Polytetrafluoroethylene dispersion liquid for copper-clad plate and preparation and application thereof

Abstract

This invention relates to the field of semiconductor technology, providing a polytetrafluoroethylene (PTFE) dispersion for copper-clad laminates, its preparation, and its application. This PTFE dispersion is formulated by post-processing a PTFE polymer solution. The emulsifier content in the PTFE dispersion is 1.0% to 1.8% of the dry weight of the PTFE resin. The PTFE dispersion obtained by the method proposed in this invention is an environmentally friendly product. The small amount of emulsifier decomposes without residue during product processing, ensuring the appearance, color, and performance of the product. Furthermore, the emulsion remains stable and does not settle over a long period of storage. The resulting PTFE copper-clad laminate exhibits good sheet formability, excellent appearance, low dielectric loss factor, low water absorption, and stable CTE, meeting the needs of the semiconductor field.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, specifically to a polytetrafluoroethylene dispersion for copper-clad laminates, its preparation, and its application. Background Technology

[0002] Polytetrafluoroethylene (PTFE) materials possess excellent dielectric properties (low dielectric constant and dielectric loss, etc.), as well as good chemical and thermal stability. With the increasing trend towards higher frequencies and speeds in communication and electronic products, the market demand for PTFE copper-clad laminates is growing rapidly, and they are widely used in the manufacturing industries of communication equipment, computers, automotive electronics, and home appliances.

[0003] In the fabrication of PTFE copper-clad laminates, PTFE dispersion impregnation is commonly used. However, the traditional impregnation technique involves fiberglass-reinforced laminates, which often have fiberglass clumps in certain areas of the XY plane with insufficient adhesion and gaps between the clumps. The dielectric constants at the clumps and gaps are approximately 6 and 3, respectively. If a critical conductor is perfectly aligned with the patterns on the clumps and gaps, this conductor will have different dielectric constants in several small isolation regions. At high or extremely high digital frequencies, these differences in dielectric constants can affect circuit performance, exhibiting a "fiberglass effect" at high frequencies. This leads to increased common-mode noise (EMI) and variations in differential amplitude (SI), ultimately impacting signal transmission.

[0004] Furthermore, PTFE dispersions also suffer from poor stability. For example, patent application CN1754894A discloses a modified polytetrafluoroethylene and its manufacturing method. Specifically, it discloses that: modified polytetrafluoroethylene is obtained by polymerizing tetrafluoroethylene and comonomers, controlling the amount of modified monomers to be 0.1% to 1.0% of the modified polytetrafluoroethylene, and the average primary particle size of the modified polytetrafluoroethylene is 0.22μm to 0.5μm. A large amount of nonionic wetting agent is added, and through chemical concentration, a dispersion with an emulsifier content of 13% is obtained. The dispersion has excellent film-forming properties and good light transmittance, but it has a common problem in terms of storage stability. It is very easy to settle and needs to be stirred once a week. The storage conditions of the dispersion are high. At the same time, the amount of surfactant residue is large during application, making it unsuitable for the semiconductor field. Patent application CN200580051041.2 describes an aqueous dispersion of PTFE containing 55wt%–75wt% polytetrafluoroethylene (PTFE) particles with an average particle size of 100nm–500nm, 0.0001%–0.02% perfluorooctanoic acid (APFO) or other specific fluorinated carboxylates with 8 carbons relative to PTFE, 1%–20% of a specific nonionic surfactant relative to PTFE, and 0.01%–0.3% perfluorohexanoic acid (APFO) or other specific fluorinated carboxylates with 5–7 carbons relative to PTFE. This dispersion exhibits good frictional stability and prevents thickening. However, it suffers from poor storage stability due to the large particle size, which makes it prone to sedimentation and requires weekly stirring. This necessitates stringent storage conditions, and the high surfactant residue during application makes it unsuitable for the semiconductor industry.

[0005] Therefore, there is an urgent need to study a polytetrafluoroethylene dispersion with good performance suitable for copper-clad laminates. Summary of the Invention

[0006] This invention provides a polytetrafluoroethylene (PTFE) dispersion for copper-clad laminates, its preparation, and its application. Specifically, the emulsifier content in the PTFE dispersion for copper-clad laminates is controlled to be 1.0% to 1.8% of the dry weight of the PTFE resin, in order to obtain copper-clad laminates with good sheet formability, good appearance and color, low dielectric loss factor, low water absorption, and stable CTE, which have excellent comprehensive properties and meet the requirements of the electronics field.

[0007] This invention provides a polytetrafluoroethylene dispersion for copper clad laminates, which is prepared by post-processing a polytetrafluoroethylene polymer solution. The emulsifier content in the polytetrafluoroethylene dispersion is 1.0% to 1.8% of the dry weight of PTFE resin, preferably 1.2% to 1.6%.

[0008] The inventive principle of this invention is:

[0009] In traditional polytetrafluoroethylene (PTFE) dispersions, the emulsifier content is typically set at 4%–8%. However, experiments have shown that PTFE dispersions with high emulsifier content, when processed using casting molding, result in copper-clad laminates with several problems: ① difficulty in flocculation, with the flocculant easily turning black during high-temperature sintering, affecting the appearance; ② the surfactant containing a large number of difficult-to-remove impurities (such as fluorinated terminal groups), resulting in a grayish-black substrate with high dielectric loss and poor dielectric uniformity. Therefore, this invention proposes adding a very small amount of emulsifier during post-processing. Because the emulsifier content is extremely low, flocculation is facilitated, and the surfactant readily volatilizes completely during high-temperature sintering. Thus, the problems of poor substrate appearance, high dielectric loss, and poor dielectric uniformity are solved.

[0010] The dry weight of the PTFE resin in this invention is calculated based on the weight of the emulsion after testing the solid content according to the method of ASTM D4441-2004.

[0011] The polytetrafluoroethylene dispersion for copper-clad laminates provided by the present invention has an average particle size of 0.20 μm to 0.23 μm.

[0012] Furthermore, in the prior art, since polytetrafluoroethylene dispersions are thermodynamically unstable systems, low emulsifier content can lead to poor transport stability. When transported as an intermediate product, the Brownian motion between emulsion particles and the collision between the particles and the container wall during transport cause shear forces, making the emulsion particles prone to demulsification. Moreover, poor storage stability also exists. Therefore, this invention controls the average particle size of the polytetrafluoroethylene polymer to be 0.20 μm to 0.23 μm. By reducing the particle size, the problem of emulsion particle sedimentation can be solved, as well as issues related to mixing uniformity with fillers, dielectric uniformity, and reduced dielectric loss and water absorption during processing.

[0013] The average particle size test method of this invention is: wet method using Malvern laser particle size analyzer (enterprise testing standard Q / 45090448-8).

[0014] The polytetrafluoroethylene dispersion for copper-clad laminates provided by the present invention has a solid content of 28% to 32%. When the emulsifier content is 1.0% to 1.8%, if the solid content is too high, the emulsion stability is poor, and demulsification or sedimentation is likely to occur during transportation and storage; while if the solid content is too low, the product cost increases, and less material is obtained at one time during application, increasing the number of operations and posing a risk of batch-to-batch instability.

[0015] The polytetrafluoroethylene dispersion for copper-clad laminates provided by the present invention uses an environmentally friendly nonionic surfactant as the emulsifier.

[0016] Environmentally friendly nonionic surfactants are one or more types of isomeric alcohol polyoxyethylene ethers or secondary alcohol polyoxyethylene ethers, mixed in proportion, with branched secondary alcohol polyoxyethylene ethers from Dow Chemical Company (such as TMN-10) being preferred.

[0017] The polytetrafluoroethylene dispersion for copper-clad laminates provided by the present invention contains a thickener.

[0018] The thickener is an acrylonitrile polymer (such as Acrysol ASE), a carboxylated ethylene polymer (such as Carbol 934), a waterborne polyurethane, or a polyhydroxyethyl cellulose (such as Natrosol), with a waterborne polyurethane (such as Dow Acrysol RM-2020NPR) being preferred.

[0019] The polytetrafluoroethylene dispersion for copper-clad laminates provided by the present invention has a thickener content of 0.8‰ to 1.8‰ of the dry resin weight, preferably 1.0‰ to 1.5‰.

[0020] The polytetrafluoroethylene dispersion for copper-clad laminates provided by the present invention has a total content of alkali metals and magnetic materials ≤30ppm.

[0021] Preferably, the total content of alkali metals and magnetic materials in the polytetrafluoroethylene dispersion for copper clad laminates is ≤10ppm.

[0022] This invention controls the total content of alkali metals and magnetic materials in polytetrafluoroethylene (PTFE) dispersions within the aforementioned range, significantly improving the transport and storage stability of PTFE dispersions. This is because: Traditional PTFE dispersion preparation processes involve various raw materials containing certain amounts of alkali metals and magnetic materials, such as deionized water and paraffin wax. In particular, nonionic surfactants (emulsifiers) added to enhance transport and storage stability and processing performance often use KOH or NaOH as catalysts during production, where the alkali metals and magnetic materials have the greatest impact. These alkali metals and magnetic materials compress the electric double layer thickness of the emulsion colloid. Furthermore, fluorinated anionic surfactants (negatively charged) are used during polymerization, while positively charged metal cations attract each other, reducing the water interface layer. PTFE emulsions are thermally unstable systems that undergo Brownian motion. When they become thinner, the particles tend to agglomerate and form large particles, which accelerates the settling rate or causes demulsification due to shear force. This affects the transport and storage stability of the PTFE dispersion. In addition, excessive alkali metal and magnetic material content can also affect the dielectric loss of the substrate.

[0023] The present invention also provides a method for preparing the polytetrafluoroethylene dispersion for copper-clad laminates as described above. The post-processing process is as follows: an emulsifier and a thickener are added to the polytetrafluoroethylene polymer solution and mixed evenly (e.g., low speed, thorough stirring, stirring temperature 20℃~50℃, stirring speed 10 rpm~15 rpm), and then a pH adjuster is added to adjust the specific gravity of the emulsion to obtain the polytetrafluoroethylene dispersion for copper-clad laminates.

[0024] According to the preparation method of polytetrafluoroethylene dispersion for copper clad laminate provided by the present invention, after adding emulsifier and thickener, the mixture is thoroughly stirred and homogenized, and then cation exchange resin is added.

[0025] During the emulsion preparation process, appropriate amounts of emulsifiers and thickeners are added and then adsorbed and removed by cation exchange resin. This avoids alkali metals and magnetic materials compressing the double electric layer thickness of the emulsion colloid and appropriately increases the emulsion viscosity, thereby improving the storage stability of the emulsion. At the same time, a very small amount of surfactant is beneficial for downstream processing applications and decomposes without residue during high-temperature sintering.

[0026] According to the preparation method of polytetrafluoroethylene dispersion for copper clad laminate provided by the present invention, the amount of cation exchange resin added is 4% to 10% of the dry weight of PTFE resin.

[0027] According to the preparation method of polytetrafluoroethylene dispersion for copper clad laminate provided by the present invention, the cation exchange resin is Dow IRC76, Dow IRC83, Rohm and Haas 252H or Rohm and Haas IRP64.

[0028] Preferably, the cation exchange resin is Dow IRC76.

[0029] According to the preparation method of polytetrafluoroethylene dispersion for copper clad laminate provided by the present invention, the adjustment of emulsion specific gravity refers to adding deionized water to adjust to a suitable density range.

[0030] According to the preparation method of polytetrafluoroethylene dispersion for copper clad laminate provided by the present invention, the pH adjuster is sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide or ammonia, wherein the content of ammonia (NH3) is 25% to 28% w / %.

[0031] Preferably, the pH adjuster is tetramethylammonium hydroxide, manufactured by Wuhan Kemic Biomedical Technology Co., Ltd.

[0032] According to the method for preparing polytetrafluoroethylene dispersion for copper-clad laminates provided by the present invention, the preparation steps of the polytetrafluoroethylene polymerization liquid are as follows:

[0033] (1) Add stabilizers and dispersants to the aqueous reaction medium;

[0034] (2) Add a modifier to the reaction system after the oxygen analysis is qualified, raise the temperature, and then continuously add gaseous tetrafluoroethylene monomer to carry out polymerization.

[0035] The initiator is gradually added during the addition of tetrafluoroethylene monomer.

[0036] According to the method for preparing polytetrafluoroethylene dispersion for copper-clad laminates provided by the present invention, the preparation steps of the polytetrafluoroethylene polymerization liquid are as follows:

[0037] (1) Add the stabilizer and a portion of the dispersant to the aqueous reaction medium; the portion of the dispersant refers to a dispersant that accounts for 40% to 50% of the total amount of dispersant added;

[0038] (2) Add a modifier to the reaction system after the oxygen analysis is qualified, raise the temperature, and then continuously add gaseous tetrafluoroethylene monomer to carry out polymerization.

[0039] The initiator and the remaining dispersant are gradually added during the addition of tetrafluoroethylene monomer. The remaining dispersant is a solution of the remaining dispersant (dissolved in deionized water, e.g., 35g of dispersant dissolved in 2L of deionized water) that is continuously and uniformly added to the polymerization system when the amount of tetrafluoroethylene reaches a certain level, and the addition is completed when the amount of tetrafluoroethylene reaches a certain level.

[0040] In the above method of the present invention, the aqueous reaction medium used is deionized water, and its amount is 50% to 70% of the volume of the reaction vessel, preferably 60% to 70%.

[0041] Passing the oxygen analysis means that the oxygen content in the reaction system is ≤30ppm;

[0042] The stabilizer is solid paraffin or a saturated hydrocarbon with ≥12 carbon atoms, preferably solid paraffin, with a melting point of 56℃~58℃, and the amount used is 1.0%~8.0% of the mass of deionized water, preferably 3.0%~6.0%.

[0043] The dispersant is a perfluorooctanoic acid ammonium substitute, such as perfluorinated or fluorinated polyether carboxylates, perfluorinated or fluorinated alkyl carboxylates (salts), perfluorinated or fluorinated alkyl sulfonates (salts), etc., preferably perfluorinated or fluorinated polyether carboxylates, and the amount used is 0.08% to 0.28% of the weight of deionized water in the polymerization system, preferably 0.1% to 0.22%.

[0044] The modifier is a perfluoroalkyl olefin or a perfluoroalkyl vinyl ether, and may be one or more of perfluoropropylene, trifluorochloroethylene, vinylidene fluoride, perfluorobutylethylene, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and perfluoron-propyl vinyl ether, with perfluorobutylethylene being preferred. The amount added is 0.003% to 0.011% of the mass of deionized water, preferably 0.003% to 0.0095%.

[0045] The total amount of gaseous tetrafluoroethylene monomer added is 40% to 60% of the weight of deionized water, preferably 45% to 57%;

[0046] The initiator can be an inorganic initiator, an organic initiator, or a composite initiator (inorganic and organic initiators used in combination). Inorganic initiators are alkali metal persulfates, such as ammonium persulfate and potassium persulfate; organic initiators are peroxides, such as benzoyl peroxide and succinic acid peroxide. Succinic acid peroxide is preferred as the initiator, and its dosage is 0.01%–0.07% of the weight of deionized water in the polymerization system, preferably 0.02%–0.05%. The initiator is added as follows: when the reactor is heated to the feeding temperature, the gaseous monomer tetrafluoroethylene is added to the reaction pressure, and an aqueous solution containing the initiator (e.g., 10g (pure) succinic acid peroxide dissolved in 0.5L of deionized water) is added through a metering pump.

[0047] By controlling the dispersant addition method and maintaining a constant reaction temperature during polymerization, the average particle size distribution range of the emulsion can be effectively controlled, ensuring uniform and consistent particle size growth. Adding a small amount of modifier effectively controls the average particle size and improves the machinability of the product.

[0048] In this invention, a modifier is added during the polymerization process, and the reaction temperature is controlled at 74±1℃ and the reaction pressure at 2.5MPa. When the polymerization reaction proceeds to an emulsion solid content of approximately 31%, stirring is stopped, the gaseous monomer is recovered, the mixture is evacuated, and the material is discharged to obtain a polytetrafluoroethylene polymer liquid with an average particle size of 0.20μm to 0.23μm. A small amount of emulsifier and a trace amount of thickener are added, followed by an appropriate amount of cation exchange resin. After low-speed stirring and preparation in a mixing tank, an emulsion with a solid content of 28% to 32% is obtained. This emulsion exhibits excellent storage stability; after stirring or shaking once every half month, the emulsion can be stored for up to 8 months.

[0049] The present invention provides the application of the polytetrafluoroethylene dispersion for copper-clad laminates as described above, and uses the polytetrafluoroethylene dispersion for copper-clad laminates as described above to prepare polytetrafluoroethylene copper-clad laminates.

[0050] The polytetrafluoroethylene dispersion in this invention has a small average particle size and a narrow distribution range, which satisfies the requirement of uniform mixing with fillers during application and reduces water absorption. The low emulsifier content reduces the amount and residual rate of additives in the substrate while ensuring stability during transportation and storage, thus reducing the impact on the substrate's appearance and dielectric loss. The low content of alkali metals and magnetic materials reduces dielectric loss.

[0051] This invention provides a polytetrafluoroethylene (PTFE) dispersion for copper-clad laminates, its preparation, and its application. By eliminating the use of PFOA as a dispersant during polymerization and employing a small amount of environmentally friendly emulsifier in post-processing, and by controlling the reaction temperature and dispersant addition method during polymerization, a structural design with uniform primary particle morphology and appropriate particle size is achieved. Adding a trace amount of thickener reduces the probability of collisions between colloidal particles during thermal motion, improving emulsion stability. The emulsion containing nonionic surfactants and thickeners undergoes cationic adsorption and removal, controlling the total content of alkali metals and magnetic materials within a certain range to prevent alkali metals and magnetic materials from compressing the electric double layer thickness of the emulsion colloid, thus improving emulsion stability. The PTFE dispersion obtained using this method is a green and environmentally friendly product. The small amount of emulsifier decomposes without residue during product processing, ensuring the appearance, color, and performance of the product. Furthermore, the emulsion remains stable and does not settle over a long period of storage. Polytetrafluoroethylene copper-clad laminates are produced through processing. These laminates have good sheet formability and appearance, and possess excellent comprehensive properties such as low dielectric loss factor, low water absorption, and stable CTE, meeting the needs of the semiconductor field. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0053] Example 1

[0054] A method for preparing a polytetrafluoroethylene dispersion, comprising the following steps:

[0055] (1) Clean the 50L stainless steel high-pressure reactor, add 32L of high-purity deionized water with a purity of not less than 16MΩ, 65g of dispersant perfluoropolyether ammonium carboxylate and 2kg of paraffin, then seal the reactor, evacuate and replace with nitrogen, and analyze the oxygen content. When the oxygen content is ≤30ppm, it is qualified.

[0056] (2) After the oxygen analysis is qualified, add 2g of perfluorobutylethylene, heat the reactor to 72℃, add the gaseous monomer tetrafluoroethylene, and bring the pressure inside the reactor to 2.5MPa. Then, add an aqueous solution containing 10g (pure) of peroxysuccinic acid (10g (pure) of peroxysuccinic acid dissolved in 0.5L of deionized water) through a metering pump. During the reaction, maintain the pressure inside the reactor at 2.5MPa and the temperature at 74±1℃. Depending on the polymerization rate, initiator can be added as needed, and the number of additions depends on the reaction rate. When the amount of tetrafluoroethylene added reaches 17kg, the reaction ends. The gaseous monomer is recovered, the mixture is cooled and discharged, and the paraffin is separated to obtain a polytetrafluoroethylene polymerization liquid with a solid content of 31%.

[0057] (3) Post-treatment: Add 1.4% of nonionic surfactant (Dow TMN-10) and 1.5‰ of thickener (Dow Acrysol RM-2020NPR) to the polytetrafluoroethylene polymerization liquid with a solid content of about 31%. Add 6% of cation exchange resin (Dow IRC76) to the liquid. Keep the mixture at 40°C in a jacketed mixing tank and stir at 10 rpm for 3.5 hours. Add pH adjuster (tetramethylammonium hydroxide). Add deionized water to adjust the specific gravity of the emulsion. Filter to obtain a polytetrafluoroethylene dispersion with a solid content of about 30%.

[0058] Example 2

[0059] A method for preparing a polytetrafluoroethylene dispersion, comprising the following steps:

[0060] (1) Clean the 50L stainless steel high-pressure reactor, add 32L of high-purity deionized water with a purity of not less than 16MΩ, 30g of dispersant perfluoropolyether ammonium carboxylate and 2kg of paraffin, then seal the reactor, evacuate and replace with nitrogen, and analyze the oxygen content. When the oxygen content is ≤30ppm, it is qualified.

[0061] (2) After the oxygen analysis is qualified, add 2g of perfluorobutylethylene. Heat the reactor to 72℃, add the gaseous monomer tetrafluoroethylene, and bring the pressure inside the reactor to 2.5MPa. Add an aqueous solution containing 10g (pure) of peroxysuccinic acid (10g (pure) of peroxysuccinic acid dissolved in 0.5L of deionized water) through a metering pump. During the reaction, maintain the pressure inside the reactor at 2.5MPa and the temperature at 74±1℃. Depending on the polymerization rate, initiator can be added as needed, and the number of additions depends on the reaction rate. When the amount of tetrafluoroethylene added reaches 3kg, continuously and uniformly add the remaining 35g of dispersant solution to the polymerization system, and finish adding when the amount of tetrafluoroethylene added reaches 7kg. When the amount of tetrafluoroethylene added reaches 17kg, the reaction ends, the gaseous monomer is recovered, the product is cooled and discharged, and the paraffin is separated to obtain a polytetrafluoroethylene polymerization liquid with a solid content of 31%.

[0062] (3) Post-treatment: Add 1.2% of nonionic surfactant (Dow TMN-10) and 1.0‰ of thickener (Dow Acrysol RM-2020NPR) to the polytetrafluoroethylene polymerization liquid with a solid content of 31%. Add 6% of cation exchange resin (Dow IRC76) to the mixture and stir at 15 rpm for 3.5 hours in a jacketed mixing tank at 40°C. Add pH adjuster (tetramethylammonium hydroxide) and deionized water to adjust the emulsion specific gravity. Filter to obtain a polytetrafluoroethylene dispersion with a solid content of about 30%.

[0063] Comparative Example 1

[0064] A method for preparing a polytetrafluoroethylene dispersion is basically the same as that in Example 1, except that: no cation exchange resin is added in step (3), and the stirring time is reduced to 1.5 hours accordingly to obtain a polytetrafluoroethylene dispersion with a solid content of about 30%.

[0065] Comparative Example 2

[0066] A method for preparing a polytetrafluoroethylene dispersion is basically the same as that in Example 1, except that in step (3), the mixture is stirred at low speed at 15°C for 3.5 hours in a jacketed mixing tank to obtain a polytetrafluoroethylene dispersion with a solid content of about 30%.

[0067] Comparative Example 3

[0068] A method for preparing a polytetrafluoroethylene dispersion is basically the same as that in Example 1, except that in step (3), the mixture is stirred at low speed at 60°C for 3.5 hours in a jacketed mixing tank to obtain a polytetrafluoroethylene dispersion with a solid content of about 30%.

[0069] Comparative Example 4

[0070] A method for preparing a polytetrafluoroethylene dispersion is basically the same as that in Example 1, except that perfluorobutylethylene, a modifier, is not added in step (2), and a polytetrafluoroethylene dispersion with a solid content of about 30% is obtained.

[0071] Comparative Example 5

[0072] A method for preparing a polytetrafluoroethylene dispersion, comprising the following steps:

[0073] (1) Clean the 50L stainless steel high-pressure reactor, add 32L of high-purity deionized water with a purity of not less than 16MΩ, 8g of dispersant perfluoropolyether ammonium carboxylate, and 2kg of paraffin, then seal the reactor, evacuate it and replace it with nitrogen, and analyze the oxygen content. When the oxygen content is ≤30ppm, it is qualified.

[0074] (2) After the oxygen analysis is qualified, add 2g of perfluorobutylethylene. Heat the reactor to 72℃, add the gaseous monomer tetrafluoroethylene, and bring the pressure inside the reactor to 2.5MPa. Add an aqueous solution containing 10g (pure) of peroxysuccinic acid (10g (pure) peroxysuccinic acid dissolved in 0.5L deionized water) through a metering pump. Maintain the reactor pressure at 2.5MPa and the temperature at 74±1℃ during the reaction. Depending on the polymerization rate, initiator can be added as needed, with the number of additions depending on the reaction rate. When the amount of tetrafluoroethylene added reaches 3kg, continuously and uniformly add the remaining 42g of dispersant solution (perfluoropolyether ammonium carboxylate solution) to the polymerization system, completing the addition when the amount of tetrafluoroethylene added reaches 8kg. When the amount of tetrafluoroethylene added reaches 17kg, the reaction ends. Recover the gaseous monomer, cool and discharge the material, separate the paraffin wax, and obtain a polytetrafluoroethylene polymerization liquid with a solid content of approximately 31%.

[0075] (3) Post-treatment: Add 6% of the dry resin material of nonionic surfactant (Dow TMN-10) and vacuum concentrate to a certain specific gravity. Add pH adjuster (tetramethylammonium hydroxide) to adjust the specific gravity of the emulsion. Filter to obtain a concentrated dispersion of polytetrafluoroethylene with a solid content of 60%.

[0076] Comparative Example 6

[0077] A method for preparing a polytetrafluoroethylene dispersion is basically the same as that in Example 1, except that the amount of nonionic surfactant added in step (3) is 0.8% of the dry resin material, and a polytetrafluoroethylene dispersion with a solid content of about 30% is obtained.

[0078] Comparative Example 7

[0079] A method for preparing a polytetrafluoroethylene dispersion is basically the same as that in Example 1, except that the amount of nonionic surfactant added in step (3) is 2.0% of the dry resin material, and a polytetrafluoroethylene dispersion with a solid content of about 30% is obtained.

[0080] The polytetrafluoroethylene dispersions in Examples 1-2 and Comparative Examples 1-7 were tested using the following methods:

[0081] Test method for particle size: GB / T 19077.1-2008.

[0082] Test method for solid content: ASTM D4441-2004.

[0083] Test methods for alkali metal and magnetic material content: JY / T 015-1996.

[0084] Test method for sediment content (as a percentage of PTFE): ASTM D4441-2004.

[0085] The test results are as follows:

[0086] Table 1 shows the performance test results of the polytetrafluoroethylene dispersion.

[0087]

[0088] The polytetrafluoroethylene dispersions from Examples 1, 2, and Comparative Examples 1-7 were used to prepare polytetrafluoroethylene copper-clad laminates. The specific steps are as follows:

[0089] (1) The polytetrafluoroethylene dispersion, ceramic powder and short glass fiber in Examples 1, 2 and Comparative Examples 1 to 7 were mixed evenly by wet method and then a polymeric flocculant was added for coagulation.

[0090] (2) After drying the coagulated material, add lubricant for maturation;

[0091] (3) The matured material is extruded and calendered to obtain a green substrate sheet, which is then dried;

[0092] (4) Cover both sides of the dried green substrate with copper foil, sinter, and cool to room temperature after pressure holding to obtain polytetrafluoroethylene copper-clad laminate.

[0093] The above preparation process can be carried out with reference to the preparation process diagram of the 615 and 1020 type composite material samples in Figure 1 of the literature title: Influence of TiO2 particle size on dielectric loss and water absorption of PTFE-based composite materials.

[0094] The properties of the polytetrafluoroethylene copper-clad laminate prepared above were tested using the following methods:

[0095] The test method for loss factor is GB / T 12636-90.

[0096] The test method for water absorption rate is GJB1651A-2017.

[0097] The test results are as follows:

[0098] Table 2 shows the performance test results of polytetrafluoroethylene copper clad laminate.

[0099]

[0100] analyze:

[0101] As can be seen from Comparative Example 1 and Example 1, the dispersion after cation exchange resin in Example 1 can significantly reduce the loss factor of copper-clad laminate. This is because cation exchange resin can effectively reduce the content of alkali metals and magnetic materials in the dispersion, making the dispersion more stable during transportation and storage, and performing better when used to prepare copper-clad laminate.

[0102] As can be seen from Comparative Examples 2 and 3 and Example 1, the stirring temperature and time have a significant impact on the removal efficiency of alkali metals and magnetic materials, as well as the content of precipitates.

[0103] As can be seen from Comparative Example 4 and Example 1, the addition of the modifier has a significant effect on the average particle size of the dispersion. Smaller particle size makes the dispersion more stable during transportation and storage.

[0104] As can be seen from Comparative Example 5 and Example 1, although the emulsifier content increases when emulsifier is added according to conventional emulsion, the content of alkali metals and magnetic materials also increases at the same time. The storage stability is comparable to that of the emulsion in Example 1, but in the later processing and application, a large amount of flocculant needs to be added or flocculation is not possible at all, resulting in the copper-clad laminate with extremely poor performance in terms of appearance and dielectric loss.

[0105] As can be seen from Comparative Examples 6 and 7 and Example 1, the amount of emulsifier added affects the stability of the dispersion and the performance of the copper-clad laminate obtained.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A polytetrafluoroethylene dispersion liquid for a copper-clad plate, which is prepared by post-treating a polytetrafluoroethylene polymerization liquid, characterized in that, The emulsifier content in the polytetrafluoroethylene dispersion is 1.0% to 1.8% of the dry weight of the PTFE resin; The average particle size of the polytetrafluoroethylene polymerization liquid is 0.20µm~0.23µm; The preparation steps of the polytetrafluoroethylene polymerization liquid are as follows: (1) Add the stabilizer and dispersant to the aqueous reaction medium; (2) Add a modifier to the reaction system after the oxygen analysis is qualified, raise the temperature, and then continuously add gaseous tetrafluoroethylene monomer to carry out polymerization; The initiator is gradually added during the addition of tetrafluoroethylene monomer; The modifier is a perfluoroalkyl olefin or a perfluoroalkyl vinyl ether; The solid content of the polytetrafluoroethylene dispersion for copper-clad laminates is 28%~32%; The emulsifier is an environmentally friendly nonionic surfactant; the environmentally friendly nonionic surfactant is an isomeric alcohol polyoxyethylene ether and / or a secondary alcohol polyoxyethylene ether. The polytetrafluoroethylene dispersion for copper-clad laminates contains a thickener; The post-treatment includes adding the emulsifier and the thickener, stirring thoroughly to mix evenly, and then adding the cation exchange resin; the stirring temperature is 20℃~50℃.

2. The polytetrafluoroethylene dispersion for a copper-clad plate according to claim 1, characterized by, The thickener content is 0.8‰~1.8‰ of the dry resin weight.

3. The polytetrafluoroethylene dispersion for a copper-clad plate according to claim 1, characterized by, The total content of alkali metals and magnetic materials in the polytetrafluoroethylene dispersion for copper clad laminates is ≤30ppm.

4. The polytetrafluoroethylene dispersion for a copper-clad plate according to claim 3, characterized by, The total content of alkali metals and magnetic materials in the polytetrafluoroethylene dispersion for copper clad laminates is ≤10ppm.

5. The method for producing a polytetrafluoroethylene dispersion liquid for a copper-clad plate according to any one of claims 1 to 4, characterized by, The post-processing process is as follows: emulsifier and thickener are added to the polytetrafluoroethylene polymerization liquid and mixed evenly. Then, cation exchange resin is added and pH adjuster is added to adjust the specific gravity of the emulsion to obtain polytetrafluoroethylene dispersion for copper clad laminate.

6. The method for producing a polytetrafluoroethylene dispersion liquid for a copper-clad plate according to claim 5, characterized by, The amount of cation exchange resin added is 4% to 10% of the dry weight of PTFE resin.

7. The method for producing a polytetrafluoroethylene dispersion liquid for a copper-clad plate according to claim 6, characterized by, The cation exchange resin is Dow IRC76, Dow IRC83, Rohm and Haas 252H, or Rohm and Haas IRP64.

8. The method for producing a polytetrafluoroethylene dispersion liquid for a copper-clad plate according to claim 7, characterized by, The cation exchange resin used is Dow IRC76.

9. The method for producing a polytetrafluoroethylene dispersion liquid for a copper-clad plate according to any one of claims 5 to 8, characterized by, The preparation steps of the polytetrafluoroethylene polymerization liquid are as follows: (1) Add the stabilizer and a portion of the dispersant to the aqueous reaction medium; the portion of the dispersant refers to the dispersant that accounts for 40% to 50% of the total amount of dispersant added; (2) Add a modifier to the reaction system after the oxygen analysis is qualified, raise the temperature, and then continuously add gaseous tetrafluoroethylene monomer to carry out polymerization; The initiator and the remaining dispersant are added gradually during the addition of tetrafluoroethylene monomer.

10. Use of a polytetrafluoroethylene dispersion for a copper clad plate, characterized by, The polytetrafluoroethylene dispersion of the copper-clad laminate according to any one of claims 1 to 4 is used to prepare polytetrafluoroethylene copper-clad laminate.

Images