Molding process and application of epoxy resin product

Abstract

The invention discloses a forming process and application of an epoxy resin product. The molding process comprises the following steps: mixing preparation raw materials including epoxy resin, silica powder and an anhydride curing agent, and carrying out casting molding to obtain an epoxy resin product, wherein the conditions of casting molding are as follows: first-stage curing: curing at 105-120 DEG C for 3-10 hours; second-stage curing is conducted, specifically, curing is conducted for 16-22 h at the temperature of 130-135 DEG C; wherein the epoxy resin is solid bisphenol A type epoxy resin, the epoxy value of the epoxy resin is 2.4-2.65 Eq / kg, and the viscosity of the epoxy resin at 120 DEG C is 370-550 mPa.s. According to the process, an epoxy resin product with excellent performance can be prepared, the appearance quality of the molded epoxy resin product is good, and the process can be used for producing large-size and high-voltage-grade insulating products. The invention further provides application of the forming process.

Description

Technical Field

[0001] The invention relates to the technical field of epoxy materials, and in particular to a molding process of an epoxy resin product and application thereof. Background Art

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

[0003] With the continuous development of technology, such as the increase in voltage level or product size, higher requirements are placed on the safety, reliability and appearance of materials. It is difficult for existing epoxy materials to simultaneously guarantee comprehensive performance such as electrical performance and mechanical performance, and it is difficult to effectively take into account the appearance of the molded product while improving the comprehensive 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 with high molding difficulty.

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

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

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

[0007] The first embodiment of the present invention relates to a molding process for an epoxy resin product, comprising the following steps: mixing raw materials including epoxy resin, silicon powder, and anhydride curing agent, and performing casting molding to obtain an epoxy resin product; wherein the casting molding conditions are: first stage curing: curing at 105-120° C. for 3-10 hours; second stage curing: curing at 130-135° C. for 16-22 hours;

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

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

[0010] Casting molding adopts segmented curing. The curing temperature of the first stage is relatively low, which helps to reduce the curing stress inside the material and reduce the occurrence of internal defects. The curing temperature of the second stage is appropriately increased, which can make the cross-linking process more complete and improve the strength and toughness of the material. The curing temperature of the second stage is not too high, which can reduce energy consumption, shorten cooling time and improve processing efficiency.

[0011] By reasonably controlling the segmented curing process parameters, the problems of poor material toughness and stress concentration caused by excessively high curing temperature are avoided, thereby ensuring the performance of the epoxy resin. At the same time, the multiple advantages of product appearance quality and production efficiency are taken into account to meet the requirements of large-scale industrial production, especially in the field of large-size, high-voltage insulating products (such as GIS terminals, composite bushing terminals and other cable accessories). It has significant application prospects.

[0012] In terms of raw materials, specific bisphenol A epoxy resin, anhydride curing agent and silicon powder are selected as the main raw materials to obtain excellent electrical properties, mechanical properties, durability and flame retardancy. Bisphenol A epoxy resin has low cost, good mechanical properties and electrical insulation. Its suitable epoxy value ensures the smoothness of curing, ensures the high strength and high toughness of the product, and avoids cracking problems in high or low temperature environments. The reaction of anhydride curing agents is relatively mild. After curing, the product has a low shrinkage rate and high dimensional stability, which reduces internal stress, significantly enhances the mechanical and electrical properties of the product under different temperature environments, and improves the service life of the product. As a filler, silicon powder has excellent thermal stability, dimensional stability and electrical insulation compared with conventional flame retardant fillers; its low expansion coefficient and excellent strengthening and toughening effect improve the strength and toughness of the material, while reducing dielectric loss. The environmental protection and cost advantages of silicon powder make the material have a wider application prospect 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 powder for the first time at a temperature where the epoxy resin is heated to a liquid state to obtain a first mixture; adding an anhydride curing agent to the first mixture, mixing for a second time to obtain a second mixture, and using the second mixture for casting molding.

[0014] First, mix the epoxy resin and silica powder and other components to avoid premature reaction of the curing agent, reduce the pouring viscosity, and help improve the molding speed and production efficiency. The process is simple and easy to operate, and can stably produce epoxy resin products with excellent electrical properties, mechanical properties and appearance quality, especially 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 adding the anhydride curing agent into 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, demoulding, and continuing to cure at 130-135° C. for 12-15 hours. In actual production, part of the second stage of curing is carried out in the mold, and then demoulding is performed for post-curing, which can shorten the cooling time of the mold and improve production efficiency.

[0019] According to some embodiments of the present invention, the casting molding includes preheating the mold before casting. The preheating temperature is reasonably selected according to the amount and temperature of the casting material so that the temperature of the casting material after entering the mold is close to the curing temperature, reducing the process fluctuation caused by the temperature difference. For example, when the temperature of the casting material is lower than the actual curing temperature, the preheating temperature of the mold can be appropriately increased. The mold preheating time is easy to reasonably select based on experience and the size of the mold to make the temperature as uniform as possible. Especially for large-sized molds, the temperature difference is reduced through the preheating process to prevent unevenness during the curing process.

[0020] According to some embodiments of the present invention, the temperature is lowered before demoulding to facilitate smooth demoulding. The present invention does not restrict the cooling rate, and 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. Properly increasing the cooling rate can improve production efficiency.

[0021] According to some embodiments of the present invention, the anhydride curing agent includes at least one of a first methyltetrahydrophthalic anhydride and a second methyltetrahydrophthalic anhydride and a composition of 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 can be selected to be 0.1%, 0.5%, 1%, 2%, 3% or any value therebetween.

[0022] By using an appropriate amount of 2,4,6-tris(dimethylaminomethyl)phenol to modify methyltetrahydrophthalic anhydride, the ring-opening reaction of the epoxy group can be effectively promoted, making it easier for the epoxy molecules to react chemically with methyltetrahydrophthalic anhydride, thereby accelerating the curing rate of the epoxy resin. On this basis, a lower curing temperature and a shorter curing time can be selected within a limited range of process parameters, thereby 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 combination of the second methyltetrahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol; and optionally, the anhydride curing agent is 30 to 45 parts, for example, specifically 30 parts, 35 parts, 40 parts, 45 parts or any value therebetween.

[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°C for 9-10 hours; second stage curing: curing at 130-135°C 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 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 the composition of the second methyltetrahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol, and the casting molding conditions are: the first stage curing: curing at 105-110°C for 3-5h, the second stage curing: curing at 130-135°C for 16-20h.

[0027] According to some embodiments of the present invention, the anhydride curing agent is selected from the composition of the second methyltetrahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol, and the second stage curing includes: curing at 130-135°C for 4-5 hours, demolding, and continuing to cure 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 a combination of 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 to 30 parts by mass, for example, specifically 20 parts, 25 parts, 28 parts, 30 parts or any value therebetween; the second methyltetrahydrophthalic anhydride and 2,4,6-tris (dimethylaminomethyl) phenol composition is 10 to 20 parts, for example, specifically 10 parts, 14 parts, 18 parts, 20 parts or any value therebetween, and the casting molding conditions are: first stage curing: curing at 111 to 115°C for 6 to 7 hours, second stage curing: curing at 130 to 135°C for 17 to 21 hours. Specifically, the second stage curing includes: after curing at 130 to 135°C for 5 to 6 hours, demoulding, and continuing to cure at 130 to 135°C for 12 to 15 hours.

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

[0031] It should be understood that the temperature parameters of the first stage curing and the second stage curing can be appropriately adjusted according to specific needs to obtain corresponding product performance. For example, when the temperature or time of the first stage curing is shortened, the temperature and time of the second stage curing can be correspondingly extended. For a more active curing system (for example, a composition comprising a second methyltetrahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol), the temperature and / or time of the two stages of curing can be appropriately shortened. Therefore, the process parameters listed above are only for reference examples and are not intended to be restrictive provisions.

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

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

[0034] According to some embodiments of the present invention, the average particle size of the silicon powder is 25 to 40 μm, for example, 25 μm, 30 μm, 35 μm, 40 μm or any value therebetween.

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

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

[0037] According to some embodiments of the present invention, the raw materials for preparation further include toner, and the mixing includes: mixing the raw materials for preparation including epoxy resin, silica powder, anhydride curing agent, and toner. Toner is used for coloring, and the present invention has no special requirements on the type and amount of toner, which can be freely selected according to coloring requirements. For example, common types such as iron oxide red, chrome yellow, chrome green, and titanium dioxide can be used. The amount of toner is usually determined according to the coloring depth and hiding power, and the reference amount is 0.1% to 5% of the mass of the epoxy resin.

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

[0039] According to some embodiments of the present invention, before adding the anhydride curing agent to the first mixture, the anhydride curing agent is preheated to reduce the temperature difference caused by the addition of the curing agent, so that casting and molding can be carried out quickly after mixing, thereby improving production efficiency, reducing the heating time of the curing agent, reducing the volatilization of the curing agent, and avoiding affecting the overall performance of the product due to subsequent uneven preheating.

[0040] In practical applications, the temperature of the first mixture and the anhydride curing agent before the second mixing is appropriately controlled according to the curing temperature of the subsequent casting molding, so that the temperature of the two after mixing is close to the curing temperature, so that casting molding can be carried out directly. In addition, in order to reduce the volatilization of the curing agent, the preheating temperature of the anhydride curing agent should be kept at a low level as much as possible.

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

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

[0043] According to some embodiments of the present invention, vacuum degassing is performed after the first mixing. The present invention does not restrict the conditions of the vacuum degassing. For example, the vacuum degree of the vacuum degassing can be controlled to be no greater than 50Pa.

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

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

[0046] The present invention has no restriction on the time of vacuum degassing treatment in all steps, which can be reasonably selected according to the volume of the material; when the volume of the material increases, the degassing time can be appropriately extended. In addition, there is no restrictive requirement for the stirring process, and a lower stirring rate can be selected to achieve moderate stirring, avoid filler sedimentation, and promote uniform mixing of the materials.

[0047] According to some embodiments of the present invention, the casting 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 0.1-0.5°C / min.

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

[0050] The products prepared by this molding process have excellent appearance, electrical insulation properties and mechanical properties, and are suitable for high-voltage, large-size electrical insulation products, such as cable accessories.

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

[0052] The molding process and material formulation of the present invention significantly improve the performance of the product (such as electrical insulation performance and mechanical properties), and can obtain excellent appearance quality, thereby improving the product yield. These advantages enable the product to be used in harsh environments, such as voltage conditions up to 330kV, thereby enhancing the reliability and stability of the product.

[0053] According to some embodiments of the present invention, the insulating product includes cable accessories, such as GIS terminals, composite bushing terminals, combined prefabricated joints, double-way heads, etc.

[0054] As used herein, reference to numerical ranges includes the end values ​​and any subset range within the range; and reference to the above includes the number itself, for example, reference to 2 and above includes 2.

[0055] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 These are example pictures showing whether the product sample appearance is qualified or not.

[0057] Figure 2 This is an example of the X-ray test results of a product sample, where Figure 2 a shows the presence of bubbles inside the resin. Figure 2 b shows the presence of bubbles at the interface between the resin and the metal insert. DETAILED DESCRIPTION

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

[0059] In the following examples and comparative examples, the relevant raw materials are described as follows:

[0060] Epoxy resin: bisphenol A epoxy resin, epoxy value 2.44-2.63 Eq / kg, viscosity (120°C) 370-550 mPa·s.

[0061] Curing agent A: methyltetrahydrophthalic anhydride, acid value of 660-685 mgKOH / g, viscosity of no more than 50 mPa·s, anhydride mass content of more 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 30 μm and a mass purity of more than 99.5%.

[0064] Toner: Red iron oxide, average particle size is 30 μm.

[0065] Unless otherwise specified, the raw materials or equipment involved are conventional raw materials or equipment that can be purchased commercially.

[0066] Example 1

[0067] In this embodiment, an epoxy resin material is prepared, which includes the following raw materials by weight: 100 parts of epoxy resin, 42 parts of curing agent (curing agent A), 250 parts of filler, and 1 part of color powder.

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

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

[0070] 2) Keeping the mixture at a constant temperature, vacuum degassing the mixture while stirring, with a vacuum degree of no more than 50 Pa, for 180 to 240 minutes, until no obvious bubbles appear on the surface of the mixture;

[0071] 3) Under a constant temperature of 60°C, the curing agent is subjected to vacuum degassing treatment while being stirred, with a vacuum degree of no more than 100 Pa, and the treatment time is 60 to 90 minutes, until there are no obvious bubbles on the surface;

[0072] 4) The treated mixture and curing agent are conveyed to a static mixer by pressure according to the proportion, and then poured into a mold preheated for 4 to 5 hours at 125 to 130°C. In a forced air oven, the initial curing is carried out according to the molding process of curing at 118°C for 9 hours and 135°C for 7 hours;

[0073] 5) Cooling the mixture to 100-110°C at a rate of 0.55°C / min in a blast oven and demoulding the mixture;

[0074] 6) Curing at 135°C for 15 h, and then cooling to room temperature at a cooling rate of 0.15°C / min.

[0075] Example 2

[0076] In this embodiment, an epoxy resin material is prepared, which includes the following raw materials by mass: 100 parts of epoxy resin, 42 parts of curing agent (28 parts of curing agent A, with a mass percentage of 66.7%; 14 parts of curing agent B, accounting for 33.3%), 250 parts of filler, and 1 part of color powder.

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

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

[0079] 2) Keeping the mixture at a constant temperature, vacuum degassing the mixture while stirring, with a vacuum degree of no more than 50 Pa, for 180 to 240 minutes, until no obvious bubbles appear on the surface of the mixture;

[0080] 3) Under a constant temperature of 60°C, the curing agent is subjected to vacuum degassing treatment while being stirred, with a vacuum degree of no more than 100 Pa, and the treatment time is 60 to 90 minutes, until there are no obvious bubbles on the surface;

[0081] 4) The treated mixture and curing agent are conveyed to a static mixer by pressure according to the proportion, and then poured into a mold preheated for 4 to 5 hours at 125 to 130°C. In a forced air oven, the initial curing is carried out according to the molding process of curing at 112°C for 7 hours and 135°C for 6 hours;

[0082] 5) Cooling the mixture to 100-110°C at a rate of 0.55°C / min in a blast oven and demoulding the mixture;

[0083] 6) Curing at 135°C for 15 h, and then cooling to room temperature at a cooling rate of 0.15°C / min.

[0084] Example 3

[0085] In this embodiment, an epoxy resin material is prepared, which includes the following raw materials, calculated by weight: 100 parts of epoxy resin, 42 parts of curing agent (curing agent B), 250 parts of filler, and 1 part of color powder.

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

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

[0088] 2) Keeping the mixture at a constant temperature, vacuum degassing the mixture while stirring, with a vacuum degree of no more than 50 Pa, for 180 to 240 minutes, until no obvious bubbles appear on the surface of the mixture;

[0089] 3) Under a constant temperature of 60°C, the curing agent is subjected to vacuum degassing treatment while being stirred, with a vacuum degree of no more than 100 Pa, and the treatment time is 60 to 90 minutes, until there are no obvious bubbles on the surface;

[0090] 4) The treated mixture and curing agent are conveyed to a static mixer by pressure according to the proportion, and then poured into a mold preheated for 4 to 5 hours at 125 to 130°C. In a forced air oven, the initial curing is carried out according to the molding process of curing at 108°C for 5 hours and 135°C for 5 hours;

[0091] 5) Cooling the mixture to 100-110°C at a rate of 0.55°C / min in a blast oven and demoulding the mixture;

[0092] 6) Curing at 135°C for 15 h, and then cooling to room temperature at a cooling rate of 0.15°C / min.

[0093] Comparative Example 1

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

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

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

[0097] 2) Keeping the mixture at a constant temperature, vacuum degassing the mixture while stirring, with a vacuum degree of no more than 50 Pa, for 180 to 240 minutes, until no obvious bubbles appear on the surface of the mixture;

[0098] 3) Under a constant temperature of 60°C, the curing agent is subjected to vacuum degassing treatment while being stirred, with a vacuum degree of no more than 100 Pa, and the treatment time is 60 to 90 minutes, until there are no obvious bubbles on the surface;

[0099] 4) The treated mixture and curing agent are conveyed to a static mixer by pressure according to the proportion, and then poured into a mold preheated for 4 to 5 hours at 125 to 130°C. In a forced air oven, the initial curing is carried out according to the molding process of curing at 126°C for 9 hours and 135°C for 7 hours;

[0100] 5) Cooling the mixture to 100-110°C at a rate of 0.55°C / min in a blast oven and demoulding the mixture;

[0101] 6) Curing at 135°C for 15 h, and then cooling to room temperature at a cooling rate of 0.15°C / min.

[0102] Comparative Example 2

[0103] In this comparative example, an epoxy resin material is prepared, which includes the following raw materials, calculated by mass: 100 parts of epoxy resin, 42 parts of curing agent (28 parts of curing agent A, with a mass percentage of 66.7%; 14 parts of curing agent B, accounting for 33.3%), 250 parts of filler, and 1 part of color powder.

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

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

[0106] 2) Keeping the mixture at a constant temperature, vacuum degassing the mixture while stirring, with a vacuum degree of no more than 50 Pa, for 180 to 240 minutes, until no obvious bubbles appear on the surface of the mixture;

[0107] 3) Under a constant temperature of 60°C, the curing agent is subjected to vacuum degassing treatment while being stirred, with a vacuum degree of no more than 100 Pa, and the treatment time is 60 to 90 minutes, until there are no obvious bubbles on the surface;

[0108] 4) The treated mixture and curing agent are conveyed to a static mixer by pressure according to the proportion, and then poured into a mold preheated for 4 to 5 hours at 125 to 130°C. In a forced air oven, the initial curing is carried out according to the molding process of curing at 124°C for 7 hours and 135°C for 6 hours;

[0109] 5) Cooling the mixture to 100-110°C at a rate of 0.55°C / min in a blast oven and demoulding the mixture;

[0110] 6) Curing at 135°C for 15 h, and then cooling to room temperature at a cooling rate of 0.15°C / min.

[0111] Comparative Example 3

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

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

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

[0115] 2) Keeping the mixture at a constant temperature, vacuum degassing the mixture while stirring, with a vacuum degree of no more than 50 Pa, for 180 to 240 minutes, until no obvious bubbles appear on the surface of the mixture;

[0116] 3) Under a constant temperature of 60°C, the curing agent is subjected to vacuum degassing treatment while being stirred, with a vacuum degree of no more than 100 Pa, and the treatment time is 60 to 90 minutes, until there are no obvious bubbles on the surface;

[0117] 4) The treated mixture and curing agent are conveyed to a static mixer by pressure according to the proportion, and then poured into a mold preheated for 4 to 5 hours at 125 to 130°C. In a forced air oven, the initial curing is carried out according to the molding process of curing at 122°C for 5 hours and 135°C for 5 hours;

[0118] 5) Cooling the mixture to 100-110°C at a rate of 0.55°C / min in a blast oven and demoulding the mixture;

[0119] 6) Curing at 135°C for 15 h, and then cooling to room temperature at a cooling rate of 0.15°C / min.

[0120] Test Case

[0121] 1. Product Testing

[0122] According to the methods of Examples 1 to 3 and Comparative Examples 1 to 3, 110 to 330 kV epoxy bushings were prepared respectively, and metal inserts (such as copper or aluminum) were pre-embedded in the epoxy bushings. Before casting, the metal inserts were placed in the mold in advance to ensure that the final product had built-in metal inserts. Subsequently, the prepared epoxy bushings were subjected to appearance inspection, X-ray inspection, and electrical performance tests.

[0123] 1) Appearance inspection

[0124] Experimental group: The experimental group is set up with 6 groups, namely experimental groups 1 to 6. Experimental groups 1 to 6 adopt the molding processes of Examples 1 to 3 and Comparative Examples 1 to 3, respectively. Each group of Examples 1 to 3 is provided with 50 product samples, totaling 150 samples. Each group of Comparative Examples 1 to 3 is provided with 10 product samples, totaling 30 samples. The volume and weight of each product sample are equivalent.

[0125] Test method: In a well-lit environment, visually inspect the surface of the product sample to see if it is smooth and whether there are shrinkage marks. If the surface is smooth and there are no shrinkage marks, it is qualified; if these conditions are not met, it is considered unqualified. Count the surface quality of each group of samples and calculate the appearance qualification rate. Figure 1 , the left picture shows qualified products, and the right picture shows unqualified products. Figure 1 As shown, the left picture shows qualified products, and the right picture shows unqualified products. It is worth noting that Figure 1 The nonconforming appearance shown in the photo to the right is a typical example and may vary in reality. Shrink marks may not appear obvious in the photo due to the reflection effect when shooting. However, they can be observed more clearly by visual inspection and the unevenness of the surface can be clearly felt by touch.

[0126] 2) X-ray inspection

[0127] Experimental group: There are 6 experimental groups, namely experimental groups 1 to 6. Experimental groups 1 to 6 adopt the molding processes of Examples 1 to 3 and Comparative Examples 1 to 3 respectively. Each group has 5 product samples, totaling 30 samples. Each product sample is selected from the qualified appearance samples in the appearance inspection experimental group in Section 1.

[0128] Experimental method: Place the sample in an X-ray test chamber and observe whether there are bubbles inside the sample resin or at the interface between the resin and the metal insert. If bubbles are detected at any position, the sample is considered unqualified. Figure 2 , Figure 2 a shows an example of X-ray detection results of bubbles inside the resin; Figure 2 b shows an example of X-ray detection results of bubbles at the interface between resin and 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 for reference, and other results may appear in actual detection, or both types of bubbles may exist at the same time.

[0129] 3) Electrical performance test

[0130] Experimental group: In the X-ray inspection experimental group in Section 2, product samples that passed the X-ray inspection were selected for testing. Products that failed the appearance and X-ray inspection did not meet the test conditions.

[0131] Experimental method: Tests are carried out in the following order at ambient temperature: a. Partial discharge test: the test voltage is gradually increased to 222 kV and maintained for 10 seconds, then slowly decreased to 190 kV, and detected whether there is visible discharge exceeding 5 pC background noise; 2) AC withstand voltage test: the test voltage is gradually increased to 318 kV and maintained for 30 minutes, and the sample is detected for flashover or breakdown; 3) Partial discharge test: the test voltage is gradually increased to 222 kV and maintained for 10 seconds, then slowly decreased to 190 kV, and detected whether there is visible discharge exceeding 5 pC background noise.

[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 to 3 all showed excellent appearance quality, met the requirements of relevant national standards for sealing performance and electrical performance, and had no bubbles and air gaps inside, with good bonding interfaces, and were suitable for the production of high-voltage and large-volume cable accessories. In contrast, Comparative Examples 1 to 3 had a violent reaction due to the excessively high molding temperature during the initial curing process, resulting in shrinkage marks of varying degrees, and poor appearance quality. In addition, the violent reaction also caused the viscosity of the material to increase rapidly, and the voids caused by curing shrinkage were not filled in time by the material, thereby generating bubbles and affecting the product yield.

[0137] 2. Test piece test

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

[0139] 1) Mechanical properties:

[0140] Experimental group: There are 6 experimental groups, namely experimental groups 1 to 6. Experimental groups 1 to 6 adopt the molding processes of Examples 1 to 3 and Comparative Examples 1 to 3, respectively. Each group has 5 product samples, totaling 30 samples, and the volume and weight of each product sample are equivalent.

[0141] Experimental method: At room temperature, the impact strength, flexural strength and compressive strength are tested in accordance with GB / T 2567-2021.

[0142] 2) Tg

[0143] Experimental group: There are 6 experimental groups, namely experimental groups 1 to 6. Experimental groups 1 to 6 adopt the molding processes of Examples 1 to 3 and Comparative Examples 1 to 3, respectively. Each group has 3 product samples, totaling 18 samples, and the volume and weight of each product sample are equivalent.

[0144] Experimental method: At room temperature, Tg is carried out according to GB / T 19466-2019.

[0145] 3) Heat deformation temperature

[0146] Experimental group: There are 6 experimental groups, namely experimental groups 1 to 6. Experimental groups 1 to 6 adopt the molding processes of Examples 1 to 3 and Comparative Examples 1 to 3, respectively. Each group has 5 product samples, totaling 30 samples, and the volume and weight of each product sample are equivalent.

[0147] Experimental method: At room temperature, the heat deformation temperature is carried out according to GB / T 1634-2019.

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

[0149] Table 2

[0150]

[0151] From the experimental results in Table 2, the samples of Examples 1 to 3 and Comparative Examples 1 to 3 all exhibit good mechanical and thermal properties. During the curing process, the higher the temperature and the longer the time, the higher the degree of curing, which is more conducive to the intermolecular cross-linking to form a three-dimensional network structure and improve the strength, but at the same time the mobility of the molecular chain is limited, resulting in a slight decrease in toughness.

[0152] In the initial curing stage, the material gradually changes from a liquid state to a solid state with a certain strength. Among them, the temperature of the first stage of curing has a greater impact on the appearance quality. Through the coordination of multi-stage curing processes, excellent appearance quality can be obtained on the basis of ensuring mechanical properties and thermal properties. Although comparative examples 1 to 3 meet the use requirements in terms of mechanical properties and thermal properties, these properties are mainly for material test pieces. In the actual product process, if the epoxy resin surface has defects such as shrinkage, unevenness or roughness, it is difficult to fit tightly with components such as stress cones during engineering installation, and it is easy to be mixed with air. During long-term power-on operation, air may cause partial discharge, lead to creepage, and even cause breakdown of the epoxy resin insulation layer. Therefore, the appearance quality significantly affects the safety of line operation, especially in high-voltage line applications, there are huge operating risks. The epoxy resin material of this embodiment has excellent comprehensive performance and a high product appearance yield, which can better meet the application requirements of insulating products such as large-size and high-voltage grade cable accessories.

[0153] The present invention has been described in detail above in conjunction with the embodiments, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

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

2. The molding process of the epoxy resin product according to claim 1, characterized in that: The mixing includes: mixing the raw materials including epoxy resin and silicon powder for the first time at a temperature where the epoxy resin is in a liquid state to obtain a first mixture; adding an anhydride curing agent to the first mixture and mixing for the 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, before adding the acid anhydride curing agent to the first mixture, the acid anhydride curing agent is preheated; Optionally, a vacuum degassing treatment is performed after the first mixing.

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

4. The molding process of the epoxy resin product according to claim 1, characterized in that: The anhydride curing agent includes 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%.

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

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

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

8. The molding process of the epoxy resin product according to claim 1, characterized in that: The raw materials for preparation also include color powder, and the mixing is: mixing the raw materials for preparation including epoxy resin, silicon powder, anhydride curing agent and color powder.

9. The molding process of the epoxy resin product according to claim 1, characterized in that: The casting molding includes preheating the mold before casting; and / or uniformly cooling the mold after casting.

10. Use of the molding process of the epoxy resin product according to any one of claims 1 to 9 in the preparation of insulating products.

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