US3372082A

US3372082A - Hollow filaments of a tetrafluoroethylene polymer and process for preparing them

Info

Publication number: US3372082A
Application number: US415327A
Authority: US
Inventors: Kometani Yutaka; Koda Yutaka; Sugino Tadahiko; Izumi Hirokazu
Original assignee: Daikin Industries Ltd
Current assignee: Daikin Industries Ltd
Priority date: 1963-12-06
Filing date: 1964-12-02
Publication date: 1968-03-05
Anticipated expiration: 1985-03-05
Also published as: DE1494574A1; GB1085983A

Description

March 5, 1968 YUTAKA KOMETANI ETAL 3,372,082

HOLLOW FILAMENTS OF A TETRAFLUOROETHYLENE POLYMER AND PROCESS FOR PREPARING THEM Filed Dec. 2, 1964 United StatesPatent fice 3,372,082 Patented Mar. 5, 1968 3,372,082 HOLLOW FILAMEN'IS 0F A TETRAFLUORO- ETHYLENE POLYMER AND PROCESS FOR PREPARING THEM Yutaka Kometani, Hyoga-ken, Yutaka Kuda, Osaka-fu, Tatiahiko Sugino, Osaka-shi, and Hirokazu Izumi, Amagasaki-slxi, Japan, assignors to Daikin Kogyo Kabushiki Kaisha, Osaka-shi, Japan Filed Dec. 2, 1964, Ser. No. 415,327 Claims priority, application Japan, Dec. 6, 1963, 38/ 65,774 4 Claims. (Cl. 161-178) ABSTRACT F THE DISCLOSURE Hollow filaments consisting of a tetrafluoroethylene polymer layer and an empty space cavity Within, said empty space cavity comprising from 5 to 90 percent in terms of Sb Sufi-Sb wherein Sa is the total area of the tetrafiuoroethylene polymer layer at a given cross-section of said hollow filament, and Sb is the total area of the empty space cavity formed therein at said given section produced by extruding a mixture of a viscose and an aqueous dispersion of a tetrafluoroethylene polymer at a temperature ranging from 50 to 100 C. into a setting medium selected from the group consisting of a bath containing sulfuric acid in the order of from 6 to 60 percent by weight, a bath containing sulfuric acid in the order of at most 6 percent by weight and a sulfuric acid salt in the order of at least 5 percent by weight, a bath containing hydrochloric acid in the order of from l to 3() percent by weight, and a bath containing nitric acid in the order of from l to 50 percent by weight, and heating the resultant filament product to coalcsce the tetrafluoroethylene polymer forming said filament product, said starting spinning mixture comprising cellulose in the order from 0.4 to 8 percent by weight and a tetrafiuoroethylene polymer in the order of from 70 to 99 percent by weight 0f the combined weight of said cellulose and polymer.

This invention relates to hollow filaments or fibers of tetrafluoroethylene polymers. The invention further pertains to the manufacture of said filaments having an empty space or cavity within the body.

Tetraiiuoroethylene polymers have a high order of stability to heat and chemicals, which properties make them very useful for various purposes. But their inertness to melting or dissolving necessitates to apply a specific procedure for the shaping of fibrous structures therefrom. As disclosed in British Patent 767,015 and United States Patent 2,772,444, the desired filaments are generally produced by emulsion spinning from a mixture of la matrix-forming material and an aqueous dispersion of a tetrafluoroethylene polymer. Such spinning procedure, however, is carried out under the conditions which are confined to the production of filaments all ha'ving the body stuffed or filled up with the starting tetraiiuoroethylene polymer. In other words, there has not yet been reported in the prior art either the provision of hollow filaments of tetrafiuoroethylene polymers having an empty space or cavity within the body or a process for the manufacture of said hollow filaments from tetraiiuoroethylene polymers.

The inertness to melting or dissolving of said tetrafiuoroethylene polymers, further, precludes the application thereto of the known methods for the manufacture of filaments or fibers having hollow structures out of such polymers as polyester, polyvinyl alcohol, polyvinyl chloride or polyamide which can be easily melted or dissolved. According to such methods, the desired hollow filaments are generally produced by melt spinning comprising extruding a fused polymer from a spinneret having a specific structure, or by solution spinning comprising extruding a polymer solution containing an additive, such as volatile or frothing agent, into a setting medium, allowing the additive employed to evaporate or froth in the course of the spinning procedure.

It is accordingly one object of this invention to provide hollow filaments having an empty space cavity within the body from tetrafluoroethylene polymers.

Another object of the invention `is the provision of hollow filaments excelled in a high order of bulkiness and a low order of specific gravity resulting from the aforesaid empty space cavity within the body and having a high order of insulation to heat and of compressive elasticity.

A further object of the invention is the provision of hollow filaments pronounced in a reduction in cost per unit due to the -aforesaid characters.

A still further object of the invention is the provision of a process for the manufacture of the hollow filaments having the aforesaid characters from tetraiiuoroethylene polymers.

A still another object of the invention is the provision of a process for converting almost all amount of the tetrafiuoroethylene polymers employed into the desired hollow filaments.

A still further object of the invention is the provision of a process for the manufacture of hollow filaments out of tetrafiuoroethylene polymers which can be carried out without the use of volatile or frothing agent. A

Other objects and specific features of this invention will become apparent in view of the subsequent description.

According to the principles of this invention, the hollow filaments of the same consist of a body layer of the tetrafiuoroethylene polymer employed and an empty space cavity within the body in the range of from 5 to percent at a given cross section. The term empty space cavity as employed herein is defined as below:

Sa+S b X wherein Sa is the total area of the tetrafluoro-ethylene polymer layer at a given cross section of the hollow filaments examined, and Sb is the total empty area at said cross section of the hollow filaments examined.

In order to afford a fuller understanding of this invention, there are appended illustrative drawings, in which:

FIGURE 1 is an enlarged cross sectional view of a hollow filament of this invention;

FIGURE 2 is an enlarged cross sectional view of a hollow filament -bundle of this invention; and

FIGURE 3 is an enlarged cross sectional view of a conventional fibrous bundle shown as a comparison.

As will be apparently seen from the drawings, the spun filaments of this invention respectively consist of a polymer layer part 1 and an internal cavity or empty space part 2 formed within the body of the filament. The polymer layer part 1 is filled up with a continuous layer of the polymer employed, and the internal cavity part 2 is completely devoid of the polymer employed, as shown in FIGURES 1 and 2, whereas -any member constituting the conventional fibrous bundle is entirely filled up with the material employed as shown in FIGURE 3, and the most desir-able range of the empty space cavity in terms of the aforesaid formula is from 30 to 60 percent.

The internal cavity of the filaments of this invention generally constitutes an elongated continuous space. In some instances, however, some laments exhibit an internal cavity having a discontinuous portion, but the existence of such discontinuous portions is in a quite negligible order in view of theentire length of the elongated filaments.

According to the principles of this invention, a spinning mixture of a viscose and an aqueous Adispersion of a tetrauoroethylene polymer is continuously extruded at from 50 to 100 C. into -a setting medium consisting of sulfuric acid in the order of from 6 to 60 percent by weight. Alternatively, said spinning mixture may be extruded into a setting medium comprising sulfuric acid in the range of 6 percent or less by weight and a sulfuric acid salt in the order of at least 5 percent by weight; or hydrochloric acid in the order of from 1 to 30 percent by weight; or nitric acid in the range of from 1 to 50 percent by weight.

According to the principles of this invention, the average rate of cavity formation reaches as high as 70 to 100 percent. The term cavity formation or cavity formation rate as employed herein is defined -as below:

Percent cavity formation rate:

For example, when a filament bundle given consists of all hollow filaments as shown in FIGURE 2, the cavity formation rate thereof is 100 percent, whereas the cavity formation rate of the conventional filament bundle having no hollow filaments as shown in FIGURE 3 is 0 percent.

The tetrafluoroethylene polymers employed in this invention contain at least 70 percent by weight of tetraiiuoroethylene ingredients. Said polymers include polytetrafluoroethylene and copolymers f tetrafluoroethylene with polymerizable materials, such as hexafluoropropropylene, trifiuorochloroethylene or vinyl chloride. Said polymers, further, must be of a molecular weight sufficient ly high to be fiber-forming, and the higher the molecular weight, the better results are obtained, because the physical properties of the filaments obtained are improved in accordance with a rise in the molecular Weight of the starting polymer.

The tetrauoroethylene polymers are employed in this invention in the form of aqueous dispersion prepared by emulsion polymerization or by dispersing the polymer in the form of particles in the aqueous medium. To the resultant dispersion there may be added a surface active agent, where necessary, and the dispersion is mixed with a viscose. The resultant spinning mixture is very stable and there areformed no substantial precipitates of the high molecular weight susbtances employed. The cellulose content present in the spinning mixture must be in the order of from 0.4 to 8 percent by weight, preferably from l to 5 percent by weight, and the tetraffuoroethylene polymer content present comprises from 70 to 99 percent by weight, preferably from 75 to 97 percent by weight, of the combined weight of said polymer and cellulose.

In this invention, the composition ratio of the setting medium is an important factor. The acid concentration of the setting medium varies in accordance with the species of the acid employed. Sulfuric acid is employed in a concentration ranging from 6 to 60 percent by weight, preferably from to 50 percent by Weight. There must be added a sulfuric acid salt in the order of at least 5 percent by weight when the sulfuric acid employed is in the order of 6 percent or less by Weight. Hydrochloric acid is employed in a concentration ranging from 1 to 30 percent by weight, preferably from 4 to 20 percent by weight;

and nitric acid in the order of from 1 to 50 percent by weight, preferably from 3 to 40 percent by weight.

In this invention, the addition of a salt is imperative in the aforesaid instance where the sulfuric acid employed is in .the order of 6 percent or less by weight. In other instances, however, said addition is not critical. The salts added include metal salts of the acid employed, such as alkali metal, alkali earth metal, magnesium, zinc, aluminum, chrome, manganese, copper, iron and the like metal salts, of which natrium salt and zinc salt are preferable. These salts are employed either singly or in mixture of 2 or more species.

The temperature applied to the setting medium which is also one of the important factors of this invention and rather higher than the conventional temperature, ranges from 50 to 100 C. The desirable temperature is determined in accordance with the species of the components constituting the setting medium. The desirable temperature applied to the sufuric acid coagulating bath ranges from 70 to 95 C.; the desirable temperature applied to the hydrochloric acid bath is between 50 and 70 C., and that applied to the nitric acid bath is in the order from 55 to 90 C.

The spinning mixture containing any of the aforesaid polymers and a viscose is filtered, deaerated and extruded into the setting medium as specified before. The hole diameter of the spinneret and the draft during spinning vary over a wide range, but it is desirable to accommodate these conditions so as to produce a filament having a cross sectional area of the polymer part forming the filament, not including the internal cavity space, in the order of not less than 5 105 cm?. The filaments obtained at this stage of coagulation are not sufficiently strong, because particles of the tetrafiuoroethylene polymer employed is adhesively imbedded in the cellulose matrix.

The filaments obtained are subjected to the conventional coalescing procedure as described in United States Patent 2,772,444 after washing and drying, comprising heating the filaments at a temperature higher than the fusing point of the tetrafluoroethylene polymer employed. Polytetrafiuoroethylene, for instance, is subjected to a temperature higher than the transition temperature of 327 C., preferably to a temperature in the range of 350 to 450 C. The cellulose matrix is thereby decomposed, and the polytetra'fiuoroethylene employed coalesces.

Thus, the desired hollow filaments having from 5 to 90 percent empty space cavity are obtained in such a high cavity formation ratio as from 70 to 100 percent. The resultant structures-are drawn and heat-treated according to the conventional method where desirable.

The theoretical reasons for the formation of internal cavities within the body of the filaments of this invention are not necessarily apparent. There are however employed a setting medium having an appropriate order of concentration in terms of the acid employed, and a temperature ranging from 50 to 100 C., so that the spinning mixture extruded in the setting medium instantaneously coalesces, forming a fast-hardening surface layer, and the internal portion of the resultant filaments is forced to harden progressively and retardedly and attracted to the fasthardening surface layer, forming a hollow space or cavity within the body of each of the filaments obtained.

The hollow filaments of this invention possess excelled heat-resistance and chemical stability and a low order of coefficient of friction. The hollow cavities formed within the body of the laments impart a bulkiness to the filaments, reducing the cost per unit volume. The application of polytetrafiuoroethylene fibers or fabrics has hitherto been confined to a limited area despite their suitable properties, because the market price of said fibers or fabrics remained exceedingly high. The structures of this invention however are inexpensive in cost price, so that the structures can be profitably employed as a desirable material for manufacturing packings, lubricating articles for bearings, filtering fabrics, safety clothings and the like chemicaland heat-resistant articles. The excelled heatinsulating property and compressive elasticity of the structures of this invention which cannot be achieved with the conventional structures of polytetrafiuoroethylene, can further be profitably utilized for the manufacture of articles requiring such properties, such as felt and the like.

In order to afford a fuller understanding of this invention, there are provided preferred examples which are illustrative only and in which percent compositions and parts are all by weight.

Example I In an autoclave was placed a mixture of 0.13 gram of ammonium persulfate, 3.6 grams of ammonium perfluorooctanoate, and 36' grams of paraffin in 1200 cc. of water. There were then introduced 600 grams of tetrafluoroethylene, and the polymerization reaction was carried out at 60 C. under a pressure of 28 kg./cm.2, which pressure was maintained by continuous supply of tetrafiuoroethylene. When 600 grams of tetrafiuoroethylene were consumed, the reaction was suspended. To the resultant aqueous emulsion of a concentration of 33 percent of polytetrafiuoroethylene was added sodium dodecylbenzen sulfonate in the order of about 3 percent on the basis of the weight of the polymer.

A wood pulp containing about 95 percent of a-cellulose, on the other hand, was dipped for 2 hours in an aqueous solution containing 17.5 percent of caustic soda at 20 C., compressed to the order of a compression ratio of 2.5, pulverized, and immediately xanthated with 65 percent of carbon disulfide. The resultant xanthate was dissolved in dilute caustic soda, producing a viscose containing 4 percent of cellulose and 2 percent of caustic soda in total, and having a polymerization degree of 650.

With 1 part of the viscose thus prepared were mixed 2 parts of the polytetrafiuoroethylene emulsi-on as specified above. The mixture was then filtered, deaerated, and extruded at 75 C. through a spinnerent containing 20 holes of 0.2 millimeter diameter into a coagulating bath consisting of l percent of sulfuric acid, 20 percent of sodium sulfate, and 5 percent of zinc sulfate. The resultant filaments were washed with water, sintered in the air heated to 375 C. for 100 seconds, and stretched 4 times the original length at 320 C. The filament bundle thus obtained measured 1162 denier .and displayed a cavity formation ratio iof 85 percent, a tenacity of 1.2 grams per denier, and an elongation of 63 percent. An average empty space cavity of ythe resultant hollow filaments is 32.5 percent.

lExample 2 A wood pulp containing about 92 percent of cellulose was d-ipped at 20 C. in an aqueous solution containing 17 percent of caustic soda, compressed t-o the order of a compression ratio of 2.4, pulverized, raged at 30 C. for 48 hours, and xanthated with carbon disulfide added in the order of `60 percent on the basis of the weight of the tva-cellulose. The resultant xanthate was dissolved in alkali and aged at 25 C. for 40 hours, producing a viscose containing 8 percent of cellulose and 6 percent of caustic soda, and having a polymerization degree of 300 and a :salt value `of 6.

The polytet'rauoroethylene emulsion of Example 1 was condensed to the order of concentration of 60 percent polymer, and 1 par-t of the resultant icondensed emulsion was mixed with 1 pant of the viscose as prepared in the abo've specified manner. The mixture was filtered, `deaerated, and extruded at 75 C. through a spinneret having 20 holes of 0.3 millimeter diameter into a coagulating bath containing percent of sulfuric acid. The resultant filaments were washed with walter, sintered in air heated to 380 C. for 80 seconds, and `stretched 4 times the original length. The filament bundle thus Iobtained measured 254 denier and displayed a cavity formation rate of 98 percent, a tenacity of 1.41 grams per denier, and an elongation of 40 percent.

Example 3 A mixture of 2 parts of the polytetrafiuoroethylene emulsion of Example 2 and 3 parts of the viscose of Example 1 was filtered, deaerated, an-d extruded at 50 C. through a spinneret containing 20 holes of 0.-1 millimeter diameter linto a setting medium consisting of 10 percent of hydrochloric acid. The resultant filaments were washed with water and heated at 370 C. for 100 seconds and stretched 5 times the original length at 340 C. The filament bundle thus obtained displayed a cavity formation rate lof 98 percent.

Example 4 The spinning mixture of Example 1 was extruded int-o a coagulating `bath containing 4 percent of nitric acid and 6 percent of sodium nitrate at 80 C., and the resultant filament were treated under the same conditions as employed in Example 1, producing a filament bundle displaying a cavity formation rate of '100 percent. An average emp-ty space cavity of the resultant 'hollow filaments lwas `43.0 percent.

Example 5 A spinning mixture was prepared by adm-ixing 1 part of a 30 percent aqueous ldispersion of 4:1 molar copolymer of tetrafiuoroethylene and hexafiuoropropylene with 1 part yof viscose ldescribed in Example 1, and the mixture was extruded at 60 C. into .a coagulating bath cont-aining 20 percent of nitric acid. The resultant filaments were washed with water and s'intered in the air heated fto 350 C. for 40 seconds, producing a -lament bundle having a cavity formation rate of 96 percent.

In view of the foregoing, it will be apparent to those who are skilled in the art that there may be made various changes and modifications in the invention without departing from the scope and spirit of the same. It is accordingly requested that the invention be interpreted rather broadly and not limited to the specific embodiments of the same except as defined in the appended claims.

We claim:

1. A hollow filament consisting of a tetrauoroethylene polymer layer and an empty space cavity within, said empty space cavity comprising from 5 to 90 percent in terms of secshxw0 References Cited UNITED STATES PATENTS 2,772,444 12/ 1956 Burrows et al. 264--127 2,855,321 10/1958 Bachlott 264-188 X 3,194,861 7/1965 Bley 264-191 X ROBERT F. WHITE, Primary Examiner.

T. J. `CARVIS, Assistant Examiner.