A production method of an ultra-smooth MLCC release base film

Abstract

The application discloses a production method of an ultra-smooth MLCC release base film, and comprises the following steps: (1) adopting an in-situ melt polycondensation method, adding terephthalic acid, ethylene glycol and a hydroxyl-terminated dendritic polymer into a polymerization kettle to perform esterification reaction and polycondensation reaction, and preparing dendritic polymer modified PET copolyester chips; (2) adopting a core-shell emulsion polymerization method to prepare fluorosilicon modified polyacrylate coating liquid; (3) adding an adhesion promoter, a curing agent and a solvent into the fluorosilicon modified polyacrylate coating liquid prepared in the step (2), uniformly stirring, and preparing coating liquid; (4) preparing a single-layer PET base film through melt extrusion and bidirectional stretching process by using the dendritic polymer modified PET copolyester chips prepared in the step (1), and coating the coating liquid prepared in the step (3) on the surface of the base film to obtain the ultra-smooth MLCC release base film. The application solves the problem that the coating on the ultra-smooth surface is easy to peel off, and improves the mechanical properties of the base film.

Description

Technical Field

[0001] This invention relates to the field of MLCC release film technology, and specifically to a method for producing an ultra-smooth MLCC release film. Background Technology

[0002] MLCCs are among the most widely used passive components in the electronics industry. Due to their small size, high capacitance density, and high reliability, they are widely used in smartphones, tablets, automobiles, and various consumer electronics products. The MLCC release film plays a crucial role in supporting and protecting the ceramic film during the casting process, requiring characteristics such as high flatness, low roughness, stable release force, high residual adhesion, good paste compatibility, and high tensile strength.

[0003] Release film consists of two parts: a base film and a release layer. The base film is usually made of polyester material, with PET polyester base film being the most widely used. However, ordinary polyester base film cannot meet the process requirements of MLCC because its surface is not smooth enough and has high roughness, which will cause uneven coating after the release agent is applied, directly affecting the processing performance of the release film.

[0004] In existing technologies, multi-layer co-extrusion processes have been used to reduce the surface roughness of release film base films. For example, an ABC three-layer structure is laminated onto the surface of the PET core layer, with nano-graphite and inorganic fillers added to the surface layer to achieve an anti-adhesion effect; another approach uses an ABA-type structure, adding nano-silica particles to the A layer to reduce surface roughness. However, multi-layer co-extrusion processes require sophisticated equipment and involve complex process control, and the effect of simply adjusting the base film formulation to reduce roughness is nearing its limit. Furthermore, the interfacial adhesion between the release layer and the base film in existing technologies is insufficient, especially on ultra-smooth surfaces, where the release layer is prone to peeling. How to achieve an ultra-smooth base film surface while ensuring good coating adhesion is a pressing technical challenge that needs to be addressed. Summary of the Invention

[0005] In view of the above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide a method for producing an ultra-smooth MLCC release film.

[0006] The technical solution of this invention is: a method for producing an ultra-smooth MLCC release film, comprising the following steps:

[0007] (1) In situ melt polycondensation method is used to add terephthalic acid, ethylene glycol and hydroxyl-terminated dendritic polymer into a polymerization reactor for esterification and polycondensation reaction to obtain dendritic polymer modified PET copolyester chips.

[0008] (2) Fluorosilicone modified polyacrylate coating liquid was prepared by core-shell emulsion polymerization;

[0009] (3) Add adhesion promoter, curing agent and solvent to the fluorosilicone modified polyacrylate coating liquid obtained in step (2), stir evenly, and obtain the coating liquid.

[0010] (4) The dendritic polymer modified PET copolyester chips obtained in step (1) are melt extruded and biaxially stretched to prepare a single-layer PET base film. After biaxial stretching, the film is heat-set. During the biaxial stretching process, after longitudinal stretching and before transverse stretching, the coating liquid obtained in step (3) is coated on the surface of the base film. Then, transverse stretching and heat setting are performed. After drying and curing, an ultra-smooth MLCC release base film is obtained.

[0011] Furthermore, the chemical structural formula of the hydroxyl-terminated dendritic polymer is as follows:

[0012] .

[0013] Furthermore, the preparation of the fluorosilicone-modified polyacrylate coating solution in step (2) includes the following sub-steps:

[0014] (21) Add diethylene glycol dimethyl ether solvent to the reaction vessel, heat to 120°C, add the first group of monomers and initiator dropwise. The initiator is azobisisobutyronitrile and tert-butyl peroxide (2-ethylhexanoate). After the reaction is kept at the temperature, cool down, add ammonia water, and emulsify with water to form a macromolecular emulsifier. The first group of monomers includes acrylic acid, butyl acrylate, methyl methacrylate, hydroxypropyl acrylate and hydroxyethyl methacrylate.

[0015] (22) Add emulsifier to the macromolecular emulsifier obtained in step (21). The emulsifier is sodium dodecylbenzenesulfonate and alkylphenol polyoxyethylene ether. Heat to 95°C and add one-third of the total amount of initiator. After the blue phase appears, add the remaining initiator and the second group of monomers at the same time. Keep the reaction at the temperature to obtain the core layer polymer. The second group of monomers includes acrylic acid, butyl acrylate, methyl methacrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate and fluorinated monomers.

[0016] (23) Based on the core polymer, add the silicon-containing monomer vinyltrimethoxysilane and continue the reaction to polymerize the silicon-containing monomer in the shell layer to obtain a fluorosilicone modified core-shell polyacrylate emulsion.

[0017] Furthermore, the fluorinated monomer is dodecafluoroheptyl methacrylate, which is added at a rate of 4.0% to 5.0% of the total mass of the second group of monomers; the amount of vinyltrimethoxysilane added is 1.0% to 3.0% of the total mass of the second group of monomers.

[0018] Furthermore, in step (3), the adhesion promoter is an epoxy silane coupling agent, and its addition amount is 3.0%~8.0% of the liquid solid content of the fluorosilicone modified polyacrylate coating.

[0019] Further, in step (3), the solvent is a mixture of ethyl acetate and butyl acetate, with a mass ratio of ethyl acetate to butyl acetate of 3:2; and in step (3), the curing agent is an isocyanate curing agent.

[0020] The beneficial effects of this invention are:

[0021] In-situ modification of PET with hydroxyl-terminated dendritic polymers improves the mechanical properties of the base film without altering the heat resistance of PET.

[0022] Fluorosilicone modified polyacrylate coating liquid prepared by core-shell emulsion polymerization has extremely low surface tension in the coating due to the fluorine-containing monomers. The silicon-containing monomers hydrolyze and condense during the film formation process to form a Si-O-Si three-dimensional cross-linked network. The synergistic effect of the two makes the coating surface smooth.

[0023] As an adhesion promoter, epoxy-based silane coupling agent significantly improves the interfacial bonding force between the coating and the PET base film through chemical bonding, solving the problem of easy peeling of the coating on the ultra-smooth surface.

[0024] The coating process is set after longitudinal stretching and before transverse stretching. The coating liquid undergoes transverse stretching and heat setting together with the base film, resulting in a denser interface between the coating and the base film. Detailed Implementation

[0025] To provide a more intuitive and complete understanding of the technical solution of this invention, the following non-limiting features are described:

[0026] A method for producing an ultra-smooth MLCC release film includes the following steps:

[0027] (1) In situ melt polycondensation method is used to add terephthalic acid, ethylene glycol and hydroxyl-terminated dendritic polymer into a polymerization reactor for esterification and polycondensation reaction to obtain dendritic polymer modified PET copolyester chips.

[0028] (2) Fluorosilicone modified polyacrylate coating liquid was prepared by core-shell emulsion polymerization;

[0029] (3) Add adhesion promoter, curing agent and solvent to the fluorosilicone modified polyacrylate coating liquid obtained in step (2), stir evenly, and obtain the coating liquid.

[0030] (4) The dendritic polymer modified PET copolyester chips obtained in step (1) are melt extruded and biaxially stretched to prepare a single-layer PET base film. After biaxial stretching, the film is heat-set. During the biaxial stretching process, after longitudinal stretching and before transverse stretching, the coating liquid obtained in step (3) is coated on the surface of the base film. Then, transverse stretching and heat setting are performed. After drying and curing, an ultra-smooth MLCC release base film is obtained.

[0031] The chemical structural formula of the hydroxyl-terminated dendritic polymer is:

[0032] .

[0033] The preparation of the fluorosilicone-modified polyacrylate coating solution in step (2) includes the following sub-steps:

[0034] (21) Add diethylene glycol dimethyl ether solvent to the reaction vessel, heat to 120°C, add the first group of monomers and initiator dropwise. The initiator is azobisisobutyronitrile and tert-butyl peroxide (2-ethylhexanoate). After the reaction is kept at the temperature, cool down, add ammonia water, and emulsify with water to form a macromolecular emulsifier. The first group of monomers includes acrylic acid, butyl acrylate, methyl methacrylate, hydroxypropyl acrylate and hydroxyethyl methacrylate.

[0035] (22) Add emulsifier to the macromolecular emulsifier obtained in step (21). The emulsifier is sodium dodecylbenzenesulfonate and alkylphenol polyoxyethylene ether. Heat to 95°C and add one-third of the total amount of initiator. After the blue phase appears, add the remaining initiator and the second group of monomers at the same time. Keep the reaction at the temperature to obtain the core layer polymer. The second group of monomers includes acrylic acid, butyl acrylate, methyl methacrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate and fluorinated monomers.

[0036] (23) Based on the core polymer, add the silicon-containing monomer vinyltrimethoxysilane and continue the reaction to polymerize the silicon-containing monomer in the shell layer to obtain a fluorosilicone modified core-shell polyacrylate emulsion.

[0037] The fluorinated monomer is dodecafluoroheptyl methacrylate, which is added at a rate of 4.0% to 5.0% of the total mass of the second group of monomers; the amount of vinyltrimethoxysilane added is 1.0% to 3.0% of the total mass of the second group of monomers.

[0038] In step (3), the adhesion promoter is an epoxy silane coupling agent, and its addition amount is 3.0% to 8.0% of the solid content of the fluorosilicone modified polyacrylate coating liquid.

[0039] In step (3), the solvent is a mixture of ethyl acetate and butyl acetate, with a mass ratio of ethyl acetate to butyl acetate of 3:2; in step (3), the curing agent is an isocyanate curing agent.

[0040] Example 1

[0041] (1) Preparation of dendritic polymer-modified PET copolyester: 350g PTA, 210g EG and hydroxyl-terminated dendritic polymer (0.75% of PET mass) were added to a polymerization reactor, and a titanium-based catalyst was added. Esterification reaction was carried out at 250℃ and 0.25MPa. Esterification was stopped when the water output reached 95% of the theoretical water output. The temperature was raised to 282℃ and the vacuum was drawn to 80Pa for polycondensation reaction. When the stirring current reached the set value, the material was discharged and pelletized to obtain dendritic polymer-modified PET copolyester chips.

[0042] (2) Preparation of fluorosilicone modified coating solution:

[0043] (21) Preparation of macromolecular emulsifier: Add 20g of diethylene glycol dimethyl ether solvent to a 500mL three-necked flask, stir and heat to 120℃, add the first group of monomers (7g acrylic acid, 24g butyl acrylate, 32g methyl methacrylate, 2.6g hydroxypropyl acrylate, 1.2g hydroxyethyl methacrylate) and initiator (2g azobisisobutyronitrile, 2g tert-butyl peroxide (2-ethylhexanoic acid)) dropwise, and add the monomers dropwise over 2.5h. Keep warm for 1h, cool down and add ammonia water, then add water to emulsify and form macromolecular emulsifier;

[0044] (22) Core layer polymerization: Add emulsifier (1.5g sodium dodecylbenzenesulfonate, 0.5g alkylphenol polyoxyethylene ether) to the macromolecular emulsifier obtained in step (21), heat to 95°C, add one-third of the total amount of initiator (2g ammonium persulfate, 2g sodium bicarbonate, 70g water), after the blue phase appears, simultaneously add the remaining initiator and the second group of monomers (1.2g acrylic acid, 44g butyl acrylate, 54g methyl methacrylate, 5.6g hydroxypropyl acrylate, 2.8g hydroxyethyl methacrylate, 5g dodecafluoroheptyl methacrylate), add for 3.5h, keep warm for 1h;

[0045] (23) Shell polymerization: Add 2.25g of vinyltrimethoxysilane (2.0% of the total mass of the second group of monomers), adjust the pH to 6.5, continue the reaction for 2h, cool to room temperature, adjust the pH to neutral, filter and discharge to obtain fluorosilicone modified core-shell polyacrylate emulsion.

[0046] (3) Preparation of coating solution: Add 5.0% epoxy silane coupling agent, 2.0% isocyanate curing agent and 75g mixed solvent (ethyl acetate: butyl acetate = 3:2, mass ratio) to the fluorosilicone modified core-shell polyacrylate emulsion obtained in step (2), stir evenly, and obtain a coating solution with a solid content of 40%.

[0047] (4) Preparation and online coating of PET base film: The dendritic polymer modified PET copolyester chips obtained in step (1) are melt-extruded by a twin-screw extruder and stretched longitudinally at 85°C with a stretching ratio of 3.0. After longitudinal stretching and before transverse stretching, the coating liquid obtained in step (3) is uniformly coated on the surface of the base film with a coating thickness of 2.5 μm. Then, transverse stretching is performed at 110°C with a stretching ratio of 3.5. After heat setting at 235°C and hot air drying at 120°C, UV curing, and winding, an ultra-smooth MLCC release base film is obtained.

[0048] Example 2

[0049] The difference between Example 2 and Example 1 is as follows: in step (1), the amount of hydroxyl-terminated dendritic polymer added is 0.5% of the mass of PET; in step (23), the amount of silicon-containing monomer vinyltrimethoxysilane added is 1.0% of the total mass of the second group of monomers; in step (3), the amount of epoxy silane coupling agent added is 3.0% of the emulsion solid content; the amount of isocyanate curing agent added is 1.5% of the emulsion solid content; and the amount of mixed solvent added is 80g.

[0050] Example 3

[0051] The difference between Example 3 and Example 1 is as follows: in step (1), the amount of hydroxyl-terminated dendritic polymer added is 1% of the mass of PET; in step (23), the amount of silicon-containing monomer vinyltrimethoxysilane added is 3.0% of the total mass of the second group of monomers; in step (3), the amount of epoxy silane coupling agent added is 8.0% of the emulsion solid content; the amount of isocyanate curing agent added is 3.0% of the emulsion solid content; and the amount of mixed solvent added is 70g.

[0052] Comparative Example 1

[0053] The difference between Comparative Example 1 and Example 1 is that no hydroxyl-terminated dendritic polymer is added in step (1), i.e., pure PET chips are used.

[0054] Comparative Example 2

[0055] The difference between Comparative Example 2 and Example 1 is that no epoxy silane coupling agent is added in step (3).

[0056] Comparative Example 3

[0057] The difference between Comparative Example 3 and Example 1 is that no fluorinated monomer is added in step (22) and no silicon-containing monomer is added in step (23), that is, unmodified pure acrylic emulsion is used.

[0058] Comparative Example 4

[0059] The difference between Comparative Example 4 and Example 1 is that the amount of dodecafluoroheptyl methacrylate added in step (22) is 2.5% (i.e. 2.82g) of the total mass of the second group of monomers, while the other components and amounts are consistent with those in Example 1.

[0060] The performance comparison of the release films prepared in each embodiment and the comparative example is shown in the table below:

[0061] Example 1 ≤6nm Level 0 Level 0 Approximately 26% Example 2 ≤8nm Level 0 Level 1 Approximately 18% Example 3 ≤7nm Level 0 Level 0~1 Approximately 20% Comparative Example 1 ≤8nm Level 0 Level 0 — Comparative Example 2 ≤6nm Level 2 Shedding Approximately 26% Comparative Example 3 ≥15nm Level 0 Level 0 Approximately 26% Comparative Example 4 ≥12nm Level 0 Level 1 Approximately 26%

[0062] According to Comparative Example 1 and Comparative Example 1, the tensile strength of the base film is significantly improved and the surface roughness is further reduced after adding the terminal hydroxyl dendritic polymer, indicating that the dendritic polymer modification of PET is beneficial to improving the mechanical properties and surface smoothness of the base film.

[0063] According to Comparative Example 1 and Comparative Example 2, although the surface roughness can still reach ≤6nm when no epoxy silane coupling agent is added, the coating adhesion is significantly reduced to level 2, and the coating falls off after boiling in water. This indicates that the epoxy silane coupling agent plays a key role in improving the interfacial bonding between the coating and the base film.

[0064] Based on Comparative Examples 1, 2, and 3, it is evident that the amount of vinyltrimethoxysilane added significantly affects the overall performance of the coating. When the amount of vinyltrimethoxysilane added is too low (e.g., 1.0%), the Si-O-Si crosslinking density formed by silane hydrolysis and condensation is insufficient, resulting in limited improvement in coating density and adhesion. When the amount of vinyltrimethoxysilane added is too high (e.g., 3.0%), excessive silane coupling agent may undergo self-condensation in the system, forming microscopic gel particles, which conversely damages the smoothness of the coating. Simultaneously, excessively high crosslinking density increases the brittleness of the coating and enhances interfacial stress. Therefore, the optimal amount of vinyltrimethoxysilane added is 2.0% of the total mass of the second group of monomers, at which point the coating exhibits excellent smoothness, adhesion, and mechanical properties.

[0065] According to Comparative Example 1 and Comparative Example 3, without the addition of fluorine-containing monomers and silicon-containing monomers, the surface roughness of the coating increases significantly to ≥15nm, which cannot meet the requirements of the MLCC ultra-thin casting process. This indicates that fluorine-silicon modification is indispensable for achieving ultra-smooth coating.

[0066] Based on Comparative Example 1 and Comparative Example 4, it can be seen that when the amount of dodecylfluoroheptyl methacrylate added is reduced from 4.44% (Example 1) to 2.5% (Comparative Example 4), although the coating adhesion still reaches grade 0, the surface roughness increases significantly from ≤6nm to ≥12nm. This is because when the amount of dodecylfluoroheptyl methacrylate added is insufficient, the enrichment and orientation of the fluorinated side chains on the coating surface are inadequate, and a complete and dense low surface energy layer cannot be formed, resulting in a decrease in the smoothness of the coating. Therefore, the amount of dodecylfluoroheptyl methacrylate added needs to reach more than 4.0% to fully exert the surface modification effect of the fluorinated monomer in the fluorosilicone synergistic system and achieve ultra-smooth coating.

[0067] The selection of the transverse stretching temperature is based on the cold crystallization behavior of PET. The glass transition temperature of PET is about 70℃. At 110℃, the mobility of PET molecular chain segments is significantly enhanced, which is conducive to the smooth progress of transverse stretching orientation. At the same time, 110℃ is near the starting temperature of PET cold crystallization. Moderate crystallization helps to improve the mechanical strength and dimensional stability of the base film, but it needs to be combined with a subsequent heat setting process at 235℃ to eliminate the internal stress caused by excessive crystallization.

[0068] Comparative Example 1, which did not add dendritic polymer, had a base film with significantly lower tensile strength than the examples. It was prone to breakage during subsequent MLCC processing and could not meet the requirements of practical applications. Its tensile strength improvement rate had no practical comparative significance.

[0069] This invention improves the mechanical properties of the base film by in-situ modification of PET with hydroxyl-terminated dendritic polymers without altering the heat resistance of PET. The introduction of hydroxyl-terminated dendritic polymers forms a cross-linked network or cage effect, inhibiting the diffusion of degradation products and the transmission of chain reactions, thereby increasing the initial decomposition temperature. The hydroxyl-terminated dendritic polymers are chemically bonded to the PET backbone through polycondensation, forming "rivet-like" nodes. These branching points restrict the slippage of the molecular chains under stress, playing a dual role of chemical bonding and physical entanglement. This effectively transfers stress within the molecular chains, thus improving the copolyester material's resistance to yielding. Simultaneously, the introduction of the dendritic structure increases the local mobility of the chain segments, making the material more prone to orientation alignment during stretching, thereby improving the elongation at break.

[0070] The present invention uses a core-shell emulsion polymerization method to prepare a fluorosilicone modified polyacrylate coating liquid. The fluorine-containing monomer imparts extremely low surface tension to the coating, and the silicon-containing monomer hydrolyzes and condenses during the film formation process to form a Si-O-Si three-dimensional cross-linked network. The synergistic effect of the two makes the coating surface smooth.

[0071] As an adhesion promoter, epoxy-based silane coupling agent significantly improves the interfacial bonding force between the coating and the PET base film through chemical bonding, solving the problem of easy peeling of the coating on the ultra-smooth surface.

[0072] The coating process is set after longitudinal stretching and before transverse stretching. The coating liquid undergoes transverse stretching and heat setting together with the base film, resulting in a denser interface between the coating and the base film.

Claims

1. A method for producing an ultra-smooth MLCC release film, characterized in that... Includes the following steps: (1) In situ melt polycondensation method is used to add terephthalic acid, ethylene glycol and hydroxyl-terminated dendritic polymer into a polymerization reactor for esterification and polycondensation reaction to obtain dendritic polymer modified PET copolyester chips. (2) Fluorosilicone modified polyacrylate coating liquid was prepared by core-shell emulsion polymerization; (3) Add adhesion promoter, curing agent and solvent to the fluorosilicone modified polyacrylate coating liquid obtained in step (2), stir evenly, and obtain the coating liquid. (4) The dendritic polymer modified PET copolyester chips obtained in step (1) are melt extruded and biaxially stretched to prepare a single-layer PET base film. After biaxial stretching, the film is heat-set. During the biaxial stretching process, after longitudinal stretching and before transverse stretching, the coating liquid obtained in step (3) is coated on the surface of the base film. Then, transverse stretching and heat setting are performed. After drying and curing, an ultra-smooth MLCC release base film is obtained.

2. The method for producing an ultra-smooth MLCC release film according to claim 1, characterized in that: The chemical structural formula of the hydroxyl-terminated dendritic polymer is: 。 3. The method for producing an ultra-smooth MLCC release film according to claim 1, characterized in that: The preparation of the fluorosilicone-modified polyacrylate coating solution in step (2) includes the following sub-steps: (21) Add diethylene glycol dimethyl ether solvent to the reaction vessel, heat to 120°C, add the first group of monomers and initiator dropwise. The initiator is azobisisobutyronitrile and tert-butyl peroxide (2-ethylhexanoate). After the reaction is kept at the temperature, cool down, add ammonia water, and emulsify with water to form a macromolecular emulsifier. The first group of monomers includes acrylic acid, butyl acrylate, methyl methacrylate, hydroxypropyl acrylate and hydroxyethyl methacrylate. (22) Add emulsifier to the macromolecular emulsifier obtained in step (21). The emulsifier is sodium dodecylbenzenesulfonate and alkylphenol polyoxyethylene ether. Heat to 95°C and add one-third of the total amount of initiator. After the blue phase appears, add the remaining initiator and the second group of monomers at the same time. Keep the reaction at the temperature to obtain the core layer polymer. The second group of monomers includes acrylic acid, butyl acrylate, methyl methacrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate and fluorinated monomers. (23) Based on the core polymer, add the silicon-containing monomer vinyltrimethoxysilane and continue the reaction to polymerize the silicon-containing monomer in the shell layer to obtain a fluorosilicone modified core-shell polyacrylate emulsion.

4. The method for producing an ultra-smooth MLCC release film according to claim 3, characterized in that: The fluorinated monomer is dodecafluoroheptyl methacrylate, which is added at a rate of 4.0% to 5.0% of the total mass of the second group of monomers; the amount of vinyltrimethoxysilane added is 1.0% to 3.0% of the total mass of the second group of monomers.

5. The method for producing an ultra-smooth MLCC release film according to claim 1, characterized in that: In step (3), the adhesion promoter is an epoxy silane coupling agent, and its addition amount is 3.0% to 8.0% of the solid content of the fluorosilicone modified polyacrylate coating liquid.

6. The method for producing an ultra-smooth MLCC release film according to claim 1, characterized in that: In step (3), the solvent is a mixture of ethyl acetate and butyl acetate, with a mass ratio of ethyl acetate to butyl acetate of 3:2; in step (3), the curing agent is an isocyanate curing agent.

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