WO1988005096A1

WO1988005096A1 - Low density mineral wool panel and method

Info

Publication number: WO1988005096A1
Application number: PCT/US1988/000157
Authority: WO
Inventors: David Graham Izard
Original assignee: Usg Interiors, Inc.
Priority date: 1987-01-12
Filing date: 1988-01-12
Publication date: 1988-07-14
Also published as: KR890700715A; ZA8864B; EP0296242A4; AU1243588A; EP0296242A1; AU611668B2; JPH01501859A; NZ223122A; BR8804822A

Abstract

A method for the manufacture of very low density mineral wool structural panels on a moving foraminous support wire (40). A dilute aqueous furnish of mineral wool, lightweight aggregate, cooked wheat starch, cationic guar gum and non-ionic surfactant is formed, mixed to form a small amount of delicate non-resilient bubbles and ionically couple the mineral surfaces to the starch and gum, and deposited upon the wire (40) to form an open, porous entangled mass which is rapidly stripped of water and dried in a flow-through configuration (49).

Description

LOW DENSITY MINERAL WOOL PANEL AND METHOD

Background of the Invention

Field of the Invention

This invention relates to mineral wool fibrous products.

More particularly, it relates to a method for manufacturing strong, structural panels of mineral fiber that are very lightweight, about 3-10 pounds per cubic foot (50-160 kg/m³) density, and which may be used as acoustical ceiling tiles, thermal insulating panels, sound absorbing panels, pipe and beam insulation and the like products.

Description of the Prior Art

The water felting of dilute aqueous dispersions of mineral wool and lightweight aggregate is known. A dilute dispersion is flowed onto a moving foraminous support wire screen for dewatering to a mat first by gravity and then by vacuum suction means. The wet mat, still containing about 60-80% water, is dried over a number of hours in heated convection drying ovens; and the product is cut and optionally top coated, such as with paint, to produce lightweight structural panels such as acoustical ceiling products.

It is also known to form stable foams with mineral wool. U.S. Patent 4,447,560 suggests a low density sheet by forming a first slurry of fiber that contains synthetic rubber latex solids. A detergent slurry is then formed, and the two slurries admixed to about 15% solids consistency, agitated to a stable foam, and oven dried. The extremely time consuming and energy intensive drying of the stable foam from 15% solids is a severe economic detriment.

It has also been suggested that lightweight foams of attenuated glass fibers might be formed into extremely lightweight pipe wrap of about 1-3 pounds per cubic foot (16-50 kg/m³) density in U.S. Patent 3,228,825. Such foams are not "structural" in the sense of not capable of supporting their own weight without visible sagging, bending or collapsing when supported only at the edges of the panel, as in a suspended ceiling grid. According to this patent, microscopic bubbles are generated and uniformly incorporated with lightweight aggregate and attenuated glass fiber mixtures through a "binder fiber" glue of extremely fine sized and very highly refined cellulosic fibrilles.

Furthermore, it is known to flocculate inorganic clay in dilute dispersions of mineral fiber with starch grains by adding extremely small amounts of a flocculant such as polyacrylamide. As disclosed in U.S. Patent 3,510,394, the flocculant must be added just before the slurry is dewatered in order that clumps or flocs form among the fibers undergoing gravity drainage to a felted wet mat to prevent significant dispersal and loss of starch and clay with the drainage water.

Further, U.S. Patent 4,062,721 discloses avoiding foam in the forming box so that there is no or minimal foaming when the mat is laid onto the forming wire and during initial gravity drainage, but a foam develops thereafter.

An object of the present invention is to provide low density yet strong mineral panels such that panels having densities between about 3-10 pounds per cubic foot (50-160 kg/m³) will have a modulus of rupture of at least about 60 pounds per square inch.

Summary of the Invention

The present invention teaches the addition of a delicately foaming binder and a slightly ionic coupling cationic guar gum along with an essentially non-foaming nonionic surfactant dispersing agent into the mixer and thereafter depositing upon the forming wire such an open porous entangled fibrous mass as to allow through-air stripping of water and drying to result in a very stong, low density mineral wool panel. According to the process, drainage time is reduced rather than increased as suggested by the prior art; and the manufacture of very low density products capable of supporting their own weight without visible sagging, bending or collapsing when supported only at the edges of the panels, as in a suspended ceiling grid, are furthermore attained.

When a nonionic polyethanoxy surfactant, such as a polyethanoxy ether of ethyl alcohol, is added to a furnish containing a wheat starch binder having some residual protein fraction, such as about 6% protein residual content, and a small amount of a cationic guar gum or guar bean meal derivative, such as a trimethylammoniopropyl guar chloride polymer, there is a combined effect of some slight initial foaming of the formulation along with an effective ionic coupling action of the ingredients to each other and a wetted dispersal of the mineral wool so as to form a very open, porous entangled mass of mineral wool and lightweight aggregate capable of rapid drainage and rapid drying by passing large volumes of heated dry air at a rapid rate through the wet mat. Brief Description of the Drawings

The Figure is a schematic diagram of a mineral board manufacturing process in accordance with the present invention. Description of the Preferred Embodiments

A mixing tank 10 containing a motor driven impeller 12 mixes an aqueous slurry 14 containing from about 3% to about 6% solids. The composition of the solids in slurry 14 should be between the following limits: Ingredients Amounts

Mineral Wool about 25-95%

Lightweight Aggregate up to about 40%

Wheat Starch about 10-30%

Cationic Guar Derivative about 0.03-1%

Nonionic Surfactant about 0.5-3%

Clay up to about 5%

The binder, preferably a commercial wheat starch containing about 6% protein fraction (such as GENVIS 600 starch from Ogilvie Mills, Icc.) is dispersed in a portion of the process water in mixing tank 16 with high shear cyclone mixer 18 and then heated to a temperature between about 135° and 190°F (57°-88°C) to cook the starch. There is no substantial increased viscosity apparent with this starch during the cooking cycle and, after cooling, the starch binder is fed to mixing tank 10. It is important that no substantial viscosity increase of the slurry is provided by the binder as such is detrimental to maintaining a rapid rate of dewatering and drying the wet mat.

In order to achieve better dispersion of the mineral wool and aggregate in the dilute slurry and to aid in open porous mat formation, a nonionic polyethanoxy surfactant was added to the slurry in mixing tank 10. It is preferred to use an about 2% solution form, such as IGEPAL polyethoxylate from GAF Chemicals Corporation. The early addition of the cationic guar gum derivative flocculants in order to establish thorough dispersion of the mineral wool and lightweight aggregate with ionic coupling of the wheat starch binder protein via the cationic guar onto the mineral surfaces and further along with a low foaming prior to the slurry passing through the flow box 30 and being deposited upon the forming wire 40.

The mineral fiber for use in the present invention may be any of the conventional fibers prepared by attenuating a molten stream of basalt, slag, granite or other vitreous mineral constituent drawn linearly through orifices, referred to commonly as textile fibers, or tangentially off the face of a spinning cup or rotor, referred to as wool fibers. Included also are ceramic fibers and the like and aromatic polyamid fibers and the like. Porous bonded mats or batts of fibers may be used as well as individual fibers to form structures of the invention.

The lightweight aggregate preferably is an inorganic lightweight aggregate of exfoliated or expanded volcanic glass origin. Such aggregate includes the well known expanded perlite, exfoliated vermiculite, exfoliated clays and the like products which are available in a variety of mesh sizes. Generally expanded perlite is preferred for reasons of avai labi lity and economy .

The homogeneously mixed, and ionically coupled and slightly foamed slurry is deposited on the wire 40 as a very open, porous entangled mass of mineral wool and lightweight aggregate with a small amount of uniformly sized transient bubbles of air. The air occupies about 10-30% by volume of the wet entangled mass at this time, the remainder of the interstices between the lightweight aggregate and preferred nonionic polyethanoxy surfactant is a low foaming water soluble surfactant of dinonylphenoxy poly(ethyleneoxy) ethanol having a molecular weight of about 995. Similar polyethanoxy ethers of ethyl alcohol are commercially available and may be used.

The cationic bean meal derivative, such as a commercially available powdered polymer of trimethylammoniopropyl guar (GENDRIV from Henkel Corporation) like guar 2-hydroxy-3 (trimethyl-amino)-propyl ether chloride is added to the main mixing tank 10, where it readily disperses in the mix water to form a solution of appropriate concentration exhibiting flocculating and solids retention capability with the mineral wool and lightweight aggregate, such as expanded perlite, ingredients that are also added directly to mixing tank 10. The guar derivative tends to flocculate the mineral wool and the effect is enhanced with the addition of small amounts of clay.

The cationic guar derivative was added to mixing tank 10 last after thorough homogeneous mixing of all the other ingredients, with mixing continued for a few seconds before transferring the slurry from mix tank 10 by pump 20 to flow box 30. The function of the flow box 30 is to spread a uniform layer of slurry 32 across the width of a mixing wire belt 40, commonly called the wire, to form an open, porous wet mat 62. The open, porous mat 62 is preferrably of a thickness to yield a finished product having a thickness between about 1/4 and 2 inches.

It is important in the process of the present invention that the nonionic polyethanoxy surfactant be a low foaming surfactant and that it be added early in the mixing, as in mixing tank 10, along with the early addition of the cationic quar gum derivative flocculant in order to establish thorough dispersion of the mineral wool and lightweight aggregate with ionic coupling of the wheat starch binder protein via the cationic quar onto the mineral surfaces and further along with a low foaming prior to the slurry passing through the flow box 30 and being deposited upon the forming wire 40.

The lightweight aggregate preferably is an inorganic lightweight aggregate of exfoliated or expanded volcanic glass origin. Such aggregate includes the well known expanded perlite, exfoliated vermiculite, exfoliated clays and the like products which are available in a variety of mesh sizes. Generally expanded perlite is preferred for reasons of availability and economy.

The homogeneously mixed, and ionically coupled and slightly foamed slurry is deposited on the wire 40 as a very open, porous entangled mass of mineral wool and lightweight aggregate with a small amount of uniformly sized transient bubbles of air. The air occupies about 10-30% by volume of the wet entangled mass at this time, the remainder of the interstices between the lightweight aggregate and mineral fiber comprising water, and the aqueous slurry at this point containing still about 3-6 weight % solids. The open lightly foamed wet mass is deposited from forming box 30 onto a bottom scrim cover sheet 43 above the wire 40 as the slurry and scrim 43 float through a first flooded section 42 on the moving wire 40.

Discharge of water from the open wet slightly foamed mass occurs in high vacuum drainage section 44, as a top cover sheet 47 is optionally laid over the open wet porous foam mass via roller 36. In high vacuum section 44 a couple of very brief bursts of a pressure differential equivalent to about 3-20 (.8-.5m) inches of mercury busts the bubble walls of the slight foam that had been formed and strips water from the wet mass. It was observed in this section of the process that in a matter of 1-3 seconds the foam has collapsed and the draining liquid coats the contact points on the highly voided, open, entangled mass of the fiber and aggregate scrim cover sheet (s). Continued water stripping and drying are enabled by a continued vacuum in sections 46 and 48, along with passing high volumes of high velocity dry heated air through the mat without total collapse of the highly voided, open structural configuration. Therby structural mineral panels having a density of about 3-10 pounds per cub foot (50-160 kg/m³), and preferably about 3-6 pounds per cubic foot (50-100 k/m³) with a modulus of rupture of about 60-120 pounds per square inch (42,000-84,000 kg/m³) measured with the nonwoven fiber glass scrim cover sheets in place on the panel are obtained in a matter of about 10 minutes or less total time from depositing the open, slightly foamed slurry containing about 3-6 weight % solids above wire 40 from form box 30 through final through-air water stripping and drying section 49. At the time the panel passes through section 48 the moisture content is less than about 3% moisture. Of course, a fully dried panel may be obtained by augmenting through-air drying with supplemental conventional convection drying (not shown in the drawing) in a matter of a couple additional minutes drying time.

In the foregoing, the mat was formed upon and became an integral part of the final panel product with 1 or 2 fiber glass nonwoven scrim cover sheets. Such sheets may be of paper, woven glass fiber, non-woven glass fiber and the like open, porous sheet materials. A particularly preferred cover sheet is a non-woven fiber scrim, such as battery type scrim, having a weight of about 0.4-2.5 pounds per hundred square feet of scrim. It is envisioned in alternative embodiments that the top scrim 47 may be left off and, after the water stripping and drying section 49, a viscous, screedable pulp such as that set forth in U.S. Patents 1,769,519; 1,996,033; or 3,246,063 may be applied as an overlay and the wet pulp surface textured by suitable means to provide a pleasing appearance, and the composite panel-overlay dried in a conventional convection drying oven (not shown in the drawing). Alternatively, both top and bottom scrims may be in place before application of such a pulp overlay. In addition, conventional finishing operations such as the application of various prime, texture, or protective coatings of a paint or texture and the like may be applied to the panels produced in accordance with the present invention.

The following specific examples will further illustrate various specific embodiments of the present invention. Unless specified to the contrary, all amounts are expressed as parts by weight on a total dry solids weight basis. Of course, it is to be understood that these examples are by way of illustration only and are not be construed as limitations on the present invention.

EXAMPLE 1

Having reference to the FIGURE, a cationic guar bean meal derivative (guar 2-hydroxy-3 (trimethylammonio)-propyl ether chloride, GENDRIVE 158 from Henkel Corporation) was dispersed in water by mixer 16 to form a solution. Mineral wool, expanded perlite aggregate, dinonylphenoxypoly (ethyleneoxy) ethanol (IGEPAL-DM710 from GAF Chemicals Corporation) nonionic polyethanoxy surfactant, and CTS ball clay were added to main mixer 10 and mixed for 4 minutes. The cationic guar derivative solution was added to main mixer 10 for flocculation and mixed for 5 seconds before passing the dilute dispersion to forming box 30. On a solids basis, the final proportioning in main mixer 10 was 44.45% mineral wool, 29.15% expanded perlite, 22.95% wheat starch having 6% residual protein fraction (GENVIS 600 from Ogilvie Mills Inc. cooked at 190°F (88°C) in mixer 16), 1.68% CTS-2 clay and 1.68% nonionic polyethanoxy surfactant in about 3% solids dispersion. The ordinarily first gravity drainage box section of the wire 40 was flooded with water to the level of the scrim and the dilute furnish passed from the main mixer to the flow box 30 and deposited onto the scrim (battery grade 2.4 pounds per hundred square feet (.12 kg/m²) of nonwoven fiber glass scrim). It was observed that a very homogeneous open, entangled mass of mineral wool and lightweight aggregate having a small number of small delicate nonresilient foam bubbles interspersed therein was desposited in the flooded section 46. The application of a few short (1 second) bursts of vacuum pressure differential equivalent to about 15 inches (.4 m) of mercury in high vacuum section 44 immediately collapsed the small amount of foam and rapidly stripped voluminous amounts of water from the interstices of the wet mass comprising bottom cover sheet 43, top sheet 47 and core 41 of open porous entanglement of fiber, lightweight aggregate and clay that was still about 75% by weight moisture. Because of the open, porous nature, that water was readily stripped from the wet panel and the panel dried by rapidly passing large volumes of heated dry air through the panel first in the hooded low vacuum section 46 (providing vacuum pressure differential equivalent to about 5 inches

(0.1m) of mercury) and secondly in the through-air-flow drier zone 48-49 (provided with a pressure differential equivalent to about 14 inches (0.4m) of water across the surface of the mass) and having a positive air flow rate-volume-velocity of about 300 (8.5 m³) (generally, from about 50 (1.4 m³) to about 350 (10 m³) ) cubic feet per minute of air per one square foot (.09 m³) of wet mat surface. Generally, the heated dry air may be provided at a temperature of about

37°-205°C, preferably about 175°C. The time for passage from the flow box 30 through the through-air drying section 48 varied considerably, depending upon core thickness of about 1/8th inch (.003m) through 2 inches (.05m) thickness, generally from about 2 to 10 minutes. Several runs were made which produced material having uniform thickness, density, and strength properties. During this time, the average core thickness range was 0.445-0-0.490 inches at 6.3-7.0 pounds per cubic foot density range. The addition of a paint coat added another 2.5 pounds per cubic foot to the core density. The average modulus of rupture (tested with the face panel down) was 120 pounds per square inch and acoustical properties testing exhibited an average noise reduction coefficient of 0.75.

EXAMPLE 2 In a series of short static board forming runs, various of the components were evaluated for effect in panel formation by "halving" and then doubling the presently preferred amount of the particular component as used in Example 1. As part of these evaluations, the weight of the produced panel after the through-air-drying procedure (T-A-D weight) was measured; and then the samples were placed in a convection oven and dried overnight to a constant weight (Oven weight) for comparison and the difference in weight from through-air drying to bone dry weight was determined. Representative results are set forth in the Table.

From the results set forth in the Table, it may be seen that doubling the amount of lightweight aggregate greatly increased the moisture content of the through-air dried panel. This sample exhibited considerable viscosity increase in preparation. Doubling the amount of the wheat starch having a residual protein fraction dramatically increased moisture also. This sample exhibited considerable viscosity increase in preparation. It was stated above that the wheat starch with a minor protein residual fraction did not increase viscosity of starch binder upon cooking the starch; and it is evident that the preferred levels of this binder helps maintain a low viscosity furnish and greatly aids stripping water from and. drying the wet panel by passage of air through the open, porous entangled structural mass.

Doubling the amount of the low foaming dispersant-surfactant nonionic polyethanoxylate did not significantly change the nature of the rather delicate, non-resilient bubbles; did not significantly inhibit bursting of the bubbles and stripping of water by through-air passage; and did not result in significant separation of fiber and aggregate during water stripping. A number of previous attempts encountered considerable layering of the ingredients due to perlite segregating and floating and starch and wool fiber segregating and sinking, and the layering destroying the rapid through-air drainage. It thus appears essential to provide the combination of a starch having residual protein fraction to provide a binder which does not increase in viscosity and thereby hold water which would defeat through-air water stripping; with a slightly foaming nonionic polyethoxylate dispersant-surfactant to disperse the wool and aggregate coupled with the cationic guar gum derivative to keep the wool and aggregate dispersed yet in entangled engagement, thereby avoiding segregation and layering during through-air drainage.

From the foregoing, it is apparent that the present invention provides a method for manufacturing structural mineral panel products of widely varying densities, properties and uses. Various panel thicknesses from about l/8th inch through 2 inches (.003-.05m) or more may be formed. Very lightweight products having densities ranging from about 3 through about 10 pounds per cubic foot (50-160 kg/m³) or more may be formed from a dilute mineral fiber furnish. Additional ingredients and other adjuvants customary in the art for particular added purposes may be present, even in major amounts, for their known effects. For example, dyes, pigments, antioxidants, water repellants, fire retardants, biocides and the like may be added. Additonal conventional steps for forming particular various manufactured articles, such as cutting, trimming, shaping, adding slots, tabs and the like for ceiling grid suspension or other mountings; painting, texturing, surface overlaying and the like decorating and finishing features including protective top coatings may be performed without departing from the spirit and scope of the present invention. Various apparatus may be utilized as mixing vessels including turbine and impeller mixers of various configuration and design, and various flow boxes including flotation foaming cells and conventional forming head boxes as used in conventional batch and continuous foraminous support wire forming operations may be used.

Claims

WHAT IS CLAIMED IS

1. A low density structural mineral wool panel comprising at least one facing sheet of porous fiber scrim; an open, porous entangled mass of mineral wool and lightweight aggregate core, said core further containing about 10-30% wheat starch having a residual protein fraction, a small amount of cationic guar bean and a small amount of nonionic polyethanoxy surfactant dispersant for the mineral wool.

2. The panel of Claim 1 having a second facing sheet of porous fiber scrim.

3. The panel of Claim 1 having a density of about 3-10 pounds per cubic foot (50-160 kg/m³) and a modulus of rupture of at least about 60 pounds per square inch (42,000 kg/m²).

4. The panel of Claim 1 containing about 0.01-1% of trimethylammoniopropyl guar chloride.

5. The panel of Claim 1 containing about 0.01-3% of nonionic dinonylphenoxypoly (ethanoxy) ethanol having a molecular weight around 1000 and having about 15 ethylene oxide units.

6. A method for manufacturing a low density structural mineral wool panel on a moving foraminous support wire which comprises: a. forming a dilute aqueous furnish of mineral wool, lightweight aggregate, about 10-30% starch which upon cooking does not exhibit significant viscosity increase, about 0.01-1% of a cationic guar bean and about 0.01-3% of nonionic polyethanoxy surfactant-dispersing agent for the mineral wool; b. passing the aqueous furnish onto a first flooded section of the foraminous wire, forming an open, porous structural mass of entangled fiber and aggregate having bubbles and water in the interstitial spaces of the entangled fiber mass ; c. collapsing the bubbles and stripping water from the wet entangled mass without substantially collapsing the open, porous structural mass by applying a vacuum pressure differential equivalent to about 3-20 inches of mercury; and d. further stripping water from the wet mass and drying the wet mass without substantially collapsing the open, porous structural mass by applying vacuum pressure differential equivalent to about 5-70 inches (.13-1.8m) of water and simultaneously passing heated dry air through the open entangled structure.

7. The method of Claim 6 in which said starch is wheat starch having a residual protein fraction.

8. The method of Claim 6 in which said starch is wheat starch having about 6% residual protein fraction.

9. The method of Claim 6 in which said guar is trimethylammoniopropyl guar chloride.

10. The method of Claim 6 in which said nonionic is dinonylphenoxypoly (ethyleneoxy) ethanol.

11. The method of Claim 6 in which said nonionic is dinonylphenoxypoly (ethyleneoxy) ethanol having a molecular weight around 1000 and having about 15 ethylene oxide units.