EP1866469A1

EP1866469A1 - Thermally bound non-woven material

Info

Publication number: EP1866469A1
Application number: EP06707417A
Authority: EP
Inventors: Armin Greiner; Klaus Veeser; Holger Schilling; Günter Frey; Ralph Berkemann
Original assignee: Carl Freudenberg KG
Current assignee: Carl Freudenberg KG
Priority date: 2005-04-04
Filing date: 2006-03-04
Publication date: 2007-12-19
Anticipated expiration: 2026-03-04
Also published as: DE102005015550B4; PL1866469T3; US20080308490A1; WO2006105836A1; KR100942879B1; KR20070116279A; DE102005015550C5; EP1866469B1; DE102005015550A1; CN101151406A; US8481437B2; ES2429537T3; US20120129032A1; US8124550B2; DK1866469T3; CN101151406B

Abstract

The invention relates to a thermally bound non-woven material containing a low-shrinkage dual-component core-sheath fibre consisting of a crystalline polyester core and a crystalline polyester sheath which has a melting point at least 10°C lower than the core, the heat-shrinkage characteristic of said fibre being less than 10% at 170°C.

Description

title

Thermally bonded nonwoven fabric

Description Technical area

The invention relates to a thermally bonded nonwoven fabric having improved thermal and chemical stability. The invention further relates to a use of this nonwoven fabric.

State of the art

The document EP 0340 982 B1 discloses melt-bondable fibers and nonwovens made therefrom. The melt-bondable fibers are bicomponent fibers consisting of a first at least partially crystalline polymer component and a second component adhering to the surface of the first component comprising a compatible blend of polymers comprising at least one amorphous polymer and at least one at least partially crystalline polymer. The melting temperature of the second component should be at least 30 ° C below the first component, but at least equal to or greater than 13O ⁰ C. Furthermore, the weight ratio of the amorphous polymer of the second component to the at least partially crystalline polymer of the second component in the range of 15: 85 to 90: 10 and be sized so that the bonding of the bicomponent fibers is prevented with a similar bicomponent fiber and that the first component of the core and the second component of the shell in the form of a sheath Core configuration forms spun bicomponent fiber. This bicomponent fiber is blended with conventional polyester fibers and thermally bonded to a nonwoven fabric which is made into a nonwoven web by application of abrasive particles.

From the document JP 07-034326 heat-binding conjugate fibers are known, which have a sheath-core configuration and whose core consists of a polyester containing polyethylene terephthalate (PET) as the main component and the sheath of a copolymerized polyester or a side-by-side Conjugate fiber is made, which consists of a polyethylene terephthalate and a copolymerized polyester. The copolymerized polyester is the lower melting component and contains butylene terephthalate units and butylene isophthalate units as repeating structural units. A nonwoven fabric made from these bicomponent fibers is said to have excellent thermal resistance and fatigue resistance to compressive loads, so it can be used as an alternative material to polyurethane upholstery, especially in the automotive field.

In addition, it is possible to produce thermally bonded nonwovens from a mixture of undrawn and stretched PET fibers. For these nonwovens, however, binding under heat and pressure in a calender is necessary. The binding capacity of the unstretched, amorphous PET fibers is not based on a melting process, but on the crystallization process of PET, which starts above 90 ⁰ C, if there are still crystallizable parts. Such nonwoven fabrics have a high meet chemical and thermal stability. However, the manufacturing process allows low flexibility. For example, it is not possible with undrawn PET fibers to activate their binding ability several times, since this is at an irreversible below the melting temperature process. Also, the bonding in nonwovens with basis weights> 150g / m ² with unstretched PET fibers is difficult, since in the calendering process, the heat from the outside can not penetrate far enough into the interior of the nonwoven web. There will always be a more or less pronounced gradient.

Presentation of the invention

The object of the invention has been found to provide a thermally bonded nonwoven fabric which shows improved properties in terms of its thermal stability, in particular the tendency to shrink of the resulting nonwoven fabrics. In addition, due to the chemical stability in the

Comparison to fibers containing copolymers of monomer mixtures such as e.g. Isophthalic acid / terephthalic acid contained, increased.

According to the invention the object is achieved by a thermoplastic bonded nonwoven fabric containing a low-shrinkage core-sheath bicomponent fiber. The low-shrinkage core-sheath bicomponent fiber consists of a crystalline polyester core and a crystalline polyester coating which melts at least 10 ^° C., and has a hot-air shrinkage at 170 ^° C. of less than 10%, preferably less than 5%. A corresponding nonwoven fabric has a thermal Maßäπderung (shrinkage and Bausch) of less than 2% at temperature loads of 150 ⁰ C (1 h). For the purposes of this invention, crystalline is understood as meaning a polyester polymer which has a melting enthalpy (DSC) of> 40 Joule / g and whose width of the melt peak (DSC) preferably precipitates at <40 ° C. at 10 ° C./min. Preferably, the sheath of the low-shrinkage bicomponent fiber consists of a homogeneous polyester polymer prepared from a monomer pair, which is formed to greater than 95% only from a polymer pair. In the case of the polyester described in the claims, this means that the polymer consists of> 95% of a single dicarboxylic acid and a single dialcohol.

The mass ratio of core and cladding component is typically 50:50, but may vary between 90:10 and 10:90 for specific applications.

Particular preference is given to a nonwoven fabric in which the sheath of the low-shrinkage core-sheath bicomponent fiber consists of polybutylene terephthalate (PBT), poly-trimethylene terephthalate (PTT) or polyethylene terephthalate (PET).

Further preferred is a nonwoven fabric wherein the core of the low shrink core-sheath bicomponent fiber is polyethylene terephthalate or polyethylene naphthalate (PEN).

The nonwoven fabric according to the invention may be dependent on the respective

Use other fibers besides the low-shrink core-sheath bicomponent fiber. Preferably, the use of 0 to 90% by weight of e.g. monofilament standard polyester fibers together with the low-shrinkage bicomponent fiber.

The nonwoven fabric according to the invention preferably consists of low-shrink core-sheath bicomponent fibers with a titre in the range between 0.1 and 15 dtex. The nonwoven fabric according to the invention has a basis weight between 20 and 500 g / m ² . The nonwoven fabric according to the invention reaches at a Basis weight of eg 150-190g / m ² a bending stiffness determined according to ISO 2493 transverse to the machine direction of greater than 1 Nmm.

The method of making the thermally bonded nonwoven web is to lay the fibers into a nonwoven web, thermally bond and, if necessary, compact immediately thereafter. In the method, the fibers of the nonwoven fabric according to the invention dwell in a thermofusion oven, which enables a uniform temperature control of the binder fibers. Preferably, the low-profile sheath-core bicomponent fibers in an be paper laid process wet-laid and placed dried or airlaid process stocking according to one carding or, and then bonded at temperatures of 200-270 ⁰ C and, optionally, through a calender or a press plant with Roll temperatures which are below the melting point of the shell polymer, preferably <170 ° C, densified. This compression is preferably carried out immediately after the binding process in the dryer with still hot fibers. However, the structure of the fibers also allows subsequent thermal treatments, since the binding process can be activated several times.

The resulting thermally bonded nonwoven fabrics have shrinkage and bulk values in the range of <2%, preferably <1%.

The nonwoven fabrics according to the invention are suitable as a liquid filter medium, membrane support web, gas filter medium, battery separator or nonwoven fabric for the surface of composites due to their high thermal stability, their low shrinkage tendency and their chemical aging stability. This is especially true for use as an oil filter medium for use in automotive engines. The invention will be explained in more detail with reference to FIGS. These show:

Figure 1 is a diagram in which the maximum tensile forces of the nonwovens A and B are as index after storage in air and oil based on the respective new state (DIN 53508 and DIN 53521).

Fig. 2 is a diagram in which the maximum tensile force extension of the nonwovens A and B after storage at 150 ⁰ C in air and oil are based on the respective new condition (DIN 53508 and DIN 53521); Fig. 3 is a diagram in which the maximum tensile forces of the nonwovens A and B are at different temperatures as an index based on the respective new state (DIN EN 29073-03).

4 is an electron micrograph of a membrane support nonwoven fabric bound with undrawn polyester fibers (nonwoven fabric E, comparative example);

5 is an electron micrograph of a membrane support nonwoven fabric, which according to the invention consists of 100% low-shrink PET / PBT bicomponent fiber (nonwoven fabric F);

6 shows a DSC curve of a bicomponent fiber A with a crystalline sheath polymer (here PET / PBT, according to the invention);

Fig. 7 DSC curve of a bicomponent fiber B with amorphous sheath polymer (here PET / CoPET, prior art).

Test Methods

bending stiffness

The bending stiffness is determined according to ISO 2493 in Nmm. Thermal dimensional change (shrinkage)

The sample (DIN A4-sized pattern) is provided with markings in the longitudinal and transverse direction, which have a distance of 200 mm. After storing the sample for 1 hour at 150 ⁰ C in a convection oven and then cooling for 20 minutes at room temperature, the dimensional change is determined. This is given, in each case for the longitudinal and transverse directions in percent relative to the initial value. The signs before the percent value indicate whether the dimensional changes are positive (+) or negative (-). The mean value is formed from at least six individual values (measurements).

Thermal dimensional change (Bausch)

The sample (DIN A4-sized sample) is provided with markings on which the thickness is determined in accordance with ISO 9073/2. After storage of the sample for 1 hour at 150 ⁰ C in a convection oven and then cooled for 20 minutes at room temperature, the thickness (ISO 9073/2) is determined again at the markers. The pad (B) is given as a percentage and calculated as follows:

B [%] = (thickness after storage x 100 / thickness before storage) - 100

The mean value is formed from at least six individual values (measurements).

Test of hot air shrinkage

20 individual fibers are tested. The fiber is provided with a biasing weight as described below. The free fiber end is in one Clamped clamp of a terminal plate. The length of the clamped fiber is determined (Lt). Subsequently, the fiber is suspended without weight hanging freely 10 minutes at 170 ⁰ C in a convection oven. After at least 20 minutes of cooling at room temperature, the same weight piece from the determination of Li is again attached to the fiber and the new length determined after the shrinking process (L ₂ ). The percentage hot air shrinkage is calculated from:

HS [%] = (Σ L ₁ - Σ L ₂ ) * 1 OO / Σ Li

Size of preload weight

in the suspended state, the fiber should appear entreplexed. If the crimping is too strong, the next higher weight should be selected.

Enthalpy of fusion (DSC)

In a DSC instrument from Mettler Toledo, the sample is weighed out and heated with a temperature program of 10 ° C / min from ⁰ ° C to 300 ⁰ C. The area under the obtained endothermic melting peaks is related with the weight of fiber and the associated masses of the shell or core component, the enthalpy of fusion of the respective components in J / g.

example 1

Nonwoven A represents a drained, carded and thermally bonded nonwoven having a basis weight of 190g / m ^2. This nonwoven fabric consists of 75% of a low shrink PET / PBT bicomponent fiber having a sheath melt point of 225 ° C and a core to sheath ratio of 50: 50 and 25% of conventional PET fibers. The thickness is 0.9 mm and the air permeability 850 l / m ² s at 200 Pa. 14OgZm ^{2 of} the fibers are carded over carding with transverse stretcher, the remaining 50g / m ² are carded longitudinally. The nonwoven fabric is bonded in a thermal fusion furnace at about 240 ⁰ C and calibrated with an initial press unit to the target thickness.

Comparative example

Nonwoven fabric B was produced analogously to nonwoven fabric A. The difference is the use of conventional PET / Co-PET bicomponent fibers with a jacket melt point of about 200 ^° C. and the reduction of the furnace temperature to 230 ^° C. The resulting basis weight, thickness and air permeability are comparable.

The advantages of the nonwoven fabric A according to the invention over the comparative nonwoven fabric B are shown below:

^• The width of the fleece after the dryer decreases only about 9% for nonwoven A, whereas for nonwoven B there is about 21% width loss. • The flexural stiffness across nonwoven fabric A is 15% higher

• The thickness increase after storage at 150 ⁰ C (S & Brmischθ dimensional change) is nonwoven fabric A at 1, 5% in nonwoven fabric B at 4.7%.

• The thermal and chemical stability when stored at 150 ^° C. in air and oil is markedly improved for nonwoven fabric A (FIGS. 1 and 2). The graphs clearly show a greater destruction of nonwoven B when stored in engine oil. Specifically, the embrittlement in Figure 3 indicates a chemical stability problem of nonwoven fabric B in oil.

• The maximum tensile forces at different temperatures show a significantly better course for nonwoven A (FIG. 3).

Example 2

The nonwoven fabrics C and D represent wet laid, dried and thermally bonded nonwovens having a basis weight of 198 g / m ² and 182 g / m ^2. These nonwoven fabrics consist of 72% of a low-shrinkage PET / PBT bicomponent fiber with a sheath melt point of 225 ° C and a core-shell ratio of 50:50 and 28% of conventional PET fibers. The fibers are present as dispersible short cut fibers. The fibers are laid down on a wire belt in the paper-laying process, dried and thermally bonded in a second dryer. The outstanding properties of these nonwovens lie in the very good mechanical test values, as well as their excellent shrinkage behavior (Table 2). A comparison with nonwovens made from conventional bicomponent fibers with CoPET sheath is not possible in this case, since such fibers have hitherto not been usable on this nonwoven fabric due to the high shrinkage values had or latitudinal losses of at least 20%, the wet nonwovens according to the invention show width losses of about 3%.

Table 2: Test values of nonwovens C and D

Especially when used in the wet-laying process with separate dryers for the dewatering and for the thermal fusion, the low-shrinkage bicomponent fibers according to the invention offer advantages, since these fibers are multiply activatable in comparison to / around extended binder fibers or in the first

Do not completely finish the drying process.

The nonwovens A.C.D according to the invention are particularly suitable for use as motor oil filter medium in motor vehicles.

Example 3

For use as membrane backing nonwovens, calendered PET nonwoven fabrics (comparative example, nonwoven fabric E) are made of a mixture of stretched and unstretched monofilament PET fibers prior art. Due to the calendering process, there is a risk of surface sealing, especially for heavy nonwovens with basis weights> 150 g / m ² , since high roll temperatures or slow production speeds are necessary for good penetration of the nonwoven fabric in order to bring the necessary heat into the interior of the nonwoven fabric. Sealed surfaces harbor the risk of film formation, which in turn leads to poor membrane adhesion and lower flow rates (comparative nonwoven fabric E). Figures 4 and 5 demonstrate the different surfaces of a conventional nonwoven fabric (comparative example, nonwoven fabric E, Figure 4) and the surface of a nonwoven fabric according to the invention (nonwoven fabric F, Figure 5).

The complete absence of surface seals in nonwoven fabric F (FIG. 5) is also evident when comparing the test values of the two nonwovens. Thus, the air permeability of nonwoven fabric F is increased by an order of magnitude, with comparable other test values (Table 3).

Table 3: Test values of nonwoven E and F

The use of conventional bicomponent fibers with copolymers in the sheath has in this area because of the high shrinkage - and the associated weight fluctuations - and often not given food approval of the shell polymers not enforced. The nonwovens according to the invention of the corresponding bicomponent fibers overcome both obstacles, since they are low in shrinkage and easily allow food approvals by the construction of homopolymers.

Example 4

In order to further demonstrate the differences of the nonwoven fabrics of the present invention over conventional bicomponent nonwoven fabrics having coats based on copolymers, FIGS. 6 and 7 show DSC (differential scanning calorimetry) curves of crystalline clad polymer fibers (fiber A, here PBT) with DSC curves of conventional bicomponent fibers (fiber B, here CoPET). When evaluating the enthalpies of fusion of the lower melting component, it can be seen that the sheath of fiber B has a significantly lower enthalpy of fusion in J / g than fiber A.

The enthalpy of fusion is a direct measure of the crystalline content in the polymer. The core-sheath ratios of the two fibers are 1: 1, which results in the following enthalpies of fusion of the fiber sheaths:

Fiber A 63 J / g fiber B 29 J / g

As a measurement reference, the core of both fibers can serve here, which consists of PET in both. The melting enthalpy values obtained are comparable (59 J / g vs. 54 J / g).

Regardless of the measured values, when comparing the DSC curves, the low peak height and the broader peak base are characteristic of fiber cladding based on copolymers (here CoPET). By the incorporation of comonomers such as e.g. Isophthalic acid in polyethylene terephthalate, both the melting point and the crystallinity or willingness to crystallize the polymer is reduced. The nonwoven fabrics according to the invention are thus based on fibers of the fiber A type.

Claims

claims

1. A thermally bonded nonwoven fabric comprising a low-shrinkage core-shell bicomponent fiber, wherein the low-shrinkage core-shell

Bicomponent fiber consists of a crystalline polyester core and at least 10 ⁰ C lower melting, crystalline polyester shell and has a heat shrinkage at 170 ⁰ C of less than 10%.

2. Nonwoven fabric according to claim 1, characterized in that the sheath of the low-shrink core-sheath bicomponent fiber consists of> 95% of a homogeneous polyester polymer, which is not a copolymer.

Nonwoven fabric according to claim 2, characterized in that the sheath of the low-shrink core-sheath bicomponent fiber consists of polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT) or polyethylene terephthalate (PET).

Nonwoven fabric according to claim 1, characterized in that the core of the low-shrinkage core-sheath bicomponent fiber consists of polyethylene terephthalate (PET) or polyethylene naphthalate (PEN).

5. Nonwoven fabric according to one of claims 1 to 4, characterized in that the low-shrinkage core-sheath bicomponent fiber has a titer between 0.1 and 15 dtex.

6. Nonwoven fabric according to one of claims 1 to 5, characterized in that the low-shrinkage core-sheath bicomponent fiber is a core Sheath ratio between 10:90 and 90:10, preferably 50:50.

7. Nonwoven fabric according to one of claims 1 to 6, characterized in that it contains up to 90% by weight of one or more further fibers.

8. Nonwoven fabric according to one of claims 1 to 7, characterized in that the nonwoven fabric is wet.

9. Nonwoven fabric according to one of claims 1 to 7, characterized in that the nonwoven fabric is drained.

10. Nonwoven fabric according to one of claims 1 to 9, characterized in that the low-shrinkage Kem-sheath Bikomponeπtenfaser has a titer between 0.1 and 15 dtex.

11. Nonwoven fabric according to one of claims 1 to 10, characterized in that it has a basis weight between 20 and 500g / m ² .

12. Nonwoven fabric according to one of claims 1 to 11, characterized in that it has a flexural strength transversely> 1 Nmm at a basis weight> 150g / m ² .

13. Nonwoven fabric according to one of claims 1 to 12, characterized in that it after 1 h at 150 ⁰ C, a thermal dimensional change (Bausch and

Shrinkage) of <2%, preferably <1%.

14. Use of a nonwoven fabric according to any one of claims 1 to 13 as a liquid filter medium, Membranstützvliesstoff, gas filter medium, Battery separator or nonwoven for the surface of composites.

15. Use of a nonwoven fabric according to claim 14 as an oil filter medium for motor vehicle engines.