JPH04320406A - Method for removing unpolymerized hydroxyl monomer from fluorocopolymer solution - Google Patents

Abstract

PURPOSE:To completely remove an unpolymerized hydroxyl monomer from a fluorocopolymer soln. contg. the monomer without forming a gel in the resulting polymer. CONSTITUTION:A polymer soln. obtd. by the soln. polymn. of a fluoromonomer, a hydroxyl monomer, and an alkyl vinyl ether is evaporated to dryness in the presence of an alcohol boiling at a temp. in the range of from 50 deg.C lower than to 30 deg.C higher than the m.p. of the hydroxyl monomer to remove an unpolymerized hydroxyl monomer from the soln.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a compound suitable for paints obtained by radical copolymerization of a monomer mixture consisting of a fluorine-containing monomer, a hydroxyl group-containing monomer, and an alkyl vinyl ether in an organic solvent. The present invention relates to a method for removing unpolymerized hydroxyl group-containing monomers from a fluorine copolymer solution. The fluorine-containing copolymer from which unpolymerized hydroxyl group-containing monomers have been removed by the method of the present invention has excellent pigment dispersibility and is crosslinked with a polyvalent isocyanate compound to form a coating film with excellent physical properties. do.

0002

[Prior art and its problems] Fluorine-containing copolymers obtained by copolymerizing fluorine-containing monomers, hydroxyl group-containing monomers, and alkyl vinyl ethers have excellent weather resistance, durability, gloss, etc. Because it is soluble in solvents, it is attracting attention for use in solvent-based paints, especially two-component room-temperature curing solvent-based paints. The fluorine-containing copolymer having the above structure is usually synthesized by solution polymerization in a polymerization medium such as fluoroalkane, butyl acetate, and xylene. After the low boiling point fluorine-containing monomer has been purged, the polymer solution obtained after polymerization can be used as a solvent-based paint, either as it is, or by further concentrating the polymer solution and replacing the solvent with another paint solvent. It is used.

However, in the above synthesis method, when a hydroxyl group-containing monomer to be copolymerized with the fluorine-containing monomer and the alkyl vinyl ether is a monomer that does not have very high copolymerizability, the resulting fluorine-containing Copolymer type paints contain a large amount of unpolymerized hydroxyl group-containing monomers, resulting in a problem in that paint performance is significantly inferior. In order to solve the above problems, the polymer solution obtained by polymerization is poured into a poor solvent, the fluorine-containing copolymer is precipitated, and then dissolved again in an appropriate solvent, or the polymer solution Methods such as heating to evaporate to dryness to completely remove the hydroxyl group-containing monomer have been adopted, but the former method has the problems of being complicated and requiring the use of a large amount of solvent. In the latter case, there is a problem that gelation occurs or the polymer has an excessively high molecular weight during the evaporation to dryness process.

[0004] A method for obtaining a fluorine-containing copolymer solution suitable for paints by copolymerizing a fluorine-containing monomer, a hydroxyl group-containing monomer, and an alkyl vinyl ether in an organic solvent,
In addition to the above, when copolymerizing fluoroolefins, hydroxyalkyl vinyl ethers, and alkyl vinyl ethers, a lower alkylbenzene and an alkanol having 2 to 4 carbon atoms and a boiling point lower than the alkylbenzene are used together as a polymerization solvent, and an alkali metal is added to the polymerization solution. A technical means of adding carbonate has been proposed (Japanese Patent Publication No. 1-49405). According to the method described in the above publication, a fluorine-containing copolymer with excellent storage stability can be obtained even if the polymer solution is heated and concentrated to a certain extent, but in this method, the polymer solution is evaporated to dryness. Therefore, when applied to a polymer solution containing a large amount of unpolymerized hydroxyl group-containing monomer, the concentration operation is necessary because the hydroxyl group-containing monomer generally has a higher boiling point than the lower alkylbenzene or lower alcohol. There was a problem in that even after the hydroxyl group-containing monomer was removed, a permissible amount or more of the hydroxyl group-containing monomer remained in the polymer solution. In addition, in the above method, if the polymer solution is evaporated to dryness to completely remove the hydroxyl group-containing monomer, gelation or an excessive increase in the molecular weight of the polymer will occur, as shown in the comparative example below. That's what I was going to do.

[0005]

[Problems to be Solved by the Invention] In the present invention, in order to completely remove an unpolymerized hydroxyl group-containing monomer from a fluorine-containing copolymer solution, the polymer solution is evaporated to dryness. The purpose of the present invention is to provide a removal method that employs a simple technical means of removing the particles and does not cause the above-mentioned problems.

[0006]

[Means for Solving the Problems] As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a temperature near the boiling point of an unpolymerized hydroxyl group-containing monomer is added to a polymer solution to be evaporated to dryness. By the presence of an alcohol with a boiling point,
The present inventors have discovered that the problems of gelation or excessively high molecular weight of the polymer can be significantly suppressed, and have completed the present invention. That is, in the present invention, a fluorine-containing copolymer solution obtained by radical copolymerization of a monomer mixture consisting of a fluorine-containing monomer, a hydroxyl group-containing monomer, and an alkyl vinyl ether in an organic solvent is added to the hydroxyl group-containing monomer. The fluorine-containing compound is heated in the presence of an alcohol having a boiling point in the range of 50°C or higher than the boiling point of the polymer and 30°C or lower than the boiling point of the polymer to evaporate to dryness. This is a method for removing unpolymerized hydroxyl group-containing monomers from a polymer solution.

The present invention will be explained in more detail below. As mentioned above, the essential monomers used in the present invention are fluorine-containing monomers, hydroxyl group-containing monomers, and alkyl vinyl ethers. Specific examples of fluorine-containing monomers include vinyl fluoride, fluorinated Examples include vinylidene, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene and hexafluoropropylene.

Hydroxyl group-containing monomers include hydroxybutyl vinyl ether, hydroxycyclohexyl vinyl ether, allyl alcohol, ethylene glycol monoallyl ether, diethylene glycol monoallyl ether, vinyl hydroxyethyl acetate, hydroxyethyl crotonate, 2-hydroxypropyl crotonate, Examples include 3-hydroxypropyl crotonate, 3-hydroxybutyl crotonate, 4-hydroxybutyl crotonate, 5-hydroxypentyl crotonate, 6-hydroxyhexyl crotonate, and diethylene glycol monoester crotonate.

As the alkyl vinyl ether, methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, t-
Butyl vinyl ether, n-pentyl vinyl ether,
Examples include n-hexyl vinyl ether, n-octyl vinyl ether, cyclopentyl vinyl ether, and cyclohexyl vinyl ether.

Furthermore, in the present invention, other radically polymerizable monomers may be used in combination with the above-mentioned essential monomers as necessary. Examples of such monomers include vinyl acetate, vinyl propionate, and butyric acid. Carboxylic acid vinyl esters such as vinyl, vinyl pivalate, vinyl caproate, vinyl laurate, vinyl cyclohexanecarboxylate, vinyl benzoate; Olefins such as ethylene and propylene; Chlorinated olefins such as vinyl chloride and vinylidene chloride; Allyl alcohol, Allyl group-containing compounds such as allyl glycidyl ether; crotonic acid, methyl crotonate, ethyl crotonate, diethylene glycol monocrotonate, and the like.

From the viewpoint of yield and weather resistance of the obtained fluorine-containing copolymer, the preferred proportions of the monomers used in the present invention are 10 to 70 mol % of the fluorine-containing monomer and 3 to 70 mol % of the hydroxyl group-containing monomer. 40 mol%, alkyl vinyl ether 2-50
Mol% and other radically polymerizable monomers 0-85 mol%
It is.

As the polymerization medium, tetrahydrofuran,
Ethers such as dioxane; aromatic hydrocarbon compounds such as benzene, toluene, xylene, and ethylbenzene; alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol; ethyl acetate, n-propyl acetate, Esters such as n-butyl acetate; ketones such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone;
Examples include halogen-containing compounds such as 1,1,2-trifluoro-1,2,2-trichloroethane, 1,1,1-trichloroethane, and trichloroethylene. The above solvents may be used alone or in combination of two or more. The amount of solvent used is 10% of the total amount of monomers to be copolymerized.
Approximately 5 to 1000 parts by weight per 0 parts by weight.

As the polymerization initiator, polymers such as diisopropyl peroxydicarbonate, tertiary butyl peroxy pivalate, benzoyl peroxide, lauroyl peroxide, ditertiary butyl peroxide, tertiary butyl hydroperoxide, and methyl ethyl ketone peroxide are used. Examples include oxides and azo compounds such as azobisisobutyronitrile and azobisisovaleronitrile. The amount of polymerization initiator used depends on the polymerization temperature, the target molecular weight of the copolymer, etc.
Although selected as appropriate, the total amount of monomers to be copolymerized is 100
The amount may be about 0.01 to 10 parts by weight. Furthermore, as a decomposition inhibitor of alkyl vinyl ether during copolymerization,
As described in JP-A-57-34107, an appropriate amount of alkali metal carbonates such as sodium carbonate and potassium carbonate may be added to the polymerization solution. In addition, the appropriate polymerization temperature is about 30 to 100°C, and the polymerization pressure is 1
~100kg/cm2, more preferably 3~10kg/cm2
cm2 is appropriate.

[0014] In the present invention, when the polymer solution is evaporated to dryness, the alcohol used for the purpose of preventing gelation or excessive increase in molecular weight of the polymer is, as described above, a hydroxyl group-containing alcohol to be subjected to polymerization. An alcohol having a boiling point in the range of 50°C less than the boiling point of the monomer and 30°C added to the boiling point, and is appropriately selected and used depending on the type of hydroxyl group-containing monomer. . The alcohol may be present by either adding it to the polymerization reaction solution as part of the polymerization solvent or adding it to the polymer solution after polymerization. If an alcohol with a boiling point lower than 50°C lower than the boiling point of the hydroxyl group-containing monomer is used, the alcohol will evaporate from the polymer solution before evaporation to dryness, so there will be no gelling prevention effect; If an alcohol whose boiling point exceeds the boiling point of the hydroxyl group-containing monomer by 30°C is used, the alcohol used will remain in the polymer because it is difficult to remove the alcohol itself.
Poor pigment dispersibility required when used as a paint. More preferable alcohols have a boiling point that is 20°C lower than the boiling point of the hydroxyl group-containing monomer to be subjected to polymerization, and a temperature that is 20°C lower than the boiling point of the hydroxyl group-containing monomer to be subjected to polymerization.
It is an alcohol having a temperature range of 100.degree. C. higher, and more preferably a polyhydric alcohol having such a boiling point. Since polyhydric alcohol can prevent gelation even if used in a smaller amount than monohydric alcohol having a similar boiling point, the alcohol can be easily removed.

When the above-mentioned compound is used as the hydroxyl group-containing monomer, an alcohol having a boiling point of 130° C. or higher, specifically amyl alcohol, isoamyl alcohol, 2
-Methyl-1-pentanol, 1-hexanol, cyclohexanol, 1-octanol, 2-octanol, 2-ethyl-1-hexanol, 1-decanol, benzyl alcohol, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, etc.
Hydrolic alcohol; dihydric alcohols such as ethylene glycol, 1,2-propylene glycol, 1,3-propanediol, and diethylene glycol can be selected and used.

For example, as a hydroxyl group-containing monomer, a boiling point of 1
When using hydroxybutyl vinyl ether at 80°C, 1-hexanol, cyclohexanol, 1
-octanol, 2-octanol, 2-ethyl-1-
Hexanol and ethylene glycol can be used, more preferably 1-octanol (boiling point 195°C)
and ethylene glycol (boiling point 197°C). In addition, when hydroxyethyl crotonate having a boiling point of 210°C is used as the hydroxyl group-containing monomer, 1-octanol, 2-octanol, 2-ethyl-1-hexanol, ethylene glycol, 1,2-propylene glycol and 1,3-propanediol etc. can be used,
More preferably, 1,3-propanediol (boiling point 21
4°C) and ethylene glycol. The preferred amount of alcohol used is about 1.5 to 15 times the weight of the hydroxyl group-containing monomer contained in the polymer solution. The amount of the hydroxyl group-containing monomer contained in the polymer solution can be easily determined by gas chromatography measurement of the polymer solution.

The polymer solution to which alcohol has been added is evaporated to dryness under normal pressure or reduced pressure to remove unpolymerized hydroxyl group-containing monomers, the added alcohol, and other low molecular weight components. Ru. Evaporation to dryness is performed until the amount of hydroxyl group-containing monomers and other low molecular weight components contained in the evaporation residue is at least 2% by weight or less, preferably 1% by weight.
It should continue until: In evaporation to dryness, the main components of low molecular weight components contained in the residue are unpolymerized hydroxyl group-containing monomers with relatively high boiling points or added alcohols, so the amount of low molecular weight components in the residue If it exceeds 2% by weight, a fluorine-containing copolymer suitable for paints cannot be obtained. The evaporation to dryness is preferably carried out under reduced pressure using a device such as a thin film distiller that can provide a large evaporation surface. The solid fluorine-containing copolymer obtained by the above method is soluble in organic solvents such as toluene, xylene, and butyl acetate, and its solution viscosity is also lower than that of the polymer before drying. , there is only a slight increase, making it extremely suitable as a solvent-based coating. The fluorine-containing copolymer obtained by the method of the present invention includes a curing agent that can react with hydroxyl groups, a pigment, a fluidity regulator, an ultraviolet absorber,
Various additives such as dispersion stabilizers and antioxidants and other resins may be added as necessary.

[0018]

[Examples] The present invention will be explained in more detail with reference to Examples below. Example 1 130 g of xylene was added to a stainless steel autoclave with an internal volume of 500 cc and equipped with a stirrer, and 40 g of vinyl acetate, 30 g of ethyl vinyl ether, 25 g of hydroxyethyl crotonate, 4 g of potassium carbonate, and 3 g of dilauroyl peroxide were charged, followed by solidification and desorption with liquid nitrogen. After removing dissolved air by repeating the process three times, 130 g of chlorotrifluoroethylene was introduced, and the temperature was raised to 65°C to start polymerization. After that, polymerization was carried out for 8 hours, and the reaction was stopped by cooling.
Purge unreacted chlorotrifluoroethylene. After taking out the obtained solution, it was filtered through a G-3 glass filter to remove potassium carbonate. Analysis by gas chromatography revealed that 7 g of hydroxyethyl crotonate remained in the polymerization solution. Since the boiling point of hydroxyethyl crotonate is 210°C, 40 g of 1-octanol with a boiling point of 195°C was added to the obtained polymer solution, and it was evaporated on a hot plate at normal pressure at a heating temperature of 220°C. The mixture was dried to obtain a fluoropolymer. The yield of polymer was 83%. The entire amount of the obtained fluoropolymer is soluble in organic solvents such as xylene, toluene, and butyl acetate, and the solid content concentration is 50 wt%.
As a xylene solution, it was maintained at 70° C. for 3 days and its storage stability was evaluated. As a result, the viscosity before evaluation was 400 cps and after evaluation was 450 cps, and the viscosity change was as low as 13%.

Example 2 10 g of ethylene glycol having a boiling point of 197°C was added to the polymer solution obtained in Example 1, and the mixture was evaporated to dryness in the same manner as in Example 1 to obtain a fluoropolymer. Ta. The entire amount of the obtained fluoropolymer is soluble in organic solvents such as xylene, toluene, and butyl acetate, and the solid content concentration is 5.
As a result of holding it as a 0wt% xylene solution at 70°C for 3 days and evaluating its storage stability, the viscosity before evaluation was 400cp.
s, 440 cps after evaluation, and the viscosity change was as low as 10%.

Example 3 105 g of xylene and 25 g of ethanol were added to a stainless steel autoclave with an internal volume of 500 cc and equipped with a stirrer, and 40 g of ethyl vinyl ether, 42 g of cyclohexyl vinyl ether, and 25 g of hydroxybutyl vinyl ether were added.
, 4 g of potassium carbonate, and 3 g of azobisisobutyronitrile were charged, and polymerization was carried out in the same manner as in Example 1. After the polymerization, unreacted chlorotrifluoroethylene was purged, and the resulting polymer solution was mixed with G- The mixture was filtered through a 3-glass filter to remove potassium carbonate. Analysis by gas chromatography revealed that 5 g of hydroxybutyl vinyl ether remained in the polymerization solution. Since the boiling point of hydroxybutyl vinyl ether is 180°C,
60 g of 1-octanol having a boiling point of 195° C. was added to the obtained polymer solution, and it was evaporated to dryness on a hot plate at normal pressure at a heating temperature of 220° C. to obtain a fluoropolymer. The yield of polymer was 86%. No gelled product was generated in the obtained fluoropolymer, and no abnormal increase in the solution viscosity of the polymer was observed.

Example 4 20 g of ethylene glycol was added to the polymer solution obtained in Example 3 and evaporated to dryness in the same manner as in Example 1 to obtain a fluoropolymer. No gelled product was generated in the obtained fluoropolymer, and no abnormal increase in the solution viscosity of the polymer was observed.

Comparative Example 1 The polymer solution obtained in Example 3 (containing ethanol used as a polymerization solvent) was evaporated to dryness without adding the alcohol defined in the present invention. , a fluoropolymer was obtained. The obtained fluoropolymer was insolubilized in organic solvents such as xylene, toluene, and butyl acetate.

Comparative Example 2 The polymer solution obtained in Example 3 was concentrated using a rotary evaporator to the extent that substantially no ethanol remained in the solution. As a result of measuring the amount of hydroxybutyl vinyl ether in the obtained xylene solvent polymer concentrate by gas chromatography, it was found to be 4.6.
It was found that g exists.

[0024]

Effects of the Invention According to the present invention, fluorine-containing monomers, hydroxyl group-containing monomers, and alkyl vinyl ethers can be easily obtained without relying on complicated operations such as precipitating a polymer from a polymer solution into a poor solvent. The unpolymerized hydroxyl group-containing monomer can be easily removed from a fluorine-containing copolymer solution obtained by radical copolymerization of a monomer mixture consisting of The fluorine copolymer does not contain any gelled material, and no abnormal increase in solution viscosity is observed. The fluorine-containing copolymer obtained by the present invention has excellent pigment dispersibility and forms a coating film with excellent physical properties when crosslinked with a polyvalent isocyanate compound or the like.

Claims (1)

[Claims] [Claim 1] A fluorine-containing copolymer solution obtained by radical copolymerization of a monomer mixture consisting of a fluorine-containing monomer, a hydroxyl group-containing monomer, and an alkyl vinyl ether in an organic solvent; The fluorine-containing copolymer is heated in the presence of an alcohol having a boiling point in the range of 50°C below the boiling point of the body and below 30°C above the boiling point to evaporate to dryness. A method for removing unpolymerized hydroxyl group-containing monomers from a combined solution.