JPS609977B2 - Binder for plaster moldings - Google Patents

Description

[Detailed description of the invention] The present invention relates to a binder for gypsum molded bodies.

Conventionally, polyacrylamide and polyacrylic acid have been known as binders for gypsum moldings, but when these are used, the hydration reaction of gypsum hemihydrate is significantly inhibited and it takes a long time to harden, which is a serious drawback. be. For example, when polyacrylamide is used in an amount of 5% by weight based on gypsum hemihydrate, it takes more than 6 hours for the gypsum to harden. Moreover, in the case of polyacrylic acid, it does not harden even after 24 hours. The present invention provides a new binder for gypsum moldings that does not substantially retard the curing of gypsum and can impart sufficient strength to the obtained gypsum moldings, in place of the above-mentioned known binders for gypsum moldings. It is.

That is, in the present invention, 45 to 95 mol% of acrylamide and 5
The present invention relates to a binder for gypsum molded bodies whose active ingredient is a copolymer containing ~55 mol% of a hydrophobic monomer as a constituent monomer.

The binder for gypsum moldings of the present invention uses as an active ingredient a copolymer obtained by copolymerizing acrylamide and a hydrophobic monomer in a predetermined ratio, thereby overcoming the serious drawbacks of conventional binders of this type. The disadvantage of slowing down the hardening time of plaster can be completely eliminated, and excellent strength can be imparted to the plaster molded product.

In particular, this effect of increasing product strength even exceeds that of polyacrylamide, which is commonly used as this type of binder. Acrylamides used in the binder for gypsum molded bodies of the present invention include acrylamide and methacrylamide. In addition, as the hydrophobic monomer, various hydrophobic monomers that can be copolymerized with the above acrylamides are used.
can be used. Examples include acrylonitriles such as acrylonitrile and methacrylonitrile: methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, dimethylaminoethyl acrylate, Acrylic acid esters such as tylaminoethyl and corresponding methacrylic acid esters; vinyl esters such as vinyl acetate and vinyl propionate; styrene, Q-methylstyrene,
Examples include styrenes such as vinyltoluene. These can be used alone or in combination. The ratio of the acrylamide and the hydrophobic monomer used is 45 to 95 mol% of the acrylamide, preferably 70 to 90 mol%.
The mole % and hydrophobic monomer should be in the range of 5 to 55 mole %, preferably 10 to 30 mole %. If the acrylamide content is less than 45 mol%, the physical strength of the resulting gypsum molded product using the binder will decrease, so it is preferable.
do not have. Furthermore, if the acrylamide content exceeds 95 mol %, that is, if the hydrophobic monomer content is less than 5 mol %, this is not preferable because the curing of the gypsum will be delayed. The binder for gypsum molded bodies of the present invention can be obtained by copolymerizing the above-mentioned acrylamide and a hydrophobic monomer in a predetermined ratio.

The copolymerization method is not particularly limited, and various conventionally known methods can be widely applied. For example, acrylamide and a hydrophobic monomer in the above specified proportions may be copolymerized in an aqueous medium in the presence of a polymerization initiator at a temperature of about 10 to 9,000 ℃. At this time, a method of emulsion polymerization using a surfactant or a protective colloid can also be adopted. Any known protective colloid can be used, but nonionic ones are preferred, such as hydroxyethyl starch, polyvinyl alcohol, and the like. When using the binder for gypsum molded bodies of the present invention, it is generally necessary to mix it with hemihydrate gypsum and an appropriate amount of water, then mold and dry it.

At this time, inorganic materials such as asbestos, rock wire, glass fiber, and steel wire, and organic fibers such as cotton, hemp, synthetic fibers, and wood pulp may be added to the mixture as reinforcing agents, if necessary. Further, when the desired molded product is a gypsum board (3), base paper for school board or the like can be used as a reinforcing agent. In the above, the amount of the binder of the present invention to be used is usually in the range of about 0.01 to 1% by weight based on solid content based on hemihydrate gypsum. Further, when the molded product to be obtained is a gypsum board, the amount is preferably about 0.1 to 1% by weight based on 4-hemihydrate gypsum. Thus, according to the invention:
A gypsum molded product having high strength and low water absorption and exhibiting the desired effects of the present invention can be obtained in a relatively short time without substantially delaying the hardening of the gypsum.

Examples and comparative examples will be given below to clarify the characteristics of the present invention.

Example 1 2 353.6 times of a 50% aqueous solution of acrylamide, 23.2 times of acrylonitrile, 10 times of inpropyl alcohol, 60 times of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500) and 460 times of water were charged into the four-way flask. The temperature was raised under a nitrogen stream, and when the temperature reached 65 qo, a solution of 2 quarts of potassium persulfate dissolved in 100 quarts of water was added.

Thereafter, it was kept warm for 3 hours at a temperature of 70 to 75 pm. After the polymerization is completed, it is cooled to obtain a solid content of 20.1%, pH 3.2, and viscosity (B
An aqueous dispersion of a copolymer with a specific ps of 370 (as measured by a type viscometer of 2000 or less) was obtained. This will be referred to as binder 1. Example 2 2 Into the four-way flask, 303 g of a 50% aqueous solution of acrylamide, 48.5 g of acrylonitrile, and 10 g of inpropyl alcohol were added.
Prepare 100 units of a 10% aqueous solution of 0) and 436 units of water,
Thereafter, in the same manner as in Example 1, the solid content was 22.8% and the pH was 4.
8 An aqueous dispersion having a viscosity of 2800 ps was obtained.

This is referred to as binder 0. Example 3 2 Into the four-piece flask, 229 g of a 50% aqueous solution of acrylamide, 85.5 g of acrylonitrile, 10 g of inpropyl alcohol, and vorivinyl alcohol (degree of polymerization 50
Prepare 100 units of a 10% aqueous solution of 0) and 473 units of water,
Thereafter, in the same manner as in Example 1, the solid content was 22.9% and the pH was 3.
An aqueous dispersion having a viscosity of 0 and a viscosity of 10 ps was obtained.

This is referred to as binder m. Example 4 2 46.5 tons of vinyl acetate, 1.2 tons of polyethylene glycol allyl ether, 10 tons of inpropyl alcohol, and 343 tons of water were charged into the 2-four-meter flask, and the temperature was raised under a nitrogen stream until it reached 7,000, and then acrylamide was added. 5
A mixture of 307 g of 0% aqueous solution, 1 g of potassium persulfate, and 292 g of water was added dropwise over a period of 3 hours, and after the dropwise addition was completed, the temperature was kept at 8,000 ℃ for 1 hour.

After polymerization is completed, it is cooled to a solid content of 20.1%, pH 4, and viscosity 2.
An aqueous dispersion of 40 ps was obtained. This will be referred to as binder W. Example 52 296 times of a 50% aqueous solution of acrylamide, 52 times of methyl methacrylate, 5 times of inpropyl alcohol, 50 times of a 10% aqueous solution of vorivinyl alcohol (degree of polymerization 500) and 490 times of water were placed in the four-way flask. Same as 1, solid content 21.5%,
An aqueous dispersion having a viscosity of 175 ps and a pH of 3.0 was obtained.

This will be referred to as binder V. Example 6 2 Into the four-piece flask, 292.8 hours of a 50% aqueous solution of acrylamide, 53.6 hours of styrene, 10 hours of inpropyl alcohol, 3.3 hours of sodium dodecylbenzenesulfonate (water ratio 40%), and 520 minutes of water were added. Thereafter, in the same manner as in Example 1, an aqueous dispersion having a solid content of 22.7%, a pH of 3.1, and a viscosity of 8500 ps was obtained.

This will be used as a binder. Example 7 2 Into the four-piece flask, add 128.8% of a 50% aqueous solution of acrylamide and 35% of dimethylaminoethyl methacrylate.
．． 6 days, 17.3 times of 62.5% sulfuric acid and 805 times of water were charged, and the mixture was heated up and overflowed under a nitrogen stream, and when it reached 65q0, 2
10 parts of a solution of 10 parts of potassium persulfate dissolved in 10 parts of water was added.

Thereafter, the temperature was kept at 70 to 80°C for 4 hours. After the polymerization was completed, it was cooled to obtain an aqueous dispersion having a solid content of 9.9%, a pH of 4.7, and a viscosity of 260 ps. This will be used as a binder plate. Comparative Example 1 2 In a four-way flask, 400 g of a 50% aqueous solution of acrylamide, 10 g of inpropyl alcohol, and 480 g of water were added.
After that, the solid content was reduced to 20% in the same manner as in Example 1. An aqueous dispersion having a pH of 3.4 and a viscosity of 420 ps was obtained.

This will be used as a comparison binder. <Application Test> Gypsum molded bodies were created using the binder 1 to skin obtained in Examples 1 to 7 above and the binder (polyacrylamide) obtained in Comparative Example.

i) Curing time Aqueous solution containing 0.5 ta of binder as solid content 67
200 g of gypsum was taken in a beaker, and then 100 g of gypsum was added to the takaazusa and mixed for 5 minutes to obtain a gypsum composition.

Immediately a thermometer was inserted into the center and the time until the maximum temperature was reached was measured. (JISR 9112) ii) Bending strength The composition obtained in the same manner as above 2i) was
After casting into a mold of 0.0 mm x 1.5 mm, the mold was placed in a circulating dryer adjusted to 60° C. for 2 hours to dry.

Then 20oo, 65%R. Measurements were made on samples that were conditioned all day and night under the same conditions. 1 result for each binder
Table 1 shows the average values of the Kawago samples.

Table 1

Claims (1)

[Scope of Claims] 1. A binder for gypsum moldings, the active ingredient of which is a copolymer comprising 45 to 95 mol% of acrylamide and 5 to 55 mol% of a hydrophobic monomer. 2. The binder according to claim 1, wherein the hydrophobic monomer is an acrylonitrile. 3. The binder according to claim 1, wherein the hydrophobic monomer is an acrylic ester. 4. The binder according to claim 1, wherein the hydrophobic monomer is a vinyl ester. 5. The binder according to claim 1, wherein the hydrophobic monomer is a styrene. 6. The binder according to claim 1, wherein the constituent monomers are 70 to 90 mol% of acrylamide and 10 to 30 mol% of a hydrophobic monomer.