SE446105B - PROCEDURE FOR MANUFACTURING POLYMER FILMS WITH HIGH DRAWINGS AND MODULES - Google Patents

Description

1o_ 'i d¿jï »: s1ua1o99 7- o for evaporation of all or most of the solvent from the filament. The temperature in the shaft is kept below the melting point of the polymer, so that it precipitates when the solvent evaporates. This increases the mechanical strength of the filament, which is still very low at the exit of the spinneret. The strength is further increased at the following stretching process at temperatures below the melting point of the polymer.

According to the present invention, the evaporation of the solvent from the filament immediately after spinning is not promoted during the cooling phase. The filament can be cooled to below the solution temperature and especially to below the swelling point of the polymer in the solvent in any suitable way, for example by allowing the filament to pass through a water bath or through a shaft during the deposition or very little air is blown through the shaft. Any evaporation of the solvent from the filament often occurs spontaneously and cannot be prevented. This does not cause harm as long as the evaporation is not actively promoted and the amount of solvent in the filament is not reduced to too low a value, for example to less than 25% by weight of solvent, based on the polymer, and preferably not to less than equal weight of solvent and polymer. The evaporation of the solvent may be reduced or prevented by performing the spinning in an atmosphere containing vapor of the solvent.

Upon cooling to below solution temperature and especially to below the swelling temperature of the polymer in the solvent, the polymer precipitates out of solution and a gel forms. A filament consisting of this polymer gel has sufficient mechanical strength for further treatment, for example by means of guides, rollers, etc., which are usually used in spinning. A filament of this kind is heated to a temperature between the swelling point of the filament in the solvent and the melting point of the polymer and is stretched at this temperature.

This can be done by passing the filament into a zone containing gaseous or liquid medium, which is kept at the required temperature. A tube furnace with air as a gaseous agent is very suitable, but it is also possible to use a liquid bath or any other suitable device. A gaseous medium is easier to handle and is therefore preferred. When the filament is stretched, the solvent will evaporate or, if liquid medium is used, the solvent dissolves in the liquid used. Preferably, evaporation is assisted by suitable means, for example removal of solvent vapors, for example by allowing gas or air to flow past the filament in the stretching zone. At least a part of the solvent should evaporate, but preferably most of the solvent should evaporate, so that at the end of the stretching zone a very small amount, for example not more than a few percent, calculated on the solid, of the solvent is left in the filament. The filament finally obtained must be solvent-free and it is convenient to apply conditions such that the filament is free or practically solvent-free already in the stretching zone. surprisingly, it has been possible according to the invention to produce filaments which are considerably stronger than filaments of the same material, manufactured using the now common dry spinning processes, i.e. with the methods described in the above-mentioned publications of Juyn lament with considerably higher tensile strength and modulus. and Bigg, filaments with a higher modulus have admittedly been manufactured, but the tensile strength leaves much to be desired. In addition, the productivity of these methods is low.

The process according to the invention differs from the usual dry-spinning processes in that a filament containing a considerable amount of solvent for the spinnable material is stretched at a temperature at which the spinnable material is at least swellable in the solvent, with removal of the solvent, while in the commonly used spinning processes solution-free filaments are exposed to the stretch. A requirement for dry spinning is that the linear polymer is soluble in a suitable solvent. For each soluble polymer, a number of solvents are known. The person skilled in the art can without difficulty choose a suitable solvent from the gel and the solution is time-dependent. 8000997-0 these, the boiling point of which is not so high that it becomes difficult to evaporate the solvent from the filament and not so low that it is too volatile and prevents filament formation due to rapid evaporation, or must be used under pressure to prevent this.

Dissolution of a polymer in a solvent suitable for the purpose involves swelling. When solvents are absorbed and the volume increases, a highly swollen gel is formed which, however, due to its consistency and dimensional stability, must still be considered as a kind of solid. It is generally believed that the polymer consists of ordered (crystalline) and less ordered (amorphous) regions. It is assumed that the ordered areas act as anchoring points and thus provide dimensional stability to the gel. The formation of a certain polymer can be dissolved in a given solvent just above a certain temperature. Below this solution temperature only swelling takes place and to the extent that the temperature is lower the swelling will be lower to a certain point where it becomes negligible.

The swelling point or swelling temperature is considered to be the temperature at which a distinct increase in volume and a distinct absorption of solvent, 5-10% of the weight of the polymer, occurs. For the sake of simplicity, it can be said that the swelling temperature above which stretching is to take place is the temperature at which 10% solvent is indisputably absorbed by the swelling polymer. In dry spinning processes of the type commonly used, 5-30% by weight of solution is usually used for technical and economic reasons. Such solutions are also suitable for the process according to the invention, although it is generally suitable to use a lower concentration. Preferably, solutions of 1-5% by weight are used. Even lower concentrations can sometimes be used, although these do not bring benefits and are unsuitable from an economic point of view.

Suitable stretching conditions can be easily determined by eg experiment. The tensile strength and modulus of the filaments are, within certain limits, approximately proportional to the stretching ratio. one thus chooses greater stretching ratio.

As the filaments should be stronger, the elongation ratio must be at least 5 and preferably at least 10 and preferably above 20. High elongation ratios, 30-40 and t.o.m. higher, it can be applied without disadvantage, which gives filaments whose tensile strength and modulus are considerably higher than those achieved with the hitherto common processes.

In dry spinning processes of the usual kind, the diameters of the spinning openings in the spinning nozzles are usually ¿small. In general, these diameters are 0.02-1.0 mm. Especially if small spinning openings, equal to or less than 0.2 mm, are used, the spinning process becomes very sensitive to the presence of contaminants in the spinning solution, so it must be carefully freed from and kept free of solid contaminants. In most cases, filters are arranged at the spinnerets. Despite this, it has been shown that the spinneret must be cleaned after a short time of use and that clogging often occurs. In the method Q according to the invention, larger spinnerets can be used, of more than 0.2 mm and for example 0.5-2.0 mm or more, since considerably higher stretching conditions can be applied and in addition lower polymer concentrations in the spinner solution are generally used. .

The invention is not limited to the production of strong filaments of certain polymers, but can generally be used for materials which can be dry spun into filaments.

Polymers which can be spun by the process of the present invention are, for example, polyolefins, for example polyethylene, polypropylene, ethylene-propylene copolymers, polyoxymethylene, polyethylene oxide, polyamides, for example the different types of nylon, polyesters, for example polyethylene terephthalate, polyacrylonitrile, vinyl polymers, for example polyvinyl alcohol, polyvinylidene fluoride.

Polyolefins, for example polyethylene, polypropylene, ethylene-propylene copolymers and higher polyolefins, can be easily dissolved in hydrocarbons, for example saturated aliphatic and cyclo-. as well as aromatic hydrocarbons, or mixtures thereof, for example mineral oil fractions. Very suitable are aliphatic or cyclic hydrocarbons, for example nonane, decane, undecane, dodecane, tetralin, decalin, etc., or mineral oil fractions with a corresponding boiling range. Polyethylene and polypropylene are preferably dissolved in decalin or cloth. The process is particularly suitable for the production of filaments of polyolefin, especially polyethylene.

It is also possible to make filaments of solutions of two or more polymers in the same solvent, for which purpose the polymers need not be miscible with each other. For example, it is possible to dissolve together in decalin or dodecane polyethylene and polypropylene, whose melts are immiscible, and spin the solution thus obtained. Filaments according to the invention can be used for many different purposes. They can thus be used as reinforcement in many different kinds of materials, for which reinforcement with fibers or filaments is known, for cover yarns, and for all possible applications in which low weight in combination with high strength is desirable. Of course, the scope for possible applications is not limited to the above.

The invention is further illustrated by the following examples, to which, of course, the invention is not limited.

Example 1 A high molecular weight polyethylene, with fi w 1,5 1.5 x 106 was dissolved in decalin at 14,500 to a 2% solution (weight).

This solution is spun through a spinneret with a spinneret of 0.5 mm diameter at 130 ° C. The filament was passed through a water bath at room temperature, where it was cooled. The cooled, 0.7 mm thick filament, which appeared to be gel-like and still contained about 98% solvent, was first passed through a tube furnace heated to 12,000 and stretched using different stretching conditions.

The process in this example is illustrated by a diagram shown in the accompanying drawings in Fig. 1, while Figs. 2 and 3 show the tensile strength and modulus, respectively, as a function of the tensile ratio.

A modulus of more than 60 GPa and a tensile strength of close to 3 GPa can be achieved, while the modulus of polyethylene filaments produced in a conventional manner is 2-3 GPa and the tensile strength of about 0.1 GPa. The values of modulus and tensile strength of filaments with different tensile ratios according to Figs. 2 and 3 are given in the following Table 1.

Polyethylene filaments with a tensile strength of more than 1.2 GPa can be easily produced according to the following invention.

Table 1 Sample Tensile Module GPa Tensile Strength Ratio GPa 1 1 2.4 0.09; 2 3 5.4 0.27 3 7 17.0 0.73 4 8 17.6 0.81 ll 23.9 1.32 6_ 12 37.5 1.65 7 13 40.9 1.72, 8 15 41.0 1.72 9 17 43.1 2, 11 69.0 2.90 11 32 90.2 3.02 Eåemëëiå According to the procedure described in Example 1, a 2% (by weight) solution of a mixture of equal parts high molecular weight polyethylene, HW = 1.5 x 106, and a poly- = 3.0 x 106, at 14 ° C and obtained high molecular weight propellant, Üw 7 was coated at 13 ° C with the draw ratio 20. na filaments had a tensile strength of 1.5 GPa. ëšëmšáeš In the same manner as in Example 1, a 2 ~% (weight) solution of isotactic polypropylene was spun with fi w = 3.0 x 106 at l40 ° C and stretched at l30 ° C with a draw ratio of 20 l GPa.

The tensile strength of the obtained filament was

Claims (5)

son0997-o ß PATENTKRAV 1. A process for producing polymer filaments having a high tensile strength and modulus, wherein a solution of the polymer in a suitable solvent is spun into a filament through a spinneret, the resulting filament is filled and then stretched, characterized in that a solution of 1-30% by weight of polymer is spun at a temperature above the solution temperature of the polymer in the solvent, the resulting filament is cooled below the solution temperature without promoting the evaporation of the solvent to form a polymeric gel filament, the gel filament is brought to a temperature in the range the solvent and the melting point of the polymer and are stretched at a temperature in said range with at least partial elongation of the solvent still remaining in the filament, the filament to be stretched containing at least Z% by weight of solvent, with respect to the polymer, and the filament being stretched to a stretching ratio nde of at least 5. Process according to Claim 1, characterized in that the polymer used is a polyolefin. 3. A method according to claim 1 or 2, characterized in that a 1-5% by weight polymer solution is spun. _ 4. A method according to claims 1-3, characterized in that a filament containing at least 100% by weight of solvent, based on the polymer, is stretched. 5. A method according to claims 1-4, characterized in that the stretching ratio is at least lÛ.