Low-temperature fast-curing epoxy prepreg for battery cover and preparation method of low-temperature fast-curing epoxy prepreg

Abstract

The invention discloses a low-temperature fast-curing epoxy prepreg for a battery cover and a preparation method of the low-temperature fast-curing epoxy prepreg, and particularly relates to the field of preparation of epoxy prepregs. The method comprises the following steps: premixing an epoxy resin matrix and a solvent, adding a curing agent, an accelerant, a flexibilizer and a KH-550 silane coupling agent, adding the flexibilizer, and carrying out high-speed shearing dispersion; selecting electronic-grade glass fiber cloth; controlling the viscosity of the glue solution and the dipping speed, and carrying out dipping and baking treatment; segmented baking is adopted, the pre-drying temperature is 65-85 DEG C / 30-50 sec, and the pre-curing temperature is 95-110 DEG C / 30-50 sec; the curing temperature is 115-120 DEG C, and the curing time is 2-4 minutes. A low-temperature segmented curing process is adopted, the temperature is accurately controlled, excessive curing or insufficient pre-curing of the resin is avoided, and low-temperature rapid curing is achieved.

Description

Technical Field

[0001] The present invention relates to the field of epoxy prepreg preparation, and in particular to a low-temperature fast-curing epoxy prepreg for a battery cover and a preparation method thereof. Background Art

[0002] Consumer electronic products, such as battery covers for mobile phones and tablets, usually need to be lightweight and durable, and may have requirements for production cycles. Therefore, low-temperature fast curing should refer to rapid curing at relatively low temperatures, which can save energy, improve production efficiency, and avoid potential damage to composite materials (such as leather, coatings, etc.) caused by high temperatures.

[0003] Chinese patent CN109504033A discloses a flexible prepreg and a method for preparing the same. The prepreg comprises a reinforcing material and an epoxy resin composition attached to the reinforcing material after impregnation and drying. The epoxy resin composition comprises the following raw materials in parts by weight: 80-120 parts of epoxy resin, 30-50 parts of phenoloxy resin, 25-45 parts of phenoxy resin, 20-40 parts of flexible long-chain resin, 15-35 parts of benzoxazine resin, 10-30 parts of phosphorus-containing phenolic resin, 10-20 parts of core-shell rubber, 20-60 parts of filler, 5-15 parts of flexible amine curing agent, 5-15 parts of acid anhydride curing agent, 8-12 parts of flexible long-chain resin curing agent, 4-8 parts of curing accelerator, and 20-60 parts of additives. However, although this patent adds a variety of curing agents, which can reduce the curing temperature to a certain extent, this patent requires a long baking time, especially under low temperature conditions, it takes more than ten hours to fully cure. Even if the temperature is increased to 180°C, the curing time still needs 2-3 hours, which is a long curing time.

[0004] Chinese patent CN116284918A discloses a method for preparing a high-toughness, fast-curing epoxy prepreg for a mobile phone battery cover, comprising the following steps: epoxy resin glue batching, epoxy resin glue preparation, reinforcing material impregnation, epoxy prepreg preparation, epoxy prepreg cutting, and target epoxy prepreg storage. The production of cured epoxy prepregs requires epoxy resin glue and reinforcing material, and the raw materials of the epoxy resin glue are, by mass, 30-50 parts of phosphorus-containing epoxy resin, 20-40 parts of phenoxy resin, 45-65 parts of base epoxy resin, 10-15 parts of isocyanate-modified epoxy resin, 4-6 parts of dicyandiamide, 2-4 parts of diaminophenylsulfone, and 5-10 parts of epoxy accelerator. The reinforcing material is preferably glass fiber cloth. This patent is an earlier patent of the applicant, but the curing conditions of the fast-curing epoxy semi-cured sheet in this patent are a temperature of 135-150°C and a curing time of 8-10 minutes. At the same time, most of the glass fiber battery covers of consumer electronic products are 3D one-piece molded (special-shaped parts, non-planar molding), and the 3D one-piece molding equipment uses a molding method. If the curing time is too long, the production efficiency is extremely low. Therefore, the development of fast-curing products meets industry needs. Summary of the Invention

[0005] To this end, the present invention provides a low-temperature, fast-curing epoxy prepreg for a battery cover and a preparation method thereof, in order to solve the problems of the prior art.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] According to the present invention, a method for preparing a low-temperature, fast-curing epoxy prepreg for a battery cover is provided, the method comprising:

[0008] Step 1: Preparation of resin glue

[0009] First, premix the epoxy resin matrix and solvent under low-speed stirring, then add the curing agent, accelerator, KH-550 silane coupling agent and toughening agent, continue low-speed stirring and high-speed shear dispersion to make the materials dispersed evenly;

[0010] Step 2: Strengthen the substrate

[0011] Use electronic grade glass fiber cloth with a thickness of 2116 or less that has been treated with fiber opening and coupling agent;

[0012] Step 3: Impregnation and semi-curing

[0013] Control the viscosity of the glue and the dipping speed to carry out dipping;

[0014] Using segmented baking:

[0015] The pre-drying temperature is 65-85℃ / 30-50sec, and the pre-curing temperature is 95-110℃ / 30-50sec;

[0016] Curing temperature is 115-120℃, and curing time is 2-4min.

[0017] Furthermore, in step 1, the epoxy resin matrix includes a bisphenol F epoxy resin, a modified epoxy resin containing a flexible segment, a phosphorus-containing epoxy resin, a phenoxy resin, and an isocyanate-modified resin. For example, preferably, bisphenol F is the main component, accounting for 40-50%, the flexible modified epoxy resin is 10-20%, the phosphorus-containing epoxy resin is 15-25%, the phenoxy resin is 5-10%, and the isocyanate-modified resin is 5-10%.

[0018] Furthermore, the solvent is acetone or butanone.

[0019] Furthermore, the curing agent is a microencapsulated dicyandiamide curing agent.

[0020] Furthermore, the accelerator is a mixture of an imidazole accelerator and a tertiary amine. As an example, the preferred imidazole accelerator is 2-ethyl-4-methylimidazole, and the preferred tertiary amine accelerator is DMP-30.

[0021] Furthermore, the mass ratio of the imidazole accelerator to the tertiary amine is 1:0.5-1:2.

[0022] Furthermore, the toughening agent is core-shell rubber and fumed silica.

[0023] As an example, the mass percentage of each component is: epoxy resin matrix 60-70%, providing the main resin network; solvent 20-25%, adjusting the viscosity of the glue to facilitate dipping; curing agent 4-6%, low-temperature activation cross-linking; accelerator 1.5-3%, accelerating the curing reaction; toughening agent 3-5%, improving toughness + anti-settling / thixotropy; KH-550 silane coupling agent 5-8%, improving mechanical strength.

[0024] Furthermore, in the step 1, the mixing temperature is controlled below 50°C.

[0025] Furthermore, in step three, the viscosity of the glue solution is 13-30s; the dipping speed is 12-18m / min, and the glue content is 39-60%.

[0026] Furthermore, in step 3, the pre-drying temperature is designed using a temperature gradient. As an example, a preferred temperature gradient design method is 65°C → 85°C, with each stage maintained for 15-25 seconds.

[0027] Furthermore, in step 3, the pre-curing temperature is constant, for example, preferably 110° C. / 30-50 seconds → cooling to room temperature.

[0028] The present invention has the following advantages:

[0029] This invention utilizes low-speed and high-speed shear dispersion methods to ensure uniform material dispersion, improving the homogeneity and mechanical properties of the resin system. This invention utilizes electronic-grade glass fiber cloth with a thickness of 2116 or less, treated with a fiber opening treatment and a surface coupling agent, significantly enhancing the interfacial bonding between the glass fiber cloth and the resin and reducing microporous defects. This invention utilizes a low-temperature, segmented curing process, precisely controlling the temperature to prevent excessive resin flow and achieving low-temperature, rapid curing (≤120°C / 2-4 minutes). DETAILED DESCRIPTION

[0030] The following describes the implementation of the present invention using specific embodiments. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. Obviously, the embodiments described are only a portion of the present invention, not all of it. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0031] Epoxy resin modified with flexible segments: Sailvi, CTBN-modified flexible epoxy resin, product number HQ-3600S;

[0032] Bisphenol F epoxy resin: Olin, DER TM 354;

[0033] Phosphorus epoxy resin: Olin Corporation, phosphorus epoxy resin, PROLOGIC TM BF-140;

[0034] Phenoxy resin: Japan's Mitsubishi Chemical, JER4250;

[0035] Isocyanate modified resin: BASF, Lupranate MM103C modified isocyanate;

[0036] Microencapsulated dicyandiamide curing agent: EH-3842 low-temperature curing microencapsulated dicyandiamide, Chengdu Yuanhang Technology Co., Ltd.

[0037] Non-microencapsulated dicyandiamide curing agent: CAS 461-58-5, Shandong Xinheng Chemical Co., Ltd.

[0038] Surface coupling agent treatment: KH-550 silane coupling agent, CAS 919-30-2;

[0039] Dicyandiamide: CAS No. 461-58-5;

[0040] Diaminophenylsulfone: CAS No. 4273-98-7;

[0041] 2-Ethyl-4-methylimidazole: CAS 931-36-2;

[0042] DMP-30: CAS 90-72-2;

[0043] Fumed silica: CAS112945-52-5

[0044] Core-shell rubber: Japan Kanebuchi, MX-125;

[0045] Electronic grade glass fiber cloth, Changzhou Xingao Insulation Materials Co., Ltd., 2116, warp and weft density: 60*58, thickness: 0.085, basis weight: 105g / ㎡.

[0046] Example 1

[0047] Raw materials: epoxy resin matrix 60%; solvent 25%; curing agent 4%; accelerator 2%; toughening agent 4%; KH-550 silane coupling agent 5%;

[0048] Among them, epoxy resin matrix: bisphenol F type epoxy resin 40%, flexible modified epoxy resin 15%, phosphorus-containing epoxy resin 25%, phenoxy resin 10%, isocyanate modified resin 10%;

[0049] A preparation method of a low-temperature fast-curing epoxy prepreg for a battery cover:

[0050] Step 1: Preparation of resin glue

[0051] Add epoxy resin matrix (bisphenol F epoxy resin, flexible modified epoxy resin, phosphorus-containing epoxy resin, phenoxy resin, isocyanate modified resin) and solvent (acetone or butanone) into the reaction kettle and stir at low speed for 30 minutes at a speed of 300 rpm.

[0052] Add microencapsulated dicyandiamide curing agent and continue stirring at 300 rpm for 20 minutes.

[0053] An accelerator (2-ethyl-4-methylimidazole: DMP-30 mass ratio of 1:0.5) was added and stirred at 300 rpm for 15 minutes.

[0054] Core-shell rubber, KH-550 silane coupling agent and fumed silica were added, and a high-speed shear disperser was started (speed 5000 rpm, time 20 minutes) to disperse the materials uniformly.

[0055] Step 2: Strengthen the substrate

[0056] Use 2116 electronic grade glass fiber cloth, which has been treated with fiber opening and surface coupling agent;

[0057] Step 3: Impregnation and semi-curing

[0058] Use a vertical dipping machine to control the glue viscosity at 13-30s, dipping speed at 12m / min, and glue content at 45%;

[0059] Using segmented baking:

[0060] Pre-drying temperature is 65℃→85℃(30-50sec), pre-curing temperature is 95-110℃ / (30-50sec);

[0061] Curing temperature is 115℃ and curing time is 2-4min.

[0062] Example 2

[0063] Raw materials: epoxy resin matrix 65%; solvent 20%; curing agent 4%; accelerator 2%; toughening agent 4%; KH-550 silane coupling agent 5%;

[0064] Among them, bisphenol F type epoxy resin 45%, flexible modified epoxy resin 15%, phosphorus-containing epoxy resin 20%, phenoxy resin 10%, isocyanate modified resin 10%;

[0065] A preparation method of a low-temperature fast-curing epoxy prepreg for a battery cover:

[0066] Step 1: Preparation of resin glue

[0067] Add epoxy resin matrix (bisphenol F epoxy resin, flexible modified epoxy resin, phosphorus-containing epoxy resin, phenoxy resin, isocyanate modified resin) and solvent (acetone or butanone) into the reaction kettle and stir at low speed for 30 minutes at a speed of 250 rpm.

[0068] Add microencapsulated dicyandiamide curing agent and continue stirring at 250 rpm for 20 minutes.

[0069] An accelerator (2-ethyl-4-methylimidazole: DMP-30 mass ratio of 1:1) was added, and the mixture was stirred at 250 rpm for 15 minutes.

[0070] The core-shell rubber, KH-550 silane coupling agent and fumed silica were added, and the high-speed shear disperser was started (rotation speed 6000 rpm, time 20 minutes).

[0071] Step 2: Strengthen the substrate

[0072] Use 2116 electronic grade glass fiber cloth, which has been treated with fiber opening and surface coupling agent;

[0073] Step 3: Impregnation and semi-curing

[0074] Use a vertical dipping machine to control the glue viscosity at 13-30s, dipping speed at 15m / min, and glue content at 50%;

[0075] Using segmented baking:

[0076] Pre-drying temperature is 65℃→85℃(15-30sec), pre-curing temperature is 95-110℃ / (30-50sec);

[0077] Curing temperature is 118℃ and curing time is 2-4min.

[0078] Example 3

[0079] Raw materials: epoxy resin matrix 68%; solvent 20%; curing agent 4.5%; accelerator 1.5%; toughening agent 3%; KH-550 silane coupling agent 5%;

[0080] Among them, bisphenol F type epoxy resin 50%, flexible modified epoxy resin 10%, phosphorus-containing epoxy resin 25%, phenoxy resin 10%, isocyanate modified resin 5%;

[0081] A preparation method of a low-temperature fast-curing epoxy prepreg for a battery cover:

[0082] Step 1: Preparation of resin glue

[0083] Add epoxy resin matrix (bisphenol F epoxy resin, flexible modified epoxy resin, phosphorus-containing epoxy resin, phenoxy resin, isocyanate modified resin) and solvent (acetone or butanone) into the reaction kettle and stir at low speed for 30 minutes at a speed of 200 rpm.

[0084] Add microencapsulated dicyandiamide curing agent and continue stirring at 200 rpm for 20 minutes.

[0085] An accelerator (2-ethyl-4-methylimidazole: DMP-30 mass ratio of 1:1) was added and stirred at 200 rpm for 15 minutes.

[0086] The core-shell rubber, KH-550 silane coupling agent and fumed silica were added, and the high-speed shear disperser was started (rotation speed 8000 rpm, time 30 minutes).

[0087] Step 2: Strengthen the substrate

[0088] Use 2116 electronic grade glass fiber cloth, which has been treated with fiber opening and surface coupling agent;

[0089] Step 3: Impregnation and semi-curing

[0090] Use a vertical dipping machine to control the glue viscosity at 13-30s, dipping speed at 18m / min, and glue content at 45%;

[0091] Using segmented baking:

[0092] The pre-drying temperature is 65℃→85℃(30-50sec), and the pre-curing temperature is 110℃(30-50sec);

[0093] Curing temperature is 120℃ and curing time is 2-4min.

[0094] Comparative Example 1

[0095] This comparative example provides a method for preparing a low-temperature, fast-curing epoxy prepreg for a battery cover:

[0096] The microcapsule curing agent of Example 1 was replaced by a flexible amine curing agent, which was a mixture of poly-1,4-butylene glycol bis(4-aminobenzoate) and poly(1,4-butylene glycol-3-methyl-1,4-butylene glycol) ether bis(4-aminobenzoate) in a weight ratio of 2:1; the anhydride curing agent was an alternating copolymer of styrene and maleic anhydride, with a molar ratio of styrene to maleic anhydride of 3:1 and a weight-average molecular weight of 60,000. The flexible long-chain resin curing agent was a mixture of modified isocyanate, isocyanate-terminated polyurethane prepolymer, and isocyanate-terminated silicone prepolymer in a weight ratio of 1:1.2:2.2; the isocyanate was a mixture of diphenylmethane diisocyanate, dimethylbiphenyl diisocyanate, and polymethylene-p-phenylene isocyanate in a weight ratio of 2.5:1.5:1.

[0097] Curing temperature 115℃, curing time 6h;

[0098] Other details are exactly the same as in Example 1.

[0099] Flexible amine curing agents have relatively low activity and react slowly at lower temperatures, resulting in extended curing times. Furthermore, in Comparative Example 1, the entire curing system includes multiple types of curing agents, namely, flexible amine curing agents, anhydride curing agents, and flexible long-chain resin curing agents. These curing agents may interact and restrict each other, resulting in a reduced overall curing reaction rate and extended curing times. The reaction rates of various curing agents and matrices such as epoxy resins may differ, and the reaction stages of different curing agents are asynchronous, making it impossible to form an effective synergistic curing effect, thereby extending the duration of the entire curing process.

[0100] Comparative Example 2

[0101] This comparative example provides a method for preparing a low-temperature, fast-curing epoxy prepreg for a battery cover:

[0102] The microcapsule curing agent of Example 1 was replaced by a non-microencapsulated dicyandiamide curing agent.

[0103] Curing temperature is 180℃ and curing time is 3h.

[0104] Comparative Example 3

[0105] This comparative example provides a method for preparing a low-temperature, fast-curing epoxy prepreg for a battery cover:

[0106] In this comparative example, the bisphenol F epoxy resin is 30% and the flexible modified epoxy resin is 25%; the other contents are completely the same as those in Example 1.

[0107] Comparative Example 4

[0108] This comparative example provides a method for preparing a low-temperature, fast-curing epoxy prepreg for a battery cover:

[0109] In this comparative example, bisphenol F epoxy resin is 50% and flexible modified epoxy resin is 5%; the other contents are completely the same as those in Example 1.

[0110] Comparative Example 5

[0111] This comparative example provides a method for preparing a low-temperature, fast-curing epoxy prepreg for a battery cover:

[0112] Using segmented baking:

[0113] The pre-curing temperature is constant at 120° C. for 30-60 seconds. Other steps are the same as those in Example 1.

[0114] Comparative Example 6

[0115] This comparative example provides a method for preparing a low-temperature, fast-curing epoxy prepreg for a battery cover:

[0116] No segmented baking is used: no pre-drying step; otherwise, the same as in Example 1.

[0117] Comparative Example 7

[0118] This comparative example provides a method for preparing a low-temperature, fast-curing epoxy prepreg for a battery cover:

[0119] The microcapsule curing agent in Example 1 was replaced with dicyandiamide and diaminophenylsulfone.

[0120] Curing temperature is 150℃ and curing time is 8min.

[0121] Experimental example

[0122] The performance indicators of Examples 1-3 and Comparative Examples 1-6 are compared, as shown in Table 1.

[0123] Table 1

[0124]

[0125] In Comparative Example 1, although the performance and feasibility of the mixed curing agents are comparable, the reaction is slow and the production efficiency is low. In Comparative Example 2, non-microcapsule dicyandiamide is used as a curing agent, which requires a higher temperature for curing. It is impossible to achieve a smaller melt viscosity at low temperature and the curing is incomplete, resulting in the semi-cured surface resin not being leveled and the interior not reaching a dense state, making the board appearance poor, heat resistance poor, and the bonding strength between the prepreg layers and the bonding strength between the prepreg and the leather material poor. In Comparative Example 3, the flexible segment ratio is too high, which reduces the cross-linking density and rigidity, and the ability to resist thermal stress, composite shrinkage stress, etc. decreases and the warpage becomes larger; the flexible resin improves the interface toughness, but excessive amounts cause the resin and fiber bonding to decrease; the increase in flexible segments causes a slight decrease in thermal stability; the imbalance in the flexible resin ratio may cause phase separation and shorten the shelf life. In Comparative Example 4, the proportion of bisphenol F is high and the cross-linking density is large, but the lack of flexibility leads to a decrease in bending strength; the rigid resin is dominant, with high tensile strength but insufficient toughness; the high-rigidity resin improves bending resistance, but is prone to brittle fracture; excessive rigidity leads to a decrease in interfacial bonding; high cross-linking density improves thermal stability; the resin system has good homogeneity, but insufficient flexibility makes it easy to break when bent. In Comparative Example 5, constant temperature pre-curing leads to uneven solvent volatilization and lack of cross-linking gradient; uneven curing reaction rate and local stress concentration; the pre-curing stage is not optimized, and the interfacial bonding strength is slightly reduced; local defects in the cross-linked network affect thermal stability; the simplified curing process may lead to an increase in the proportion of residual solvents and other volatiles, reducing heat resistance. In Comparative Example 6, there is no pre-curing step, and one-step curing leads to insufficient cross-linking and a loose network; the lack of pre-curing leads to poor bonding between the resin and the fiber; incomplete curing significantly reduces the overall strength of the material; the risk of interfacial delamination increases; the cross-linking density is low and the thermal decomposition temperature is significantly reduced; the uncured residual components are susceptible to thermal expansion or volatilization, leading to blistering and delamination. Comparative Example 7 uses dicyandiamide and diaminophenylsulfone as curing agents, which require higher temperatures for curing. Curing at low temperatures results in incomplete mechanical properties and poor adhesion to leather and interlayers. The present invention, through microcapsule curing technology, a staged baking process, and resin system optimization, achieves synergistic improvements in reactivity, mechanical strength, peel strength, and heat resistance while achieving rapid low-temperature curing (≤120°C / ≤90s), resulting in significantly better overall performance than the comparative example.

[0126] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made thereto. Therefore, such modifications and improvements, without departing from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for preparing a low-temperature fast-curing epoxy prepreg for a battery cover, characterized in that: The method comprises: Step 1: Preparation of resin glue First, premix the epoxy resin matrix and solvent, then add the curing agent, accelerator, toughening agent and KH-550 silane coupling agent, and then add the toughening agent and disperse it evenly by continuous low-speed stirring and high-speed shearing. Step 2: Strengthen the substrate Use electronic grade glass fiber cloth; Step 3: Impregnation and semi-curing Control the viscosity of the glue and the dipping speed to carry out the dipping process; Using segmented baking: The pre-drying temperature is 65-85℃ / 30-50sec, and the pre-curing temperature is 95-110℃ / 30-50sec; Curing temperature is 115-120℃, and curing time is 2-4min.

2. The method for preparing a low-temperature fast-curing epoxy prepreg for a battery cover according to claim 1, characterized in that: In the step 1, the epoxy resin matrix includes bisphenol F epoxy resin, flexible segment-modified epoxy resin, phosphorus epoxy resin, phenoxy resin and isocyanate modified resin.

3. The method for preparing a low-temperature fast-curing epoxy prepreg for a battery cover according to claim 1, characterized in that: The curing agent is a microencapsulated dicyandiamide curing agent.

4. The method for preparing a low-temperature fast-curing epoxy prepreg for a battery cover according to claim 1, characterized in that: The accelerator is a mixture of an imidazole accelerator and a tertiary amine.

5. The method for preparing a low-temperature fast-curing epoxy prepreg for a battery cover according to claim 4, characterized in that: The mass ratio of the imidazole accelerator to the tertiary amine is 1:0.5-1:

2.

6. The method for preparing a low-temperature fast-curing epoxy prepreg for a battery cover according to claim 1, characterized in that: The toughening agents are core-shell rubber and fumed silica.

7. The method for preparing a low-temperature fast-curing epoxy prepreg for a battery cover according to claim 1, characterized in that: In the step 1, the mixing temperature is controlled below 50°C.

8. The method for preparing a low-temperature fast-curing epoxy prepreg for a battery cover according to claim 1, characterized in that: In the step 3, the viscosity of the glue is 13-30s; and the dipping speed is 12-18m / min.

9. The method for preparing a low-temperature fast-curing epoxy prepreg for a battery cover according to claim 1, characterized in that: In the step 3, the pre-drying temperature is designed with a temperature gradient.

10. The method for preparing a low-temperature fast-curing epoxy prepreg for a battery cover according to claim 1, characterized in that: In the step 3, the pre-curing temperature is constant.

Images