CA2385307A1

CA2385307A1 - Process for the manufacture of synthetic leather

Info

Publication number: CA2385307A1
Application number: CA002385307A
Authority: CA
Inventors: Kurt Jorder; Dieter Groitzsch; Horst Lorenz
Original assignee: Individual
Current assignee: Carl Freudenberg KG
Priority date: 1999-09-16
Filing date: 2000-09-15
Publication date: 2001-03-22
Also published as: CN1375025A; DE19944441A1; EP1216322A1; JP2003509596A; WO2001020072A1; KR20020041440A; MXPA02002834A; BR0014045A

Abstract

The invention relates to a method for producing synthetic leather from a non-woven containing microfibers. According to the invention, the production method involves processing a thermoplastic microfiber with a titer of 0.05 to 1.0 dtex and hot-water soluble fibers with a titer of 4 to 6 dtex in a weight % ratio of 90:10 to 30:70 to form a non-woven having a surface area weight of 80 to 1000 g/m2. Said non-woven is impregnated with an aqueous binding agent-dispersion of a viscoelastic substance with a weight ratio of 25:75 to 75:25 of non-woven viscoelastic substance whereby fixation of said viscoelastic substance is achieved by cross-linking or vulcanization and the hot-water soluble fibers are subsequently extracted from said non-woven.

Description

PROCESS FOR THE MANUFACTURE OF SYNTHETIC LEATHER
DESCRIPTION
The invention relates to a process for the manufacture of microfibre synthetic leather containing non-woven material.
Synthetic leathers, on the basis of non-woven materials, are today almost exclusively composed of microfibres. It has been shown that homogeneous microfibres as such can either not at all be processed on teasels or only at extremely low production speeds which are economically not justifiable. Multi-component fibres are therefore preferably used, such as matrix-fibrils-fibres or island-in-sea type fibres or those with other distribution of the preferably bi-component fibre components, and with a fibre titre which can be teased without speed loss. The cross-sections of such ftbres preferably have an orange structure or a pie or ring pie structure. Such mufti-component fibres (conjugate fibres, mufti-constituent fibres) can consist of at least two, preferably however up to 18 segments.
Individual fibre segments of the generally two polymers alternate so that fibre boundary surfaces are formed after each segment, such as, for example, polyethylene terephthalate/polyamide 6. The separation of these mufti-component fibres into isolated, ultra fme microfibres is achieved with different methods. For example, one of the two fibre components is dissolved away with organic solvents so that the other fibre component which is insoluble in the organic solvent remains as microfibre. This method is costly, little environmentally friendly and associated with high material loss as well as the accumulation of polymer containing solvents, whereby the reconditioning of the used solvent is carried out either by solvent recapture or by use for energy purposes.
An environmentally friendly and today preferred separation of the bi-component fibres is carried out by the splitting of the fibres with the help of high pressure water jets.
The bi-component split fibres are either made of chemically strongly different thermoplastics which do not have high mutual adhesion forces or are admixed with anti-adhesive additives which lower the adhesion forces for chemically similar fibre polymers such as, for example, polyolefins. A synthetic leather with soft hand is known from document JP 05078986, which at least on one side includes a non-woven material layer of melt-blown polyethylene terephthalate microfibres of a diameter of 0.1 to 6.0 micrometres. The softness is achieved in that the non-woven material is coated with a dressing of cold water soluble polyvinyl alcohol prior to the impregnation with polyurethane from organic solvents such as dimethyl formamide. After the impregnation and coagulation of the polyurethane solution with water (so called migration method) and the subsequent washing steps for the purpose of the removal of the organic solvent, the polyvinyl alcohol is simultaneously removed from the non-woven material. The after treatment of the so obtained synthetic leather is carried out in known manner by grinding, dying and washing.
Document US-A 4,390,566 describes the manufacture of a synthetic leather in which split microfibres are used, among others. The microfibre non-woven material is impregnated prior to the binder application with a water soluble dressing solution referred to as temporary filler, which after the solidification of the binder application is again washed out. Polyvinyl alcohol (PVA) poly-s-caprolactone, carboxymethylcellulose (CMC) or starch are used as temporary water soluble fillers.
It is an object of the invention to provide a process that allows the manufacture of a very soft synthetic leather of improved properties. It is a further object of the invention to make the manufacture more cost efficient and environmentally friendly.
This object is achieved in accordance with the invention by a process wherein thermoplastic microfibres with a titre of 0.05 to 1.0 dtex and hot water soluble fibres with a titre of 4 to 6 dtex are processed at a total weight ratio of 90:10 to 30:70 into a non-woven material with a surface weight of 80 to 1000 g/mz, and an aqueous polymer-dispersion of a viscoelastic substance is applied and solidified at a weight ratio of 25:75 to 75:25, whereby an extraction of the hot water soluble fibres is subsequently carried out.
Preferably, the process in accordance with the invention is one wherein the titre of the thermoplastic microfibres is 0.1 to 0.3dtex, the weight ratio of the microfibres to the hot water soluble fibres is 70:30 to 50:50 % per weight, the surface weight of the non-woven material is 100 to 500 g/mz, and the ratio of the non-woven material to the viscoelastic substance prior to the removal of the hot water soluble fibres is 35:65 to 65:35 % per weight.
It is especially preferred according to the process in accordance with the invention that the thermoplastic fibres are split fibres.
It is further preferred that the split fibres consist of polyethylene terephthalate/polyamide 6, polyethylene terephthalate/polyamide 6.6, polyethylene terephthalate/polypropylene, or polyethylene terephthalate/polyethylene.
Hot water soluble fibres made of polyvinyl alcohol, poly-e-caprolactone, carboxymethylcellulose, or starch are preferably used in a process in accordance to the invention.

2 This solidification and splitting of the fibrous non-woven is preferably carried out by way of high-pressure water jets.
It is further preferred that an aqueous polymer dispersion of polyurethane, nitrite-butadiene caoutchouc or styrole-butadiene caoutchouc is used as the binder material.
It is preferably provided in accordance with the process of the invention that the thermoplastic fibres are admixed with fillers such as pigments, hydrophobicity increasing agents, hydrophiticity increasing agents, compounds for the reduction of the wetabitity with alcohots, fats and oils, antistatic agents and/or anti-microbially active agents.
In a preferred embodiment of the process, it is provided that an after treatment is carried out by buffing, grinding or sanding.
It is especially preferred in accordance with the process of the invention that the dissolving of the hot water soluble fibres is carried out simultaneous with an extraction dying, especially in an autoclave.
The process in accordance with the invention is not only simple, which means it needs fewer process steps, but at the same time allows a more cost efficient and environmentally friendly manufacture of the synthetic leather.
With the process in accordance with the invention, the use of organic solvents for the liberation of the microfibres as well as for the application of the binder coagulation can be omitted.
The manufacture in accordance with the invention of a synthetic leather is carried out in the manner that a fibrous sheet is manufactured from endless fibres, staple fibres, or short cut fibres with the help of the lrnown fibre deposition techniques. This fibrous sheet consists of at least two fibre components, whereby at least one of the fibre components is a bicomponent fibre splittable with high pressure water jets. Such split fibres consist of at least two thermoplastic polymer components, P1 and P2, which are alternatively aligned in series and in segment shape about the fibre axis. Centred as well as eccentricat fibre axis arrangements are thereby possible. The number of the segments is between 2 and 30, preferably however between 4 and 24. The overall titre of a so-called high fibre is between 0.8 and 5.0, preferably between I .0 and 3.3 dtex. In accordance with the invention, other geometric arrangements of the fibre polymers P 1 and P2 are possible with the prerequisite that the fibres are split into at least 80%
microfibres under strong mechanical or hydrodynamic forces, such as with a high-pressure water jet treatment. Polymer pairs P1 and P2 are preferably used the common interfaces of which do not exert high adhesion forces onto each other. Known P1/P2 pairs are, for example, polyethylene terephthalate/potyamide 6, polyethylene terephthatate/polyamide 6.6, polyethylene terephthalate/polypropylene and polyethylene terephthalate/polyethylene.
Chemically closely related P1/P2 pairs such as, for example, polypropylene and polyethylene or their copolymers are provided in the known manner at their interfaces with separating agents which guarantee the splitability. Polyolefms catalysed with metalocene can also be used as polymer components P1 andlor P2.
The fibre polymer components P 1 and P2 can be spun dyed, white pigmented, or provided with agents which impart onto the fibre polymer components hydrophytic or hydrophobic properties or a reduced wetablity with alcohol, other organic liquids, fats or oils. The fibre polymer components can be further provided with anti-static agents or anti-microbial active agents.
At least a second fibre component is used in accordance with the invention apart from the split fibres which consist in part or up to 100% of a hot water soluble polymer, whereby the hot water soluble portion in the non-woven material is 10:70% per weight. Within the context of the invention, hot water solubility of the fibre means a solubility below 5% in water under the conditions of high-pressure water jet treatment and a solubility of at least 95% in water of a temperature of about 98 °C, or in pressurized vessels at temperatures above 100°C. Hot water soluble fibres within the context of the invention are also those fibres which only on pressure treatment in an autoclave go into solution or are swollen to such a degree that they are at least up to 95% removed from the non-woven material under these conditions in a washing step. Preferred hot-water soluble fibres are those made of polyvinyl alcohol or poly-e-caprolactone.
Apart from the splittable and hot water soluble fibres, the nonwoven material can also include other fibres, but non-woven materials of the two mentioned fibre types are preferred. The weight ratio of split fibres and hot water soluble fibres is 90:10 to 30:70, preferably 70:30 to 50:50.
The hot water soluble fibres can be present in lightly cross linked form. Hot water soluble fibres can also be used as fibres which only have coating of a hot water soluble polymer, which means have a sheath- core structure. Furthermore, fibres with a side by side structure are suitable, which are made of different polymers only one of which is hot water soluble. The split fibre, in accordance with the invention does not have a hot water soluble coating. The inclusion of the hot water soluble fibres is carried out statically according to their proportion, for example, by carding or the air laid process or the deposition on an inclined sieve according to the Fourdrinier method. In the case of split fibre endless filaments, the hot water soluble fibres are blown with the help of an air stream laterally into the endless filaments exiting from the spinning nozzle and shocked as well as stretched by a directional air stream prior to the deposition of the filaments onto a sieve band, or the addition is carried out through a separate spinning beam. The split fibres and the hot water soluble fibres used preferably have a crimped structure.
The fibre is deposited into a non-woven sheet, are transferred to a drainage sieve and subjected to a high-pressure water jet treatment. In a first step and at a low water jet pressure only an entangling of the fibres to a non-woven material with high tear resistance is achieved. The splitting of the split fibres into microfibres with titres between 0.05 and 1.0 dtex, preferably 0.1 to 0.3 dtex is subsequently carried out with one or more high pressure water jet beams. The fineness of the liberated microfibres can be adjusted by way of the titre of the split fibres in the unsplit condition and the number of the segments. In order to prevent water jet lanes in the non-woven material, at least the last water jet beams are set into an oscillating movement perpendicular to the machine transport direction.
Furthermore, denser sieves can be used for prevention of the lane formation, which cause a reflection and scattering of the impinging water jets and thereby cause a blurnng of the water jet lanes. According to the process in accordance with the invention, non-woven materials with a surface weight of 80 to 1000 g/m2 are produced, preferably 100 to 500 g/mZ. The non-woven is preferably additionally mechanically needled prior to the hydrodynamic treatment. The process in accordance with the invention is controlled in such a way that after the splitting into microfibres a maximum of 3 to 5 % per weight of the hot water soluble fibres are dissolved from the non-woven material by the water jet needling and splitting process. The resulting solidified non-woven material is dried and impregnated with an aqueous binder dispersion in a generally known manner by the dry-in-wet application method. The application can be carried out by painting on, splashing from one side, or by full immersion impregnation in a foulard. A one sided application of the binder dispersion can be transported by application of a vacuum to the opposite side of the non-woven material. The binder application is carried out in relation to the previously manufactured fibrous non-woven, which means prior to the dissolving of the hot water soluble fibres at the ratio of 25:75 to 75:25 % per wt., preferably 35:65 to 65:35 % per wt. Self cross-linking polymers are used as primers which carry the active groups in the polymer or are admixed with cross-linkers. During the selection of the polymer dispersions or the cross-linker, it must be ensured that the reactive groups in the hot water soluble fibres either remain uncross-linked or that the degree of cross linking is maintained so low that the water solubility for the removal of the portion in accordance with the invention is maintained. Polymer dispersions of polyurethane, nitrile-butadiene caoutchouc and/or styrol-butadiene caoutchouc are used as primers within the context of the invention. Primers which smudge during the buffing or grinding with sandpaper or on ceramic rollers are not binders within the meaning of the invention. The primers can be admixed with known compounds, such as inorganic white pigments, color pigments, grip improvers, such as, for example, silicone, cellulose dust, optical brighteners, antistatics, bacteriostatics. The non-woven material is dried after the binder application, whereby thus a thermal coactivation and cross linking or vulcanization is carried out previously. The synthetic leather obtained is advantageously subsequently buffed and pre-ground. The removal of the hot water soluble fibres is carried out either without pressure under hot water washing conditions or in an autoclave at float temperatures above 100°C. The hot water soluble fibre is thereby removed from the microfibre non-woven material. The dissolving of the hot water soluble fibre can preferably also be combined with extraction dying when high dying temperatures are used anyway, especially in the autoclave. Extremely soft, full synthetic leathers with an exceptional haptic are obtained with the process in accordance with the invention. For improvement of the microfibre velours, further after-treatment steps are preferably carried out such as the dressing for grip improvement or the fine grinding of the surfaces.
Example A fibre pile is produced from 80 parts per wt. of a polyester-polyamide split fibre with a titre of 2.2 dtex and a fibre length of 51 mm and 20 parts per wt. of a polyvinyl alcohol fibre with a titre of 1.4 dtex and a fibre length of 88 mm, which pile is densified by intensive needling.
The resulting non-woven is subjected to a high pressure water jet treatment in which about 90% of the polyester-polyamide fibres are split into microfibres. The non-woven material is subsequently impregnated with a binder composed of aqueous dispersions which include 70% per wt. polyurethane, 20% per wt.
polyvinyl alcohol, 5% per wt.
color pigments and the remainder fillers and grip improvers as solid components. After the drying of the impregnated nonwoven material, the polyvinyl alcohol fibres are removed to more than 95% per weight from the non-woven material by a hot water wash treatment. The resulting synthetic leather has a very round hand and can be processed into a material with a nubuck optic by subsequent grinding.

Claims

1. Process for the manufacture of a synthetic leather made of a microfibre containing non-woven, characterized in that thermoplastic microfibres with a titre of 0.05 to 1.0 dtex and hot water soluble fibres with a titre of 4 to 6 dtex are processed at a weight ratio of 90:10 to 30:70 into a non-woven material with a surface weight of 80 to 1000 g/m2 and that an aqueous polymer dispersion of a viscoelastic substance is applied in a weight ratio of 25:75 to 75:25 of non-woven to viscoelastic substance and solidified.

2. Process according to claim 1, characterized in that the titre of the thermoplastic microfibres is 0.1 to 0.3 dtex, the weight ratio of the microfibres to the hot water soluble fibres is 70:30 to 50:50%
per weight, the surface weight of the non-woven is 100 to 500 g/m2, and the ratio of the non-woven to the viscoelastic substance prior to removal of the hot water soluble fibres is 35:65 to 65:35% per weight.

3. Process according to claim 1 or 2, characterized in that the thermoplastic fibres are split fibres.

4. Process according to claim 3, characterized in that the split fibres consist of polyethylene terephthalate/polyamide 6, polyethylene terephthalate/polyamide 6.6, polyethylene terephthalate/polypropylene, or polyethylene terephthalate/polyethylene.

5. Process according to claim 1 or 2, characterized in that hot water soluble fibres made of polyvinyl alcohol, poly-.epsilon.-caprolactone, carboxymethyl cellulose or starch are used.

6. Process according to one of claims 1 to 5, characterized in that the solidification and splitting of the fibrous non-woven is carried out with high pressure water jets.

Process according to one of claims 1 to 6, characterized in that an aqueous polymer dispersion of polyurethane, nitrile butadiene caoutchouc, or styrole butadiene caoutchouc is used as binder.

8. Process according to claim 3 or 4, characterized in that the thermoplastic fibres are admixed with fillers such as pigments, hydrophobicity or hydrophilicity agents, compounds for the reduction of wetability with alcohol, fats and oils, antistatic agents and/or antimicrobial agent.

9. Process according to one or more of claims 1 to 8, characterized in that an after treatment is carried out by buffing, grinding or sanding.

10. Process according to one or more of claims 1 to 9, characterized in that the removal of the hot water soluble fibres is carried out simultaneously with an extraction dying, especially in an autoclave.