Process of making a yarn

Details Process of making a yarn Process of making a yarn

1999-06-11

2001-10-16

Tentoni, Leo B. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Forming continuous or indefinite length work

Shaping by extrusion

C264S210500, C264S210600, C264S210700, C264S210800, C264S211120

Reexamination Certificate

active

06303063

ABSTRACT:

TECHNICAL FIELD AND BACKGROUND OF THE INVENTION
The present invention concerns an improved method for making a plastics material yarn and the yarn made by the method, especially but not exclusively, a method of manufacturing our yarn from polypropylene or polyethylene or a blend of these materials to provide a dental floss or tape.
Polytetrafluoroethylene (PTFE) has been recognised as a material which, in yarn form, gives satisfactory results in certain specialist applications, for example, dental floss or tape. PTFE is a relatively costly material and there is a desire to provide a yarn exhibiting the same overall characteristics as PTFE but being formed from a less expensive material.
SUMMARY OF THE INVENTION
According to one aspect of this invention there is provided a method of converting a plastics material into a yarn, comprising heating the plastics material to melt it, passing melted material through an extrusion die to form an extruded filament, and thereafter cooling the filament.
According to another aspect of the present invention there is provided a method of converting a plastics material into a yarn, comprising heating the material to melt it, pumping melted material through an extrusion die to form an extruded filament, cooling the extruded filament, passing the extruded filament through a first draw roller assembly while elevating the temperature of the filament, heating the filament in a heating zone as it exits from the first draw roller assembly and, thereafter, passing the filament through a second draw roller assembly operating at a different linear speed than the first draw roller assembly and spooling the filament exiting the second draw roller assembly.
The plastics material may comprise a polymeric plastics material, which may be selected from the group comprising polyalkenes. Suitably, the material comprises one or more polyalkenes formed from one or more of C
2
-C
3
alkenes. Suitably, the plastics materials is polyethylene or polypropylene, a blend of polyethylene and polypropylene, or a co-polymer of ethylene and propylene. The plastics material may be provided in the form of granules.
Where the plastics material is a co-polymer of ethylene and propylene, the material may comprise from 0 to 100% wt/wt of said co-polymer, preferably from 0 to 60%, and more preferably from 0 to 40% of said co-polymer.
The material may further include polytetrafluoroethylene (PTFE), for example in an amount of 5 to 10% wt/wt.
The material may comprise a rubberising product comprising a propylene polymer with ethene. For example, a product sold under the trade mark ADFLEX can be used. Alternatively, any other similar such product can be used. The material may comprise from 0 to 100% wt/wt of said product, preferably from 0 to 60% wt/wt, more preferably, from 0 to 40% wt/wt. The use of the rubberising product has the effect of rendering to the yarn a more rubbery texture. This can be advantageous when the yarn is to be used as a dental floss.
The material may include an ethylene vinyl acetate polymer, which may be a co-polymer, the co-polymer including a vinyl acetate, preferably at 7 to 18% wt/wt. An example of a suitable such co-polymer is sold under the trade mark EVATANE by Elf Atochem UK Ltd.
The material may include from 0 to 100% wt/wt of said ethylene vinyl acetate polymer, preferably 0 to 60% wt/wt, more preferably 0 to 40% wt/wt.
Silica may be added to the plastics material. Preferably, the silica is added in the form of particles. Preferably, silica is added to the material in an amount of 1% to 5% wt/wt. The silica may be added to the material prior to or during heating thereof. The silica may be a coloured silica.
A silicone may be added to the material. The silicone may be linear polydimethyl silicone, suitably one sold by Dow Corning under the designation ME50-001 SILICONE MASTERBATCH. The silicone may be added in an amount 1-50% wt/wt, preferably 5-20% wt/wt, more preferably 10-15% wt/wt.
In the first embodiment, the rollers in the first heated draw roller assembly are rotating such as to impart to the filament a speed which may lie within the range 0-200 m per minute, preferably within the range 5 to 40 m per minute. More preferably it is 20 m per minute.
The temperature of the rollers in the first heated draw roller assembly of the first embodiment may lie within the range 0-200° C., preferably within the range 80 to 160° C. More preferably it is 95° C. The temperature in the heating zone at the exit from the first draw roller assembly may lie within the range 0-200° C., preferably within the range 80 to 140° C. More preferably it is 120° C.
Preferably the second draw roller assembly operates at a higher speed than the first draw roller assembly. In a first embodiment of the invention the second draw roller assembly is heated.
The temperature of the rollers in the second heated draw roller assembly of the first embodiment may lie within the range 0-200° C., preferably within the range 80 to 140° C. More preferably it is 90° C.
The rollers of the second heated draw roller assembly of the first embodiment are rotating such as to impart to the filament a speed which may lie within the range 0-1000 m per minute, preferably within the range 50 to 250 m per minute. More preferably it is 80 m per minute.
In a second embodiment, the filament may be passed through an intermediate draw roller assembly arranged downstream of the first draw roller assembly and upstream of the second draw roller assembly.
In the second embodiment the extruded filament may be further heated in a second heating zone as the filament exits the intermediate draw roller assembly. Conveniently, the filament is substantially not heated as it passes through the intermediate draw roller assembly.
In the second embodiment, the rollers in the first draw roller assembly are rotating such as to impart to the filament a speed which may lie within the range of 16-50 m per minute, conveniently substantially 32 m per minute.
Preferably, the first draw roller assembly of the second embodiment comprises a plurality of rollers, conveniently five. The temperature of at least one of the rollers in the first draw roller assembly of the second embodiment may lie in the range of 50-100° C., conveniently 96-100° C. Conveniently the roller of the first draw roller assembly arranged furthest downstream thereof is heated. Preferably, the roller immediately upstream of said furthest downstream roller is also heated.
The temperature of the first mentioned heating zone at the exit from the first draw roller assembly of the second embodiment may lie in the range of 100-135° C., conveniently 116-177° C.
The temperature of the second heating zone at the exit from the intermediate draw roller assembly may lie in the range of 100-150° C., conveniently substantially 150° C.
The intermediate draw roller assembly may comprise a plurality of rollers, conveniently five. The rollers in the intermediate draw roller assembly are rotating such as to impart to the filament a speed which may lie in the range 150-250 m per minute, conveniently substantially 175 m per minute.
The second draw roller assembly in the second embodiment may comprise a plurality of rollers, conveniently five. The rollers in the second draw roller assembly are rotating such as to impart to the filament a speed which may lie in the range 100-250 m per minute, conveniently substantially 160 m per minute, for example 158 m per minute.
The extruded filament may be cooled as it passes through the second draw roller assembly of the second embodiment. At least one of the rollers of the second draw roller assembly is at a temperature in the range 5-15° C., conveniently 11-12° C. Conveniently, the roller of the second draw roller assembly arranged furthest downstream thereof is cooled. Preferably, the roller immediately upstream of said furthest downstream roller is also cooled.
In one embodiment, flattering means is provided to flatten the filament. The flattening means may comprise at least one roller, and preferably a pair of flattening rollers between which

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