DE4029337C1 - Flat fleece absorbent - Google Patents

Abstract

Flat compound fleece absorbent is claimed. The fleece hasas an upper layer a soft water permeable fleecy layer ofpolypropylene fibres under which is a tissue layer andsuperabsorbent particles and/or cellulose fluff. The fleece ismade as a continuous strip by feeding into the slit between twocalender rollers a 10-15 g/m<2> wt. poly-propylene fibre fleecestrip and simultaneously a 22 g/m<2> wt. tissue strip tocompletely cover the surface of the polypropylene fleece. Therollers comprise one smooth roller heated to 130<d>eg.C and oneroller embossed with points heated to a surface temp. of 175<d>eg.C.The tissue layer is supplied to the slit so that it covers thehalf circumference of the embossed roller. A linear pressure of80 daN/cm is maintained in the slit.

Description

The invention relates to a method for the production a unilaterally absorbent, flat composite nonwoven body, which as a top layer a soft, water-permeable, optionally with a surfactant impregnated nonwoven web Polypropylene spinning or staple fibers, under which as the next layer a tissue web with a weight per square meter is arranged around 22 g. Located under the tissue train superabsorbent particles and / or cellulose fluff.

Such composite nonwoven bodies are used, in particular, as nonwoven webs used by disposable diapers or sanitary napkins. Your task consists essentially in the form and cohesion of the To ensure absorbent body for fluid body exudates. Furthermore, the superabsorbent particles in the interior of the absorbent body do not trickle to its surface. Furthermore must the naturally hydrophobic polypropylene nonwoven, which is on the outside of the absorbent body, permeable for aqueous body fluids. These must also be distributed evenly throughout the absorbent body.

These requirements are in commercial absorbent bodies achieved in that the top layer is a soft, absorbent, preferably 15 g / m² heavy, optionally with a the wettability-promoting surfactant impregnated nonwoven fabric Web of polypropylene spinning or staple fibers is present under which as the next layer, a tissue web with a weight per square meter  attached to 22 g. Due to their pronounced hydrophilic properties, the tissue layer acts as a liquid distributor perpendicular to the flow direction.

Nonwoven fabric and tissue, however, do not form a single entity, but instead will be on the production line for the absorbent body in processed separate process steps. This occurs at the upper nonwoven web tensile loads of about 10 N / 5 cm on; therefore, this one may show only slight elongation.

Because of the extremely low wet strength of the tissue web and the fact that these production reasons only loose under the Cover nonwoven web was, was the superabsorbent powder or -Gel so far inadequate in the wet state of the absorbent body stated:

EP 03 74 910 A1 deals with a generic composite nonwoven body, wherein a compound of the polyolefin fibers of two respective outer nonwoven cover layers with the Tissue fibers of the underlying web by thermal Calendering takes place. The two cover fleece layers are thereby calendered with each other over the whole area. It arises a firm connection between the cover fleece layers and the Absorbent body, preferably over the entire surface of the nonwoven fabric distributed. The thickness of the cover fleece used ranges between 4 g / m² and 300 g / m².

The solidification temperature is below the melting temperature the polyolefin fibers are: oversteps namely the Calender surface temperature is the melting point of polypropylene, the previously partially crystalline fibers would be melted and thus destroyed. As molten polyolefin one not  has more measurable strength, tears the fleece immediately after calender exit and would therefore no longer processable. In addition, the calender surfaces are immediately involved molten polypropylene, which is another operation would make impossible.

But now the roller temperatures are well below the Melting point of the polyolefin is maintained, the tissue material even poorly adhere to the nonwoven fibers. Shape and Cohesion of the absorbent body, as he said in the European Patent application is made after several times Soaking no longer guaranteed.

The gauge, in the manufacturing process, the roll temperature in no case above the melting temperature of the polyolefin For example, it is clear from the journal Chemical Fibers / Textile Industry 37/89 vintage (November 1987), namely the article "Thermobonding: Growing market for PP staple fibers "by P. Olivieri et al., Page 1104, 3rd column, first complete paragraph, and page 1106, fig. 12; further from a public lecture "Improving quality in the Thermobond process ", held by Dr.-Ing. D. Müller on the Index 87-congress, where under the chapter "Influence of temperature" is taught, "the roll surface temperatures so adjust that the fibers below the melting temperature stay ", and a temperature increase" only up to one maximum value can be achieved (can), at even higher temperature there is a drop in strength ".

Out of these constraints so far could be a solid connection between polyolefin fibers of the cover layer and the tissue fibers can not be achieved. The permanent hydrophilicity of the tissue  Railway also does not come with repeated Durchnässung Wear, because of the loose contact between tissue and Hydrophobic Hüllvliesstoff the hydrophobic properties predominate, especially since the body fluid first with the hydrophobic Outside of the diaper construction comes into contact.

It is conceivable to produce a composite nonwoven body in which the outer nonwoven fabric and the underlying tissue web are completely connected to each other. A problem consists in the fact that, because of the absence of reactive, functional groups and the low surface tension of polypropylene, the tissue material only bad adheres to the nonwoven fibers.

EP 00 06 647 A3 also deals with disposable, absorbent Composite nonwoven bodies, their hydrophobic outer nonwoven layers Basis weights of 5 to 25 g / m² and preferably made of spun polyolefin fibers. The absorbent inner layer is with the outer layers through Minimal edge or point bonding. Regarding the Method and in particular the connection temperatures applies the above.

The object of the present invention is to provide a one-sided absorbent, flat composite nonwoven body with the To produce features of the preamble of claim 1 such that the mentioned disadvantages are overcome, d. H. that, without melting destruction of the polyolefin fiber topcoat, yet there is such a strong heat-embossing connection to the tissue layer, that shape and cohesion of the absorbent body also after repeated wetting are not impaired. The superabsorbent powder or gel must be safe even when wet  be held together. When laminating together Tissue and carrier nonwoven web must be neither heat nor by mechanical influences the structure of one of these tracks be destroyed. The aim is a one-step, continuous Method.

The solution to this problem consists in a method with the Mark of the claim.

The invention contains the surprising finding that under certain process conditions also by simple thermal Calendering a solid compound of polyolefin fibers and Tissue fibers can be achieved:

The invention overcame the prejudice that a Such roller consolidation of polypropylene nonwovens only at Roll temperatures could be carried out, which is about 30 ° C. lower than the melting point of the polypropylene. According to the In contrast, the invention is the surface temperature of the embossed roller 175 ° C, thus lies above the melting point of the Polypropylene. The smooth counter roll has a - usual - Surface temperature of 130 ° C. The tissue train, which of a roll is withdrawn, covered to the inlet to the nip half the circumference of the embossed roller, not just off spatial reasons is advantageous, but by the longer Residence time in the hot area also a preheating of the tissue Material allows.

The nip pressure in the nip is set to 80 daN / cm. At the same time, the roll nip continuously becomes the polypropylene nonwoven fabric supplied, which in the gap over the entire surface on the Tissue web rests and faces the smooth roller.  

Thus, both a firm anchoring of the cellulose fibers of the Tissue web in the polypropylene fiber matrix as well a good one Welding the polypropylene fibers with each other achieved. The tissue material is usually one square meter around 22 g.

The laminate obtained according to the invention has, because of its Stretching properties have good processability, as in the examples will still be occupied numerically.

The required hydrophilic properties of the Hüllvliesstoffs of the composite nonwoven body can be made in a known manner by vulcanization the fibers or the nonwoven, d. H. by order of one Surfactants can be achieved. This surfactant lowers the surface tension the aqueous body fluid so far that this the Moisten Polyolefinvlies and can penetrate. Furthermore should dissolve the surfactant in the body fluid and from the Absorbing absorbent or adsorbed, so that the Hüllvlies shortly after use the hydrophobic properties of a non-viable polypropylene fiber nonwoven. This will achieved that as little body fluid on the surface of the absorbent body is retained and the nonwoven itself feels dry. A rewet is so, even under pressure on the absorbent body, largely avoided. The usage such surfactants is not subject matter the present invention; These are z. B. fatty alcohol (ether) sulfates, alkylarylsulfonates, ethoxylated alkylphenols and alkanol ethoxylates.  

With the embossing conditions according to the invention can thus for the first time a combination of only the beneficial properties of both Sheet materials are achieved. Although the embossed roller so unorthodoxly 10 ° C above the melting range of the polypropylene is heated, and although the polypropylene nonwoven only has 10 to 15 g / m² basis weight, is both a firm anchoring of the cellulose fibers of the tissue web in the Polypropylene fiber matrix as well as a good welding of the Polypropylene fibers achieved among themselves. A "flow" of the Polypropylene and thus a destruction of the cover fleece structure surprisingly does not take place.

Table 1 shows the individual layers of the composite nonwoven body inherent positive qualities, all for themselves remain:

Table 1

The following example quantitatively refers to the properties of the composite nonwoven body produced according to the invention To be received.  

A particular advantage of the method according to the invention is the cost savings: because the tissue material is indispensable Component in almost all marketable diaper constructions is, leads the anticipation of its processing during nonwoven production at no increased expense. But can the basis weight and thus the costs of the outer nonwoven fabric are significantly reduced.

example

A laminate produced according to the claims from a polypropylene fiber nonwoven fabric of 12 gsm and a commercial one Tissue paper of 22 g / m² already has an elongation at 10 N / 5 cm, which is about a non-woven fabric of 23 g / m² without tissue (Table 2).

The tightness is, as can be seen on the sieve test result, also better with the laminate and stays in the wet Condition preserved as that with the polypropylene fiber fleece Welded tissue also has a better wet tensile strength has (Table 2).

The soaking test shows that the non-activated Laminate achieves shorter test repetition times as with the design of the invention washed out no finish can be (Table 2).

For the assessment of the penetration was a standardized Measuring method used, which is the penetration time ("Strike-through") in seconds.  

For determining the permeability of the laminate Superabsorbent particles became the sieve test with defined Screenings used. The sieve residue was measured in percent.

Laminate: 12 g / m² PP nonwoven fabric with 22 g / m² paper Elongation at 10 N / 5 cm (%) 7.6 Sieve test (% residue) 70 Strike through (s) @ 1st exam 60 1st repetition 130 2nd repetition 130

Claims (1)

A process for the production of a single-sided absorbent, flat composite nonwoven body which has as the uppermost layer a soft, water-permeable nonwoven web of polypropylene staple or staple fibers, under which the next layer is a tissue web, which comprises superabsorbent particles and / or cellulose fibers. Fluff are, in the form of a continuous web, by calendering in the nip between a heated smooth and a punctiform embossed, heated calender roll, wherein the nip continuously a 10 to 15 g / m² polypropylene nonwoven web and at the same time about 22 g / m² feeding heavy tissue web from a roll which covers the entire surface of the nonwoven web, and wherein the smooth roller heated to 130 ° C, characterized in that the tissue web is covered to the inlet to the nip half the circumference of the embossed roll, that the embossed roller to 175 ° C surface temperature behei zt and that one sets the line pressure in the gap to 80 daN / cm.