AU608463B2 - Low density mineral wool panel and method - Google Patents

Description

APPLICATION ACCFPTED AD AMENDMENTS A LLO WtVV i c i

AUSTRALIA

Form PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Short Title: Int. Cl: Application Number: Lodged: Complete Specification-Lodged: Accepted: Lapsed: Published: Priority: a o0 This document contains the amendments made under Section 49 and is correct for printing.

Related Art: Patent of Addition to 12435/88

B

TO BE COMPLETED BY APPLICANT Name of Applicant: USG INTERIORS, INC., oe 0

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0 0 0 a 0 0 Address of Applicant: 101 South Wacker Drive, Chicago. Illinois, 60606, United States of America Actual Inventor: Address for Service: GRIFFITH HACK CO., 601 St. Kilda Road, Melbourne, Victoria 3004, Australia.

Complete Specification for the invention entitled: LOW DENSITY MINERAL WOOL PANEL AND METHOD The following statement is a full description of this invention including the best method of performing it known to me:- 6 'LOW DENSITY MINERAL WOOL PANEL AND METHOD BACKGROUND OF THE INVENTION 0 q 4 0 FIELD OF THE INVENTION o o@ This invention relates to fibrous mineral. wool. 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 density, and which may be used as acoustical ceiling tiles, thermal insulating panels, sound absorbing painels, pipe and beam insulation and similar products.

10DSCITONO0T0PIO R 0 0 000 6 00 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 first by gravity and th~en by vacuum suction means to form a mat. 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 tiles.

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 fibe than contains synthetic rubber latex solids. detergent slurry then formed, and the two slurries admixed to about 15% solids consistenc y, agitated to a stable foam, and oven dried. The extremely ww i i. 11 3 time consuming and energy intensive drying of the stable foam from 15% solids is a severe economic detriment.

U.S. Patent No. 3,228,825 teaches a fclted glass fiber product which is highly porous and has exceptional flexibility and flexural strength. A "binder fiber," exemplified by a highly pulped cellulose fiber, completely coats the glass fibers and provides the interlocking sites necessary for felting. When greater mass integrity and strength are desired, a suitable resinous binder is added.

Furthermore, is 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 9 flocculant must be added just before the slurry is dewatered in order that clumps or flocs form among the fibers undergoing gravity drainage t 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 teaches the avoidance of foam in the forming box so that the gravity drainage of water is not slowed but the development of a foam thereafter in the S sneet in order to increase the pressure differential across S the sheet during vacuum dewatering.

S' An object of tho prosont invention is to provido lew ,2 density yet strong mineral panels such that aving densities between about 3-10 s per cubic foot will have a modulus o at re of at least about 60 pounds per cubic SUMMARY OF THE INVENTION The present invention provides a low.density structural nanel comprising at least one facing sheet of fiber scrim and an open, porous core of entangled mineral wool and lightweight aggregate, about 10% to 30% by weight of a starch which has been cooked to a temperature approaching but not reaching its gelation point, a small amount of a cationic 3a guar bean meal derivative, and a small amount of a non-*,onic surfactant.

The present invention also provides a method for manufacturing a low density structural panel which comprises: a) cooking an aqueous dispersion of a starch to a temperature approaching but not reaching its gelation point; b) forming a dilute aqueous slurry of mineral wool,-alightweight aggrogate, a non-ionic surfactant, from about 0.3 to about 1.8% by weight of the cooked starch, and a cationic guar bean meal derivative; c) passing Lne slurry onto a foraminous wire and forming an open, porous structural mass of entangled fiber and aggregate having bubbles and water in the interstices of o« the entangled fiber mass; 0 0 1 5 d) collapsing the bubbles and stripping water from the 0 wet mass without collapsing the open, porous structure o 00 o0O o' thereof by applying a vacuum to create a pressure o o differential across the mass of from about 3 to about 0 0o inches of mercury; and e) further stripping water from the wet mass and drying it without collapsing it by creating a pressure differential across the mass of from about 0.4 to about 5 inches of o.oo mercury and passing air through it.

0 0f o S a. C C St CC t C C C C 3b When a nonionic surfactant, such as a polyethyleneoxy ether of ethyl alcohol, is added to a furnish containing an ungelled starch binder 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 air at a rapid rate through the wet mat.

00 Soo BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a mineral board manufacturing S process in accordance with the present invention.

Goo 0a 00 o FIGS. 2 and 3 are graphs of the viscosity/temperature relationship o oc oo. 5 of 6% by weight solutions of GENVIS 600 wheat starch and Staley pearl 0oo0 corn starch, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS ag0 The mixing tank 10 of FIG. 1 is equipped with the motor driven 0 o impeller 12 which mixes an aqueous slurry containing from about 3% to o 00 O 6ZO about 6% solids by weight. The composition of the solids in the slurry *aod should be between the following limits: 0 0 0 *sa Ingredients Amounts by weight) oo o: Mineral Wool about 25-95% 1 o 0 Lightweight Aggregate up to about Starch about 10-30% Cationic Guar Derivative about 0.03-3.5% Nonionic Surfactant about 0.5-3.5% Clay up to about 7% Thus, the slurry may contain from about 0.75% to about 5.7% mineral wool, up to about 2.4% lightweight aggregate, from about 0.3% to about 1.8% starch, from about 0.0009% to about 0.21% of the cationic guar -4derivative, from about 0.015% to about 0.21% of the non-ionic surfactant, and up to about 0.42% of the clay.

It is important that no substantial viscosity increase is provided by the binder to the slurry because that would be detrimental to maintaining a rapid rate of dewatering and drying of the fibrous mass on the forming wire.

For this reason, the starch used as the binder in this invention is cooked to a temperature approaching but not reaching its gel point in order to attain the necessary adhesiveness yet avoid the consequences of a swollen binder that would bridge over voids and passages in the fibrous mass and impede drainage. The gel point, the temperature at which gelatinization of the starch commences, may be determined by 0S 0 6Oat plotting the viscosity/temperature curve and observing the inflection point. It is recognized that the apparent gel point changes as the s o" 15 starch concentration changes but the gel point of a dilute solution is 08 0 00, an approximation of the true gel point as shown by Sandstedt, R.M. and 06 Abbott, R.C. in CEREAL SCIENCE TODAY, Vol. 9, No. 1, 1964. Therefore, 'a the gel point of a 6% by weight solution of GENVIS 600 wheat starch (Ogilvie Mills) is shown at A in FIG. 2 herein which is an amylogram drawn by a VISCO/amylo/GRAPH instrument when the viscosity of the starch solution is measured as the temperature of the solution is raised 1.5 0

C

0 o6 a" a per minute and the general operating procedure outlined in Bulletin C £G f of C.W. Brabender Instruments, Inc. is followed. The gel point of a 6% re solution of Staley pearl corn starch is shown at B in FIG. 3, which is "tL' 25 an amylogram drawn in like manner.

The preferred binder is the wheat starch, which contains about 6% of a protein fraction. It is dispersed at a high shear rate in a portion of the process water and then heated to a temperature between 1350 and 190°F to cook the starch. There is no substantial increased viscosity apparent with this starch during the cooking cycle even at the high end of the range. After cooling, the starch binder is fed to mixing tank 10. It is suitable to stop the cooking of this and other starches at a temperature about 1°F lower than the gel point to ensure that swelling of the starch grains is minimal. It is preferred to cook -C

F

0 0 0 0 0 00 0 0 0 o 00 0 0 0 00 0 O OO 0 00 0000 Q00 0 0 o o o o a 00 0 0 6 So 0 0 the wheat starch and the pearl corn starch at a temperature of from about 168 to about 172 0

F.

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 surfactant is added early to the slurry in mixing tank It is preferred to use an about 2% solution of a low foaming water soluble surfactant such as IGEPAL DM-710 dinonylphenoxy poly(ethyleneoxy) ethanol having a molecular weight of about 995 (sold by. GAF Chemicals). Similar ethers of ethyl alcohol are commercially available and may be used. Other low foaming surfactants having an HLB (hydrophilic-lipophilic balance) of about 13 are contemplated also.

The cationic guar bean meal derivrtive, such as guar 2-hydroxy-3 (trimethylamino)-propyl ether chloride, a commercially available powdered polymer (GENDRIV 158 from Henkel Corporation), is added to the 15 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. The guar derivative tends to flocculate the mineral wool and aggregate and the effect is enhanced by the addition of small amounts of clay.

Because it hydrates rapidly, the cationic guar derivative is added to mixing tank 10 last after thorough homogeneous mixing of all the other ingredients, and mixing is 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 across the width of a moving wire belt 40, commonly called the wire, to form an open, porous wet mat. The open, porous mat is preferably of a thickness to yield a finished product having a thickness between about 1/4 and 2 inches.

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 polyamide fibers and the like.

-6- The lightweight aggregate preferably is 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, 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 0 Coe comprising water, and the aqueous slurry at this point containing still 0 0 o about 3 to 6 weight solids. The open, lightly foamed wet mass is 0 0 deposited from forming box 30 onto a bottom scrim cover sheet 43 above 00 0 15 the wire 40 as the slurry and scrim 43 float through a first flooded o 00 section 42 on the moving wire 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 o*o00 20 high vacuum section 44 a couple of very brief bursts (about 1 second) of 00 ga pressure differential equivalent to about 3-20, preferably about 4 to SOo about 6, inches of mercury break the bubble walls of the slight foam .090 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 to 3 So 25 seconds the foam has collapsed and the draining liquid coats the contact ,os points on the highly voided, open, entangled mass of the fiber and aggregate and scrim cover sheet(s).

Continued water stripping and drying are enabled by a continued pressure differential of about 4 to about 6 inches of mercury in section 46, and a differential of from 5 to about 70 inches of water (about 0.4 to 5 inches Hg) in section 48, along with passing high volumes of high velocity heated air through the mat without total collapse of the highly voided, open structural configuration. Thereby, structural mineral panels having a density of about 3 to 10 pounds per cubic foot, and preferably about 3 to 6 pounds per cubic foot with a modulus of rupture

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-7of at least 60 pounds per square inch and preferably bout to 120 pounds per square inch, measured with the nonwoven fiber class scrim cover sheets in place on the panel, are obtained in a matter of about 10 minutes or less total time from depositing the slurry on the wire 40 through final through-air stripping and drying sections 48 and 49. At the time the panel passes through section 48 the moisture content is less than about by weight.

In the foregoing, the mat was formed upon 1 or 2 cover sheets. Such sheets may be of paper, woven glass fiber, non-woven glass fiber and similar sheet materials. A particularly preferred cover sheet is a non-woven glass fibe: scrim, such as battery type scrim, having a weight of about 00. 0.4-2.5 pounds per hundred square feet. It is envisioned in o:oo~i alternative embodiments that the top scrim 47 may be left off 0 0o and, after the water stripping and drying section 49, a o 0 0 oO_ viscous, screedable pulp such as the set forth in U.S.

S patents 1,769,519; 1,996,033; and 3,246,063 may be applied as 0 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 0.00 bottom scrims may be in place before application of such a 000oo 0o° pulp overlay. In addition, conventional finishing operations such as the application of various prime, texture, or protective coatings may be applied to the panels produced in accordance with the present invention.

The following specific examples will further tC S illustrate various specific embodiments of the present (:ccP 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 to be construed as limitations on the present invention.

i -7a- EXAMPLE 1 Mineral wool, expanded perlite aggregate, dinonylphenoxpoly (ethyleneoxy) ethanol, water wheat starch (GENVIS 600) cooked at 190 0 F, and CTS-2 ball clay (from Kentucky-Tennessee Clay Co.) were added to mixer 10 and mixed for 4 minutes. A solution of guar 2-hydroxy-3 (trimethylamino)-propyl ether chloride was added to mixer for 0 0 0 00 0 0 00 0 0000oooo oo* 00 0 0 0 a 94 0 c C I0I tCC i -8flocculation and mixed for 5 seconds before passing the dilute dispersion to forming box 30. On a solids basis, the final proportioning in the mixer 10 was 44.45% mineral wool, 29.15% expanded perlite, 22.95% wheat starch, 0.08% of the cationic guar and 1.68% of both the nonionic surfactant and the clay 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 43 and the dilute furnish passed from the mixer 10 to the flow box 30 and deposited onto the scrim (battery grade 2.4 pounds per hundred square feet 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 o 0oo therin was deposited in the flooded section 42. The application of a 0oo000 few short (1 second) bursts of vacuum pressure differential equivalent 0 15 to about 15 inches of mercury in high vacuum section 44 immediately 000 0 oo o collapsed the small amount of foam and rapidly stripped voluminous oo amounts of water fxom the interstices of the wet mass comprising bottom 0000 oooo 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 moistuye. Because of the open, porous nature, that water was readily 0o1 stripped from the wet panel and the panel dried by rapidly passing large 0 0 0 O0 volumes of heated dry air through the panel first in the low vacuum 0 oe0 section 46 (providing a pressure differential equivalent to about 0oo inches of mercury) and secondly in the through-air-flow drier zone 48-49 0000 25 provided with a pressure differential equivalent to about 14 inches of 0 water (1 inch of mercury) across the surface of the mass and having a 0: 0 positive air flow rate-volume-velocity of about 300 (generally, from So about 30 to about 350) cubic feet per minute of air per square foot of wet mat surface. Generally, the heated air may be provided at a temperature of about 37°-205°C, preferably about 175 0

C.

Several runs were made which produced material having uniform thickness, density, and strength properties. The time for passage from the flow box 30 through the through-air drying section 48 varied from about 2 to 10 minutes, depending upon the core thickness of about 1/8th inch through 2 inches. The average core thickness range was 0.445-0.490 J r)- -9inch and the density range was 6.3-7.0 pounds per cubic foot. 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 painted face 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 their 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 Soo (T-A-D weight) was n'.asured: and then the samples were placed in a oa convection oven and dried overnight to a constant weight (Oven weight) o 0 o 90 for comparison and the difference in weight from through-air drying to coo 15 bond dry weight was determined. Representative results are set forth in 0 0 0 o oo the Table following Example 4. Because the purpose of this study was QoeO only to assess the moisture holding tendency of the various components, no attempt was made to reach the 3% moisture level by the .hrough-air-drying procedure.

0 @0 EXAMPLE 3 9 s' The general procedure of Example 1 is followed except that tbe cooking temperature of the starch is about 170 0 F. The moisture contr.?- "eaoo is reduced to below 3% in 10 minutes. Results similar to those of Oue Example 1 are obtained.

a g a EXAMPLE 4 The general procedure of Example 1 is followed except that pearl corn starch from Staley is used in place of the wheat starch and it is cooked at about 168 0 F. The moisture content is reduced to below 3% in minutes. Results similar to those of Example 1 are obtained.

-i 1 -L i- Y r r 0 0 00 0 0 0 0 0 0 00 00 0 00 0 000 0

C

0 00 0 00 0 0 0 C 0 0 000 0 0 C 0 0 0 C 000 C 0 0 00 00 0 0 00 4 00 COMPONENT71 PERCENT (WT.)

SOLIDS

TABLE

DEN!31TY THTI(JNSS (PCF) (INCHE9S$ WEIGHT (LB) T-A-D OVEN

WEIGHT

DIFFERENCE MOISTURE

PERLITE

SAMPLE

SAMPLE

SAMPLE

SAMPLE

STARCH

SAMPL2

SAMPLE

SAMPLE

GUAR

SAMPLE

SAMPLE

SAMPLE

SAMPLE

NONE

14.6% 29.2% 58.3% ii. 50 23.0% 45.9% 9.20 7.53 6 .64 5.40 6.76 5.89 5.65 5.83 5.78 6.33 6.61 0.28 0.37 0.46 0.62 0.49 0.44 0.42 0.51 0.52 0.49 0.46 0.28 0.26 0.30 0.42 0.32 0.27 0.46 0.38 0.32 0.33 0.32 0.22 0.23 0.25 0.28 0.28 0.22 0.20 0.25 0.25 0.26 0.25 0.06 0.03 0.05 0.14 0.04 0.05 0.26 0.13 0.07 0.07 0.07

NONE

0.04% 0.08% 0.16% 000 0 0 6 06 0 0 o 6 6 6 o 6 6 0 0 0 6 0 o 0 o 0 a 00 0 .0 000 .0 0.0 .0 3 7o~ -11- TABLE (continued) COMPONENT PERCENT (wt.)

SOLIDS

DENSITY THICKNESS (PCF) (INCHES) WEIGHT (LB) T-A-D OVEN

WEIGHT

DIFFERENCE

PERCENT,

MOISTURE

SURFACTANT

SAMPLE 12 SAMPLE 13 SAMPLE 14 SAMPLE 15

CLAY

SAMPLE 16 SAMPLE 17 SAMPLE 18

NONE

0.84% 1.68% 3.36%

NONE

3.3 6% 6.72% 5.82 6.31 6.03 6.22 5.84 6.16 6.21 0.5-i 0.47 0.50 0.48 0.52 0.49 0.50 0.29 0.31 0.34 0.33 0.37 0.36 0.48 0.25 0.25 0.25 0.25 0.26 0.25 0.28 0.04 0.06 0.09 0.08 0.11 0.11 0.20

I-

.0.

y~.

t

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i _1 1 I i s~bif -12- From the results set forth in the Table, it may be seen that doubling the amount of lightweight aggregate from 29% to 58%. greatly increased the moisture content of the through-air dried panel. Doubling the amount of the wheat starch 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 in viscosity upon cooking; it is evident that the recited levels of this binder help maintain a low viscosity furnish and greatly aids stripping water from and drying the wet panel by pasage of air through the open, porous entangled structural mass.

Doubling the amount of the low foaming non-ionic surfactant did not 006 significantly change the nature of the rat. Dr delicate, non-resilient bubbles, did not significantly inhibit bursting of the bubbles and a I stripping of water by through-air passage and did not result in o oo o, o 14 significant separation of fiber and aggregate during water stripping. A 0 o I number of previous attempts had encountered considerable layering of the qoog 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 solution which has not increased in viscosity o000 20 upon cooking so that it will not hold water and thereby defeat 0 o through-air water stripping and a slightly foaming nonionic surfactant t disperse the wool and aggregate coupled with the cationic guar gum o 0 0 derivative to keep the wool and aggregate dispersed yet in entangled o0G engagement, thereby avoiding segregation and layering during through-air 0 25 drying.

o* oo From the foregoing, it is apparent that the present invention 0 0 provides a method for manufacturing structural mineral panel products of widely varying densities, properties and uses. Various panel thicknesses from about 1/8th inch through 2 inches or more may be attained. Very lightweight products having densities ranging from about 3 through about 10 pounds per cubic foot 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 accounts, for their known effects. For example, II I Il L l :jt -13dyes, pigments, antioxidants, water repellants, fire retardants, biocides and the like may be added. Additional 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 similar decorating and finishing features 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 J, wire forming operations may be used.

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o o 0 9 a 064a 0 oar 0 0

Claims (19)

1. A low density structural panel comprising at least one facing sheet of fiber scrim and an open, porous core of entangled mineral wool, 10% to 30% by weight of a starch which has been cooked to a temperature approaching but not reaching its gelation point, a small amount of a cationic guar bean meal derivative, and a small amount of a non-ionic surfactant.

2. The panel of claim 1 wherein the starch has been cooked to temperature about 1 0 F lower than its gel point.

3. The panel of claim 1 characterized further by a density of 3-10 pounds per cubic foot and a modulus of rupture of at least 60 pounds per square inch.

4. The panel of claim 1 wherein the amounts of the guar derivative and of the surfactant are from 0.03 to and from 0.5 to 3.5% by weight respectively.

The panel of claim 1 wherein the surfactant has an HLB number of about 13.

6. The panel of claim 5 wherein the surfactant is dinonylphenoxy poly (ethyleneoxy) ethanol. o 0 S

7. The panel of claim 1 wherein the starch content is 0 about 23%.

8. The panel of claim 1 wherein the guar derivative is guar 2-hydroxy-3 (trimethylamino)-propyl ether chloride. 00 oo.

9. The panel-of claim 1 characterized further by the presence of up to 7% by weight of ball clay.

TPh panel according to any one of the preceding claims characterized further by the presence of up to 0 C lightweight aggregate. 0 0

11. A method for manufacturing a low density structural 00.0: panel which comprises: cooking an aqueous dispersion of a starch to a temperature approaching but not reaching its gelation point; 7 V- 01 I I b) forming a dilute aqueous slurry of mineral wool, a non-ionic surfactant, from 0.3 to 1.8% by weight of the cooked starch, and a cationic guar bean meal derivative; c) passing the slurry onto a foraminous wire and forming an open, porous structural mass of entangled fiber having bubbles and water in the interstices of the entangled fiber mass; d) collapsing the bubbles and stripping water from the wet mass without collapsing the open, porous structure thereof by applying a vacuum to create a pressure differential across the mass of from 3 to 20 inches of mercury; and e) further stripping water from the wet mass and drying it without collapsing it by creating a pressure differential across the mass of from oo 0.4 to 5 inches of mercury and passing air through it. oo.

12. The method of claim 11 wherein the cooking temperature for the starch is 1° F below its gelation point. o, o°

13. The method of claim 11 wherein an aqueous slurry of o the mineral wool, aggregate and surfactant is mixed before 0 the uooked starch is added. a oo 0 .o00

14. The method of claim 11 wherein the cationic guar derivative is added to a slurry of the wool, aggregate, surfactant, and starch. C

15. The method of claim 11 wherein the guar derivative *E is guar 2-hydroxy-3 (trimethylamino)-propyl ether chloride. 'I

16. The method of claim 11 wherein the surfactant has an HLB number of about 13.

17. The method of claim 11 wherein the pressure differential in step c is from 4 to 6 inches of mercury.

18. The method of claim 11 wherein the air is passed through at a volume velocity of from 50 to 350 cubic feet per 11 4 -16- minute per square foot of the surface the wet mass at which the air is directed.

19. The method of any one of the preceding claims wherein the aqueous slurry includes a lightweight aggregate. DATED THIS 4th DAY OF January 1991 USG INTERIORS, INC. By Its Patent Attorneys GRIFFITH HACK CO. Fellows Institute of Patent Attorneys of Australia 0 000 0 o e 00** So 0 0 0 0o 0 0000 S0 oio o0 0o 0 *e 0 0o 0000 00 0 0 0 LI