NZ223123A - Making a light structural fibre/resin binder panel - Google Patents

Description

r : : 1 ' " ' r" - - - 1- - t i 7 ' <r<-->tt2/2c,.x ;£ O <s •' ' ■ " ' : •• •. wrj p.o. • . "/«&?/ ^ Wit.*' NEW ZEALAND PATENTS ACT, 1953 No.: Date: COMPLETE SPECIFICATION e N>V, {& , i* ■■ ) -7 JAt^988"^ METHOD FOR MANUFACTURE OF LIGHTWEIGHT FROTHED MINERAL WOOL PANEL /ffwe, USG Interiors, Inc., a corporation of the State of Delaware, of 101 South Wacker Drive, Chicago, Illinois 60606, U S A hereby declare the invention for which Jrf we pray that a patent may be granted to vrf&lus, and the method by which it is to be performed, to be particularly described in and by the following statement: - Followed by -la- METHOD FOR MANUFACTURE OF LIGHTWEIGHT FROTHED MINERAL WOOL PANEL ^ •> h j-i y Background of the Invention C . ) Field of the Invention This invention relates to mineral wool fibrous products.

More particularly, it relates to a method of making strong structural panels of mineral wool fiber that are lightweight, about 5-12 pounds per cubic foot 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. By such methods, an about 3 weight % dispersion furnish of mineral wool, lightweight aggregate, binder and other adjuvants are flowed onto a moving foraminous support screen for dewatering, such as that of an Oliver or Fourdrinier mat forming machine, at line speeds of about 10-50 feet per minute. The dispersion dewaters by gravity and then vacuum suction means; the wet mat is dried over about 3-12 hours in heated convection ovens; and the product cut and optionally top coated such as with a paint, to produce lightweight structural panels such as acoustical ceiling products. Such methods cannot "achieve low density products below about 12 pounds per cubic foot.

It is also known to form stable foams with mineral wool. U.S. patent 4,447,560 suggests a low density insulation sheet may be made by forming a first slurry of fiber containing synthetic rubber latex solids. A second slurry is formed of a detergent, and the two slurries admixed to 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. -la- 7.23123 It has been suggested that lightweight foams of attenuated glass fibers might be formed into very lightweight products of about 1-3 pounds per cubic foot density in U.S. patent 3,228,825. According to this patent, microscopic bubbles are generated and, in order to achieve uniform incorporation of lightweight aggregate and attenuated glass fiber mixtures with the bubbles, a "binder fiber" glue of very highly refined cellulosic fibrilles is required. The proposed product would appear to be an extremely flexible one incapable of structural panel usage. A structural panel, by definition is capable of supporting its own weight without visible sagging, bending, or collapsing when supported only at the edges i of the panel. It is believed that this proposed process has never been commercialized or found to be of practical interest.

Further, it is known that paper webs constituted mainly by noble cellulose fibers and fibrilles may be formed from foams. The basic formation of the cellulose fiber manufacture gives rise to highly fractured fiber fragments and fibrilles having a jagged, fuzzy, microstructured surface to aid entanglement and entrapment of microscopic sized foam bubbles.

Further, U.S. 4,062,721 discloses addition of a surfactant foaming agent to-a mineral fiber furnish. The addition is after the furnish is in the flow head box in order that minimum foam be present in the sheet as it is laid on the mat forming wire and during an initial gravity drainage period. This is followed by conventional convection drying over long times. It teaches that addition of the foaming agent to the slurry in the mixing tank is unsatisfactory as requiring excessively long drainage times to maintain a satisfactory production rate.

It is an object of the present invention to provide low density structural mineral fiber panels on a moving foraminate support wire but without having to dry very large amounts of water out of a wet mass which will at least offer the public a useful choice.

I NEW ZEALAND PATENT OFFICE -2- - 9 MAR 1990 j pew* I 'ECEIVED 22312 In accordance with the invention there is provided a method of manufacturing a lightweight structural mineral panel on a moving foraminate support wire comprising: A. Forming a dilute fiber furnish in water of mineral fiber and organic resin latex binder; B. Mixing said furnish and a small amount of cationic amine-based surfactant frothing aid that contains at least one long chain aliphatic radical of Cg-C22 carbon atoms effective to form a transitory froth of air bubbles; C. Depositing the froth on a water flooded section of the support wire; D. After a brief interval of time sufficient for the froth to mature into a homogeneous mass of about 1/64-1/16 inch diameter bubbles, applying a vacuum pressure differential to the froth equivalent to about 8-20 inches of mercury to burst the bubbles and strip water from the wet mass; E. Stripping additional water from the wet mass by applying a vacuum pressure differential to the wet mass equivalent to about 5-20 inches of water; and F. Drying the wet mass by passing heated dry air through the wet mass by passing heated dry air through the wet mass at a rate of about 50-350 cubic foot per minute per square foot of surface of the mass. Basically, in accordance with the present invention, a weak, resilient or viscous and therefore fairly stable mass of homogeneous bubbles about l/64th inch diameter comprising about 15-45% by volume of air that exhibit rapid foam drainage is generated between the mixing tanks and the mat forming wire. This is in contrast to a stable foam, wherein bubble size is very small and uniform, with each bubble behaving as a stable, rigid sphere when subjected to stresses. The resilient, tightly packed spheres in a stable foam exhibit a great degree of resistance to deformation and exhibit a high viscosity or resistance to dewatering of the liquid film of the bubble when acted upon by small stress forces and are slow to drain liquid from the foam film. In the present invention, transitory bubbles are generated with the aid of a cationic amine-based surfactant and rapidly dewater to concentrate the solids in the liquid forming the film or wall of the bubble under quiescent conditions as they i /£vv ■ZtfALAND • ''A! ENl Of-'FJCE 9 MAR 1990 ~:c£ iv ED first contact a flooded section of the forming wire. Thereafter, they readily dewater and coalesce to a wet set substrate ,without bubbles remaining upon application of first high vacuum shock and " ~ further vacuum stripping of water without collapse of the highly permeable, highly voided solids structure which will remain in place for rapid drying of the wet mass by passing large volumes of heated air through the structure. Integral to the present invention, the highly voided mass of rapidly dewatering bubbles is formed upon at least one pervious woven or non-woven mesh or scrim facing. Coalescence occurs when the froth of fragile, weakly resilient air bubbles is present in the generating mass such that air constitutes about 3 0-45% by volume of the generating foam mass, while the liquids-solids interface forming the bubble wall constitute about 1-20% solids consistency. The froth, under essentially quiescient conditions, dewaters to a point where it is about 10-30% solids consistency. It is believed, at this point, the preferred binder constituents have coated the fiber and aggregate surfaces and have become sufficiently tacky at entangled fiber and aggregate contact points as to retain the open, porous structural configuration of the highly voided entanglement of fibers with lightweight aggregate and scrim cover sheet upon collapse of the bubbles. Upon application of sufficient stress, such as by brief application of high vacuum suction equivalent to about 6-14 inches of mercury, the shock bursts the bubble walls and the increased viscosity or tacky binder further coats the contact points of the entanglement of fiber, aggregate and scrim in the highly voided mass as additional liquid drains from the wet mass. This provides further wet structural integrity to the panel and allows a rapid through-air drying of the panel.

Brief Description of the Drawings 1 2? J.t2? a foamed mineral Figure 1 is a simplified schematic diagram of board manufacturing process in accordance with the present invention.

Figure 2 is a top view cross section of the process showing the frothing head forming box apparatus of Figure 1.

Figure 3 is a side view sectional of the same portion of the process as Figure 2.

Description of the Preferred Embodiments The applicants have now discovered a process for rapidly forming shaped fibrous products such as acoustical ceiling board and,the like structural board products which combine low densities with good strengths. In accordance with the present invention, a modified wet process is employed wherein the dilute aqueous slurry is foamed to a delicate froth, which froth dewaters and matures under quiescent conditions and is then ruptured by a first vacuum shock to a sufficiently porous, open structure that is capable of being rapidly and economically stripped of water and dried by further vacuum and the passage of heated air through the opened porous structure.

The products made according to the process of the invention are fibrous products. The fibers may be inorganic or organic, whether natural or synthetic, or combinations of the foregoing. Typical fibers useful in the present invention include organic fiber such as polyester, polyamide and polyolefin fibers; and mineral fibers such as mineral wool, glass wool, kaolin and the like other known conventional fibers. The preferred fiber for the present invention is predominantly of mineral fiber composition such as of blown mineral wool. Expressed in terms of the dry by weight total solids content of the board composition, the fibers « are suitably present in an amount of about 20-65% by weight, and preferably present in an amount of about 30-40% by weight.

Another essential solid ingredient is an inorganic lightweight aggregate of exfoliated or expanded mineral of volcanic origin generally having a dry loose bulk density of about 2-6 pounds per cubic foot (pcf) such as of exfoliated vermiculite, expanded per-lite, and the like. Particle sizes of the lightweight aggregate are generally about 12 to about 100 mesh. Preferred lightweight aggregate comprises expanded perlite having a top size of about 100 mesh (150 micrometers) with about 73% of the particles passing 425 mesh (32 micrometers). The lightweight aggregate may be present in an amount by weight dry total solids basis of about 20-70% and preferably about 30-40%.

Another essential solid ingredient is the binder. The binder may be any of the conventionally used binders but organic resin latexes are preferred. Suitable resin latexes include polyvinyl acetate, vinyl acetate/ acrylic copolymers, and styrene-butadiene. Various homopolymer, copolymer and mixtures thereof may be used. Generally the binder will constitute about 5-30 % by weight of the dry board composition. Only about one-fourth to about one-half of binder added in initial formulation of the furnish will be retained in the wet mass on the screen. The remainder passes through the screen with the drainage water. Thus the furnish to the forming "wire may contain about 5-50 weight % of latex solids to allow for losses through the wire. Polyvinyl acetate latexes are particularly suitable, and when employed, a small amount such as about 1-10% by weight of the emulsion, of polyvinyl alcohol may be added as a suspension aid and to enhance the bonding strength of the resin.

The other essential ingredient is a cationic surfactant frothing aid which, in combination with the foregoing ingredients in water, will generate delicate, rapidly draining bubbles. Such surfactant is a weakly forming cationic amine-based surfactant having at least one long chain (8-22 carbon atoms) aliphatic • v- radical. Such amine materials include primary and secondary amines such as cocoamine and disoyamine; fatty diamines and their salts such as tridecylether amine acetate; polyethanoxy derivatives such as cocoamine having about 16 moles of ethyxylation; alkyl ether amines such as hexyloxypropylamine, decyloxypropylamine, octyl ether amine, decyl ether amine, octyl ether amine acetate, decyl ether amine acetate and isodecyl ether amine acetate; and quaternary ammonium salts such as trimethylcoco ammonium chloride. Quarternary ammonium compounds are preferred as providing the most homogeneous bubbles. The frothing aid may be added in quite variable amounts depending upon the effect desired and the foam producing level of the particular cationic amine-based surfactant utilized. Generally amounts may satisfactorily range from about 0.2% to about 2.5% by weight based upon total solids of the dry panel product. Slightly less and somewhat more may be used but without further apparent advantage.

Optionally the furnish composition may include some coarse cellulose fibers to aid cohesiveness of the core of the panel.

Such fibers, conveniently derived by slushing newspaper in a high shear high intensity mixer, are generally about 1/16-1/4 inch in length with some fibers being up to about an inch long. If present, they may be added in amounts up to about 15% by weight total dry solids, preferably less than about 5% and most preferably less than about 3% by weight is added.

In carrying out the process of the present invention, a dilute fiber furnish of about 1-5% solids consistency is formed, in one or more mixing vessels, comprising mineral fibers, lightweight aggregate, binder and a small amount of cationic amine-based surfactant and agitated to a froth. All of the ingredients may be added to a single mixing vessel preferably adding the cationic 223123 amine surfactant frothing aid last- It is preferred to add the aggregate and the frothing aid in later mixers if a plurality of mixers is used. It is believed that the bubble formation with the surfactant is aided by a residual amount of surfactants customarily present in the latex binder, -and bubble attachment to mineral surfaces is enhanced by the cationic surfactant. The general froth is laid upon, and/or overlaid with a permeable, nonwoven-fiber scrim panel facing sheet on the moving foraminate wire. The froth is allowed to age and mature for a few seconds time under essentially quiescent conditions, over a flooded section of the wire to a point where the liquid making up the walls of the bubbles has an about 10-30% solids consistency. It is believed at this point the binder has become sufficiently tacky to retain the structural configuration of the highly voided entanglement of mineral fibers, lightweight aggregate and the cover sheet upon collapse of the bubbles. Upon application of stress such as by brief application of high vacuum suction (providing a pressure differential equivalent to about 8-20, and preferably 6-14, inches of mercury) the bubbles burst, further dewatering the highly voided mass, which is then stripped of remaining water by continued vacuum (pressure differential of about 5-20 inches of water) and through air dried by passing heated.dry air through the mat (at a rate of about 50-350 cubic feet per minute per square foot of mat surface) to produce a structural mineral wool panel having a density of about 5-12 pounds per cubic foot and flexural strengths of about 30 to 45 pounds per square inch for the core (excluding top and bottom cover sheets).

EXAMPLE I The following Example should be read with reference to FIGURE 1 which shows a simplified process diagram in accordance with the present invention.

' ■ ZEALAND ' J '• tent office ~8~ " 9 MAR 1990 ^ Received 723123 A dilute mineral fiber furnish was prepared by charging mineral wool, perlite, a coarse paper fiber aqueous slurry from pulping unprinted fly leaf in a slush maker, a 45 % solids dispersion of X-LINK 2828 polyvinyl acetate resin latex from the National Starch and Chemical Corporation, ADOGEN 4 61 cocotrimethyl ammonium chloride from the Sherex Chemical Company and water for suspension to mix tank 10 equipped with motor driven impeller 12 and valve 14. Flows from the mix tank were adjusted by valve 14 to provide a total 3% solids consistency furnish proportioned on a dry solids basis to about 33% perlite, about 33% mineral wool, about 15% coarse paper fiber, about 15% polyvinyl acetate and about 1.5% quaternary ammonium chloride.

A pump 20 transferred the homogeneous mixing furnish to a modified flow head box 30 on a conventional moving foraminate support wire belt, commonly referred to as the wire 4 0. The functions of the modified head box 3 0 are to allow the furnish now developing to a froth of bubbles to age, consolidate and mature the solids in the frothing mass for a few seconds and to apply an even layer of dewatering froth solids across the width of wire 40. The enlarging and then convoluting channelization to and through the modified head box as more particularly shown in FIGURES 2 and 3, enhances this maturation and consolidation of the developing froth. By providing smoothing roller 34 on wire 40, a velocity transition zone to a flooded first section 42 on the wire 4 0 was established to allow further maturation and consolidation of the foam.

A continuous bottom cover sheet 4 3 such as of nonwoven Battery scrim having a weight of .8—2 pounds per hundred square feet was laid onto wire 4 0 before the foaming mass cascaded out of the head box 30. Also, preferably, a top sheet 45 of the same scrim -9 — WEW ZEALAW§ — PATENT OFFICE •9MAR1990 Received 22 3 1 2 was overlaid onto the foaming mass. Feeding the top cover sheet 45 under smoothing roll 34 and then under caliper roll 36 provided an intimate contacting of sheet 45 to the core foam mass 47 and assisted in smoothing out the surfaces of the core mass 47.

The froth cascading out of head box 30 was deposited upon and then floated through flooded section 42 for about a second before encountering the vacuum sections 44, 46 and 48. In high vacuum section 44, a vacuum pressure differential equivalent to about 14 inches of mercury was applied across the froth to burst the bubbles and strip water from the wet mass without collapsing the open, voided structure of the mass 47. In vacuum section 46 a pressure differential equivalent to about 14 inches of water was maintained and in vacuum section 48 it was lessened and augumented with positive pressure dry air heated to about 200°F and passed through the mass 47 by blower 50 of drier 49 providing a velocity of 150 cubic feet per minute per square foot of mat surface. The time for a section of froth to pass through section 48 was about ten minutes. Conventional oven drying would have required about 3 hours.

The resulting panel from section 48 was nominal 1/2 inch thiclcness and composed of a center core 47 of uniformly distributed voids averaging about 1/16-1/64 inch diameter between the two scrim cover sheets 43 and 45. The panel had a density of about 6.5 pounds per cub foot and was quite strong although flexible. In fact the core was tested after stripping off the top scrim cover sheet and found to have a modulus of rupture of about 30 pounds per square inch and modulus of elasticity of about 5,700 pounds per square inch.

In further evaluations the amount of perlite was varied between -.about 26% and about 43%. The amount of mxneral wool used was varied in an opposite manner by the. same amount so that the sum of the perlite and mineral wool accounted for 66% by weight of the total solids of the furnish. It was found that increases .5 1 Z in the perlite-to—mineral wool ratio yielded a progressively lighter, weaker and more flexible core in linear fashion. On a weight basis, the strength of the core remained relatively constant when these values were corrected for the changed density of the samples. It was also found that about 2% of the perlite processed through the line became broken and settled out on the bottom facing sheet. Also the flooded section 42 contained about one-half to three-fourths of the polyvinyl acetate added in the mix tank. Of course recycling water from the flooded section 42 to the mix tanks 10 eliminated this potential loss of binder.

Various finished core thicknesses from about 1/8 inch through 1 inch or more may be provided.

EXAMPLE 2 In a series of laboratory evaluations a number of cationic amine-based surfactants were evaluated for floating an expanded perlite containing a generally unfloatable fraction of shattered, crushed., shard amount to about 14% by weight of the perlite sample. The perlite was formed, into a 1% dispersion with water by mixing for one minute in a Lightnin Model V-7 propeller mixer at a mixing setting of 4 0 with loading levels of the surfactant between 0.5 and 1.5% by weight. The following were found to lower the unfloated fraction down to the range of 2-5% unfloated at this surfactant loading level: Primary Amine and Secondary Amine ARMFFN C - Cocoamine ARMEEN SD- Soyamine Alkyl Ether Amine ADOGEN 180 - n ether amine ADOGEN 18 3 - ether amine AROSURF MG—70A3 isodecyl ether amine acetate AROSURF MG-70A5 C,n ether amine acetate AROSURF MG-98A3 Cg_-LQ ether amine acetate Tomah PA-10 hexyloxypropylamine Tomah PA-14 decyloxypropylamine Fatty Diamine AROSURF MC-8 3A tridecyl ether diamine acetate Ethoxvlated Amine AROSURF MG-160 ethoxylation grade cocoamine Tomah E-14-2 ethoxylated fatty amine Quaternary Ammonium Salt ADOGEN 461 cocotrimethyl ammonium chloride // " h /'•V 223123

Claims (16)

WHAT WE CLAIM IS:

1. A methoa of manufacturing a lightweight structural mineral panel on a moving foraminate support wire comprising: A. Forming a dilute fiber furnish in water of mineral fiber and organic resin latex binder; B. Mixing said furnish and a small amount of cationic ^mine-based surfactant frothing aid that contains at least one long chain aliphatic radical of cg~c22 carbon atoms effective to form a transitory froth of air bubbles; C. Depositing the froth on a water flooded section of the support wire; D. After a brief interval of time sufficient for the froth to mature into a homogeneous mass of 1/b4—i/lb inch diameter bubbles, applying a vacuum pressure differential to the froth equivalent to 8-20 inches of mercury to burst the bubbles and strip water from the wet mass; E. Stripping additional water from the wet mass by applying a vacuum pressure differential to the wet mass equivalent to 5-20 inches of water; and F. Drying the wet mass by passing.heated dry air through the wet mass at a rate of 50-350 cubic foot per minute per square foot of surface of the mass.

2. The process ot Claim 1 in which said fiber is a mineral wool.

3. The process of Claim 1 in which said binder is a polyvinyl acetate latex.

4. The process of Claim 1 in which said furnish comprises by weight of total solids 20-65% fiber, 20-705 lightweight aggregate, and 5-50% binder. -13- ;=y- new zealand patent office j " 9 MAR 1990 Received 223123

5. The process of Claim 1 in which said furnish comprises by weight of total solids 30-40% fiber, 30-40% lightweight aggreqate, and . 10-30% binder.

6. The process of Claim 1 in which said furnish comprises by weight of total solids 20-65% mineral wool, 20-70% expanded perlite and 5-30% polyvinyl acetate.

7. The process of Claim 1 in which in step D brief pulses of high vacuum pressure are applied to the^fogth.

8. The process of Claim 1 in which in step D the vacuum pressure is equivalent to 8-20 inches of mercury.

9. The process of Claim 1 in which in step E the vacuum pressure is equivalent to 5-20 inches of water.

10. The process of Claim 1 in which in step F heated dry air is provided at a rate of 50-350 cubic feet per minute of air per square foot of surface area of the mass.

11. The process of Claim 1 in which said surfactant is a quaternary ammonium compound.

12. The process of Claim 1 in which said surfactant is a quaternary ammonium chloride.

13. The process of Claim 1 in which said surfactant is tri-methyl long chain aliphatic (ci2~C22^ quaternary ammonium salt.

14. The process of Claim 1 in which said surfactant is coco-trimethyl ammonium chloride.

15. The method of claim 1 wherein: In step A. said dilute fiber furnish formed in water includes, by weight of total solids 20-65* mineral fiber, 20-70% expanded perlite, and 5-302; polyvinyl acetate;;In step B. said furnish is mixed with 0.22 to 2.5% by weight of said cationic amine-based surfactant frothing aid;;In step F. said dry heated air is passed through said mass at a rate;223123;of 150-350 cubic feet per minute of air per square foot surface area of the mass; and further comprising:;In step G. recovering a lightweight of panel having a density of 5-12;pounds per cubic foot.;

16. A method of manufacturing a lightweight structural mineral panel according to any one of claims 1 to 15 substantially as herein described with reference to the accompanying drawings.;*i or 1—' Per ■ .r.w zealand 1h,£nt office "9 MAR 1990 I R^CE/VED