US3914497A - Non-woven batts possessing excellent tensile strength, tear strength and initial modulus - Google Patents

Abstract

Non-woven batts possessing excellent tensile strength, tear strength and initial modulus are comprised of isotactic polypropylene substrate fibers bonded together by an ethylenepropylene random copolymer, said copolymers advantageously having an ethylene content of between about 3 to 20 mole percent. The ethylene-propylene random copolymer is desirably present in the proportion of approximately 5 to 75 weight percent relative to the weight of the isotactic polypropylene fibers.

Description

United States Patent [191 Kanehira et al.

[ Oct. 21, 1975 NON-WOVEN BATTS POSSESSING EXCELLENT TENSILE STRENGTH, TEAR STRENGTH AND INITIAL MODULUS [75] Inventors: Hiroshi Kanehira, Kurashiki; Syozi Kurosaki, Okayama, both of Japan [73] Assignee: Kuraray Co., Ltd., Kurashiki, Japan [22] Filed: Sept. 11, 1973 [21] Appl. No.: 396,136

[30] Foreign Application Priority Data Sept. 14, 1972 Japan 47-72427 [52] US. Cl. 428/288; 156/181; 156/283 [51] Int. Cl. B32B 5/28; D04B H58 [58] Field of Search 161/170, 150, 157, 252;

[56] References Cited UNITED STATES PATENTS 3,049,466 8/1962 Erlich 161/150 3,393,685 7/1968 Mumpower 161/170 3,501,369 3/1970 Derlich 161/170 3,502,538 3/1970 Petersen 161/170 3,671,383 6/1972 Sakata 161/252 FOREIGN PATENTS OR APPLICATIONS 3,511,784 8/1960 Japan 4,226,830 12/1967 Japan Primary Examiner-George F. Lesmes Assistant ExaminerEllis P. Robinson Attorney, Agent, or Firm-Bacon & Thomas [5 7 ABSTRACT 4 Claims, No Drawings NON-WOVEN BATTS POSSESSING EXCELLENT TENSILE STRENGTH, TEAR STRENGTH AND INITIAL MODULUS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to novel non-woven batts, e.g.,

non-woven fabrics, comprised of isotac'tic polypropylene substrate fibers which are bonded together by an ethylene-propylene randomcopolymer, said copoly-:

meradvantageously having an ethylene content of approximately 3 to 20 mole percent. These novel batts possess excellent tensile strength, tear strength and initial modulus. The non-woven batts ofrthis invention exhibit particularly advantageous properties when in the configuration of a spun-bonded, non-woven batt.

2. Description of the Prior-Art Spun-bonded, non-woven batts or fabrics have been developed with superior tensile strength as compared to non-woven batts of staple fibers. See U.S. Pat. No. 3,338,992 and U.S. Pat. No. 3,341,394yHowever, nonwoven batts irreproachable from a practical viewpoint cannot be obtained according to the methods disclosed therein regardless of the polymer selected. The prior art teaches a method of incorporating small amounts of adhesive fiber into the substrate fibers with subsequent melting of the adhesive fibers to effect bonding of the substrate fibers. For instance, it is taught that polycaproamide (Nylon 6) fibers or a copolymer or mixture of polycaproamide and polyhexamethylene adipamide (Nylon 66) can be employed as-the adhesive fibers for polyhexamethylene adipamide substrate fibers, and that fibers comprising a copolymer of ethylene terephthalateand ethylene isophthalate, or polyethylene terephthalate fibers having a low degree of molecular orientation, can be utilized as the adhesive fibers for polyethylene terephthalate substrate fibers.

Furthermore, in U.S. Pat. No. 3,322,607 and U.S. Pat. No. 3,276,944, it is disclosed that self-bonded, non-woven fabrics may be prepared from isotactic polypropylene or copolymers composed mainly of ethylene and propylene. However, as is clear from the results shown in the comparative examples, infra, these self-bonded, non-woven batts-do not possess the excellent mechanical properties which can be obtained according to this invention.

Still further, Japanese Patent Publication No. 11784/60 and Japanese Patent Publication No. 26830/67 disclose that the tenacity of shaped articles prepared from polypropylene fibers can be improved by forming thereon a coating of an ethylene-propylene copolymer containing an organic peroxide, a curing agent and the like. The ethylene content of the ethylene-propylene copolymer used in this proposal ranges from 20 to 80 mole percent, with 55 mole percent the norm.

Although various attempts have-been made to improve the tenacity of non-woven, fabrics composed mainly of isotactic polypropylene fibers described hereinabove, bonded non-woven batts, e.g., non-woven fabrics and the like, obtained according to these methods are still unsatisfactory as illustrated in the following comparative examples.

In addition to the foregoing methods incorporating adhesive fibers with substrate fibers, there have also beenemployed for similar .purpose methods of spraying an adhesive rubber latex onto nonwoven batts or im- SUMMARY OF THE INVENTlON Accordingly, it is the primary object of this invention to obviate deficiencies in the prior art thereby yielding a non-woven batt of polypropylene fibers bonded together by an ethylene-propylene random copolymer, which batt exhibits excellent mechanical properties.

It is another object of the present invention to provide such a non-woven batt wherein polypropylene continuous filaments are employed to yield a spunbonded, non-woven batt.

It has now been found that among the bonding methods detailed hereinabove, the method of incorporating a component capable of melting (hereinafter referred to as the hot melting component and represented by the ethylene-propylene copolymer) along with the substrate fibers, and melting that component to bond the substrate fibers, is most desired; and that in the case of isotactic polypropylene substrate fibers, optimum results are obtained when an ethylene-propylene random copolymer, especially one having an ethylene content of approximately 3m 30 mole percent, is employed as the adhesive component in an amount of approximately 5 to 75,weight percent relative to the weight of the substrate fibers.

DETAILED DESCRIPTION or THE INVENTION The substrate fibers of the non-woven batts of this invention are comprised of isotactic polypropylene. While the lengths of thesubstrate fiber is not particularly critical, e.g., fiber length, staple fiber length, etc.,-

improve the mechanical properties thereof and it is the most prominent feature of this invention that a specific adhesive component be utilized. Furthermore, it is indispensible that this hot melting component be a random copolymer of ethylene and propylene monomers,

if the intended objects of this invention are.to be attained.

If an ethylene-propylene block copolymer were to be.

incorporated as the hot melting component, even if the ethylene content be within the range specified by this invention, substantial improvement in mechanical properties would not be realized. The physical properties of such a block copolymer resemble those of a blend of polypropylene and polyethylene and neither polymer is itself suited as the adhesive component.

Not only is it important to this invention that the adhesive be a random copolymer, it is also necessary that the ethylene content of the random copolymer be lower than the propylene content, i.e., be lower than 50 percent, and most preferably be within the range of from 3 to 20 mole percent. Should the ethylene content be lower than 3 mole percent, the bonding operation experiences difficulties due to the small difference-between the melting points of the hot melting component and the substrate fibers. Should the ethylene content exceed 20 mole percent, particularly the 50 mole percent or more illustrated in Japanese Patent Publication No. 1 1784/60, the elastic properties of the batt reside in the .hot melting component and, therefore, marked degradation of the initial modulus is observed. The hot melting component according to the invention is ad vantageously crystalline and has a melting point at least 10C. lower than the melting point of the substrate fibers; the most preferred ethylene content of the hotmelting component utilized in this invention is about 4 to 6 mole percent.

While the hot melting component may take any one of a number of physical forms, for instance, fiber, film or powder, it is indispensible that the hot melting component be incorporated into the isotactic polypropylene substrate fibers in the approximate proportion of from to 75 weight percent relative to the weight of the substrate fibers. When the amount of the hot melting component is less than 5 weight percent, no prominent improvement of mechanical properties, particularly tensile strength, is observed; should the amount of the hot melting component exceed 75 weight percent, the tear strength is drastically reduced. It is preferred that the hot melting component be incorporated in an amount of approximately 7 to 30 weight percent relative to the weight of the substrate fibers to yield nonwoven batts of high tenacity, high tear strength and high initial modulus.

In accordance with the preferred embodiment of this invention, both the hot melting component and the substrate are in fibrous form, most preferably in filamentary form. To facilitate the accurate monitoring of the proper proportions of each component, bothmay be extruded from the same spinneret or, alternatively, from adjacent spinnerets. In either case, the fibers filaments or yarn thus extruded are accummulated on a receiving surface disposed therebelow. To aid in such deposition technique, there can be disposed below the spinneret head either a filament or yarn suction device or a device for generating a charge of static electricity or electrostatic field. It is also within the ambit of this invention to extrude the filaments from a large diameter orifice spinneret in combination with the utilization of high pressure fluids. Optionally, the hot melting component may be added in the form of either fibers, staple fibers or powder, or the like, to the isotactic polypropylene substrate fibers and intimately admixed therewith, most desirably such forms of the hot melting component are simply added to an existing non-woven batt comprised of the isotactic polypropylene fibers on the surface of the said batt or at the interior thereof, or both.

Further in attaining the objects of this invention, the hot melting component is melted by means of any suitable heat treatment and then the batt is subjected to pressure, desirably concurrently therewith, to effect the bonding between and among the substrate fibers and thus consolidate the batt. The heat treatment should be carried out at a temperature between not higher than the melting point of the substrate fiber and lower than that of the hot melting component by up to 20C. or less. Preferably, this treatment is conducted at a temperature within the range of the melting point of the substrate fiber and higher than 10C. lower than the melting point of the hot melt component. Conventional hot pressing techniques, i.e., with hot rolls or hot presses, may be employed for this purpose. For example, there can be employed that method comprising inserting the non-woven batts incorporating the hot melting component between hot pressure plates or hot pressure rollers to melt the said hot melting component and simultaneously consolidate the fabric. By this particular hot press treatment, the ethylene-propylene random copolymer component incorporated in the non-woven batt is substantially completely melted and the substrate fibers are thence bonded to one another, concomitantly resulting in the disappearance of any fluff from the surface of the said non-woven batt. Consequently, there is thus obtained a non-woven batt having a high tensile strength, a high tear strength and a high initial modulus.

As will be seen from the examples and comparative examples which follow, the isotactic polypropylene non-woven batts of this invention exhibit mechanical properties much higher than those which can be attained with non-woven batts of isotactic polypropylene consolidated by means of hot melt techniques other than those specified according to the invention. Thus, in order to further illustrate the invention and the advantages thereof, such specific examples are given, it being understood that the same are intended merely as illustrative and in no wise limitative.

EXAMPLES 1 AND 2 AND COMPARATIVE EXAMPLES 1 TO 9 Isotactic polypropylene having a melt index of 30 was extruded at a rate of 80 g/min from a spinneret maintained at 265C. and having 20 orificies, each with a diameter of 1.2 mm. An ethylene-propylene random copolymer having an ethylene content of 5 mole percent and a melt index of 5 was extruded at a rate of 16 g/min from a spinneret maintained at 280C. and having 4 orifices, each of the same diameter as above. These extruded filaments (yarn) were all stretched by means of corresponding, individual take-up rollers positioned 5 cm below each spinneret. The take-up rate was about 3800 m/min in the case of the polypropylene yarn and about 1800 m/min in the case of the copolymer yarn. Both types of the stretched yarns were next introduced into an air nozzle disposed below the take-up rollers and subsequently deposited on a moving metal wire net having a suction machine at the lower portion thereof. Thence was obtained a soft, flexible non-woven fabric having a weight of g/m The non-woven fabric thus formed was hot-pressed at 158C. for 3 minutes under a pressure of 0.5 Kg/cm between metal wire nets of mesh, to thereby melt the ethylene-propylene random copolymer filaments present in the non-woven fabric. It was observed that uniform bonding was attained throughout the sectional direction of the batt with no surface fluffs thereon. Properties of the resultant non-woven fabrics are shown in Table I.

In accordance with the foregoing method, nonwoven fabrics were prepared by employing various hot melting polymers (in each case, the weight of the nonwoven fabric was 100 g/m Properties of these nonwoven fabrics are also shown in Table 1. In comparative Examples 4 and 7, the hot melting polymer was employed in powder form.

the non-woven fabrics of isotactic polypropylene filaments (Example 4). The results of these latter experiments are shown in Table 2.

TABLE 2 Melting Polymer to lsotactic Polypropylene TABLE 1 Ex. Hot-Melting Mixing Ratio Melting No Polymer of Hot Melting Treatment Thickness 1 Polymer to of Non-Woven lsotactic Temp. Time Fabrics after Tensile Initial Tear Remarks Polypropylene Melting Treat- Strength Modulus Strength (bonding Flbers (parts) (C) (min.) ment (mm) (Kg/cm) (Kg/mm) (Kg) conditions) Ex. I ethylene-propylene 20 158 3 0.30 8.0 15.2 6.2 no fluffs on random copolymer th sh r (ethylene content; surface 5 mole Ex; 2 ditto (ethylene (cgrgtent; l6 mole i 155 3 0.32 7.5 11.0 8.3 ditto D Comparditto (ethylene I ativc content; mole 4 158 3 0.38 29 13.6 7.1 fluffs on Ex. 1 the sheet surface Comparditto (ethylene 85 l58 3 0.28 7.0 l6.l 3.0 film-like ative content; 5 mole (excessive Ex. ,2 bonding) Comparditto (ethylene I0 I58 3 0.40 2.4 13.0 7.l insufficient ative content; 2 mole bonding Ex. 3

. g 165 3 0.25 5.0 l7.4 2.0 film-like,

semi- I transparent Comparditto (ethylene [0 M0 3 0.35 5.2 6.7 8.5 ative content; 28 mole Ex. .4 Comparethylene-propylene I60 3 0.40 2.5 l3.6 7l fluffs on ative block copolymer the sheet Ex. 5 (ethylene content; surface 7 mole Comparisotactic poly- 10 160 3 0.40 3.6 13.3 8.0 insufficient ative propylene having bonding Ex. 6 low molecular orientation I65 3 0.25 5.0 16.5 2.5 film-like Comparatactic poly- 10 I40 3 0.40 L8 8.2 6.3 ative propylene Ex. 7 Comparhigh density l0 M5 3 0.41 4.0 9.6 7.5 ative polyethylene Ex. 8 Compar ethylene-vinyl 10 140 3 0.42 5.0 7.4 6.1 ative acetate copolymer Ex. 9 (vinyl acetate content; mole As is apparent from the results shown in Table 1, only TABLE 2 Cont1nued non-woven fabrics according to this invention have excellent mechanical properties in the sense of tensile st r- Example 'P 3 Example 4 ength, tear strength and initial modulus. Differences in Hot Melting ethylene-propylene ethylene-propylene values relative to these properties, between the non- Polymer randmn Wimlymer randm Polymer (ethylene content; (ethylene content; woven fabrics obtained in the Examples according to 4 mole 10 mo|e this invention and those obtained in the Comparative Examples, are markedly probative. azfi i gzi Temperature (C) 160 160 EXAMPLES 3 AND 4 Melting Treatment Time (min.) 3 3 Thickness of 0- The procedures of Examples 1 and 2 were repeated Non-Woven Fabrics in the same manner, except that the hot melting comm) ponent was not incorporated in the form of filaments Tensile strength 7.3 7.4 but was mixed in the form of staple fibers with the nonl l 5 5 13 0 woven fabrics of isostatic polypropylene filaments (Exz z u ample 3) or was sprinkled in the form of powder onto '(Tar; Strength 6.6 6.2

As will be seen from the results shown in Table 2, non-woven fabrics having properties equivalent to those non-woven fabrics obtained by the spun-bonding method can be obtained by other various methods according to the invention.

COMPARATIVE EXAMPLES 10 AND 11 The procedures of Example 1 were repeated in the same manner, except that in one instance the hot melting filaments of the ethylene-propylene random copolymer having an ethylene content of 5 mole percent were not incorporated, namely, isotactic polypropylene filaments alone were employed (Comparative Example 10), and in the second instance the hot melting filaments alone were employed, namely, the isotactic polypropylene filaments were not used (Comparative Example l l Mechanical properties of the obtained nonwoven fabrics (each being a self-bonded non-woven fabric) are shown in Table 3.

TABLE 3 Example N0. Comparative Comparative Example l Example 11 Tensile Strength (Kg/cm) 3.2 2 3 Initial Modulus (Kglmm 16.8 6 Tear Strength (Kg) 5 0 4 9 can be made without departing from the spirit of the invention. It is intended, therefore, that the invention be limited only by the scope of the following claims.

What is claimed is: v

1. A non-woven batt having high tensile strength, high tear strength and high initial modulus, which comprises a batt of isotactic polypropylene substrate fibers bonded together by means of an ethylene-propylene random copolymer wherein the ethylene content of said ethylene-propylene random copolymer is from 4 to 6 mole percent and is present in the approximate proportion of 5 to weight percent relative to the weight of said isotactic polypropylene substrate fibers.

2. A non-woven batt according to claim 1, wherein said ethylene-propylene random copolymer is present in the approximate proportion of 7 to 30 weight percent relative to the weight of said isotactic polypropylene substrate fibers.

3. A non-woven batt according to claim 1, wherein said isotactic polypropylene component is in the form of continuous filaments.

4. A non-woven batt according to claim 2, wherein said isotactic polypropylene component is in the form of continuous filaments.

Claims (4)

1. A NON-WOVEN BATT HAVING HIGH TENSILE STRENGTH, HIGH TEAR STRENGTH AND HIGH INITIAL MODULUS, WHICH COMPRISES A BATT OF ISOTACTIC POLYPROPYLENE SUBSTRATE FIBERS BONDED TOGETHER BY MEANS OF AN ETHYLENE-PROPYLENE RANDOM COPOLYMER WHEREIN THE ETHYLENE CONTENT OF SAID ETHYLENE-PROPYLENE RANDOM COPOLYMER IS FROM 4 TO 6 MOLE PERCENT AND IS PRESENT IN THE APPROXIMATE PROPORTION OF 5 TO 75 WEIGHT PERCENT RELATIVE TO THE WEIGHT OF SAID ISOTACTIC POLYPROPYLENE SUBSTRATE FIBERS.

2. A non-woven batt according to claim 1, wherein said ethylene-propylene random copolymer is present in the approximate proportion of 7 to 30 weight percent relative to the weight of said isotactic polypropylene substrate fibers.

3. A non-woven batt according to claim 1, wherein said isotactic polypropylene component is in the form of continuous filaments.

4. A non-woven batt according to claim 2, wherein said isotactic polypropylene component is in the form of continuous filaments.