Microfibrous product and the use thereof for the preparation of covers and cases

Abstract

The invention refers to a process for the preparation of a microfibrous non-woven fabric based on polyester or polyamide microfibers immersed in a polyurethane matrix, and having a thickness equal to or less than 0.65 mm, a flat or slightly mottled appearance and a nap length of less than 350 μm. The non-woven fabric is used for the preparation of coverings for consumer goods, particularly for the preparation of covers and cases for electronic products.

Claims

1. A process for preparing a microfibrous non-woven fabric based on polyester or polyamide microfibres immersed in a polyurethane matrix, comprising the steps of: A) spinning a bicomponent fibre with an island in the sea structure, wherein the island component is microfibrous and the sea component, immiscible therewith, is soluble in solvents; B) preparing a felt via a process of mechanical needle or water punching of the bicomponent fibre; C) impregnating the felt with an adhesive; D) dissolving the sea component in a selective solvent; E) impregnating the felt with a polyurethane binding agent solution and removing the adhesive by dissolution in an organic solvent or water; F) submitting the felt as per step E) to buffing on both faces, by rotating abrasive paper strips over both faces in a concurrent direction of orientation; G) submitting the felt as per step F) to dyeing; H) brushing the dyed felt on both faces so as to lend a concurrent orientation to the fibres on both faces; I) cutting the product of step H) in the direction of thickness so as to produce two identical laminates, each of half thickness, wherein the dyeing step G) is performed before the cutting step I).

2. The process according to claim 1, wherein said bicomponent fibre comprises polyester or polyamide microfibres and said sea component comprises polystyrene (PS).

3. The process according to claim 1, wherein said bicomponent fibre obtained in step A) is ironed, curled and cut to yield a flock fibre.

4. The process according to claim 1, wherein said felt obtained in step B) through the mechanical needle or the water punching process has a density comprised between 0.1 and 0.3 g/cm.sup.3 and a unit weight comprised between 300 and 550 g/m.sup.2.

5. The process according to claim 1, wherein, in step C), the adhesive is a polyvinyl adhesive.

6. The process according to claim 2, wherein, in step D), the polystyrene sea component is dissolved in trichloroethylene.

7. The process according to claim 1, wherein, in step F), the buffing is carried out with an abrasive paper having a mesh value lower than 500 mesh.

8. The process according to claim 1 wherein, in step H), the dyed semi-finished product is submitted to a first brushing in a wet state and a second brushing after drying.

9. The process according to claim 8, wherein said first brushing is carried out on both faces.

10. The process according to claim 8, wherein said second brushing is applied after drying on both faces with a rotation of the brushes concurrent with the orientation of the fibres.

11. A microfibrous non-woven fabric with a thickness equal to or less than 0.65 mm and a flat or slightly mottled appearance obtainable with the process according to claim 1.

12. The microfibrous non-woven fabric according to claim 11, having a nap length equal to or less than 350 μm.

13. A covering for consumer goods, obtainable by the non-woven fabric according to claim 11.

14. The covering according to claim 13, said covering being a cover or case for consumer goods.

15. The covering according to claim 13, wherein said consumer goods are selected from the group consisting of: portable devices for recording or reproducing sounds or images, portable entertainment devices, sports weapons or equipment, devices for personal well-being or health, telephones, handheld computers, laptops, and other electronic devices.

16. A method of using the non-woven fabric according to claim 11, the method comprising: providing a portion of said non-woven fabric, and preparing a covering for a consumer good using said portion of said non-woven fabric.

17. A process for preparing a microfibrous non-woven fabric based on polyester or polyamide microfibres immersed in a polyurethane matrix, comprising the steps of: A) spinning a bicomponent fibre with an island in the sea structure, wherein the island component is microfibrous and the sea component, immiscible therewith, is soluble in solvents; B) preparing a felt via a process of mechanical needle or water punching of the bicomponent fibre; C) impregnating the felt with an adhesive; D) dissolving the sea component in a selective solvent; E) impregnating the felt with a polyurethane binding agent solution and removing the adhesive by dissolution in an organic solvent or water; F) submitting the felt as per step E) to buffing on both faces, by rotating abrasive paper strips over both faces in a concurrent direction of orientation; G) submitting the felt as per step F) to dyeing; H) brushing the dyed felt on both faces so as to lend a concurrent orientation to the fibres on both faces; I) cutting the product of step H) in the direction of thickness so as to produce two identical laminates, each of half thickness, wherein, in step H), the dyed semi-finished product is submitted to a first brushing in a wet state and a second brushing after drying.

18. The process according to claim 17, wherein said first brushing is carried out on both faces.

19. The process according to claim 17, wherein said second brushing is applied after drying on both faces with a rotation of the brushes concurrent with the orientation of the fibres.

20. The process according to claim 7, wherein said mesh value is lower than 400 mesh.

21. The process according to claim 8, wherein said first brushing is carried out on both faces using bush-hammered rollers with a direction of rotation concurrent with the orientation of the fibres.

22. The microfibrous non-woven fabric according to claim 11, wherein the fabric has a thickness equal to or less than 0.60 mm.

23. The microfibrous non-woven fabric according to claim 12, having a nap length equal to or less than 300 μm.

24. The covering according to claim 14, wherein said consumer goods are electronic products.

25. The method according to claim 16, wherein said covering is selected from the group consisting of covers and cases.

26. The method according to claim 25, wherein said consumer good is an electronic product.

27. The process according to claim 17, wherein said first brushing is carried out on both faces using bush-hammered rollers with a direction of rotation concurrent with the orientation of the fibres.

Description

(1) Further characteristics and advantages of the invention are illustrated herein below in detail, also with reference to the attached figures, wherein:

(2) FIG. 1 shows a non-woven fabric with a mottled appearance, according to the definition provided hereinabove;

(3) FIG. 2 shows a non-woven fabric with a slightly mottled appearance, according to the definition provided hereinabove;

(4) FIG. 3 shows a non-woven fabric with a flat appearance, according to the definition provided hereinabove;

(5) FIG. 4 is a photograph of the non-woven fabric of Example 1, taken with a scanning electron microscope (SEM); the photograph shows the measurement of the nap length;

(6) FIG. 5 is a photograph of the non-woven fabric of Example 2, taken with a scanning electron microscope (SEM); the photograph shows the measurement of the nap length;

(7) The present invention concerns a process for obtaining a microfibrous non-woven fabric based on polyester or polyamide microfibres immersed in a polyurethane matrix and comprising the steps of:

(8) A) spinning a bicomponent fibre with an island in the sea structure, in which the island component is microfibrous and the sea component, immiscible therewith, is soluble in solvents;

(9) B) preparing a felt via a process of mechanical needle or water punching of the bicomponent fibre;

(10) C) impregnating the felt with a polyvinyl adhesive;

(11) D) dissolving the sea component in a selective solvent;

(12) E) impregnating the felt with a polyurethane binding agent solution and removing the polyvinyl adhesive by dissolution in an organic solvent or water;

(13) F) submitting the felt as per step E) to buffing on both faces, by rotating abrasive paper strips over both faces in a concurrent direction of orientation;

(14) G) submitting the felt obtained in step F) (raw) to dyeing;

(15) H) brushing the dyed product thus obtained on both faces so as to lend a concurrent orientation to the fibres on both faces;

(16) I) cutting the product as per step H) in the direction of thickness so as to produce two identical laminates, each of half thickness.

(17) The bicomponent fibre comprises polyester or polyamide microfibres, preferably polyethylene terephthalate (PET) (the island component) and a sea component preferably consisting of polystyrene (PS). The polyester microfibres preferably have a fibre count ranging between 0.10 and 0.25 dtex, more preferably between 0.12 and 0.20 dtex.

(18) The bicomponent fibre obtained in step A) is then ironed, curled and cut to yield a short fibre (flock), preferably having a fibre count ranging between 3.5 and 4.5 dtex, a length ranging between 40 and 60 mm, and a crimp frequency ranging between 3 and 7 crimps/cm.

(19) In a preferred embodiment, the flock fibre comprises 50% to 70% polyester by weight and 30% to 50% polystyrene by weight. The fibre section is preferably constituted by 16 microfibres of polyester englobed in polystyrene.

(20) The intermediate felt product obtained in step B) by means of the needle punching process, has a density comprised between 0.1 and 0.3 g/cm.sup.3 and a unit weight comprised between 300 and 550 g/m.sup.2.

(21) In step C), the polyvinyl adhesive is preferably an aqueous solution of polyvinyl alcohol (PVA). Impregnation is carried out at a temperature permitting dimensional shrinkage of the fibres, preferably at 95 to 98° C. Subsequently, the felt undergoes calendering to achieve a shrinkage in the thickness of over 8%.

(22) In step D), the polystyrene sea component is dissolved preferably in trichloroethylene. Preferably, the felt remaining is submitted to gradual calendering until a density exceeding 0.2 g/cm.sup.3 is reached.

(23) Step E) begins by preparing an elastomeric polyurethane in an organic solvent, preferably dimethylformamide (DMF). The procedure for preparing elastomeric polyurethane is known in the field and, specifically, described in the patent application EP 0584511.

(24) Once the elastomeric polyurethane has been obtained, the steps for impregnation of the felt and coagulation of the polyurethane are preferably conducted for a time period ranging from 30 minutes to two hours, at a temperature below 50° C.

(25) The polyvinyl adhesive is then removed by washing with hot water, preferably boiling water. Then one proceeds by drying the felt impregnated with polyurethane.

(26) In step F), the felt thus obtained is buffed with abrasive paper strips on the upper face so as to free the microfibres and generate the nap; the felt is rewound and submitted to buffing on the lower face, so that the direction of rotation of the abrasive paper strips generates a nap with a concurrent orientation between the upper and the lower surface. The abrasive paper preferably has a mesh value lower than 500 mesh, more preferably lower than 400 mesh. The intermediate product of the process thus generated is defined as the raw product.

(27) In step G), the raw product is dyed according to the technologies traditionally employed for synthetic leathers. These dyeing processes are described, for example in the following patent applications: EP 0584511 and EP 1323859.

(28) In step H), the semi-finished dyed product is preferably submitted to two brushings: a first brushing in a wet state and a second brushing after drying. The first brushing is carried out on both surfaces, preferably using bush-hammered rollers with a direction of rotation concurrent with the orientation of the fibres. The second brushing is applied after drying, and in this case as well, on both surfaces with a rotation of the brushes concurrent with the orientation of the fibres.

(29) At the end of the above-described process, there is obtained a microfibrous non-woven fabric based on polyester or polyamide, impregnated with polyurethane, characterised by a thickness equal to or less than 0.65 mm, preferably equal to or less than 0.60 mm, and by a flat or slightly mottled appearance. The nap length is preferably equal to or less than 350 μm, more preferably equal to or less than 300 μm. The non-woven fabric thus has a very thin texture and a homogenous surface with a flat or slightly mottled appearance.

(30) Owing to these characteristics, the non-woven fabric is ideal for use in the preparation of coverings for consumer goods, preferably covers and cases for consumer goods, including for example portable devices for recording or reproducing sounds or images, portable entertainment devices, sports weapons or equipment, devices for personal well-being or health, telephones, handheld computers, laptops and other electronic devices. Therefore, the subject matter of the invention also relates to these coverings, particularly covers and cases for consumer goods.

EXAMPLES

Example 1

(31) A) A bicomponent flock is prepared, constituted by microfibres of polyethylene terephthalate (PET) (0.14-0.16 dtex) in a sea of polystyrene (PS), with the following characteristics:

(32) 1. fibre count: 4.2 dtex

(33) 2. length: 51 mm

(34) 3. curling frequency: 4-5/cm

(35) In particular, the composition by weight of the flock is 57% PET and 43% PS. The fibre section is constituted by 16 microfibres of PET englobed by the PS.

(36) B) An intermediate felt product is prepared by means of the punching of the bicomponent flock so as to obtain a product with a density comprised between 0.170 and 0.210 g/cm.sup.3 and a unit weight comprised between 400 and 480 g/m.sup.2.

(37) C) The intermediate felt product is impregnated with an aqueous solution of PVA at a concentration of 12% and dried; subsequently it is immersed in a trichloroethylene bath until complete elimination of the sea of PS and dried.

(38) D) An elastomeric polyurethane is prepared separately in a solution of dimethylformamide (DMF). In a first step (pre-polymerisation), polycaprolactone (PCL) and polytetrahydrofuran (PTHF) with a molecular weight of 2000 amu are reacted at 63° C., under agitation, with diphenylmethane diisocyanate (MDI) in an isocyanate/diol molar ratio of 2.7/1. After 2.5 hours of reaction, DMF is added so as to obtain a 25% pre-polymer solution with a free NCO content of 1.46%.
E) Maintaining the solution of pre-polymer obtained in step D) at 38° C., water and dibutylamine (DBA) are added so as to obtain a polyurethane-polyurea with a molecular weight of 15000 amu. The solution is heated to a temperature of 63° C. and maintained under agitation for 8 hours until reaching a final viscosity of 20,000 cP at 20° C. The solution is diluted to 14% by weight with DMF and Tinuvin® 622 and Tinuvin® 234 are added thereto. Following coagulation in water, the polymer contained in the solution is capable of generating high-porosity structures.
F) The felt obtained in step C) is impregnated with the polyurethane solution and, after a residence time of about 1 hour at a temperature lower than 48° C., it generates a coagulated product. The latter is washed in a bath of boiling water so as to completely remove the PVA content and is then dried. The material thus obtained is buffed with abrasive paper strips on the upper face so as to free the microfibres and generate the nap; the material is rewound and submitted to buffing on the lower face, so that the direction of rotation of the abrasive paper strips generates a nap with a concurrent orientation between the upper and the lower surface.
G) The raw intermediate product obtained in step F) is dyed according to the technologies traditionally employed for synthetic leathers.
H) The wet dyed product is submitted to brushing on both surfaces using bush-hammered rollers with a direction of rotation concurrent with the orientation of the fibres. After drying, a second brushing is applied, and in this case as well, by working on both surfaces with a rotation of the brushes concurrent with the orientation of the fibres.
I) The product obtained in step H) is cut in half in the direction of thickness so as to obtain two identical laminates, each of half thickness.
L) The finished product obtained has a homogenous surface with a flat appearance and a nap length between 135 and 170 μm; the nap length is shown in the photograph appearing in FIG. 4.

Example 2

(39) A) A bicomponent flock is prepared, constituted by microfibres of PET (0.19-0.21 dtex) in a sea of PS, with the following characteristics:

(40) 1. fibre count: 4.2 dtex

(41) 2. length: 51 mm

(42) 3. curling frequency: 5-6/cm

(43) In particular, the composition by weight of the flock is 80% PET and 20% PS. The fibre section is constituted by 16 microfibres of PET englobed by the PS.

(44) B) An intermediate felt product is prepared by means of the punching of the bicomponent flock so as to obtain a product with a density comprised between 0.170 and 0.210 g/cm.sup.3 and a unit weight comprised between 400 and 480 g/m.sup.2.

(45) C) The intermediate felt product is impregnated with an aqueous solution of PVA at a concentration of 12% and dried; subsequently it is immersed in a trichloroethylene bath until complete elimination of the sea of PS and dried.

(46) D) An elastomeric polyurethane is prepared separately in a solution of DMF. In a first step (pre-polymerisation), PCL and PTHF with a molecular weight of 2000 amu are reacted at 63° C., under agitation, with MDI in an isocyanate/diol molar ratio of 2.7/1. After 2.5 hours of reaction, DMF is added so as to obtain a 25% pre-polymer solution with a free NCO content of 1.46%.
E) Maintaining the solution of pre-polymer obtained in step D) at 38° C., water and DBA are added so as to obtain a polyurethane-polyurea with a molecular weight of 15000 amu. The solution is heated to a temperature of 63° C. and maintained under agitation for 8 hours until reaching a final viscosity of 20,000 cP at 20° C. The solution is diluted to 14% by weight with DMF and Tinuvin® 622 and Tinuvin® 234 are added thereto. Following coagulation in water, the polymer contained in the solution is capable of generating high-porosity structures.
F) The felt obtained in step C) is impregnated with the polyurethane solution and, after a residence time of about 1 hour at a temperature lower than 48° C., it generates a coagulated product. The latter is washed in a bath of boiling water so as to completely remove the PVA content and is then dried. The material thus obtained is buffed with abrasive paper strips on the upper face so as to free the microfibres and generate the nap; the material is rewound and submitted to buffing on the lower face, so that the direction of rotation of the abrasive paper strips generates a nap with a concurrent orientation between the upper and the lower surface.
G) The raw intermediate product obtained in step F) is dyed according to the technologies traditionally employed for synthetic leathers.
H) The wet dyed product is submitted to brushing on both surfaces using bush-hammered rollers with a direction of rotation concurrent with the orientation of the fibres. After drying, a second brushing is applied, and in this case as well, by working on both surfaces with a rotation of the brushes concurrent with the orientation of the fibres.
I) The product obtained in step H) is cut in half in the direction of thickness so as to obtain two identical laminates, each of half thickness.
L) The finished product obtained has a surface with a slightly mottled appearance, a nap length varying from 175 to 220 μm and a nap that is less dense and homogeneous compared to the preceding example; the nap length is shown in the photograph of Example 2.

Example 3 (Comparative Example)

(47) A) A bicomponent flock is prepared, constituted by microfibres of PET (0.14-0.16 dtex) in a sea of PS,

(48) with the following characteristics:

(49) 1. fibre count: 4.2 dtex

(50) 2. length: 51 mm

(51) 3. curling frequency: 4-5/cm

(52) In particular, the composition by weight of the flock is 57% PET and 43% PS. The fibre section is constituted by 16 microfibres of PET englobed by the PS.

(53) B) An intermediate felt product is prepared by means of the punching of the bicomponent flock so as to obtain a product with a density comprised between 0.170 and 0.210 g/cm.sup.3 and a unit weight comprised between 400 and 480 g/m.sup.2.

(54) C) The intermediate felt product is impregnated with an aqueous solution of PVA at a concentration of 12% and dried; subsequently it is immersed in a trichloroethylene bath until complete elimination of the sea of PS and dried.

(55) D) An elastomeric polyurethane is prepared separately in a solution of DMF. In a first step (pre-polymerisation), PCL and PTHF with a molecular weight of 2000 amu are reacted at 63° C., under agitation, with MDI in an isocyanate/diol molar ratio of 2.7/1. After 2.5 hours of reaction, DMF is added so as to obtain a 25% pre-polymer solution with a free NCO content of 1.46%.
E) Maintaining the solution of pre-polymer obtained in step D) at 38° C., water and DBA are added so as to obtain a polyurethane-polyurea with a molecular weight of 15000 amu. The solution is heated to a temperature of 63° C. and maintained under agitation for 8 hours until reaching a final viscosity of 20,000 cP at 20° C. The solution is diluted to 14% by weight with DMF and Tinuvin® 622 and Tinuvin® 234 are added thereto. Following coagulation in water, the polymer contained in the solution is capable of generating high-porosity structures.
F) The felt obtained in step C) is impregnated with the polyurethane solution and, after a residence time of about 1 hour at a temperature lower than 48° C., it generates a coagulated product. The latter is washed in a bath of boiling water so as to completely remove the PVA content and is then dried.
G) The product obtained in step F) is cut in half in the direction of thickness so as to obtain two identical laminates, each of half thickness.
H) The material thus obtained is buffed with abrasive paper strips on the upper face so as to free the microfibres and generate the nap;
I) The raw intermediate product obtained in step H) is dyed according to the technologies traditionally employed for synthetic leathers, but the reduced physical mechanical properties of the material make this step a particularly crucial, as there is a high incidence of splitting and tearing that markedly reduce the manufacturing yield.
L) The wet dyed product is submitted to brushing using bush-hammered rollers with a direction of rotation concurrent with the orientation of the fibres. After drying, a second brushing is applied, with a rotation of the brushes concurrent with the orientation of the fibres.
M) The finished product obtained has a surface with a highly mottled effect (mottling) and nap length typical of the microfibrous material of the prior art.

(56) The mechanical properties have been determined for the raw semi-finished products obtained with the process of the invention (Example 1), with the known process of the prior art (which is similar to that described in Example 3 without the greater thickness of the product realised), and with the process of Comparative Example 3.

(57) TABLE-US-00001 Raw Raw semi-finished semi- product finished obtained product with the obtained Raw process of with the semi-finished the invention process of product (Example 1) the prior art of Example 3 Thickness 1.03 0.74 0.57 (mm) UNIT WEIGHT 354 242 180 (g/m.sup.2) DENSITY 0.344 0.327 0.315 (g/m.sup.3) 20% Modulus L 6.1 3.8 2.4 (Kg/cm) T 1.4 0.9 0.5 ELMENDORF L 2.9 1.1 1.5 Tear Strength T 1.2 0.7 0.8 (Kg) TENACITY L 15.7 8.1 6.0 (Kg/cm) T 9.5 6.2 3.6 ELONGATION AT L 76.2 64.4 71.1 BREAK T 135.2 120.5 112.4 (%) [NOTE: L = Longitudinal - C = Transversal]

(58) The semi-finished product obtained with the process of the prior art, which provides that the splitting step precede the dyeing step, has modulus and tenacity values that lend adequate resistance to the dyeing process. Reducing the thickness to that required by the application, with the process being equal, the tenacity characteristics in a longitudinal direction (winding direction of the non-woven fabric) and above all, in a transversal direction (see Example 3), drop to levels that are too low to allow for adequate resistance of the product to the stresses inflicted during the dyeing process. The problem can be resolved with the process constituting the subject matter of the invention (see Example 1), in which the raw semi-finished product has modulus and tenacity values that are even higher than those of the known process and thus highly suitable for withstanding the stresses of the dyeing process.