WO2023142947A2 - Environmentally-friendly fluoropolymer concentrated aqueous dispersion, preparation method therefor and application thereof - Google Patents

Abstract

An environmentally-friendly fluoropolymer concentrated aqueous dispersion, a preparation method therefor and an application thereof. The fluoropolymer concentrated aqueous dispersion disclosed herein comprises fluoropolymer particles dispersed in an aqueous solvent and a polyvinylpyrrolidone-based polymer represented by formula (I). The presence of the polyvinylpyrrolidone-based polymer represented by formula (I) enables the provided fluoropolymer concentrated aqueous dispersion to have the advantages of low viscosity and good stability, and the polyvinylpyrrolidone-based polymer represented by formula (I) has good biodegradability and water solubility, and is environmentally-friendly. The provided fluoropolymer concentrated aqueous dispersion can be used for producing a fluoropolymer anti-dripping agent, and impregnating porous glass and porous metal, or served as a dielectric coating, and has characteristics such as good appearance and low conductivity.

Description

Concentrated aqueous dispersion of an environment-friendly fluoropolymer and its preparation method and application technical field

The invention relates to the technical field of coatings, in particular to a concentrated aqueous dispersion of an environment-friendly fluorine-containing polymer, a preparation method and application thereof.

Background technique

Fluoropolymers (such as polytetrafluoroethylene, etc.) have excellent chemical stability, good electrical properties, and low surface energy, and are widely used in chemical, aerospace, military and other industries. Fluoropolymer aqueous dispersions are widely used It is widely used in the anticorrosion of oil platforms, reactors, aircraft, and oil pipelines in the production of non-stick materials in daily life.

The solid content of the initial aqueous dispersion of fluorine-containing polymer particles obtained from fluorine-containing polymer units is generally less than 30%, and contains a large amount of water. It is not suitable for direct preparation and use of coatings. It needs to be concentrated to a higher concentration before it can be used. Usually, it can be used A starting aqueous dispersion of fluoropolymer particles with a solids content generally less than 30% is concentrated to about 60% solids by chemical concentration, electroconcentration or vacuum concentration to obtain a concentrated aqueous dispersion of fluoropolymer.

In the process of preparing concentrated aqueous dispersions of fluoropolymers, it is usually necessary to add surfactants to the dispersion to help the fluoropolymer particles to stabilize in a certain concentration (usually 40-70% solids) in the water phase. However, such surfactants currently used are mainly polyoxyethylene ether surfactants, such as trimethyl nonyl polyoxyethylene ether (TMN series), fatty alcohol polyoxyethylene ether (APEO series), alkanes Nonionic surfactants such as phenol polyoxyethylene ether (NPEO, OPEO), and other anionic surfactants are used in combination, such as patent documents CN109517096A, CN1551909A and US2011144255A1. However, such polyoxyethylene ether surfactants have poor biodegradability and are not environmentally friendly, which limits the wide application of concentrated aqueous dispersions of such fluoropolymers.

Contents of the invention

The present invention aims to provide a concentrated aqueous dispersion of fluoropolymer and its preparation method and application.

In a first aspect of the present invention, there is provided a concentrated aqueous dispersion of a fluoropolymer comprising fluoropolymer particles dispersed in an aqueous solvent, a polyvinylpyrrolidone-based polymer represented by the following formula (I): and optionally a non-fluorinated anionic surfactant:

(C ₆ H ₉ NO) _n (I)

In formula (I), n can be 9-450;

Wherein, based on the weight of the fluoropolymer particles, the total content of the polyvinylpyrrolidone-based polymer and the optional non-fluorinated anionic surfactant may be 2-16 wt%.

In some embodiments, the molecular weight of the polyvinylpyrrolidone-based polymer may be 1,000-100,000, optionally 3,000-60,000.

In some embodiments, the polyvinylpyrrolidone-based polymer can be selected from one or more of the following: K12, K15, K17, K25, K30, wherein the K values represent the viscosity of polyvinylpyrrolidone (PVP) aqueous solution grade.

In some embodiments, based on the weight of the fluoropolymer particles, the content of the polyvinylpyrrolidone-based polymer may be 2-12 wt%, optionally 4-10 wt%.

In some embodiments, the non-fluorinated anionic surfactant is selected from one or more of the following: alkyl sulfate, polyoxyethylene fatty alcohol ether sulfate, fatty acid salt, alcohol ether carboxylate, Alkylphenol ether carboxylate, stearate, alkylbenzene sulfonate, α-olefin sulfonate, α-sulfomonocarboxylate, fatty acid ester sulfonate, succinate sulfonate, Alkyl naphthalene sulfonate, alkyl glyceryl ether sulfonate, petroleum sulfonate, lignin sulfonate, alkyl carboxylate; further optionally, the non-fluorinated anionic surfactant is selected from the following One or more of: sodium dodecyl sulfate (SDS), ammonium dodecyl sulfate (AESA-70), sodium dodecylbenzenesulfonate (SDBS), dodecyl diphenyl ether disulfonate sodium lauryl ether sulfosuccinate (SLDED), disodium laureth sulfosuccinate (MES), sodium dihexyl sulfosuccinate, sodium dioctyl sulfosuccinate (OT-75), potassium stearate , sodium lauryl carboxylate and sodium lauryl alcohol polyoxyethylene ether carboxylate.

In some embodiments, the non-fluorinated anionic surfactant is present in an amount of 0-12 wt%, optionally 0-10 wt%, based on the weight of the fluoropolymer particles.

In some embodiments, based on the weight of the concentrated aqueous dispersion of fluoropolymer, the solid content of the fluoropolymer particles may be 40-75 wt%, optionally 50-70 wt%, further optionally 55-65wt%.

In some embodiments, the fluoropolymer particles can include polytetrafluoroethylene particles, modified polytetrafluoroethylene particles, or combinations thereof.

In some embodiments, the particle size of the fluoropolymer particles may be 0.15-0.40 μm, optionally 0.20-0.35 μm.

The second aspect of the present invention provides the preparation method of the concentrated aqueous dispersion of the fluoropolymer provided by the first aspect of the present invention, it comprises the following steps:

S1: Adding a polyvinylpyrrolidone-based polymer represented by the following formula (I) and an optional non-fluorinated anionic surfactant to an initial aqueous dispersion of fluoropolymer particles, optionally while preparing the When the initial aqueous dispersion of fluoropolymer particles is added to the polymerized units of said fluoropolymer, a polyvinylpyrrolidone-based polymer represented by the following formula (I) is added to obtain a concentrated initial aqueous dispersion of fluoropolymer particles Dispersions;

S2: Concentrating the concentrated initial aqueous dispersion of fluoropolymer particles obtained in step S1;

(C ₆ H ₉ NO) _n (I)

In formula (I), n can be 9-450;

Wherein, based on the weight of the fluoropolymer particles in the concentrated initial aqueous dispersion of the fluoropolymer, the polyvinylpyrrolidone-based polymer represented by formula (I) and the optional non-fluorinated anionic surfactant The total content can be 2-16wt%, optionally 2-12wt%, further optionally 4-10wt%.

In some embodiments, the non-fluorinated anionic surfactant may be added in an amount of 0-12 wt%, optionally 0-10 wt%, based on the weight of the fluoropolymer particles.

In some embodiments, the concentrated initial aqueous dispersion of fluoropolymer particles has a solids content of 15% fluoropolymer particles based on the weight of the concentrated initial aqueous dispersion of fluoropolymer particles. -35wt%, optionally 20-30wt%.

In some embodiments, the preparation method may further include the step of adding a polymerization initiator and an emulsifier to the comonomer of the fluoropolymer to prepare an initial aqueous dispersion of the fluoropolymer; wherein the The polymerization initiator may include persulfate, organic peroxide or a combination thereof, optionally ammonium persulfate, potassium persulfate, succinic acid peroxide or a combination thereof; the emulsifier may include a fluorocarbon emulsifier , hydrocarbon emulsifier or its combination, can be perfluoro 2-methyl-3-oxahexanoic acid ammonium, perfluoro 2,5-dimethyl-3,6-dioxanonanoic acid sodium, perfluoro Sodium hexyl acetate, potassium ω-hydrogen perfluoroheptanoate, etc. And before adding the polyvinylpyrrolidone-based polymer represented by formula (I) to the initial aqueous dispersion of the fluoropolymer particles, the fluorine-containing polymer can also be removed by ultrafiltration or contact with a strong basic ion exchange resin. An emulsifier in the initial aqueous dispersion of polymer particles, in which case the concentrated aqueous dispersion of fluoropolymer prepared is free or substantially free of fluorinated anionic surfactants.

In some embodiments, when the polyvinylpyrrolidone-based polymer represented by formula (I) is added to the polymerized units of the fluoropolymer when preparing the initial aqueous dispersion of fluoropolymer particles, Concentrated aqueous dispersions of fluoropolymers with improved stability are obtained.

The third aspect of the present invention also provides that the concentrated aqueous dispersion of fluoropolymer provided by the first aspect of the present invention is useful in impregnating porous fabrics, porous metals, as dielectric coatings or in the production of fluoropolymer anti-dripping agents. in the application.

The concentrated aqueous dispersion of the fluoropolymer provided based on the above technical scheme comprises a polyvinylpyrrolidone (PVP)-based polymer represented by formula (I) (and optionally a non-fluorinated polyvinylpyrrolidone with good biodegradability and water solubility). Anionic surfactants), without polyoxyethylene ether surfactants, can provide concentrated aqueous dispersions of fluoropolymers with both low viscosity and good stability characteristics, and polyvinylpyrrolidone ( PVP) series polymers (and optional non-fluorinated anionic surfactants) have characteristics such as good biodegradability and water solubility, so they are more environmentally friendly compared to the polyoxyethylene ether surfactants commonly used in the prior art. friendly. The results of the examples prove that the viscosity of the concentrated aqueous dispersion of the fluoropolymer provided by the present invention is not more than 25mPa·s, preferably not more than 22mPa·s; and both have good mechanical stability and storage stability. The storage time can be as long as 5 weeks, 8 weeks, or even 10 weeks without sedimentation, and the conductivity of the coating prepared by it is less than 1μS in the elution test, which can be used for circuit board coating and impregnation of porous fabrics And porous metals, and can be used to produce fluoropolymer anti-dripping agents, etc.

Detailed ways

Hereinafter, the concentrated aqueous dispersion of fluoropolymer provided by the present invention and its preparation method and application will be described through specific embodiments. However, the following descriptions are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

A "range" disclosed herein is defined in terms of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive and may be combined arbitrarily, ie any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are contemplated. Additionally, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5. In this application, unless otherwise stated, the numerical range "a-b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article, and "0-5" is only an abbreviated representation of the combination of these values. In addition, when expressing that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

If there is no special description, all the implementation modes and optional implementation modes of the present application can be combined with each other to form new technical solutions.

If there is no special description, all the technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

If there is no special description, the "comprising" and "comprising" mentioned in this application mean open or closed. For example, the "comprising" and "comprising" may mean that other components not listed may be included or included, or only listed components may be included or included.

In this application, the term "or" is inclusive unless otherwise stated. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied by either of the following: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; or both A and B are true (or exist).

In the description herein, it should be noted that, unless otherwise specified, "several" in "one or several" means two or more.

Concentrated aqueous dispersions of fluoropolymers are widely used in chemical, aerospace, military and other industries due to their excellent chemical stability, good electrical properties, and low surface energy. At present, in the preparation of concentrated aqueous dispersions of fluoropolymers, the starting of fluoropolymer particles is usually carried out under the combined action of nonionic surfactants (polyoxyethylene ether surfactants) and anionic surfactants. The aqueous dispersion (an aqueous dispersion of fluoropolymer particles having a solids content of about 15-35% formed from the polymerization of the comonomers of the fluoropolymer) is obtained by concentration. However, the commonly used polyoxyethylene ether surfactants have poor biodegradability and are not friendly to the environment, which limits the application of concentrated aqueous dispersions of such fluoropolymers.

The inventors have noticed through a large number of studies that when the polyvinylpyrrolidone (PVP) series polymer shown in the formula (I) is added into the initial aqueous dispersion of fluoropolymer particles as a surfactant (and any selected non-fluorinated anionic surfactants with good biodegradability and water solubility), without adding commonly used polyoxyethylene ether surfactants, low viscosity, good stability, and low conductivity can be obtained Concentrated aqueous dispersions of fluoropolymers, thereby providing an environmentally friendly concentrated aqueous dispersions of fluoropolymers.

In a first aspect of the present invention, there is provided a concentrated aqueous dispersion of a fluoropolymer comprising fluoropolymer particles dispersed in an aqueous solvent, a polyvinylpyrrolidone-based polymer represented by the following formula (I), and Optional non-fluorinated anionic surfactants:

(C ₆ H ₉ NO) _n (I)

In formula (I), n can be 9-450;

Wherein, based on the weight of the fluoropolymer particles, the total content of the polyvinylpyrrolidone-based polymer and the optional non-fluorinated anionic surfactant may be 2-16 wt%. When the total content of polyvinylpyrrolidone polymer and optional non-fluorinated anionic surfactant is less than 2wt%, it will not be able to effectively suppress the increase of the viscosity of the aqueous dispersion, and the stability of the dispersion is relatively poor, and the obtained product It cannot be used as a coating; when the total content of polyvinylpyrrolidone-based polymers and optional non-fluorinated anionic surfactants is higher than 16% by weight, it will lead to excessively high surfactant content in the concentrated aqueous dispersion obtained during production, and May deteriorate the viscosity characteristics and stability of the product.

In some embodiments, the higher the degree of polymerization of the polyvinylpyrrolidone-based polymer, the higher the average molecular weight, and the better the mechanical stability. However, if the polymerization is too high, the greater the average molecular weight, the greater the viscosity of the dispersion. May be difficult to handle. Therefore, the degree of polymerization of the polyvinylpyrrolidone polymer in the present invention is preferably 9-450, and the molecular weight is preferably 1000-100000, more preferably 3000-60000, such as 3000-5000, 5000-10000, 10000-20000, 20000-30000, 40000-50000 etc. Optionally, the polyvinylpyrrolidone-based polymer can be selected from one or more of the following: K12, K15, K17, K25, K30, K60, K90 and K120, among which K12, K15, K17, One or more of K25 and K30 can be obtained commercially, and the above K values all represent the viscosity grade of the PVP aqueous solution.

In some embodiments, based on the weight of the fluoropolymer particles, the content of the polyvinylpyrrolidone-based polymer may be 2-12 wt%, optionally 4-10 wt%.

In some embodiments, the non-fluorinated anionic surfactant can be selected from one or more of the following: alkyl sulfate, polyoxyethylene fatty alcohol ether sulfate, fatty acid salt, alcohol ether carboxylate , Alkylphenol ether carboxylate, stearate, alkylbenzene sulfonate, α-olefin sulfonate, α-sulfomonocarboxylate, fatty acid ester sulfonate, succinate sulfonate , alkyl naphthalene sulfonate, alkyl glyceryl ether sulfonate, petroleum sulfonate, lignosulfonate, alkyl carboxylate; further optionally, the non-fluorinated anionic surfactant can be selected from One or more of the following: sodium dodecyl sulfate (SDS), ammonium dodecyl sulfate (AESA-70), sodium dodecylbenzenesulfonate (SDBS), dodecyl diphenyl ether Sodium Disulfonate (SLDED), Disodium Lauryl Ether Sulfosuccinate (MES), Sodium Dihexyl Sulfosuccinate, Sodium Dioctyl Sulfosuccinate (OT-75), Stearin Potassium Lauryl Carboxylate, Sodium Lauryl Carboxylate and Sodium Laureth Carboxylate.

In some embodiments, the non-fluorinated anionic surfactant is present in an amount of 0-12 wt%, optionally 0-10 wt%, based on the weight of the fluoropolymer particles.

In some embodiments, based on the weight of the concentrated aqueous dispersion of fluoropolymer, the fluoropolymer particles may have a solids content of 40-75 wt%, optionally 50-70 wt%, further optionally 55-65wt%.

In some embodiments, the fluoropolymer particles may include polytetrafluoroethylene (PTFE) particles, modified polytetrafluoroethylene particles, or combinations thereof. Among them, modified PTFE is PTFE that contains a small amount of copolymerization modification with other comonomers in the polymer, and its content is limited to not producing melt fluidity. As other comonomers, hexafluoropropylene (HFP), chlorine Trifluoroethylene (CTFE), perfluoroalkyl vinyl ether (PAVE), vinylidene fluoride (VdF), vinylidene fluoride, or hexafluoroethylene and vinylidene fluoride, etc.

In some embodiments, the particle size of the fluoropolymer may be 0.15-0.40 μm, optionally 0.20-0.35 μm, such as 0.20 μm, 0.25 μm, 0.30 μm and 0.35 μm.

In a second aspect of the present invention, there is also provided a process for the preparation of a concentrated aqueous dispersion of fluoropolymer, comprising the steps of:

S1: Adding a polyvinylpyrrolidone-based polymer represented by the following formula (I) and an optional non-fluorinated anionic surfactant to an initial aqueous dispersion of fluoropolymer particles, optionally while preparing the When the initial aqueous dispersion of fluoropolymer particles is added to the polymerized units of said fluoropolymer, a polyvinylpyrrolidone-based polymer represented by the following formula (I) is added to obtain a concentrated initial aqueous dispersion of fluoropolymer particles Dispersions;

S2: Concentrating the concentrated initial aqueous dispersion of fluoropolymer particles obtained in step S1;

(C ₆ H ₉ NO) _n (I)

In formula (I), n can be 9-450;

wherein, based on the weight of the fluoropolymer particles in the concentrated initial aqueous dispersion of fluoropolymer particles, the polyvinylpyrrolidone-based polymer represented by formula (I) and optionally the non-fluorinated anionic surfactant The total content of can be 2-16wt%, optionally 2-12wt%, further optionally 4-10wt%. wherein a total amount of 2-16 wt% of polyvinylpyrrolidone represented by formula (I) is added thereto during the concentration process (or during both polymerization and concentration) of the initial aqueous dispersion of fluoropolymer particles Based on polymers and optional non-fluorinated anionic surfactants, it can effectively avoid the problem of viscosity increase of aqueous dispersions during the concentration process, and obtain products with good stability; on the other hand, compared to the commonly used poly As the oxyethylene ether surfactant, the polyvinylpyrrolidone polymer represented by formula (I) and an optional non-fluorinated anionic surfactant are more friendly to the environment.

In some embodiments, the non-fluorinated anionic surfactant is present in an amount of 0-12 wt%, optionally 0-10 wt%, based on the weight of the fluoropolymer particles.

In some embodiments, the concentrated initial aqueous dispersion of fluoropolymer particles has a solids content of 15% fluoropolymer particles based on the weight of the concentrated initial aqueous dispersion of fluoropolymer particles. -35wt%, optionally 20-30wt%.

In some embodiments, the above preparation method may further include the step of adding a polymerization initiator and an emulsifier to the comonomer of the fluoropolymer to prepare the initial aqueous dispersion of the fluoropolymer particles. Wherein the polymerization initiator is a free radical initiation, and a persulfate with a longer half-life may be selected, such as potassium persulfate or ammonium persulfate; potassium permanganate or oxalic acid with a shorter half-life may also be selected. In addition to the preferred persulfate initiators of the present invention, small amounts of short chain dicarboxylic acids capable of reducing coagulum, such as succinic acid or succinic acid generating initiators such as disuccinic acid peroxide (DSP), may also be added. The amount of the emulsifier may account for 0.1-0.5 wt% of the fluoropolymer produced by polymerization, which may include a fluorocarbon emulsifier, a hydrocarbon emulsifier or a combination thereof, optionally perfluoro 2-methyl-3 - Ammonium oxahexanoate, sodium perfluoro-2,5-dimethyl-3,6-dioxanononanoate, sodium perfluorohexyl acetate, potassium ω-hydrogen-containing perfluoroheptanoate, etc. And before adding the polyvinylpyrrolidone-based polymer represented by formula (I) to the initial aqueous dispersion of fluoropolymer particles, the fluoropolymer particles can also be removed by ultrafiltration or contacting with an anion exchange resin, etc. emulsifier in the initial aqueous dispersion. Therefore, the concentrated aqueous dispersion of fluoropolymer finally provided by the present invention may or may not contain emulsifiers, that is, the concentrated aqueous dispersion of fluoropolymer finally provided by the present invention may or may not contain fluorinated anions Surfactant.

In some embodiments, when the polyvinylpyrrolidone-based polymer represented by formula (I) is added to the polymerized units of the fluoropolymer when preparing the initial aqueous dispersion of fluoropolymer particles, Concentrated aqueous dispersions with lower viscosity and better stability are obtained.

In some embodiments, the concentration in step S2 can use chemical concentration method, electric concentration method or vacuum concentration method, etc., so that the solid content of fluoropolymer particles in the concentrated aqueous dispersion is 40-75wt%, optional 50-70wt%, further optionally 55-65wt%.

It has been verified that the concentrated aqueous dispersion of the fluoropolymer prepared by the present invention has characteristics such as low viscosity, high shear stability and high storage stability, and has high CCT (critical cracking thickness) when used as a coating ), and has a low elution conductivity, so in a third aspect the present invention also provides the above-mentioned concentrated aqueous dispersion of fluoropolymers in impregnating porous metals, porous fabrics, as dielectric coatings or in the production of fluorine-containing Polymer anti-dripping agent, etc., can be widely used in chemical industry, machinery, petroleum, medicine, electronics, optics and other fields, and exhibits strong wear resistance, good surface gloss, good film forming and The film has the characteristics of high limit film crack thickness and crack resistance.

In some embodiments, the porous fabric can be glass cloth, and glass cloth is divided into two types: alkali-containing glass cloth and alkali-free glass cloth. When alkali-containing glass cloth is impregnated with a concentrated aqueous dispersion of fluoropolymer, a nonstick grade fluoropolymer varnished cloth (such as PTFE varnished cloth) is obtained, which can be used for sealing and cleaning food, fertilizer, soy milk and blood products Anti-sticking and anti-corrosion treatment of rollers in textile and printing and dyeing industries of sanitary conveyor belts and chemical industries, leak prevention of tents and roofs, etc. When the concentrated aqueous dispersion of fluoropolymer is impregnated with alkali-free glass cloth, electrical insulating fluoropolymer varnished cloth can be obtained, which can be used as insulation groove, inter-turn insulation and wrapping insulation in aircraft engines and motors, etc. It can also be used as a microwave material for vacuum pumps, radars, electronic instruments, televisions, computers, and satellite communications by hot pressing into laminated sheets and foil sheets.

Example

Hereinafter, examples of the present application will be described. The embodiments described below are exemplary and are only used for explaining the present application, and should not be construed as limiting the present application. If no specific technique or condition is indicated in the examples, it shall be carried out according to the technique or condition described in the literature in this field or according to the product specification. The reagents or instruments used were not indicated by the manufacturer, and they were all commercially available conventional products.

Impregnation of glass cloth

The alkali-free glass cloth was treated with the concentrated aqueous dispersion of fluoropolymer prepared according to the present invention in the following sequence. Plain weaving density of glass cloth: 60 (line/25mm) in length, 46 (line/25mm) in width, and 0.05mm in thickness. The glass cloth used is a product of plain weave cloth with neat warp and weft, no cracks, broken ends and other defects after hot washing.

①Impregnate glass cloth once with concentrated aqueous dispersion of fluoropolymer, dry at about 100°C, bake at about 280-290°C, and then fire at about 380°C for 3 minutes. Leave to cool at room temperature.

②Impregnate the above-mentioned impregnated product in the concentrated aqueous dispersion of the same fluoropolymer to contain the impregnated solution, dry at about 100°C, and fire at about 380°C for 3 minutes. The coated concentrated aqueous dispersion of fluoropolymer was then observed for bubbling.

③Repeat the immersion, drying, and firing processes of ② to obtain a coated glass cloth formed by a film with a solid content of fluoropolymer of about 60-65% and a film thickness of about 80 μm.

Performance Testing

Solid content of concentrated aqueous dispersions: determined from the weight loss of each aqueous dispersion after drying at 150° C. for 1 hour.

Viscosity of the concentrated aqueous dispersion: Take 500ml at 25°C to measure the viscosity on an NDJ-1 rotational viscometer.

Mechanical stability of the concentrated aqueous dispersion: use a high-speed emulsifier, test conditions: 25°C, emulsifier speed 10,000rpm, high-speed shearing for 5 minutes, observe whether the emulsion is broken, if it is not broken, the stability is good; otherwise, it is stable Poor sex.

Storage stability of concentrated aqueous dispersions: Take a quantitative amount of concentrated aqueous dispersions of fluoropolymers, store them at room temperature, and observe the status of the dispersions every other week;

CCT Test of Coatings Formed from Concentrated Aqueous Dispersions: Fill the container with the dispersion to be tested and remove with a straw if there is foam. Immerse the degreased aluminum plate (18×4×4mm ² ) into the dispersion, take out the plate and hang it at an angle of 45° to dry, let the plate dry for 5 minutes, then heat it at 380°C for 10 minutes, cool the plate and use a microscope to grade the coating layer of cracks. The maximum film thickness without cracking is taken as the critical film thickness (μm).

Chromaticity test of coated glass cloth: use Konica Minolta CM-5 colorimeter to test L, a and b of coated glass cloth, by subtracting the chromaticity L0, a0 of the glass cloth before coating and b0 to calculate the changes in chromaticity values ΔL, Δa and Δb. When the yellowness index Δb is less than 1, the dispersion is considered good, and when the value is equal to or greater than 1, the dispersion is considered poor. A dispersion is considered poor when cracks in the coating are observed.

Elution conductivity of coated glass cloth: immerse coated glass cloth in 10 times the mass of distilled water for 1 week, and measure the conductivity of the eluent with a conductivity tester manufactured by Lacom. The conductivity is less than 1 μS, indicating that the ionic components are hardly dissolved, which is considered good; while the conductivity exceeds 1 μS, it is considered poor.

Example 1

In a 5L stainless steel high-pressure reactor equipped with a jacket and a horizontal stirrer, add 3000g of deionized water and 80g of paraffin, heat the contents of the reactor to 70°C, and vacuumize the reactor, replace it with nitrogen and replace it with tetrafluoroethylene (TFE) purge. Add 0.02g of polymerization initiator ammonium persulfate, 3g of fluorine-containing emulsifier (sodium perfluorohexyl acetate), 1wt% of BASF PVP K12 (based on the weight of polytetrafluoroethylene particles, the same below), and the control reaction pressure is 2.5MPa , continuously feed TFE through the compressor. By means of emulsion polymerization, a starting aqueous dispersion of polytetrafluoroethylene particles is prepared. The solids content of this dispersion was about 20% by weight and the average particle size of the polytetrafluoroethylene particles was about 250 nm.

Get the initial aqueous dispersion of 2kg polytetrafluoroethylene particles (wherein contain the sodium perfluorohexyl acetate of about 0.2wt% based on the weight of polytetrafluoroethylene particles), add the BASF PVP K12 of 5wt%, carry out vacuum concentration, gained concentrated The solids content of the aqueous dispersion was 60.9% by weight. The storage stability is good, and no precipitation occurs when placed for 10 weeks. The performance test results are shown in Table 1 below.

Example 2

In a 5L stainless steel high-pressure reactor equipped with a jacket and a horizontal stirrer, add 3000g of deionized water and 80g of paraffin, heat the contents of the reactor to 70°C, and vacuumize the reactor, replace it with nitrogen and replace it with tetrafluoroethylene (TFE) purge. Add 0.02g of polymerization initiator ammonium persulfate, 3g of fluorine-containing emulsifier (sodium perfluorohexyl acetate), 1wt% of BASF PVP K17, control the reaction pressure to 2.5MPa, and continuously feed TFE through the compressor. By means of emulsion polymerization, a starting aqueous dispersion of polytetrafluoroethylene particles is prepared. The solids content of this dispersion was about 25% by weight, and the average particle size of the polytetrafluoroethylene particles was about 250 nm.

Take 2kg of the initial aqueous dispersion of polytetrafluoroethylene particles, add 5wt% of BASF PVP K17, and carry out vacuum concentration. The solid content of the resulting concentrated aqueous dispersion is 61.8wt%. The storage stability is good, and no precipitation occurs when placed for 10 weeks. The performance test results are shown in Table 1 below.

Example 3

According to Example 2, the difference is that 2kg of the initial aqueous dispersion of polytetrafluoroethylene particles is taken, and 4wt% of BASF PVP K17 is added thereto for vacuum concentration, and the solid content of the gained concentrated aqueous dispersion is about 62.4wt%. The storage stability is good, and no precipitation occurs when placed for 10 weeks. The performance test results are shown in Table 1 below.

Example 4

According to Example 2, the difference is that 2kg of the initial aqueous dispersion of polytetrafluoroethylene particles is taken, and 9wt% of BASF PVP K17 is added thereto for vacuum concentration, and the solid content of the gained concentrated aqueous dispersion is about 61.7wt%. The storage stability is good, and no precipitation occurs when placed for 10 weeks. The performance test results are shown in Table 1 below.

Example 5

In a 5L stainless steel high-pressure reactor equipped with a jacket and a horizontal stirrer, add 3000g of deionized water and 80g of paraffin, heat the contents of the reactor to 70°C, and vacuumize the reactor, replace it with nitrogen and replace it with tetrafluoroethylene (TFE) purge. Add 0.02g of polymerization initiator ammonium persulfate, 3g of fluorine-containing emulsifier (sodium perfluorohexyl acetate), 1wt% of BASF PVP K30, control the reaction pressure to 2.5MPa, and continuously feed TFE through the compressor. By means of emulsion polymerization, a starting aqueous dispersion of polytetrafluoroethylene particles is prepared. The solid content of this dispersion is about 30 wt%, and the average particle size of the polytetrafluoroethylene particles is 250 nm.

Take 2kg of the initial aqueous dispersion of polytetrafluoroethylene particles, add 5wt% of BASF PVP K30, and carry out vacuum concentration, and the solid content of the resulting concentrated aqueous dispersion is 61.6wt%. The storage stability is good, and no precipitation occurs when placed for 10 weeks. The performance test results are shown in Table 1 below.

Example 6

According to Example 5, the difference is that 2 kg of the initial aqueous dispersion of polytetrafluoroethylene particles is taken, and 3 wt% of BASF PVP K30 is added thereto for vacuum concentration, and the solid content of the resulting concentrated aqueous dispersion is about 61.4 wt%. A small amount of precipitation appeared when standing for 8 weeks. The performance test results are shown in Table 1 below.

Example 7

According to Example 5, the difference is that 2kg of the initial aqueous dispersion of polytetrafluoroethylene particles is taken, and 7wt% of BASF PVP K30 is added thereto for vacuum concentration, and the solid content of the gained concentrated aqueous dispersion is about 62.2wt%. A small amount of precipitation appeared when standing for 5 weeks. The performance test results are shown in Table 1 below.

Example 8

In a 5L stainless steel high-pressure reactor equipped with a jacket and a horizontal stirrer, add 3000g of deionized water and 80g of paraffin, heat the contents of the reactor to 70°C, and vacuumize the reactor, replace it with nitrogen and replace it with tetrafluoroethylene (TFE) purge. Add 0.02 g of polymerization initiator ammonium persulfate, 3 g of fluorine-containing emulsifier (sodium perfluorohexyl acetate), control the reaction pressure to 2.5 MPa, and continuously feed TFE through the compressor. By means of emulsion polymerization, a starting aqueous dispersion of polytetrafluoroethylene particles is prepared. The solid content of this dispersion is about 20 wt%, and the average particle size of the polytetrafluoroethylene particles is 250 nm.

Take 2kg of the initial aqueous dispersion of polytetrafluoroethylene particles, add 6wt% of BASF PVP K17, and carry out vacuum concentration. The solid content of the resulting concentrated aqueous dispersion is 61.6wt%, and a small amount of precipitation occurs when placed for 8 weeks. The performance test results are shown in Table 1 below.

Example 9

According to Example 8, the difference is that 2kg of the initial aqueous dispersion of polytetrafluoroethylene particles is taken, and 2wt% of BASF PVP K17 is added thereto for vacuum concentration, and the solid content of the gained concentrated aqueous dispersion is about 55.2wt%. A small amount of precipitation appeared after standing for 5 weeks. The performance test results are shown in Table 1 below.

Example 10

According to Example 8, the difference is that 2kg of the initial aqueous dispersion of polytetrafluoroethylene particles is taken, and 12wt% of BASF PVP K17 is added thereto for vacuum concentration, and the solid content of the gained concentrated aqueous dispersion is about 64.2wt%. A small amount of precipitation appeared after standing for 5 weeks. The performance test results are shown in Table 1 below.

Compare 1-4

Comparative Example 1 was carried out according to the steps of Example 1, except that the surfactant used was polyvinyl alcohol (PVOH, BASF, molecular weight 20000). The resulting concentrated aqueous dispersion had a solids content of about 60% by weight. A small amount of precipitation appeared after standing for 4 weeks. The performance test results are shown in Table 1 below.

Comparative Example 2 was carried out according to the steps of Example 1, except that the surfactant used was polyacrylamide (PAM, BASF, molecular weight 1000). The resulting concentrated aqueous dispersion had a solids content of about 60% by weight. Partial precipitation appeared after standing for 1 week, and the storage stability was poor. The performance test results are shown in Table 1 below.

Comparative Example 3 was carried out according to the steps of Example 1, except that the surfactant used was branched chain secondary alcohol polyoxyethylene ether (TERGITOL ^™ TMN-10, molecular weight 500-700). The resulting concentrated aqueous dispersion had a solids content of about 59.8 wt%. A small amount of precipitation appeared after standing for 4 weeks. The performance test results are shown in Table 1 below.

Comparative Example 4 was carried out according to the steps of Example 8, except that the surfactant used was 5wt% BASF PVP K30 and 1wt% TMN-10. The resulting concentrated aqueous dispersion had a solids content of about 60% by weight. A small amount of precipitation appeared after standing for 4 weeks. The performance test results are shown in Table 1 below.

As can be seen from the above table 1, the concentrated aqueous dispersions prepared by using a kind of other nonionic surfactants in Comparative Examples 1-3 cannot obtain satisfactory mechanical stability and storage stability; During the preparation of the initial aqueous dispersion of tetrafluoroethylene particles and in the subsequent concentration process, the polyvinylpyrrolidone (PVP) series polymer represented by the formula (I) is added step by step, and the polyvinylpyrrolidone (PVP) series polymer represented by the formula (I) is added directly to the polyvinylpyrrolidone (PVP) series polymer in Example 8-10. Add the polyvinylpyrrolidone (PVP) series polymer represented by the formula (I) of metering in the initial aqueous dispersion of tetrafluoroethylene particle as surfactant, all can obtain and have low viscosity, good mechanical stability and storage simultaneously. Concentrated aqueous dispersion of stabilized fluoropolymer. Specifically, the viscosity of the concentrated aqueous dispersion of polytetrafluoroethylene obtained is no more than 25mPa·s, preferably no more than 22mPa·s, and all have good mechanical stability and storage stability, and the storage time at room temperature It can be as long as 5 weeks, 8 weeks, or even 10 weeks without sedimentation, and even shows a better stability effect than when adding two surfactants (comparative example 4, TMN-10+K30). Especially when the total amount of polyvinylpyrrolidone (PVP) polymer represented by formula (I) is 4-10wt%, it has a better stabilizing effect, and because polyvinylpyrrolidone (PVP) represented by formula (I) The polytetrafluoroethylene based polymer has good biodegradability, so the concentrated aqueous dispersion of polytetrafluoroethylene prepared by it is environmentally friendly.

On the other hand, compared to Comparative Examples 1-4, the concentrated aqueous dispersions prepared in Examples 1-10 have a larger crack-free thickness (CCT), and the concentrated aqueous dispersions of PTFE prepared in Examples 1-10 When the dispersion is impregnated with glass cloth, the whiteness of the glass cloth (the yellowing index Δb is all less than 1) is good, and the conductivity of the elution test is low (<1 μS).

Examples 11-15

Embodiment 11-15 is to carry out according to the step of embodiment 8, and difference only is that the surfactant used and content are different. Specifically:

The surfactant used in Example 11 is 10wt% BASF PVP K17+1wt% sodium dodecylbenzenesulfonate (SDBS).

The surfactant used in Example 12 is 5wt% BASF PVP K17+2wt% sodium dodecylbenzenesulfonate (SDBS).

The surfactant used in embodiment 13 is 5wt% BASF PVP K17+5wt% sodium lauryl carboxylate.

The surfactant used in Example 14 is 1wt% BASF PVP K17+10wt% sodium dihexylsulfosuccinate.

The surfactant used in Example 15 is 1wt% BASF PVP K17+1wt% sodium dodecyl sulfate (SDS).

The performance test results of the concentrated aqueous dispersions of polytetrafluoroethylene prepared in Examples 11-15 are shown in Table 2 below.

Table 2: Concentrated aqueous dispersion of polytetrafluoroethylene prepared in Examples 11-15 and determination of processing performance by dipping

From the results recorded in Table 2, it can be seen that when the initial aqueous dispersion of polytetrafluoroethylene particles is concentrated, it is also possible to add the polyvinylpyrrolidone (PVP) polymer represented by the formula (I) and non- Fluorinated anionic surfactant, the concentrated aqueous dispersion of polytetrafluoroethylene that prepares also all has characteristics such as low viscosity, good mechanical stability and storage stability concurrently, and the polyvinylpyrrolidone ( PVP) series polymers and non-fluorinated anionic surfactants all have characteristics such as good biodegradability and water solubility, so compared with the polyoxyethylene ether surfactants with poor biodegradability in the prior art, they are harmful to the environment. more friendly. On the other hand, the concentrated aqueous dispersions prepared in Examples 11-15 also had a large crack-free thickness (CCT), and when the concentrated aqueous dispersions of polytetrafluoroethylene prepared in Examples 11-15 were used to impregnate the glass cloth, the glass The cloth whiteness (the yellowing index Δb is all less than 1) is good, and the conductivity of the elution test is low (<1μS).

The embodiments described here are only for illustration (as an illustration), and various modifications or changes made by the skilled person should also be included in the essential scope of the patent application.

Industrial Applicability

The invention provides a concentrated aqueous dispersion of an environmentally friendly fluoropolymer and the application of the preparation method, which can be used to produce fluoropolymer anti-dripping agents, impregnate porous glass, porous metal or use as a dielectric coating , and has good appearance and low electrical conductivity, suitable for industrial applications.

Claims (14)

1. A concentrated aqueous dispersion of a fluoropolymer comprising fluoropolymer particles dispersed in an aqueous solvent, a polyvinylpyrrolidone-based polymer represented by the following formula (I), and optionally a non-fluorinated anionic surfactant agent:

   (C ₆ H ₉ NO) _n (I)

   In the formula (I), n is 9-450;

   Wherein, based on the weight of the fluorine-containing polymer particles, the total content of the polyvinylpyrrolidone-based polymer and the optional non-fluorinated anionic surfactant is 2-16 wt%.
2. The concentrated aqueous dispersion of fluoropolymer according to claim 1, wherein the polyvinylpyrrolidone-based polymer has a molecular weight of 1,000-100,000, optionally 3,000-60,000.
3. The concentrated aqueous dispersion of fluoropolymer according to claim 2, wherein the polyvinylpyrrolidone-based polymer is selected from one or more of the following: K12, K15, K17, K25 and K30.
4. The concentrated aqueous dispersion of fluoropolymer according to any one of claims 1-3, wherein the polyvinylpyrrolidone-based polymer is present in an amount of 2-12 wt%, based on the weight of the fluoropolymer particles , optional 4-10wt%.
5. The concentrated aqueous dispersion of fluoropolymer according to any one of claims 1-4, wherein the non-fluorinated anionic surfactant is selected from one or more of the following: alkyl sulfate, poly Oxyethylene fatty alcohol ether sulfate, fatty acid salt, alcohol ether carboxylate, alkylphenol ether carboxylate, stearate, alkylbenzene sulfonate, α-olefin sulfonate, α-sulfomono Carboxylate, fatty acid ester sulfonate, succinate sulfonate, alkylnaphthalene sulfonate, alkyl glyceryl ether sulfonate, petroleum sulfonate, lignosulfonate, alkyl carboxylate.
6. The concentrated aqueous dispersion of fluoropolymer according to claim 5, wherein said non-fluorinated anionic surfactant is selected from one or more of the following: sodium lauryl sulfate, lauryl sulfuric acid Ammonium, sodium dodecylbenzene sulfonate, sodium dodecyl diphenyl ether disulfonate, disodium lauryl polyoxyethylene ether sulfosuccinate, sodium dihexyl sulfosuccinate, dioctyl sulfosuccinate Sodium sulfosuccinate, potassium stearate, sodium lauryl carboxylate and sodium laureth carboxylate.
7. The concentrated aqueous dispersion of fluoropolymer according to any one of claims 1-6, wherein the non-fluorinated anionic surfactant is present in an amount of 0-12 wt based on the weight of the fluoropolymer particles %, optional 0-10wt%.
8. The concentrated aqueous dispersion of fluoropolymer according to any one of claims 1-7, wherein the solids content of the fluoropolymer particles is, based on the weight of the concentrated aqueous dispersion of fluoropolymer, 40-75wt%, optionally 50-70wt%, further optionally 55-65wt%.
9. The concentrated aqueous dispersion of fluoropolymer according to any one of claims 1-8, wherein the fluoropolymer particles comprise polytetrafluoroethylene particles, modified polytetrafluoroethylene particles, or combinations thereof.
10. The concentrated aqueous dispersion of fluoropolymer according to any one of claims 1-9, wherein the particle size of the fluoropolymer particles is 0.15-0.40 μm, optionally 0.20-0.35 μm.
11. A method for preparing a concentrated aqueous dispersion of fluoropolymers, comprising the steps of:

    S1: Adding a polyvinylpyrrolidone-based polymer represented by the following formula (I) and an optional non-fluorinated anionic surfactant to an initial aqueous dispersion of fluoropolymer particles, optionally while preparing the When the initial aqueous dispersion of fluoropolymer particles is added to the polymerized units of said fluoropolymer, a polyvinylpyrrolidone-based polymer represented by the following formula (I) is added to obtain a concentrated initial aqueous dispersion of fluoropolymer particles Dispersions;

    S2: Concentrating the concentrated initial aqueous dispersion of fluoropolymer particles obtained in step S1;

    (C ₆ H ₉ NO) _n (I)

    In the formula (I), n is 9-450;

    wherein, based on the weight of the fluoropolymer particles in the concentrated initial aqueous dispersion of fluoropolymer particles, the polyvinylpyrrolidone-based polymer represented by formula (I) and optionally the non-fluorinated anionic surfactant The total content is 2-16wt%, optionally 2-12wt%, further optionally 4-10wt%.
12. The preparation method according to claim 11, wherein based on the weight of the concentrated initial aqueous dispersion of fluoropolymer particles, the fluoropolymer particles in the concentrated initial aqueous dispersion of fluoropolymer particles The solid content is 15-35wt%, optionally 20-30wt%.
13. The preparation method according to claim 11 or 12, wherein based on the weight of the fluoropolymer particles, the non-fluorinated anionic surfactant is added in an amount of 0-12wt%, optionally 0-10wt%.
14. Use of concentrated aqueous dispersions of fluoropolymers according to any one of claims 1-10 for impregnating porous fabrics, porous metals, as dielectric coatings or in the production of fluoropolymer anti-drip agents.