JP2909131B2 - Polyvinyl alcohol-based polymer, method for producing the same, and method for providing water resistance - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a novel polyvinyl alcohol-based polymer having a reactive acetal group, a method for producing the same, and a method for making the polymer water-resistant.

B. Conventional technology Conventionally, polyvinyl alcohol is a typical water-soluble polymer due to its excellent film-forming properties and excellent film properties, such as synthetic fibers, films, warp sizing agents, paper coating agents, adhesives, binders, and emulsifiers. Has been used in various fields. In such various fields, it is often necessary to improve the water resistance, and a number of methods for waterproofing polyvinyl alcohol have been conventionally proposed. For example, a method of adding aldehydes such as formalin, acetaldehyde, glyoxal, glutaraldehyde, a method using a boric acid compound,
A method using N-methylol urea, N-methylol melamine and the like in combination has been used, but none of them has yet developed sufficient water resistance.

Also, introducing a crosslinkable group into polyvinyl alcohol itself,
Attempts have been made to develop water resistance. For example, Japanese Patent Publication No. 31765/1988 discloses a resin having excellent water resistance using polyvinyl alcohol having an N-methylol group or an N-alkoxymethyl group as a crosslinkable group. This resin has outstanding water resistance,
There was a drawback that slightly severe conditions were required for acidic conditions and drying temperature conditions required for the development of water resistance. JP-A-56-125446 discloses a polyvinyl alcohol having an acetoacetyl group as a crosslinkable group, but has a disadvantage that the stability of a solution containing the polyvinyl alcohol is not very good. I was

As described above, despite many attempts, it has been the current situation that a sufficiently satisfactory method for making polyvinyl alcohol water resistant has not been obtained.

C. Problems to be Solved by the Invention The present invention provides a polyvinyl alcohol-based polymer having no such problems, a method for producing the same, and a method for making the polymer water-resistant.

D. Means for Solving the Problems The present inventors have conducted intensive studies to improve the above drawbacks, and as a result, a polyvinyl alcohol-based polymer containing a structural unit represented by the following general formula.

(Where n is an integer of 0 to 8, R ₁ is hydrogen or a methyl group, R ₂ is hydrogen or an alkyl group having 1 to 4 carbon atoms, R ₃ and R ₄ are hydrogen or an alkyl group having 1 to 8 carbon atoms. Have been found to be able to overcome the above drawbacks, and have completed the present invention.

 Next, the present invention will be described in detail.

In the polyvinyl alcohol-based polymer of the present invention, in the structural unit represented by the above general formula (I) (hereinafter sometimes abbreviated as an acetal-containing group), n is selected from an integer of 0 to 8. However, usually 1 or 2 is used. As R _1, both hydrogen and methyl are preferably used. R ₂ is usually hydrogen or a methyl group, but there is no problem even if it is an alkyl group having 2 to 4 carbon atoms.

When the carbon number of R ₂ , R _3, and R ₄ is larger than the above value, the physical properties of the polyvinyl alcohol-based polymer film may be reduced.

The content of the acetal-containing group in the polyvinyl alcohol-based polymer of the present invention is 0.1 to 50 mol%, preferably 0.2 to 30 mol%, and more preferably 0.5 to 12 mol%. When the amount of the acetal-containing group is extremely small, the effects of the present invention cannot be sufficiently exerted. When the amount is too large, the excellent film properties inherent to the polyvinyl alcohol-based polymer cannot be exhibited.

The saponification degree of the polyvinyl alcohol portion of the polyvinyl alcohol-based polymer of the present invention is usually at least 50 mol%,
In most cases, it is 70 mol% or more.

The polymerization degree of the novel polyvinyl alcohol-based polymer of the present invention is appropriately selected usually from the range of 50 to 4,000. The degree of polymerization referred to here is the intrinsic viscosity ([η], dl / g unit) of a completely saponified polyvinyl alcohol-based polymer in water.
It is measured at 0 ° C. and calculated using the following equation.

When the degree of saponification and the degree of polymerization of the polyvinyl alcohol-based polymer are out of the above-mentioned ranges, the film properties of the polyvinyl alcohol-based polymer may not be sufficiently exhibited.

The method for producing the polyvinyl alcohol-based polymer of the present invention includes vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, fatty acid vinyl such as vinyl versatate, especially vinyl acetate and an acetal group represented by the following general formula. A method of radical copolymerization with a monomer is preferred.

(Where n is an integer of 0 to 8, R ₁ is hydrogen or a methyl group, R ₂ is hydrogen or an alkyl group having 1 to 4 carbon atoms, R ₃ and R ₄ are hydrogen or an alkyl group having 1 to 8 carbon atoms. Specific examples of the monomer represented by the general formula (II) include
N-2,2-dimethoxyethyl (meth) acrylamide,
N-2,2-diethoxyethyl (meth) acrylamide,
N-3,3-di-i-propoxypropyl (meth) acrylamide, N-3,3-di-t-butoxypropyl (meth) acrylamide, N-methyl-N-2,2-dimethoxyethyl (meth) acrylamide , N-methyl-N-2,
2-diethoxyethyl (meth) acrylamide, N-methyl-N-6,6-dimethoxyhexyl (meth) acrylamide, N-methyl-N-6,6-di-i-propoxyhexyl (meth) acrylamide, N- Ethyl-N-3,3
-Dimethoxypropyl (meth) acrylamide and the like.

For the copolymerization of the vinyl ester and the acetal group-containing monomer represented by the general formula (II), conventionally known methods such as bulk polymerization, solution polymerization, emulsion polymerization, and suspension polymerization are appropriately selected. Solution polymerization using a compound as a solvent is convenient. By saponifying the copolymer obtained after the polymerization, the polyvinyl alcohol-based polymer of the present invention can be obtained. In this case, an alkali catalyst is preferable as the saponification catalyst. Performing saponification using an acid catalyst is not preferred because the resulting polymer often becomes insoluble in water. As the alkali catalyst, hydroxides of alkali metals and alkaline earth metals such as sodium hydroxide, potassium hydroxide and magnesium hydroxide, ammonia, amines and the like are used. The saponification may be carried out in water, but it is more convenient and convenient to carry out the transesterification in an alcohol solvent.

In copolymerization, other monomers may be coexistent and introduced into the polymer without impairing the gist of the present invention. Examples of such a monomer include α-offlains such as ethylene and propylene;
(Meth) acrylic acid and salts thereof or alkyl esters thereof, vinyl chlorides such as vinyl chloride and tetrafluoroethylene, (meth) acrylamide, dimethyl (meth) acrylamide, 2-acrylamido-2-methyl-propanesulfonic acid and The salt, 3- (meta)
Amide monomers such as acrylamidopropyltrimethylammonium chloride, N-methylolacrylamide, N-butoxyethylacrylamide, N-vinylpyrrolidone, maleic anhydride, itaconic acid, maleic acid, fumaric acid, crotonic acid, and salts thereof or Their alkyl esters, allyl acetate, allyl alcohol,
Isopropenyl alcohol, vinyltrimethoxysilane and the like. The amount of such a monomer to be introduced is 10 mol% or less, preferably 5 mol% or less, and more preferably 3 mol% or less.

The polyvinyl alcohol copolymer of the present invention can be applied to various uses of conventionally known polyvinyl alcohol.
In particular, in applications where water resistance is required for the film after application, the effects of the present invention are remarkably exhibited, so that the film can be suitably used. When water resistance is required, before applying the coating liquid containing the polyvinyl alcohol-based copolymer of the present invention, the pH of the coating liquid is made acidic by adding an acid, and then dried by applying. The present inventors have found that the coating has a surprising property of being water-resistant. Further, the coating film thus obtained has excellent water resistance such that it is insoluble in water at room temperature and also in heating water. Furthermore, there is no need for heat treatment of the coating to bring out water resistance like general polyvinyl alcohol, and even in a relatively mild dry state of, for example, about 50 ° C., extremely excellent water resistance is expressed. .

In order to bring out the above-mentioned water resistance, it is preferable to add an acid to the coating solution before coating as described above to make the pH of the coating solution acidic. Examples of the acid to be added include mineral acids such as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid, and organic sulfonic acids such as p-toluenesulfonic acid, acetic acid, benzoic acid, oxalic acid, maleic acid, citric acid,
An organic acid such as tartaric acid is preferably used. Acid salts such as ammonium chloride, aluminum sulfate, and titanium ammonium sulfate, which are not acids themselves, or salts which generate an acidic substance when dried are also preferably used. Further, pigments that exhibit acidity in water may be used. There is no particular limitation on the amount of such an acidic property or salt that generates an acidic substance when dried, but usually a catalytic amount may be used, and the amount of the salt may be based on the polyvinyl alcohol-based polymer of the present invention.
0.01 to 10% by weight is preferably used. In particular, when an acidic substance is added in advance to the solution containing the polyvinyl alcohol-based polymer of the present invention, the pH of the solution is preferably adjusted to 1 to 5, more preferably 1.5 to 4.5. If the pH is too low, the storage stability of the solution becomes poor, and the viscosity or gelation tends to occur, which is not preferable. Conversely, if the pH is too high,
It is not preferable because the water resistance of the coating after application may be insufficient.

The polyvinyl alcohol-based polymer of the present invention is used as a coating liquid as described above, mainly dissolved in water.
At this time, depending on the purpose, alcohols such as methanol, ethanol, and propanol, dimethyl sulfoxide, N, N-
Use of dimethylformamide or the like as a solvent may not be any problem. Depending on the purpose, conventionally known polyvinyl alcohol, synthetic water-soluble polymers such as polyacrylamide, starches, celluloses, natural water-soluble polymers such as chitosan, oxidized starch, modified starch such as amino-modified starch are used in combination. You can do it. Further, a resin such as a methylol melamine resin, a polyamide epichlorohydrin resin, polyethyleneimine, a polyamide polyurea, melamine, or an initial condensate of urea and formalin may be added. Furthermore, depending on the purpose,
Aldehydes such as glyoxal, diamines such as ethylenediamine, boric acid, borax and the like, clay, talc,
Additives such as pigments such as charcoal and various dyes, plasticizers and surfactants may be used in combination.

E. Examples Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto. In the following, "parts" or "%" is used unless otherwise specified.
It means "parts by weight" or "% by weight".

Example 1 A polymerization vessel equipped with a reflux condenser was charged with 2400 parts of vinyl acetate, 550 parts of methanol and 13 parts of N-2,2-dimethoxyethyl methacrylamide, and the system was purged with nitrogen while heating to 60 ° C. Next, 7 parts of 2,2'-azobisisobutyronitrile and 50 parts of methanol were added to initiate polymerization. 20 after the start of polymerization
Over a period of 0 minutes, polymerization was carried out at 60 ° C. in a nitrogen stream while 275 parts of a 25% strength methanol solution of N-2,2-dimethoxyethyl methacrylamide was added at a constant rate. 200 minutes after the start of the polymerization, 1000 parts of methanol was added, and the mixture was cooled to terminate the polymerization. At this time, the polymerization rate of vinyl acetate was 48%. The remaining vinyl acetate was distilled off while adding methanol vapor to this, and a 37% methanol solution of polyvinyl acetate having a dimethylacetal group was obtained. To 500 parts of the methanol solution, 99.5 parts of methanol and 17.2 parts of a 10% sodium hydroxide methanol solution were added, and a saponification reaction was carried out at 40 ° C. The obtained gel was pulverized, washed well with methanol, and dried to obtain a dimethyl acetal group-containing polyvinyl alcohol (referred to as polymer [A]).
During D ₂ O of the polymer [A], ¹ H-NMR spectrum measured at 50 ° C.: (Japan Electronic Co. measured by format GSX-270) Figure -
It is shown in FIG. In the spectrum of FIG. 1, the absorption at δ 1.3 ppm is N
Α- of 2,2-dimethoxyethyl methacrylamide unit
The absorption peak at δ 3.44 ppm clearly indicates the presence of a methine proton to which a dimethoxy group is bonded in the same unit. The peak at δ 3.36 ppm in FIG. 1 is a methyl group of methanol remaining due to slightly insufficient drying, and a hydroxyl group of water or a vinyl alcohol unit is irradiated so that absorption is not observed. Measuring. The content of N-2,2-dimethoxyethyl methacrylamide units calculated from FIG. 1 was 2.9 mol%, and the degree of saponification of vinyl acetate units was 97.0 mol%. Also,
The intrinsic viscosity of the polymer [A] measured at 30 ° C. in water is 0.844 d.
l / g, and the polymerization degree obtained from the polymerization was 1730.

100 parts of a 10% aqueous solution of the polymer [A] was prepared, and concentrated HCl was added thereto to adjust the pH to 2. The solution was poured on a PET frame and dried in a hot air dryer at 50 ° C. for 4 hours.
A 2 μm film was obtained. A sample having a size of 4 × 3 cm was cut out from the film, and after measuring the weight, the sample was dried in a dryer at 105 ° C. for 3 hours, and then the weight was measured to determine the dry solid content (S%). . Separately (and W _1.) Cut weight film of the same size after measuring, pulling the glass substrate was immersed for 2 hours in water at 90 ° C., wipe well adhering water with paper, weight (and W _2.) Was measured. further,
This (and W _3.) Weight After drying overnight at 105 ° C. were measured. Next, the weight swelling degree and the elution content were calculated using the following equations. (This test is called a water resistance test.) Table 2 shows the results.

Examples 2 to 6 Polymers [B] to [F] were prepared in the same manner as in Example 1 except that the charged components and the amounts thereof were changed, and the polymerization time and the amount of sodium hydroxide used during the saponification reaction were changed. Was synthesized. The changed conditions and the results are shown in Table-1.

A water resistance test was carried out using the obtained polymers [B] to [F] in the same manner as in Example 1 except that the acid used was changed. The results are shown in Table 2.

Comparative Example 1 A polyvinyl alcohol having a polymerization degree of 1750 and a saponification degree of 98.5 mol% was tested in the same manner as in the water resistance test of Example 1. The results are shown in Table 2.

Comparative Example 2 A modified polyvinyl alcohol having a content of N-methoxymethylacrylamide units of 8.8 mol%, a saponification degree of 96.9 mol%, and a polymerization degree of 2200 obtained by saponifying a copolymer of N-methoxymethylacrylamide and vinyl acetate was used. The test was conducted in the same manner as in the water resistance test of Example 1 except that the test was used. The results are shown in Table 2.

F. Effects of the Invention It is not clear why the polyvinyl alcohol of the present invention has extremely excellent water resistance, but the acetal group in the polyvinyl alcohol-based polymer of the present invention is hydrolyzed by an acid catalyst to form an aldehyde group, It is presumed that the aldehyde group and the hydroxyl group of polyvinyl alcohol form a ketal bond and crosslink during drying.

As is clear from the above examples, the polyvinyl alcohol-based polymer of the present invention has extremely excellent water resistance, and can be suitably used in various application fields requiring water resistance. Specific examples of such application fields include fibers, films, sheets, pipes, molded products such as separation membranes, sizing agents for fibers, paper processing agents, adhesives, additives for emulsions, emulsion stabilizers for emulsion polymerization, suspensions for emulsions. Examples include a dispersant for turbid polymerization, a pigment dispersant, a binder, a photosensitive resin, and additives for cement and mortar.

[Brief description of the drawings]

FIG. 1 shows the ¹ H-NMR spectrum of the polymer [A] of Example 1.

Claims (4)

(57) [Claims] (1) a structural unit represented by the following general formula:
0 mol%, saponification degree 50 mol% or more and polymerization degree 50
Up to 4000 polyvinyl alcohol polymers. (Where n is an integer of 0 to 8, R ₁ is hydrogen or a methyl group, R ₂ is hydrogen or an alkyl group having 1 to 4 carbon atoms, R ₃ and R ₄ are hydrogen or an alkyl group having 1 to 8 carbon atoms. Represent each) 2. The polyvinyl alcohol-based polymer according to claim 1, wherein a radical copolymerization of a fatty acid vinyl and a monomer represented by the following general formula is carried out, followed by saponification using an alkali catalyst. Manufacturing method. (Where n is an integer of 0 to 8, R ₁ is hydrogen or a methyl group, R ₂ is hydrogen or an alkyl group having 1 to 4 carbon atoms, R ₃ and R ₄ are hydrogen or an alkyl group having 1 to 8 carbon atoms. Represent each) 3. The method of claim 1, wherein the polyvinyl alcohol-based polymer is dissolved in water, and an acid catalyst is added thereto, followed by drying. 4. The method for making a polyvinyl alcohol-based polymer water-resistant according to claim 1, wherein the polyvinyl alcohol-based polymer according to claim 1 is dissolved in water, ammonium chloride is added, and then the polymer is dried.