Sprayable liner for supporting the rock surface of a mine

Abstract

The invention provides a liner which is the product of reaction of a (a) hydrophilic prepolymer bearing isocyanate groups; and (b) a water-borne polyurethane dispersion, the polyurethane bearing groups that are reactive to isocyanate groups.

Description

FIELD OF THE INVENTION

[0001] The invention relates to an elastomeric polymeric film that can be used, for example, to assist in protecting from rock bursts in a mine. The invention also relates to a method for providing support to rock surfaces.

BACKGROUND OF THE INVENTION

[0002] Underground mining requires support of the roof and walls of the mine to prevent injury due to rock bursts. Several materials have been used for this purpose, including shotcrete, wire mesh, as well as sprayable liner compositions. Both shotcrete and wire mesh are difficult to handle and apply in the underground mines, more particularly in deep mining applications. The application of shotcrete/gunite is labor intensive and the linings are brittle, are lacking in significant tensile strength, and toughness, and are prone to fracturing upon flexing of the rock during mine blasting. More significantly, shotcrete/gunite develops its desired minimum strength of 1 Mpa only slowly. The sprayable liners that develop strength quickly are toxic during spray application, whereas, liners that are have low toxicity during spray application are not flexible enough and require more than four hours to develop the minimum strength desired to be useful in the mining environment. As such a tough, flexible, quick strength developable liner system having low toxicity is in need.

[0003] Calder et al, in U.S. Pat. No. 5,716,71 1 have described a two part polyurethane composition preferably containing a layer of inorganic material.

[0004] Sengupta et al. in Canadian Patent Application No. 2,107,496 describes an in situ geosynthetic barrier as a secondary containment barrier for a petroleum-oil-lubricant facility.

[0005] JP 57104798, assigned to Takenaka Komuten, describes a water barrier structure for tunnels using water reactive grout composed of isocyanate and curing agent.

[0006] DE 3343212 assigned to MC-Bauchemie Muller describes two component polyurethane sealant linings for tunnels based on a sprayable polyether and liquid crude isocyanate.

[0007] U.S. Pat. No. 4,142,030, assigned to Bayer, describes a inorganic-organic polyurethane-poly-silica gel composite which is made by mixing an organic polyisocyanate, an aqueous silicate solution and/or an aqueous silica sol and an organic compound with at least one NCO-reactive H-atom and at least one ionic and/or non-ionic hydrophilic group allowing the resultant system to react completely, which can be sprayed on walls in mines to prevent accidents.

[0008] Gasper in U.S. Pat. No. 4,476,276 has described a sealing composition containing up to 60% by weight fillers by reacting water-soluble polyurethane prepolymer with water containing latex that is capable of preventing leakages.

[0009] The effect of spraying either monomeric polyisocyanate and/or a polymer containing a high percent (about 8 to 15% or more) of isocyanate groups and reacting these compounds with either a hydroxy- or amine-containing polyol, as described in the prior art, especially in a confined area, such as an underground mine, can be very serious from a toxicity standpoint, as some isocyanate is released into the atmosphere and can be ingested. To minimize ingestion a water curtain is normally provided, which is an additional, undesirable step.

SUMMARY OF THE INVENTION

[0010] The present invention minimizes the above-described toxicity effects by lowering the amount of free isocyanate groups in the composition used to form a coating on a surface, and by utilizing a large amount of water-borne polyurethane dispersion. In addition, the method of the present invention does not generate measurable heat. This result, again, is advantageous, as heat encourages volatilization, and consequent ingestion of isocyanate and of any other toxic agents present.

[0011] The invention provides a liner which is the product of reaction of:

[0012] (a) a hydrophilic prepolymer bearing isocyanate groups; and

[0013] (b) a water-borne polyurethane dispersion, the polyurethane bearing groups that are reactive to isocyanate groups.

[0014] In another aspect, the invention provides a method for providing a surface with a liner, the method comprising

[0015] (I) applying to the surface

[0016] (a) a hydrophilic prepolymer bearing isocyanate groups, and

[0017] (b) a water-borne polyurethane dispersion, the polyurethane bearing groups that are reactive to isocyanate groups; and

[0018] (II) allowing the applied components (a) and (b) to react to form the liner.

DETAILED DESCRIPTION OF THE INVENTION

[0019] Preferred features of the polyurethane used in component (b) include (i) that it has a molecular weight in the range of from about 100,000 to about 700,000; (ii) that it is in the form of particles of a size from about 30 to about 1000 nm, more preferably from about 30 to about 500 nm; (iii) that a film prepared from the polyurethane has a modulus of at least about 6.89 MPa at 100% elongation, more preferably about 13.79 MPa at 100% elongation, and most preferably about 20.69 Mpa at 100% elongation; (iv) that a film prepared from the polyurethane has a value of Tg greater than about 40° C., more preferably greater than about 50° C.; and (v) that the polyurethane is used as a dispersion in water containing no co-solvent.

[0020] The groups on the polyurethane which are reactive to isocyanate groups are preferably alcohol, or amino groups, more preferably primary amino groups.

[0021] The product of the reaction of hydrophilic prepolymer and the polyurethane dispersion is a gelatinous mass, as the hydrophilic moieties of the hydrophilic prepolymer absorb water that is the vehicle of the polyurethane. This gelatinous mass is sometimes referred to as a gel or hydrogel, and it can be used, for example, as a liner in a mine. Reaction times to convert the prepolymer to the gel can be on the order of less than a minute to several hours. The formed gel generally develops a minimum strength of about 1 Mpa within about four hours, preferably within about 2-4 hours. The tensile strength of the liner after it is completely formed (fully cured) is preferably about 6-12 Mpa, more preferably about 10-12 Mpa at room temperature. When the composition of the present invention is applied at colder temperatures or under high humidity conditions, longer periods of time can be required for the composition to become fully cured.

[0022] The weight ratio of the component (a) to component (b) is preferably in the range of from about 1:3 to about 1:10, more preferably from about 1:4 to about 1:7 and most preferably from about 1:5 to about 1:6. However, to increase the hydrophobicity of the resulting liner it is desirable to use as little of component (a) as possible.

[0023] Some of the isocyanate groups of the hydrophilic prepolymer can react with water to form carbamic acid moieties which immediately decarboxylate to generate amines. These amines can then react with other isocyanate groups to lead to crosslinking of the prepolymer. Water is absorbed into the ethylene oxide matrix of the product leading to formation of the gel. The liner of the present invention is preferably gas-tight and flexible. The liner of the invention preferably has an elongation at break of from about 100 to about 1000%, more preferably from about 100 to about 800%, most preferably from about 200 to about 400%. The resulting liner is, therefore, preferably, a water-insoluble, cross-linked, water-containing gelatinous mass having a high degree of elasticity.

[0024] The liners produced according to the invention can be used to support rock surfaces in a mine. For such applications, the liners are preferably thick, around 0.5 mm to 6 mm, when formed completely and after removal of aqueous solvent.

[0025] Water-borne polyurethanes and processes for their preparation are known. Examples of such water-borne polyurethanes and such processes are described in “Advances in Urethane Science and Technology”, Waterborne Polyurethanes; Rosthauser, James W.; Nachtkamp, Klaus; 1989, Vol. 10, pp. 121-162, Mobay Corp., Pittsburgh, Pa., the description of which is incorporated herein by reference. The water-borne polyurethane dispersion can be made, for example, according to one of the methods described in this reference. Other suitable examples of water-borne polyurethane dispersions and processes for their preparation are described in U.S. Pat. No. 5,312,865; U.S. Pat. No. 5,555,686; U.S. Pat. No. 5,696,291; U.S. Pat. No. 4,876,302, and U.S. Pat. No. 4,567,228. The disclosures of these patents are incorporated herein by reference. A preferred method for forming the water-borne polyurethane dispersion is the prepolymer method.

[0026] The water-borne polyurethane dispersion is preferably hydrophobic in nature to reduce or prevent hydrolysis of its polymeric backbone. The hydrolytic resistance of the polyurethane polymer can depend on the backbone of the polyol that is used as a precursor in its synthesis. Normally adipic acid based polyester polyols are more resistant to hydrolysis than phthalate-based polyester polyols. The polyurethane dispersions made from prepolymers having polyols based on polycarbonate or dimer acid diol have higher hydrolytic resistance.

[0027] A suitable water-borne polyurethane polymer is NeoPac™ 9699, a water-borne urethane/acrylic based polyurethane (total solids 40%; viscosity 100 cps at 25° C.; elongation 160%, 100% modulus, 26.2 MPa; Tensile, PSI 4400) from Neoresins, Ontario, Canada; HD 2334, a polyether water-borne urethane dispersion (Solids 45%; elongation 200%; 100% modulus; 17.24 MPa, tensile; psi 3500) from C. L. Hauthaway & Sons Corporation, Mass., USA; Hybridur™ 540, a polyester-acrylate based urethane dispersion from Air Products, USA; and Hybridur™ 580, an acrylic-urethane dispersion, from Air Products & Chemicals Inc., Pa., USA.

[0028] The amount of water present in these commercially available polyurethane dispersions ranges from about 50 to 65% by wt. This range is normally satisfactory for use in the invention, and no need is seen to depart from this range. Use of amounts of water outside of this range are, however, within the scope of this invention, and the percentage of water can be readily adjusted.

[0029] Other water-borne non-polyurethane polymeric emulsions such as emulsions of acrylic, acrylic styrene, styrene butadiene, vinyl acetate, or acrylic polymers that form a continuous liner film may replace part of the polyurethane polymer dispersion. Examples include Acronal™ S-305D, a butyl acrylate/styrene copolymer, from BASF, and Rhoplex™ 2848 and Rhoplex™ 2438 (acrylic emulsions from Rohm & Haas Company). However, these emulsions generally reduce the initial (4 hrs) and ultimate tensile strengths, and generally cannot provide the desired strength of the resulting liner of at least about 1 Mpa tensile strength within about 4 hours, preferably within about two hours.

[0030] The hydrophilic prepolymer is preferably a urethane-containing polymer bearing isocyanate groups and can be formed by reacting a hydrophilic polyol with an excess of polyisocyanate. This step is followed by purifying the hydrophilic prepolymer of unreacted polyisocyanate or, preferably, by quenching the unreacted polyisocyanate with a compound that is reactive to isocyanate groups, so that the prepolymer contains less than about 0.5 weight percent of unreacted polyisocyanate.

[0031] Unless the amount of unreacted polyisocyanates present in the mixture containing the hydrophilic prepolymer is lowered through a purification step, or effectively reduced by, for example, quenching the isocyanate groups of the polyisocyanates, the presence of the polyisocyanate can result in considerable toxicity. It was surprisingly found that by removing or quenching the unreacted polyisocyanates according to the process of the present specification, liners of superior strength were produced. Other advantages include reduced toxicity, and lowered heat generation.

[0032] The hydrophilic prepolymer can be purified from unreacted monomeric polyisocyanate by processes and/or methods using, for example, falling film evaporators, wiped film evaporators, distillation techniques, various solvents, molecular sieves, or organic reactive regent such as benzyl alcohol. U.S. Pat. No. 4,061,662 removes unreacted tolylene diisocyanate (TDI) from an isocyanate prepolymer by contacting the prepolymer with molecular sieves. U.S. Pat. Nos. 3,248,372, 3,384,624, and 3,883,577 describe processes related to removing free isocyanate monomers from prepolymers by solvent extraction techniques. It is also possible to distill an isocyanate prepolymer to remove the unreacted diisocyanate according to U.S. Pat. No. 4,385,171. It is necessary to use a compound which is only partially miscible with the prepolymer and has a higher boiling point than that of the diisocyanate to be removed. U.S. Pat. Nos. 3,183,112, 4,683,279, 5,051,152 and 5,202,001 describe falling film and/or wiped film evaporation. According to U.S. Pat. No. 5,502,001, the residual TDI content can be reduced to less than 0.1wt. % by passing the prepolymer at ˜100° C. through a wiped film evaporator, while adding an inert gas, especially nitrogen, to the distillation process to sweep out the TDI. The disclosures of all of these references are incorporated herein by reference.

[0033] Unreacted polyisocyanates can be quenched with an amine, preferably a secondary amine, more preferably a monofunctional secondary amine, an alcohol, for example, an arylalkyl alcohol, preferably in the presence of a tertiary amine catalyst, such as, triethylamine, or an alkoxysilane bearing a functional group that is reactive to isocyanate groups, for example, an amine. The unreacted polyisocyanates are more preferably reacted with an arylalkyl alcohol, such as benzyl alcohol, used with a tertiary amine. The unreacted polyisocyanates are most preferably reacted with an arylalkyl alcohol, such as benzyl alcohol used in conjunction with an alkoxysilane bearing a secondary amino group. The unreacted polyisocyanates can be quenched without substantially affecting the terminal isocyanate groups from the hydrophilic prepolymer.

[0034] Examples of suitable amines include N-alkyl aniline, for example, N-methyl or N-ethyl aniline and its derivatives, diisopropylamine, dicyclohexylamine, dibenzylamine, or diethylhexylamine.

[0035] Example of suitable alcohols include arylalkyl alcohols, for example, benzyl alcohol, and alkyl-substituted derivatives thereof.

[0036] Examples of suitable silanes include Dynasylan™ 1189 (N-(n-butyl)-aminopropyltrimethoxysilane, Dynasylan™ 1110 (N-methyl-3-Aminopropyltrimethoxysilane), and Silquest™ A-1170 (bis (trimethoxysilylpropyl)amine available from Osi Co., and Silquest™ Y-9669 (N-phenyl)-gamma-aminopropyltrimethoxysilane.

[0037] When alcohols are used to quench the unreacted polyisocyanates, the application of heat is generally required to reduce the reaction time. Reactions with amines can be conducted, however, at ambient temperature for a relatively shorter period of time.

[0038] The amount of unreacted polyisocyanates present in the reaction mixture comprising the hydrophilic prepolymer following the reaction with the amine, alcohol or silane is preferably 0, but can range up to about 0.5 weight percent.

[0039] A preferred method of purifying the hydrophilic prepolymer (a) is by the method of U.S. patent application Ser. No., filed on even date herewith, Attorney's Docket No. 57017US002, the disclosure of which is incorporated herein by reference.

[0040] A suitable hydrophilic polyol for use in the preparation of the hydrophilic prepolymer bearing isocyanate groups is a polyether polyol having at least two, preferably three, hydroxyl groups, and a number average molecular weight in the range of from about 2,000 to about 20,000, preferably about 2,000 to about 5,000, most preferably about 4,000 to about 5,000, and having random ethylene oxide units and higher alkylene oxide units in a mol ratio of ethylene oxide (EO) to higher alkylene oxide of 1:1 to 4:1. The higher alkylene oxide can be selected from the group consisting of propylene oxide (PO), butylene oxide, pentylene oxide, hexylene oxide and mixtures thereof. The hydrophilic polyol is preferably a polyoxyethylene-propylene polyol comprising, for example, 50 to 70% EO and 30 to 50% PO. A particularly preferred polyether triol is one comprising approximately 68% EO and approximately 32% PO. Alternate ratios of EO:PO can be used in preparing the hydrophilic polyol of the present invention provided that the hydrophilicity of the resulting polyol is not significantly adversely affected. These ratios can be determined by routine testing.

[0041] Commercially available polyol precursors useful in making the above described water-soluble isocyanate-terminated prepolymers are the hydrophilic polyols, e.g., a polyG™ triol, such as “polyG™-83-84”, available from Arch Chemicals. The degree of overall hydrophilicity of the prepolymeric mixtures can be modified by varying the ratio of ethylene oxide to propylene oxide in the hydrophilic polyol, or by using small amounts of poly(oxyethylene-oxypropylene) polyols sold under the trademark “Pluronic”, such as Pluronic-L35, F38, and P46, or hydrophilic polyols with heteric oxyethylene-oxypropylene chain sold as Polyol Functional Fluids, such WL-580, WL-600, and WL-1400.

[0042] The hydrophilic prepolymer bearing isocyanate groups can be prepared, for example, by reacting a polyisocyanate with a copolymer of polyoxyethylene-propylene polyol using an NCO/OH equivalent ratio of about 5:1 to about 1.05:1, preferably a ratio of about 2.0:1 to 2.5:1. The preparation of isocyanate-terminated prepolymers is disclosed in, for instance, U.S. Pat. Nos. 4,315,703 and 4,476,276 and in references mentioned in those patents. The disclosures of these patents are incorporated herein by reference. Preferably, aromatic isocyanate is used for its greater reactivity rate than aliphatic isocyanate. Benzoyl chloride can be added during prepolymer preparation to avoid side reactions of polyisocyanate.

[0043] Polyisocyanates that can be used to prepare the hydrophilic prepolymer having isocyanate groups include aliphatic and aromatic polyisocyanates. The preferred polyisocyanates are aromatic polyisocyanates. One of the most useful polyisocyanate compounds that can be used is tolylene diisocyanate, particularly as a blend of 80 weight percent of tolylene-2,4-isocyanate, and 20 weight percent of tolylene-2,6-isocyanate; a 65:35 blend of the 2,4- and 2,6-isomers is also useable. These polyisocyanates are commercially available under the trademark “Hylene”, as Nacconate™ 80, and as Mondur™ RD-80. The tolylene isocyanates can also be used as a mixture with methylene diisocyanate. Other useable polyisocyanate compounds that can be used are other isomers of tolylene diisocyanate, hexamethylene-1,6-diisocyanate, diphenyl-methane-4,4′-diisocyanate, m- or p-phenylene diisocyanate and 1,5-naphthalene diisocyanate. Polymeric polyisocyanates can also be used, such as polymethylene polyphenyl polyisocyanates, such as those sold under the trademarks “Mondur” MRS, and “PAPI”. A list of useful commercially available polyisocyanates is found in Encyclopedia of Chemical Technology by Kirk and Othmer, 2nd Ed., Vol. 12, pages 46, 47, Interscience Pub. (1967).

[0044] Preferably, no solvent is used to dilute the hydrophilic prepolymer. However, a solvent can be used if necessary. Solvents that can be used to dissolve the prepolymer are water-miscible, polar organic solvents that are preferably volatile at the ambient conditions of the environment where the sealing composition is to be used. The solvent chosen should be such that the resulting solution of prepolymers and solvent will not freeze at the ambient conditions present in the environment where the mixed composition of the invention is to be applied. For example, where the ambient temperature is about 50° F., a solution of about 60-90 weight percent of prepolymer solids in dry acetone is an effective composition. Other useful water-miscible solvents include methyl acetate, tetrahydrofuran dimethyl formamide ethylene glycol monoethyl ether acetate (sold under the trade designation “Cellosolve” acetate), N-methyl pyrrolidone, and diethyl acetal, and hydrophilic plasticizers, such as Atpol™ 1120, available from Uniquema, Belgium.

[0045] Other additive ingredients can be included in the composition of the present invention. For example, viscosity modifiers can be included to increase or decrease the viscosity, depending on the desired application technique. Fungicides can be added to prolong the life of the gel and to prevent attack by various fungi. Other active ingredients can be added for various purposes, such as substances to prevent encroachment of plant roots, and the like. Other additives that can be included in the composition of this invention, include, without limitation, rheological additives, fillers, fire retardants, defoamers and coloring matters. Care should be exercised in choosing fillers and other additives to avoid any materials which will have a deleterious effect on the viscosity, reaction time, the stability of the liner being prepared, and the mechanical strength of the resulting liner.

[0046] The additional filler materials that can be included in the composition of the present invention can provide a more shrink-resistant, substantially incompressible, and fire retardant composition. Any of a number of filler compositions have been found to be particularly effective. Useful fillers include water-insoluble particulate filler material having a particle size of about less than 500 microns, preferably about 1 to 50 microns and a specific gravity in the range of about 0.1 to 4.0, preferably about 1.0 to 3.0. The filler content of the cured composition of the present invention can be as much as about 10 parts filler per 100 parts by weight cured composition, preferably about 5 parts to about 20 parts per 100, more preferably, about 2 parts to about 5 parts per 100.

[0047] Examples of useful fillers for this invention include expandable graphite such as Grafguard™ 220-80B or Grafguard™ 160-1SOB (Graftech, Ohio, USA), silica such as quartz, glass beads, glass bubbles and glass fibers; silicates such as talc, clays, (montmorillonite) feldspar, mica, calcium silicate, calcium metasilicate, sodium aluminosilicate, sodium silicate; metal sulfates such as calcium sulfate, barium sulfate, sodium sulfate, aluminum sodium sulfate, aluminum sulfate; gypsum; vermiculite; wood flour; aluminum trihydrate; carbon black; aluminum oxide; titanium dioxide; cryolite; chiolite; and metal sulfites such as calcium sulfite. Preferred fillers are expandable graphite, feldspar and quartz. The filler is most preferably expandable graphite. The amount of filler added to the composition of the invention should be chosen so that there is no significant effect on elongation or tensile strength of the resulting liner. Such amounts can be determined by routine investigation.

[0048] When filler is added to the composition of the invention, the resulting liner can also be fire retardant. The liner preferably should meet the fire retardant specifications of CAN/ULC-S102-M88 or ASTM E-84. These tests determine bum rate and the amount of smoke generation.

[0049] The components (a) and (b) of the composition of the invention are preferably mixed immediately before being applied to a surface. As an example of the mixing process, components (a) and (b) can be pumped using positive displacement pumps and then mixed in a static mixer before being sprayed onto a surface. The mixture of the two components can then be sprayed onto a substrate with or without air pressure. The mixture is preferably sprayed without the use of air. The efficiency of mixing depends on the length of the static mixer.

[0050] Objects and advantages of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention.

EXAMPLES

[0051] Test Methods:

[0052] Test method ASTM D-638-97 was used for measuring tensile strength and elongation. The tests were performed using an Instron Model 44R1122 with a crosshead speed of 200 mm/min.

[0053] Liners that were made in accordance with the present invention have passed the Dynamic Stress Membrane Materials testing. Small-scale tests confirmed that the lining material met the basic requirements set by both the liner manufacturer and members of the mining industry. For small scale testing, the liner material was applied by hand mixing components (a) and (b) of the inventive composition to the surface of granite core samples (2 inches (5.1 cm) in diameter and 4 inches (10.2 cm) long) leaving a 6 mm gap at each end. A leading mining company supplied the granite cylinders. A crush test was carried out at Golder Associates, in London, Ontario, after the samples were left for 4 hours and 24 hours at room temperature. Force was applied on the cylinders by a compressive load using a soft, uncontrolled testing machine to maximize the potential energy available to sustain a violent type of failure of the cylinders. The granite cylinders were failed without damaging the applied liner on the cylinders.

[0054] Large granite cylinders (7.5 inch (about 19 cm) in diameter and 19 inch (about 48 cm) long) were sprayed using a pump system and mixed in a static mixer with two different liner compositions using three different thicknesses. These tests were carried out in Sudbury, Ontario in CANMET Lab. Again, the cylinders were crushed without affecting the applied liners.

[0055] Prepolymer 1:

[0056] A general description of prepolymer preparations that can be used to prepare prepolymer A is given in U.S. Pat. No. 4,476,276, the disclosure of which is incorporated by reference, especially the preparation of prepolymers A, B and C of U.S. Pat. No. 4,476,276.

[0057] An amount of benzoyl chloride 0.04% (based on the total amount of polyol and tolylene diisocyanate (TDI)) was blended at room temperature under an inert atmosphere with 1 equivalent of polyether triol (a copolymer of ethylene oxide and propylene oxide sold under the trade designation polyG-83-34, mol. wt. 5400, available from Arch Chemicals), thereafter, 2.4 equivalents of an 80:20 mixture of 2,4 tolyene diisocyanate: 2,6 tolylene diisocyanate (Mondur™ TD-80 available from Bayer Corporation, USA) was added to the resultant mixture with agitation, producing a moderate exotherm that was maintained at 80-85° C. until the reaction was completed. The solution of the prepolymer was then cooled to room temperature. The solution contained prepolymers having on average 3.0 to 3.2 weight percent isocyanate groups, and 1.2-2.4 weight percent monomeric TDI, as determined by NMR techniques.

[0058] Prepolymer 2:

[0059] In a 3-necked 2 L round bottom flask, equipped with a mechanical stirrer and a thermometer, 1271.3 g of Prepolymer 1 was added under an argon atmosphere, 98.1 g (30 molar percent with respect to the total NCO groups in Prepolymer 1) of Silquest™ A-1170 bis (trimethoxysilylpropyl)amine (available from Osi Co.) was added dropwise to the prepolymer at 25° C. under argon and with stirring (250 rpm). The reaction was exothermic causing a 0-10° C. increase in temperature. The reaction mixture was collected after 2 h. The monomeric TDI content was found to be below 0.5 weight percent, as determined by NMR.

[0060] Prepolymer 3:

[0061] In a 3-necked 2 L round bottom flask, equipped with a mechanical stirrer and a thermometer, 1280.0 g of Prepolymer 1 and 320.0 g of dry acetone were added under argon atmosphere. 134.8 g (40 molar percent with respect to the total NCO groups in the prepolymer of Example 1) of Silquest™ A-1170 bis (trimethoxysilylpropyl)amine was added dropwise to the solution at 25° C. under argon and with stirring (900 rpm). The reaction mixture was collected after 2 h. The monomeric TDI content was found below 0.1 weight percent, as determined by NMR.

[0062] Prepolymer 4:

[0063] In a 3-necked 250 ml round bottom flask, equipped with a mechanical stirrer and a thermometer, 205.9 g of Prepolymer 1) of N-ethyl aniline was then added to the prepolymer while stirring at 25° C. The mixture was collected after 2 h. The monomeric TDI content was found to be below 0.2 weight percent, determined by NMR.

[0064] Prepolymer 5:

[0065] In a 3-neck round bottom flask, equipped with a mechanical stirrer and a thermometer, 200 g of Prepolymer 1 was added under argon. 2.74 g (15 molar percent with respect to the total NCO groups in Prepolymer 1) of N-ethyl aniline was added dropwise to the prepolymer at 25° C. under argon and with stirring (250 rpm). The reaction was kept at room temperature for 2 h. Then 7.52 g (15 molar percent with respect to the total NCO groups in the prepolymer #1) Silquest™ A-1170 bis (trimethoxysilylpropyl)amine was added to the mixture under argon and with stirring. The reaction was kept at room temperature for 2 h before collection. The monomeric TDI content was found to be below 0.3 weight percent, as determined by NMR.

[0066] Prepolymer 6:

[0067] In a 3-neck 250 ml round bottom flask, equipped with a mechanical stirrer and a thermometer, 201.0 g of Prepolymer 1 was added under argon. 2.45 g (15 molar percent with respect to the total NCO groups in Prepolymer 1) of benzyl alcohol was added to the prepolymer under argon. The temperature was then raised to 85C. and the reaction was carried out for 2 h. After the reaction mixture was cooled to room temperature, 7.52 g (15 molar percent with respect to the total NCO groups in Prepolymer 1) Silquest™ A-1 170 bis (trimethoxysilylpropyl)amine was added the mixture under argon and stirring. The reaction was kept at room temperature for 2 h before collection. The monomeric TDI content was found below 0.2 weight percent, as determined by NMR.

Examples 1-5

[0068] Examples 1-5 provide data for liners formed using NeoPac™ 9699 polyurethane dispersion and different prepolymers. The samples were made by quickly injecting 4.0 g of a prepolymer to 20 g of NeoPac™ 9699 (40%) solid polyurethane dispersion (from NeoResin Canada) followed by mixing the two components with a spatula and spreading the mixture on a polyester film to a thickness of about 2 to 3 mm. The film surface was not smooth due to rapid gelling of the two components. The value of tensile strength of these samples, and the components used to produce them are provided in Table 1. The results indicate that prepolymers with a low amount of monomeric diisocyanate (except for example 9, which is quenched with 40 molar percent mono-functional amine) can provide the same or better tensile strength as compared to example 7, a liner formed by unmodified prepolymer and polyurethane dispersion. Although Example 9 does not demonstrate a tensile strength of 1 Mpa after 4 hours, it does demonstrate good results after three days. 1 TABLE 1 Tensile properties at 4 h Tensile properties at 3 days Strength Elong. Strength Elong. ExampleNo. Prepolymer (Mpa) (%) (Mpa) (%) 1 1 1.3 305 9.1 550 2 2 1.2*  840* 10.2 330 3 4 0.9 800 10.2 330 4 5 1.6 630 9.2 350 5 6 1.7 660 8.9 380 *Value at 3 hr.

Comparative Examples 1 and 2 and Examples 6-8

[0069] The samples of the following examples and comparative examples were made by injecting 4.5 g of prepolymer quickly to 20 g of each dispersion along with 2 g of fused silica, mixing with spatula and spreading on a polyester film to about thickness of 1.9 mm to 3 mm. The films were not very smooth due to rapid gelling of the two components. The values of tensile strength of these samples, and the components used to produce them are provided in Table 2. Comparative Example 1 does not use a polyurethane, and Comparative Example 2 uses a polyurethane that has a low modulus. 2 TABLE 2 Tensile Strength Example Amount (Mpa) No. Components of Composition (g) After 4 hours C-1 Prepolymer 3 (A) 4.5 0.34 Vancryl ™ 937 (B) 16.8 Fused Silica 2.0 C-2 Prepolymer 3 (A) 4.5 0.44 Luphen ™ 3528 (B) 20 Fused Silica 2.0 6 Prepolymer 3 (A) 4.5 1.12 Hauthane ™ HD-2334 (B) 18.0 Fused Silica 2.0 7 Prepolymer 3 (A) 4.5 2.08 NeoPac ™ R-9699 (B) 20 Fused Silica 2.0 8 Prepolymer 3 (A) 4.5 1.23 Hybridur ™ 450 (B) 20 Fused Silica 2.0

[0070] Vancryl™ 937 is a 48% solid acrylic-styrene based emulsion available from Air Products, USA. Luphen™ 3528 is a 40% solid low modulus polyurethane dispersion from BASF, USA. Hauthane™ HD-2334 is a 45% solid polyether based polyurethane dispersion from Hauthaway & Sons Corporation. NeoPac™ R-9699 is a 40% solid polyester-polyacrylate based polyurethane co-polymer, available from Neo Resins Canada. Hybridur™ 450 is a 40% solid, polyester-polyacrylate based polyurethane co-polymer, available from BASF, USA.

Example 9

[0071] Liners were made by spraying component A (Prepolymer 4) which contains less than 0.1 weight percent of free TDI and component B (Neorez™ R-9699) at a weight ratio of 1:5 with 2 separate pumps and mixing components A & B in a static mixer. The compositions formed were smooth and showed higher tensile values compared to hand mixed samples. The resulting hand-made and pump-sprayed films were then tested after 4 hours to determine their tensile strengths. The strengths were also evaluated after 3 days and after several weeks. The results are shown in Table 3. 3 TABLE 3 4 hr.* 1 day* 2 days* 7 days* 7 days** Tensile Strength 1.8 9.4 10.9 12 15 (Mpa) % Elongation 700 406 310 252 225 *Samples were left at ambient temperature **Samples were left at 50° C. for 2 days and then 1 day at RT.

Example 10

[0072] A test was conducted in which a control gel containing no fire retardants and samples containing several different fire retardants were ignited with an open flame. A sample prepared from 4 g of Prepolymer 1 or 2, 20 g of component NeoPac™ 9699 and 0.25-1.0 g of the expandable graphite Grafguard™ 220-80B (Graftech, Ohio, USA) showed self-extinguishability. A sample prepared with the expandable graphite Grafguard™ 160-150B also demonstrated self-extinguishability but to a lower extent.

[0073] Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. It should be understood that this invention is not intended to be unduly limited by the illustrative embodiments and examples set forth herein and that such examples and embodiments are presented by way of example only with the scope of the invention intended to be limited only by the claims set forth herein as follows.

Claims

1. A liner comprising the product of reaction of:

(a) a hydrophilic prepolymer bearing isocyanate groups; and

(b) a water-borne polyurethane dispersion, the polyurethane bearing groups that are reactive to isocyanate groups.

2. A liner according to claim 1, wherein the polyurethane used in component (b) has a molecular weight in the range of from about 100,000 to about 700,000.

3. A liner according to claim 1, wherein the polyurethane of component (b) is in the form of particles of a size from about 30 to about 1000 nm.

4. A liner according to claim 1, wherein a film prepared from the polyurethane used in component (b) has a modulus of at least about 14 MPa at 100% elongation.

5. A liner according to claim 1, wherein a film prepared from the polyurethane used in component (b) has a value of Tg greater than about 40° C.

6. A liner according to claim 1, wherein the dispersion of the polyurethane contains no co-solvent.

7. A liner according to claim 1 which develops a strength of at least about 1 MPa within about 4 hours.

8. A liner according to claim 1, wherein said prepolymer is formed by reacting a polymer bearing hydroxyl groups with a polyisocyanate to form a urethane-containing polymer bearing isocyanate groups, which is purified by removing unreacted polyisocyanate or by quenching unreacted polyisocyanate with a compound that is reactive to isocyanate groups.

9. A liner according to claim 1, wherein the polyurethane dispersion is in admixture with a dispersion of an acrylate polymer, an acrylate polymer, an acrylic-styrene copolymer, a styrene-butadiene copolymer, or a vinyl acetate polymer.

10. A liner according to claim 1, wherein the weight ratio of component (a) to component (b) is in the range of from about 1:3 to about 1:10.

11. A liner according to claim 1, further comprising at least one additive selected from the group consisting of rheological additives, fillers, fire retardants, defoamers and coloring matters.

12. A liner comprising

(a) the product of reaction of:

(1) a hydrophilic prepolymer derived from a polyether polyol and bearing isocyanate groups derived from an aromatic polyisocyanate; and

(2) a water-borne polyester-acrylate based polyurethane dispersion, the polyurethane bearing groups that are reactive to isocyanate groups; and

(b) expandable graphite.

13. A method for providing a surface with a liner, the method comprising

(a) applying to the surface

(1) a hydrophilic prepolymer bearing isocyanate groups, and

(2) a water-borne polyurethane dispersion, the polyurethane bearing groups that are reactive to isocyanate groups; and

(b) allowing the applied components (a) and (b) to react to form the liner.

14. A method according to claim 13, wherein the polyurethane used in component (b) has a molecular weight in the range of from about 100,000 to about 700,000.

15. A method according to claim 13, wherein the polyurethane of component (b) is in the form of particles of a size from about 30 to about 1000 nm.

16. A method according to claim 13, wherein a film prepared from the polyurethane of component (b) has a modulus of at least about 14 Mpa at 100% elongation.

17. A method according to claim 13, wherein a film prepared from the polyurethane of component (b) has a value of Tg greater than about 40° C.

18. A method according to claim 13, wherein the dispersion of the polyurethane contains no co-solvent.

19. A method according to claim 13, wherein the liner develops a strength of at least about 1 Mpa within about 4 hours.

20. A method according to claim 13, wherein said prepolymer (a) is formed by reacting a polymer bearing hydroxyl groups with a polyisocyanate to form a urethane-containing polymer bearing isocyanate groups, which is purified by removing unreacted polyisocyanate or by quenching unreacted polyisocyanate with a compound that is reactive to isocyanate groups.

21. A method according to claim 13, wherein the polyurethane dispersion (b) is in admixture with a dispersion of an acrylate polymer, an acrylate polymer, an acrylic-styrene copolymer, a styrene-butadiene copolymer, or a vinyl acetate polymer.

22. A method according to claim 13, wherein the weight ratio of component (a) to component (b) is in the range of from about 1:3 to about 1:10.

23. A method according to claim 13, further comprising at least one additive selected from the group consisting of rheological additives, fillers, fire retardants, defoamers and coloring matters.

24. A method according to claim 13, wherein the thickness of the liner is in the range of from about 0.5 mm to about 6 mm.

25. A method according to claim 13, wherein said surface is in a mine opening.

26. A method for providing a surface with a liner, the method comprising

(a) applying to the surface

(1) a hydrophilic prepolymer derived from a polyether polyol and bearing isocyanate groups derived from an aromatic polyisocyanate;

(2) a water-borne polyester-acrylate based polyurethane dispersion, the polyurethane bearing groups that are reactive to isocyanate groups; and

(3) expandable graphite; and

(b) allowing the applied components (a) and (b) to react to form the liner.

27. A mine opening lined with a liner formed by the method of claim 13.

28. A mine opening lined with a liner formed by the method of claim 26.