KR930009346B1 - Process for producing molded articles - Google Patents

Abstract

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Description

Manufacturing method of molding

The present invention relates to a process for producing moldings comprising hydraulic materials and used as materials in construction, civil engineering and shipbuilding, and moldings comprising hydraulic materials.

A method of adding polyvinyl alcohol (hereafter referred to as PVA) to improve the mechanical properties and formability of moldings including hydroponic materials such as cement, gypsum and granulated slugs. Is known. For example, Japanese Patent Laid-Open No. 45934/1974 describes a method of incorporating PVA into pulp cement to improve the bending and impact strength of the pulp cement sheet, and Japanese Patent Laid-Open No. 77655/1986 US Pat. No. 209950/1986 describes a method of using PVA to increase flexural strength, impact strength and dimensional stability and to prevent cracking of slag or gypsum plates.

In order to improve mechanical properties and surface appearance and to prevent cracking, Japanese Patent Laid-Open Publication Nos. 50017/1974 and 239377/1985 describe the use of PVA for cement moldings, and Japanese Patent Laid-Open Publications. No. 137719/1976 describes the use of PVA for lightweight concrete.

It is stable even in high pH systems, does not interfere with hydration reactions of hydraulic materials, is water soluble and can be dispersed into matrices such as cement, for example, to bind hydraulic material particles to each other or in rigid films in moldings. It is because it improves the characteristic of a hydraulic composition by forming it.

Japanese Patent Laid-Open Publication No. 13328/1972 describes that adding boron compounds to an aqueous slurry composition comprising cement and PVA powder can reduce the amount of PVA used.

Japanese Patent Laid-Open No. 184754/1984 discloses that replacing the PVA powder with silyl group-modified PVA in an aqueous slurry composition comprising cement and PVA powder can improve the strength of the molding.

Recently, moldings made from hydraulic materials of the same specification as above have been conventionally produced by large-scale autoclave-curing. The requirement for mass production of moldings from hydroponic materials is firstly that the product must have high mechanical strength and dimensional stability, not crack, and secondly, be productive. There is no indication of a method for producing a molding from a hydraulic material or a molding made from a hydraulic material that satisfies all of the above requirements.

Accordingly, it is an object of the present invention to provide a method for effectively producing moldings having high bending strength, deflection (flexibility) and dimensional stability by autoclaving-curing an aqueous composition comprising a hydraulic material.

It is still another object of the present invention to provide a molding comprising a hydroponic material and having high bending strength, high deflection (flexibility) and dimensional stability at bending.

As a result of the careful study, the inventors have found that an aqueous composition comprising (A) a hydraulic material and (B) a polyvinyl alcohol powder, wherein (B) the polyvinyl alcohol powder is based on the weight of the (A) hydraulic material. It is found that the above problems can be solved by a method of producing a molding comprising a hydraulic material, characterized by autoclave-curing at a temperature of 100 ° C. or more.

The invention also relates to (A) hydraulic material and (B) polyvinyl alcohol, wherein (B) polyvinyl alcohol has a structure comprising (B) PVA, which is once dissolved and dispersed in the form of islands to solidify. Alcohol comprises (A) in an amount of 0.1 to 20% by weight, based on the weight of the hydraulic material.

Any hydroponic material which solidifies upon reaction with water can be used in the process of the invention as (A) hydraulic material, examples of which include various types of Portland cement, gypsum, granulated slugs, rock fibers, Inorganic materials such as magnesium carbonate and calcium silicate.

(B) PVA powders used in the present invention include conventional PVA unmodified, silyl group-modified PVA, and various other modified PVAs. (B) PVA may have any degree of polymerization, preferably 500 or more, and more preferably 1,500 or more. Having a degree of polymerization of greater than about 500 (B) PVA provides moldings with very good properties (eg mechanical strength) when autoclave-cured at temperatures above 100 ° C., which can be seen from the high strength of the PVA film. As can be seen, (B) the PVA powder has a firming strength. (B) PVA may have any degree of hydrolysis, preferably at least 80 mol%, more preferably at least 90 mol%, most preferably at least 95 mol%. In the present invention, the hydrolysis degree of (B) PVA is preferably 98 mol% or more in the case of not using a substance that increases the viscosity of the (B) PVA aqueous solution. (B) PVA, having a degree of hydrolysis of at least 80 mol% and in powder form, is homogeneously dispersed into the aqueous composition, so that, when autoclaving-curing the aqueous composition, (B) the high bond strength of the PVA powder and (B) the PVA film High strength results in moldings with notable high flexural strengths.

(B) The PVA powder may have any average particle size, preferably with a 16-mesh passage size, more preferably with a 42-mesh passage size, the smaller the average particle size the better.

The aqueous composition used in the present invention comprises (A) hydraulic material and (B) PVA powder, wherein (B) PVA powder is 0.1 to 20% by weight, more preferably based on the weight of (A) hydraulic material. Preferably in an amount of 0.5 to 5% by weight. When the amount of (B) PVA incorporated is less than 0.1% by weight, (B) PVA does not provide the effect of reinforcing the molding. On the other hand, if the amount exceeds 20% by weight, the water resistance and fire resistance of the obtained molding will decrease.

In order to further improve the strength of the moldings, it is preferred to add (C) reinforcing fibers to the used aqueous composition. (C) The reinforcing fibers are added in an amount of 0.1 to 10% by weight, more preferably 0.5 to 5% by weight, based on the total weight of the solids. (C) When reinforcing fibers are added in an amount of at least 0.1% by weight, the obtained molded article is greatly reinforced and the connection effect of the green sheet is increased. However, in amounts exceeding 10% by weight, problems with dispersibility arise and often the reinforcing effect is impaired. Conventional reinforcements used for cement or the like can be used for the purposes of the present invention, but preferably (A) reinforcements are used that provide substantial results in the reinforcement of moldings comprising hydraulic materials. Examples of such preferred reinforcements include fibers of polyvinyl alcohol, acrylic, olefins, carbon and aramid, and pulp such as synthetic pulp, wood pulp and highly crushed wood pulp, all reinforcements being referred to herein as "fiber". Indicated. These fibers may be used alone or in combination.

In order to increase the effect of (B) PVA, it is also preferable to add (D) substance which increases the viscosity of (B) PVA aqueous solution.

In the present invention, (B) the substance which increases the viscosity of the PVA aqueous solution, when added in an amount of 5% by weight based on the weight of the dry (B) PVA, (B) the viscosity of the PVA aqueous solution When not added, it is made into 2 times, preferably 4 times, and more preferably, (B) the substance which makes a PVA aqueous solution into a gel. Particularly preferred among the above-mentioned materials (D) is crosslinking (B) PVA, which is water insoluble at temperatures below 100 ° C. and autoclave cures at temperatures above 100 ° C. to produce crosslinks that are soluble in water. It is a crosslinking agent of (B) PVA which increases the viscosity of (B) aqueous PVA solution obtained by.

(B) Examples of the substance (D) which increases the viscosity of the PVA aqueous solution include boric acid; Borax; Calcium borate; Magnesium borate; Aluminate; Zirconium salts; Trivalent chromium formed when the alkali metal chromate or dichromate is reduced; 4-valent titanium formed when oxidizing titanium trichloride; Vanadate; And copper ions. Dyes (eg Congo Red) and organic materials (eg gallic acid) can also be used. (B) Among the substances (D) which increase the viscosity of the PVA aqueous solution, boric acid or a derivative thereof is preferable, and calcium borate is particularly preferable. When (A) the hydraulic material used provides calcium ions, (B) when crosslinking PVA, it is water insoluble at temperatures below 100 ° C. and autoclave cured at temperatures above 100 ° C. It is most preferred to use one of the crosslinking agents of (B) PVA (e.g. boric acid, borax or calcium borate) that produces and increases the viscosity of the (B) aqueous PVA solution obtained by the autoclave curing. Therefore, in the present invention, (B) the substance which increases the viscosity of the PVA aqueous solution is at a temperature of 100 ° C. or more, while preventing (B) PVA powder from dissolving during the process before autoclave curing. When autoclave hardening, (B) PVA powder is melt | dissolved in water.

In the present invention, (B) PVA, when present in the aqueous composition, is used in the form of a powder which is hardly soluble in water. Thus, the notable reinforcing effect of (B) PVA is that almost all PVA (B) powders remain in the aqueous composition when the aqueous composition is prepared by the wet process, so that PVA (B) which is not dissolved even when the aqueous composition is used in the form of an aqueous slurry. It is believed that the powder does not increase the viscosity of the aqueous slurry but is autoclaved and cured at a temperature of 100 ° C. or higher (under wet heating) to dissolve and exert a reinforcing effect. In particular, when used in a mixed state of (D) material, in particular (B) which crosslinks (B) PVA, the reinforcing effect is further increased, presumably (B) PVA which dissolves during autoclave curing in the moldings. It seems to be because it does not move much and remains in the initial position to exert high bonding force.

(B) The effect of the addition of the material (D) which increases the viscosity of the PVA aqueous solution increases with increasing amount. The addition amount is added in an amount of 1% by weight or more, preferably 1 to 50% by weight, more preferably 5 to 20% by weight, based on the weight of (B) PVA.

The process for producing the molding of the present invention may be any one selected from processes such as a wet lamination process, a flow-on process, an extrusion process, a dry process, and the like.

The aqueous compositions used in the present invention are (A) any additives commonly added to conventional aqueous compositions comprising hydraulic materials such as inorganic fillers such as silica powder and fly ash, and sand, ballast ) And other fillers such as lightweight fillers. The aqueous composition may comprise a bubble.

The aqueous composition used in the present invention may have any solid concentration, depending on the process used, for example, it is suitable to use at a solid concentration of 2 to 90% by weight.

The manufacturing process of the present invention is characterized by autoclaving and curing the above-mentioned aqueous composition at a temperature of 100 ° C. or higher. The temperature should be at least 100 ° C, preferably 120 to 180 ° C, more preferably 140 to 170 ° C. There is no particular limitation on the autoclave curing process time, but preferably 1 to 30 hours, more preferably 8 to 20 hours are suitable. If the autoclave curing process time is 1 hour or less, the hydroponic reaction will be completed in an incomplete state, and if the time exceeds 24 hours, the quality of (B) PVA will deteriorate.

The moldings obtained by the process of the invention are particularly excellent in mechanical strength and dimensional stability.

There is no particular restriction on the conditions of its execution if pre-curing (hereinafter, referred to as "primary curing") before autoclave-curing. Thus, autoclave curing can be done directly without performing the primary cure, or the primary cure is performed at a temperature below 100 ° C. Primary curing is preferably carried out at a temperature of 10 to 100 ℃, more preferably 70 to 100 ℃. There is no particular limitation on the vapor pressure in the gas phase when performing primary curing, but high vapor pressure is preferred, with saturated vapor pressure being most preferred. In order to control the vapor pressure in the gas phase, processes such as vaporization are used. The primary curing can be carried out for any time, preferably until the composition has cured to such an extent that the mold used can be easily removed. The primary curing is for example carried out for 1 day to about 1 week at room temperature or for 5 to 48 hours at temperatures below 100 ° C. when cured with heating.

Surprisingly, after primary curing at a specific temperature selected among the above conditions (ie, a temperature of 70 to 100 ° C.), it is preferably mixed with material (D) which increases the viscosity of (B) aqueous PVA solution, 100 When autoclave curing under wet heating conditions of < RTI ID = 0.0 > C < / RTI > or above, where (B) PVA powder is likely to be dissolved, a molded article having a notable high strength can be obtained.

The process for producing the moldings of the invention can be easily obtained by autoclave curing of moldings comprising hydroponic materials and having very good mechanical properties and dimensional stability. Thus, the process of the present invention can be said to have a very good industrial value.

Now, the moldings of the present invention will be described in detail.

(A) hydraulic material and (B) PVA are as above-mentioned as an aqueous composition used by the method of this invention. The moldings of the present invention preferably comprise (D) materials which increase the viscosity of (C) reinforcing fibers and / or (B) aqueous PVA solutions as described above, which can provide high strength to the moldings. (C) The reinforcing fibers are preferably included in an amount of 0.1 to 10% by weight based on the total weight of the solids. The material (D) comprises preferably in an amount of at least 1% by weight, more preferably 1 to 50% by weight and most preferably 5 to 20% by weight based on the weight of (B) PVA.

The moldings of the present invention are characterized by a structure comprising (B) PVA, once dissolved and dispersed in the form of islands in the molding, where (B) PVA islands are distributed as homogeneously as possible. It is preferable. (B) The shape of the PVA island can be any shape, for example, spherical, modified spherical, spherical or modified spherical including a cavity site therein, and (B) the concentration of PVA is largest in the center There is a form, such as a spherical or deformed sphere, that decreases with distance. The size of the islands can be any size, with an average maximum diameter of preferably 0.05 to 3 mm, more preferably 0.1 to 1 mm. Molded parts that do not have a structure comprising (B) PVA dispersed therein in the form of discrete islands, such as (B) PVA extending continuously, (B) PVA remaining as an undissolved solid or insufficiently dissolved Insufficient strength can only be obtained in moldings having a structure containing (B) PVA.

In the present invention, when the hydraulic material (A) includes cement, the molded article includes a tobermorite gel which can be measured by a scanning electron microscope. Moldings comprising tobermorite gels are excellent in strength and dimensional stability.

The moldings of the present invention can be produced by any process, for example the method described in the method for producing moldings of the present invention.

The moldings of the present invention are commonly used as materials such as roofing, outer and inner wall boards, road construction and embankment protection blocks and the like.

Other features of the present invention will become apparent from the following examples which are provided to further illustrate the invention but are not intended to limit the invention.

In the following examples and control examples, unless otherwise indicated, "%" and "parts" mean "% by weight" and "parts by weight", respectively.

EXAMPLE

[Examples 1 to 14 and Control Examples 1 to 10]

(1) Manufacturing method of sample (wet process)

As a hydraulic material, a conventional Portland cement, a PVA powder having a degree of polymerization of 1,700 and a 60-mesh passthrough size of 98 mol%, and other additives shown in Table 1 are used. An aqueous composition is prepared using the above ingredients in the mixing ratios shown in Table 1 (Examples 1-14) and Table 2 (Control Examples 1-10). The aqueous composition is made into an aqueous slurry with a solid concentration of 40%, then poured into a mold and pressed to a solid concentration of 70 to 80% (dry) to form a plate having a thickness of 0.8 cm. The thickness is within the range generally used for conventional cement plates obtained by conventional long-net, one-layer wet processes.

The plates thus obtained are cured under the conditions shown in Table 1 (Examples 1 to 14) and Table 2 (Control Examples 1 to 10).

(2) How to measure

[Bulk specific gravity]

According to JIS A 5413, the sample fraction is dried at 105 ± 5 ° C. for 24 hours in a hot air drying oven, and then the weight and volume are measured to calculate the bulk specific gravity.

[Bending strength and deflection during bending]

Using a span length of 5 cm, the flexural strength is measured according to JIS A 1408 "Method of Bending Test for Boards of Buildings" with the maximum deflection at the center as the deflection upon bending. The deflection at larger flexures indicates the high flexibility of the test specimens and thus the usefulness as a molded article.

Length Change Rate (Dimensional Stability)

JIS A 5416 is applied. The unit length of each specimen dried at 60 ° C. for 1 day is selected as the base length. The specimen is then immersed in water for 1 day to absorb the water and measure the length to obtain the rate of change of length.

(3) results

The measurement results are shown in Table 1 (Examples 1 to 14) and Table 2 (Control Examples 1 to 10).

(4) microscopic measurement

Observation of the cross sections of the moldings obtained in Examples 1 to 14 by scanning electron microscopy shows PVA solidified once dissolved in a homogeneously dispersed molding in the form of discrete islands with the shape of modified spheres.

The moldings were also found to contain tobermorite gels.

The dispersion state of PVA in each molding can be confirmed by observing with a stereomicroscope after coloring the PVA with iodine.

Observation of the cross section of the moldings obtained in Comparative Examples 1 to 4 with a scanning electron microscope showed that the PVA was dispersed in the form of islands but only incompletely dissolved.

[Control Examples 11-14]

(1) Production method of sample (wet process)

Examples 1, 2, 4 and 5 were repeated except that the aqueous composition was prepared using PVA aqueous solution instead of PVA powder. The use of aqueous PVA solution increases the viscosity of the water composition, which results in some problems such as reduced filterability during the process.

(2) measuring method

It is the same as the method of Examples 1-14.

(3) results

The measurement results are shown in Table 2.

(4) microscopic measurement

Observation of the cross section of the moldings obtained in Comparative Examples 11 to 14 with a scanning electron microscope revealed that the PVA was not dispersed in the form of islands in the molding.

TABLE 1

1) The gas phase is controlled at saturated vapor pressure by vaporization.

TABLE 2

1) The gas phase is controlled at saturated vapor pressure by vaporization.

2) No dispersed island structure is found.

[Examples 15 to 16 and Control Examples 15 to 20]

(1) Sample preparation method (dry process)

Aqueous compositions are prepared with the same PVA powder, boric acid, conventional Portland cement and Toyoura standard sand as used in Examples 1-14, with a water / cement ratio of 40% in the composition shown in Table 3. The aqueous compositions thus prepared were poured into molds each having a size of 25 cm x 25 cm x 0.8 cm and cured under the conditions shown in Table 3 to obtain a plate.

(2) measuring method

It is the same as the method of Examples 1-14.

(3) results

The measurement results are shown in Table 3.

(4) microscope measurement

Observation of the cross sections of the moldings obtained in Examples 15 and 16 by scanning electron microscopy shows the PVA once dissolved in the homogeneously dispersed moldings in the form of discrete islands with the shape of modified spheres.

This molding was also found to contain a tobermoride gel.

The dispersion state of PVA in each molding can be confirmed even if observed with a stereoscopic microscope after coloring PVA with iodine.

Scanning electron microscopy of the cross sections of the moldings obtained in Control Examples 15, 17, 19 and 20 showed that the PVA was dispersed in the form of islands but only incompletely dissolved.

Controlled Examples 21 and 22

(1) Sample preparation method (dry process)

An aqueous composition is prepared according to the same process as in Examples 15 and 16, except that an aqueous PVA solution is used instead of the PVA powder.

(2) measuring method

Same as the method of Examples 15 and 16.

(3) results

The measurement results are shown in Table 3.

(4) microscopic measurement

Scanning electron microscopy of the cross sections of the moldings obtained in Comparative Examples 21 and 22 revealed that the PVA was not dispersed in the form of islands in the molding.

TABLE 3

1) The gas phase is controlled at saturated vapor pressure by vaporization.

2) No dispersed island structure is found.

Claims (12)

Aqueous comprising (A) a hydraulic material and a powder of (B) polyvinyl alcohol having a degree of hydrolysis of at least 90 mol% in an amount of 0.1 to 20% by weight based on the weight of the (A) hydraulic material. A method for producing a molding comprising autoclaving curing the composition at 100 ° C. or higher. The method of claim 1 wherein the composition further comprises (C) reinforcing fibers. The amount of at least 1% by weight of the aqueous composition according to claim 1, wherein the aqueous composition increases the viscosity of the aqueous solution of polyvinyl alcohol (B) based on the weight of the powder of polyvinyl alcohol (B). Method for producing a molding further comprising a. The method of claim 1 wherein the aqueous composition is cured at a temperature below 100 ° C. and then the cured aqueous composition is autoclaved at a temperature of 100 ° C. or higher. The method of claim 3 wherein the aqueous composition is cured at a temperature below 100 ° C., and then the cured aqueous composition is autoclaved. The method for producing a molded product according to claim 1, wherein the (A) hydraulic material is a simmet. The material according to claim 4 or 5, wherein the material (D) which increases the viscosity of the aqueous solution of (B) polyvinyl alcohol, is water-insoluble at less than 100 ° C. and at least 100 ° C. or less with the (B) polyvinyl alcohol. And (B) a crosslinking agent of polyvinyl alcohol which is dissolved in water by autoclave curing in order to increase the viscosity of the aqueous solution of (B) polyvinyl alcohol produced by this autoclave curing. 8. The method according to claim 7, wherein the material (D) for increasing the viscosity of the aqueous polyvinyl alcohol solution (B) is boric acid or a derivative thereof. 0.1. Based on the weight of (A) hydraulic material and (A) hydraulic material. (B) polyvinyl alcohol having a hydrolysis degree of 90 mol% or more in an amount of 20 to 20% by weight, wherein (B) the polyvinyl alcohol is once dissolved and dispersed in a form of islands to be solidified. Moldings having a structure. 10. The molding according to claim 9, further comprising (C) reinforcing fibers. 10. The molding according to claim 9, further comprising (B) an amount of at least 1% by weight based on the weight of the (B) polyvinyl alcohol of the material (D) which increases the viscosity of the aqueous polyvinyl alcohol solution. 10. The molding according to claim 9 comprising a tobermorite gel.