Process for rapid dyeing of composite synthetic sheet material designed to imitate natural leather

Abstract: A process for dyeing composite synthetic material having a porous polyurethane matrix and a fiber reinforcement (e.g. nonwoven fabric, polyamide, polyethylene or polyester fibers) embedded in the matrix, and from which to produce a sheet product similar to natural leather. The entire section of the material, consisting of the porous matrix and reinforcement, is treated with dyeing substances (hot-polymerizable plastic resins with a water or organic base, pigments, premetallized azoic dyes) by alternately winding the composite material, in strip form, on and off two opposed rollers and through a tank containing a bath of the dyeing substances in solution or emulsion form, so as to feed the strip of composite material reciprocatingly through the bath. The rollers and tank may be housed in a pressurized container for operating at temperatures of over 100°C.

Description: The present invention relates to a process for rapid dyeing of composite synthetic sheet material from which to produce, via appropriate chemical processing, a product similar to natural leather. In particular, the present invention applies to a chemical process for processing any known type of synthetic (or "imitation") leather, consisting of sheet material comprising a porous (vesicular) polymer matrix embedded with natural or synthetic fibers, and which provides for transforming said synthetic leather into a product identical in appearance and "feel" to natural leather, and as described in Italian Patents n. 1.178.956 and 1.211.465 filed by the present Applicant. The above Italian patents, relate to the chemical processing of sheet materials with a vesicular matrix (i.e. having evenly distributed micropores) incorporating or not natural or synthetic reinforcing fibers, for producing imitation leather closely resembling and even indistinguishable to the naked eye from natural leather, by processing the raw material normally used for producing SOFRINA (registered trade mark) of KURARAY CO. LTD. The chemical process also includes a dyeing stage, which consists of one or more operations using azoic dyes (e.g. BASACRIL - registered trade mark) and ammonia, and, successively or in a mixture, premetallised dyes or specific metal compounds for the matrix fibers (e.g. NYLON (registered trade mark) fibers), such as aniline, ISOLAN, TELON, LANACROM, ACIDOL (registered trade marks). The dyeing stage is performed using both tanning technology, in rotary drums, and textile technology, using JET or FLOW type dyeing machines, the strips of sheet material for processing being formed into bales in the first case, and, in the second, being joined end to end into loops which are fed on to the machines and recirculated. Whichever of the above methods is employed, the dyeing stage requires continuous, accurate metering of the dye solution components, and a processing time of several hours, thus resulting in relatively high processing cost. Moreover, and particularly in the case of rotary drums, a continuous check cannot be kept on the quality of the processed material, so that whole lots of material may possibly be ruined in the event of inaccurate dyeing parameters. Finally, numerous in-process handling operations are required of the sheet material, which, being in strip form, is normally in rolls which must be unrolled for forming the material into bales or loops and subsequently reformed into rolls. A similar dyeing process for the above specified materials is also disclosed in GB-A-2206363, which substantially corresponds to the already cited Italian Patent No. 1211465. It is also known form GB-A-1107035 a dyeing process for traditional textiles (never used for materials having fibers embedded in a porous matrix) wherein the textile in strip form is fed reciprocatingly in a dyeing bath: this process assures satisfactory results only with a relatively long treating time. It is an object of the present invention to provide a process for dyeing sheet material of the aforementioned type more rapidly and relatively cheaply, and which at the same time provides for minimum in-process handling of the material and continuous control of the dyeing stage. According to the present invention, there is provided a process for dyeing composite synthetic sheet material designed to imitate natural leather as claimed in claim 1. A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawing, which shows a schematic section of an apparatus for implementing the dyeing process according to the present invention. Extensive research and testing by the Applicant's technicians has shown that, providing the strip is subjected to a given amount of mechanical traction, dyeing a strip of vesicular material by simply immersing it in a bath of dye provides, for a given dye solution/emulsion formula and other given physical-chemical operating parameters, for drastically reducing dyeing time, even by as much as over 60%, as compared with rotary drum and/or textile machine dyeing methods. This translates into an average reduction in dyeing time ranging from several to a few hours (e.g. from 6 to little less than 3 hours) with substantially no change in the end result (colour quality and distribution over the strip, life and stability), thus enabling a drastic reduction in dyeing cost. Moreover, an immersion process provides for more easily controlling the physical and chemical parameters of the bath (temperature, concentration, pH, etc.) as well as for eliminating any handling of the material for processing, which, being in roll form, may simply be unwound into the bath and subsequently rewound. What is more, at least part of the material being processed is constantly out of contact with the dye solution/emulsion, thus enabling it to be quality checked. The material for dyeing, which, to achieve the above results, must necessarily comprise a porous matrix (and, preferably, a fiber reinforcement selected from a group consisting of nonwoven fabric, polyamide, polyethylene or polyester fibers embedded in the matrix), is processed chemically in strip form, over its entire section consisting of the porous matrix and reinforcement (if any), with dyeing substances containing appropriate (known) auxiliary additives, by feeding the strip of vesicular material reciprocatingly and at a predetermined speed inside a bath containing a solution and/or emulsion of said dyeing substances and additives, and by maintaining the strip taut. The synthetic material in strip form is fed reciprocatingly inside the bath by alternately winding and unwinding the strip on and off two opposed rollers having means for maintaining the strip at a predetermined tension and guiding it through a tank located between the rollers and containing the dye bath. More specifically, and as shown in the accompanying drawing, a strip 1 of known microporous (vesicular) synthetic sheet material, in particular made of polyurethane with embedded polyamide fibers free to move inside the porous matrix (e.g. the raw material for producing SOFRINA - registered trade mark), is processed in an apparatus 2 defined by a pressure casing 3 housing a tank 4 and two opposed powered rollers 5, 6 at the opposite longitudinal ends of tank 4. Tank 4 contains a dye bath 7 of known composition, and, according to the purely indicative example shown, a powered tensioning cylinder 10. Strip 1 is formed into a roll 11, which is mounted on to roller 5, unwound off roller 5 into tank 4 and through bath 7, and rewound on to roller 6 from which, by inverting the rotation direction of rollers 5 and 6, it may subsequently be unwound and fed through tank 4 in the opposite direction, and rewound on to roller 5, so as to feed strip 1 reciprocatingly inside bath 7. By means of motors 12, tensioning cylinder 10 may be moved vertically inside tank 4 and bath 7, so as to adjust as required the tension of strip 1 traveling back and forth through bath 7 in tank 4. Apparatus 2 also presents means for controlling the temperature of bath 7, e.g. a heating/cooling coil 15; known sensor means (not shown), such as a thermometer, pH meter and level sensor; and supply means for bath 7, wash solutions, and acid and base pH-correcting solutions, all of known type and therefore not shown for the sake of simplicity. Preferably, operating pressure is above atmospheric, and bath 7 is maintained at a temperature of over 100°C, by virtue of pressure apparatus 3, inside which rollers 5 and 6 and tank 4 are housed, being fluidtight and hence pressurizable; and tensioning cylinder 10 is so positioned by motors 12 as to feed strip 1 reciprocatingly through bath 7 at a tension of no less than 30 Nw/sq.cm of cross section of strip 1. Powered rollers 5 and 6 are so operated as to feed strip 1 reciprocatingly through bath 7 at an average linear speed of roughly 20 m/minute and, at any rate, ranging from 8 to 40 m/minute. Operating with the above parameters and traditional dye formulas, the dyeing stage, by immersing and feeding strip 1 reciprocatingly in bath 7, takes from 30 minutes to 4 hours, at the end of which, strip 1 is dyed evenly and stably, and presents an excellent appearance. The present invention will now be described further by means of a number of practical examples. However, not all the examples are in full accordance with all the features of claim 1. EXAMPLE 1 Twelve strips of raw "SOFRINA" material of KURARAY Co. LTD - Japan (a vesicular synthetic material comprising a microporous polyurethane matrix embedded with NYLON (registered trade mark) fibers, and a compact polyurethane surface coating printed to imitate natural leather), each 10 m long, 0.8 mm thick and weighing 182 kg, are divided into four lots of 3 strips each; and the strips in the first two lots, A and B, are dyed using an aqueous solution of 3% by weight of LEVADERM (registered trade mark) as follows: The strips in lot A are folded and tied into bales measuring cm 250 x 120 x 120, and are loaded into a roughly 5.6 m 3 rotary drum of the type used for tanning. Into the drum, rotating at a speed of 15 rpm, are fed 300 liters of the above 3% aqueous solution in LEVADERM, and the strips are treated with the solution for 65 minutes at 40°C and 75 minutes at 60°C, the temperature being adjusted slowly, for a total of roughly 6 hours. After being washed with 650 liters of water, the bales are taken out, the strips rewound, and the colour checked. The strips in lot B, wound into a roll, are treated on a JEGGER processing machine corresponding to the machine shown schematically in the accompanying drawing. Each roll is mounted on to a powered roller from which it is unwound on to a second roller, opposite the first, and vice versa, so as to feed the strip reciprocatingly inside a tank between the rollers and containing 60 liters of the above 3% LEVADERM solution. The strip is held between the rollers at a tension of 40 Nw/sq.cm and is fed through the tank containing the solution at a speed of 30 m/minute. Ambient pressure is applied, and a temperature of 40°C maintained for 30 minutes, after which, the temperature is gradually raised to 94°C for 2.5 h. At the end of the operation, the strips, still in roll form, are colour checked. The strips in lots C and D are tied into bales as for lot A, and are treated in a 5.6 m 3 drum rotating at a speed of 15 rpm, first with 300 liters of an aqueous solution of surface-active agents at 60°C for 20 minutes, then with 300 liters of an aqueous solution of 30% by weight of chromium sulphate at 60°C and with a pH of 3.2. After 40 minutes, the pH is raised to 7.1 by adding NaOH 10N and precipitating the hydroxide with abundant coagulation. After rinsing, the drum is fed with 300 liters of an aqueous solution of 6% by weight of aspartic aldehyde for 40 minutes, followed by 300 liters of a 30% solution by weight of sulphited fatty esters (sulphited whale oil - "sperm oil") for 45 minutes. The strips in lot C are then dyed in a rotary drum as for lot A, and those in lot D are formed into a roll and dyed as for lot B. When compared, the strips in lots A and C present the same colour and uniform shading as those in lots B and D: the dyeing operation of lots A and C, however, required roughly 6 hours as compared with only 3 hours for lots B and D. EXAMPLE 2 Twelve strips as in Example 1 are divided into two lots E and F of 6 strips each. The strips, unrolled and stitched into a loop, are treated on a JET type dyeing machine using the same solutions and operating parameters as lots C and D, except that, following precipitation with chromium sulphate and before being treated with glutaric aldehyde solution, they are treated with 650 liters of an aqueous emulsion of 7% by weight of APRITAN PQ (registered trade mark), a known maleic styrene filler used in tanning, and 2% by weight of BASITAN MN (registered trade mark) and 3% by weight of TANIGAN PAK (registered trade mark), known synthetic-tannin-based retanning agents used in the tanning industry. The strips in lot E are then dyed on the JET machine by treating them with 650 liters of an aqueous solution of 3% by weight of LEVADERM (registered trade mark), a known polyurethane dye, and 3% by weight of SELLASET (registered trade mark), a specific known dye for polyamide fibers, for 4 hours at 98°C. The strips in lot F, on the other hand, are removed from the JET machine, formed into a roll, after first unstitching the loop, and treated with an identical dye solution (3% by weight of LEVADERM and 3% by weight of SELLASET) for 2 h at 98°C and atmospheric pressure using a JEGGER machine and the same parameters as for lots B and D. In this case also, when compared, lots E and F presented the same colour alongside a marked difference in the duration of the dyeing stage. EXAMPLE 3 Twenty-four strips of the same material as in Example 1, but with the compact polyurethane surface coating removed mechanically by means of a blade (and thus consisting solely of the microporous matrix and fiber reinforcement), are divided into two lots (1 and 2) of 12 strips each, and treated on a JET type machine with 500 liters of an aqueous solution of 3% aniline and 5% 24Bé ammonia (weight percentages calculated according to the weight of the strips) for 90 minutes. After washing in water, the strips are then dyed using the following formulas: The strips in lot 1 are dyed on the JET machine as follows: 1.a) - Three strips are treated at 95°C for 120 minutes with a dye solution consisting of a water mixture of TELON A-3RL, ISOLAN K-3GLS and TELON FRL (registered trade marks) in respective proportions of 1.6%, 0.2% and 0.3% of the weight of the strips. 1.b) - Three strips are treated at 30°C for 15 minutes with a dye solution comprising 300% by strip weight of water, and 1% by strip weight of ABEGAL SW (registered trade mark). The temperature is then raised to 110°C in 90 minutes, 5% by strip weight of premetallized dyes (LANACROM and IRGALAN - registered trade marks) are added, and the strips treated for a further 60 minutes. 1.c) - Three strips are treated for 90 minutes, and by raising the temperature from 30 to 96°C, with a dye solution comprising, by strip weight, 300% water, 3% AVOLAN IW (registered trade mark), 10% ASTRAGAL (registered trade mark) and 5% ISOLAN K-PRL (grey). After washing, the treatment is repeated twice for 50 and 90 minutes respectively, to eliminate the AVOLAN and reduce the ISOLAN to 2% and the ASTRAGAL to 4%. 1.d) - Three strips are treated at 30°C for 60 minutes with a dye solution comprising, by strip weight, 200% water and 30% organic pigments (IRGAFIN - registered trade mark). Acetic acid is then added to bring the pH to 3.5, the temperature is raised to 80°C, 2% of TELON and 10% of ASTRAGAL are added, and the temperature is raised to 110°C for 90 minutes. At this point, the temperature is lowered to 60°C, and a further dyeing operation is performed by raising the temperature to 110°C in 60 minutes. The strips in lot 2 are dyed using the same solutions and compositions, but on a JEGGER machine and with the same operating parameters as in Example 1, except that the speed of the strip through the tank ranges from 8 to 40 m/minute, and the strip tension from 30 to 38 Nw/sq.cm, with the following dye solution in the tank: 2.a) - Three strips are treated with the solution as per point 1.a) maintained in the tank at 95°C for 1 h. 2.b) - Three strips are treated with the complete solution as per point 1.b) (ABEGAL + LANACROM + IRGALAN) maintained in the tank at 110°C for 1.5 h, and 1.5 bar pressure. 2.c) - Three strips are treated only once with the complete solution as per point 1.c) (AVOLAN 3%, ISOLAN 10%, ASTRAGAL 5%) at 110°C and 1.6 bar pressure for 1.5 h. 2.d) - Three strips are treated with the complete solution as per point 1.d) (IRGAFIN 30%, TELON 2%, ASTRAGAL 10%) at 110°C and 1.5 bar pressure for a total of 2.5 h, acetic acid being added after 30 minutes' treatment to vary the pH and precipitate the pigments. Samples taken from the strips in each lot were then subjected to dry comparative colour inspection using a spectrophotometer, after first being treated with synthetic perspiration, alcohol, water, and prolonged exposure to sunlight (BLUE scale evaluation). The results were substantially identical for the three-strip groups in each lot treated with the same dye bath. The lot 2 samples, however, treated by tensioning the strip to less than 32 Nw/sq.cm as it is fed through the dye bath, presented a lighter and, above all, less evenly distributed colour as compared with the corresponding samples in lot 1.

Claims: A process for dyeing a composite synthetic sheet material designed to imitate natural leather, said sheet material comprising: (i)- a porous matrix; and (ii)- a fiber reinforcement selected from a group consisting of non-woven fabric, polyamide, polyethylene or polyester fibers; wherein the reinforcement is embedded in said matrix; said process comprising the step of processing chemically said synthetic sheet material with dyeing substances over its entire section consisting of said porous matrix and said reinforcement, wherein the sheet material is processed in a strip form by feeding the strip (1) of composite material reciprocatingly and at a predetermined speed inside a bath (7) containing a solution and/or emulsion of said dyeing substances, and by maintaining the strip (1) taut; characterized in that, in combination: (iii)- said synthetic material in strip form (1) is fed reciprocatingly inside said bath (7) by alternately winding said strip of synthetic material on and off two opposed rollers (5,6) having means (10) for maintaining a predetermined tension of the strip (1) and for guiding the strip (1) through a tank (4) located between the rollers (5,6) and containing said bath (7) of dyeing substances; (iv)- the treatment is effected, preferably, at a pressure greater than atmospheric pressure, and preferably by maintaining the bath (7) at a temperature of over 100°C; said rollers (5,6) and said tank (4) being housed inside a sealed apparatus (3); and (v)- said strip (1) of synthetic material is fed reciprocatingly through said bath (7) of dyeing substances at a tension of no less than 30 Nw/sq.cm. A process as claimed in Claim 1, characterized by the fact that said strip (1) of synthetic material is fed reciprocatingly through said bath (7) of dyeing substances at an average linear speed ranging from 8 to 40 m/minute. A process as claimed in Claim 1 or 2, characterized by the fact that said dyeing stage by feeding said strip (1) reciprocatingly inside said bath (7) lasts from 30 minutes to 4 hours.

Inventors: POLETTO GIORGIO, POLETTO, GIORGIO
Applicants: LORICA SUD S R L, LORICA SUD S.R.L.
Application year: 1993
Main classification: D06B3
IPC codes: D06P7, D06B3, D06P3, D06N3