JP2849445B2 - Cement admixture - Google Patents

Description

The present invention relates to a cement admixture.

B. Conventional technology Conventionally, a method of mixing a water-soluble polymer such as a polymer emulsion, a latex or a PVA or a methylcellulose into a cement has been widely used in order to improve various mechanical properties of the cement (mortar or concrete). And is known to have a certain effect.

C. Problems to be Solved by the Present Invention These admixtures are expected to have little effect on the improvement in preventing the formation of a latency layer which weakens the bending strength or surface strength, which is an essential disadvantage of cement. It is the current situation.

In recent years, high-temperature autoclave curing at 140 to 180 ° C. has been performed in order to produce a high-strength cement molded product with a short curing time. Under the conditions of high temperature, high humidity, and high alkali, most of the conventional admixtures are decomposed, deteriorated, and the like, and a large effect is not obtained.

In view of the above-mentioned current situation, the present invention has been intensively studied for the purpose of improving various physical properties of cement. As a result, by mixing the PVA polymer of the present invention with cement, flexural strength, compressive strength, and wear resistance (surface strength) are obtained. It has been found that a cement composition which is excellent in mechanical strength such as the above and gives an excellent cement composition which does not impair these effects even in high-temperature curing. Also, a remarkable improvement in the adhesive force to the adherend is an excellent feature of the present invention.

D. Means for Solving the Problems The present inventors have repeatedly studied the cement admixture, and as a result, one or more kinds selected from a polymer of vinyl pivalate and a copolymer of vinyl pivalate and vinyl acetate Of saponification obtained by saponification of polymer
It has been found that when an admixture composed of a PVA-based polymer of 50 mol% or more is used, an excellent cement molded product not found in the conventional cement admixture can be obtained, and the present invention has been completed. The PVA-based polymer of the present invention is a commercially available PVA
For higher syndiotacticity, water resistance, heat resistance, moisture and heat resistance and excellent mechanical performance described above when used as a cement admixture because of its excellent durability, It is thought that good durability is given even in the presence of high temperature and high alkali in autoclave curing.

PVA having a degree of saponification of 50 mol% or more obtained by saponifying one or two or more polymers selected from the polymer of vinyl pivalate and the copolymer of vinyl pivalate and vinyl acetate used in the present invention. A polymer obtained by polymerizing or copolymerizing vinyl pivalate or vinyl pivalate and vinyl acetate by a known polymerization method such as lump, solution, suspension, emulsification or the like is saponified by a known method. It can be obtained by:

The saponification degree of the PVA-based polymer is at least 50 mol%, preferably at least 70 mol%. If the saponification degree is lower than 50 mol%, the above-mentioned various properties are lowered and the water resistance is deteriorated. The degree of polymerization of the PVA-based polymer is preferably 100 to 10,000, more preferably 300 to 5,000. As the composition of the copolymer of vinyl pivalate and vinyl acetate, the molar composition of vinyl pivalate in the copolymer is 0.5 mol% or more, preferably 5 mol% or more, and more preferably 10 mol% or more. Give performance. The composition of vinyl pivalate in the copolymer is 0.5 mol%
If it is less than 10%, the mechanical properties and durability of the cement may be undesirably reduced.

When the PVA-based polymer used in the present invention is used as a cement admixture, the PVA-based polymer may be added to the cement in the form of a fine powder or dissolved in water and added. If syndiotacticity is high
Since it may not be dissolved in water at 100 ° C. or lower, it is necessary to dissolve at a high temperature in a pressurized container such as an autoclave.

The cement admixture of the present invention is used by mixing it with cement and, where necessary, fine aggregates or aggregates (eg, sand, gravel, etc.).

In the present invention, the amount of the PVA-based polymer to be added is preferably 0.01 to 30% by weight, more preferably 0.05 to 10% by weight, based on the cement. When the amount is less than 0.01% by weight, the effect is substantially the same as in the case where it is not added, and the effect is not seen. When the amount exceeds 30% by weight, the fluidity of the cement tends to be deteriorated, and such a large amount needs to be added. Because there is no.

Although the PVA-based polymer of the present invention exhibits high effects even when used alone, other admixtures such as a polymer emulsion or latex, ordinary PVA, modified PVA or a cellulose derivative may be used in combination. Undoubtedly, a good effect can be obtained by the combined use depending on the purpose.

The cement admixture of the present invention is excellent in mechanical strength such as bending, compressive strength and abrasion resistance (surface strength), has a high adhesive strength to adherends, and withstands autoclave curing at high temperatures and exhibits high performance. It is a feature of the present invention to provide a cement composition. Although the reason why the admixture of the present invention has the remarkable performance as described above is not fully understood,
A PVA polymer having a saponification degree of 50 mol% or more obtained by saponifying one or two or more polymers selected from a polymer of vinyl pivalate and a copolymer of vinyl pivalate and vinyl acetate is , High adhesion to calcium silicate compounds or bones, which are components of cement,
The above-mentioned remarkable performance is exhibited by suppressing the transfer of free water from the cement to the surface by suppressing the water retention of the PVA polymer and suppressing the formation of a weak layer (latency layer) on the cement surface. It is estimated to be.

E. Examples Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to these Examples. In the following, “parts” and “%” mean “parts by weight” and “% by weight”, respectively, unless otherwise specified.

Example 1 A reaction vessel equipped with a stirrer was charged with 600 parts of vinyl pivalate monomer and 160 parts of methanol, and the system was purged with nitrogen by bubbling nitrogen gas. Separately, a solution prepared by dissolving 0.0625 part of 2,2'-azobisisobutyronitrile as an initiator in 20 parts of methanol was prepared, and nitrogen was replaced by bubbling with nitrogen gas. The temperature of the reaction vessel was raised, and when the internal temperature reached 60 ° C., a methanol solution in which an initiator was dissolved was injected to initiate polymerization. After 190 minutes, when the polymerization rate reached 45%, the system was cooled to stop the polymerization, the unreacted vinyl pivalate monomer was removed under reduced pressure while occasionally adding t-butanol, and the t- A butanol solution was used. Subsequently, t-butanol was removed under reduced pressure,
A 32.8% solution of polyvinyl polypivalate in tetrahydrofuran was obtained. Next, 30.5 parts of this solution was weighed and placed in a reactor equipped with a stirrer and a reflux condenser, heated to 60 ° C, purged with nitrogen by flowing nitrogen gas, and maintained at 60 ° C, and then separately prepared. Solution of 25% potassium hydroxide in nitrogen
21 parts were added and stirred well. The system gelled in about 10 minutes, but after further holding at 60 ° C. for 100 minutes, 6.8 parts of acetic acid was added together with 20 parts of methanol to neutralize potassium hydroxide. Subsequently, after the gel was pulverized, Sox Soxhlet washing with methanol was performed to obtain PVA. Obtained PVA 0.5
To the mixture, 10 parts of acetic anhydride and 2 parts of pyridine were added, and the mixture was sealed and heated at 120 ° C. for 8 hours to acetylate. The obtained polyvinyl acetate was precipitated in n-hexane, and re-precipitated twice in an acetone-n-hexane system, and purified. Obtained PV
A was dissolved in d ₆ -DMSO and NMR was measured.
The viscosity-average degree of polymerization determined from 99.4 mol%, syndiotacticity 61.5 mol%, and [η] of polyvinyl acetate obtained by acetylation and measured at 30 ° C. in acetone was 2080.

0.5 part of this PVA polymer fine powder (80 mesh pass product) is added to 100 parts of Portland cement and 300 parts of Toyoura standard sand, and 6.5 parts of water is added and kneaded so that the flow value of the mortar becomes 170. And molded in accordance with JIS-R5201 “Physical Testing Method for Cement”.
(° C., 65% RH). This was immersed in water to determine whether calcium hydroxide was eluted from the cement. Further, after 20 minutes, the mortar after kneading is applied to a mortar plate (prepared by cement / sand cured for 1/2 week for 4 weeks, 40 × 40 mm) so as to have a thickness of 3 mm. Laminated. After curing under standard conditions for 4 weeks, use a measuring jig and pull the speed using an autograph.
The adhesive strength was measured at 1 mm / min. Table 1 shows the measurement results.

For comparison, the case where the PVA polymer in Example 1 was not used (Comparative Example 1) or the case where ordinary PVA (degree of saponification 98.
Table 1 also shows the results of measurement performed in the same manner as in Example 1 (Comparative Example 2) when 6 mol% and a degree of polymerization of 1780 were used.

The composition of the present invention using the saponified polymer of vinyl pivalate (Example 1) has remarkably excellent mortar strength and adhesive strength and remarkably small dissolution of calcium hydroxide as compared with each comparative example. I understand.

Examples 2 to 5 In place of the PVA-based polymer used in Example 1, vinyl pivalate and vinyl acetate were copolymerized, and then saponified in the same manner as in Example 1 to produce PVAs having different compositions. Note that P
The copolymer composition of VA was determined from NMR of a copolymer of vinyl pivalate and vinyl acetate before saponification. The procedure was performed in the same manner as in Example 1 except that the used PVA-based polymer was used. PVA used
Are shown in Table 2 and the results are shown in Table 3. It can be seen that all have high strength and adhesive strength.

Example 7, Comparative Example 3 In the same manner as in Example 1 using the PVA (Example 7) used in Example 1 and the PVA (Comparative Example 3) used in Comparative Example 2, according to JIS-R5201. After molding, the mixture was cured at a high temperature of 180 ° C. for 10 hours in an autoclave, and then the physical properties of the cement were measured. The results are shown in Table 3.

F. Effects of the Invention The present invention relates to a cement admixture. It is composed of a PVA polymer having a saponification degree of 50 mol% or more obtained by saponifying one or two or more polymers selected from a polymer of vinyl pivalate and a copolymer of vinyl pivalate and vinyl acetate. By using as a cement admixture, it has excellent mechanical strength such as bending, compressive strength and abrasion resistance (surface strength), has high adhesion to adherends, and withstands high temperature autoclave curing and has high performance. It is characterized by giving a cement composition that exerts its effect, and has extremely high industrial value.

Claims (1)

(57) [Claims] 1. A polyvinylidene having a degree of saponification of 50 mol% or more obtained by saponifying one or more polymers selected from a polymer of vinyl pivalate and a copolymer of vinyl pivalate and vinyl acetate. Cement admixture composed of alcoholic polymer.