Process for stretching a film web

Abstract

The invention relates to a process for the stretching of a starting film web of thermoplastic polymer material, which comprises at least one low-melting polymer component and at least one high-melting polymer component, the process comprising at least the following steps: heating of the starting film web to an at least partly molten state in which the at least one low-melting polymer component exists in a molten liquid state and the at least one high-melting polymer component does not exist in the molten liquid state, by at least one heating roller and cooling down by passing the partly molten film web through a cooled roller nip, the film being stretched between the at least one heating roller and the cooled roller nip. The films produced may be laminated together with a non-woven fabric.

Claims

1. A process for the manufacture of a non-woven fabric-film laminate, the process comprising: heating of a starting film web of thermoplastic polymer material, the thermoplastic polymer material comprising at least one low-melting polymer component and at least one high-melting polymer component, to an at least partly molten state in which the at least one low-melting polymer component exists in a molten liquid state and the at least one high-melting polymer component does not exist in the molten liquid state, by a first heating roller, and passing the partly molten film web to a second heating roller, wherein the first and second heating roller are operated at different velocities, so that the film web is stretched between the first and the second heating roller, and wherein, additionally, a non-woven fabric web is passed over the second heating roller and is passed through a cooled roller nip together with the film web, wherein the melting point of the non-woven fabric web is above the crystallite melting point of the at least one low-melting polymer component and optionally, the at least one high-melting component of the starting film web, and wherein the film web is heated, jointly with the non-woven fabric web, to a temperature in which the at least one low-melting polymer component and optionally, the at least one high-melting polymer component as a whole or part thereof, of the starting film web exist in the molten liquid state and below the melting point of the non-woven fabric web by the second heating roller.

2. The process according to claim 1, wherein the film web is stretched at a stretching ratio of at least 1:1.5.

3. The process according to claim 1, wherein the film web is stretched at a stretching ratio of at least 1:2.

4. The process according to claim 1, characterized in that the starting film web contains 50 to 75% by weight of filler.

5. The process according to claim 1, wherein the starting film web comprises 15 to 85% by weight of the low-melting polymer component and 85 to 15% by weight of the high-melting polymer component, based on 100% by weight of the low-melting and the high-melting polymer components.

6. The process according to claim 1, wherein at least one of the low-melting polymer components comprises polyethylene and at least one of the high-melting polymer components comprises polypropylene.

7. The process according to claim 1, wherein the heating of the starting film web is performed up to 5 to 20 C. below the crystallite melting point of the at least one high-melting polymer component by the first heating roller.

8. The process according to claim 1, wherein the film web is stretched at a stretching ratio of at least 1:1.2.

9. The process according to claim 1, wherein the film web is subjected to cooling in the cooled roller nip to at least 10 to 30 C. below the crystallite melting point of the at least one low-melting polymer component.

10. The process according to claim 1, wherein the starting film web contains 1 to 75% by weight of filler.

11. The process according to claim 10, wherein the filler is chalk.

Description

EXAMPLE

(1) A starting material film web with a formulation according to Table 1 was manufactured according to the blowing method, the film containing the polypropylene with the lower melting point (140 C.) having been coextruded to serve as the outer layer.

(2) TABLE-US-00001 TABLE 1 Film formulation Crystallite melting Amounts in point parts by weight Component C. 55 LDPE 112 20 LLDPE-butene.sup.1 121 10 Polypropylene 162 10 Random-polypropylene- 140 co-polymer.sup.2 5 TiO.sub.2-White- concentrate, pigment and additives .sup.1MFR 1.0 at 190 C./2.16 kg .sup.2Propylene-ethylene-copolymer with 10% by weight of ethylene

(3) The conditions when blowing the film tube are apparent from Table II below.

(4) TABLE-US-00002 TABLE II Blowing conditions Annular die 550 mm diameter Die nip 1.2 mm Tube diameter 1590 mm Basis weight of film 14 g/m.sup.2 Extruder temperature 240 C.

(5) The film tube obtained was cut open in longitudinal direction and wound onto two rollers. The film width was 2.5 m.

(6) This starting film web was subjected to the process shown in the FIGURE as follows. After taking off the starting film web 2 from the roller 1, it passes via the deflecting rollers 3, 4 and the pressing roller 5 onto the heating roller 6. The heating roller (HZ) 6 is an anti-adhesively coated steel roller, which is heated by heat supply to a surface temperature according to Table III. The heating roller 6 is driven at a web velocity of 100 m/min. From the heating roller 6 the film web passes into the cooling roller nip formed by the roller pair 7/8, which is driven at a web velocity which is higher than the heating roller, depending on the desired degree of stretching. The velocity difference between heating roller and cooling nip results in the degree of stretching. For example, a heating roller velocity of 100 m/min and a cooling roller velocity of 300 m/min bring about a stretching ratio of 100:300 or 1:3. The roller 8 is designed as a smooth roller or as a roller with a textured surface. The roller pair 7/8 is water-cooled (approximately 15 C.). The rollers 7/8 forming the nip are driven in such a manner that the stretching ratios set out in Table III below are attained. This made it possible to obtain films having the basis weights stated in Table III. Table III also shows tests, in which heating was insufficient, thereby causing tearing off of the films.

(7) TABLE-US-00003 TABLE III Heating roller Stretching Production Basis weight (HZ) temperature ratio at >5 min [g/m.sup.2] 105 C. 1:1.50 tearing 117 C. 1:2.00 possible 7.0 117 C. 1:3.50 tearing 124 C. 1:3.50 possible 4.0

(8) Surprisingly, it was found that stretching ratios higher than 1:1.50 are possible as soon as the starting film web is in the liquid molten state of the lowest-melting polyethylene-component (LDPE) during the stretching process. Thus, at a stretching temperature (surface temperature of the heating cylinder) of 117 C. (55% LDPE-content in the liquid molten state) is was possible to obtain a stretching ratio of 1:2.0, i.e. a 14 g/m.sup.2 starting film was able to be stretched to 7.0 g/m.sup.2. At a stretching temperature of 124 C. (55% LDPE- and 20% LLDPE-content in the liquid molten state) it was even possible to obtain a stretching ratio of 1:3.5, i.e. a 14 g/m.sup.2 starting film was able to be stretched to 4.0 g/m.sup.2.

(9) The example shows that the process according to the invention enables the manufacture of films having very low basis weights.

(10) The thin films obtained can subsequently be bonded to non-woven fabrics to form laminates for the purpose of improved handling. Suitable processes are adhesive bonding. In the alternative, thermo-lamination, as described above, may be performed, in which case the non-woven fabric is laminated onto the outer polypropylene layer.