JPH0680709A - Dispersant - Google Patents

Abstract

PURPOSE:To provide a dispersant which can give a polymer having a high absorption rate of plasticizer and being amenable to the removal of residual monomer comprising uniform porous particles of a polymer containing repeating units of a specified alpha-olefin. CONSTITUTION:A copolymer obtained by copolymerizing a vinyl ester with 1-10mol% 4 C or lower alpha-olefin is saponified to obtain a dispersant comprising a modified polyvinyl alcohol of a degree of saponification of 50-99mol% and a degree of polymerization of 100-8000.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dispersant comprising a modified polyvinyl alcohol, and more particularly to a dispersant for emulsion polymerization and suspension polymerization of vinyl compounds and a pigment dispersant.

[0002]

2. Description of the Related Art Polyvinyl alcohol (hereinafter abbreviated as "PVA") is widely used as a dispersant for emulsion polymerization of vinyl compounds, particularly vinyl esters represented by vinyl acetate. The vinyl ester polymer emulsion obtained by emulsion polymerization is used in the fields of various adhesives, paints, paper or fiber processing.

However, the vinyl ester polymer emulsion is excellent in adhesiveness and workability, but has a drawback that the water resistance of the film is poor and the emulsion viscosity has a large temperature dependency, and these properties are emulsion polymerization. It is known that it depends largely on the dispersant used in the above.

That is, PV as a dispersant for emulsion polymerization
A generally includes so-called "completely saponified PVA" having a saponification degree of about 98 mol% and "partially saponified PVA" having a saponification degree of about 88 mol%. When the former is used, the water resistance is relatively good. However, there is a drawback that the viscosity of the emulsion increases remarkably at low temperature and gelation easily occurs. On the other hand, when the latter PVA is used, there is a drawback in that the water resistance of the film is inferior although the viscosity increase and gelation tendency of the emulsion at low temperature are improved.

In order to improve such a defect, both PVA's are used in combination and PVA with an intermediate saponification degree is used, but both the water resistance of the film and the small temperature dependence of the emulsion viscosity are used. Is not satisfied enough. In addition, in order to improve the water resistance of the film, urea resins and various crosslinking agents have been added to a polymer emulsion obtained by using partially saponified PVA as an emulsifier. Although water resistance is improved to some extent by these methods, workability during use is deteriorated due to an increase in viscosity, etc., and satisfactory results have not been obtained.

In suspension polymerization of vinyl chloride and other vinyl compounds, partially saponified PVA and cellulose derivatives such as methyl cellulose and carboxymethyl cellulose have been used as dispersants.

In the suspension polymerization of vinyl compounds, the dispersant is an important factor that controls the quality of the polymer obtained, and generally, the performance required for the dispersant is (i)
Shows high dispersion power even when used in a small amount, and has the function of making the particle size distribution of the resulting polymer particles as sharp as possible.
(Ii) In order to increase the absorption rate of the plasticizer to facilitate processability and to facilitate removal of the vinyl monomer remaining in the polymer particles, the formation of fish eyes in the molded product is further prevented. Therefore, it has a function of making the polymer particles as uniform and porous as possible, and (iii) has a function of forming polymer particles having a high filling specific gravity.

However, the above-mentioned dispersants for suspension polymerization which have been conventionally used do not satisfy these required performances, have a low ability to make the polymer particles porous, and have a plasticizer absorption rate of the polymer. There is a drawback that it is difficult to remove the residual vinyl monomer without increasing the value. In general, a dispersant is required to have a high dispersibility and to form a dispersion having a relatively low viscosity and a high concentration.

[0009]

The object of the present invention is to solve the drawbacks of the conventional PVA dispersants for emulsion polymerization and suspension polymerization, and to obtain excellent water resistance of the formed film when used for emulsion polymerization of vinyl compounds. It is possible to give a polymer emulsion with low temperature dependence of viscosity, and when used for suspension polymerization of vinyl compounds, it is composed of uniform porous particles, has a high plasticizer absorption rate, and is easy to remove residual monomers. Another object of the present invention is to provide a dispersant capable of producing various polymers.

Another object of the present invention is to provide a dispersant having a high dispersibility for pigments and other substances to be dispersed and capable of producing a dispersion having a relatively low viscosity and a high concentration.

[0011]

The above object is achieved by the dispersant of the present invention, that is, a dispersant comprising a modified polyvinyl alcohol containing 1 to 10 mol% of an α-olefin unit having 4 or less carbon atoms. .

Modified PV containing 1 to 10 mol% of α-olefin unit having 4 or less carbon atoms used in the present invention
A is obtained by saponifying a copolymer of vinyl ester and α-olefin having 4 or less carbon atoms. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate and the like, and vinyl acetate is preferable from the economical point of view.

The α-olefin copolymerized with the vinyl ester has a carbon number of 4 or less, and examples thereof include ethylene, propylene, n-butene and isobutylene.
Ethylene is preferable from the viewpoint of water resistance of the polymer film obtained. The content of α-olefin in the modified PVA is 1 to 10
It is mol%, preferably 2 to 8 mol%. When the content of the α-olefin is less than 1 mol%, the above-mentioned remarkable effect cannot be obtained, while when it exceeds 10 mol%, the water solubility is decreased and the above-mentioned effect is also obtained. Absent.

Other functional groups such as a carboxyl group, a lactone group, an amide group and an amino group may be introduced into the modified PVA of the present invention within the range not impairing the gist of the present invention. The modified PVA of the present invention has a saponification degree of 50.
It is preferably in the range of mol% to 99 mol%. The degree of polymerization is appropriately selected within the range of 100 to 8,000.

Typical uses of the modified PVA of the present invention are as dispersants for emulsion polymerization and suspension polymerization of vinyl compounds. Representative examples of emulsion polymerization and suspension polymerization of vinyl compounds include emulsion homopolymerization of vinyl ester represented by vinyl acetate and emulsion of vinyl acetate with ethylene, propylene, vinyl chloride, acrylic acid esters, and methacrylic acid esters. Copolymerization; as well as vinyl chloride, styrene,
Examples include suspension polymerization of methyl methacrylate and other methacrylic acid esters.

When the modified PVA of the present invention is used as a dispersant for emulsion polymerization, it is used in an amount of 0.1 to 20% by weight, preferably 0.3 to 15% by weight, based on the vinyl compound. If the amount used is less than 0.1% by weight, the polymerization stability is poor, and
If it exceeds 5% by weight, the water resistance of the obtained emulsion decreases. Although the modified PVA emulsion polymerization dispersant of the present invention is preferably used alone, other protective colloids and emulsifiers can be used as long as the object of the present invention is not impaired. For example, conventional PVA, starch, polyacrylamide, hydroxyether cellulose, conventionally known nonionic emulsifiers, anionic emulsifiers and the like can be used in combination.

When the modified PVA dispersant of the present invention is used as a dispersant for suspension polymerization, it can be used in the same manner as a conventional PVA dispersant. Further, the modified PVA dispersant of the present invention exhibits a high dispersive power to many substances to be dispersed including inorganic pigments and organic pigments, and thus can be used in place of conventional dispersants in many fields. In particular, when used as a dispersant for pigments, it produces a dispersion liquid having a low viscosity and good dispersion stability as compared with many conventional dispersants.

[0018]

INDUSTRIAL APPLICABILITY When the modified PVA dispersant of the present invention is used as a dispersant for emulsion polymerization of vinyl compounds, it is possible to obtain a polymer emulsion having excellent water resistance of the formed film and having a small temperature dependence of viscosity. Further, when it is used for suspension polymerization of a vinyl compound, suspension polymer particles having a sharp particle size distribution and porosity and a large packing specific gravity can be obtained. This suspension polymer has the characteristics that the absorption rate of the plasticizer is high, the residual monomer is easily removed, the powder is less scattered during handling, and the bite into the molding machine is good.

Further, the modified PVA dispersant of the present invention exhibits a high dispersive power with respect to the substance to be dispersed. In particular, when used as a dispersant for pigments, it is possible to form a dispersion liquid having a low viscosity and good dispersion stability as compared with many conventional dispersants.

[0020]

EXAMPLES The modified PVA dispersant of the present invention will be specifically described below with reference to Examples. In each example, “part” is based on weight. Example 1 (Production of modified PVA) A reactor equipped with a stirrer was charged with 100 parts of vinyl acetate and 30 parts of methanol, and after nitrogen substitution, 3 parts of ethylene was added. A solution in which 2,2'-azobisisobutyronitrile was dissolved as an initiator was prepared, and nitrogen substitution was carried out by bubbling with nitrogen gas. The temperature of the reaction vessel charged with the above monomers was raised, and when the internal temperature reached 60 ° C., the initiator solution was injected to initiate polymerization. After 3 hours, when the polymerization rate reached 48%, it was cooled. After removing ethylene, the unreacted vinyl acetate monomer was removed under reduced pressure to obtain a methanol solution, and a NaOH methanol solution was added to saponify. The modified PVA thus obtained had a degree of polymerization of 1,200, a degree of saponification of 90.0 mol% and an ethylene content of 7.2 mol%.

(Emulsion polymerization of vinyl acetate) In the reactor equipped with a stirrer, a reflux condenser, a thermometer and a dropping funnel, the PV
20 g of A was dissolved in 240 g of water. Next, 20 g of vinyl acetate was added, and when the internal temperature reached 70 ° C., 0.3 g of hydrogen peroxide and 0.5 g of tartaric acid were added to initiate polymerization. Subsequently, 180 g of vinyl acetate and 0.
3 g was added continuously over 3 hours. After the addition was completed, the internal temperature was maintained at 80 ° C. for 1 hour for aging. After cooling, 20 g of dibutyl phthalate was added to give a nonvolatile content of 48.0%,
An emulsion with a viscosity of 12,000 cp at 30 ° C. was obtained.

The emulsion thus obtained was subjected to the following tests. (1) Temperature Dependence Evaluation of Emulsion Viscosity The emulsion viscosity was measured at 30 ° C. and 0 ° C., and the temperature dependency was evaluated by the viscosity ratio (0 ° C./30° C.). (2) Low-temperature storage stability It was left at −5 ° C. for 24 hours and observed for changes in emulsion. (3) Water resistance A paper / paper adhesion test was conducted under the following conditions, followed by curing and drying for 1 day, immersion in water at 30 ° C. for 24 hours, then peeling, and checking the adhesion state. B: good, C: poor). Paper: B liner, 25 mm x 50 mm large, 5 pieces each Application amount: 40 g (wet) / m ² Pressing: Pressing once with a hand roller Curing: 23 ° C, 65% RH, 24 Hr Results are shown in Table 1. Show.

Examples 2 and 3 (Production of modified PVA) Example 1 except that the monomer composition was changed.
Two types of modified PVA were produced by the same operation as in. (Emulsion Polymerization of Vinyl Acetate) Emulsion polymerization of vinyl acetate was carried out in the same manner as in Example 1 using each of the above PVA as a dispersant, and the obtained emulsion was evaluated. The results are shown in Table 1.

Comparative Examples 1 and 2 (Production of PVA) Unmodified PVA was obtained in the same manner as in Example 1 except that the monomer composition was changed. (Emulsion polymerization of vinyl acetate) Emulsion polymerization of vinyl acetate was carried out in the same manner as in Example 1 using each of the above-mentioned unmodified PVA as a dispersant, and the obtained emulsion was evaluated. The results are shown in Table 1.

[0025]

[Table 1] From the results in Table 1, it is apparent that the modified PVA dispersant of the present invention can form a film having good water resistance, and that an emulsion having a small temperature dependence of emulsion viscosity can be obtained.

Examples 4 to 6 and Comparative Example 3 (Vinyl Chloride Suspension Polymerization) Modified PVA and unmodified PVA were produced by repeating substantially the same operation as in Example 1 except that the monomer composition was changed. did. Suspension polymerization of vinyl chloride was carried out by the following method using these as a dispersant alone or together with other PVA.

40 parts of deionized water in a glass-lined autoclave, 0.75% by weight of a 2 wt% aqueous solution of PVA-based dispersant.
Parts and 5 of diisopropyl peroxydicarbonate
0.009 parts of 0% by weight toluene solution was charged, and the interior of the autoclave was degassed to 50 mmHg to remove oxygen, then 30 parts of vinyl chloride monomer were charged, and the mixture was stirred under stirring to 57
Polymerization was performed by raising the temperature to ° C. At the start of the polymerization, the pressure in the autoclave was 8.5 kg / cm ² G, but it reached 4.5 kg / cm ² G 7 hours after the start of the polymerization, so the polymerization was stopped at this point, and unreacted vinyl chloride was removed. Purge the monomer,
The contents were taken out and dehydrated and dried. Table 2 shows the physical properties and the amount of the PVA-based dispersant used, and Table 3 shows the characteristic ability of the obtained vinyl chloride resin. The polymerization yield of the vinyl chloride resin was 85%, and the average degree of polymerization was 1050.

The characteristics of the obtained vinyl chloride resin were evaluated according to the following criteria. (1) Particle size distribution: It was measured by dry sieve analysis using a wire mesh based on Tyler mesh. (2) Filling specific gravity: Measured according to JIS K6721-1959.

(3) Uniformity of particle porosity: 100 parts vinyl chloride resin, 50 parts dioctyl phthalate, 1 part dibutyltin maleate, 1 part cetyl alcohol, titanium white 0.1.
1 part of a mixture of 25 parts and 0.1 part of carbon black
Knead for a predetermined time (3 minutes, 5 minutes, 7 minutes) with a roll at 50 ° C to create a sheet with a wall thickness of 0.2 mm, and allow light to pass through the sheet to allow 100 cm ^{2 of} fish to be contained in the sheet.
I counted the number of eyes. The more the fish eyes disappear in a short time, the better the uniformity of particle porosity.

(4) Absorption of plasticizer: Using a planetary mixer connected to a plastograph, 100 parts of vinyl chloride resin and 50 parts of dioctyl phthalate were put into a container kept at 80 ° C., and each time while stirring. The kneading torque was recorded for each time, and the kneading time at the point where the kneading torque decreased was displayed. The shorter the time, the better the absorbability of the plasticizer. (5) Residual vinyl chloride monomer: A certain amount of vinyl chloride resin was dissolved in tetrahydrofuran and the content of vinyl chloride monomer in the vinyl chloride resin was quantified by gas chromatography.

[0031]

[Table 2]

[0032]

[Table 3] From the results in Table 3, when the suspension polymerization is carried out by using the modified PVA dispersant of the present invention alone or in combination with a conventionally known PVA, it is composed of uniform porous particles, the plasticizer absorption rate is large, and the residual monomer is removed. It can be seen that a vinyl polymer that is easy to obtain is obtained.

Examples 6 and 7 and Comparative Examples 4 and 5 (Preparation of Calcium Carbonate Dispersion) Modified PVA and unmodified PVA were prepared by the method according to the above-mentioned examples, and calcium carbonate was prepared by using them as dispersants. (Shiraishi Kogyo P-
A paste having a concentration of 60% by weight of 3) was obtained. This paste was allowed to stand at 20 ° C. for 3 months, and its dispersion state was evaluated by a three-stage method (A: no change in dispersion state, B: slight sedimentation, C: significant sedimentation). For comparison, a paste was prepared using sodium polyacrylate as a dispersant and evaluated in the same manner. The results are shown in Table 4.

[0034]

[Table 4] From the results in Table 4, it can be seen that the modified PVA dispersant of the present invention gives a dispersion having low viscosity and good dispersion stability.

Claims (4)

[Claims] 1. An α-olefin unit having 4 or less carbon atoms is used as 1 unit.
Dispersant consisting of modified polyvinyl alcohol containing 10 to 10 mol%. 2. A dispersant for emulsion polymerization of a vinyl compound comprising the modified polyvinyl alcohol according to claim 1. 3. A dispersant for suspension polymerization of a vinyl compound, which comprises the modified polyvinyl alcohol according to claim 1. 4. A pigment dispersant comprising the modified polyvinyl alcohol according to claim 1.