GB2107644A

GB2107644A - Laminated products

Info

Publication number: GB2107644A
Application number: GB08130729A
Authority: GB
Inventors: George Jerry Kleinerman; Malcolm Rodney Searle
Original assignee: Porvair PLC
Current assignee: Porvair PLC
Priority date: 1981-10-12
Filing date: 1981-10-12
Publication date: 1983-05-05
Also published as: GB2107644B

Abstract

A grain leather like material comprising a leather substrate and a coloured or embossed or coloured and embossed microporous polyurethane layer or foil at least 0.1 mm thick adhered by a thermoset or cured adhesive to the substrate, the layer or foil having a grain appearance which is substantially undamaged by heating to 130 DEG C while stretched by up to 20% for 2 minutes. A process for producing such material is also disclosed.

Description

SPECIFICATION Laminated products The present invention relates to the production of leather-like materials incorporating a strength im parting portion derived from natural leather provided with an artificial grain appearance layer of polyurethane. The invention extends to the product itself and to a method of making the product.

Cow and other animal hides are graded before use for high quality purposes such as shoe leather and products having damage caused by insects such as warble flies which cause holes in the grained surface or scars caused by damage to the animal when alive or by damage to the hide when being processed afterslaughterwill render the hide and leather made from it of less value. In addition in the preparation of thin grain leather a proportion of the back flesh surface ofthe hide which contains a coarserfibrous structure than the grain surface is often split off to reduce the thickness of the material and increase its suppleness. This cut-away layer is referred to as a split. This can be used for coarse types of suede but if it can be given a surface of grain leather appearance its value can be increased substantially.

There have been a number of proposals for doing this. One which gives excellent surface appearances is made by replicating a desired grain surface appearance by taking a moulding of an acutal leather with a silicone resin, pouring a curable polyurethane into the moulding and then before the polyurethane has cured depositing a split into the fluid polyurethane, allowing the composite to cure and then stripping off the silicone mould for reuse.

The trade has however assessed this process as being extremely expensive and only useful for certain specialist activities.

Other techniques which have been tried have involved transferring a thin elastomeric polymer coating mounted on a polyesterfilm onto the leather split which is first coated with a thermoplastic resin emulsion. Typically 30 to 35 grams per square foot of this binder emulsion has to be used for splits such as cowhide. It has been found however that this coating being very thin has been susceptible to fibres from the split wearing through the artificial surface unacceptably rapidly. In addition the binder is thermoplastic and thus if the coated split is to be subjected to shoe-making processes involving heat treatment as in lasting, particularly as in steam or wet lasting, then there is a risk that the bond between the grain leather film and the split substrate can become labile and the product be damaged.This is particularly important because at this stage money will have been spent on converting the product into a shoe.

Other processes involve spread or spray coating onto splits a layer of polyurethane solution to produce an approximately 250 grams per square metre deposit following which a finish is applied to the coating the following day.

All these processes suffer from the disadvantage of severely reducing the water vapour permeability of the split, requiring subsequent processing to impart a grain leather-like finish or embossed finish to the material or run the risk that the bond between the coating and the split can become labile during the subsequent shoe making operations.

There is thus a need for a process which will enable preformed or prefinished leather-like sur faces, e.g. grain or patent leather-like surfaces, to be applied to splits and low quality hides economically and without severely reducing water vapour per meability using a bonding system which is not labile in subsequent treatment processes and using bond ing conditions which are readily attainable in con ventional tanneries and which do not permanently damage any pre-embossed characteristics which may be given to the grain layer which is being applied to the split. Thus for example the bonding system needs to be able to be carried out at temperatures which do not damage the preformed, e.g. fused embossed or glossed, or prefinished, e.g.

solvent spray consolidated or fused or solvent printed, surface. Desirably, the process should also provide the means for increasing the substance (thickness) of the splits or hides.

The invention will be described with reference to cowhide splits but it will be appreciated that it can be used with other materials such as damaged grain leathers, side leathers, skivers and goatskin, cabretta, pig or sheep skin or indeed any other leather product or hide product which provides a sufficient strength for the end purpose to which it is intended to put the material but which has a surface appearance which needs upgrading to a more grain leather-like appearance.

According to one aspect of the present invention a kit of parts for assembly into a grain leather-like material comprises a leather substrate provided on its surface, which will be inside the laminate, with thermosettable or curable adhesive, and a microporous polyurethane layer orfoil at least 0.1 mm thick, the surface of the foil which will afford an outside surface ofthe laminate being preformed or prefinished, the said adhesive being settable or curable at temperatures below those which would cause significant permanent damage to the said preformed or prefinished surface of the foil.

The layer or foil preferably has a grain appearance which is substantially undamaged by heating to 130"C while stretched by up to 20% for 2 minutes.

The invention also extends to a process for the production of a grain leather-like material in which a kit of parts in accordance with the invention is used and the microporous foil, with its preformed or prefinished surface facing out, is laminated by heat and pressure to the surface of the leather substrate carrying the thermosettable or curabe adhesive at a temperature such that no significant permanent damage is caused to the said preformed or prefinished surface of the foil.

According to another aspect of the invention a grain leather-like material comprises a leather substrate and a coloured or embossed or coloured and embossed microporous polyurethane layer or foil at least 0.1 mm thick adhered by a thermoset or cured adhesive to the substrate, the layer or foil having a grain appearance which is substantially undamaged by heating to 130"C while stretched by up to 20% for 2 minutes.

According to a further aspect of the invention, a process for the production of a grain leather-like material comprises treating a surface of a leather substrate with a thermosetting or curable adhesive in an amount of not more than 10 grams of solids per square foot, and laminating preformed or prefinished, e.g. a coloured or embossed or coloured and embossed, microporous polyurethane layer or foil by heat and pressure to the adhesive treated surface of the leather.

The term preformed means a material which has had a visible pattern embossed in its surface whilst the term prefinished means that foil has been given a finish such that on bending with the surface inwards a leather-like pattern of creases is observed, i.e. the surface exhibits the so-called "grain break" characteristics observable in natural leather.

The leather substrate may comprise leather splits or low substance (low thickness) leather and is preferably substantially free from sizing and/or filling.

The adhesive treated leather substrate is preferably allowed to dry before lamination of the layer or foil, and the laminated material and its constituent parts prior to lamination are preferably all water vapour permeable.

The microporous polyurethane layer or foil is one which has been preformed or prefinished at a temperature which is greater and preferably at least 10"C or 20"C greater and especially at least 300C greater than the maximum temperature encountered by it during the lamination.

Where the layer or foil is preformed it may have been embossed by a contoured roller or flattened e.g. glossed by a smooth roller. It will preferably have been preformed at a temperature in excess of 140 C. In this case, the layerorfoil is laminated by heat and pressure to the adhesive treated surface of the leather at a laminating temperature such as to thermoset or cure the adhesive, the laminating temperature being below that at which the polyurethane layer was embossed.

The polyurethane layer or foil is preferably 0.2 mm to 1.5 mm thick and it may be coloured. The foil may be coloured by being dyed or pigmented through its bulk and in addition or alternatively it maybe given a surface colouration by a surface finishing process, e.g. by a solvent spray finish and heated air blast such as disclosed in British Patent Specification No.

1190551 or by a sprayed or printed or coated thin solvent and polymer containing layer with simultaneous heating, e.g. by an air blast as in British Patent Specification Nos. 1325850 and 1324541 or by a thin coagulated and solvent evaporated coating process such as described in British Patent Specification No. 1325928 optionally followed by one or both of the two earlier referred to processes.

Such surface colouration processes are preferably carried out prior to any embossing which is undertaken.

Embossing may be carried out using embossed rollers with or without an intervening release sheet so as to produce any desired pattern of indentations and lines so as to replicate any natural skin finish or embossed pattern which may be desired. A gloss finish either embossed or plane can be achieved by the interposition of a strippable polymer film and when a plane roller is used this can produce a high gloss finish such as is referred to as a "patent leather" finish. A process for producing such a finish using an interposed smooth film and defined conditions of temperature and pressure is described in British Patent Specification No. 1352512.

The microporous foil preferably has an apparent density of at least 0.1 grams/cc, especially an apparent density in the range 0.25 to 0.8 grams/cm3, and is desirably an open cell system so that the product is water vapour permeable.

The adhesive is preferably a heat activatable cross-linkable polyurethane adhesive which may be applied in amounts of up to 10 grams of solids per square foot, preferably 1 or 2 to 7 and especially about 3.5 grames per square foot. It is preferably cross-linkable at a temperature in the range 65 to 110 C, under pressures of between 20 and 1500 p.s.i.

and with dwell times ranging from 2 to 30 seconds.

The preferred conditions are, a heat in the range 75 to 100"C, a pressure in the range 30 to 1000 p.s.i. and a dwell time of 3 to 15 seconds e.g. 5 to 10 seconds preferably using a pressure of between 50 p.s.i. and 500 p.s.i.

The adhesive is preferably a cross-linkable polyurethane adhesive and is applied at a dry weight of 20 to 40 grams per square metre and is allowed to dry for 1.5 to 20 hours at a temperature not in excess of 450C.

The laminating is then preferably carried out at a temperature in the range 75 to 90"C for 5 to 15 seconds at a pressure of 25 to 750 p.s.i., typically 50 to 250 p.s.i.

The polyurethane adhesive may be an aqueous emulsion and this is satisfactory for ordinary end uses of the leather-like material. However where high resistance to prolonged contact with water is required we have found that solvent based adhe sives provide much enhanced results, e.g. adhesives in which the polyurethane is dissolved in a solvent e.g. an adhesive consisting of soluble polyurethane prepolymer and a soluble cross-linking agent, e.g. a polyfunctional isocyanate prepolymer produce good results. Such adhesives are thus preferred.

The conditions which have to be achieved in the lamination are that a good bond should be produced but that the temperature, dwell time and pressure should not be such as to damage the preformed or prefinished surface, e.g. distortion of a grain pattern, permanently or cause any significant penetration of the polyurethane foil by the fibres in the substrate. in addition excessive pressures should not be used because this can cause permanent compression of both the foil and the hide derived material. Clearly the particular laminating conditions which must be used can be arrived at by simple tests on the basis of this teaching to suit the particular microporous polyurethane foil which is being used, the particular curing requirements of the adhesive and the particu lar compression characteristics of the hide derived material.

In particularwhen higher temperatures are used shorter dwell times can be used.

When we refer to lack of distortion of a grain pattern we do not exclude the possibility that if some slight damage is imparted to the grain of the microporous layer during lamination it can be removed by gentle reheating to a temperature of for example 100 to 105'such that the material can either be post-treated after lamination to restore the grain surface or the heating used during lasting can be relied upon to achieve this.

The heat and pressure are preferably applied by a plain unengraved or a fine hair cell plate which can be applied directly to the top free or grain surface of the microporous foil.

The embossing of the microporous foil may be carried out at temperatures in the range 140 to 150 C and at pressure of the order of 50 to 100 p.s.i.

Embossing carried out in this way is stable to further processing at 1000C even at the much higher pressures referred to for the lamination.

A further aspect of the invention is that it provides the means for increasing the substance (thickness) of the leathers and splits processed according to the invention to a level which makes them satisfactory for use as upper leather material for the manufacture of footwear. Thin bovine splits at about 1.3-1.4 mm and low substance leathers such as Indian Kips at 0.7-1.1 mm and pigskin which is generally 0.8-1.3 mm thick, are reiatively plentiful and inexpensive but despite adequate mechanical strength are considered too low in substance for use in shoe uppers.

As during its lamination to leathers and splits by the process of the invention the polyurethane foil itself undergoes only a slight reduction in thickness, its thickness can be selected in such a way as to raise the substance of the leathers or splits to be laminated, to the level required. This level is generally 1.5 to 2.2 mm, frequently 1.7 to 2.0 mm.

Another aspect of the present invention is that its products, consisting largely of leather, can be processed in shoe manufacturing factories in a manner verysimilarto natural leather.

A still further aspect of the present invention is that its products combine the hygiene and comfort properties (moisture absorption and permeability to water vapour) associated with natural leathers, with the superior functional properties (scuff- and abrasion resistance, resistance to water penetration and easy clean characteristics) typical of high quality synthetic upper materials.

The invention may be put into practice in various ways and a number of specific examples will be given to illustrate the invention.

EXAMPLE 1- Preparation of the microporous foil.

A homogeneous dispersion of Micronised sodium chloride, mean particle size 10 micron 300 parts Thermoplastic polyurethane polymer solution, 33% solids in dimethylformamide (DMF) 300 parts DMF 100 parts Carbon black 5 parts was extruded onto a moving woven strainless steel endless carrier. The extrudate was next coagulated to sheet form by passing it through a tank of a water salt DMF blend, containing 12% DMF and 8% sodium chloride. The sheet was next stripped off the carrier and residual sodium chloride and DMF leached out by passing the sheet through a series of hot water tanks and pressure nips. The sheet was then dried.

The dried sheet had a microporous open cell structure, was 0.5 mm thick and its water vapour permeability was 180 g per square metre per hour.

The upper surface of the sheet was given a black pigmented polaurethane finish by printing. The sheet was subsequently embossed with a grain pattern at 145"C at a pressure of 70 p.s.i. The coloured and embossed sheet was 0.42 mm thick and had a water vapour permeability of 69 g per square metre per hour.

Preparation of the hide and application ofadhesive.

Portions of Brazilian full chrome retanned cowhide split 1.7 to 1.9 mmsthick, having an area of 80 inches by 25 to 30 inches, weighing approximately 1400 grams per square metre and having a fairly smoothtextured but generally uniform surface were used in this experiment.

The denser surface of the split which would have been in the interior of the hide and which had not been given any sizing or filling was then spray-coated with an aqueous emulsion of cross-linkable polyurethane adhesive. The emulsion was an aliphatic polyurethane containing 25% solids and containing a melamine formaldehyde resin to render it cross-linking at 100"C. The aliphatic polyurethane was self cross-linking at higher temperatures.

This aliphatic polyurethane material when cured as a 1 inch thick solid layer at 1 500C had a 100% modulus of 250 kg per square centimetre, a tensile strength of 380 kg per square centimetre and an elongation at break of 240%. The 25% solids formulation had a pH of 7.5 to 8.5 and a viscosity of less than 100 poise. It was applied in an amount of 2.4 grams per square foot and the hide then allowed to dry in aiq The foil described above was then applied under three different lamination conditions, the split being on the bed of a laboratory press and the platen of the press coming down onto the embossed top surface of the foil. The split was cushioned from the bed by about 5 to 6 mms thickness of polyurethane foil as described above (as four separate sheets). The platen was heated to 100"C. Four conditions were used, Examples 1A, 1B, 1C and 1D. Example 1A used 700 p.s.i. and 20 seconds. This produced a good bond but there was distortion of the grain of the polyurethane foil and some strike through of fibres from the split and this distortion and strike through were difficult to remove even after heating at 1 10"C for two minutes. The conclusion was that this was an excessive pressure and an excessive dwell time for this particular combination.

Example 1 B used 500 p.s.i. and 10 second and this produced a good bond with much less distortion, the degree of distortion being commercially acceptable.

Example 1C used 500 p.s.i. and 5 seconds and again there was a good bond and here there was only minimal distortion and this was the preferred lamination conditions for this foil and adhesive and split.

Example 1 D used 1,000 p.s.i. for 3 seconds. This produced a good bond but there was excessive compressing of the foil and the leather and distortion of the grain of the foil which was permanent at 150 C. These conditions were again considered to be excessive for this particular combination.

In the experiments just described the specimens processed were of the same size as the platen of the laboratory press used. The pressure applied by the platen was therefore distributed over an area equal to that of the platen and can therefore be termed specific pressure. It will be appreciated that had the specimens been smaller than the platen - as is almost invariably the case during processing on full size tannery presses - then the actual pressure per unit area applied to the laminate would have been greater than the specific pressure.

Moreover, the combinations of pressure and dwell time found in the experiments just described to avoid distortion of the grain of the polyurethane foil and excessive compression of the foil and the leather, apply to the particular grade of leather and to the nature and thickness of the back up material used for cushioning the leather from the bed of the press. With less compressible leather and more compressible back up materials pressures higher than those quoted would have produced satisfactory results.

Examples 1B and 1C produced a dry bond strength between the leather and the foil of 1.2 kg per centimetre width and a wet bond strength of 1.0 kg/cm width. The material had a water vapour permeability of 57 grams per square metre per hour.

Bond strengths of the materials of the invention were measured using a tensile testing machine. A 1 cm wide strip of the material was used and the foil/split bond separated at one end by an amount sufficient for the separated free ends to be clamped in sets of jaws set 2 cm apart. The initial separation was by moistening the material in that area with Cellosolve. The jaws were then separated at a cross head speed of 10 cm/min, the tensile reading being noted. "Dry Strength" was measured in this way with the material dry. "Wet Strength" was measured in this way with the material thoroughly wet.

Resistance to water penetration was determined using a Bally penetrometer on which the material was flexed in a manner simulating conditions of wear, one surface of the material being in contact with water. The measurement taken was of the duration of flexing which was just sufficient to cause water to penetrate through the sample from one face to the other. 30 minutes was thought to be a good result; a time of more than 2 hours being excellent.

Water vapour permeability was measured by the method described in British Patent Specification No.

1273524 at page 12 lines 44 to 62. Examples 1B and 1C had a flex life of in excess of 20 hours at 0 C. Flex life was measured by the method described in British Patent Specification No. 1273524 at page 13 lines 1 to 46.

EXAMPLE 2 In another experiment the same type of polyurethane foil and cowhide leather split were laminated on the laboratory press using the same adhesive blend.

The conditions were: Adhesive deposit 2.5 g/sq.ft.

Platen temperature 92"C Dwell time 10 seconds Specific pressure 200 p.s.i.

The laminate had a dry bond strength of 1.25 kg/cm width and resisted delamination on wet flex testing for 80,000 flexes.

EXAMPLE 3 In this example the microporous polyurethane foil was produced as described in Example 1 except that the extrudate was thicker. The polyurethane foil when dried was 0.7 mm thick and after application of the finish and embossing its thickness was between 0.62 and 0.65 mm and its water vapour permeability was 65 g/sq metre per hour.

Three types of leather were used in this example: Pigskin of Japanese origin with a fairly smooth back; French cowhide Butt splits with a uniform fluffy surface; Full chrome retanned Madras side leather splits.

The Madras side leathers used are known in the trade as Grade 6n top splits. These are splits which have retained their corium (grain) layer but despite substantial sizing and filling much insect and scar damage is very obvious. Their substance varies from 0.7 to 1.1 mm and is mostly 0.9 to 1.0 mm. Because of poor surface appearance and low substance these splits are not normally suitable for footwear and are mostly used forfancy leather goods.

The leathers were treated with the same aliphatic polyurethane emulsion containing melamine-formaldehyde resin as in Example 1 and were allowed to drain air.

Lamination of polyurethane foil to the pretreated leathers were carried out on a hydraulic tannery press provided with a smooth heated metal platen and a highly compressible rubber back up plate. The lamination conditions were: platen temperature 90"C, pressure gauge setting 1420 p.s.i., dwell time 5 seconds. The temperature was thermostatically controlled and pressure and dwell time automatically pre-set. The press had a pre-set pressure gauge and the dwell time was quoted from the time the pre-set pressure was reached, plate release being automatic at the end of the pre-set dwell times.

The results obtained were as follows:

Madras side Cowhide leather Butt Corium Reverse Pigskin split side side Adhesive deposit, g/sq .ft. 2.1 3.5 2.2 3.5 Bond strength, kg/cm width 1.15 1.45 0.2 1.4 Water vapour permeability, g/m2 hour 53 49 50 54 Total thickness, mm 1.4-1.5 1.7-1.8 1.4-1.5 1.4-1.5 Thickness of foil in the product, 0.55 0.50 - 0.55 mm Dynamic waterproof ness (Bally penetro meter) hours > 2 > 2 - > 2 The products had an attrictive uniform grain leather-like appearance with defects other than outright holes and flay cuts completely masked. The substance of the laminated leathers was 0.5 to 0.55 mm higherthan it would have been had the leathers been processed under similar conditions without the polyurethane foil. The products had ample permeability to water vapour for comfort in wear when made into shoes, a scuff resistance better than that of most conventional leathers, a high degree of resistance to water penetration and easy clean properties typical of high quality synthetic upper materials.

In the case of the Madras side leather splits it became apparent that the smooth heavily filled grain (corium) side does not lend itself to the development of high bond strength to the polyurethane foil, but that very good results are obtained by laminating the foil to the reverse side which is hairy and substantially unfilled.

Shoes made from pigskin and from cowhide splits laminated to polyurethane foil have been found to go through the shoe manufacturing process in a very similar manner to conventional leather shoes, and had good appearance and shape retention and have been found to be comfortable in wear.

Details of the nature of the polyurethane from which the foil is made and of the foil itself priorto preforming or prefinishing are given in British Patent Specification No. 1352512 referred to above to which attention is directed.

Details of how the open cell microporous foil may be made and prefinished are also given in the same specification and attention is directed thereto in those respects as well.

As mentioned above the microporous foil preferably has an apparent density in the range of 0.25 to 0.8 g/cm3 more preferably in the range of 0.35 to 0.6 g/cm3. Typically the density of the polyurethane itself is about 1.2; it will therefore be apparent that in the neighbourhood of 1/3 to 3/4 of the volume of the microporous material is air. The sheet preferably has a percent elongation at break of above 50% (e.g. in the range of about 300 to 400% or more); a tensile strength above 35 Kg/cm2 (e.g. in the range of about 60 to 100); an eiastic modulus above 2 Kg/cm2 (e.g.

in the range of about 4 to 9) and a notch tear strength above 2 (e.g. in the range of 3 to 5) Kg per mm of thickness. It should desirably permit the passage of water vapour; thus its water vapour transmission should be at least 200 g/m2/24 hours measured as in ASTM E 96-66, procedure B). Also it is desirable that at least the upper surface of the sheet, after suitable finishing, be resistant to the passage of liquid water, e.g. the finished sheet should have a hydrostatic head (British Standard 2823/1957) of above 100 mm Hg. While the polyurethane usually shows a tension set below 100%, the preferred microporous polyurethane sheets generally recover completely with substantially no permanent set (under standard dry conditions at room temperature) after being stretched 100%.

All measurements referred to herein are made at room temperature (e.g. 230C) unless the test method specifies otherwise.

Typical embossing patterns conventionally used in the artificial leather art may be used as the pre-embossing in the present invention.

EXAMPLE 4 An adhesive was manufactured in the following way. A 25% solution of a hydroxyl-terminated urethane prepoltmer was made up in butyl acetate heated to 60"C, under agitation. 0.16% of brown organic dyestuff was added as a colour aid in further processing to assist in assessing even application of the adhesive. The solution had a viscosity of 6.4 poise at 25"C.

For application to a leather substrate 100 parts of the above mixture were combined with 5 parts of a polyfunctional isocyanate prepolymer cross-linking agent used as a 75% solution in ethyl acetate and intimately mixed.

The crosslinking agent is itself a reaction product of a polyhydric alcohol and a polyfunctional isocyanate. It thus has low volatility generally asociated with polyfunctional isocyanate prepolymers, any free di ortri-isocyanate being present in negligible amounts only.

When freshly made, the blend had a viscosity of 5.5 poise at 25"C and had adequate rheological properties for application to leather substrates by gravure printing. On standing, the curing reaction proceeds slowly also in solution but the blend can be satisfactorily used for a period of at least 8 hours at 25"C provided it is stored in tightly sealed containers so as to exclude atmospheric moisture.

The adhesive mixture was applied to the surface of the leather substrate by gravure printing to give 20-40 g/m2 dry weight typically 30 g/m2 dry weight and allowed to dry at a temperature not in excess of 45 Cfor a minimum of 11/2 hours and a maximum of 20 hours, the material remaining substantially uncured during this period of time, e.g. at not above 25"C and relative humidities not in excess of 70% RH, when being held for periods at the upper end of this range of holding times. A foil, as used in Example 1, was then laid on the prepared leather and the two were combined by placing the lay-up in a tannery press and pressing for 5-15 seconds, typically 10 seconds, at 75-90"C, typically 80"C and 25 p.s.i. to 750 p.s.i., typically 50 to 250 p.s.i.The bonded piece was then removed from the press and allowed to cool.

Full bond strength was achieved after 24 hours at ambient temperature when the bond strength between the layers was in the range 1.0 kg/cm to 2.5 kg/cm. The product had a water vapour permeability of 35 to 45 g/m2/hour. It resisted delamination on wet flex testing for in excess of 150,000 flexes.

EXAMPLE 5 A foil as used in Example 1 (apparent density 0.45 g/cm3) was laminated to a full chrome tanned bovine split using the adhesive mixture described in Example 4. The adhesive was applied to the split at a rate of 3.2 g/sq. ft. expressed as dry deposit, and the bonding was carried out after 4 hours drying at ambient temperature. The bonding conditions were: Platen temperature 90 C Dwell time 15 seconds Specific pressure 45 p.s.i.

The laminates had a dry bond strength of between 1.0 and 1.2 kg/cm width and water vapour permeability of 35 to 40 g/m2/hour.

When a higher density microporous polyurethane foil (0.47 mm thick, weight 270 glum2, apparent density 0.57 g/cm3) was laminated under the same conditions, the dry bond strength was between 1.2 and 1.7 kg/cm width and the water vapour permeability was 40 g/m2/hour.

The adhesive system can be made up wholly or partly in solvents other than butyl acetate. Suitable classes of solvents include esters (e.g. ethyl acetate, cellosolve acetate), ketones (e.g. methyl isobutyl ketone, cyclohexanone), ethers (e.g. tetrahydrofur- an, 1.4dioxan) and chlorinated hydrocarbons (e.g.

trichlorethylene). Aromatic hydrocarbons can be used as diluents. Those solvents within the above classes that comprise in addition an hydroxyl group should not be used because of affecting the -NCO to -OH balance. For the same reason, the moisture content of the solvents should be kept low and hygroscopic solvents avoided.

The adhesive system can also be applied to the leather substrate by roller- or curtain-coating or by spraying. The choice of application method will affect selection of the solvent, concentration of adhesive solids in the solution and, to a degree, the proportion of crosslinking agent. Thus for application by spray the adhesive solids concentration can be reduced to 10%, and the amount of crosslinking agent solution adjusted to 4 parts per 100 parts of 10% polyol solution.

It will be obvious to those skilled in the art that adhesive systems consisting of other polymeric polyols and polyfunctional isocyanate propolymers, or indeed curable adhesive systems of different chemical composition, can be used with similar results in operating the invention.

The kit of parts, product and process of the invention are applicable in the industrial scale production of enhanced appearance leather based products wherein low quality leather materials are given improved appearance and properties and added value.

Claims

1. A kit of parts for assembly into a grain leather like material comprising a leather substrate provided on its surface, which will be inside the laminate, with thermosettable or curable adhesive, and a microporous polyurethane layer or foil at least 0.1 mm thick, the surface of the foil which will afford an outside surface of the laminate being preformed or prefinished, the said adhesive being settable or curable at temperatures below those which would cause significant permanent damage to the said preformed or prefinished surface of the foil.

2. A kit of parts as claimed in Claim 1 in which the layer or foil has a grain appearance which is substantially undamaged by heating to 1300C while stretched by up to 20% for 2 minutes.

3. A kit of parts as claimed in Claim 1 or Claim 2 wherein the leather substrate comprises leather splits.

4. A kit of parts as claimed in Claim 1,2 or 3 wherein the leather substrate comprises low substance leathers.

5. A kit of parts as claimed in any of Claims 1 to 4 wherein the leather substrate is substantially free of sizing and/orfilling.

6. A kit of parts as claimed in any of Claims 1 to 5 wherein the polyurethane layer or foil is from 0.2 mm to 1.5 mm thick.

7. A kit of parts as claimed in any one of Claims 1 to 6 in which the microporous foil has an apparent density of at least 0.1 grams/cc.

8. A kit of parts as claimed in Claim 7 in which the microporous foil has an apparent density in the range 0.25 to 0.8 grams/cc.

9. A kit of parts as claimed in Claim 1 substantially as specifically described herein with reference to the examples.

10. A grain leather like material comprising a leather substrate and a coloured or embossed or coloured and embossed microporous polyurethane layer or foil at least 0.1 mm thick adhered by a thermoset or cured adhesive to the substrate, the layerorfoil having a grain appearance which is substantially undamaged by heating to 1300C while stretched by up to 20% for 2 minutes.

11. A material as claimed in Claim 10 wherein the leather substrate comprises leather splits.

12. A material as claimed in Claim 10 or Claim 11 wherein the leather substrate comprises low subst ance leathers.

13. A material as claimed in any of Claims 10 to 12 wherein the leather substrate is substantially free of sizing and/orfilling.

14. A material as claimed in any of Claims 10 to 13 wherein the polyurethane layer or foil is from 0.2 mm to 1.5 mm thick.

15. A material as claimed in any of Claims 10 to 14 which is water vapour permeable.

16. A grain leather like material substantially as specifically described in the Examples.

17. Aprocessfortheproduction of a grain leather like material in which a kit of parts as claimed in any one of Claims 1 to 8 is used and the microporous foil with its preformed or prefinished surface facing out is laminated by heat and pressure to the surface of the leather substrate carrying the thermosettable or curable adhesive at a temperature such that no significant permanent damage is caused to the said preformed or prefinished surface of the foil.

18. A process for the production of a grain leather like material wherein a surface of a leather substrate is treated with a thermosetting or curable adhesive in an amount of not more than 10 grams of solids per square foot, a preformed or prefinished microporous polyurethane layer or foil being laminated by heat and pressure to the adhesive treated surface of the leather.

19. A process as claimed in Claim 17 or Claim 18 wherein the substrate comprises leather splits.

20. A process as claimed in Claim 17 or Claim 18 wherein the substrate comprises low substance leather.

21. A process as claimed in any of Claims 17 to 20 wherein the substrate is subtantially free of sizing and/orfilling.

22. A process as claimed in any of Claims 16 to 20 wherein the adhesive is a polyurethane adhesive dissolved in a solvent.

23. A process as claimed in Claim 22 wherein the adhesive coated substrate is allowed to dry before lamination of the layer or foil thereto.

24. A process as claimed in any of Claims 17 to 23 wherein the adhesive is cross-linkable at a temperature in the range of 65" to 1 100C under a pressure of 20 to 1500 p.s.i. with dwell times ranging from 2 to 30 seconds.

25. A process as claimed in Claim 24 in which the adhesive is a cross-linkable polyurethane adhesive and is applied at a dry weight of 20 to 40 grams per square metre and is allowed to dry for 1.5 to 20 hours at a temperature not in excess of 45"C.

26. A process as claimed in Claim 24 or Claim 25 in which the laminating is carried out at a temperature in the range 75 to 90"C for 5 to 15 seconds at a pressure of 25 to 750 p.s.i.

27. A process as claimed in any Claims 17 to 26 wherein the layer or foil is 0.2 mm to 1.5 mm thick.

28. A process as claimed in any of Claims 17 to 27 wherein the layer or foil is water vapour permeable.

29. A process as claimed in any of Claims 17 to 28 wherein the layer or foil has, priorto lamination, been embossed at a temperature in excess of 140"C.

30. A process as claimed in any of Claims 17 to 29 wherein the layer or foil has, prior to lamination, been embossed, the temperature of lamination being below that at which the layer or foil was embossed.

31. A process for the production of a grain leather like material substantially as described in the Examples.

32. A grain leather like material produced by the process of any of Claims 17 to 31.