Method of making tough, flexible mats and tough, flexible mats

[0001] The present invention relates to methods for producing fibrous non-woven mats for use in the manufacture of ceiling panels and for other applications where similar requirements exist, and mats thus produced.

Background [0002] US 20031124932 discloses a fibrous nonwoven comprising a fiber blend comprising 5 to 30 percent by weight of polymeric fibers and 70 to 95 percent by weight of glass fibers that are bonded together with an adhesive that is at least partially cured.

[0003] EP-A-0583086 discloses an aqueous binder comprising a mixture of water and a resin made from a polyacrylic acid homol or copolymer and a polyol. The binder is used in nonwovens containing heat resistant fibers, such as glass fibers or polyester fibers.

[0004] Ceiling panels are commonly used to make a ceiling in a building and can be made of various materials including mineral fibers, cellulose fibers, glass fiber, wool, metal and plastic. It is usually preferred that such ceiling panels exhibit good structural properties, such as rigidity and resilience, as well as good fire resistance characteristics. In some applications, it would also be beneficial if the ceiling panel had sound-absorbing properties.

[0005] It would be beneficial to provide a ceiling panel exhibiting excellent structural properties, fire resistance and soundproofing, and also very light. In addition, to facilitate the reduction of transport and storage costs, it would be even more beneficial if the ceiling panels could be pressed to a fraction of their normal size for packaging and then allow their resilient return to normal size for installation and operation. Such a ceiling panel was designed by others using a fibrous non-woven mat, see published US Patent Application No. 20020020142, filed April 23, 2001. Unfortunately, ordinary fibrous non-woven mats did not meet all the requirements of this design, according to which the mat should be able, after being cut, folded and pressed, to resiliently return to its original shape and orientation while avoiding the release of toxic gases when exposed to fire. The DURAGLAS ™ 8802 mat from Johns Manville, bonded with acrylic plastic, wet layered, a mixture of fiberglass and polyester, did not perform satisfactorily in such a ceiling tile due to excessive flammability and excessive bending at ambient temperatures. The present invention overcomes these problems and meets this need for a suitable mat for making a ceiling tile according to the aforementioned published US patent application

Summary of the Invention [0006] The present invention relates to a method of making a fibrous non-woven mat having unique properties in terms of bending and recovery, especially after cutting and folding. The method includes:

EP 1 541 763 B1

a) dispersing the fibers to form a dispersion, which dispersion comprises glass fibers and synthetic polymer fibers,

b) applying the dispersion onto a moving permeable forming belt to form a fibrous web,

c) applying the aqueous resin binder to the wet web and removing any excess binder to obtain the desired binder content in the wet web, and

d) drying the wet web and curing the resin in the binder to form a resin bound fibrous non-woven fabric, the improvement comprising:

e)

i) a fiber dispersion containing about 2 to about 35 weight percent polyester fibers and about 98 to about 65 weight percent glass fibers, and ii) using as a water binder a mixture comprising water and a resin made from a polyacrylic acid polyol homopolymer or copolymer.

[0007] According to a preferred aspect, the present invention provides a method of making a fibrous non-woven mat with good strength and return to normal after cutting and folding, comprising:

a) dispersing fibers including polymeric fibers and glass fibers in an aqueous mixture to form a dispersion,

b) dehydrating this mixture on a moving forming sieve to form a wet fibrous web,

c) applying the aqueous resin binder to the wet web and removing excess binder to obtain the desired binder content in the wet web, and

d) drying the wet web and at least partially curing the resin in the binder to form a fibrous non-woven resin-bound mat, wherein;

i) the dispersion contains about 5 to about 20 weight percent synthetic polymer fibers and about 95 to about 80 weight percent glass fibers, based on the total weight of the fibers in the dispersion, and ii) the aqueous binder contains a mixture of water and a resin made from a homopolymer or copolymer polyacrylic acid and polyol and is present in the final dry mat in an amount between about 15 and about 25 weight percent based on the weight of the dry mat.

[0008] The ratio of glass fibers to polyester fibers may be as outlined above, and is preferably about 5 to about 20 weight percent. polyester fibers to about 95 to about 80 weight percent glass fibers, and most preferably about 8 to about 16 weight percent polyester fibers and about 92 to about 84 weight percent glass fibers. The binder content may vary up to about 35 weight percent. ready-made dry mat and from about 10 percent by weight, except that about 20 percent by weight is most preferred, although the binder content is in the range of 15-25 percent by weight is beneficial. Fibrous non-woven mats containing a blend of glass fibers and polymer fibers as described above and bound by a hardened binder, as well as the amounts described above, are also encompassed by the present invention. Although an aqueous dispersion of these fibers is preferably prepared and the web is formed in a wet molding machine such as an oblique screen machine, Dry Laid machines and processes including continuous fiber strand forming processes can also be used to produce the mats of the present invention.

[0009] The mats of the present invention comprise a fiber blend containing about 98 to about 65 weight percent, preferably about 80 to about 95 weight percent, and most preferably about 92 to about 84 weight percent. glass fibers and about 2 to about 35 weight percent, preferably 5 to about 20 weight percent, and most preferably about 8 to about 16 weight percent. synthetic polymer fibers in a nonwoven web, the fibers in the web being bonded together with a hardened binder that contains, prior to drying and curing, a homopolymer or copolymer of polyacrylic acid and polyol. The amount of binder in the finished mat is preferably in the range of about 10 to about 35 weight percent, based on the weight of the dry finished mat, more preferably in the range of about 15 to about 32 weight percent, and most preferably about 25 +/- 5 weight percent. The mat also shows a perfect return to normal after cutting and folding. It can be folded many times, kept folded for a long time and will continue to exhibit a resilient return to portrait orientation in the ceiling panel web of the type disclosed in published US Patent Application No. 20020020142.

[0010] It has been found that as a result of combining the use of a blend of glass fibers and polymer fibers with a binder made of a polyacrylic acid homolymer or copolymer, a fibrous non-woven mat with unexpectedly high tensile strength and recovery after cutting and folding, as well as unexpected high fire resistance when taking into account the amount of oxygen in the binder. In the manufacture of mats for use in the compressible ceiling panel mentioned above, preferably the degree of mat cure, i.e. its wet tensile strength divided by its dry tensile strength, multiplied by 100, is at least 35 percent, more preferably at least 40 percent. The mats of the present invention meet the National Fire Protection Association's (NFPA) Method # 701 Flammability Test. Taber stiffness of such mats is above about 40 gram-centimeters, preferably above about 50, and most preferably above about 55. The air permeabilities of the mats are preferably in the range of about 14,158 m³/ min / 0.093 m² (500) to approximately 19,822 m³/ min / 0.093 m²(700 cubic feet / minute / square foot). When the term "substantially free of phenol-formaldehyde resin and urea" is used, this means that the mat does not contain them at all or the content is so small that the mats meet the NFPA flammability test.

[0011] By modifying the above method, a mat with different characteristics is produced in the drying / curing step. The modification consists in lowering the temperature in the furnace, so that the binder in the mat is cured only to the state "B". This can be achieved by heating the mat in the oven to only about 121.1 ° C (250 degrees F). Such modified mats can be thermoformed to the desired shape or folded and then heated to completely cure the binder. The desired mat shape will then be preserved. Such molded shapes can have many applications, such as preforms for SRIM (structured reactive injection) and laminating processes, pleated filters and many other applications.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0012] The mat according to the invention can be used for the production of ceiling panels, harmonica filter products and other products requiring a fibrous mat with good resilience, recovery characteristics, flexibility, strength and integrity after cutting and folding. Such mats preferably contain about 65 to about 90 weight percent. fiber and about 10 to about 35 weight percent binder. The fibers are a mixture of polymeric fibers and inorganic fibers such as

EP 1 541 763 B1 like glass or carbon fibers. The blend may contain about 2 to about 35 weight percent polymer fibers, and inorganic fibers may be present in the fibrous web in an amount between about 98 weight percent. and 65 weight percent, based on the weight of the fibers in the mat. Preferably, the polymer fibers, such as polyester fibers, are present in an amount between about 5 and about 20 weight percent, most preferably from about 8 to about 16 weight percent, such as about 12 weight percent.

[0013] The polymer fibers are preferably polyester fibers, but it can also be any polymer fiber such as polypropylene, nylon, PBT, polyacrylonitrile, polybenzimidazole and other known polymer fibers with similar resilience and high enough softening temperature to withstand the temperatures used in the process of making the mat, and in subsequent processes in which the mats are used. The preferred diameter of polyester fibers is about 1.5 denier, except that both length and diameter can be changed, provided that the aspect ratio, length to diameter ratio, remains within the range suitable for satisfactory dispersion of the fibers in the aqueous glass fiber suspension suitable for producing a web in a wet film forming machine, such as a diagonal screen forming machine, such as VOITH HYDROFORMER® or SANDY HILL DELTAFORMER®. The preferred length of 1.5 denier polyester fibers is 0.635 cm (0.25 inches).

[0014] The denier of the polyester fibers may be from about 0.8 to about 6 deniers, and to obtain a good dispersion, the fiber length will often vary depending on the denier, as is well known. Synthetic polymer fibers may or may not be longer when the denier is increased. In the event of tangling and / or entanglement causing the formation of tufts or tufts during dispersion, the length of the synthetic polymer fibers must be reduced to achieve good dispersion. [0015] Glass fibers, preferably E glass fiber 2.54 cm (one inch) long and 16 microns in diameter, with chemical sizing applied, are well known. One of the fiber products preferred for use in accordance with the invention is M117, a wet cut fiber product available from Johns Manville Corporation, Denver, CO, but any type of fiberglass of length and diameter suitable for processes can be used Wet laid. Any type of permanent glass fiber can be used, such as A, C, S, R, E and other types of glass fibers. Preferably, the average diameter of the glass fibers will be from about 8 to about 20 microns. Preferably, the fiber length for glass fibers will be from about 0.635 cm (0.25) to about 3.81 cm (1.5 inches), preferably from about 1.27 cm (0.5) to about 3.175 cm (1, 25), and most preferably from about 1.778 cm (0.7) to about 2.794 cm (1.1 inches).

[0016] The webs of fiber blends are bonded together using an aqueous binder composition applied with a curtain coater, by dipping and extruding, roller coating or other known impregnation method in a known manner, and the resulting wet saturated binder lying on a wire mesh or sieve is passed through through one or more vacuum chambers to remove enough binder to achieve the desired binder content in the mat. The level of binder in the mats of the invention may be from about 10 to about 35 weight percent. the finished dry mat, preferably about 15 to about 30 weight percent, and most preferably from about 20 to about 30 weight percent, such as about 25 +/- 3 weight percent. The binder composition is cured by applying heat, i.e. the binder composition is a thermosetting composition.

[0017] The binder composition comprises a polyacrylic acid homopolymer or copolymer. Preferably, the average molecular weight of the polyacrylic acid polymer is below 10,000, more preferably below

5000, and most preferably about 3000 or less, with about 2000 being preferred. Application

The low molecular weight polyacrylic acid polymer in the low pH binder formulation may result in the final product showing excellent structure recovery and stiffness. The binder formulation may also contain at least one additional polycarboxylic polymer, such as, for example, the polycarboxylic polymer disclosed in US Patent No. 6,331,350.

[0018] The binder composition also contains a polyol containing at least two hydroxyl groups. The polyol is preferably sufficiently volatile so that it can substantially remain available for reaction with the polyacid in the composition during its heating and curing. The polyol may be a compound with a molecular weight below about 1000, containing at least two hydroxyl groups, such as, for example, ethylene glycol, glycerol, pentaerythritol, trimethylolpropane, sorbitol, sucrose, glucose, resorcinol, catechol, pyrogallol, glycolated ureas, 1, 4-cyclohexanediol, diethanolamine, triethanolamine and certain reactive polyols, such as, for example, -hydroxyalkylamides, such as, for example, bis [N, N-di (hydroxyethyl)] adipamide, which can be prepared according to US Patent Nos. 6331350 and 4076917. The polyol can be an addition polymer containing at least two hydroxyl groups, such as, for example, polyvinyl alcohol, partially hydrolyzed polyvinyl acetate and homopolymers or copolymers of hydroxyethyl (meth) acrylate, (meth) hydroxypropyl acrylate and the like. Most preferably, the polyol is triethanolamine (TEA).

[0019] The ratio of the number of carboxyl equivalents, anhydride or polyacid salt to the number of hydroxyl equivalents in the polyol may be about 1 / 0.01 to about 1/3. Preferably there is an excess of carboxyl equivalents, anhydride or their polyacid salt to hydroxyl groups in the polyol, for example from about 1 / 0.4 to about 1/1, more preferably from about 1 / 0.6 to about 1 / 0.8, and most preferably from about 1 / 0.65 to about 1 / 0.75. A low ratio, e.g. about 0.7: 1, is advantageous when combined with a low molecular weight polycarboxylic polymer and a low binder pH.

[0020] The binder composition may also contain a catalyst. Preferably, the catalyst is a phosphorus-containing accelerator, which may be a compound with a molecular weight below about 1000. For example, the catalyst may include an alkali metal polyphosphate, an alkali metal dihydrogen phosphate, poly phosphoric acid, alkylphosphinic acid, and mixtures thereof.

[0021] Additionally or alternatively, the catalyst may comprise an oligomer or polymer containing phosphorus-containing groups, such as, for example, acrylic and / or maleic acid addition polymers prepared in the presence of sodium hypophosphite, addition polymers made from ethylenically unsaturated monomers in the presence of phosphate salts as transfer agents or chain terminating addition polymers containing acid-functional monomer residues such as, for example, copolymerized phosphoethyl methacrylate and similar phosphonic acid esters and copolymerized vinylsulfonic acid monomers and their salts and mixtures thereof.

[0022] The catalyst may be used in an amount of from about 1% to about 40%, by weight based on the total weight of the polyacrylic acid polymer and polyol. Preferably, the catalyst is used in an amount of from about 2.5% to about 10%, by weight based on the total weight of the polyacrylic acid polymer and polyol.

[0023] The binder formulation may also contain processing aids such as, for example, emulsifiers, pigments, fillers, migration aids, curing agents, coalescing agents, wetting agents, biocides, plasticizers, organic silanes, anti-foaming agents, coloring agents, waxes and antioxidants. The binder composition can be prepared by mixing the polymer in the form of a polyacrylic acid and a polyol together. Mixing techniques known in the art can be used to achieve such mixing.

[0024] Preferably, the pH of the binder composition is low, for example, about 3 or below, preferably about 2.5 or below, and most preferably about 2 or below. The pH of the binder can be adjusted by adding a suitable acid, such as sulfuric acid. Such a low pH binder can provide processing advantages, also providing a product that exhibits excellent recovery and rigidity properties. Examples of processing advantages include lowering the temperature or shortening the curing time.

[0025] To increase the fire resistance of the ceiling panel, flame retardant material may be used. The flame retardant material can be introduced into the ceiling panel by, for example, admixing with an aqueous binder. Any flame retardant material suitable for use in a fiber mat may be used, including, for example, organic phosphonate. Such organic phosphonate is available from Rhodia, based in Cranbury, New Jersey, under the trade name Antiblaze NT.

[0026] The glass and polyester fibers that constitute the base material can be formed into a structure suitable for use as a ceiling panel, such as a mat. Any suitable fiber forming agents can be used. For example, the fibers may be formed by the methods described in US Patent Nos. 5,824,013, 5,772,846, 4,112,174, 4,681,802, and 4,810,576.

[0027] Advantageously, a dilute suspension of glass and polyester fibers can be made and deposited on an inclined moving wire forming screen to dehydrate the slurry and form a wet non-woven fiber mat. For example, the Hydroformer available from Voith-Sulzer based in Appleton, Wisconsin or Deltaformer available from Valmet / Sandy Hill based in Glenns Falls, New York may be used. Other machines for wet mats can be used.

[0028] After the wet, uncured web has been formed, it is preferably transferred to a second moving screen passing through a binder application station where the aqueous binder described above is applied to the mat. The binder can be applied to the structure by any suitable means including, for example, air or airless spraying, hardfacing, saturation, roller coating, pour coating, dutch deposition, coagulation or dipping and squeezing. [0029] Excess binder, if present, removes to obtain the desired level of binder in the mat. The web is formed and the binder level is adjusted to reach the binder content in the finished dry mat as outlined above and produce the product in the form of a dry mat preferably having a basis weight between about 861.83 g / 9.29 m² (1.9 pounds / 100 square feet) to about 1202.02 g / 9.29 m² (2.65 lb / 100 square feet), preferably from about 907.19 g / 9.29 m2 (2 lb / 100 square feet) to about 1156.66 g / 9.29 m2 (2.55 lb / 100 ft square meters), such as about 1,111.30 g (2.45) +/- 340,195 g / 9.29 m2 (0.75 pounds / 100 square feet). The wet mat is then preferably transferred to a movable oven belt, which transports the wet mat through a drying and curing oven, such as, for example, an oven with an air passage, with a blast of air from below or with a blow of air. If necessary, the wet mat can be slightly compacted before curing to get the finished product with the specified thickness and surface finish.

[0030] In the oven, the bound web can be heated to achieve drying and / or curing to form a dry mat bound with cured binder. For example, heated air can be passed through the mat to remove water and cure the binder. For example, the heat treatment can be carried out at 204.4 ° C (400 F.) or higher, but preferably the mat is at or near hot air temperature for only a few seconds at the end of the oven. The duration of the heat treatment can be any suitable time, such as from about 3 seconds to 5 minutes or

EP 1 541 763 B1 longer, but usually shorter than 3 minutes, preferably shorter than 2 minutes and most preferably shorter than 1 minute. The average specialist in the field, based on the present disclosure, is able to change curing conditions to optimize or modify the mat so that it has the required properties. [0031] Drying and curing operations can be carried out in two or more different stages. For example, the binder composition may first be heated at a temperature and time sufficient for substantial drying, but not until the composition has cured, and then heated for a second period at a higher temperature and / or for a longer time to bring about cure. This procedure, known as "stage B," can be used to obtain a binder-treated nonwoven, for example, in the form of a coil that can be cured at a later stage, with or without molding or shaping to achieve a specific configuration, simultaneously with the process curing.

[0032] The following examples are provided for illustrative purposes and in no way limit the scope of the present invention.

EXAMPLE 1 [0033] The fibers were dispersed in ordinary sieve water in a known manner to form a suspension that contained 90% by weight 2.54 cm (1 ") glass fibers (John Manville's M117 fiber) with an average fiber diameter of about 16 microns, and 10% polyester fiber 1.5 to 0.635 cm (1/4 ") in length. The wet web was formed from a slurry using a Voith Hydroformer® apparatus. The wet web was then saturated with a polyacrylic acid / polyol binder composition using a curtain coating machine and excess aqueous binder was removed until the binder content in the finished mat was about 25%, based on the weight of the finished dry mat. The binder formulation is available from Rhom & Haas based in Philadelphia, PA under the trade name TSET ™. The bound mat was then heat treated with a peak temperature of 204.4 ° C (400 degrees F.) for about 3 seconds to dry the mat and cure the binder. The weight of this mat was about 1,111.30 g / 9.29 m² (2.45 pounds / 100 square feet) and had the following characteristics:

Thickness 1.0668 mm +/- 0.0762 mm (42 +/- 3 mils)

Tensile strength - machine direction = 40.8233 kg / width 7.62 cm (90+ pounds / 3 inches) Transverse direction to the machine direction -27.2156 kg / width 7.62 cm (60+ pounds / 3 inches) [ [0034] This mat behaved satisfactorily as cut and folded vertical connecting bands between the exposed mat and the ground mat in the production of ceiling panels manufactured in accordance with published US Patent Application No. 20020020142. This mat showed excellent recovery after incision and folding. It can be folded many times, kept folded for extended periods, and should still exhibit a resilient return to portrait orientation in the vertical bands of the above-mentioned ceiling panel.

EXAMPLE 2 [0035] The same fiber types were dispersed in ordinary sieve water in a known manner to form a slurry that contained 88 wt.% E glass fibers 2.54 cm (1 inch) with an average fiber diameter of about 16 microns and 12% polyester fiber 1.5 up to 0.635 cm (1/4 ") long. Wet ribbon

EP 1 541 763 B1 was formed from a slurry using a Voith Hydroformer® apparatus. The wet web was then impregnated with TSET ™, a polyacrylic acid / polyol aqueous binder resin composition, using a curtain coating machine, and excess aqueous binder removed to achieve a binder content in the finished mat of about 28%, based on the weight of the finished dry mat. The bound mat was then subjected to heat treatment with a peak temperature of 170 degrees C. for 5-15 seconds to dry the mat and cure the binder. The weight of this mat was about 1179.34 g / 9.29 m²(2.60 pounds / 100 square feet) and had the following characteristics:

Thickness - 1.0922 mm +/- 0.127 mm (43 +/- 5 mils)

Tensile strength - machine direction - 40.8233 kg / width 7.62 cm (90+ pounds / 3 inches) Transverse direction to the machine direction -27.2156 kg / width 7.62 cm (60+ pounds / 3 inches) [ [0036] This mat behaved satisfactorily as cut and folded vertical connecting webs between the exposed mat and the ground mat in the production of ceiling panels manufactured in accordance with published US Patent Application No. 20020020142. This mat showed excellent recovery after incision and folding. It can be folded many times, kept folded for extended periods, and should still exhibit a resilient return to portrait orientation in the vertical bands of the above-mentioned ceiling panel.

EXAMPLE 3 [0037] The same types of fibers were dispersed in ordinary sieve water in a known manner to form a slurry that contained 92% by weight 2.54 cm (1 inch) glass fibers with an average fiber diameter of about 16 microns and 12% fiber polyester 1.5 to 0.635 cm (1/4 ") long. The wet web was formed from a slurry using a Voith Hydroformer® apparatus. The wet web was then saturated with TSET ™, a polyacrylic acid / polyol aqueous binder composition, using a curtain coating machine, and excess aqueous binder was removed to reach the binder content in the finished mat of about 28%, based on the weight of the finished dry mat. The bound mat was then heat treated with a peak temperature of about 204.4 ° C (400 degrees F) for about 3 seconds to dry the mat and cure the binder. The weight of this mat was approximately 1043.26 g / 9.29 m2 (2.30 lb / 100 sq ft) and had the following properties:

Thickness - 1.016 mm +/- 0.127 mm (40 +/- 5 mils)

Tensile strength - machine direction - 40.8233 kg / width 7.62 cm (90+ pounds / 3 inches) Transverse direction to the machine direction -27.2156 kg / width 7.62 cm (60+ pounds / 3 inches) [ [0038] This mat behaved satisfactorily as cut and folded vertical connecting webs between the exposed mat and the ground mat in the production of ceiling panels manufactured in accordance with published US Patent Application No. 20020020142. This mat showed excellent recovery after incision and folding. It can be folded many times, kept folded for extended periods, and should still exhibit a resilient return to portrait orientation in the vertical bands of the above-mentioned ceiling panel. The mats of the present invention also show surprisingly high fire resistance when considering the oxygen content of the binder used in these mats. Such mats meet the NFPA flammability test.

[0039] By modifying the above method, a mat with different characteristics is produced in the drying / curing step. The modification consists in lowering the temperature in the furnace so that the binder in the mat is cured only to the state "B". This can be achieved by heating the mat in the oven to only about 121.1 ° C (250 degrees F). The time at reduced maximum temperature can be changed, but usually the time is about 30 seconds. Such modified mats can be thermoformed to the desired shape or folded and then heated to completely cure the binder. The desired mat shape will then be preserved. Such molded shapes can have many applications, such as preforms for SRIM (structured reactive injection) and laminating processes, accordion filters and many other applications.

[0040] Although the invention has been described with reference to preferred embodiments, it will be appreciated that variants and modifications may be made as will be apparent to those skilled in the art. To simply illustrate the variants falling within the scope of the present invention, carbon fiber can be incorporated into the binder to affect the color, as do titanium dioxide particles when a white mat is desired. In addition, flame retardants such as organic phosphates such as ANTI-BLAZETM NT from Rhodia, Cranburry, NJ can be included in the aqueous binder composition. Such variants and modifications should be considered as falling within the scope and scope of the appended claims.