DK143767B - UNWOVEN PRODUCT OF SYNTHETIC POLYMER MONOFILAMENTS - Google Patents

Description

(19) DENMARK (¾

| Ρ (12) SUBMISSION WRITING (n> 11 + 3767 B

DIRECTORATE OF THE PATENT AND TRADEMARKET SYSTEM

(21) Application No. 3862/70 (51) | nt.ci, 3 Q () 4 H 3/00 (22) Insertion day 24 Jul. 1970 (24) Race day 24 Jul. 1970 (41) Aim. available Jan 26 1971 (44) Posted 5 Oct. 1 981 (86) International application no.

(86) International Filing Day (85) Continuation Day “(62) Stock Application No."

(30) Priority 25 · Jul. 19 ^ 9, 845075 US

(71) Applicant CHEVRON RESEARCH COMPANY, San Francisco, US.

(72) Inventor Phillip Harold Parker, US.

(74) Clerk of the International Patent Office.

(54) Nonwovens of synthetic polymer monofilaments.

This invention relates to a nonwoven synthetic polymer monofilament which has an elongated cross-section and is randomly and substantially spaced apart at intersection points.

Nonwoven products of oriented monofilaments have been manufactured and used for many different textile and related uses. Primarily they have been used for rugs, insulation and disposable clothing. Generally, such articles have been made by spinning monofilaments from spinnable synthetic polymers, stretching the newly spun filaments, and placing them on a collection surface. Much of the technique relating to these articles relates to the v) manner in which the freshly wound filaments are stretched in order to increase the tensile strength of the filaments. The strength of such freshly spun monofilaments has been improved by stretching them between rollers rotating at different speeds. More recently, they have been stretched using "spin stretching technique". By "spin stretching", partially cooled, partially crystalline filaments are introduced into a pneumatic nozzle. The nozzle works according to the ejector principle. That is, the expanding gaseous medium passing through the nozzle carries and accelerates the filaments thereby being stretched or oriented.

Development work on methods of depositing the stretched filaments has been aimed at improving the isotropic properties of the finished, nonwoven product produced by the filaments. This development work has usually been about special patterns in which the stretched filaments are deposited on the collection surface in order to keep the filaments apart, ie. not tangled or bundled.

The filaments, which have been used to make nonwoven products, have mostly been circular in cross section. Certain non-circular, including oblong, cross-sectional filaments have been proposed to be equivalent to circular cross-sectional filaments for use in nonwoven materials. In the related yarn technique, monofilaments of non-circular cross-section have been used to simulate natural fiber shapes which give a special appearance or increase the covering capacity. To date, it has not been recognized that cross-sectional shape of the filaments significantly affects the strength properties of the nonwoven products made therefrom.

However, the present invention is based on the recognition that the strength properties of the nonwoven product are precisely influenced by the cross-sectional shape of the filaments. The nonwoven product according to the invention is characterized in that the monofilaments have substantially rectangular cross sections. which aspect ratio of the pages is at least approx. 3: 1. It has been found that the product in this case not only unexpectedly has better strength properties than similar products with circular cross-section monofilaments, but also better strength properties than similar products in which the filaments also have a rectangular cross-section, but without meeting the stated aspect ratio requirement. This observation is particularly surprising given the fact that individual circular cross-sectional monofilaments and individual elongated cross-sectional monofilaments have substantially the same strength properties.

The filaments included in the product according to the invention usually have a cross-section with a side ratio (the ratio of the cross-sectional length to the cross-sectional width) in the region of approx. 3: 1 to about 8: 1. Filaments of substantially rectangular cross-section include filaments having two sets of substantially parallel and flat surfaces which intersect with substantially straight lines (true rectangle), as well as filaments having two slightly rounded opposing planar surfaces if respective ends are connected via rounded, smaller surfaces. The surfaces of these filaments will essentially be smooth. That is, they are relatively smooth and free of large projections of any kind.

3 143767

The particular cross-sectional shape obtained by monofilaments depends on the opening from which they are spun and the extrusion conditions, and partly on the extent to which they are oriented or stretched. Oriented elliptical cross-sectional monifilaments are usually formed by extruding the polymeric melt from openings of substantially rectangular cross-section. Such monofilaments emerge from the openings with rectangular cross sections, but as they are stretched, their cross sections are transformed into elliptical shape. Oriented monofilaments having substantially rectangular cross-section can be made by spinning the melt from a nozzle with substantially rectangular cross-sections, the long sides being somewhat concave. As such monofilaments are stretched, the concave sides of the rectangle flatten out to become substantially parallel. Apparatus for producing monofilaments with elongated cross-section are well known, see e.g. U.S. Patent No. 3,178,770, In the nonwoven product of the invention, preferably, filaments 2 are used whose cross-sectional area is between about 0.00005 and about 0.008 mm. The finely spun monofilaments usually have an initial cross-sectional area of approx. 0.004-4.0 2 o mm when coming out of the die, but is brought down to a cross-sectional area of the indicated approx. 0.00005 to approx. 0.008 mm. Expressed as a circular filament, this is equivalent to reducing the diameter from approx. 0.10 - 1.0 mm down to 10 - 100 microns (1-60 denier). This stretch is made after the filaments are partially cooled and while the polymer is at least partially crystalline.

The filaments used are, according to the invention, preferably made of substantially crystalline, stereoregular polypropylene. They will have fracture strengths of approx. 2-5 g per denier and extensions of approx.

50-400%, depending on the specific stretching conditions.

This stretch orientates the polymer structure and greatly increases the tensile strength of the filament. Although roll stretching or spinning stretching can be used, spinning stretching is preferred to the monofilaments used to make the nonwoven product of the invention.

Accordingly, the fresh-spun monofilaments are usually fed into a bundle of approx. 5-500, into the main chamber on a pneumatic nozzle. Air or other inert gases can be used as the gaseous stretching medium. In order to sufficiently stretch the monofilaments, the airspeed will usually be about 200-800 m per minute. second in the main chamber. Air moving at these speeds will pick up the monoflament bundle and pull the filaments at speeds greater than 500 m per second. The stretching speed will preferably be between 2500 and 5000 m per minute and up to the speed that causes the filaments to rupture. minute. Special nozzle designs can be used to keep the individual monofilaments apart as they pass through the nozzle. Other methods, such as charging the filaments, can also be used to prevent them from filtering together.

The monofilaments thus stretched can be placed on a collection surface as they emerge from the pneumatic nozzle. If the filaments have been stretched over rollers instead of being spun-stretched, they can be inserted into a pneumatic filament feeder. Such apparatus is well known and operates on the same principle as the pneumatic spinning nozzle. However, the gas velocities are below the velocities at which the filaments are stretched in the feed apparatus. In order to prevent the gas coming out of the nozzle with the filaments from entangling the filaments as they deposit on the collecting surface, or in blowing them away from the surface, the surface may be a wire mesh or other, perforated or porous agent which allows gas to pass through.

Removal and / or spreading of the gas coming out of the high speed nozzle can be facilitated by suction on the side of the pierced or porous collection surface opposite to the side on which the filaments are laid.

The collecting surface will move away from the zone into which the bundles of non-entangled, substantially parallel filaments are laid. This movement away from the deposition zone can conveniently be achieved by using an endless net as the collection surface. In order to form tissues which have essentially isotropic fracture strength properties, the rate at which the filaments are advanced on the collection surface will be several times as high as the rate at which the surface moves away from the deposition zone. Usually, the rate of filament feeding will be about 10-1000 times the speed at which the surface moves away from the deposition zone.

Filament patterns in the depositional zone tissue will depend on the relative movement of the filaments and. collecting surface. By moving the deposition device across the removal direction or by holding the deposition stationary and moving the filaments, in the first case by oscillating the depositor and in the second case by controlling the filaments by means of guides, different filament patterns can be obtained. The pattern should not be such that it significantly affects the isotropy of the layered tissue. One may incorporate a variable amount of non-elongated cross-sectional monofilaments into the nonwoven products, provided that such added filaments do not completely eliminate the enhanced strength properties obtained by using the invention with the defined rectangular cross-section. Such fibers with other shapes affect In particular, fibers of a circular or circular cross-section can be incorporated into the nonwoven product. The presence of such fibers improves the grip of the resulting product by reducing its stiffness.

By appropriately selecting the ratio of round to rectangular fibers, goods can be obtained which have both improved grip and high strength.

5 143767

The tissue of monofilaments of rectangular cross section thus laid has improved strength properties compared to corresponding tissue of circular cross section monofilaments.

The weight of the article according to the invention usually ranges from approx. 15 to 2. o 1500 g / m. Its density will usually be 0.2 to 0.7 g per liter. cm. It will usually be 0.1 to 7.5 mm thick.

The resulting nonwoven material is useful as such for insulation, paper reinforcement, nonwoven reinforcement, and filters. If desired, it can be further treated by needle perforation, calendering or heat sealing, depending on its intended final use. The material is also suitable for other known treatments, such as adhesive bonding. These bonded fabrics are useful as rugs, sack or bag material, paper or textile reinforcement, felt rugs, nonwoven textiles etc.

As a general rule, the finished nonwoven product made with filaments of rectangular cross section has better strength properties than similar products made using conventional monofilaments.

The synthetic polymers of which the filaments consist are those which can be spun or otherwise formed into monofilaments. Examples of such polymers include crystalline polypropylene, crystalline polyethylene, poly-4-methyl-1-pentene and copolymers thereof, polyvinyl chloride, polyesters such as polyethylene terephthalate, and polyamides such as nylon.

The invention will be explained in greater detail below by means of some examples as well as some comparative examples, in which last the nonwoven product is made of filaments of a different cross-section than that of the invention. Unless otherwise stated, the percentages indicated are weight percentages.

Comparative Example A

Substantially crystalline commercially available stereoregular polypropylene having a flow rate of the melt of 4 was melted in an extruder whose last extruder zone had a temperature of 320 ° C. It was then melt spun through a 2-hole spinning nozzle with 1.0 mm diameter round holes. The spin nozzle temperature was 300 ° C. The polymer was extruded at a rate of 4.1 g / well / minute.

The resulting circular cross-sectional filaments then fell 9 3/4 m to a pneumatic nozzle, which accelerated the filaments to a linear velocity of 2190 m / s. minute, whereby the filaments were stretched. The filaments were then collected on a mesh with an underlying vacuum to form a tissue or mat. The mat was slightly compressed between two rollers for easier handling.

The breaking strength of these filaments, and the breaking strength of the tissue or mat were determined by usual ASTM tests. These properties are given in Tables I and II, respectively.

6 14.3767

Comparative Example B

Filaments and a mat were made under conditions similar to those mentioned in Comparative Example A, except that the filaments were accelerated to 4750 m / s. minute after being melt spun using the pneumatic nozzle. The breaking strength of these filaments and the breaking strength of the mat made therefrom are also given in Tables I and II.

Comparative Example C

Filaments and a mat were prepared under conditions similar to those of Comparative Example B, except that the filaments were extruded at a rate of 3.3 g / hole / minute and accelerated to 4840 m / min. minute using the pneumatic nozzle. The breaking strength of these filaments is shown in Table I and the mating strength of the mat shown in Table II.

Example 1

Filaments and a mat were made under conditions similar to those of Comparative Example A, except that the spinning nozzle had 3 rectangular openings 3.0 mm long and 0.3 wide. The filaments were extruded at a rate of 2.8 g / hole / minute and accelerated to 2010 m per minute using the pneumatic nozzle. The filament properties are shown in Table I and the mat properties in Table II.

Example 2

Filaments and a mat were made under conditions similar to those of Example 1, except that the filaments were accelerated to 3650 m / s. minute using the pneumatic nozzle. The filament properties are listed in Table I and the mat properties in Table II.

Comparative Example D

Filaments and a mat were prepared under conditions similar to those of Example 1, except that the filaments were extruded at a rate of 3.3 g / hole / minute and accelerated to 4200 m / min. minute using the pneumatic nozzle. Filament properties are shown in Table I and the mat properties in Table II.

Comparative Example E

Filaments and a mat were made under conditions similar to those of Example 1, except that the spinning nozzle had 3 rectangular openings 2.0 mm long and 0.5 mm wide. The filaments were extruded at a rate of 3.3 g / hole / minute and accelerated to 4750 m / min. minute using the pneumatic nozzle. Filament properties are shown in Table I and the mat properties in Table II.

143767 7

Comparative Example F

According to Comparative Example A, the nonwoven mat was passed through a needle tissue to produce a needle-stitched nonwoven fabric with about 30 needle-2 needles per minute. cm. The results of a fracture strength test with the resulting product are shown in Table III.

Example 3

The nonwoven mat of Example 1 was needle-stitched as indicated in Comparative Example F. The results of a fracture strength test with the resulting product are shown in Table III.

Comparative Example G

The nonwoven mat according to Comparative Example C was 135 ° C pressed in a hot calender machine for heat sealing the fibers. The breaking strength of the heat-sealed, nonwoven product is shown in Table IV.

Comparative Example H

According to Comparative Example E, the nonwoven mat was heat sealed in a similar manner to that of Comparative Example G. The breaking strength of the heat-sealed nonwoven product is shown in Table IV.

Comparative Example I

The nonwoven mat of Comparative Example D was heat sealed in a similar manner to that of Comparative Example G. The breaking strength of the heat-sealed nonwoven product is shown in Table IV.

8 163767

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