Laminate Material Having a Microfibrous Polyurethanic Base Sheet and Process for Its Preparation

The present invention relates to a novel laminated material comprising a microfibrous polyurethanic base sheet coupled with a functional substrate.

Microfibrous polyurethane sheets are known in the art as leather substitutes having good properties of softness and crease and, in the case of the abraded surface type, also of smoothness and suede or velours-like touch. Examples of such products and of their preparation are disclosed e.g. in U.S. Pat. Nos. 3,531,368 and 3,889,292 and in UK patent N. 1,329,710.

These known leather substitutes have been extensively used in the field of clothing. However these products have many drawbacks when used in other fields such as trimming in autovehicles and furniture, where their mechanical properties make them unsuitable for this application.

In the art it is known, e.g. in italian patent applications No. 21457-B/89 and No. 21457-B/89, the basic idea of improving the microfibrous imitation leather properties by forming a laminate of the base sheet and one or more functional substrates.

By functional substrate is meant a separately prepared substrate such as knitted or woven fabric, expanded polymer foam, waterproofing films, paper, etcetera. More than one substrate may be adhered to the same base sheet of imitation leather.

While the idea looked easy to implement, serious problems were encountered in order to meet the physical requirements of most demanding uses, such as trim covers for autovehicles. These problems led to modify the composition of the base sheet, and eventually to substitute polyurethane with other elastomers, e.g. chloroprene rubber, acrylic rubber etc., according to the end use of the laminated material.

It is an object of the present invention to solve above cited problems and to provide an imitation leather microfibrous polyurethanic base sheet that is suitable for any kind of laminated material, independently of its end use.

It is a further object of the invention to provide a process for the preparation of a laminated material having such a multi-purpose microfibrous polyurethanic base sheet.

According to the present invention, there is provided a laminate material having a microfibrous polyurethanic base sheet backed with a functional substrate, wherein said polyurethanic base sheet comprises 50 to 90% by weight of a polyester or polyamide microfiber felt of from 0.05 to 0.80 denier. The other complementary component of the base sheet, i.e. the polyurethanic polymer, is 10 to 50% by weight of the base sheet and is a polyurethanic polymer having polyurethane and polyurea bonds and average molecular weight corresponding to a polymer solution viscosity within the range from 10,000 to 50,000 centipoise (cps) when the solution is 25% by weight in dimethylformamide at a temperature of 20.degree. C. The resulting base sheet has final weight within 140 to 450 g/cm.sup.2 and density within 0.20 to 0.40 g/cm.sup.3.

The laminate trimming material according to this invention is prepared through a process comprising the steps of: preparing a felt of polyester or polyamide microfibers of from 0.05 to 0.80 denier, preparing a solution of a polyurethane-polyurea polymer having an average molecular weight corresponding to a polymer solution viscosity within the range from 10,000 to 50,000 centipoise (cps) when the solution is 25% by weight in dimethylformamide at a temperature of 20.degree. C., impregnating said felt with said polyurethane-polyurea polymer to such an extent as to obtain, after coagulating and drying steps, a polyurethanic base sheet containing from 50 to 90% by weight of said felt and from 10 to 50% by weight of said polyurethane-polyurea polymer and final weight within 140 to 450 g/m.sup.2 and density within 0.20 to 0.40 g/cm.sup.3, and bonding the polyurethanic base sheet thus obtained with a functional substrate comprising one or more substrate materials.

The peculiar combination of microfiber felt and of the polyurethane-polyurea polymer above disclosed provides an imitation leather base that is suitable for any kind of laminated material, even those to be used in demanding and severe conditions such as those met in autovehicle trimming.

Furthermore, the invention provides specific laminated materials having outstanding performances in their specific uses. An example of these materials is the laminated imitation leather wherein the base sheet is coupled with a woven fabric consisting of mixed cotton and polyethylene terephthalate fibers in a ratio cotton/PET within the range from 30/70 to 45/55. This laminated autovehicles seats where the substrate is a woven fabric autovehicles seats were the substrate is a woven fabric. When the laminated material has to be provided with flame retarding or fireproofing properties, the use of the invention base sheet compensate the otherwise inevitable loss of softness and/or mechanical properties resulting from known techniques involving backside coating of base sheet with a fire retarded composition.

According to a preferred aspect of the invention, fire retarded laminate material are comprising a base sheet as above disclosed, wherein the felt microfibers are obtained from a copolymer of polyethylene terephthalate and a glycol of formula ##STR1##

This and other examples and aspects of the invention will be hereinafter disclosed.

According to a preferred embodiment of the present invention, microfibers used for preparation of the felt are polyethylene terephthalate or polyamide 6 or polyamide 6--6. These fibers are preferably of from 0.05 to 0.4 denier.

The felt is prepared according to any suitable method known in the art, e.g. as disclosed in U.S. Pat. Nos. 3,562,374 and 3,706,613 here enclosed by reference.

The polyurethanic polymer has average molecular weight corresponding to a polymer solution viscosity within the range from 10,000 to 50,000 and preferably from 15,000 to 30,000 centipoise (cps) when the solution is 25% by weight in dimethylformamide at a temperature of 20.degree. C.

The resulting base sheet has final weight within 140 to 450 g/m.sup.2 and density within 0.20 to 0.40 g/cm.sup.3.

Preferred weight is from 180 to 260 g/cm.sup.2 and preferred density from 0.200 to 0.300 g/cm.sup.3.

Most preferably, said polyurethanic polymer is the reaction product obtained by reacting 3-isocyanate methyl3,5,5-trimethylcyclohexyl isocyanate, or a diisocyanate of formula

where R is a benzene or cyclohexane group, with a mixture of polyester glycols and polyesters glycols having an average molecular weight of from 1900 to 2100; and by extending the resulting prepolymer by reaction with a chain extender.

Suitable chain extenders are aromatic amines such as 4,4'-diamine diphenylmethane or aliphatic diamines such as 4,4'-diamine dicyclohexylmethane.

A preferred chain extender is water. It was found that the use of water as a chain extender provides the base sheet with an increased softness and an improved touch to such an extent as to compensate most of the loss of those properties occurring upon backing of the base sheet with the required functional substrates.

Preferred polyester glycols are polycaprolactone glycol (PCL), polytetrametylene adipate glycol (PTMAG) and polyethylene and polypropylene adipate glycols (PEAG and PPAG respectively), and preferred polyethers are polyoxytetramethylene glycol (PTHF) and polyoxy ethylene and propylene glycols (PEG and PPG respectively). The polyether glycol/polyester glycol ratio in the glycols mixture is within 1/4 to 4/1 and most preferably of about 3/1.

The water used to react with prepolymer to extend the polymer chain is provided in a molar ratio water/glycols within 1.50 to 1.71 and most preferably within 1.57 to 1.65. The reaction is carried out at a temperature within 30.degree. to 80.degree. C.

In following example II, preparation of a base sheet by reaction with water is disclosed. A more detailed disclosure of the preparation of a polyurethane-polyurea polymer solution by extension reaction with water is recited in Italian patent application No. MI92-A-001945 filed Aug. 6, 1992 in the name of Alcantara S. p. A. and herein enclosed by reference.

The functional substrate to be adhered to the base sheet is depending on the end use of resulting laminated material. Consequently, also bonding means may vary according to the kind of substrate material.

A first kind of substrate is woven or knitted fabric. This substrate material is used in order to give the base sheet improved mechanical properties for use as trim cover on autovehicles seats and on furniture (chairs, sofas, etc.). It has been found that outstanding performances are obtained when the woven fabric is composed by mixed cotton and polyester fibers in a ratio of from 55 to 75 parts of polyester fibers and 30 to 45 parts of cotton fibers. Alternatively, when a knitted fabric is required, i.e. when the trim cover has to be more yielding, a nylon knitted fabric gives the best results.

When the laminate material has to be provided with fireproof or flame retarding properties, this is obtained by using the above disclosed copolymer of polyethylene terephthalate with a glycol of formula ##STR2## as polymer for the microfiber felt.

This copolymer is commercially available, e.g. from the firm Enichem in Acerra (Italy) under the trade name FIDION SR. The same or others flame retarded copolymers, e.g. those produced by Hoechst (Germany) may be used to obtain knitted or woven fabrics to be adhered to the base sheet according to the invention, besides or alternatively to use of above disclosed flame retarded felt.

When the felt is obtained according to the method disclosed in above cited US patents, the flame retarded copolymer is preferably coextruded with a styrene polymer or copolymer having the following properties: relative viscosity 1.78.+-.0.03, max. moisture 400 ppm, softening point 87.degree. C., weight density 1.05, apparent density 0.65, rest angle 32.

The felt is needle punched to obtain a felt weight and density according to the invention, and this styrene matrix is thereafter dissolved in the usual way, i.e. after impregnation with polyvinyl alcohol.

The invention will now be further disclosed with reference to the following examples.

A polyethylene terephthalate microfiber felt was prepared according to known techniques in the following way. Fibers were coextruded with a content of about 57 parts by weight of polyethylene terephthalate, 40 parts of polystyrene copolymer and 3 parts of polyethylene glycol, the latter being included within the styrene matrix. The extruded fiber was about 3.8 denier and had 16 PET microfibers in the styrene matrix, said microfibers being about 0.10-0.11 denier, drawing ratio 2.5/1, 5 crimps/cm, 51 mm length. The fiber was needle punched to obtain an intermediate felt of fibers having a density of 0.195 g/cm.sup.3 and a weight of 540 g/m.sup.2.

This intermediate felt was then immersed in a 20% water solution of polyvinyl alcohol, dried and treated with perchloroethylene to dissolve the polystyrene matrix and obtain a microfiber felt still comprising polyvinyl alcohol.

Separately a polyurethanic solution was prepared reacting 2 moles of 4,4'-diphenylmethane diisocyanate and 1 mole of a mixture of PTHF (molecular weight 1976) and PCL (molecular weight 1958) in a molar ratio of 3/1 at 65.degree. C. for 3 hours. The thus obtained prepolymer was dissolved in dimethylformamide to obtain a 25% solution (by weight). A 25% (by weight) solution of 0.825 moles of 4,4'-diaminodiphenylmethane and 0.175 moles of n-dibutylamine in dimethylformamide (DMF) was prepared and added to the prepolymer solution at a temperature of 65.degree. C. The mixture was reacted for 30 hours until a 25% by weight solution free of NCO groups was obtained. The resulting polyurethane-polyurea polymer had an average molecular weight corresponding to a polymer solution viscosity of about 20,000 centipoise (cps) at a temperature of 20.degree. C. (i.e. to a calculated m.w. of about 22,000).

The polyurethanic solution was diluted with DMF to have a 13% solution by weight, the felt was then immersed in above cited solution, the excess of solution removed by expression and the impregnated felt coagulated in water to remove polyvinyl alcohol and obtain a sheet that after drying contains 68.+-.3% by weight of microfiber felt and 32.+-.3% of polyurethanic polymer.

This sheet was longitudinally cut to a thickness of 1 mm and subsequently abraded to obtain the suede touch.

The thus obtained base sheet properties are recited in table I.

The same steps of example I are carried out, but for the use of a 25% (by weight) DMF solution of 1.65 moles of water as chain extender. This solution contains 0.175 moles of n-dibutylamine, is prepared and added to the prepolymer solution at a temperature of 65.degree. C., and is reacted for 6 hours upon which the reaction is complete. The resulting polyurethane-polyurea polymer has an average molecular weight corresponding to a polymer solution viscosity of about 20,000 centipoise (cps) when the solution is 25% by weight in dimethylformamide at a temperature of 20.degree. C. (i.e. a calculated MW of about 22,000).

The final base sheet properties are recited in table I.

The same steps as in Example I were followed, but the microfiber felt was prepared from the above disclosed flame retarded copolymer of polyethylene terephthalate sold under trade name FIDION SR.

The mechanical and flame retarding properties of the resulting base sheet are recited in table I.

A woven fabric of 65/35 polyester/cotton fiber with weight of about 60 g/m.sup.2 was adhered by means of thermobonding powder (polyester or polyamide powders such as e.g. Grilltex by EMS--Switzerland) to a base sheet as obtained according to example I.

The mechanical properties of the resulting laminated sheet are recited in table I.

A flame retarded polyester woven fabric was coupled by means of thermobonding powder to a base sheet according to example II. The base sheet is previously backside coated with a flame retarded mixture comprising halogen, P and Sb compounds. These mixtures are known in the art.

The mechanical and flame retarding properties of the resulting laminated sheet are recited in table I.

A knitted fabric 100% nylon was adhered by means of a thermobonding foam layer 1.0 mm thick to a base sheet according to example II. The mechanical properties of the resulting laminated sheet are recited in table I.

A 100% flame retarded polyester fabric was adhered by means of thermobonding powder to a base sheet according to example III. The mechanical and flame retarding properties of the resulting laminated sheet are recited in table I.

A polyurethane foam layer 4 mm thick and having a density of 22 Kg/m.sup.3 is flame bonded to a base sheet according to example I. The mechanical properties of the resulting laminated sheet are recited in table I.

A flame retarded polyurethane foam layer 4 mm thick and having a density of 22 Kg/m.sup.3 is flame bonded to a base sheet according to example I, previously backside coated with known flame retarding mixtures. The mechanical and flame retarding properties of the resulting laminated sheet are recited in table I.

A laminated sheet according to example VIII is obtained except in that the base sheet is a flame retarding sheet according to example III and the polyurethane foam is flame retarded. The mechanical and flame retarding properties of the resulting laminated sheet are recited in table I.

To a laminated material according to example IV a polyurethane foam 10 mm thick and having a density of 30 Kg/m.sup.3 is flame bonded, to the thus resulting laminate a 100% nylon knitted fabric is bonded through thermobonding powders. The mechanical properties of the resulting laminated sheet are recited in table I.

A laminated material according to example XI is obtained but for the use of a 4 mm thick polyurethane foam and of a knitted polyethylene terephthalate fabric. The mechanical properties of the resulting laminated sheet are recited in table I.

To a laminated material according to example II a micropore waterproofing polyurethane film is glue bonded. The waterproofing film is manufactured by the firm Baxenden (UK). The mechanical properties of the resulting laminated sheet are recited in table I.

To a base sheet according to example I a polyurethane foam 1.5 mm thick was adhered by means of an electrobonding film. The mechanical properties of the resulting laminated sheet are recited in table I.

The base sheet according to the invention is suitable also for less demanding applications such as coupling to wallpaper (in this case the bonding agent is glue, and preferably vinyl glues), or coupling by glues or above disclosed thermobonding foams to natural or imitation leathers of poor quality with respect to the invention base sheet.