GB2053302A - Spun Non-Wovens - Google Patents

Abstract

A spun non-woven comprising separate filaments (5) and groups of at least two parallelised filaments (6, 7) in which the filaments are modified, at least in part, by the presence of polar groups. The polar groups may be introduced as fibrils (8). <IMAGE>

Description

SPECIFICATION Spun Non-Wovens Spun non-wovens, e.g. spun non-wovens of polyolefin filaments, are known. They may be produced, for example, by the processes described in German Patent Specifications Nos. 1,282,590; 1,303,569 and 1,435,461. These known processes have the aims of increasing the uniformity of deposit of the filaments and decreasing the weight per unit area. Thus, for example, spun non-wovens of high uniformity down to weights per unit area of 5 g/mZ are described and which, when they consist of polyolefins, can be used as disposable products in the field of medicine or hygiene on account of the favourable raw material costs.

Particularly for this last purpose, it is necessary to increase the wettability of the polyolefin filaments (which are water-repellent by nature) and build the spun non-wovens up completely or partially from boundary-surface-active polyolefin filaments. The pore size of such spun non-wovens is also critical, and may need adjustment. To these ends, it is proposed in U.S. Patent Specification No.

3,509,009 (column 1 5, line 52) to produce spun non-wovens with slight oxidation of the surface of the fibres. The adhesion of binders to surfaces treated in this way is improved.

According to the present invention, a spun non-woven comprises separate filaments and groups of at least two parallelised filaments, in which the filaments are modified, at least in places, by the presence of polar groups.

Suitable modifying agents include adducts of propylene oxide and/or ethylene oxide which can be introduced into the fibres or are applied to the surface thereof. In the invention, the basic filaments of which the spun non-woven is composed will usually be water-repellent. For example, the filaments may be of a polyolefin, e.g. polypropylene.

In the products of the invention, such filaments are modified, at least at their surface, by the presence of polar groups. The modification may be effected by introducing oxygen atoms into the, say, polypropylene chain in the form of polypropylene oxide or by means of hydrophilic polymers of the polypropylene glycol polyoxyethylate type, including groups of the formula HO-[CH2-CH2-O]x-[CH2-CH(CH3)-O]y- wherein x and y are the same or different integers, or one may be zero.Alternatively, for modifying the surface of the fibres, e.g. polyethylene filaments, polyethylene glycol adducts of one of the following structures may be used: RCH2O(C2H40)XC2H4OH Fatty alcohol polyoxyethylates R-(p-P h )0(C2H40)xC2H40H Alkylphenol polyoxyethylates RCO(C2H40)XC2H4OH Fatty acid polyoxyethylates RCONH(C2H40)XC2H4OH Fatty acid amide polyoxyethylates wherein R is an aliphatic radical, usually long-chain (e.g. 10 to 30 carbon atoms), e.g. C17H35, and pPh is 1 ,4-phenylene. In general, therefore, it is preferred to use oxygen-containing non-ionogenic compounds including a chain.

The modification of polypropylene filaments, and other groups of filaments described below with polypropylene glycol polyoxyethylates, is of particular interest as a means of obtaining boundarysurface-active spun non-wovens. In this case, the modification of polypropylene filaments can be carried out in stages, and the polar character is enhanced in so doing. The sequence of stages can be illustrated as: -CH2-CH(CH3)-CH2-CH(CH3)- -0-CH2-CH(CH3)-0-CH2-CH(CH3)- H0-(CH2-CH2-O)x-(CH2-CH(CH3)-O)y-(CH2-CH2-O)-H wherein x, y and z are the same or different integers or one or two of them may be zero.

A polyolefin filament can be modified in such a way to give a sheathed core structure having increasing oxygen content towards the outside where the structure is almost exclusively, for example, that of polypropylene or polyethylene glycol.

In one embodiment of a process for preparing a product of the invention, a polyethylene oxide or polypropylene oxide is added to all or part of the polyolefin filaments and groups of filaments during spinning.

During spinning, owing to the rheological conditions, there is a tendency for these polyolefin oxides to be deposited on the surface of the filaments. In order to intensify the boundary-surface-active effect, adducts of polypropylene oxide or polyethylene oxide, for example of the polypropylene glycol polyoxyethylate or alkylphenol polyoxyethylates type, e.g. as described above, may be applied after deposition of the filaments and groups of filaments to form the spun non-woven. These substances may also be applied to the unmodified polyolefin filaments after spinning and formation of the nonwoven, but the adhesion of these boundary-surface-active substances to the water-repellent polypropylene is then not so great as to the oxygen-modified polypropylene. In some cases this is desirable, as is explained below.Particularly when the spun non-woven is constructed from groups of filaments consisting of large numbers of filaments, an aqueous emulsion of the ethylene oxide or propylene oxide adduct can be so introduced between the parallel-extending filaments of the groups of filaments that, owing to the effect of surface tension, they can be distributed along the groups.

The stereoregular structure present in polypropylene is also present in some of the oxygenmodified chain molecules on account of the asymmetrical carbon atoms, which is important in the production of boundary-surface-active polyolefin filaments. It has been found, for example, that polymers of 1-propylene oxide (prepared with solid KOK catalyst) of a certain molecular weight are solid, whereas d,l-polymers of the same molecular weight are liquid. Thus, the steric configuration plays a part in boundary-surface-active coatings of, say, polypropylene oxide coatings, just as it does in, say, isotactic polypropylene of which the basic filament may be composed.Of course, a solid crystalline d,l-propylene oxide polymer can be produced by increasing the molecular weight; in the processing of certain spun non-wovens, crystallinity of the surface is not desirable.

As an alternative to the core/sheath structure of the surface modification, a fibril-like structure is also possible for obtaining boundary-surface-active polyolefin filament surfaces. It has been found that it is not necessary that the entire surface of the filaments and, consequently, of the spun non-woven built up therefrom should be modified in order to achieve a boundary-surface-active effect. On the contrary, for many practical purposes, it is sufficient if only areas of the surfaces are activated.

According to necessity, the degree of surface activation can be controlled by the percentage by these boundary-surface-active areas, for example active fibrils, forming the surface of the filaments. Itis particularly preferred that the fibril-like areas of the surface modification are incorporated along the parallel separate filaments of the groups of filaments. The polarity of the surface can be increased, in the spinning and deposition of polyolefin filaments to form a spun nonwoven, by the addition to the whole spinning composition, of more strongly polar chain-forming substances.Such substances may be, for instance, of the polypropylene oxide type which, during the spinning process, i.e. during the extrusion of the molten mass from the holes of spinnerets, accumulate, fibril-like, on parts of the surface of the filaments owing to the rheological conditions and the flow profile which develop during this operation.

Parallelised filaments are obtained by spinning filaments in groups in accordance with the process disclosed in U.S. Patent Specification No. 3,554,854, in which Figure 5 shows a spun nonwoven constructed from groups of filaments. In other words, the non-woven is constructed from parallel-extending strands of separate filaments, the parallel groups or strands of filaments being deposited in an irregular or random state. Such non-wovens are now being used increasingly as covering layers for absorbent layers of cellulose, for example in baby napkins, the polyolefin non-woven forming an outer covering for the cellulose layer. In use, the polyolefin non-woven rests directly against the skin and is intended to allow the fluids which are released to pass through so that they may be absorbed by the cellulose layer.Such polyolefin non-wovens can assume the same function in sanitary towels and tampons. The wettability and porosity of the polyolefin non-wovens are important aspects.

Moreover, the pore size should not be so large that the fluids accummulated in the cellulose layer flood back (or rewet) and not so fine that the passage of the fluids to the cellulose layer is retarded.

In the product of the invention, this problem can be avoided, since the spun non-woven consists of groups of continuous polyolefin filaments intermingled with separate filaments. The groups and the separate filaments are randomly deposited and are preferably consolidated at their points of intersection. Spot or thermal consolidation of defined micro-areas which can be effected by passing the non-woven through heated calender rolls provided with projections is preferred for many purposes.

The production of such non-wovens is described, and the products claimed per se, in our co-pending application 80 17972 which has also been filed on 2nd June (Agents Ref: GJE 618G/92).

The construction of the non-woven from a mixture of groups of filaments or parallelised strands with separate filaments is essential, because the pore size can be thereby adjusted exactly according to requirements. The groups of filaments are composed in each case of two or more parallelised separate filaments, for example by the use of spinnerets giving, in sequence, layers of separate filaments and parallelised groups of filaments and building them up into a mixed non-woven by mixing on a depositing or receiving belt. If, for a given weight per unit area, the spun non-woven is built up solely from randomly deposited separate filaments (for example, denier 1 dtex), the resultant sheet structure has a maximum coverage of area and a minimum pore size.If the same weight per unit area is built up with a non-woven consisting of groups of filaments composed in each case of ten separate filaments of the same denier, the sheet structure has a very large pore size, because the randomly deposited groups or strands of parallelised filaments give coarse pores for the same weight per unit area. Although possible, it is undesirable to reduce the pore size of a non-woven consisting of groups of filaments by spinning superposed layers and thereby achieving higher weights per unit area.

By mixing separate filaments with groups of filaments containing a defined number of separate filaments, the mixing ratio of separate filaments and groups of filaments being suitably chosen, the pore size of the polyolefin non-woven can be adjusted to the value required for a particular purpose.

Correct adjustment of the pore size is best measured in close approximation to what occurs in practice by establishing what time is required for the penetration of a certain amount of fluid through the nonwoven into a subjacent absorbent layer (for example, a cellulose layer) and by determining the amount of fluid which subsequently returns through the non-woven to the surface from the absorbent layer (wet-back) on the application of pressure.

The entire spun non-woven may be built up from polar and boundary-surface-active filaments and groups of filaments of the same kind. However, a non-woven composed of two different types of filaments and groups of filaments, a so-called mixed non-woven, may also be produced wherein some filaments and groups of filaments consist of a non-modified polyolefin and other filaments and groups of filaments consist of polar and boundary-surface-activated substances. An apparatus for producing such mixed non-wovens is described in U.S. Patent Specification No. 3,509,009 (Figures 1 7 and 18).

Here there is the possibility, as illustrated in Figure 19 of this U.S. Patent Specification, of producing a spun non-woven which is built up from layers of different kinds of filaments and groups of filaments.

In the present invention, a spun non-woven with strongly polar and boundary-surface-active filaments and groups of filaments at the surface and non-modified or only relatively slightly modified filaments in the middle can be built up. The percentage of activity of the individual layers can be increased step-by-step through the cross-section of such a product if, with spinnerets arranged in series, polyolefin increasingly activated in the direction of travel is spun or if the spinneret delivering a central layer of filaments spins unactivated material. In the latter case, two outer spinnerets can deliver boundary-surface-active filaments.

It has been found that a further increase and modification of the boundary-surface-activity of the complete product can be achieved by after-treating a spun non-woven "pre-activated" by the spinning process, with certain surfactants. Such substances are preferably deposited at those parts of the polyolefin filaments which have a relatively strong polar nature, for example owing to the presence of polar fibrils of the type described above. It is preferred however, to deposit or accumulate ethylene oxide or propylene oxide adducts between and along the parallel filaments of the groups of filaments.

Suitable surfactants include adducts of ethylene oxide or propylene oxide and fatty alcohols, mercaptans, fatty acids and amines. Such substances may be, for example, of the following formulae: RtO(CH2CH2 )xH R1S(CH2CH2 )xH RrCOO(CH2CH2 )xH R,NH(CH2CH2 )xH wherein x is an integer and R1 is an aliphatic radical, e.g. of the type defined above for R.

Polyglycerine esters of the formula R1COO(CH2CH(OH)CH2 )xH and other non-ionogenic boundary-surface-active substances of the aliphatic-cyclic type, eAg.

polyethylene ethers of alkylphenols of the formula R1-C6H4-O-(CH2-CH2-O)x-H wherein R1 and x are as defined above may also be used.

The increase in the boundary-surface-activity of the filaments making up the spun non-woven by applying such non-ionogenic surfactants must be controlled according to whether the boundarysurface-activity is to be maintained on wetting or is to decrease on intensive contact with water or an aqueous liquid. In practice, it is often desirable, for example when such spun non-wovens are employed as covering layers for highly absorbent cellulose in baby napkins or medical plasters, that, after good initial wettability, this factor is reduced in order to prevent too heavy soaking. In this case, the boundary surface-active coating should be washed away and/or transferred to the cellulose layer, the layer of spun non-woven then becoming increasingly water-repellent.It may be of advantage in such cases to produce the boundary-surface-activity by applying an oxygen-containing, non-ionogenic polypropylene or polyethylene oxide polymer to the mixed non-woven of polyolefin filaments and groups of filaments after spinning. As has already been mentioned, the porosity can then be adjusted by adjusting the mixing ratio of separate filaments to groups of filaments; the wetting can be adjusted via the ethylene oxide or propylene oxide adducts. The time of penetration of fluids and the return of fluids can be adjusted by means of the ratio of the two factors.

The following Examples illustrate the invention.

Example 1 A randomly non-woven was produced from separate polypropylene filaments and groups of polypropylene filaments using apparatus of the type described in U.S. Patent Specification No.

3,554,854 (Figure 2). Filaments spun from adjacent spinning beams respectively producing single, treble and double filaments (as opposed to the groups of three in Figure 3 of U.S. Patent Specification No. 3,554,854) were stretched and delivered to a receiving belt by means of aerodynamic stretching by air ducts and deposited to form the non-woven. The spinning process was so carried out that a weight per unit area of 15 g/m2, composed of 50% of separate filaments and 25% each of groups of two and three, was produced. The separate filament denier was 1.5 dtex (mean value). The spinneret temperature was set at 2500C. A polypropylene having a melting index (Mi) of 12-17 (2300C), measured according to DIN 53 735, was used as raw spinning material.Prior to spinning, 1% of titanium dioxide and 0.3% of optical brightener (CGMBIO by Ciba) were added to the polypropylene.

After deposition of the non-woven, it was passed,while still unbonded, at 1 200C through a calender, one steel roll of which had projections with a diameter of 1 mm and a distribution of 32/cm2, so that "spot" consolidation of the non-woven with 18% of impressed area took place. The non-woven was then impregnated with an aqueous solution of isooctylphenol-polyethoxyethanol condensed with 10 moles of ethylene oxide (e.g. Triton X 100 by Rohm and Haas). After the impregnation, the non-woven was suction-dried at 1000C using a perforated drum drier.

The pore size and wettability of the non-woven were measured by the penetration of liquid in both direction (rewet). In this operation, 30 cm3 of a 1 5% urea solution were applied to the non-woven backed with a layer of cellulose. After penetration of the liquid, a filter paper with a diameter of 1 8 cm was placed on top under a load of 3,000 g. After application of the load for 3 minutes, the filter paper was weighed and the amount of liquid which had penetrated back through the polyolefin non-woven from the layer of cellulose into the filter paper was determined. This amount did not appear to be more than 1 cm3. The speed of the original penetration was measured and found to be below 2 minutes.

Example 2 In this Example, the spinning process was carried out as in Example 1, except that the ethylene oxide adduct was added to the polypropylene oxide granules in an amount of 1% prior to spinning, together with the TiO2 and the optical brightener. In this case, a block polymer of the type HO(CH2CH2--O)X(CH(CH3)CH2O)y(CH2CH2Q)zH with 50% polyoxyethylene units in the molecule and an average molecular weight of 6500 (Pluronic P 105 by BASF Wyandotte Corp.) was employed. The remainder of the molecule was composed of polyoxypropylene units. It was found that the combination of ethylene oxide and propylene oxide adducts in a molecule gives properties which are particularly favourable.The hydrophilic properties can be adjusted satisfactorily by the proportion of condensed ethylene oxide in block polymers of propylene oxide since, in comparison, the propylene oxide exhibits water-repellent properties sooner. The degree of water-solubility of the adduct present on the polyolefin filaments and groups of filaments can thereby be adjusted. If, in the case of covering non-wovens for baby napkins, it is desired to prevent return of the fluid (urine) from the absorbent cellulose layer (wetback), as mentioned above, it is advantageous to employ higher proportions of ethylene oxide to the propylene oxide block, since the adduct is then washed away out of the polyolefin when wetting occurs and an increasing water repulsion takes place. As a result, the surface of the napkin remains dry. An amount of more than 20% of ethylene oxide in the molecule is preferred. After consolidation of the non-woven, no more adduct was added.

The rate of penetration of the liquid was somewhat lower in this case than in the preceding Example; this was evidently because not all the adduct had migrated to the surface of the filaments.

In the accompanying drawings, Figure 1 is a schematic view of a product of the invention and Figure 2 is a schematic view of part of apparatus suitable for producing such a product.

The apparatus of Figure 2 comprises three spinnerets 1,2 and 3 respectively producing single filaments and groups of three and two filaments which are deposited in layers on a band 4 travelling in the direction of the arrow. The randomly laid product, shown in Figure 1, comprises single filaments 5, two-filament groups 6 three-filament groups 7 and fibrils 8 of or in areas of surfactant.

Claims (11)

Claims

1. A spun non-woven material comprising individual filaments and groups of at least two parallelised filaments, in which the filaments are modified, at least in part, by the presence of polar groups.

2. A material according to claim 1 in which the filaments are water-repellent before modification.

3. A material according to claim 2 in which the filaments are of a polyolefin.

4. A material according to any preceding claim in which the filaments are modified by the use of an ethylene oxide or propylene oxide adduct.

5. A material according to any preceding claim in which the concentration of polar groups increasestowards the surface of the material.

6. A material according to any preceding claim in which the filaments are modified by the presence of fibrils of a substance containing polar groups on the surface of the filaments or groups of filaments.

7. A material according to any preceding claim in which the filaments and groups of filaments or the unmodified material have been modified by surface treatment with an ethylene oxide adduct of a propylene oxide block polymer containing at least 20% by weight of ethylene oxide.

8. A material according to any preceding claim in which the filaments and groups of filaments have been spun from a plurality of spinnerets and deposited randomly to form a mixed non-woven.

9. A material according to any preceding claim in which the filaments and groups of filaments are bonded at their points of intersection.

10. A material according to claim 1 substantially as described in either of the Examples.

11. A material according to claim 1 substantially as illustrated in Figure 1.

1 2. A material according to claim 1 substantially as herein described with reference to Figures 1 and 2.