JPS6142946B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an aqueous dispersion of a tetrafluoroethylene polymer and a coating formed by coating a glass fiber cloth with the dispersion. Fiber cloths made from glass fibers are useful in filters that separate particles from gas streams. Typically, glass fiber cloth is coated with a coating of a tetrafluoroethylene polymer, usually polytetrafluoroethylene (PTFE), to increase the bending life of the fiber cloth, ie, its resistance to breakage when repeatedly bent. Such coatings are particularly useful when fiberglass cloth is used as a filter bag to filter particulate solid impurities such as carbon black or fly ash present in the exhaust gas. Due to the passage of hot exhaust gas through the glass fiber cloth, during which back flushing or pulse flushing occurs, the fiber cloth is subjected to bending stress, which weakens the glass fiber cloth and causes the final This may cause breakage. Tetrafluoroethylene polymer coatings increase the bending life of the fiberglass fabric, but can also improve the resistance of the coated fiberglass fabric to being present in hot exhaust gases. Many hot exhaust gases contain sulfur oxides and water vapor, which combine to create an acidic atmosphere. Glass fiber cloth coated with conventional tetrafluoroethylene polymers is attacked by the acids present in the exhaust gases, thereby weakening the fiber cloth and shortening its bending life. Therefore, it is desirable to create a tetrafluoroethylene polymer coating that has increased resistance to acids over conventional tetrafluoroethylene polymer coatings. According to the present invention, by using a water-soluble polyhydrolyzable silane, a fluorinated acrylate water repellent, and a siloxane in the coating dispersion,
Tetrafluoroethylene polymer coating dispersions are provided that allow improved acid resistance of coated glass fiber fabrics. More specifically, the compositions of the present invention include (a) water; (b) a tetrafluoroethylene polymer having a film-enabled molecular weight of 5 to 65%, based on the weight of water and polymer; (c) 2 to 60% based on the weight of the tetrafluoroethylene polymer of the formula R ₁ Si-(OR) ₃ where R is lower alkyl, preferably alkyl having 1 to 3 carbon atoms, R ₁ is phenyl or lower alkyl, Preferably, it is substituted alkyl having 1 to 3 carbon atoms, and the substituent is selected from the group consisting of halogen, quaternary ammonium, or -NR'R'',
R′ and R″ are each H, lower alkyl, lower alkoxyalkyl, amino lower alkyl, hydroxy lower alkyl or substituted amino lower alkyl; (e) 1 to 20% by weight of a polymer of a fluorinated ester of acrylic acid; The tetrafluoroethylene polymer in the composition of the invention is either a homopolymer polytetrafluoroethylene or a copolymer of tetrafluoroethylene with a small amount of other copolymers, e.g. up to 35% by weight of the copolymer. For example, homogeneous polymers can contain small amounts of copolymerization modifiers and still retain non-melt processability. For example, preferably Cardinal, Edens, and Van Dyk U.S. Patent No. 3,142,665.
Hexafluoropropylene or perfluoro(alkyl vinyl ether) and carbon number 3 described in No.
It may contain up to 2% by weight of polymer units derived from copolymerization of ~10 perfluoroalkyl or oxyperfluoroalkyl trifluoroethylene with tetrafluoroethylene. When a large amount of these copolymerization monomers is included, the resulting copolymer can be melt-processed. Examples of such copolymers include copolymers of hexafluoropropylene and tetrafluoroethylene as described in Bro and Sandt, U.S. Pat. No. 3,946,763; Harris and Mc Cane; Copolymers of tetrafluoroethylene and higher perfluoroalkenes, such as perfluoro(alkyl vinyl ethers) having 4 to 10 carbons, such as perfluoroethyl or perfluoropropyl vinyl ether, as described in U.S. Pat. No. 3,132,123 of Selman. and copolymers of perfluoro(2-methylene-4-methyl-1,3-dioxolane) and tetrafluoroethylene, and highly fluorinated monomers, as described in Squire, U.S. Pat. No. 3,308,107. in which one hydrogen is present which does not change the fluorocarbon properties of the copolymer, such as 2-hydroperfluoroalkenes having 1 to 3 carbon atoms, such as 2-hydropentafluoropropene, ω having 3 to 10 carbon atoms -Hydroperfluoroalkene and alkyl group having 1 to 5 carbon atoms ω
-Includes copolymers of hydroperfluoro(alkyl vinyl ether) and tetrafluoroethylene. Tetrafluoroethylene polymers are non-melt processable and have a very high molecular weight, i.e., a specific melt viscosity of 1 x 10 ⁹ poise or more measured at 380°C under a shear stress of 6.5 psi, or under the same conditions. It can be melt-processable and has a melt viscosity of 1×10 ³ to 1×10 ⁶ poise. Preferably, the polymer is polytetrafluoroethylene. This polymer is preferably produced by an aqueous dispersion method of tetrafluoroethylene polymer. In this case, a sufficient amount of ionic dispersant is present to retain the polymer particles in the dispersion. The tetrafluoroethylene polymer dispersion can be redispersed in water using a suitable dispersant, or it can be used as it is. A suitable dispersant may be present in an amount up to about 6%, based on the polymer. Water-soluble polyhydrolyzable silanes are preferably
R ₁ is aminoalkyl or substituted aminoalkyl. Typical examples of these aminoalkyl groups are _{-CH2 - CH2CH2NH2 , -CH2- ( CH2} ) _2NH ( _CH2 ) _2NH2 , _-CH2- ( _CH2 ) _2N (CH ₃ ) ₂ , etc. The term lower alkyl as used herein means an alkyl group having 1 to 6 carbon atoms.
Typical silanes include γ-aminopropyltriethoxysilane; (N・N-dimethyl-3-aminopropyl)trimethoxysilane; N-trimethoxysilylpropyl-N・N・N-trimethylammonium chloride; 3-( N-styrylmethyl-2-aminoethyl)aminopropyltrimethoxysilane hydrochloride and the like. Preferably, the silane is present in an amount of 3-12%. Siloxane is a formula Preferably. However, in the formula R′ and
R'' is independently a hydrocarbyl group having 1 to 20 carbon atoms, one of R' and R'' can be hydrogen, and n is an integer from about 5 to 5000, preferably 10
~2000, most preferably 10 to 100, R is lower (i.e., 1 to 4 carbon atoms) alkyl or phenyl, and the polysiloxane is a homopolymer or has different hydrocarbyl R′ and R″ substituents. It can be a copolymer with other polysiloxanes. More preferably, R' and R'' are independently alkyl having 1 to 10 carbon atoms, aryl having 6 to 10 carbon atoms, alkaryl having 7 to 11 carbon atoms. , aralkyl having 7 to 11 carbon atoms. Preferably, the siloxane is present in an amount of 3 to 12%. The polymers of fluorinated esters of acrylic acid used in the present invention are water-repellent additives and are commonly referred to as fluorinated acrylate polymers (including methacrylates). Such polymers include "Zepel" fluorinated water repellent polymers and the like. The fluorination of the ester group is generally in the form of a perfluoroalkyl group containing from 3 to 12 carbon atoms. The polymer may be a homopolymer or a copolymer with other copolymerizable monomers, including segmented copolymers and esters that give the polymer water repellency. The repeat unit is generally the formula It is represented by However, J in the formula is H or CH ₃ , s
is an integer of 1 to 12, and Q is an organic group containing a perfluoroalkyl group having 3 to 12 carbon atoms. Examples of monomers whose repeating units are derived by polymerization (copolymerization) include the following. CH ₂ =CHCOOCH ₂ CH ₂ (CF ₂ ) ₂ CF ₃ CH ₂ =CHCOOCH ₂ CH ₂ (CF ₂ ) ₄ CF ₃ CH ₂ =CHCOOCH ₂ CH ₂ (CF ₂ ) ₈ CF ₃ CH ₂ =CHCOO(CH ₂ ) ₁₁ (CF ₂ ) ₇ CF ₃ CH ₂ =C(CH ₃ )COOCH ₂ CH ₂ N(CH ₃ )SO ₂ (CF ₂ ) ₇ CF ₃ CH ₂ =CHCOOCH ₂ CH ₂ N(CH ₂ CH ₂ CH ₃ ) SO ₂ (CF ₂ ) ₇ CF ₃ 2 CH ₂ =C(CH ₃ )COOCH ₂ CH ₂ (CF ₂ ) ₅ CF _3These water repellent additives are soluble in some organic solvents and are generally prepared in aqueous dispersions. It is available as . It is convenient to add thereto an aqueous PTFE dispersion forming a co-dispersion. Preferably, the fluorinated acrylic polymer is present in an amount of 3 to 12%. To make the coating dispersions of this invention, silanes, siloxanes, and fluorinated acrylate polymers are generally added to an aqueous dispersion of tetrafluoroethylene polymer. Temperature and pressure during manufacturing are not critical. The glass fiber cloth coating the coating dispersion of the present invention can be made from any glass such as soda-lime-silica, aluminum silicate or borosilicate, but is usually made from commercially available glass threads. It is. Typically, fiberglass cloth has a sizing agent, such as starch, on its surface. However, the glass fiber cloth is preferably cleaned prior to coating, for example by passing the glass fiber cloth through an oven heated to about 700 DEG C. to burn off the sizing, or by batch heating it in an oven. For coating glass fiber cloth, the coating dispersion is adjusted to a solids content of 5 to 30% by weight as required, and the fiber cloth is dipped into the dispersion in a convenient manner and then applied between rollers or blades. Remove excess liquid through. Alternatively, the dispersion can be sprayed onto one or both sides of the fabric. Next, the coated fiber cloth is
Heat to 100-340°C to harden and dry the film. The amount of coating on the cured and dried textile fabric can be from 3 to 20%, preferably from 6 to 15% of the total weight. If desired, the top surface of the coated glass fiber cloth can be coated with a dispersion of a water-repellent fluorinated acrylic polymer. EXAMPLE ``PTFE Dispersion'' is a polytetrafluorocarbon compound having a nominal solids content of 60%, having an average of 10 ethylene oxide units, and stabilized with an octaphenoxy polyethylene oxide dispersant neutralized with ammonium hydroxide. means an aqueous dispersion of ethylene. "Silane _" means γ _{- aminopropyltriethoxysilane} ( _{H2NCH2CH2CH2Si} [ _OCH2CH3 ] _{3 )} . "Siloxane" means a 35% emulsion of methylphenylsiloxane polymer. "Water repellent" means a fluoroacrylate copolymer dispersant. "Dispersion A" had a solids content of 55%, had an average of 10 ethylene oxide units, and was stabilized with an octaphenoxy polyethylene oxide dispersant neutralized with ammonium hydroxide. Fluoropropylene (89.5/
10.5) means a copolymer of "Dispersion B" has a solids content of 55% and is made of tetrafluoroethylene/perfluoroethylene stabilized with an octaphenoxy polyethylene oxide dispersant having an average of 10 ethylene oxide units and neutralized with ammonium hydroxide. Propyl vinyl ether (97/3) copolymer. The coating dispersion was made by adding water to the PTFE dispersion and then adding the other ingredients. The amounts of each component of the coating dispersion are listed in each example along with the amount of dry coating on the glass fiber cloth (%). A 15 x 15 cm (6 x 6 inch) piece of fiberglass cloth is dipped into the coating dispersion and partially dried by squeezing between rollers. Next, add 250 fiber cloth unless otherwise specified.
Cure for 10 minutes at °C. Coverage was determined by heating the fabric, cleaning it, weighing it, and curing and drying it again. The samples were tested for bending life in the warp direction using an MIT bending tester type 2 (Tinius Olson Co.). Width 1.3cm
(1/2 inch) test piece, 1.8 or 2.3Kg (4
Tension was applied to the fabric using a weight of 5 lbs. Samples were conditioned prior to testing as described below. Unless otherwise specified, five or six samples were tested under each of the conditions listed below. Conditions At the time of manufacture Samples were conditioned for 24 hours at 72°C and 50% relative humidity at least 24 hours prior to testing. Acid treatment: 232℃ or 260℃ (450℃) in an air circulation furnace.
Heat the sample for 4 hours at 500 °C or 500 °C.
(If it has not been heated for a long time). The sample is then immersed in 1.0N sulfuric acid kept at 80°C for 5 minutes. Remove the sample from the acid and incubate at 232℃ (450〓) for 5 minutes.
Heat to. Repeat the acid soak a total of 4 times. Next, the fiber cloth was heated to 232°C or 260°C (450° or 500°).
Heat for 22℃ (72〓) and relative humidity 50 before testing.
%. Example 1 Burlington 484 fiber cloth 15×
Place 15 cm (6 x 6 inch) pieces in a recirculating air oven at 350 m
Heat-process by placing at ℃ (662〓) for 10 minutes. The sample is dipped into the coating dispersion described below, squeezed dry, cured, and dried at 250°C (482°C) for 10 minutes. Six fabric samples are coated with each composition. These samples are tested three times during manufacture and after acid treatment.
Six 1/2 inch (1.3 cm) samples were taken from each piece and tested using a 2.3 Kg (5 lb) weight.
Conditioning method, 18 samples per composition were tested.

[Table] We analyzed these test results and created reliability standards for relative evaluation. As a result, silane,
The composition containing siloxane and a water repellent had significantly better bending life in the warp direction after acid treatment than the other two compositions. Confidence limit is 99% or higher. Example 2 The same method and same fiber cloth as in Example 1 were used. The following table shows the coating composition and results.

[Table] Comparative Examples A, B, C, and D did not have as good a bending life after acid treatment as Sample 1, which is a sample of the present invention. Example 3 The method of Example 1 was repeated, but the fabric used was Clark
Sehwebel Style) 6758, and the sizing was removed by heat treatment. The composition and results of the coating composition are shown in the table below.

Table: Dispersions A and B are melt processable polymers. The coated fabrics were cured for 10 minutes at the temperatures indicated below and tested for warp bend life using a 4 pound weight.

【table】

TABLE Compositions 1 and 3 were cured below the melting temperature of the polymers in Dispersions A and B. Therefore, the bending life in the warp direction is initially low. Although compositions 1 and 3 have low initial values, they exhibit good acid resistance after acid treatment. Compositions 2, 4, 5 and 6 advantageously use PTFE with a melt processable polymer. This is because the bending life in the warp direction during manufacturing is improved several times. Example 4 The method of Example 1 was followed, but the fabric used was Clark Schwebel Style 6758, the sizing was removed by heat treatment, and the coating dispersion was soaked and wrung. dry,
After curing and drying at 250°C for 10 minutes, the coated fabric was dipped into a second dispersion containing only the water repellent, squeezed dry, and cured at 250°C for 10 minutes. The composition and results of the coating composition are shown in the following table.

【table】

[Table] Composition 1 did not undergo a second coating with a water repellent, and its bending life in the warp direction during manufacture was the worst among the four. Composition 2, which contained the highest amount of water repellent among compositions 2-4 in the second coating composition, had the best longitudinal bending life after acid treatment.

Claims (1)

[Scope of Claims] 1 (a) water, (b) a tetrafluoroethylene polymer having a film-forming molecular weight of 5 to 65% based on the weight of water and polymer, (c) a tetrafluoroethylene polymer 2 to 60% based on the weight of the formula R ₁ Si-(OR) ₃ where R is lower alkyl, preferably alkyl having 1 to 3 carbon atoms, R ₁ is phenyl or lower alkyl, preferably having 1 carbon number ~3 substituted alkyl, the substituents being selected from the group consisting of halogen, quaternary ammonium, or -NR′R″;
R′ and R″ are each H, lower alkyl, lower alkoxyalkyl, amino lower alkyl, hydroxy lower alkyl or substituted amino lower alkyl; 1 to 20% by weight of a hydrocarbyl siloxane; (e) 1 to 20% of a polymer of fluorinated acrylic acid by weight of a tetrafluoroethylene polymer. 2. The coating dispersion according to claim 1, wherein the tetrafluoroethylene polymer is polytetrafluoroethylene. 3. The silane has the formula R ₁ Si(OR) ₃ where R is -CH ₃ or _-C2H5 , _R1 is substituted lower alkyl, and the substituent is in _the γ position and is amino- or an amino substituent. 4. The coating dispersion according to claim 3, wherein the silane is γ-aminopropyltriethoxysilane. 5. The coating dispersion according to claim 3, wherein the silane is γ-aminopropyltrimethoxysilane. Coating dispersion according to claim 3. 6. Coating dispersion according to claim 3, wherein the siloxane is an alkyl or alkyl/phenyl siloxane.