DE19640607A1 - Gas-permeable, dimensionally stabilised nonwoven fabric - Google Patents

Abstract

Gas-permeable, dimensionally-stable non-woven fabric (I)made from thermoplastic polymers or materials (II) by the melt blowing process. Material (I) is obtained from a base fabric (I') which has no dimensional stability when first produced, by subjecting fabric (I') to one or more further treatments or leaving it for a further reaction time. Also claimed is a process for the production of (I) by making melt-blown fabric (I'), laying it down on a support which preserves the dimensions of (I'), and stabilising it by treatment or further reaction as above.

Description

The invention relates to the melt-blow method provided fleeces that are not sufficient immediately after generation Own intrinsic and or dimensional stability and only then as dimensionally stable, self-supporting fleeces can be isolated, if by post-treatment or post-reaction time a there is sufficient dimensional stability and a process for the manufacture and use of such nonwovens.

The meltblown process was invented around 1950. First reports come from Wente (Wente, Van A., Superfine Thermoplastic Fibers, Industrial Engineering Chemistry, Vol. 48, pp. 1342-1346.

Further descriptions can be found e.g. B. in DE-OS 19 64 060 and in DE-OS 23 08 242. In the process, this is in one Extruder melted polymer to a special spinneret out of their holes a variety of polymer threads be squeezed out, which directly through the spinneret tip hot air flowing in parallel is subjected to fine fibers, on an all-round, open storage sieve or an open, rotating drum, usually under or inside there is a negative pressure without additional consolidation form self-supporting fleece.

The nonwovens produced by the meltblown process have today a wide range of applications. Examples are the use in Disposable diapers, as insulation material, as packaging material, as Battery separators, as adsorption material (oil, fat,..), As  Filter material, as a substrate for synthetic leather, in construction, etc. . It is crucial for the use of meltblown nonwovens that very fine fibers down to less than 1 µm in the meltblowing process Diameter can be generated. Allow these fine fibers e.g. B. the production of filter nonwovens with very fine pores Hot melt adhesive fleeces with low basis weight (<25 g / m2), higher Activation surface and soft handle or from fleeces to Scattering of light in skylight windows around the incident light to distribute evenly and with high luminous efficacy.

A limited number is available in the state of the art Raw materials known, which by means of the melt-blow technique Nonwovens can be processed. In particular, the process requires Polymers that are suitable (no polymer degradation, apparatus conditional limits. . . .) Processing temperature a low Have melt viscosity and completely amorphous or partially crystalline stallin solidify, such as B. polypropylene, polyethylene, polyamide 6, polyamide 66, polybutylene terephthalate, polycarbonate, poly (4- methyl-1-pentene), polyphenylene sulfide, polyether sulfone, polyviny lidendifluoride, etc. . These polymers generally have the Property immediately after the fleece formation on the circumferential Storage screen or the rotating storage drum a dimension to result in stable fleece with a non-stick surface.

So-called hotmelts, which are chemically mostly the groups of the Co polyester, copolyamides, copolyolefins or thermoplastic Belong to polyurethanes, e.g. B. after melting, because their segmented structure of soft and hard segments, in again solidified over a longer period of sticky Properties that even separate carrier films make impossible and thus in the production of foils or nonwovens the use of release agents or spacers (waxes and or organic additives). The added funds have an effect on the other hand, it often negatively affects the original adhesive properties properties (specific adhesion to substrates) or the activators availability of the hot melt adhesive. With supported foils or  Nonwovens exist as with freely produced foils or nonwovens Hotmelts continue to pose the risk of recrystallization the wound extrudate is blocked on the roll, d. H. that permanently bond the individual layers together.

These properties of the hotmelts, called technical masses polymers with specific properties for various applications represent interesting raw materials for the meltblowing technique, are the main reason why only a few have been selected so far Raw materials of this type can be processed in the melt-blow process. So far, only the stickiness of the generated Considered fibers. The dimensional stability of the nonwovens produced was a prerequisite.

EP 0 628 650 A1 describes e.g. B. a method of manufacture of carrier and release agent-free, thermo-activatable nonwovens based on hydroxyl polyester polyurethanes with viscosities of 600 to 3500 mPa * s and their use for gluing and adhesive layers of different substrates. For the manufacture is additionally a storage belt with a specific Surface tension necessary.

Another example of a hotmelt adhesive fleece that looks like the melt-blow method can be produced describes the EP 0 557 889 A1. Here very specific copolyolefins or Ter polymers with a high proportion of polypropylene as suitable Po described polymers, with a special in the melt-blowing process Spinneret used for the production of core-sheath fibers must become.

About the use and suitability of comparable polymers, such as thermoplastic hotmelt adhesives, can be crosslinked afterwards thermoplastic polymers or reactive thermoplastic Enamel materials for the melt-blow process are no information mations before.

Based on this state of the art, there is the task of Invention in self-supporting nonwovens, based on the Melt viscosity, suitable for the melt-blow process Generate standard hotmelts or comparable polymers without that the melt-blow process has to be significantly modified.

This task is solved by melt-blow nonwovens with the Features according to claim 1. Accordingly, the idea is based the invention dimensionally stable, self-supporting melting Blown nonwovens made from hotmelts or comparable polymers Level of a non-dimensionally stable base fleece, through its post-treatment or waiting for a post-reaction time, too produce.

Advantageous refinements result from the Unteran sayings. A method for producing the invention Melt-blow nonwovens are described in claims 13 to 20. Claims 11 and 12 relate to selected applications options.

The solution according to the invention is characterized in that a variety of melt-blow nonwovens from commercially available Hotmelts or comparable polymers that are available in various applications for product or process improvements can lead or open up through the new applications will.

Dimensionally stable nonwovens are used in this publication gas permeable nonwovens understood that without a supportive Layer are mechanically so stable that the dimension of a square blank with a side length of 1 m, which on a Side is fixed to a width of 1 meter and on the opposite lying side (based on the entire width) with a weight is loaded, which corresponds to 50 times the fleece weight, less than 10% increases in length or decreases in width and  its width and length according to the distance of the weight deviate less than 5% from the original dimensions.

The minimum basis weight is 5 g / m2 went out. By the term dimensionally stable fleece is not excluded that such a fleece z. B. from protection or Handling reasons or for application-specific reasons until for processing or during use with support layers or bearers are or remain. Which later described benen carrier can also together with the invention Nonwovens are processed or together with the invention Fleece the application-specific end product (e.g. Represent filter material). In such cases, the fleeces according to the invention deliberately placed on these carriers without that the intention is to separate them subsequently. In the opposite part, there will be z. B. the adhesive properties of the fleece during manufacturing used to without an additional adhesive to produce a full-surface composite, the stability liability z. B. by additional grid-shaped ultrasound or thermal welding can be supported. In the sense of the However, invention also exists in these cases if no additional treatment (e.g. ultrasonic welding) has taken place, the nonwovens according to the invention as self-supporting, to isolate dimensionally stable nonwovens (see above for definition).

The meltblown nonwovens according to the invention have the property that they initially, as not inherently stable and or dimensions stable nonwovens, not directly on the deposit screen of the meltblown Plant can be generated, but on a guided Carrier must be put down. About the occupied beam width, the Carrier speed and the polymer output results in the Basis weight of the fleece. With the known parameters of the Melt-blow process (melt temperature, productivity, Blown air volume, blown air temperature, distance nozzle / carrier etc.)  the fiber fineness, the fleece compactness and that Affect the clipboard image in the usual way.

The aim is fibers with a diameter between 0.5 and 25 µm.

As polymers come e.g. B. Consider standard hotmelts as they are in the article "Adhesive films made of thermoplastic hot melt adhesive stoffen "by D. Schultze in Kunststoffe, 85 (1995) 12, p. 2050-2055 (including bibliography). The article "New ways in the hot melt application. New ways in the preparation of hot melts "by H. Klein in Coating, 12 (1994), pp. 416-422, also deals with thermo plastic hot melt pressure sensitive adhesives, which are also used as polymers for the hot-melt adhesive fleeces according to the invention come into consideration, as well as reactive hot melt adhesives (extrusion poly merization), such as B. described in DE 44 06 977 C2 will.

In principle, however, the meltblown nonwovens according to the invention can be made from all polymers from which after Melt-blow process initially only dimensionally unstable Base fleeces can be generated, which can only be identified by a Post-treatment or waiting for a post-reaction time dimensions let it stabilize. Dimensional stabilization can e.g. B. by crystallization or by crosslinking the nonwoven Polymers are made and is not complete when generated Fleece web is rolled up together with the carrier.

Not inherently stable means that the base fleece produced up to The reel cannot be separated from the carrier without being destroyed. Most of the base fleeces are rubbery and additionally sticky.

Not dimensionally stable means that the base fleece is completely or can be detached in a partially non-destructive manner that  however the dimension z. B. by stretching, shrinking or curling changes.

Post-treatment of the basic fleece or waiting for the post-treatment reaction time has the goal of increasing the stability of the fleece change that it can be removed non-destructively from the carrier can. This is usually achieved by Crystallization or chemical cross-linking the mechanical Stability of the fibers is increased and that by appropriate Measures the adhesion between carrier and fleece is reduced. It is for the time of the process of dimensional stabilization it is important that the base fleece adheres to the carrier is kept in its shape. It is also important that it to none during the process of dimensional stabilization Gluing between the back of the carrier and the fleece edition comes.

It should not only be taken into account that the ratios of Change hot melt to hot melt or from polymer to polymer can, but also that z. B. already the change in stored area mass decisive changes in Procedure may make necessary.

Overall, however, it has been shown that the process without large expenses are customizable and especially the carrier a weighty but not decisive limitation Role.

All web-shaped materials can be used as supports on which the base fleece can be stored dimensionally fixed, together men can be wound up with the base fleece without blocking and from which are affected by post-treatment or post-reaction dimensions Separate the stabilized meltblown nonwoven non-destructively to let.  

Are unsuitable for. B .. foils the impact of the fibers shrink or melt, webs on which that Base fleece cannot adhere, coated or dimensionally stable impregnated sheets, their coating or impregnation with react irreversibly or stick to the base fleece etc.

Gas-tight sheets can be made of metal, plastic (foils) or z. B. Paper exist. Dense paths usually make it difficult Melt-blow process, since the blown air cannot be extracted and the so-called fiber flight occurs due to fiber tearing. Due to the Consistency of the fibers of the base fleece (stickiness, softness) the tendency to fly without suction is less than with the traditional polymers for the meltblown process. The advantage of closed webs is that the dimensionally stabilized Fleece, if no additional measures are taken, of which in the Are usually easier to remove than porous, gas-permeable Carriers.

Nonetheless, gas permeable supports are preferred because of the Melt-blow process is easier to control and therefore easier tailor-made fleeces can be realized. An advantage of porous, gas-permeable supports is that even at high Blown air quantities the so-called fiber flight can be avoided. With high amounts of blown air per melt mass ejected on the other hand produce nonwovens with very fine fibers that offer diverse advantages. The air permeability of the wearer is therefore preferably <at a differential pressure of 200 Pa 1000 l / m2 * s. Such carriers can be used according to the invention Melt-blow nonwovens with particularly fine fibers (soft handle), high air permeability (<5000 l / m2 * s at 200 Pa) and produce a low mass per unit area (<20 g / m2) when gluing no dense film and thus z. B. for gluing of breathable textiles are suitable.

It can also be advantageous if the back of the carrier is anti-adhesive or impregnated to bond  avoid the wrapping layers with base fleece among themselves. A suitable anti-adhesive coating (sufficient Liability for the stabilization of dimensions during storage provided that the subsequent replacement process is supported.

In practice it has been shown that with gas-permeable supports, with suitable process control, the porosity of the carrier also very large pores or mesh sizes do not become an annoying Structural embossing of the base fleece leads and that of fine porous supports (deeper anchoring in the pores) dimensions stabilized nonwovens through suitable measures (see below) can be removed non-destructively.

It follows from the knowledge gained in practice a great freedom of choice in the carrier selection, with reasons of Economic efficiency comes to the fore. So with gas-permeable supports made with higher productivity will. It can be weighed whether a cheap carrier is first is removed from the user before use or processing and Z. B. is easy to dispose of or whether you can z. B. an expensive rere, reusable carrier uses to the manufacturing costs and to reduce the transport weights and costs.

Gas permeable supports can e.g. B. papers, metal, textile and Glass fiber fabrics or knitted fabrics, plastic fabrics, extruded Plastic grids, felts, perforated or slotted foils, Spunbond nonwovens, melt-blow nonwovens, microporous membranes, etc. be.

In many cases, the carrier can already be part of the product to be manufactured later, which together with the deposited dimensionally stabilized fleece alone or with additional substrates interacts (see examples).

In the simplest case, the aftertreatment is that one  let the base fleece crystallize for so long, or with Vernet cures until a non-destructive Detachment is possible. In special cases, the above operations through temperature conditioning, moisture conditioning nation, spraying or wetting with water or specific Chemicals, crosslinking induced by moisture, IR, UV, Gamma, electron beams and the like accelerated or deliberately led.

The aftertreatment can also be modified Fiber surface to be linked or connected. modification means that z. B. a not yet cross-linked, sticky Fiber polymer by treatment with physical methods (Quran treatment, plasma treatment, flames...) And or chemical agents and or sprinkling with z. B. powdery, adsorptive filter aids (diatomaceous earth, activated carbon, PVPP, Catalysts etc.) with specific properties can be. Target can e.g. B. improved hydrophilicity or Hydrophobicity of the fibers or the fiber a porous surface to glue or with a zeta potential or specific or non-specific adsorption properties.

A special variant is made by melt-blow molding according to the invention. Nonwovens made from two or more different meltblown Fleece layers exist. These are generated in that first a base fleece according to the invention onto a suitable one Carrier is deposited and on this composite during or after the Post-treatment for dimensional stabilization Blown fleece comes to rest. This process can take place if repeated several times. It is always the same Polymer can so z. B. about the setting of different fibers fineness and pores a polymer-homogeneous multilayer filter medium with graduated filtration properties. At Nonwovens made of various polymers, such as. B. a copoly It is olefin fleece on which a copolyester fleece has been placed e.g. B. the goal of producing a hot melt adhesive fleece that on both  Fleece sides has different adhesive properties. Let it be z. B. substrates made of polyolefins and polyesters otherwise difficult to stick together using such Easily connect duo hot-melt adhesive fleeces with one another.

As a particularly effective measure to simplify replacement of nonwovens from a carrier nonwoven according to the invention have been found Treatments with liquids, especially water, have been proven. By different swelling behavior and by the under different hydrophilicity of carrier and dimensionally stabilized The bond between the two substrates is determined by a fleece such treatment is usually greatly reduced.

Humidification can be done with superheated steam / saturated steam if the Softening point of the meltblown nonwoven is correspondingly high lies. However, it is easier if a conditioning z. B. sufficient at high air humidity. Especially porous filters papers are here due to their suction and swelling assets advantageous. With particularly strong liability the carrier-fleece composite is completely wetted. This has additional the advantage that particularly thin (low basis weight) nonwovens easier during the detachment process due to the absorbed liquid are to be handled. The wetting or conditioning can shortly before the composite is rolled up, it can the entire role is treated or the treatment takes place in the sufficient time before the release action on the rolling Train.

Modification actions take place either before or during the Post-treatment that leads to dimensional stabilization or during the stripping action.

In the following, the invention will be further illustrated by means of examples are explained.  

example 1

A copolyester polymer (Cepatex 125FC) from Cepat was processed on a Reicofil melt-blowing system (manufacturer Reifenhäuser). Nonwovens with 10 g / m2, 15 g / m2 and 20 g / m2 were placed on four different carriers.
Carrier 1: Reconomic continuous printer paper 60 g / m2 from Zweckform
Carrier 2: Vacuum cleaner filter paper from Steinbeis Gessner, type VE 55
Carrier 3: Extruded PP grid from Naltex, mesh size 4 mm
Carrier 4: Spunbond fleece Daltex 50 g / m2 from Don & Low.

The freshly deposited base fleeces could be used immediately after the Fer under no circumstances can they be removed non-destructively.

After 3 days of storage, the nonwovens according to the invention could be used without Additional treatment non-destructively detached from carrier 3 and 4 will.

After three days of stabilization, the detachment from the carrier was 2 possible without any problems after the material has been raised for 1 hour Air humidity was stored.

The detachment from carrier 1 was after three days of stabilization possible without any problems after the backing paper with a wet sponge had been soaked.  

Due to the fine meltblown fibers, the nonwovens produced had a very soft feel.

Example 2

On a laboratory melt-blow system (manufacturer J) was a Copolyamide (Grilltex D 1317 GF) from EMS processed and on filed the carriers of Example 1.

The freshly filed basic fleeces could not initially dimensionally stable. The fleece produced sticks hardly, but is very elastic and not dimensionally stable.

After 3 days of storage, the dimensionally stabilized fleece settled without additional treatment from carriers 1, 3 and 4 replace.

After conditioning in high humidity, there was also a zer trouble-free detachment from carrier 2 possible.

Example 3

With the nonwovens from Example 1, various welding processes were carried out Seek with different substrates to determine suitability as a hot melt adhesive medium. The fleeces were there e.g. B. between two layers of cardboard, felt and linen brought in and. The fleeces were removed using a Iron activated at 160 ° C. In all cases, it turned out very durable composites. The cardboard and Layers of felt, but not the weld layer destroyed. As well was not only the sweat layer in the linen layers destroyed, but also torn the linen material.  

Example 4

Nonwovens from Example 1 were used for the filtration of particulate matter pensions (activated carbon, diatomaceous earth, PVPP) used and brought the desired filtration success. Several layers of fleece were used one on top of the other and in the clamped state with water vapor treated. The layers adhered firmly after this process together without changing the filter resistance and the filtration effect had changed decisively.

Example 5

Strips of the nonwovens from experiment 1 became spiral and overlapped on a perforated support core. The the resulting filter sleeve was in the overlap zones of the Filter treated with superheated steam. Through this treatment, the Layers glued together without the permeability ent has been influenced. With such filter sleeves, he was consequently filtration tests with those mentioned in Example 4 Particle suspensions carried out.

Example 6

The polymer of experiment 1 was applied as a fleece (5 g / m2) on a Polyester melt-blow fleece deposited, which is suitable for Cleanable systems (hoses, cartridges) for dedusting of process exhaust air. After the dimensional stabilization of the Hot melt adhesive fleece was not removed from the carrier, but put the composite on a needle felt, whereby the Hot-melt adhesive fleece formed the middle layer. By superheated steam activation was a stable, full-area composite  between the polyester meltblown nonwoven and the needle felt Material are generated without the air permeability of the both layers was significantly affected.

Example 7

The polymer of experiment 1 was made as a meltblown nonwoven (2.5 g / m2) on a filter paper suitable for dedusting as Carrier deposited and the composite before rolling up by a grid-shaped ultrasonic welding stabilized. Likewise, part of the composite without ultrasonic welding at elevated Humidity stored. In the latter case, after three days a non-destructive, dimensionally stable fleece according to the invention replace. The ultrasound network was used in a test device Testing for flat filter media suitable for dedusting cleaning attempts have been carried out. Compared to the not filter paper showed clear cleaning advantages.

Example 8

When gluing textiles, it is very important that The adhesive medium does not become a film during the activation process because this leads to a hard grip and crackling noises. At breathable textiles would also increase breathability lost. In one experiment, microfiltration was therefore carried out membrane (0.45 µm, PVDF, Millipore) with 4 different er melt-blow fleeces according to the invention from the polymer according to Experiment 1 occupied and the fleeces over a closed area Plate activated at 150 ° C. It was the air permeability of the Microfilter membrane measured before and after treatment. The Air permeability of the microfilter membrane was originally 0.79 l / cm2 * min at a differential pressure of 100 mbar. After  Treatment with a fleece according to the invention with the basis weight 20 g / m2 and an air permeability of 1900 l / m2 * s at 200 Pa the air permeability of the microfilter membrane was only 4 % of the original value. The surface of the membrane was almost completely covered with a closed hot melt adhesive film. At treatment with a fleece of 15 g / m2 and Air permeability was 2600 l / m2 * s at 200 Pa the microfilter membrane also only 11% of the Initial values and here too there was a clear foil like hot melt adhesive film on the membrane surface. Treated the membrane, however, with a fleece of 15 g / m2 and an air permeability of 9500 l / m2 * s at 200 Pa the residual air permeability is still 63% and it is up no larger closed film zones on the membrane surface more recognizable. In the case of a fleece according to the invention with 20 g / m2 and an air permeability of 7500 l / m2 * s at 200 Pa the remaining air permeability of the membrane is still 59%. The pattern was but much harder to handle.

The conclusion of the experimental examples is that the inventive Allow nonwovens to be produced easily and, for example, as adhesive fleece or use as a filter fleece. Using can be used as filter fleece z. B. Compounds with other filters generate media also by certain regions (grid or Areas) of the hot-melt adhesive filter fleece with the other filters media are welded tightly, while the other regions their Maintain filter effect. When bonding less porous or breathable fabrics must have nonwovens according to the invention high air permeability can be used when there are none may form gas-impermeable melt films.

Claims (20)

1. Gas-permeable, dimensionally stable nonwovens produced from thermoplastic polymers or thermoplastic compositions by the meltblowing method, characterized in that these nonwovens are produced by one or more post-treatments and or waiting for a post-reaction time from base nonwovens which are not dimensionally stable when they are formed. 2. melt-blow nonwovens according to claim 1, characterized in that the nonwovens consist of thermoplastic polymers that the group of hot melt adhesives and or Hot melt adhesives are to be assigned. 3. melt-blow nonwovens according to claim 2, characterized in that the thermoplastic polymers belong to the group of copolyesters or copolyamides. 4. melt-blow nonwovens according to any one of claims 1 to 3, characterized featured, that the thermoplastic mass of the fibers of the base nonwovens is reactive and post-polymerized in the post-reaction time and or post-linked.   5. melt-blow nonwovens according to any one of claims 1 to 4, characterized featured, that the dimensional stability in the post-reaction time was improved by a crystallization process. 6. melt-blow nonwovens according to any one of claims 1 to 5, characterized featured, that the dimensional stabilization by additional after treatments have been accelerated and or improved. 7. melt-blow nonwovens according to any one of claims 1 to 6, characterized featured, that with additional post-treatments the fiber surfaces was modified. 8. melt-blow nonwovens according to any one of claims 1 to 7, characterized featured, that the fleece consists of two or more layers with different polymers exist. 9. melt-blow nonwovens according to any one of claims 1 to 8, characterized featured, that the nonwovens have a basis weight of less than or equal to 20 have g / m2.   10. melt-blow nonwovens according to one of claims 1 to 9, characterized, that the air permeability of the nonwovens at a Differential pressure of 200 Pa is greater than 5000 l / m2 * s. 11. Use of a melt-blow nonwoven according to one of the Claims 1 to 10 as a filter medium and or as a hot-melt adhesive fleece. 12. Use of a melt-blow nonwoven according to claim 11 as hot-melt adhesive fleece for breathable, textile fabrics. 13. Process for producing dimensionally stable, gas-permeable casual melt-blow nonwovens made of thermoplastic polymers or thermoplastic compositions, characterized in that after the melt-blow process a non-dimensions stable base fleece is placed on a support that the Dimensional maintenance of this basic fleece guaranteed and on which the fleece produced during a post-reaction time and or by one or more post-treatment dimensions can be stabilized.   14. The method according to claim 13, characterized in that the meltblown process used thermoplastic Polymers from the group of hot melt adhesives and or Hot melt adhesives are to be assigned. 15. The method according to claim 14, characterized in that that the thermoplastic materials used are reactive. 16. The method according to any one of claims 13 to 15, characterized featured, that the carrier is gas permeable. 17. The method according to claim 16, characterized in that that the carrier at a differential pressure of 200 Pa has greater air permeability than 1000 l / m2 * s. 18. The method according to any one of claims 13 to 17, characterized ge features that after the end of the post-reaction time and or after Completion of aftertreatments the dimensionally stabilized Fleece is separated from the carrier. 19. The method according to claim 18, characterized in that to support the detachability of the carrier and or the dimensionally stabilized fleece are moistened.   20. The method according to claim 13 to 19, characterized in that that the carrier is used several times.