzyl ester, neopentyl glycol diisostearate, trimellitic acid tristearate, and trimellitic acid tribenzyl ester.

4. The preparation method according to claim 1, characterized in that, The emulsifier mentioned in step S1 is an environmentally friendly surfactant, selected from one or more of modified polysaccharides, polypeptide derivatives, or amino acid-based surfactants.

5. The preparation method according to claim 1, characterized in that, The dispersant mentioned in step S1 is a polycarboxylate, selected from one or more of sodium polyacrylate, sodium polymethacrylate, ammonium polyacrylate, and potassium polyacrylate.

6. The preparation method according to claim 1, characterized in that, The lubricant mentioned in step S1 is a high-performance inorganic nanoparticle selected from one or more of ultrafine, highly crystalline nano-sized mica powder, surface silane coupling agent modified layered silicate, and ultrafine hexagonal boron nitride.

7. The preparation method according to claim 1, characterized in that, The water in step S2 is heated to 60~70℃; The buffer solution is any one of 2-amino-2-methyl-1-propanol / hydrochloric acid buffer, 2-diethylaminoethanol / hydrochloric acid buffer, and triethanolamine / hydrochloric acid buffer. The pH is adjusted to 9.0~10.5; The homogenization emulsification speed is 3000~5000 rpm, and the time is 15~30 min; The temperature was lowered to 35-40℃.

8. A thin-film release agent for manufacturing thin magnesium alloy parts, prepared by the method described in any one of claims 1-7.

9. The application of a thin-film release agent as described in claim 8 for manufacturing thin magnesium alloy parts in the molding of semi-solid thin-walled magnesium alloy parts, characterized in that, The specific steps are as follows: dilute the release agent with pure water at a mass ratio of 1:80 to 1:120; use an automated micro-spraying system to perform atomized spraying on the surface of the high-temperature mold where the local hot spot temperature is 200℃ to 400℃; The spraying pressure is controlled at 0.4~0.6 MPa, and the coating is instantly self-assembled, unfolded, and dried and cured by blowing air to form a film.