KR0132668B1 - Process for flash-spinning dry polymeric plexifilamentary film-fibril strand - Google Patents

Abstract

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Description

Flash Spinning of Anhydrous Polymeric Plexi-Filament Film-Fibrill Strands

The present invention relates to a method of flash-spinning virtually anhydrous polymeric flexifilamental film-fibril strands. In particular, the present invention relates to an improved process for flash spinning virtually dry strands from a mixture of fiber forming polyolefins, methylene chloride and carbon dioxide.

US Patent No. 3,081,519 to Blaze White; And British Patents 891,943 and 891,945 describe methods for flash spinning flexifilamental film-fibrill strands from fiber forming polymers. The polymer solution in the liquid non-solvent to the polymer at its normal boiling point or below its normal boiling point is extruded into a lower temperature and substantially lower pressure medium at a pressure above the normal boiling point of the liquid at a pressure above the autogenous pressure. This flash spinning causes the liquid to evaporate to cool the extrudate, forming a plexiglass filamentous strand of polymer. Preferred polymers include polyethylene and crystalline polyhydrocarbons such as polyethylene and polypropylene.

According to US Pat. No. 3,081,519 and British Pat. No. 891,943 and 891,945, the following liquids are useful for flash spinning: aromatic hydrocarbons such as benzene, toluene and the like; Aliphatic hydrocarbons such as butane, penta, hexane, heptane, octane and isomers and homologues thereof; Alicyclic hydrocarbons such as cyclohexane; Unsaturated hydrocarbons; Halogenated hydrocarbons such as methylene chloride, carbon tetrachloride, chloroform, ethyl chloride and methyl chloride; Alcohol; ester; ether; Ketones; Nitrile; amides; Fluorocarbons; Sulfur dioxide; Carbon sulfide; Nitromethane; water; And mixtures of these liquids. In addition, the above-mentioned patent mentions that the flash spinning solution may further contain dissolved gases such as nitrogen, carbon dioxide, helium, hydrogen, methane, propane, butane, ethylene, propylene, butane and the like. In order to improve the flexifilament fibrillation, poorly soluble gases, ie gases which are dissolved in the polymer solution at a concentration of less than 7% under spinning conditions are preferred. In Example VI of US Pat. No. 3,081,519, shown by way of example only as methylene chloride and carbon dioxide as the flash spinning medium, a 13% solution of linear polyethylene in methylene chloride was saturated with carbon dioxide at a total equilibrium pressure of 1,000 psia at 200 ° C. , Flash spin at pressure of 1060 psia The concentration of dissolved carbon dioxide is 3.7%.

Trichlorofluoromethane (freon-11) was a very useful solvent for commercially preparing flexifilamental film-fibrils strands of polyethylene. However, this halocarbon outflow into the atmosphere is known to be a serious cause of depleting the earth's ozone. A general discussion of the ozone depletion problem is described, for example, in P.S. Zurer, Search Intensifies for Alternatives to Ozone-Depleting Halocarbons, Chemical Engineering News, pp. 17-20 (February 8, 1988). This problem of ozone depletion should be avoided by using methylene chloride in place of trichlorofluoromethane in conventional flash spinning.

The present invention relates to a method for flash spinning virtually anhydrous polymeric flexifilamental film-fibrils strands from a spinning mixture of methylene chloride, carbon dioxide and fiber forming polyolefins.

The present invention provides a polymeric flexifilment by forming a spinning mixture containing methylene chloride, fiber-forming polyolefins, and carbon dioxide, and then flash spinning the spinning mixture to a substantially lower temperature and pressure region at a pressure above the autogenous pressure of the spinning mixture. In a method of flash spinning a top film-fibril strand, a mixture of 9 to 25 wt% carbon dioxide, 18 to 33 wt% polyolefin and 42 to 73 wt% methylene chloride, based on the weight of the spinning mixture, It provides a process characterized by producing a substantially anhydrous strand containing together and performing the polyolefin mixing step and the flash spinning step in a temperature range of 130 to 220 ^° C.

The invention also includes novel solutions comprising 18 to 33 weight percent fiber forming polyolefin, 42 to 73 weight percent methylene chloride and 9 to 25 weight percent carbon dioxide, based on the weight of the spinning mixture.

The term polyolefin as used in the present invention means mainly saturated open chain polymeric hydrocarbons composed solely of carbon and hydrogen. Typical polyolephini include, but are not limited to, polyethylene, polypropylene, polymethylpentene; And various mixtures of ethylene, propylene and methylpentene monomers.

The term polyethylene includes not only homopolymers of ethylene but also copolymers in which at least 85% of the repeat units are ethylene units. Preferred polyethylenes have a melting point upper limit of about 130 to 135 ^° C., a density ranging from 0.94 to 0.98 g / cm ³ , and a melt index (as defined by ASTM D-1238-57T, condition E) of 0.1 to 6.0. Phosphorus homopolymer linear polyethylene.

The term polypropylene includes not only homopolymers of propylene but also copolymers in which at least 85% of the repeat units are propylene units.

The term plexi-filamentary film-fibril strand described herein is generally a plurality of thin, ribbon-like films having an arbitrary length and an average thickness of less than about 4 microns, arranged to extend the same length as the longitudinal axis of the strand. -Refers to a strand characterized by three-dimensional intact reticulated tissue of the fibril component. The film-fibrils component is intermittently joined and separated at irregular intervals at various locations across the length, width and thickness of the strand to form three-dimensional network. Such strands are described in more detail in US Pat. No. 3,081,519 to Blaze and White and US Pat. No. 3,227,794 to Anderson and Romano.

The present invention discloses a known process for producing flexifilamental film-fibrill strands by flash spinning a spinning mixture of fiber forming polyolefins in methylene chloride and carbon dioxide vapor and producing virtually anhydrous polymeric flexifilamental film-fibril strands To provide improvements. The process of the present invention utilizes a spinning mixture containing 18 to 33 weight percent fiber forming polyolefin, 42 to 73 weight percent methylene chloride and 9 to 25 weight percent carbon dioxide, based on the weight of the total spinning mixture. It requires a flash spinning step to be performed.

Under the process conditions of the present invention as described above, the flash spun strand is anhydrous or virtually anhydrous when exiting the spinneret. That is, methylene chloride is substantially not present in the strand as-spun. This is especially true when comparing strands spun from a mixture of 3.7% carbon dioxide, 13% polyethylene, and methylene chloride to Example VI of US Pat. Can be.

When the strands exiting the spinneret are anhydrous or virtually anhydrous, there are several important advantages. As in sheet formation, the movement of strands that are virtually anhydrous can be more easily controlled than wet strands by natural aerodynamic flow. Complete evaporation of the solvent residue is easier to perform on strands which are virtually anhydrous. Wet strands tend to stick to the rollers used to incorporate the strands into the sheet structure and tend to wind around the rollers and are not acceptable in view of ease of commercial production. Finally, the spinning temperature can be lowered so that less methylene chloride is evaporated. Spinning temperatures lower than those described in US Pat. No. 3,081,519 are preferred in reducing the decomposition of methylene chloride as a solvent.

Preferred fiber-forming polyolefins for use in the present invention are polyethylene and polypropylene as described in US Pat. No. 3,081,519. The polyolefin concentration is used at 18-33% weight based on the weight of the spinning mixture.

Carbon dioxide is present at a concentration of 9 to 25% by weight of the spinning mixture. In general, in order to spin anhydrous strands from the spinning mixture of the present invention, lower concentrations of polyolefin require more carbon dioxide in the spinning mixture. In order to practice the present invention, it is necessary to properly mix methylene chloride, carbon dioxide and polyolefin according to the composition, temperature and pressure of the mixture.

The temperature required for preparing the spinning mixture and for flash spinning the mixture is generally about the same, usually 130-220 ^° C.

The mixing and flash spinning steps are carried out at pressures above the autogenous pressure of the mixture. The pressure during the production of the spinning mixture is generally at least 800 psia and usually at most 2,500 psia, although pressures as high as about 8,000 psia may be used. Flash spinning pressures are generally above 600 psia, but often use slightly higher spinning pressures.

The spinning mixture preferably contains fiber forming polyolefin, methylene chloride and carbon dioxide. However, conventional flash spinning additives can be incorporated into the spinning mixture by known techniques. Such additives may function as ultraviolet stabilizers, antioxidants, fillers, dyes and the like.

The novel solution of the present invention contains 18 to 33 weight percent fiber forming polyolefin, 42 to 73 weight percent methylene chloride and 9 to 25 weight percent carbon dioxide. Preferred fiber forming polyolefins are polyethylene and polypropylene.

EXAMPLE

The present invention is sometimes illustrated by all the examples below that utilize batch processes in relatively small apparatus. Such a batch process can be converted to large scale by continuous flash spinning, which can be carried out in a device of the type described, for example, in US Pat. No. 3,227,794 to Anderson and Romano.

Polyethylene is a polymer conveniently used in the examples.

(Device)

Examples 1 and 2 in apparatus comprising a 5 gallon autoclave equipped with a drive motor, a rigidly fixed helical blade stirrer, a temperature and pressure measuring device, heating means and an inlet for filling the autoclave with the necessary components. Flexitilamentous strands are prepared for, 3 and 4. A quick acting valve from the autoclave is connected to a spinning assembly of the type disclosed in US Pat. No. 4,352,650 to Marshall, which is incorporated herein by reference. The spinning assembly includes a let-down chamber that is 13.9 cm (5.5 in) long, 0.162 cm (0.064 in), 0.147 cm (0.058 in) or 0.116 cm (0.046 in), and 0.182 cm (0.072 in), 1.72 cm (0.06 8) through a tunnel with a length of 0.68 cm (0.27 in) and an inlet diameter of 0.835 cm (0.33 in) and an outlet diameter of 1.14 cm (0.45 in) in) or a pressure drop orifice of 0.157 cm (0.062 in).

(Way)

In Examples 1, 2 and 3, the autoclave is filled with high density linear polyethylene and methylene chloride having a melt index of 0.76. Seal the autoclave, vent and begin to stir at a moderate rate. Carbon dioxide is added to the autoclave and begins to heat. When the temperature of the contents in the autoclave reaches 140 ° C, additional carbon dioxide is added to raise the internal pressure to 1500 psia. Since the addition of carbon dioxide causes significant pressure and temperature fluctuations, the pressure is stabilized for 15 minutes after each addition of carbon dioxide. The pressure drops as the carbon dioxide dissolves in the methyl chloride / polyethylene mixture. Thereafter, the autoclave is repeatedly repressurized to 1800 psia until it is determined that saturation has been reached. This indicates that a constant pressure of 1800 psia is maintained in the autoclave. Thereafter, the temperature of the autoclave is maintained at 150 ^° C. The total time for the heating and mixing steps is approximately 1 hour, calculated from when the autoclave temperature reaches 140 ^° C. Thereafter, the rotational speed of the stirrer blade is reduced to about one third of the initial speed, and the autoclave pressure, if necessary, is rapidly adjusted to 1,800 psia with nitrogen, and then the spinning mixture is also heated to 150 ^° C. Quickly open the drain valve to allow flow to the spin assembly. The results are shown in Table 1.

In Example 4, the autoclave is charged with a high density linear polyethylene of the previously used form. The autoclave is sealed, evacuated and methylene chloride is added. Thereafter, the pump is used to add the required amount of carbon dioxide under pressure. Begin to stir at an appropriate speed and begin to heat. The mixture is initially timed at 150 ^° C. and maintained at a target temperature of 170 ^° C. for 1 hour. The mixer is slowed down to about one third of the initial speed and the autoclave pressure is quickly adjusted to the desired 1,800 psia by using nitrogen or venting. Finally, the discharge valve of the spinning assembly is quickly opened to spin the mixture.

(Way)

In Examples 5 and 6 and Control Examples A and B, the autoclave was first charged with a pre-measured amount of high density linear polyethylene pellets having a melt index of 0.76. The autoclave is sealed and the air is vented to a final pressure of 1 psia (typically 0.5 psia) or less. Methylene chloride is charged into the vessel at room temperature and the polyethylene pellet is stirred appropriately to start suspension. Thereafter, the total charge of carbon dioxide is charged to the autoclave at room temperature and the autoclave contents begin to heat. Typically, the autoclave is about 150 over about 45 minutes. After heating to C it is kept at the same temperature with stirring for an additional 30 minutes. The polymer solution thus formed is heated to the final desired temperature and left to stand again for about 30 minutes with stirring to ensure homogeneity.

The total dosage of polyethylene, methylene hydrochloride and carbon dioxide is selected such that the pressure of 1800 to 1900 psia is hydrodynamically generated by the polymer solution by heating the vessel contents to the final desired temperature. In this hydraulically sufficient condition and pressure range, polyethylene, methylene chloride and carbon dioxide form a single siliceous solution in which all components are thoroughly and evenly mixed. There are no gas or vapor bubbles in the solution.

Once the solution is formed and the final temperature and pressure are obtained, stirring is promoted and nitrogen is introduced into the head portion of the vessel at the same pressure as the solvent in the vessel. Thereafter, the solution is immediately released through the spinneret. No stirring and no contact of nitrogen with the solution for more than a short time and little or no migration of nitrogen into the polymer solution. Thus, to maintain the pressure of this solution during spinning, nitrogen acts as a gas piston. Depending on the spinneret size, all solutions in the vessel are released within 1.5 to 3 minutes. The results are summarized in Table II.

Claims (6)

After forming a spinning mixture containing methylene chloride, fiber-forming polyolefins and carbon dioxide, the spinning mixture is flash-spun into a substantially lower temperature and pressure region at pressures above the autogenous pressure of the spinning mixture to form a polymeric filamentary film-fibrils A method for flash spinning strands comprising a mixture of 9 to 25 weight percent carbon dioxide, 18 to 33 weight percent polyolefin and 42 to 73 weight percent methylene chloride, based on the weight of the spinning mixture. Process for producing anhydrous strands and carrying out the polyolefin mixing step and the flash spinning step at 130 to 220 ° C. The method of claim 1 wherein the fiber forming polyolefin is polyethylene. The method of claim 1 wherein the fiber forming polyolefin is polypropylene. A solution containing 18 to 33 wt% fiber forming polyolefin, 42 to 73 wt% methylene chloride and 9 to 25 wt% carbon dioxide. A solution containing 18 to 33 weight percent polyethylene, 42 to 73 weight percent methylene chloride and 9 to 25 weight percent carbon dioxide. A solution containing 18-33 weight percent polypropylene, 42-73 weight percent methylene chloride and 9-25 weight percent carbon dioxide.