JPS5938177B2 - A curable gypsum composition that can provide water resistance while curing. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a gypsum-cured molded product that can impart water resistance at the same time as curing, and more specifically, to improve water resistance when in contact with running water and mechanical properties when dry and wet. The present invention relates to a method for producing a hardened gypsum molded product which has a remarkable combination of strength and strength.

Gypsum is known as an inexpensive molding material that is produced as a by-product during waste gas desulfurization, waste sulfuric acid treatment, phosphoric acid, manufacturing, etc.

Gypsum molded products such as so-called gypsum boards are made by kneading hemihydrate gypsum, generally called calcined gypsum, with water or reinforcing materials such as fibers to form a slurry, which is then cast into a desired mold and allowed to harden. , if necessary, by drying.

Conventional gypsum molded structures have excellent soundproofing and heat insulation properties, and are useful as building materials. However, when such gypsum molded structures come into contact with water, especially running water, they can become submerged in water. It gradually dissolves in Vc, resulting in a significant decrease in volume, and thus cannot be used in applications where there is a risk of contact with water.

In addition, gypsum alone does not have sufficient strength (and is brittle), and although these characteristics have been compensated for by the reinforcing material mentioned above, the effect is still not fully satisfactory. do not have.

Attempts are already known to significantly improve the water resistance of plaster molded structures.

For example, Japanese Patent Application Laid-Open No. 50-85629 discloses that a molded product made by mixing hydraulic gypsum and lime and further containing water is heated and dried in a normal atmosphere or cured in an atmosphere containing carbon dioxide gas. It is disclosed that a gypsum-lime hardened body is manufactured by heating and drying the gypsum-lime hardened body.

The gypsum-lime hardened body obtained by this method has a lower water absorption rate than normal gypsum hardened bodies, and has relatively high strength after water absorption, but when it comes into contact with running water, the hardened body The disadvantage is that the gypsum extrudes into the water, causing the hardened product to collapse from the surface and reduce its volume.

Further, JP-A-50-139117 describes that a cured gypsum body is immersed in a liquid containing oxalic acid or sodium oxalate to form a water-resistant film on a portion thereof.

According to this method, although the amount of extrusion into flowing water is considerably reduced compared to untreated hardened gypsum, it is extremely difficult to reduce extrusion to virtually zero, and it is still It is not completely satisfactory in that it causes a considerable volume reduction.

In addition, in gypsum hardening bodies and hydraulic compositions, hydraulic cement)
It is already known that the mechanical strength of a gypsum-cured molded product can be improved by containing Y and curing it together with cement and gypsum (for example, Japanese Patent Application Laid-Open No. 51-4216).
.

Although this method is effective in improving the dry strength of hardened plaster moldings, after the hardened plaster moldings come into contact with water, especially running water, the volume decreases significantly due to collapse etc.
It is still unsatisfactory in that the reinforcing effect is quickly lost.

(1) To the best of the inventors' knowledge, the volume reduction when immersed in running water is suppressed to virtually zero, and the mechanical strength remains at a satisfactory level after contact with water. Gypsum molded structures are still unknown.

Furthermore, the known method for producing a water-resistant gypsum cured molded article involves molding a curable gypsum composition, curing calcium sulfate having water reactivity, and then imparting water resistance to this molded product. Post-treatment operations such as immersion in a chemical or adding a component for imparting water resistance, which is pre-contained in the curable gypsum composition, to post-treatments such as curing that are separate from the gypsum. , and requires two stages of processing operations.
This method has not yet been fully satisfactory in terms of the number of steps, efficiency, and manufacturing cost.

The present inventors have developed a composition containing a hydraulic cement mainly composed of calcium sulfate and calcium silicate having water reactivity and a determined polybasic acid or a water-soluble salt thereof in a fixed quantity ratio of 'Y%. When curing in the presence of water, it is possible to impart water resistance to the plaster molding at the same time as it hardens, and the water resistance (resistance to loss of volume and weight) when brought into contact with running water is significantly improved. Furthermore, it has been found that a gypsum-reinforced molded product with significantly improved dry and wet strength can be obtained.

Therefore, an object of the present invention is to provide a method for producing a hardened gypsum molded article, which can impart water resistance to the gypsum molded article at the same time as hardening water-reactive calcium sulfate.

Another object of the present invention is that there is virtually no decrease in volume even when immersed in running water for a long period of time, and that mechanical strength is maintained not only when dry but also after contact with water. It is an object of the present invention to provide a method for producing a gypsum cured molded article at a satisfactory level.

That is, according to the present invention, calcium sulfate having water reactivity is 78.5 to 50% by weight, water-soluble cement mainly composed of calcium silicate) is 21 to 50% by weight, and oxalic acid or its water-soluble salt is 0%. .5 to 5.0% by weight, and then 35 to 90% water based on the total amount of each component is added to prepare a uniform dispersion, which is then molded and hardened. A method of manufacturing a molded body is provided.

In the present invention, calcium sulfate having water utilization reactivity is calcium sulfate known per se that can be hardened by water utilization reaction, namely α-type calcium sulfate 1/2 hydrate, β-type calcium sulfate 1/2 Calcium sulfate/anhydride having hydrate or hydraulic properties may be used.

An important feature of the present invention resides in the combination of a hydraulic cement mainly composed of calcium silicate and oxalic acid or a water-soluble salt thereof to the water-reactive calcium sulfate.

For example, when hydraulic cement is simply mixed with water-reactive calcium sulfate, the volume reduction rate after immersion in flowing water of the resulting molded bodies is as follows: is significantly large (reduced by more than 20%), and the mechanical strength when wet is also significantly reduced.

In addition, when a polybasic acid such as oxalic acid was simply added to the water-reactive calcium sulfate, the results were shown in sample no. The volume reduction rate is significantly reduced (more than 70%) and is difficult to reduce to substantially zero, and the mechanical strength decreases significantly when wet.

On the other hand, when a combination of hydraulic cement and a specific polybasic acid is blended with water-reactive calcium sulfate according to the present invention, the resulting hardened molded product has a volume reduction rate after immersion in running water. is suppressed to virtually zero, and the mechanical strength not only when dry but also when wet is suppressed to an extremely excellent level, and this fact can be easily understood by referring to the examples described later. It will be.

The reason why the cured molded product of water-reactive calcium sulfate lacks water resistance and has low wet strength is that the calcium sulfate dihydrate in the cured molded product has a water solubility that is problematic. Another possible cause is that there are quite large voids between the crystals of calcium sulfate dihydrate in the cured molded product.

In the method of the present invention, when a hydraulic cement mainly composed of calcium sulfate or calcium silicate which has water reactivity is mixed with oxalic acid or its water-soluble salt, the combination of hydraulic cement and oxalic acid will not cause hardening. It is believed that significant increases in water resistance and mechanical strength are achieved by filling the voids in the resulting calcium sulfate dihydrate crystals and forming a water-resistant coating around the crystal particles.

This estimate indicates that the cured molded product produced according to the present invention has a significantly smaller pore volume than known cured molded products, that is, 0.50 m within the pore radius range of 75A to 75000A.
, 1/g or less, and the pore volume of 0.23 ml/g or less in the pore radius range of 4,000 A to 10,000 A.

In the manufacturing method of the present invention, compared to the known method of treating a hardened gypsum body with an oxalic acid solution, the number of steps, processing efficiency, and processing cost are such that curing and waterproofing can be performed simultaneously in one step. In addition to the numerous advantages mentioned above, the manufactured product also has a number of excellent advantages.

That is, according to the above-mentioned known method, a water-resistant coating can be formed only on the surface of the cured molded product, and furthermore, since the structure is completely different between the surface portion and the inside of the cured molded product, it is possible to form a waterproof coating only on the surface of the cured molded product. Due to strain, etc. when strain or stress is applied,
This water-resistant surface coating is likely to be damaged or missing, or troubles such as peeling or the formation of voids between the water-resistant surface coating and the internal structure are likely to occur.

However, if the water-resistant coating is damaged, or if the cured compact is cut and used in the form of smaller parts, the exposed internal tissue can easily become voluminous or wet under running water. This will result in a significant decrease in strength.

On the other hand, the cured molded product manufactured by the manufacturing method of the present invention has a uniform structure from the surface to the inside, and is water-resistant treated throughout the inside, so there is no thermal strain or
There is no loss or destruction of the surface portion due to stress strain, etc., and there is no possibility of loss of water resistance even when processing such as cutting, cutting, nailing, drilling, etc. is performed.

In the present invention, by specifically selecting and using a hydraulic cement mainly composed of calcium silicate, a cured molded product that enables one-step (direct) hardening and water resistance treatment and has excellent water resistance and mechanical strength. It is extremely important to obtain

For example, quicklime, slaked lime, calcium carbonate, etc. can be considered as calcium compounds that are reactive with polybasic acids and their water-soluble salts, but these calcium compounds have satisfactory water resistance and improved mechanical strength. Visible.

The reason for this is thought to be that the reaction of these compounds with the polybasic acid is completed prior to the hardening of the water-reactive calcium sulfate.

In addition, for the purpose of filling the crystal gaps of hardened gypsum, it is possible to fill and use fine particles of silica, alumina, etc., but if these ordinary fillers are used,
Similarly, there is no improvement in water resistance or mechanical strength.

The reason for this appears to be that these fillers essentially lack the ability to form a water-resistant coating, ie, microcapsules, around the crystals of the gypsum hardened body.

On the other hand, when used in combination with hydraulic cementola mainly composed of calcium silicate, oxalic acid, etc. according to the present invention, water resistance and mechanical strength are significantly improved. The pore filling and coating formation based on the hardening reaction of the hydraulic cement itself and the reaction between the hydraulic cement and oxalic acid, etc., occur at a speed almost commensurate with the hardening reaction of the water-reactive calcium sulfate, or even slightly more. This seems to be due to the progress being made at a delayed speed.

Hydraulic cements based on calcium silicate (mainly β-2CaO・SiO2 and/or 3CaO-8iO2) include ordinary Portland cement; early-strength Portland cement, low heat-generating Portland cement, high iron oxide type Portland cement, white Special portland cement such as portland cement, titanium cement, manganese cement, chrome cement; alumina cement:
Lime alumina cement; lime mixed cement such as lime slag cement, lime volcanic ash cement; blast furnace slag mixed cement such as blast furnace cement, iron-Portland cement;
Pozzolan mixed cements such as silica cement and pozzolan cement: fly ash cement; expansive cement;
One or a combination of two or more of masonry cement and high sulfate slag cement are used.

In the present invention, the CaO content is relatively rich and Al2O
Hydraulic cements with a relatively low 3 min are particularly suitable;
CaO 60-90%, SiO2 10-30%, A
1203 is 7% or less, and the remainder is Fe2O if desired.
3. Cement consisting of MgO, SO3, etc. is most suitable.

In the present invention, oxalic acid or a water-soluble salt thereof is used, and especially sodium salt, potassium salt, etc. are used as the water-soluble salt of oxalic acid.

Ammonium salts may also be used, but in this case the mechanical strength appears to be lower than when using other salts or oxalic acid itself.

In the present invention, water-reactive calcium sulfate is 50 to 78.5% by weight, particularly 60 to 78% by weight.

Hydraulic properties) 21 to 50 weight ratio, especially 24 to 40
Weight%, oxalic acid component 0.5 to 5 weight%.

It is also very important to combine them, especially in amounts of 0.8 to 4% by weight.

That is, if the amount of calcium sulfate is less than the above range or if the amount of hydraulic cement is more than the above range, the purpose of the present invention, which is to produce a water-resistant gypsum molded body, will be deviated from. Moreover, the mechanical strength of the molded article also decreases.

On the other hand, if the amount of calcium sulfate exceeds the above range, or if the amount of hydraulic cement is less than the above range, the water resistance and mechanical strength of the final cured molded product will be significantly reduced.

Furthermore, when the amount of the oxalic acid component is less than the above range, the water resistance and wet mechanical strength of the molded product are significantly unsatisfactory compared to those within the range of the present invention.
When the total amount of oxalic acid components exceeds the above range, water resistance and mechanical strength similarly decrease significantly.

Furthermore, the most important thing to watch out for is a composition in which the amount of hydraulic cement used and the amount of polybasic acid component used are outside the scope of the present invention.

It is difficult to achieve a good balance between curing and imparting water resistance in one step, and in particular, it is impossible to produce a cured molded product with a dense and uniform internal structure.

In the present invention, reinforcing materials, fillers, etc. that are known per se can be blended.

Examples of reinforcing materials include inorganic fibers such as glass fiber, rock wool, slag wool, and asbestos, fibrous reinforcing materials made of organic fibers such as cellulose fiber, vinylon, polyester, polyamide, and polyolefin, or glass powder.

Powder reinforcing materials such as colloidal silica (white carbon) and carbon black can be used.

The fibrous reinforcement may be used in any form, such as fleece to stable, web to mat, nonwoven fabric, woven fabric, and the like.

As the filler, known fillers such as stone, sand, foamed shirasu, and foamed perlite are used.

These reinforcing materials and all fillers are not particularly limited, but include hydraulic cements mainly composed of water-reactive calcium sulfate and calcium silicate, and oxalic acid or its water-soluble salts (hereinafter, these mixtures are referred to as water-reactive cement). (sometimes referred to as a hard composition) i Q □ 500 parts by weight or less, especially 3
It is best to use it in a total amount of 0.00 parts by weight or less.

Powder, granular or short fiber reinforcing materials and fillers can be mixed with the above components to form a hydraulic composition (also reinforcing materials in the form of webs, mats, non-woven fabrics, woven fabrics, etc.) can be used. In some cases, these reinforcements are impregnated with hydraulic compositions.

Furthermore, in the present invention, per se known compounding agents 1 such as setting thickeners, accelerators, coloring agents, etc. can be added to these hydraulic compositions in per se well-known compounding ratios.

In the present invention, when producing a gypsum-cured molded article from this hydraulic composition, an amount of water (generally referred to as mixed water amount) sufficient to impart moldability and hardenability to the composition is required. to prepare a uniform dispersion.

These moisture meters differ depending on the molding method and the shape and structure of the cured molded product.

The total amount of the essential components in the hydraulic composition is in the range of 35 to 90 kg, especially 40 to 80 kg.

(Thus, in the present invention, water in the above-mentioned amount is added to the hydraulic composition to prepare a uniform dispersion, which is then molded and cured.

Molding is performed by means known per se to create wall materials, tiles, ceiling materials,
This is done by forming into flooring materials, other sheets, blocks, bricks, paving stones, sleds, and other molded products.

Of course, this uniform dispersion may be applied as an interior or exterior material for buildings, etc., as a covering material for walls, ceilings, floors or partitions, and then cured, without performing molding.

Molding and hardening of calcium sulfate by water confinement may be carried out simultaneously or in this order (generally at room temperature or 90°C).
Curing and waterproofing can be done in 1 minute to 2 days at 0°C.

The cured molded structure can be left in the atmosphere or heated to a temperature of 30 to 90° C. to further dry and ripen or ripen and complete the polymerization, if desired.

In addition, in the present invention, essential components in the hydraulic composition, namely,
The components of water-reactive calcium, calcium silicate, and oxalic acid or its water-soluble salts are:

If necessary, it is mixed homogeneously with auxiliary ingredients such as a filling cup in advance in the substantial absence of moisture, and supplied to users in the form of a one-pack composition that can be molded and hardened by adding moisture. Such a composition can also be supplied to consumers by filling it into a sealed container such as a moisture-proof sealed bag container, can, or tank made of moisture-proof paper, kraft paper, synthetic resin film, or the like.

In this case, the user can add the above-mentioned necessary water to the composition to form a uniform dispersion, and then perform the molding and curing operations (the necessary steps are significantly simplified).

The invention is illustrated by the following example.

Example Hydraulic cementola mainly composed of hydraulic gypsum and calcium silicate shown below was mixed in powder form in the proportions shown in Table 1, and this was mixed with an aqueous oxalic acid solution having the concentration and amount shown in Table 1. Mix evenly to make a paste 20mm x 20m
mX 8071!71! The material was poured into a prismatic mold and a curing reaction was performed.

The mold was cured and removed, and after being left overnight, it was dried in a hot air circulation dryer at 60° C. to prepare a prismatic directly cured and water-resistant gypsum cured molded product.

As the hydraulic gypsum used in this example, the hemihydrate gypsum shown below was selected.
α-hemihydrate] b) β-type hemihydrate gypsum (manufactured by Sannis Gypsum Co., Ltd., for ceramic shapes) (Tβ-hemihydrate) C) Dihydrate gypsum manufactured by Mizusawa Chemical Industry Co., Ltd. was heat treated at 190'C for 3 hours, β-type hemihydrate gypsum [Mβ hemihydrate] produced by leaving it to mature in the air for one week d) Phosphoric acid by-product gypsum at a slurry pH [directly 7.5~
β-type hemihydrate gypsum [Pβ
e) β-type hemihydrate gypsum [Sβ hemihydrate] produced by heat-treating industrial gypsum produced by flue gas desulfurization in the same manner as in C above [Sβ hemihydrate] Hydraulic mainly composed of calcium silicate used in this example As cement, commercially available Portland cement (manufactured by Nippon Cement Co., Ltd., designated as S) may be used alone, or calcium hydroxide (industrial slaked lime, manufactured by Tohoku Resources Development Co., Ltd., designated as C) or calcium silicate (natural Wollast
nite*W) was used as a powder mixture.

For each obtained gypsum cured molded product, the bending strength during drying and water absorption, and the weight loss rate in running water were measured by the following methods.

The obtained results are also shown in Table 1.

The bending strength was determined by using a 20 mm x 20 mvt x 80 mm prismatic gypsum molding as a test piece in a dry state and completely immersing it in pure water at a water temperature of 20 ± 5°C for 60 minutes according to the method described in JIS-A-6904. After soaking, the moisture on the surface has been absorbed and 20±5°C9
Measurements were made on samples left for 9 days under conditions of relative humidity Ill 00%.

In addition, the weight loss rate in running water was determined when the prismatic test piece was heated to 20°C.
After leaving it completely immersed in running water at +5°C and a flow rate of 2 to 3 rrL/min for 3 weeks, remove it from water and leave it overnight.
It was dried in a hot air circulation dryer at 60°C, and the weight change was determined.

In addition, in Table 1 shown below, as a comparative example (examples marked with sample number *) to clarify the present invention, hydraulic cement mainly composed of calcium silicate was prepared by adding only oxalic acid ( (sample no. 1), and when hydraulic cement was added but no oxalic acid was added (sample no. 6゜7, s, 12.13, 17.is); For cases where the amount of cement added was small (sample numbers 2.35, 38, and 40), cured gypsum molded products were prepared in the same manner as in the examples, and the bending strength test and weight loss in running water were similarly tested. , the results are also shown in Table 1.

Furthermore, in order to clarify the effect of imparting water resistance to the gypsum hardened moldings manufactured according to the present invention,
According to the method described in the publication, a water-resistant gypsum hardened molded product obtained by immersing a gypsum hardened product in oxalic acid and a gypsum hardened molded product filled with calcium hydroxide are treated by oxalic acid immersion treatment. A gypsum cured molded product produced according to the present invention was cut after molding to expose a fresh surface, and the weight loss rate in running water was measured, and the result was used as a comparative example with the present invention.

The results are shown in Table 2. The above-mentioned gypsum cured molded product was prepared by the following method.

That is, 100 g of α-type hemihydrate gypsum was dispersed in 30 g of water, mixed intimately, and poured into a prismatic mold of 20 mm x 20 mm x 80 vtw to perform a curing reaction.

After curing, the mold was removed and cured for 7 days at a temperature of 20°C and a humidity of 50%, and the cured product was immersed in an oxalic acid aqueous solution at a temperature of 20 ± 5°C and a concentration of 8g/100g for 1 hour, taken out, After leaving it for one night, it was dried in a hot air circulation dryer at 60°C.
Plaster hardened molded product by the method of Publication No. 117 (sample number 4
1) was prepared.

As another embodiment of this oxalic acid immersion treatment method, a hardened gypsum molded product prepared by the following method was selected.

That is, 80 g of the above α-type hand wash plaster and 20 g of calcium hydroxide (commercially available reagent) were taken, 60 g of water was added thereto, and the mixture was made into a homogeneous cross-wire paste.
Pour into a prismatic mold of 20 mm x 80 mm, harden, and remove from the mold at a temperature of 20°C.

After curing for 7 days at a humidity of 50 φ, it was immersed in an oxalic acid aqueous solution at a temperature of 20 ± 5 °C and a concentration of 8 g/100 g for 1 hour, taken out, left overnight, and dried in a hot air circulation dryer at 60 °C.
An oxalic acid treated product (sample number 42) of a hardened gypsum body filled with calcium hydroxide was prepared.

As a gypsum cured molded product of the present invention having a novel cut surface, sample number 4 was selected and cut to obtain a sample piece.

Furthermore, by subjecting the directly cured water-resistant gypsum cured molded product of the present invention (sample number 15) to a two-step immersion treatment with oxalic acid, the surface portion of the cured molded product was further made denser. A hardened gypsum molded product (sample number 43) that had been subjected to a hardening treatment was prepared, and the bending strength and weight loss rate in running water were measured for this gypsum molded product.

The results are shown in Table 3.

In addition, for this oxalic acid gypsum treatment method, a gypsum hardened molded product (dry product) obtained according to the same blending ratio and prescription as Sample A15 in Table 1 was selected as the gypsum hardened molded product.
This hardened gypsum body was heated to a temperature of 20±5℃ and a concentration of 8g/100g.
After soaking in an oxalic acid aqueous solution for 1 hour, leave it overnight, then soak for 6 hours.
Hardened gypsum body with improved molded surface after being dried in a 0°C hot air circulation dryer and immersed in oxalic acid (sample number 43)
was prepared.

Furthermore, in order to clarify the present invention, the pore volume distribution of the gypsum-cured molded product manufactured by the present invention and the gypsum-cured molded product serving as a comparative example thereof was measured by the following method.

The method for measuring pore volume distribution is to take a specified sample,
Pore volume of pore radius 75A to 75000A (rILt
/g) distribution was measured using a mercury intrusion porosimeter (Model AG65, manufactured by Carlo Erba, Italy).

The target gypsum hardened molded products were the above-mentioned sample number 4 (the present invention), a gypsum hardened product treated with only oxalic acid without the addition of hydraulic cement (sample number 1), and a hydraulic cement A hardened gypsum body with added but no oxalic acid (sample number 17), a hardened gypsum body treated by immersion in an oxalic acid solution (sample number 41), and a hardened gypsum body filled with calcium hydroxide. A gypsum hardened molded product obtained by soaking a gypsum hardened body in oxalic acid (sample number 42)
A total of 5 types of gypsum hardened molded products (4 types of comparative examples) were selected, and sample pieces were taken from the surface layer of the molded product, which is about 2 mm thick, and from the center of the molded product. Those 75A to 75000A with mercury intrusion porosimeter
The pore volume was determined in the range of .

The results are shown in Table 4.

As a result of the above, the gypsum-cured molded product directly cured and water-resistant treated by the method of the present invention is homogeneously cured and water-resistant, as is clear from the pore volume distribution. Even if the molded product has an exposed surface, the volume reduction rate in running water is virtually zero, and it also shows strong bending strength even after being immersed in water, making it homogeneous while taking advantage of the early hardening properties characteristic of plaster. It is well understood that the water resistance treatment is carried out in one step directly.

Claims (1)

[Claims] 1 Calcium sulfate with hydration reactivity 78.5 to 5
Hydraulic cement mainly composed of calcium silicate) 21 to 50% by weight and oxalic acid or its water-soluble salt 0
．． 5 to 5.0% by weight of each component, then add 35 to 90% by weight of water based on the total amount of each component to prepare a uniform dispersion, and then mold and harden. How the body is manufactured.