A molding process for epoxy resin products and its use

Abstract

This invention discloses a molding process for epoxy resin products and its applications. The molding process includes the following steps: mixing raw materials including epoxy resin, silica powder, and anhydride curing agent, and then casting to obtain the epoxy resin product; wherein the casting conditions are: first stage curing: curing at 105-120℃ for 3-10 hours; second stage curing: curing at 130-135℃ for 16-22 hours; wherein the epoxy resin is a solid bisphenol A type epoxy resin with an epoxy value of 2.4-2.65 Eq / kg and a viscosity of 370-550 mPa·s at 120℃. This process can not only produce epoxy resin products with excellent performance, but also produce products with good appearance quality after molding, making it suitable for the production of large-size, high-voltage insulating products. This invention also provides applications of the above molding process.

Description

Technical Field

[0001] This invention relates to the field of epoxy materials technology, and in particular to a molding process for epoxy resin products and their applications. Background Technology

[0002] In the power cable industry, insulating epoxy resin materials play a crucial role in the manufacture of related products (such as dry-type transformers, dry-type instrument transformers, insulated switches, disc insulators, support insulators, and cable accessories). Epoxy resins are widely used in these products due to their superior performance in insulation and mechanical strength.

[0003] With the continuous development of technology, such as the increase in voltage levels or product size, higher requirements are placed on the safety, reliability, and appearance of materials. Existing epoxy materials cannot simultaneously guarantee comprehensive performance such as electrical and mechanical properties, and it is difficult to effectively balance the appearance of the molded product while improving the overall performance of the material. These factors limit the application of epoxy resin materials in the field of power cables, especially in large-size, high-voltage products that are difficult to mold.

[0004] Therefore, there is a need to develop an epoxy resin molding process with better overall performance and product appearance, which can be applied to large-size, high-voltage power cable insulation products. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a molding process for epoxy resin products. This process can not only produce epoxy resin products with excellent performance, but also produce products with good appearance quality after molding, meeting the production and application requirements of large-size, high-voltage insulation products.

[0006] The present invention also proposes the application of the above-mentioned molding process.

[0007] The first aspect of this invention relates to a molding process for an epoxy resin product, comprising the following steps: mixing raw materials including epoxy resin, silica powder, and an anhydride curing agent, and then casting the mixture to obtain the epoxy resin product; wherein the casting conditions are: first stage curing: curing at 105-120℃ for 3-10 hours; second stage curing: curing at 130-135℃ for 16-22 hours;

[0008] The raw materials for preparation include, by mass, 100 parts epoxy resin, 30-50 parts acid anhydride curing agent, and 200-320 parts silica powder; wherein the epoxy resin is a solid bisphenol A type epoxy resin with an epoxy value of 2.4-2.65 Eq / kg and a viscosity of 370-550 mPa·s at 120℃.

[0009] The molding process for epoxy resin products according to the first aspect of the present invention has at least the following beneficial effects:

[0010] The casting process employs segmented curing. The first stage has a lower curing temperature, which helps reduce the curing stress inside the material and minimizes the generation of internal defects. The second stage has an appropriately higher curing temperature, which not only enables the cross-linking process to be more complete and improves the strength and toughness of the material, but also reduces energy consumption, shortens cooling time, and improves processing efficiency by ensuring that the curing temperature in the second stage is not too high.

[0011] By rationally controlling the segmented curing process parameters, the problems of poor material toughness and stress concentration caused by excessively high curing temperatures are avoided, thus ensuring the performance of epoxy resin. At the same time, it also takes into account the advantages of product appearance quality and production efficiency, meeting the requirements of large-scale industrial production. It has significant application prospects, especially in the field of large-size, high-voltage insulation products (such as GIS terminals, composite sleeve terminals and other cable accessories).

[0012] In terms of raw materials, specific bisphenol A epoxy resin, anhydride curing agents, and silica powder were selected as the main raw materials, resulting in excellent electrical, mechanical, durability, and flame retardancy properties. Bisphenol A epoxy resin is low in cost, has good mechanical properties and electrical insulation, and its suitable epoxy value ensures stable curing, guaranteeing high strength and toughness of the product and preventing cracking in high or low temperature environments. Anhydride curing agents have a relatively mild reaction, resulting in low shrinkage and high dimensional stability after curing, reducing internal stress and significantly enhancing the mechanical and electrical properties of the product under different temperature conditions, thus improving its service life. Silica powder, as a filler, exhibits superior thermal stability, dimensional stability, and electrical insulation compared to conventional flame-retardant fillers; its low coefficient of expansion and excellent reinforcing and toughening effects improve the strength and toughness of the material while reducing dielectric loss. The environmental friendliness and cost advantages of silica powder make the material have broader application prospects while ensuring performance.

[0013] According to some embodiments of the present invention, the mixing includes: mixing the preparation raw materials, including epoxy resin and silicon micro powder, at a temperature when the epoxy resin is in a liquid state for the first time to obtain a first mixture; adding an acid anhydride curing agent to the first mixture for the second mixing to obtain a second mixture; and using the second mixture for casting molding.

[0014] First, the epoxy resin and silica powder are mixed to prevent the curing agent from reacting prematurely, reducing the casting viscosity and helping to improve molding speed and production efficiency. This process is simple and easy to implement, and can stably produce epoxy resin products with excellent electrical properties, mechanical properties, and appearance quality. It is particularly suitable for large-size and high-voltage cable accessories.

[0015] According to some embodiments of the present invention, the heating temperature is 125-130°C.

[0016] According to some embodiments of the present invention, the temperature of the first mixing is 125-130°C.

[0017] According to some embodiments of the present invention, before the anhydride curing agent is added to the first mixture, the temperature of the first mixture is 125-130°C.

[0018] According to some embodiments of the present invention, the second stage of curing includes: curing at 130–135°C for 4–7 hours, demolding, and continuing curing at 130–135°C for 12–15 hours. In actual production, the second stage of curing is partially carried out inside the mold, followed by demolding and post-curing, which can shorten the mold cooling time and improve production efficiency.

[0019] According to some embodiments of the present invention, the casting process includes preheating the mold before casting. The preheating temperature is reasonably selected based on the amount and temperature of the castable material to ensure that the temperature of the castable material after entering the mold is close to the curing temperature, thereby reducing process fluctuations caused by temperature differences. For example, when the temperature of the castable material is lower than the actual curing temperature, the preheating temperature of the mold can be appropriately increased. The mold preheating time can be reasonably selected based on experience and the size of the mold to ensure as uniform a temperature as possible. Especially for large-sized molds, the preheating process reduces temperature differences and prevents unevenness during curing.

[0020] According to some embodiments of the present invention, cooling is performed before demolding to facilitate smooth demolding. The present invention does not impose a limiting requirement on the cooling rate; the cooling rate can be reasonably selected according to the size of the product and the curing temperature. For example, the cooling rate can be set to 0.1–0.6 °C / min. Appropriately increasing the cooling rate can improve production efficiency.

[0021] According to some embodiments of the present invention, the anhydride curing agent comprises at least one of a first methyltetrahydrophthalic anhydride and a composition of a second methyltetrahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol, wherein the mass fraction of 2,4,6-tris(dimethylaminomethyl)phenol in the composition is 0.1% to 3%. Specifically, the mass fraction of 2,4,6-tris(dimethylaminomethyl)phenol in the composition may be selected as 0.1%, 0.5%, 1%, 2%, 3%, or any value between therewith.

[0022] Modifying methyltetrahydrophthalic anhydride with an appropriate amount of 2,4,6-tris(dimethylaminomethyl)phenol can effectively promote the ring-opening reaction of epoxy groups, making it easier for epoxy molecules to react chemically with methyltetrahydrophthalic anhydride, thereby accelerating the curing rate of the epoxy resin. Based on this, lower curing temperatures and shorter curing times can be selected within a defined range of process parameters, thus improving production efficiency and reducing energy consumption.

[0023] According to some embodiments of the present invention, the anhydride curing agent is selected from the first methyltetrahydrophthalic anhydride, or a composition of the second methyltetrahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol; and optionally, the anhydride curing agent is 30 to 45 parts, specifically 30 parts, 35 parts, 40 parts, 45 parts or any value between them.

[0024] According to some embodiments of the present invention, the anhydride curing agent is selected from the first methyltetrahydrophthalic anhydride, and the casting molding conditions are: first stage curing: curing at 116-120℃ for 9-10 hours; second stage curing: curing at 130-135℃ for 18-22 hours.

[0025] According to some embodiments of the present invention, the anhydride curing agent is selected from the first methyltetrahydrophthalic anhydride, and the second stage of curing includes: curing at 130-135°C for 6-7 hours, demolding, and continuing to cure at 130-135°C for 12-15 hours.

[0026] According to some embodiments of the present invention, the anhydride curing agent is selected from a composition of 2,4,6-tris(dimethylaminomethyl)phenol, and the casting molding conditions are: first stage curing: curing at 105-110°C for 3-5 hours, and second stage curing: curing at 130-135°C for 16-20 hours.

[0027] According to some embodiments of the present invention, the anhydride curing agent is selected from a composition of the second methyltetrahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol, and the second curing stage includes: curing at 130-135°C for 4-5 hours, demolding, and continuing curing at 130-135°C for 12-15 hours.

[0028] According to some embodiments of the present invention, the anhydride curing agent is selected from the first methyltetrahydrophthalic anhydride and the second methyltetrahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol.

[0029] According to some embodiments of the present invention, the first methyltetrahydrophthalic anhydride is 20-30 parts by weight, specifically 20, 25, 28, 30 parts or any value therebetween; the composition of the second methyltetrahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol is 10-20 parts, specifically 10, 14, 18, 20 parts or any value therebetween. The casting molding conditions are: first stage curing: curing at 111-115°C for 6-7 hours; second stage curing: curing at 130-135°C for 17-21 hours. Specifically, the second stage curing includes: curing at 130-135°C for 5-6 hours, demolding, and continuing curing at 130-135°C for 12-15 hours.

[0030] Under the aforementioned preferred curing conditions, it is beneficial to further improve the surface quality of the product while ensuring mechanical strength and electrical insulation.

[0031] It should be understood that the temperature parameters for the first and second curing stages can be adjusted appropriately according to specific needs to obtain corresponding product performance. For example, if the first curing temperature or time is shortened, the temperature and time for the second curing stage can be extended accordingly. For curing systems with higher reactivity (e.g., compositions including dimethyltetrahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol), the temperature and / or time for both curing stages can be appropriately shortened. Therefore, the process parameters listed above are for reference only and are not intended to be restrictive.

[0032] According to some embodiments of the present invention, in the first methyltetrahydrophthalic anhydride and / or the second methyltetrahydrophthalic anhydride, the mass fraction of the anhydride is ≥40% and the acid value is ≥660mgKOH / g.

[0033] According to some embodiments of the present invention, the anhydride curing agent is 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, or any value between them.

[0034] According to some embodiments of the present invention, the average particle size of the silicon micropowder is 25 to 40 μm, specifically 25 μm, 30 μm, 35 μm, 40 μm or any value between them.

[0035] According to some embodiments of the present invention, the purity of the silicon micropowder is 99.5% or higher, by mass fraction. Using high-purity silicon micropowder can effectively reduce impurity content and further improve electrical performance.

[0036] According to some embodiments of the present invention, the content of the silicon micropowder is 200 parts, 250 parts, 300 parts, 320 parts or any value between them.

[0037] According to some embodiments of the present invention, the raw materials for preparation further include color powder, and the mixing includes: mixing the raw materials comprising epoxy resin, silica powder, anhydride curing agent, and color powder. The color powder is used for coloring. The present invention does not have special requirements on the type and amount of color powder, which can be freely selected according to coloring needs. For example, common types such as iron oxide red, chrome yellow, chrome green, and titanium dioxide can be used. The amount of color powder is usually determined according to the coloring depth and hiding power, with a reference amount of 0.1% to 5% of the epoxy resin mass.

[0038] According to some embodiments of the present invention, the raw materials for preparation further include color powder, and the mixing includes: mixing the raw materials including the epoxy resin, the silicon micro powder, and the color powder for the first time at a temperature when the epoxy resin is in a liquid state to obtain the first mixture; adding an acid anhydride curing agent to the first mixture for the second mixing to obtain the second mixture, and using the second mixture for casting molding.

[0039] According to some embodiments of the present invention, the anhydride curing agent is preheated before being added to the first mixture to reduce the temperature difference caused by the addition of the curing agent, so that it can be quickly cast after mixing, thereby improving production efficiency, reducing the heating time of the curing agent, reducing the volatilization of the curing agent, and avoiding the impact on the overall performance of the product due to uneven preheating.

[0040] In practical applications, the temperatures of the first mixture and the anhydride curing agent before the second mixing are appropriately controlled according to the curing temperature of the subsequent casting, so that the temperature after mixing is close to the curing temperature, allowing for direct casting. Furthermore, to reduce curing agent volatilization, the preheating temperature of the anhydride curing agent should be kept as low as possible.

[0041] According to some embodiments of the present invention, the curing agent is preheated to a temperature of 40–60°C. During the heating process, stirring and vacuum degassing can be performed to ensure uniform temperature and remove air bubbles.

[0042] According to some embodiments of the present invention, the first mixing and / or the second mixing includes stirring.

[0043] According to some embodiments of the present invention, a vacuum degassing process is performed after the first mixing. The present invention does not impose limiting conditions on the vacuum degassing process; for example, the vacuum level of the vacuum degassing process can be controlled to be no greater than 50 Pa.

[0044] According to some embodiments of the present invention, stirring is performed during the vacuum degassing process.

[0045] According to some embodiments of the invention, the second mixing is carried out in a static mixer.

[0046] This invention does not limit the time for vacuum degassing in all steps; the specific time can be selected reasonably based on the material volume. When the material volume increases, the degassing time can be appropriately extended. Furthermore, there are no restrictive requirements for the stirring process; a lower stirring rate can be selected to achieve moderate agitation, avoid packing material settling, and promote uniform mixing of the materials.

[0047] According to some embodiments of the present invention, the casting process is followed by uniform cooling to reduce the generation of internal stress.

[0048] According to some embodiments of the present invention, the constant cooling rate is 0.1 to 0.5 °C / min.

[0049] According to some embodiments of the present invention, the epoxy resin product includes, but is not limited to, insulating products such as cable accessories.

[0050] Products manufactured using this molding process exhibit excellent appearance, electrical insulation properties, and mechanical properties, making them suitable for high-voltage, large-size electrical insulation products, such as cable accessories.

[0051] The second aspect of the present invention relates to the application of the above-described molding process in the preparation of insulating products.

[0052] The molding process and material formulation of this invention significantly improve the performance of the product (e.g., electrical insulation and mechanical properties) and achieve excellent appearance quality, thereby increasing the product yield. These advantages enable the product to be used in harsh environments, such as at voltages up to 330kV, thus enhancing the product's reliability and stability.

[0053] According to some embodiments of the present invention, the insulating products include cable accessories, such as GIS terminals, composite sleeve terminals, prefabricated combination joints, double-ended connectors, etc.

[0054] In this article, the numerical ranges mentioned include the endpoints and any subsets within that range; "above" includes the number itself, for example, "above 2" includes 2.

[0055] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0056] Figure 1 These are example images showing whether the appearance of a product sample is up to standard.

[0057] Figure 2 Here is an example of the X-ray inspection results for a product sample, where Figure 2 a shows the presence of air bubbles inside the resin. Figure 2 b shows the presence of air bubbles at the interface between the resin and the metal insert. Detailed Implementation

[0058] The embodiments of the present invention are described in detail below. These embodiments are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0059] The raw materials used in the following examples and comparative examples are described below:

[0060] Epoxy resin: Bisphenol A type epoxy resin, epoxy value 2.44~2.63Eq / kg, viscosity (120℃) is 370~550mPa·s.

[0061] Curing agent A: Methyltetrahydrophthalic anhydride, acid value 660-685 mgKOH / g, viscosity not greater than 50 mPa·s, anhydride mass content greater than 40%.

[0062] Curing agent B: a mixture of 2,4,6-tris(dimethylaminomethyl)phenol and methyltetrahydrophthalic anhydride, wherein the mass fraction of 2,4,6-tris(dimethylaminomethyl)phenol is 1%, and the parameters of methyltetrahydrophthalic anhydride are the same as those of curing agent A.

[0063] Filler: Silica powder with an average particle size of 30μm and a purity of over 99.5%.

[0064] Pigment: Iron oxide red, with an average particle size of 30 μm.

[0065] Unless otherwise specified, all raw materials or equipment mentioned are commercially available and readily available.

[0066] Example 1

[0067] This embodiment prepares an epoxy resin material, which, by mass parts, includes the following raw materials: 100 parts epoxy resin, 42 parts curing agent (curing agent A), 250 parts filler, and 1 part color powder.

[0068] The preparation steps of epoxy resin materials are as follows:

[0069] 1) Mix epoxy resin, filler and color powder in proportion at 130℃ and stir for 60-90 minutes to make the materials uniform. During this process, the temperature is controlled between 125-130℃.

[0070] 2) Maintain constant temperature and perform vacuum degassing treatment on the mixture while stirring. The vacuum degree should not exceed 50 Pa, and the treatment time should be 180 to 240 minutes until no obvious bubbles appear on the surface of the mixture.

[0071] 3) Under constant temperature of 60℃, the curing agent is subjected to vacuum degassing treatment while being stirred. The vacuum degree is not greater than 100Pa, and the treatment time is 60-90 minutes until there are no obvious bubbles on the surface.

[0072] 4) The prepared mixture and curing agent are conveyed to a static mixer under pressure according to the ratio, and then poured into a mold preheated for 4-5 hours at 125-130℃. Initial curing is then carried out in a forced-air oven according to a molding process of curing at 118℃ for 9 hours and then at 135℃ for 7 hours.

[0073] 5) Cool the temperature in a forced-air drying oven to 100-110℃ at a rate of 0.55℃ / min, then demold.

[0074] 6) Cured at 135℃ for 15 hours, then cooled to room temperature at a rate of 0.15℃ / minute.

[0075] Example 2

[0076] This embodiment prepares an epoxy resin material, which, by mass, includes the following raw materials: 100 parts epoxy resin, 42 parts curing agent (28 parts curing agent A, 66.7% by mass; 14 parts curing agent B, 33.3%), 250 parts filler, and 1 part colorant.

[0077] The preparation steps of epoxy resin materials are as follows:

[0078] 1) Mix epoxy resin, filler and color powder in proportion at 130℃ and stir for 60-90 minutes to make the materials uniform. During this process, the temperature is controlled between 125-130℃.

[0079] 2) Maintain constant temperature and perform vacuum degassing treatment on the mixture while stirring. The vacuum degree should not exceed 50 Pa, and the treatment time should be 180 to 240 minutes until no obvious bubbles appear on the surface of the mixture.

[0080] 3) Under constant temperature of 60℃, the curing agent is subjected to vacuum degassing treatment while being stirred. The vacuum degree is not greater than 100Pa, and the treatment time is 60-90 minutes until there are no obvious bubbles on the surface.

[0081] 4) The prepared mixture and curing agent are conveyed to a static mixer under pressure according to the ratio, and then poured into a mold preheated for 4-5 hours at 125-130℃. Initial curing is then carried out in a forced-air oven according to a molding process of curing at 112℃ for 7 hours and then at 135℃ for 6 hours.

[0082] 5) Cool the temperature in a forced-air drying oven to 100-110℃ at a rate of 0.55℃ / min, then demold.

[0083] 6) Cured at 135℃ for 15 hours, then cooled to room temperature at a rate of 0.15℃ / minute.

[0084] Example 3

[0085] This embodiment prepares an epoxy resin material, which, by mass parts, includes the following raw materials: 100 parts epoxy resin, 42 parts curing agent (curing agent B), 250 parts filler, and 1 part color powder.

[0086] The preparation steps of epoxy resin materials are as follows:

[0087] 1) Mix epoxy resin, filler and color powder in proportion at 130℃ and stir for 60-90 minutes to make the materials uniform. During this process, the temperature is controlled between 125-130℃.

[0088] 2) Maintain constant temperature and perform vacuum degassing treatment on the mixture while stirring. The vacuum degree should not exceed 50 Pa, and the treatment time should be 180 to 240 minutes until no obvious bubbles appear on the surface of the mixture.

[0089] 3) Under constant temperature of 60℃, the curing agent is subjected to vacuum degassing treatment while being stirred. The vacuum degree is not greater than 100Pa, and the treatment time is 60-90 minutes until there are no obvious bubbles on the surface.

[0090] 4) The prepared mixture and curing agent are conveyed to a static mixer under pressure according to the ratio, and then poured into a mold preheated for 4-5 hours at 125-130℃. Initial curing is then carried out in a forced-air oven according to a molding process of curing at 108℃ for 5 hours and then at 135℃ for 5 hours.

[0091] 5) Cool the temperature in a forced-air drying oven to 100-110℃ at a rate of 0.55℃ / min, then demold.

[0092] 6) Cured at 135℃ for 15 hours, then cooled to room temperature at a rate of 0.15℃ / minute.

[0093] Comparative Example 1

[0094] This comparative example prepared an epoxy resin material, which, by mass parts, included the following raw materials: 100 parts epoxy resin, 42 parts curing agent (curing agent A), 250 parts filler, and 1 part color powder.

[0095] The preparation steps of epoxy resin materials are as follows:

[0096] 1) Mix epoxy resin, filler and color powder in proportion at 130℃ and stir for 60-90 minutes to make the materials uniform. During this process, the temperature is controlled between 125-130℃.

[0097] 2) Maintain constant temperature and perform vacuum degassing treatment on the mixture while stirring. The vacuum degree should not exceed 50 Pa, and the treatment time should be 180 to 240 minutes until no obvious bubbles appear on the surface of the mixture.

[0098] 3) Under constant temperature of 60℃, the curing agent is subjected to vacuum degassing treatment while being stirred. The vacuum degree is not greater than 100Pa, and the treatment time is 60-90 minutes until there are no obvious bubbles on the surface.

[0099] 4) The prepared mixture and curing agent are conveyed to a static mixer under pressure according to the ratio, and then poured into a mold preheated for 4-5 hours at 125-130℃. Initial curing is then carried out in a forced-air oven according to a molding process of curing at 126℃ for 9 hours and then at 135℃ for 7 hours.

[0100] 5) Cool the temperature in a forced-air drying oven to 100-110℃ at a rate of 0.55℃ / min, then demold.

[0101] 6) Cured at 135℃ for 15 hours, then cooled to room temperature at a rate of 0.15℃ / minute.

[0102] Comparative Example 2

[0103] This comparative example prepared an epoxy resin material, which, by mass parts, included the following raw materials: 100 parts epoxy resin, 42 parts curing agent (curing agent A 28 parts, mass percentage 66.7%; curing agent B 14 parts, mass percentage 33.3%), 250 parts filler, and 1 part color powder.

[0104] The preparation steps of epoxy resin materials are as follows:

[0105] 1) Mix epoxy resin, filler and color powder in proportion at 130℃ and stir for 60-90 minutes to make the materials uniform. During this process, the temperature is controlled between 125-130℃.

[0106] 2) Maintain constant temperature and perform vacuum degassing treatment on the mixture while stirring. The vacuum degree should not exceed 50 Pa, and the treatment time should be 180 to 240 minutes until no obvious bubbles appear on the surface of the mixture.

[0107] 3) Under constant temperature of 60℃, the curing agent is subjected to vacuum degassing treatment while being stirred. The vacuum degree is not greater than 100Pa, and the treatment time is 60-90 minutes until there are no obvious bubbles on the surface.

[0108] 4) The prepared mixture and curing agent are conveyed to a static mixer under pressure according to the ratio, and then poured into a mold preheated for 4-5 hours at 125-130℃. Initial curing is then carried out in a forced-air oven according to a molding process of curing at 124℃ for 7 hours and then at 135℃ for 6 hours.

[0109] 5) Cool the temperature in a forced-air drying oven to 100-110℃ at a rate of 0.55℃ / min, then demold.

[0110] 6) Cured at 135℃ for 15 hours, then cooled to room temperature at a rate of 0.15℃ / minute.

[0111] Comparative Example 3

[0112] This comparative example prepared an epoxy resin material, which, by mass parts, included the following raw materials: 100 parts epoxy resin, 42 parts curing agent (curing agent B), 250 parts filler, and 1 part color powder.

[0113] The preparation steps of epoxy resin materials are as follows:

[0114] 1) Mix epoxy resin, filler and color powder in proportion at 130℃ and stir for 60-90 minutes to make the materials uniform. During this process, the temperature is controlled between 125-130℃.

[0115] 2) Maintain constant temperature and perform vacuum degassing treatment on the mixture while stirring. The vacuum degree should not exceed 50 Pa, and the treatment time should be 180 to 240 minutes until no obvious bubbles appear on the surface of the mixture.

[0116] 3) Under constant temperature of 60℃, the curing agent is subjected to vacuum degassing treatment while being stirred. The vacuum degree is not greater than 100Pa, and the treatment time is 60-90 minutes until there are no obvious bubbles on the surface.

[0117] 4) The prepared mixture and curing agent are conveyed to a static mixer under pressure according to the ratio, and then poured into a mold preheated for 4-5 hours at 125-130℃. Initial curing is then carried out in a forced-air oven according to a molding process of curing at 122℃ for 5 hours and then at 135℃ for 5 hours.

[0118] 5) Cool the temperature in a forced-air drying oven to 100-110℃ at a rate of 0.55℃ / min, then demold.

[0119] 6) Cured at 135℃ for 15 hours, then cooled to room temperature at a rate of 0.15℃ / minute.

[0120] Test case

[0121] I. Product Testing

[0122] 110-330kV epoxy bushings were prepared according to the methods of Examples 1-3 and Comparative Examples 1-3, with pre-embedded metal inserts (such as copper or aluminum) inside the epoxy bushings. Before casting, the metal inserts were placed in the mold to ensure that the final product contained the metal inserts. Subsequently, the prepared epoxy bushings underwent visual inspection, X-ray inspection, and electrical performance testing.

[0123] 1) Visual inspection

[0124] Experimental group: Six groups were set up in the experimental group, namely experimental groups 1 - 6. Experimental groups 1 - 6 respectively adopted the molding processes of Examples 1 - 3 and Comparative Examples 1 - 3. Each of Examples 1 - 3 had 50 product samples, totaling 150 samples, and each of Comparative Examples 1 - 3 had 10 product samples, totaling 30 samples. The volumes and weights of each product sample were equivalent.

[0125] Experimental method: In an environment with good lighting, visually check whether the surface of the product sample is smooth and whether there are shrinkage marks. If the surface is smooth and there are no shrinkage marks, it is considered qualified; if these conditions are not met, it is regarded as unqualified. Statistically analyze the surface quality of each group of samples and calculate the visual qualification rate. As Figure 1 , the left figure shows a qualified product, and the right figure shows an unqualified product. As Figure 1 shown, the left figure shows a qualified product, and the right figure shows an unqualified product. It should be noted that Figure 1 the unqualified appearance shown in the right figure is only a typical example, and the actual situation may be different. Due to the reflection effect during photography, the shrinkage marks in the photo may not seem very obvious. However, they can be more clearly observed by actual visual inspection, and the surface unevenness can be clearly felt by touch.

[0126] 2) X-ray detection

[0127] Experimental group: Six groups were set up in the experimental group, namely experimental groups 1 - 6. Experimental groups 1 - 6 respectively adopted the molding processes of Examples 1 - 3 and Comparative Examples 1 - 3. Each group had 5 product samples, totaling 30 samples. Each product sample was selected from the visually qualified samples in the first section of the visual inspection experimental group.

[0128] Experimental method: Place the sample in the X-ray test chamber and observe whether there are air bubbles inside the sample resin or at the interface between the resin and the metal insert. Detecting air bubbles at any position is considered unqualified. Refer to Figure 2 , Figure 2 a shows an example of the X-ray detection result of air bubbles inside the resin; Figure 2 b shows an example of the X-ray detection result of air bubbles at the interface between the resin and the metal insert (the upper light-colored area is the resin, and the lower dark-colored area is the metal insert). The results in the figure are only illustrative, and other results may occur in actual detection, or both types of air bubbles may exist simultaneously.

[0129] 3) Electrical performance test

[0130] Experimental group: Select the product samples that passed the X-ray detection in the second section of the X-ray detection experimental group for testing. Products that are unqualified in appearance and X-ray detection do not meet the test conditions.

[0131] Experimental methods: The following tests were conducted in sequence at ambient temperature: a) Partial discharge test: The test voltage was gradually increased to 222kV and held for 10s, then slowly decreased to 190kV, and the presence of visible discharge with background noise exceeding 5pC was detected; b) AC withstand voltage test: The test voltage was gradually increased to 318kV and held for 30min, and the presence of flashover or breakdown of the sample was detected; c) Partial discharge test: The test voltage was gradually increased to 222kV and held for 10s, then slowly decreased to 190kV, and the presence of visible discharge with background noise exceeding 5pC was detected.

[0132] The product test results are shown in Table 1.

[0133] Table 1

[0134]

[0135]

[0136] According to the experimental results in Table 1, the product samples of Examples 1-3 all exhibited excellent appearance quality, meeting the relevant national standards for sealing and electrical performance requirements. They also showed no internal bubbles or air gaps, and had good bonding interfaces, making them suitable for the production of high-voltage, large-volume cable accessories. In contrast, Comparative Examples 1-3, due to excessively high molding temperatures during the initial curing process, resulted in a violent reaction, leading to varying degrees of shrinkage marks and poor appearance quality. Furthermore, the intensity of the reaction caused a rapid increase in material viscosity, preventing the timely filling of voids created by curing shrinkage, thus generating bubbles and affecting product yield.

[0137] II. Test piece testing

[0138] Test pieces were prepared according to the methods of Examples 1-3 and Comparative Examples 1-3, and their mechanical properties, glass transition temperature (Tg), and heat distortion temperature were tested.

[0139] 1) Mechanical properties:

[0140] Experimental Groups: Six experimental groups were set up, namely Experimental Groups 1 to 6. Experimental Groups 1 to 6 adopted the molding processes of Examples 1 to 3 and Comparative Examples 1 to 3, respectively. Each group had 5 product samples, for a total of 30 samples. The volume and weight of each product sample were equivalent.

[0141] Experimental methods: Impact strength, flexural strength and compressive strength were tested at room temperature according to GB / T 2567-2021.

[0142] 2)Tg

[0143] Experimental Groups: Six experimental groups were set up, namely Experimental Groups 1 to 6. Experimental Groups 1 to 6 adopted the molding processes of Examples 1 to 3 and Comparative Examples 1 to 3, respectively. Each group had 3 product samples, for a total of 18 samples. The volume and weight of each product sample were equivalent.

[0144] Experimental method: Tg was measured at room temperature according to GB / T 19466-2019.

[0145] 3) Heat distortion temperature

[0146] Experimental Groups: Six experimental groups were set up, namely Experimental Groups 1 to 6. Experimental Groups 1 to 6 adopted the molding processes of Examples 1 to 3 and Comparative Examples 1 to 3, respectively. Each group had 5 product samples, for a total of 30 samples. The volume and weight of each product sample were equivalent.

[0147] Experimental method: The heat distortion temperature was determined according to GB / T 1634-2019 at room temperature.

[0148] The test results of the sample are shown in Table 2.

[0149] Table 2

[0150]

[0151] As shown in Table 2, the samples from Examples 1-3 and Comparative Examples 1-3 all exhibited good mechanical and thermal properties. During the curing process, higher temperatures and longer curing times resulted in a higher degree of curing, which was more conducive to the formation of a three-dimensional network structure through intermolecular cross-linking, thus improving strength. However, at the same time, the mobility of molecular chains was limited, leading to a slight decrease in toughness.

[0152] During the initial curing stage, the material gradually transforms from a liquid state into a solid state with a certain strength. The temperature of the first curing stage significantly impacts the appearance quality. By employing a multi-stage curing process, excellent appearance quality can be achieved while ensuring both mechanical and thermal properties. Although Comparative Examples 1-3 meet the requirements for mechanical and thermal properties, these properties primarily refer to the material samples. In actual product manufacturing, defects such as shrinkage, unevenness, or roughness on the epoxy resin surface make it difficult to achieve a tight fit with stress cones and other components during installation, easily leading to air trapping. During long-term energized operation, air can trigger partial discharge, causing creepage and even breakdown of the epoxy resin insulation layer. Therefore, appearance quality significantly affects the safety of line operation, especially in high-voltage applications, posing a significant operational risk. The epoxy resin material in this embodiment exhibits excellent overall performance and a high product appearance yield, better meeting the application requirements of insulation products such as large-size, high-voltage cable accessories.

[0153] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A molding process for an epoxy resin product, characterized in that, Includes the following steps: The raw materials, including epoxy resin, silica powder, and anhydride curing agent, are mixed and then cast to obtain an epoxy resin product. The casting conditions are as follows: first stage curing: curing at 105-120℃ for 3-10 hours; second stage curing: curing at 130-135℃ for 16-22 hours. The raw materials for preparation include, by mass, 100 parts epoxy resin, 30-50 parts acid anhydride curing agent, and 200-320 parts silica powder; wherein the epoxy resin is a solid bisphenol A type epoxy resin with an epoxy value of 2.4-2.65 Eq / kg and a viscosity of 370-550 mPa·s at 120℃.

2. The molding process for epoxy resin products according to claim 1, characterized in that, The mixing process includes: first mixing the preparation raw materials, including epoxy resin and silicon powder, at a temperature where the epoxy resin is in a liquid state to obtain a first mixture; then adding an acid anhydride curing agent to the first mixture and mixing it a second time to obtain a second mixture. Optionally, the heating temperature is 125–130°C; Optionally, the temperature of the first mixing is 125–130°C; Optionally, the anhydride curing agent is preheated before being added to the first mixture; Optionally, the first mixing is followed by vacuum degassing.

3. The molding process for the epoxy resin product according to claim 1, characterized in that, The second stage of curing includes: curing at 130-135℃ for 4-7 hours, demolding, and continuing to cure at 130-135℃ for 12-15 hours.

4. The molding process for epoxy resin products according to claim 1, characterized in that, The anhydride curing agent includes at least one of methyltetrahydrophthalic anhydride and a composition of methyltetrahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol, wherein the mass fraction of 2,4,6-tris(dimethylaminomethyl)phenol in the composition is 0.1% to 3%.

5. The molding process for the epoxy resin product according to claim 4, characterized in that, The anhydride curing agent is selected from the first methyltetrahydrophthalic anhydride, and the casting molding conditions are as follows: first stage curing: curing at 116-120℃ for 9-10 hours; second stage curing: curing at 130-135℃ for 18-22 hours; Optionally, the second curing stage includes: curing at 130–135°C for 6–7 hours, demolding, and continuing curing at 130–135°C for 12–15 hours.

6. The molding process for the epoxy resin product according to claim 4, characterized in that, The anhydride curing agent is selected from a composition of 2,4,6-tris(dimethylaminomethyl)phenol, and the casting molding conditions are: first stage curing: curing at 105-110℃ for 3-5 hours, second stage curing: curing at 130-135℃ for 16-20 hours; Optionally, the second curing stage includes: curing at 130–135°C for 4–5 hours, demolding, and continuing curing at 130–135°C for 12–15 hours.

7. The molding process for the epoxy resin product according to claim 4, characterized in that, The anhydride curing agent is selected from the first methyltetrahydrophthalic anhydride and the composition of the second methyltetrahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol. By mass, the first methyltetrahydrophthalic anhydride is 20-30 parts and the composition of the second methyltetrahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol is 10-20 parts. The casting conditions are as follows: first stage curing: curing at 111-115℃ for 6-7 hours; second stage curing: curing at 130-135℃ for 17-21 hours. Optionally, the second curing stage includes: curing at 130–135°C for 5–6 hours, demolding, and continuing curing at 130–135°C for 12–15 hours.

8. The molding process for the epoxy resin product according to claim 1, characterized in that, The raw materials for preparation also include color powder, and the mixture consists of epoxy resin, silica powder, acid anhydride curing agent and color powder.

9. The molding process for the epoxy resin product according to claim 1, characterized in that, The casting process includes preheating the mold before casting; and / or cooling the mold at a uniform rate after casting.

10. The application of the molding process of the epoxy resin product as described in any one of claims 1-9 in the preparation of insulating products.

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