Coating for Fiberglass Insulation

This invention relates to coatings for fiberglass insulation articles, thereby providing the fiberglass insulation with good mechanical properties and other desirable propertties such as low emission of volatiles, fire retardation, low potential smoke generation and low air friction.

Fibrous batts, mats or boards are used to thermally insulate various surfaces, such as the inside or outside of pipes and ducts, as well as refrigerators, air conditioners, furnaces, automobile hoods and the like. Heating, cooling or ventilating systems usually use air ducts, through which flows air as the heating and cooling medium. These ducts are constructed in various shapes, for example as round tubes or having a rectangular shape. They are usually made of sheet metals, such as galvanized steel, or plastics, or fiberglass reinforced plastis, or cellulosic materials such as wood or fiberboard, and the like. The construction and method of making these ducts and conduits is described in U.S. Pat. Nos.3,092,529; 3,212,529; and 3,394,737. The inside color of these ducts is usually black so as not to see the duct throgh the vents. The inner surface of these ducts should be smooth, to allow the air to flow with as little friction as possible, to save energy in transporting the air. This is usually achieved by first coating the fiberglass insulation which is then installed in the air ducts. The coating of the fiberglass insulation normally does not interfere with the excellent noise dampening qualities of the fiberglass insulation. The duct noise is often generated by the fan and by the following air, or, in the case of refrigerators, automobiles, furnaces and the like, by the engines and motors. Generally, the fiberglass mats, or batts are coated with an aqueous coating composition, often after the surface of the fiberglass mat has first been covered with a woven or nonwoven fabric. Normally, the coatings are applied by spraying the aqueous coating composition onto the surface of the fiberglass batting.

The coating is then dried in heated ovens, or by radiant heat. These procedures are generally carried out continuously. The finished fiberglass batting is then rolled up and often compressed by applying vacuum before shipping in order to save on shipping costs.

One such coating composition is disclosed in U.S. Pat. No. 3,926,894. The coating composition of U.S. Pat. No. 3,926,894 consists of a halogenated organophosphorous plastcizer, a latex binder and a mineral filler. However, a serious disadvantage of such a coating composition is the relative volatility of the plasticizer, especially in air ducts where large volumes of heated air pas over the coating, which makes the coating environmentally undesirable because the vapors emanating from the plasticizers are quite toxic.

Accordingly, it is an object of this invention to provide a coating having good mechanical properties, low volatility of the ingredients, good fire retardation, as well as low back smoke generation.

The present invention is based on the finding that by providing a fiberglass insulation coating coposition containing two or more polymers as the binders and other optional ingredients dispersed in water, and by applying this coating by the above mentioned coating methods, one obtains a fiberglass insulation such as fiberglass mats, boards, and batts, or the like, having a superior mechanical properties as well as fire retardation, low black smoke generation, and low friction to passing air. Thus, an aqueous coating composition is provided for use on fiberglass insulation articles comprising an aqueous medium having dispersed therein solid material consisting essentially, by weight, of

(a) 3 to 26 percent, preferably 12 to 20 percent, of a strong and soft, non-halogenated, vinyl type polymer; (b) 6 to 26 percent, preferably 12 to 20 percent, of a halogenated vinyl polymer;

(c) 40 to 80 percent, preferably 50 to 70 percent, of at least one inorganic filler, selected from the group of clay, calcium carbonate, aluminum trihydrate, magnesium trihydrate, antimony oxide, barium sulfate and encapsulated asbestos, or a mixture thereof;

(d) 0.2 to 2 percent of a thickening agent; and

(e) 0.1 to 1 percent of a defoamer, if necessary.

A coating composition for fiberglass articles comprising an aqueous dispersion containing a mixture of at least two polymeric binders, as well as aluminum trihydrate, antimony oxide, and also defoaming agents, biocides, thickeners, color pigments, dispersants and the like, has now been discovered. The dried coating composition of this invention, made by applying the aqeuous coating composition to fiberglass insulation and drying the coating in a drying oven has been found to impart an exceptionally advantageous balance of properties to the fiberglass insulation which cannot be achieved by heretofore known coating compositions.

The coating composition of the present invention is prepared by first dispersing aluminum trihydrate, antimony oxide, and a colored pigment in water using a Cowles type mixer, a sand mill, a three roll mill, or a similar high energy mixing device, and then blending this pigment slip with a mixture containing two or more emulsion polymers, a surfactant or wetting agent, or a blend of surfactants if necessary, a thickener and a biocide and a defoaming agent, if required.

The properties of the fiberglass insulation coating which have to be balanced against each other are mechanical strength combined with elasticity, fire retardation, and the lack of black smoke generation when a flame is brought in contact with the coating, as well as the smoothness of the insulation surface, as not to impede the airflow through ducts.

Fire retardation of a coating is generally achieved by using in the coating composition a halogenated organophosphorous plasticizer as taught in U.S. Pat. No. 3,926,894, together with a polymeric binder and a filler or pigment. However, a serious disadvantage of such a coating is the relative volatility of the plasticizer, especially in air ducts where large volumes of heated air pass over the coating, which makes the coating environmentally undesirable. A plasticizer also contributes greatly to black smoke generation, when a flame comes in contact with the coating.

On the other hand, a flexibilizing agent is necessary in the coating, because the coating has to have enough elasticity to allow the fiberglass insulation to be able to be installed inside of rectangularly shaped ducts or other odd shaped bodies as well as in flexible type ducts without cracking or flaking-off of the coating during the installation process and as well a during later use.

Generally, aluminum trihydrate and antimony oxide or a mixture thereof may be used to inhibit this black smoke generation. However, these fillers contribute also to making the coating stiff so that a coated fiberglass insulation tends to embrittle, leading to cracks in the coating and even to flaking-off of the coating during the installation process and during later use. Formerly, a plasticizer was added to the coating composition, but for the above cited reasons, namely toxicity, this is undesirable.

It has now been found that all these above mentioned disadvantages of the coating can be overcome without loosing the other desirable properties. This is achieved by the surprizing discovery that when two polymers emulsions, one containing a halogenated polymer, the other containing a soft and strong, non-halogenated vinyl polymer, are used as the binder in the coating oen can achieve the necessary balance of properties to produce a superior fiberglass insulation product making it unnecessary to use a plasticizer in the coating formulation, thereby eliminating the environmental hazard. Since one of the polymeric binders is halogenated, one has to use only small amounts of fire retardant fillers such as aluminum trihydrate thereby limiting the embrittling effect of fillers. The binder is a very important part of the coating composition, since it bonds the fillers and pigments securely to the fiberglass insulation, thereby achieving the above mentioned smooth surface of the fiberglass insulation.

It has now been discovered that when a strong and soft vinyl polymer is used together with a halogenated polymer, as well as with moderate amounts of fillers, such as a mixture of aluminum trihydrate and anitmony oxide, one can achieve a coating which is not only mechanically strong but also elastic, without decreasing the fire retardation of the coating. The coating of this invention also generates almost no black smoke when brought in contact with a hot flame, as well as having a low emission of volatile materials when having contact with flowing air, as is the case in heating, cooling and ventilating ducts.

The coatings solids of this invention consist essentially, by weight, of

(a) 6 to 26 percent, preferably 12 to 20 percent, of a strong and soft, non-halogenated, vinyl type polymer;

(b) 6 to 26 percent, preferably 12 to 20 percent, of a halogenated vinyl polymer;

(c) 40 to 80 percent, preferably 50 to 70 percent, of at least one inorganic fillers, selected from the group of clay, calcium carbonate, aluminu trihydrate, magnesium trihydrate, antimony oxide, barium sulfate and encapsulated asbestos, or a mixture thereof; and

(d) 2 to 10 percent, preferably 3 to 8 percent, of additional ingredients consisting of defoaming agents, organic pigments, dispersants, biocides, a thickener, and the like.

The strong and soft, non-halogenated, vinyl type polymer of this invention is usually an acrylic polymer, a vinyl-acrylic polymer, a vinyl-olefin polymer or a styrene-butadiene polymer, dispersed in water, having a solids content from 30 to 60 percent, preferably from 40 to 55 percent by weight, having a glass transition temperature from -40.degree. to +20.degree. C., preferably from -30.degree. to 0.degree. C., an intrinsic viscosity from 1 to 3.5 deciliters per gram, and a Shore hardness of 20 to 60 as measured with a Durometer A. The measurement of the glass transition temperature is described in the book, "Principles of Polymer Chemistry", pp. 56 and 57by Paul Flory, Cornell University Press (1953). The intrinsic viscosity is determined by conventional techniques, i.e. in accordance with the procedure described on pages 309-314 of the book "Principles of Polymer Chemistry" by Paul Flory (Cornell University Press, 1953).

When properly cured a 10 mil film of the non-halogenated polymer has a tensile strength of from 500 to 1500 psi, preferably from 700 to 1000 psi and an elongation at break of from 500 to 1500 percent, preferably from 700 to 1200 percent as measured with an Instron tensile tester. The acrylic polymers are well known in the are and may consist, for example, of a homo- or copolymer of methyl acrylate, ethyl acrylate, isopropyl acrylate, butyl acrylate, 2-ethyl hexyl acrylate, and a n-alkyl methacrylate, such as methyl methacrylate; also present may be acrylonitrile or styrene. Small amounts of functional monomers to effect cross-linking, for example, acrylic acid and N-methylol acrylamide or the like, are also ofter present. The vinyl-acrylic polymer is often a copolymer of the above mentioned acrylic- and methacrylic esters with a vinyl ester, such as vinyl acetate or vinyl propionate. An example, of a vinyl-olefin polymer is a vinyl acetate - ethylene copolymer. Polymer dispersions or emulsions of this kind are available in commerce under the tradenames Rhoplex (Rohm and Haas Co.), Airflex (Air Products and Chemicals Co.), Elastoplast (B.F. Goodrich Co.), and Dow Latex (Dow Chemical Co.).

The halogenated polymers of this invention are often copolymers of acrylic asters, vinyl esters, ethylene and butadiene, alone or in combination, with halogenated monomers, such as vinyl chloride, vinylidene chloride, chloroprene; also with vinyl bromide, 2,3-dichloro-1,3-butadiene, halogenated vinyl esters, such as cholorovinyl acetate, halogenated acrylic esters such as chloroethyl acrylate and the like. Homopolymers of chloroprene, vinyl chloride and vinylidene chloride may also be used. Especially preferred halogenated polymers are chloroprene polymers, sold under the tradename Neoprene (DuPont Co.), vinyl chloride -ethylene copolymers sold under the tradename Airflex (Air Products and Chemicals Co.) and vinylidene chloride homopolymers, or copolymers, sold under the tradenames of Daran (W.R. Grace Co.) or RAP (Dow Chemical Co.). These polymers are sold in commerce as dispersions in water, having a solids content of from 40 to 60 percent, and having a glass transition temperature from -20.degree. to +100.degree. C., preferably from 0.degree. to 30.degree. C. and having a chlorine content by weight of from 20 to 75 percent, preferably from 30 to 60 percent.

The fillers employed in this invention are naturally occurring materials such as clays, calcium carbonate, aluminum trihydrate, magnesium trihydrate, antimony oxide, barium sulfate as well as encapsulated asbestos. Especially preferred are aluminum trihydrate and antimony oxide and mixtures thereof. They are employed in the amount, by weight of the dry coating, of from 40 to 90 percent, preferably from 50 to 70 percent.

Each of the above polymers and fillers may be employed individually, or in combination within the stated proportions to produce the coatings of this invention possessing comparable properties.

In addition to the above mentioned components of the coating, other additives may be employed as required. Among those other additives are wetting agents, such as nonionic surfactants, for example alkylphenoxypolyethoxyethanol, having alkyl groups of about 7 to 18 carbon atoms and 10 to 60 or more oxyethylene units, and the like, and anionic surfactants such as sodium lauryl sulfate and sulfosuccinates, alkyl phosphates and the like. They are employed in the amount, by weight of the dry coating of from 0.02 to 2 percent, preferably from 0.1 to 1 percent.

The coating composition of this invention also contains a thickener, usually a carboxylated acrylic polymer, polyvinyl alcohol, or hydroxyethyl cellulose. Thickeners are employed in the amount of from 0.2 to 2 percent by weight of the dry coating, to impart a viscosity to the coating composition of from 300 to 2000 cps as measured with a Brookfield viscometer. Optionally, a biocide is added to the coating composition in the amount of 0.5 to 1.2 percent by weight of the dry coating. A suitable biocide is diiodo methyl-p-tolyl sulfone, sold under the tradename Tektamer 38 by the Calgon Div. of Merk and Co. Other compatible biocides may also be used.

The color pigments employed in this invention may be carbon black or other organic color pigments. Carbon black is preferred. It is used in the amount of 0.5 to 5 percent, preferably from 1 to 3 percent by weight of the dry coating.

Often a dispersant is also added to the coating formulation to aid in the dispersion of the pigments and fillers. A suitable dispersant is Seycosperse 4, sold by the Cargil Manufacturing Co. It is used in the amount of 0.01 0.15 percent preferably from 0.05 to 0.1 percent by weight of the dry coating. Other compatible dispersant may also be used. Finally, if necessary, defoaming agents, well known in the art, may be added to the coating composition.

The coating composition of this invention has a solids content of from 30 to 75 percent, preferably from 35 to 65 percent.

The aqueous coating composition of this invention may be applied to the fiberglass insulation by roller or knife coating methods. The coating may also be applied by spraying the aqueous coating composition of this invention onto the fiberglass batting using any conventional spray equipment known in the art. For example, an air pressure sprayer sold by the Graco Company may be used. The various coating methods are well known in the art. They are described in detail, for example, in the Encyclopedia of Chemical Technology, Third Edition, Volume 6, pp. 386-426, published by John Wiley, New York, 1979.

Usually, only enough of the coating composition is applied to the fiberglass insulation to provide a continuous coating layer to the fiberglass insulation after the drying step. Generally, the add-on of the wet coating to the fiberglass insulation batting is controlled in such a way as to provide a dry coating weight of about 5 to 15 grams per square foot of fiberglass batting, preferably 7 to 10 grams per square foot of the finished fiberglass insulation

The coated fiberglass insulation is then passed through a drying oven. Drying is normally carried out at temperature of from 220.degree. F. to 500.degree. F. for periods from 30 seconds to 20 minutes, but more usually at 300.degree. F. to 350.degree. F. for from 30 seconds to 10 minutes.

The invention is illustrated in the following examples. It should be understood however that the examples are for illustrative purposes only and in no way should they be construed to be limiting the invention.

A dispersion of pigments and filler is prepared first as follows: to 155.3 g of water is added 0.5 grams of a 40 percent solution in water of a polyacrylate dispersant (Seycosperse 4, made by the Cargil Corp. may be used), 150 grams of aluminum trihydrate, 5 grams of antimony oxide, and 11.3 grams of a 40% dispersion in water of carbon black. The mixture is agitated for 10 minutes with a Cowles type high energy agitator, after which the following is added with reduced agitation: 100 grams of Elastoplast V-29 a non-halogenated acrylic polymer emulsion sold by the B.F. Goodrich Co, having the following properties: solids=52%; pH =5; glass transition temperature=-29.degree. C.; Durometer A (Shore) hardness=49; ultimate tensile strength (10 mil film, heated to 300.degree. F.)=813 psi; elongation=760%; 100g of Airflex 4514, a vinyl chloride - ethylene copolymer emulsion sold by Air Products and Chemical Corporation, having the following properties: solids=50%, pH=7; chlorine content by weight=42.5%; glass transition temperature=14.degree. C.; 1.1 grams of Seycopon G 96, a brand of sodium lauryl sulfate as a 28 percent solution in water, made by the Cargil Corporation; 0.5 grams of Tektamer 38, a biocide having as primary ingredient diiodo methyl-p-tolyl sulfone, sold by the Calgon Div. of Merkk and Co.; 8.1 grams Paragum 500, a 30 percent solution in water of a polyacrylate thickener made by the Parachem Co.; and 2 grams of a 28 percent solution of ammonium hydroxide. The finished coating composition has a viscosity of 870 cps (measured with a Brookfield viscometer, #2 spindle at 20 RPM), a pH of 8.87, and a solids content of 50 percent. A 10 mil thick dry film was prepared from this coating composition to test the mechanical properties as follows: The film was folded in half making a sharp crease. The folded film was then placed between two plates and an eight pound weight was placed on the plate for 2 hours to make the crease of the film even sharper. After that time the film was unfolded, inspected for breakage at the crease and lightly stretched. The film did not break either by creasing it or by lightly stretching it, indicating that the coating film had excellent mechanical properties.

Several pieces of fiberglass insulation, weighing 53 grams per square foot having the dimensions of 8.times.9.times.3/4 inches each were roller coated with the coating composition of Example 1, using a metal roller, to give a dry add-on of coating of 8 grams per square foot. The coated pieces of fiberglass insulation were then dried in an oven at 325.degree. F. for 5 minutes, after which each piece was covered by a smooth strongly adherent coating. The coated fiberglass insulation pieces were then subjected to the following tests:

A 11/2.times.8 strip of a coated fiberglass insulation piece was positioned next to a propane torch having a 2 inches long blue inner flame in such a way, that the tip of the blue inner flame touched the surface of the test piece at a 30 degree angle. After a 60 second exposure to the flame, the test piece was removed. The test piece did not glow or burn (also called having no "afterflame") and it gave of no visible black smoke.

A test piece was placed in a 250.degree. F. oven for 10 days, after which the piece was examined for elasticity, by flexing the piece. No breaking, cracking or flaking-off of the coating was observed.

A coating composition was prepared following the procedure and using the ingredients of Example 1, with the exception that the halogenated vinyl polymer, namely Airflex 4514, was replaced by Chlorowax 57-60, a low molecular weight chlorinated wax sold by the Diamond Shamrock Co., having a chlorine content of 57 percent. Coated test pieces of fiberglass insulation were prepared according to Example 2. The Flammability Test was not passed by the test piece. There was considerably "Afterflame" present when the testflame had been removed. After exposure to heat in the Heat Resistance Test the test piece showed poor adhesion of the coating to the fiberglass insulation, as well as cracking and flaking-off of the coating.

A test film prepared and creased according to Example 1 showed poor crease resistance as well as breakage when lightly stretched, indicating poor mechanical properties.

A coating composition was prepared using the method and ingredients of Example 1, with the exception that Elastoplast V29 was replaced by another non-halogenated acrylic emulsion, namely Rhoplex HA-8, sold by the Rohm and Haas Co., consisting of an ethyl acrylate polymer having a glass transition temperature of -20.degree. C., and an ultimate tensile strength of 350 psi, and an elongation of 450% (10 mil film, heated to 300.degree. F.). This coating showed poor mechanical properties in the folded Film Test performed according to the method of Example 1.

These examples and comparative examples show that the coating compositions produced using the instant invention are by far superior to the comparative coating compositions which are used in commerce containing either a weaker acrylic polymer as in comparative example 2, or a halogenated non-polymeric material as in comparative example 1.