JP7848055B2 - Foaming agent for gypsum board manufacturing - Google Patents

Description

This invention relates to a foaming agent for manufacturing gypsum board and a method for manufacturing gypsum board using the same.

Gypsum board is manufactured with air bubbles to reduce weight and improve sound insulation and heat insulation. In this process, foam preformed with a foaming agent is mixed with gypsum slurry and sandwiched between base paper to produce gypsum board. Generally, alkyl sulfate esters and polyoxyalkylene alkyl ether sulfates are used as foaming agents to form this foam (see Patent Documents 1-3).

Japanese Patent Application Publication No. 6-239676 Japanese Patent Application Publication No. 7-291761 Special table 2018-527163 publication

However, while these foaming agents have high foaming power, the lack of stability in the formed bubbles makes them prone to forming coarse bubbles due to the aggregation of bubbles. Coarse bubbles formed in gypsum slurry can cause blistering in surface coating materials such as base paper for gypsum boards placed on the surface. In addition, during the manufacturing process of gypsum boards, mechanical shearing can lead to the refinement of bubbles and the formation of distorted bubbles, reducing the fluidity of the gypsum slurry and potentially causing a decrease in the strength of the gypsum board and deterioration of the appearance of the board's sides.
The present invention aims to provide a foaming agent for manufacturing gypsum board that can form voids derived from bubbles that are less fine and of nearly uniform size in the gypsum board.

The inventors investigated the foaming agents to be used and confirmed that the size and uniformity of voids originating from the foam contained in the gypsum board differed depending on the type of alkyl group of the alkyl sulfate used as the foaming agent when the gypsum slurry to which foam was added was cured to produce gypsum board.
Further investigations revealed that by using an alkyl sulfate having a branched alkyl group with a specific degree of branching and number of carbon atoms as a foaming agent, the resulting gypsum board voids become approximately spherical in shape and nearly uniform in size, thus completing the present invention.

In other words, the present invention relates to the following [1] to [6].
[1] A foaming agent for the manufacture of gypsum board containing an alkyl sulfate (A) represented by the following general formula (1).
R ¹ OSO ₃ M ¹ (1)
(In the formula, R ¹ represents a branched alkyl group having 9 to 11 carbon atoms, with a branching degree of 1.8 to 3.0 obtained by subtracting 1 from the number of methyl groups determined by ^1H -NMR measurement, and M ¹ represents an alkali metal, ammonium, or organic ammonium.)
[2] The foaming agent for manufacturing gypsum board according to [1], wherein R ¹ of the general formula (1) is a branched alkyl group derived from a branched aliphatic alcohol synthesized from a propylene and/or butylene oligomer by the oxo method.
[3] The foaming agent for manufacturing gypsum board according to [1] or [2], wherein ^R1 in the general formula (1) is an alkyl group derived from an alcohol containing 80% by mass or more of a branched aliphatic alcohol having 10 carbon atoms.
[4] A foaming agent for manufacturing gypsum board according to any one of [1] to [3], further comprising at least one selected from an alkyl ether sulfate (B) represented by the following general formula (2) and an alkyl sulfate (C) represented by the following general formula (3) (excluding the one represented by the above general formula (1)).
R ² O(CH ₂ CH ₂ O) _n SO ₃ M ² (2)
(In the formula, ^R2 represents an alkyl group having 8 to 18 carbon atoms, n is an integer from 1 to 10, and ^M2 represents an alkali metal, ammonium, or organic ammonium.)
R ³ OSO ₃ M ³ (3)
(In the formula, ^R3 represents an alkyl group having 8 to 18 carbon atoms, and ^M3 represents an alkali metal, ammonium, or organic ammonium.)
[5] The foaming agent for manufacturing gypsum board according to [4], wherein the alkyl sulfate (A) is contained in an amount of 30 to 90% by mass, with the total of (A), (B), and (C) being 100% by mass.
[6] A method for producing gypsum board, characterized by comprising the steps of: blowing air into a foaming agent or an aqueous solution thereof as described in any one of items [1] to [5] to generate foam; and mixing the foam into a kneading material containing calcined gypsum and water to obtain a foamed gypsum slurry.

By using the foaming agent of the present invention in the manufacture of gypsum board, the miniaturization of air bubbles due to mechanical shear during raw material mixing is reduced, and it is possible to form approximately spherical voids of nearly uniform size in the gypsum board.

SEM image of a cross-section of the gypsum hardened body in Example 9 SEM image of a cross-section of the hardened gypsum body in Comparative Example 3

The foaming agent for gypsum board manufacturing and the method for manufacturing gypsum board according to the present invention will be described in detail below.
<Alkyl sulfate (A)>
The foaming agent for manufacturing gypsum board of the present invention contains an alkyl sulfate (A) represented by the following general formula (1).
R ¹ OSO ₃ M ¹ (1)
(In the formula, R ¹ represents a branched alkyl group having 9 to 11 carbon atoms, with a branching degree of 1.8 to 3.0 obtained by subtracting 1 from the number of methyl groups determined by ^1H -NMR measurement, and M ¹ represents an alkali metal, ammonium, or organic ammonium.)

In the general formula (1) above, R ¹ represents ^a branched alkyl group having 9 to 11 carbon atoms (hereinafter also referred to as a "highly branched alkyl group") whose degree of branching is 1.8 to 3.0, obtained by subtracting 1 from the number of methyl groups determined by 1H-NMR measurement. Examples of such highly branched alkyl groups include those derived from branched aliphatic alcohols synthesized from propylene or butylene oligomers by the oxo method. Alcohols synthesized by the oxo method are mixtures of structural isomers having multiple methyl groups, but in this case the number of methyl groups is the average value of the mixture, and the number of methyl groups in the molecule can be measured by proton NMR.

Among polybranched alkyl groups, C10 polybranched alkyl groups derived from alcohols synthesized from propylene trimers by the oxo process are preferred due to their availability. However, due to the manufacturing process, C9 and C11 alkyl groups may be present. In this case, from the viewpoint of uniformity of bubble size, the content of C10 polybranched alkyl groups is preferably 70% by weight or more, more preferably 80% by weight or more, and most preferably 90% by weight or more.

In the general formula (1) above, M ¹ is an alkali metal, ammonium, or organic ammonium. Examples of alkali metals include lithium (Li), sodium (Na), potassium (K), etc. Organic ammonium is ammonium derived from an organic amine, and examples of organic amines include alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine, as well as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, and triethylamine.
Among these, alkali metals and ammonium are preferred from the viewpoint of foaming properties, sodium and ammonium are more preferred, and ammonium is particularly preferred.

Alkyl sulfate (A) can be obtained by sulfurizing the branched aliphatic alcohol with known sulfurizing agents such as chlorosulfonic acid, sulfuric anhydride, or sulfamic acid, and then neutralizing it with sodium hydroxide, potassium hydroxide, aqueous ammonia, or an alkanolamine.

<Alkyl ether sulfate (B)>
The foaming agent for manufacturing gypsum board of the present invention may contain an alkyl ether sulfate (B) represented by the following general formula (2) for purposes such as improving the stability of bubbles.
R ² O(CH ₂ CH ₂ O) _n SO ₃ M ² (2)
(In the formula, ^R2 represents an alkyl group having 8 to 18 carbon atoms, n is an integer from 1 to 10, and ^M2 represents an alkali metal, ammonium, or organic ammonium.)

In the above general formula (2), ^R2 represents an alkyl group having 8 to 18 carbon atoms. The alkyl group having 8 to 18 carbon atoms may be a linear or branched alkyl group, and may contain two or more alkyl groups with different numbers of carbon atoms. Among these, alkyl groups having 10 to 14 carbon atoms are preferred.

In the general formula (2) above, n is the number of moles of ethylene oxide added, and is an integer from 1 to 10, preferably an integer from 1 to 5. ^M2 represents an alkali metal, ammonium, or organic ammonium, specifically those exemplified as ^M1 . Among these, alkali metals and ammonium are preferred, sodium and ammonium are more preferred, and sodium is particularly preferred.

<Alkyl sulfate (C)>
The foaming agent for manufacturing gypsum board of the present invention may further contain an alkyl sulfate (C) represented by the following general formula (3) (excluding the one represented by the general formula (1)).
R ³ OSO ₃ M ³ (3)
(In the formula, ^R3 represents an alkyl group having 8 to 18 carbon atoms, and ^M3 represents an alkali metal, ammonium, or organic ammonium.)

In the above general formula (3), ^R3 represents an alkyl group having 8 to 18 carbon atoms. The alkyl group having 8 to 18 carbon atoms may be a linear or branched alkyl group, but the aforementioned polybranched alkyl group is not included. Among these, alkyl groups having 12 to 16 carbon atoms are preferred.

The content of alkyl sulfate (A) in the foaming agent of the present invention is not particularly limited, but from the viewpoint of improving the uniformity of foam size, the total of (A), (B), and (C) is preferably 30 to 100% by mass, more preferably 60 to 90% by mass.

The content of alkyl ether sulfate (B) in the total amount of the foaming agent of the present invention is preferably 5 to 30% by mass, more preferably 5 to 15% by mass, with the sum of (A), (B), and (C) being 100% by mass, from the viewpoint of improving foam stability. Furthermore, the content of alkyl sulfate (C) is preferably 5 to 40% by mass, more preferably 5 to 25% by mass, from the viewpoint of improving foaming power.

A preferred embodiment of the foaming agent for gypsum board manufacturing of the present invention includes a formulation in which the total of (A), (B), and (C) is 100% by mass, with 30 to 90% by mass of the alkyl sulfate (A), 5 to 30% by mass of the alkyl ether sulfate (B), and 5 to 40% by mass of the alkyl sulfate (C).

The foaming agent for gypsum board manufacturing of the present invention may further contain an alcohol with 1 to 4 carbon atoms for the purpose of preventing freezing in winter in cold regions and for preservation. Examples of alcohols with 1 to 4 carbon atoms include methanol, ethanol, propanol, and butanol.

The foaming agent for gypsum board manufacturing of the present invention can be applied to either the mixing method, in which the foaming agent is directly added to the gypsum slurry, or the pre-forming method, in which the foam is mixed into the gypsum slurry beforehand. The foaming method is not particularly limited. Generally, the pre-forming method is more common, in which air is blown into a 0.01 to 10% by weight aqueous solution of the foaming agent to generate foam, and this foam is then mixed into a gypsum slurry containing calcined gypsum and water to obtain a foamed gypsum slurry.

The foaming agent for gypsum board manufacturing of the present invention can be used in the manufacture of gypsum boards for purposes of weight reduction and heat insulation, but is particularly suitable for the manufacture of lightweight gypsum boards with high strength.

The present invention will be described in further detail below based on examples, but the present invention is not limited thereto. Unless otherwise specified, percentages (%) refer to mass percentages.

Table 1 shows the alkyl composition of R ¹ , the degree of branching, and M ¹ in the general formula (1) of the alkyl sulfate (A) used in this example.
The degree of branching of a branched alkyl group is the value obtained by subtracting 1 from the number of methyl groups determined by the following measurement method.
<Method for calculating the number of methyl groups>
The alcohol used as the raw material for alkyl sulfate (A) was dissolved in deuterated chloroform, and proton NMR measurements were performed using a 400 MHz NMR spectrometer. The obtained spectrum was integrated, and the number of methyl groups was determined by dividing the integral value of the spectrum originating from methyl groups by 3, with the spectrum at 3-4 ppm being set to 2.
(Proton NMR measurement conditions)
Equipment: JEOL Ltd. JNM-ECZ400S nuclear magnetic resonance spectrometer Observation frequency: 399.78 MHz
Pulse width: 2.895 μs
Pulse repetition time: 7.18628096 sec
Total number of times: 64
Measurement temperature: room temperature (20-35℃)
Reference: 7.24 ppm
Sample tube diameter: 5 mm

Furthermore, the alkyl composition and the distribution of the number of added moles of ethylene oxide (described later) were measured by analyzing the raw material alcohol using gas chromatography (Shimadzu GC-2010 Plus).

Table 2 shows the alkyl composition of ^R2 in general formula (2) and the distribution of the number of moles of ethylene oxide added to the alkyl ether sulfate (B) used in this example, as well as ^M2 .

Table 3 shows the alkyl composition of ^R3 , the degree of branching, and ^M3 in the general formula (3) of the alkyl sulfate (C) used in this example. Note that when ^R3 consists only of linear alkyl groups, the degree of branching was set to 0.

Foaming agent compositions were prepared by conventional methods using the components listed in Tables 1 to 3 in the mass ratios shown in Table 4. The foaming properties were evaluated using the following method. The results are shown in Table 4.

<Method for evaluating foaming power>
200 g of a 0.2% aqueous solution (20°C) of the foaming agent composition was added to a juicer mixer and stirred for 10 seconds. The resulting foam was transferred to a 1000 ml graduated cylinder, and the foaming power of each foaming agent was evaluated according to the following criteria.
(1) Amount of foam immediately after preparation ◎: 500 ml or more, ○: 300 ml or more but less than 500 ml, ×: less than 300 ml (2) Half-life of foam height ◎: 10 minutes or more, ○: 5 minutes or more but less than 10 minutes, ×: less than 5 minutes

[Preparation of foamed gypsum slurry]
A sealed container equipped with a nitrogen introduction line and a foaming agent aqueous solution supply line to a foaming machine was filled with 2000 g of a 0.2% aqueous solution of the foaming agent composition and pressurized with nitrogen. A foaming machine was prepared with a nitrogen pressure of 0.2 MPa and a flow rate of 50 L/min, and foam was produced by opening the outlet valve of the sealed container and supplying the foaming agent aqueous solution at a rate of 2 L/min.

A gypsum slurry was prepared by mixing 270 parts of a 0.33% by mass aqueous solution of naphthalene sulfonic acid formalin condensate as a water-reducing agent with 300 parts of calcined gypsum. 8.55 parts of the foam prepared in the pre-forming process were added to this slurry, and the mixture was stirred at 400 rpm for 30 seconds using a cross-blade agitator to prepare a foamed gypsum slurry. The fluidity was evaluated by measuring the flow value using the following method. The results are shown in Table 4.

<Method for measuring flow values>
A hollow cylindrical tube with an upper inner diameter of 75 mm, a lower inner diameter of 85 mm, and a height of 40 mm was placed in the center of a glass plate (30 cm x 30 cm), and the mixed foamed gypsum slurry was immediately poured into the hollow tube until it was full. The hollow tube was then pulled up perpendicular to the glass plate, and the spread of the foamed gypsum slurry was measured. The diameter at the maximum extent of the spread and the diameter perpendicular to it were measured, and the average value was taken as the flow value.

[Preparation of hardened gypsum pieces]
The prepared foamed gypsum slurry was poured into a mold and allowed to harden at room temperature. After hardening, it was removed from the mold and allowed to harden in a 40°C drying oven until a constant weight was achieved to produce hardened gypsum pieces (2 cm × 2 cm × 8 cm). The average diameter and coefficient of variation of voids originating from bubbles, and the content of micropores with a diameter of less than 200 μm were calculated using the following method. The results are shown in Table 4.

<Method for measuring void diameter>
The fabricated hardened gypsum pieces were cut, and the cut surfaces were observed using a desktop electron microscope TM-3030Plus (manufactured by Hitachi High-Technologies Corporation). The captured images were analyzed using the image analysis software Image-Pro Premier (manufactured by Nippon Roper Co., Ltd.), and the average diameter of the voids was calculated.
(SEM measurement conditions)
Observation mode: Secondary electrons, Standard. Acceleration voltage: 15kV (Normal mode).
Magnification: 30x Observation range: Observation of four fracture surfaces (2 x 2 cm) of a hardened plaster piece.

The uniformity of voids and the content of microbubbles were evaluated according to the following criteria.
(1) Uniformity of voids A coefficient of variation of 0.40 or less, calculated from the void diameter and its standard deviation, was judged as acceptable.
(2) Percentage of micropores with a diameter of less than 200 μm
◎: 0%, ○: 0.1% or more and less than 10.0%, ×: 10.0% or more

It can be confirmed that the voids originating from bubbles in the gypsum board produced using the foaming agent of the present invention have few micropores and are almost uniform in size. In contrast, it can be confirmed that the gypsum board produced using the foaming agent of the comparative example contains many micropores, and their size varies.

Claims (5)

A foaming agent for the manufacture of gypsum board containing an alkyl sulfate (A) represented by the following general formula (1).
R ¹ OSO ₃ M ¹ (1)
(In the formula, R ¹ represents a branched alkyl group having 9 to 11 carbon atoms, with a branching degree of 1.8 to 3.0 obtained by subtracting 1 from the number of methyl groups determined by ^1H -NMR measurement, and M ¹ represents an alkali metal, ammonium, or organic ammonium.) A method for producing a foaming agent for manufacturing gypsum board according to claim 1,
A method for producing a foaming agent for gypsum board manufacturing, wherein the alkyl sulfate (A) is produced by sulfurizing a branched aliphatic alcohol synthesized from a propylene and/or butylene oligomer by the oxo method, and then neutralizing it. The foaming agent for manufacturing gypsum board according to claim 1, further comprising at least one selected from an alkyl ether sulfate (B) represented by the following general formula (2) and an alkyl sulfate (C) represented by the following general formula (3) (excluding the one represented by the aforementioned general formula ( 1 )).
R ² O(CH ₂ CH ₂ O) _n SO ₃ M ² (2)
(In the formula, ^R2 represents an alkyl group having 8 to 18 carbon atoms, n is an integer from 1 to 10, and ^M2 represents an alkali metal, ammonium, or organic ammonium.)
R ³ OSO ₃ M ³ (3)
(In the formula, ^R3 represents an alkyl group having 8 to 18 carbon atoms, and ^M3 represents an alkali metal, ammonium, or organic ammonium.) The foaming agent for manufacturing gypsum board according to claim 3 , wherein the alkyl sulfate (A) is contained in an amount of 30 to 90% by mass, with the total of (A), (B), and (C) being 100% by mass. A method for producing gypsum board, comprising the steps of: blowing air into a foaming agent or an aqueous solution thereof as described in claim 1 to generate foam; and mixing the foam into a kneading material containing calcined gypsum and water to obtain a foamed gypsum slurry.