Process for preparing polyurethane-backed substrates, and the substrates so produced

Abstract: Substrates having successive layers of a cellular polyurethane and a non-cellular polyurethane are prepared using certain siloxane-polyether block copolymers in the non-cellular polyurethane formulation. Said block copolymers contain 10 to 30 weight percent dialkylsiloxane units, 30 to 70 weight percent oxyethylene units and, optionally, up to 55 weight percent other oxyalkylene units. The use of the block copolymer reduces or eliminates the formation of a bubble line at the interface of the polyurethane layers, thereby improving physical and cosmetic properties of the carpet.

Description: This invention relates to the preparation of polyurethane-backed substrates, particularly textiles backed with a cellular polyurethane backing. Polyurethane-backed textiles are well-known and described, for example, in US-A-3,821,130; US-A-3,862,879; US-A-3,296,159; US-A-4,657,790; and US-A-4,696,849. There are two general types of polyurethane backings commonly used. One type is a substantially non-cellular backing which is normally coated onto the back of tufted textiles to bind the individual tufts of facing yarn to a primary scrim or grid. Such backings are often referred to as "unitary" backings. The other important type is a cellular backing which is attached to a textile to provide an attached cushion. In the carpet area, this type of backing often eliminates the need to install a separate padding material. US-A-3,941,633 discloses the manufacture of a plastic laminate in which a polyurethane foam layer is cast upon a polyurethane film and a fabric layer is bonded to the foam layer. The fabric can be bonded prior to complete curing of the foam layer thereby permitting the use of unnapped fabrics. It is often desirable to apply multiple layers of the polyurethane. This is particularly true in preparing textiles with a cellular polyurethane backing. In preparing these textiles, it is preferred to apply a substantially non-cellular polyurethane directly to the back of the textile, and then overcoat this "precoat" with a cellular polyurethane layer. The precoat layer helps bind the facing material to the textile and provides a smoother surface on which to apply the cellular layer. This in turn helps to prepare a cellular layer of uniform gauge, which is of particular importance. In order for the textile to have optimal properties, it is necessary that the bonding between the textile and the various layers be as strong as possible. Unfortunately, quite often a line of bubbles develops at the interface between successive polyurethane layers, especially between the layers of non-cellular polyurethane and cellular polyurethane. The bubble line weakens the bond between the layers to the point that they can often be easily peeled apart. When installed, forces applied to the exposed surface of the textile can cause a separation of the layers when such a bubble line is present. In addition, the presence of the bubble line is cosmetically unacceptable. Accordingly, it is desirable to prepare a polyurethane-backed textile wherein the bubble line between successive polyurethane layers is minimized or eliminated. This invention is in one aspect a process for preparing a polyurethane-backed substrate, wherein a first layer of a polyurethane-forming composition is applied to a substrate and a second layer of a polyurethane-forming composition is applied to said first layer and said layers are cured, wherein one of said first and second layers is a non-cellular polyurethane composition, and the other of said first and second layer is a cellular polyurethane composition, characterized in that said non-cellular polyurethane composition contains 0.03 to 2.0 weight percent of a polysiloxane-polyether block copolymer, said block copolymer containing 10 to 30 weight percent dialkylsiloxane units, 30 to 70 weight percent oxyethylene units and 0 to 55 weight percent other oxyalkylene units. In another aspect, this invention is a substrate having attached thereto successive polyurethane layers, wherein one of such layers is a cellular polyurethane which is attached directly to a non-cellular polyurethane layer characterized in that said non-cellular polyurethane layer contains 0.03 to 2.0 weight percent of a polysiloxane-polyether block copolymer, said block copolymer containing 10 to 30 weight percent dialkylsiloxane units, 30 to 70 weight percent oxyethylene units and 0 to 55 weight percent other oxyalkylene units. The incorporation of a block copolymer of the type described into the non-cellular polyurethane-forming composition results in a very substantial reduction, and often an elimination, of the bubble line between the polyurethane layers. This results in a stronger, more permanent bond between the layers. In this invention, a substrate is attached directly or indirectly to two adjacent polyurethane layers. One of the polyurethane layers is non-cellular, which for the purposes of this invention means that the layer has a bulk density of at least 0.8 g/cm³. The other polyurethane layer is cellular, which for the purposes of this invention means that the layer has a bulk density of less than 0.8 g/cm³, preferably less than 0.6 g/cm³, more preferably 0.05 to 0.6 g/cm³, most preferably 0.2 to 0.6 g/cm³. The two layers are advantageously formed by applying a polyurethane-forming composition to a previously formed first polyurethane layer, and then curing said composition. The non-cellular polyurethane layer is prepared from a polyurethane-forming composition containing a certain polysiloxane polyether block copolymer. Certain of these materials are known as surfactants useful in preparing polyurethane foam. The polysiloxane portion is a dialkyl siloxane, preferably dimethyl siloxane, and constitutes 10 to 30, preferably 15 to 25 weight percent of the block copolymer. The poly(alkylene oxide) portion comprises oxyethylene units in an amount from 30 to 70, preferably 30 to 50, more preferably 30 to 45, weight percent of the block copolymer. In addition, the poly(alkylene oxide) portion may contain other alkylene oxide units, particularly oxypropylene units, in an amount from 0 to 55, preferably 30 to 55, more preferably 40 to 55, weight percent of the block copolymer. These block copolymers often have terminal hydroxyl groups. The terminal hydroxyl groups from the poly(alkylene oxide) portion(s) of the block copolymer may, if desired, be capped with non-isocyanate reactive end groups so the block copolymer does not react with polyisocyanate groups in preparing the polyurethane layer. Generally, this is accomplished by reacting the terminal hydroxyl groups with a compound which will react with the hydroxyl group to form a non-isocyanate reactive end-group. Trialkyl silane, particularly trimethyl silane, and ester, especially acetate, groups, are readily introduced and are preferred for that reason. In addition, the block copolymer may contain the residues from polyhydric initiators. The molecular weight of the block copolymer is not especially critical as long as it can be thoroughly blended with the other components of the polyurethane-forming composition, although those having a molecular weight from 1000 to 100,000, preferably 3000 to 50,000, more preferably 10,000 to 50,000 are especially suitable. The block copolymer may be of the hydrolyzable (containing Si-O-C bonds) or nonhydrolyzable (containing Si-C bonds) type. Particularly suitable block copolymers are those having a dimethylsiloxane content of 15 to 25 weight percent, 30 to 45 weight percent oxyethylene units, 40 to 55 weight percent oxypropylene units, and a molecular weight from 10,000 to 50,000. The block copolymer is used in an amount sufficient to reduce the formation of bubbles at the interface of the non-cellular and cellular polyurethane layers. This is achieved when 0.03 to 2, preferably 0.1 to 0.5, weight percent of block copolymer are used, based on the weight of the polyurethane-forming composition. In addition to the block copolymer, the non-cellular polyurethane composition advantageously contains at least one isocyanate-reactive material and at least one polyisocyanate. Suitable materials and compositions for preparing substantially non-cellular polyurethanes useful for backing a substrate are described, for example, in US-A- 4,296,159 and US-A- 4,696,849. The isocyanate-reactive material advantageously comprises a relatively high equivalent weight active hydrogen-containing material having an average functionality from 1.7 to 3 and an average equivalent weight from 1000 to 5000. As used herein, the term "functionality" refers to the number of active hydrogen-containing groups (or in the case of polyisocyanate, the number of isocyanate groups) per molecule. The active hydrogen-containing groups are preferably hydroxyl groups, although carboxylic acid, thiol and primary or secondary amine groups may be present as well. As described in US-A- 4,696,849, it is preferred to use materials having an average functionality of close to 2.0. Accordingly, it is preferred that the relatively high equivalent weight material have an average actual functionality from 1.7 to 2.2, more preferably from 1.8 to 2.1. Although a variety of materials such as polyester polyols, polyether polyol and polyacetals are useful, polyether polyols are by far the most preferred, due to low cost and particularly suitable properties. Most preferred are polymers of propylene oxide, especially those having terminal ethylene oxide capping, having an equivalent weight from 1000 to 2500 and a functionality from 1.8 to 2.1. The non-cellular polyurethane composition also advantageously contains a polyisocyanate, such as described in US-A- 4,296,159 and US-A- 4,696,849. Aromatic and aliphatic polyisocyanates are useful herein, with the aromatic polyisocyanates being preferred and toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymeric MDI and their respective derivatives and prepolymers being most preferred. Sufficient polyisocyanate is advantageously used to provide a ratio of isocyanate groups to active hydrogen-containing groups of from 0.85 to 1.3, preferably from 0.95 to 1.2. As discussed in US-A- 4,696,849, the polyisocyanate preferably is substantially difunctional, preferably having a functionality from 1.95 to 2.2. In addition, it is often desirable to include in the polyurethane-forming composition a relatively low equivalent weight chain extender or cross-linker. Chain extenders are compounds having two active hydrogen-containing groups per molecule and an equivalent weight from 31 to 1000, preferably from 53 to 200. Cross-linkers are of similar equivalent weight but have in excess of two active hydrogen-containing groups per molecule. Of these, the chain extenders are preferred, as their use permits the overall composition to have a functionality of approximately 2.0. These materials are advantageously used in relatively small amounts compared to the amount of relatively high equivalent weight active hydrogen-containing material. Preferably, from 3 to 50, preferably from 3 to 30, more preferably from 5 to 20 parts of the chain extender and/or cross-linker are used per 100 parts by weight relatively high equivalent weight active hydrogen-containing material. In addition to the foregoing, various ancillary components may be used in the substantially non-cellular polyurethane-forming composition. Included among these are catalysts, blowing agents, fillers, antioxidants, colorants, antistatic agents, flame retardants and preservatives. Among these, catalysts and fillers are of particular interest. Suitable catalysts include tertiary amine compounds and organometallic catalysts. Of the organometallic catalysts, organotin, organoiron and organobismuth catalysts are of particular interest. The use of organoiron and organobismuth catalysts is described, for example, in US-A- 4,611,044. Suitable organotin catalysts include dibutyltindilaurate, dimethyltindilaurate and stannous octoate. These catalysts are advantageously used in an amount from 0.001, preferably from 0.1 part by weight, up to 5 parts by weight for tertiary amine catalysts and up to 0.5 part by weight for organometallic catalysts. It is usually desirable to employ an inorganic filler in order to reduce costs and to provide certain physical property enhancements. Suitable fillers include aluminum trihydrate, calcium carbonate, carbon black, titanium dioxide, kaolin and wollastonite. Certain of these fillers provide flame retardancy (aluminum trihydrate) or coloration (carbon black and titanium dioxide), as well as function as fillers. Fillers, when used, are advantageously used in amounts from 30, preferably from 100, up to 300, preferably up to 225, more preferably up to 205 parts by weight per 100 parts relatively high active hydrogen-containing material. Although blowing agents such as water, air, nitrogen and halogenated halocarbons may be used to produce the substantially non-cellular layer, their use is advantageously in an amount such that the density of the layer is at least 0.8 g/cm³. Most preferably, no blowing agent is used other than trace quantities of water which may be present as impurities. The substantially non-cellular polyurethane layer is advantageously formed by forming a layer of the corresponding polyurethane-forming composition onto the substrate or the cellular polyurethane layer and curing same. Methods for forming polyurethane layers on substrates are well-known and described, for example, in US-A- 4,512,831; US-A- 4,595,436; US-A- 4,657,790 and US-A- 4,696,849. When the non-cellular polyurethane composition is applied to the substrate, it may or may not be cured before subsequent application of the cellular polyurethane-forming composition. However, it is preferred to at least partially cure the non-cellular layer before applying the cellular layer, and most preferred to cure it at least to a tack-free state. Curing is readily effected by heating, such as in an oven or using infrared lamps. The cellular polyurethane layer is in direct contact with the non-cellular layer. The cellular layer is advantageously formed by applying a layer of a cellular polyurethane composition to the substrate or the non-cellular polyurethane layer and curing same. As stated before, in applying the two polyurethane layers, it is not necessary to cure the first-applied layer before applying the second layer, but such is preferred. The cellular polyurethane-forming composition advantageously comprises a relatively high equivalent weight active hydrogen-containing material, a polyisocyanate and blowing agent. The high equivalent weight active hydrogen-containing materials and polyisocyanate are as described before with respect to the non-cellular polyurethane composition. The preferred polyisocyanates are TDI, MDI and polymeric MDI as well as prepolymers and derivatives thereof. The most preferred relatively high equivalent weight active hydrogen-containing materials are polymers of propylene oxide, especially those end-capped with oxyethylene units, having an equivalent weight of from 1000 to 2500. The preferred functionality is from 2 to 3 when TDI or prepolymers or derivatives thereof are used as the polyisocyanate, and from 1.7 to 2.2 when MDI or prepolymers or derivatives thereof are used. The amount of polyisocyanate used is as described before. The blowing agent is advantageously water, a halogenated hydrocarbon, air, nitrogen, or other material which generates a gas under the conditions of the reaction of the cellular polyurethane composition. It is preferred to froth the composition using suitable equipment, in order to whip air or other inert gas into the composition. Such processes are described in US-A- 3,821,130 and US-A- 3,862,879. In such processes, some water may be included for additional density reduction. Sufficient blowing agent is used to obtain the densities described before. In addition to the foregoing components, auxiliary components such as fillers, catalysts and cross-linkers as described before with respect to the non-cellular polyurethane-forming composition, may be used. It is particularly preferred to employ an organometallic catalyst and from 50 to 150 parts of an inorganic filler per 100 parts of relatively high equivalent weight active hydrogen-containing material. In addition, addition of a small amount of a silicone block copolymer is preferred to stabilize the cells of the reaction mixture until it has cured sufficiently to maintain its cellular configuration. The choice of substrate is not especially critical, and metals, leathers, elastic films, wood surfaces, papers, cardboards and a wide variety of other materials are suitable as the substrate. Of particular interest, however, are woven and non-woven textiles. Among these, of particular interest are textiles suitable for preparing floor coverings, including jute or other webbings, scrims, woven carpets and especially non-woven carpets. The weight of the substantially non-cellular polyurethane layer is advantageously from 8 to 40, preferably from 12 to 35, ounces/square yard (275 to 1350, preferably 400 to 1200, g/m²). The weight of the cellular polyurethane layer is advantageously from 10 to 40, preferably from 15 to 35, ounces/square yard (350 to 1350, preferably 500 to 1200, g/m²). Formation of the polyurethane-forming compositions into layers and applying same to a substrate is well-known. For example, the processes described in US-A- 4,512,831; US-A- 4,515,646; and US-A- 4,657,790 are suitable for this purpose. In general, these processes involve forming a mixture of all components except the polyisocyanate and sometimes the catalyst, then blending in the polyisocyanate (and catalyst if needed) and immediately applying same to the substrate. A doctor bar or rollers are suitable for marrying the polyurethane compositions to the substrate. Curing is advantageously effected by heating, such as in an oven, by infrared heating lamps, or other suitable means. In preparing floor covering according to this invention, it is most preferred to apply the non-cellular polyurethane layer to the back of the textile, and then to overcoat this layer with a layer of a cellular polyurethane. This is particularly true when the textile is a tufted textile, as the first non-cellular layer serves to glue the tufted fibers to the primary backing material. The following examples are given to illustrate the invention and are not intended to limit the scope thereof. Unless stated otherwise, all parts and percentages are given by weight. Example 1 and Comparative Samples A-D A non-cellular polyurethane composition was prepared from the materials listed in Table 1. Carpet Sample Nos. 1-7 and Comparative Samples A, B and C were prepared in the following general procedure. All the materials except the prepolymer and catalysts were thoroughly mixed at room temperature. The prepolymer was then mixed in with the other components, followed by the catalyst. The resulting mixture was then poured onto a tufted Camalon Tm yarn level loop carpet and scraped down to form a layer having a coating weight of about 32 ounces/square yard (1075 g/m²). In preparing Sample Nos. 1-4 and Comparative Samples A and B, this coated sample was then placed on top of a 60°C aluminum plate, and a 1/8" (3 mm) layer of a cellular polyurethane composition was applied. The cellular polyurethane composition was as described in Table 2. The resulting composite and underlying aluminum plate were transferred to a 120°C oven and cured. In preparing Sample Nos. 5-7 and Comparative Sample C, the non-cellular polyurethane was cured before applying the foam-forming composition. The type and amount of block copolymer in the respective polyurethane layers, and the results of these evaluations are reported in Table 3. As can be seen from the data in Table 3, addition of a block copolymer to the non-cellular layer caused a substantial decrease in the amount and size of the bubbles at the interface of the two polyurethane layers. The inclusion of a block copolymer in the cellular layer had little effect on the bubble line. The effect of the bubble line on the physical integrity of the carpet was determined subjectively by attempting to pull the cellular polyurethane layer from the composite. In those samples with a large bubble line, the cellular layer delaminated easily at the interface with the non-cellular layer. As the size and number of the bubbles decreased, delamination became more difficult. In Sample Nos. 3-7 delamination was quite difficult, with the mode of failure often being tearing of the cellular polyurethane layer itself. Comparative Sample D was prepared by repeating Comparative Sample C, substituting a Wellco Columbia Tm tufted carpet for that used in Comparative Sample C. A bubble line containing many large bubbles was present. When this sample was again repeated with the Wellco Columbia Tm carpet and 0.125 parts Block copolymer B in the non-cellular composition (Example 8) the bubble line was essentially eliminated. When this experiment was repeated (Example 9) using no block copolymer in the cellular polyurethane composition and 0.5 part of a 6700 molecular weight block copolymer containing about 21 percent dimethylsiloxane units, 32 percent oxyethylene units and 47 percent oxypropylene units in the non-cellular polyurethane composition, the bubble line was eliminated.

Claims: A process for preparing a polyurethane-backed substrate, wherein a first layer of a polyurethane-forming composition is applied to a substrate and a second layer of a polyurethane-forming composition is applied to said first layer and said layers are cured, wherein one of said first and second layers is a non-cellular polyurethane composition, and the other of said first and second layers is a cellular polyurethane composition, characterized in that said non-cellular polyurethane composition contains from 0.03 to 2.0 weight percent of a polysiloxane-polyether block copolymer, said block copolymer containing from 10 to 30 weight percent dialkylsiloxane units, from 30 to 70 weight percent oxyethylene units and from 0 to 55 weight percent other oxyalkylene units. A process as claimed in Claim 1, wherein said first layer is at least partially cured to a tack-free state before applying said second layer. A process as claimed in Claim 1 or Claim 2, wherein said first layer is said non-cellular polyurethane composition and said second layer is said cellular polyurethane composition. A process as claimed in any one of the preceding claims, wherein said dialkylsiloxane is dimethylsiloxane and, if present, said other oxyalkylene is oxypropylene. A process as claimed in any one of the preceding claims, wherein said alkylsiloxane content is from 15 to 25 percent, said oxyethylene content is from 30 to 50 weight percent, and said other oxyalkylene content is from 30 to 55 weight percent. A process as claimed in Claim 5, wherein said block copolymer contains from 15 to 25 weight percent dimethylsiloxane units, from 30 to 45 weight percent oxyethylene units and from 40 to 55 weight percent oxypropylene units, and has a molecular weight from 10,000 to 50,000. A process as claimed in any one of the preceding claims, wherein said non-cellular polyurethane composition contains from 0.1 to 0.5 weight percent of said block copolymer per 100 parts by weight of polyol. A process as claimed in any one of the preceding claims, wherein said non-cellular polyurethane composition and/or said cellular polyurethane composition contains a relatively high equivalent weight active hydrogen-containing material having an average equivalent weight from 1000 to 5000 and an average functionality from 1.7 to 3. A process as claimed in any one of the preceding claims, wherein said non-cellular polyurethane composition comprises (a) a polymer or copolymer of propylene oxide having an equivalent weight from 1000 to 2500, an average functionality from 1.7 to 2.1 and (b) toluene diisocyanate, diphenylmethyl diisocyanate, or a prepolymer or derivative thereof. A process as claimed in any one of the preceding claims, wherein said cellular polyurethane composition comprises (a) a polymer or copolymer of propylene oxide having an average functionality from 1.8 to 2.1 and an equivalent weight from 1000 to 2500, (b) diphenylmethyl diisocyanate or a prepolymer or derivative thereof and a sufficient quantity of a blowing agent to provide the cellular polyurethane with a density from 0.2 to 0.6 g/cm³. A process as claimed in any one of the preceding claims, wherein said substrate is a textile. A substrate having attached thereto successive polyurethane layers, wherein one of such layers is a cellular polyurethane which is attached directly to a non-cellular polyurethane layer characterized in that the non-cellular polyurethane layer contains from 0.03 to 2.0 weight percent of a polysiloxane-polyether block copolymer, said block copolymer containing from 10 to 30 weight percent dialkylsiloxane units, from 30 to 70 weight percent oxyethylene units and from 0 to 55 weight percent other oxyalkylene units. A substrate as claimed in Claim 12, wherein said layers are as defined in any one of Claims 1 to 10. A substrate as claimed in Claim 12 or Claim 13, wherein the substrate is a textile.

Inventors: LAMB TERRY L, SKAGGS KENNETH W, TURNER ROBERT B, LAMB, TERRY L., SKAGGS, KENNETH W., TURNER, ROBERT B.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1990
Main classification: D06N3
IPC codes: A47G27, D06N3, B32B5, C08G18, B32B27, D06N7