US3536804A - Process for producing polyxyleneadipamide fibers - Google Patents

Description

Oct. 27, 1970 NORIHIDE FUJIMOTO ET AL 3,536,804

rnocmss FOR PRODUCING POLYXYLENEADIPAMIDE FIBERS Filed Dec. 17, 1968 2 Sheets-Sheet 1 BREAKINQSTRENGTH O l I BIREFRINGENCE (An) OF UNSTRETCHED FILAMENT FIG] ENVENTORS NORIHIDE FUJIMOTO YOICHI KAWAGUCHI KENZI SUZUKI KANJI NSHIDA MASAYOSHI SHIMADA HIDEO IKEDA TAKASH! KOBAYASH! KENICHI KOMOTO ATTORNEYS Oct. 27, 1970 NORIHIDE FUJIMOTO ET AL 3,536,804

r PROCESS FOR PRODUCING POLYXYLENEADIPAMIDE FIBERS Filed Dec. 17, 1968 2 Sheets-Sheet 2 ll I H TRANSMISSION I I WAVELENGTH (In u) 660 800 FIG.3

INVENTORS NORIHIDE FUJIMOTO YOICHI KAWAGUCHI KENJ] SUZUKI KANJI KISHIDA MASAYOSHI SHIMADA HIDEO IKEDA TAKASHI KOBAYASHI KEN ICHI KOMOTO ATTORNEYS United States Patent 3,536,804 PROCESS FOR PRODUCING POLYXYLENE- ADIPAMIDE FIBERS Norihide Fuiimoto, Takatsuki, Yoichi Kawaguehi, Tsuruga, Kenji Suzuki, Ootsu, Kanji Kishida, Takatsuki, and Masayoshi Shirnada, Hideo Ikeda, Takashi Kobayashi, and Kenichi Komoto, Ootsu, Japan, assignors to Toyo Boseki Kabushiki Kaisha, Osaka, Japan Filed Dec. 17, 1968, Ser. No. 784,329 Claims priority, application Japan, Dec. 19, 1967, 42/ 81,735 Int. Cl. D0141 /12 US. Cl. 264-210 7 Claims ABSTRACT OF THE DISCLOSURE A process for producing polyxylyleneadipamide fibers which comprises melt extruding a molten polymer of adipic acid and a xylylenediamine selected from the group consisting of meta-xylylene-diamine and a diamine mixture of meta-xylylenediamine with less than 30 mol percent of para-xylylenediamine, said polymer containing at least one hydroxyl compound selected from the group consisting of water and non-volatile alcohols in an amount of 0.050.7 mol per kg. of the polymer, through spinning orifices, quenching the extruded filaments to form unstretched filaments, stretching the unstretched filaments at 70 to 90 C. while maintaining a water content in the unstretched filaments of less than 4%, said unstretched filaments having a birefringence value (An) satisfying the formula wherein X is the molar percentage of para-xylylenediamine in the diamine mixture.

This invention relates to a process for producing polyxylyleneadipamide fibers.

The term "polyxylyleneadipamide as used in this specification and claims refers to an aromatic polyamide which consists substantially of a condensation polymer of metaxylylene diamine or a meta/para-mixed xylylenediamine containing less than 30% paraxylylene diamine and adipic acid and which has a relative viscosity 'n (as measured at 25 C. in respect of a solution of l g. polymer dissolved in 100 ml. of 96% H 80 of 1.70 to 3.60.

The polyxylyleneadipamide is a known polymer and fibers formed therefrom are known in the art as MXD6 fibers. However, it is well known that the thermal stability of the polyxylyleneadipamide at molten state is relatively low as compared with other typical polyamides such as nylon-6 and nylon-66, so that MXD6 fibers have not yet been produced commercially.

Therefore, an object of this invention is to overcome the problem of thermal degradation of polyxylyleneadipamides in molten state, thereby enabling successful meltspinning thereof.

Another object of the present invention is to provide MXD6 fibers excellent in the uniformity by overcoming the problem to be caused by thermal degradation of the polymer in the melt spinning process and controlling the spinning temperature and quenching blow.

Another object of the invention is to obtain excellent MXD6 fibers high in the novelty and whiteness and having no knob by melt-spinning the polymer in the presence of a small amount of a hydroxy compound.

Still another object of the invention is to overcome difiicuty in stretching MXD-6 fibers.

A further object of the invention is to obtain MXD6 fibers having a mechanical strength of more than 5 g./d. and are excellent in various textile uses.

The invention will be explained in detail by partly referring to the accompanying drawings wherein:

FIG. 1 is a graph showing the relation between birefringence and breaking strength of unstretched MXD6 filaments,

FIG. 2 is a graph showing the whiteness of polyxylyleneadipamides in relation to the value r (to be defined hereinafter) and relative viscosity of the polymer, and

FIG. 3 is a graph showing a contour line of whiteness in relation to the transmission (percent) of a polymer solution and wavelength (m of transmitted light.

Polyxylyleneadipamides (referred to as MXD6 polymers) were first disclosed by G. Funston et al. in 1953 (US. Pat. No. 2,766,221) and thereafter various improvements of the production of the polymers and also the production of fibers thereof (MXD6 fibers) have been proposed (U.S. Pats. Nos. 2,987,506, 2,997,463, 3,200,183, etc.). However, since the polymers are relatively low in thermal stability and are difficult to handle, particularly to form into satisfactory fibers, the MXD-6 fibers have not yet been produced commercially.

We have found that, in order to obtain excellent MXD6 fibers, it is very important to select a proper birefringence for filaments which have been melt-spun and cooled but which have not yet been stretched (hereinafter referred to as unstretched filaments).

As is known, an MXD6 polymer is melted and extruded through spinning orifices to form filaments. 'Ihe extruded hot filaments are cooled to solidify to form unstretched filaments. The unstretched filaments are then stretched for molecular orientation to improve the mechanical properties of the filaments. Usually the unstretched filament is stretched through one or two stretching steps on heated pins and/ or heated plate. However, the strength and strength unevenness of the resulting stretched filament are proportional to those in the original unstretched filament. From this fact, it has been found that, if the strength and strength unevenness of the unstretched filament are properly controlled, there are obtained a stretched filament of any desired strength and strength unevenness.

We have also found by experiments that the strength of an unstretched filament is correlated with its birefringence as shown in FIG. 1. The relation between the birefringence and breaking strength of an unstretched MXD6 filament varies depending on the particular mol percentage X (percent) of paraxylylenediamine in the xylylenediamine material constituting the polymer. The curves A, B and C represent respectively the cases wherein X is 0, l5 and 27%. As clear from FIG. 1, irrespective of X, the breaking strength becomes maximum when the birefringence (An) of the unstretched filament is about 4X10 and is decreased substantially uniformly as the birefringence reduces. Further, as the birefringence (An increases, the breaking strength is also decreased. In this case, the larger the value of X, the larger the amount of the decrease in the breaking strength. That is to say, above a fixed level (e.g. line H in FIG. 1) of breaking strength, the larger the value X, the smaller the range of the birefringence of the unstretched filament. In order to obtain satisfactorily strong and practical MXD-6 fibers, the breaking strength of the unstretched filaments should be more than 4 g./d. Thus it has been found that the birefringence (An) of unstretched filaments should satisfy the following formula:

The breaking strength (g./d.) of the unstretched filament is determined at a drawing (or stretching) rate of 500% per minute in an atmosphere of a temperature of 20 C. and humidity of 50%.

The birefringence (An) of the unstretched filament represents the degree of molecular orientation and varies depending upon the viscosity of the polymer (i.e. the polymerization degree or average molecular weight of the polymer), the spinning temperature and the draft rate at the time of spinning of the molten polymer. As a result of various experiments and observations on these relations, we have derived the following empirical formula:

An=[0.085 X Q wherein An is birefringence of unstretched filament, V is a spinning take-up velocity ,(m./min.), Q is rate of extrusion of the polymer melt (g./mm. /min.), Mn is average molecular weight of the polymer and T is spinning temperature C.). This formula has been obtained when the average molecular weight Mn is 15,000 to 30,000 and the V/ Q is 12 to 120. Usually Mn is well within the above range and V/ Q which would determine the denier of the unstretched filament is also well within the above range. Therefore, the above Formula 1 indicates that the birefringence (An) is held in any desired range by adjusting the spinning temperature T. As shown in this formula, the higher the spinning temperature T, the lower the An. If this is taken into consideration, it will be understood that if the spinning temperature becomes high to degradate the polymer, so that, as shown in FIG. 1, when the An becomes very small, irrespective of X, the breaking strength will be uniformly lowered as described above. Further, in order to make An larger, T may be made smaller. However, as shown in FIG. 1, the rate of decrease in the breaking strength with the increase in An varies depending on X. In case X is small, the upper limit of An may be large and, this means that the spinning temperature T may be low. On the other hand, in case X is large, T must be made high.

The melting point of a crystalline polymer is the temperature at which the crystal melts completely. At the melting point, the polymer is in perfectly liquid state. However, the temperature of the molten polymer in the actual spinning operation is made higher than the melting point. This is because, when the molten polymer is extruded for spinning at the melting point or a temperature slightly higher than the melting point, the viscosity will be so high that the thickness (denier) of the spun filament will be uneven and consequently the strength will be uneven. The temperature to be made higher than the melting point in order to reduce this unevenness or, in other words, the lower limit of the spinning temperature is determined by the degree of the occurrence of unevenness in the fiber. The results of measuring the Unevenness of the Unevenness of An diameter T(O.) (CV percent) (CV percent) We have found that when the spinning temperature is 270 C., the unevennesses of the An and diameter are large. Further, we have also found, through investigation in detail about the unevenness of the monofilament at temperatures between 270 and 280 C., that, below about 275 C., the unevenness increases remarkably. As a result of measuring, in the same manner as mentioned above, the An and diameter in respect of various polymers with various X values, it has been found that, when X :0, the spinning temperature must not be below 265 C., that the lower limit of the spinning temperature must be high as X increases and that their relation should be as follows when X is less than 30%:

Thus, when X is less than 30 mol percent, in order to keep the birefringence of an unstretched filament and its unevenness in a desired range, the spinning temperature T C.) must be kept as follows:

However, as described later, in case the molten polymer is spun in the presence of a small amount of a hydroxyl compound, the spinning temperature may be somewhat lowered.

The filaments freshly extruded through spinning orifices are quenched or cooled usually with an air stream. The smaller the difference between the temperature of the molten polymer as extruded through the spinning orifices and the temperature at which it is solidified, or in other words, the smaller the difference between the spinning temperature and the melting point of the polymer, the quicker the solidification of the filaments. Therefore, the higher the velocity of the cooling air stream for quenching the molten or semi-solidified filaments, the higher the likelihood of the occurrence of the unevenness in the coagulated monofilaments. .As described above, the upper limit of the spinning temperature is restricted and its difference from the melting point of the polymer is not so large as in the case of nylon-6. Therefore, the unevenness in the unstretched filament is more likely to occur. In order to reduce such unevenness, the blow velocity of the cooling air stream is an important factor. For example, an MXD6 polymer (average molecular weight 20,000, X=27%) was spun at a spinning temperature of 280 C. through a spinnerette of 24 orifices of a diameter of 0.25 mm. at a melt-extruding rate of 14.5 g./min. and a take-up speed of 600 m./min. In this case the velocity of the cooling air stream (20 C.) was varied and the unevennesses in An and the diameter of the monofilament obtained were measured. The results were as follows:

Uncvenness oi As a result of further and more detailed investigations in this respect, it has been found that, when the velocity of the cooling air stream is-higher than 1.0 m./sec., the unevenness will sharply increase. Therefore, the velocity of the cooling air blow must be less than 1.0 m./sec. in order to obtain MXD-6 fibers of a high quality having little unevenness.

The above mentioned spinning conditions (i.e. birefringence of unstretched filaments, spinning temperature, velocity of cooling air stream) are most important in this invention. However, in order to obtain more excellent MXD-6 fibers, it is further advisable to employ a high grade polymer prepared under special cares.

Thus, it has been found to be preferable to employ an MXD-6 polymer satisfying the following Formulas 2 and 3:

wherein 'r is a relative viscosity as measured at 25 C. in respect of a solution of a polymer (1 g.) dissolved in 100 ml. of 96% sulfuric acid, and r is a ratio of the mol number of nylon salt components (as used in the preparation of said polymer) to the sum of the numbers of mols of said nylon salt components and the viscosity stabilizer:

M01 number of nylon salt components Mol number of M01 number of nylon salt viscosity components stabilizer indicates that, as the value r approaches 1 (where no stabilizer is used), n can be taken in a Wider range. When r is 1, desirable polymers are those having 1 of 1.7 to 3.6. On the other hand, when r becomes smaller, the range of n that can be taken to obtain desirable polymers will become narrower, and unless r is larger than 0.95, the left side g1] of the Formula 2 cannot be satisfied.

We have further investigated about the relation of the relative viscosity (1 and the amount of the terminal groups of MXD-6 polymers and have found that when the extent of the polymerization reaction is kept substantially 098820.03, a polymer approximately "satisfying the Formula 2 can be obtained.

It has further been found that, in order to obtain a satisfactory polymer by controlling such 1 or extent of reaction, a process wherein the condensation polymerization is completed by heating the reaction mixture under a high vacuum (as conventionally adopted in the polymerization of nylon-66, polyesters or the like) must be avoided. For example, the desired control can not be effected with the conventional procedures for preparing MXD-6 polymers such as mentioned in the working examples given in US. Pats. Nos. 2,766,221 and 2,997,463.

'We have found that the desired control can be eifected by a process wherein the polycondensation reaction is conducted in the presence of steam or water vapour in contact with the molten polymer. In this case the pressure may be atmospheric, slightly above or below the atmospheric pressure. By doing this, the extent of the polycondensation reaction may be controlled almost theoretically from the water equilibrium curve between the vapor phase and molten polymer in the reaction apparatus and from the kinetics of the polycondensation rate with reverse reaction [6. V. Schulz: Z. Physik. Chem., A182, 127 (1938)].

For example, an aqueous solution of xylylenediammonium adipate salt was changed to an autoclave. Water was gradually discharged while keeping internal pressure under 4 to 10 kg./cm. at to C. When pressure rise ceased, the autoclave was sealed, and the temperature was elevated to 260 to 280 C. and the reaction was completed under an internal gauge pressure of 20 to 0 kg./cm. The molecular weight of the resulting MXD6 polymer =1.70) was approximately 10,000. This is the polymer of the lowest molecular weight which can be satisfactorily formed into filaments in this invention.

In order to regulate the value r and nreL (that is substantially the extent of the reaction) irrespective of the absolute value of are it is most important to keep a substantial equilibrium amount of water present in the molten polymer.

If the polymerization reaction is proceeded until the extent of the reaction becomes higher than 0.992, side reactions of complicated characters would easily occur in the molten polymer, causing gel formation and/or discoloration of the polymer. Such sid'e reaction is related also with the melt viscosity of the molten polymer. Thus, particularly at a high melt viscosity, a local side reaction will be more likely to occur. Therefore, even if the 7 is made to approach LII-1.0521 10.984r

above r=1 to 0.997 there may be possibility that the whiteness of the polymer becomes 0.7 to 0.65.

In this connection FIG. 3 is a graph showing a contour line of whiteness of polymer in relation with n and r. The whiteness is determined by the Formula 3 and is used to evaluate the color of the polymer itself. It is needless to say that, in case an additive such as a pigment has been added to the polymer, the color of the polymer itself should be evaluated after separating such additive.

In FIG. 2, the polymers belonging to the ranges A and B are suitable ones in this invention and the boundary line between the ranges B and C represents the empirical Formula 2. The range A represents polymers with a whiteness 0.72. The range B represents polymers with a whiteness of 0.72 to 0.65, while range C represents polymers with a whiteness of 0.65 to 0.40.

Therefore, in order to improve the whiteness of the polymer in the range B to be of a whiteness 0.7, it is necessary to add a whitening agent. It has been found that this improvement in whiteness can be accomplished by adding 10 to 1000 ppm. of a hypophosphorous acid radical (H PO If desired, hypophosphorous acids may also be added to polymers with a whiteness 50.7 to further improve the whiteness thereof.

It is surprising that many other similar compounds such as phosphoric acids and phosphorous acids are not so effective as compared with hypophosphorous acids. I

The hypophosphorus acid compounds which may be used in this invention for the above purpose are hypophosphorous acid (H PO and hypophosphorous acid metal salts, for example sodium, potassium, calcium, zinc, aluminum, manganese and cobalt salts. The proper amount of the hypophosphorous compound to be contained in the polymer is 10 to 1000 ppm. (as hypophosphorous acid radical).

It is preferable to add the hypophosphorous compound before or during the polycondensation stage in order to prevent discoloration of the polymer during the reaction and to assume uniform distribution. However, it may also 'be possible to add the hydrophosphorous compound at the time of melting the polymer prior to shaping.

For reference, the whiteness or colors of polymer distinguished with the naked eye are as follows.

As distinguished Whiteness (Ts/ T100): with the naked eye 0.7 Colorless. 0.700.65 Veryslightlyyellow. 0.65-0.60 Slightly yellow. 0.60 Yellow.

As will be apparent from the foregoing explanation, it is preferable that a substantial equilibrium amount of Water at least at the melting temperature of the polymer should be present in the polymer. Such polymer is remelted as such or as chips for shaping operation, which, therefore, is conducted under the coexistence with water. However, when the water in the polymer exceeds a certain amount (e.g. 0.5 mol/kg. polymer), the development bubbles in the polymer melt or in the filaments extruded through spinning orifices becomes non-neglisible. It has been found that such difiiculty can be overcome by replacing at least part of the water with a nonvolatile hydroxyl compound(s). Amines cannot be used because they prevent the gel formation but do not prevent the discoloration. It is preferable that the hydroxyl compound the present in the polymer in an amount of 0.05 to 0.7 mol/ kg. of the polymer at the spinning temperature.

Examples of the hydroxy compounds are aliphatic alcohols such as propyl alcohol, butyl alcohol, octyl alcohol, ethylene glycol, glycerin, pentaerythritol, neopentyl glycol, pyrogallol and cyclohexyl alcohol; saccharides such as glucose and cellobiose and their mixtures. It is convenient to add these compounds as a carrier for antioxidants and pigments.

The concentration of the hydroxyl compound to be present in the polymer at the time of melt-spinning should be such as not to greatly vary the polycondensation equilibrium at the spinning temperature. The equilibrium constant at the spinning temperature of MXD-6 polymers is to 8 X Thus the hydroxyl compound concentration should correspond to the water concentration which would keep a substantial equilibrium With the polymer satisfying the Formula 1. The water or hydroxyl compound concentration to keep an equilibrium with the polymer varies somewhat depending on the equilibrium constant, 1 and the particular viscosity stabilizer (particularly whether monofunctional or bifunctional). However, usually, the amount of 0.050.7 mol per kg. of polymer would be suflicient to prevent the gel formation.

For example, in the case of spinning a polymer of Wm of about 2.0 at 275 (3., the water concentration keeping the above mentioned equilibrium will be 0.14 mol/kg. of the polymer.

Except the above mentioned conditions, the MXD-6 polymer can be extruded through orifices and cooled to form unstretched filaments in a conventional manner.

The unstretched filament is then stretched 3 to 5 times the length at 70 to 90 C., while the water content is kept less than 4%, preferably about 3%. If desired, the stretched filaments are heat set in a conventional manner. When the Water con-tent in the filaments exceeds 4%, undesirable superdrawing phenomenon Will often occur. When the moisture absorption further increases, the filament will crystallize and will become diflicult to stretch. The thermal stretch and thermal setting may be conducted in a manner known per se (e.g. US. Pat. No. 3,200,183).

The quality of the polymer and performance of meltspinning may be evaluated with the number of knobs in the stretched fiber and also with easiness of stretching. Most important factor is the absolute amount of the degradated polymer contained in the fiber. This can be evaluated also with theamount of the insoluble polymer when the fiber is dissolved in formic acid. The relative measure can be made by measuring the intensity of fluorescence of the polymer solution (in formic acid) at the incident light of 3650 A.

As described herein before, the portion insoluble in formic acid is a gelled polymer produced when a secondary or side reaction has occurred to some extent. Further, even in polymer soluble in formic acid, fluorescence is emitted when there has occurred a side reaction. The fluorescence is believed to be caused by the presence of heterogeneous double bonds formed by the side reaction. It has been found that the polymer or its fiber made through the addition of the hypophosphorous compound is not only excellent in the whiteness but also weak in the fluorescent intensity, as compared with those not added with said compound. It is deemed therefore that the said compound has also an action of positively preventing the occurrence of secondary reaction.

The knob seen in the stretched fiber is a local unusually thick part of a diameter about 1.5 to 2 times the normal part of the fiber and a length of less than several mrn. Such knobs are known to develop in nylon-6 and other synthetic fibers but in an order of only 0 to 5 knobs per 10 111. However, in case of a polyxylyleneadipamide, there is a strong tendency that the gel formation occurs during the melt-spinning so that it has been usual that conventional MXD'6 fibers have knobs in an order of several hundred or several thousand knobs per 10 m. In order to prevent the knob formation, the presence and the amount of the hydroxyl compound in the molten state is very important as explained before. When properly selected polymer is used under the necessary cares in accordance with this invention, it is possible to produce MXD-6 fibers with the number of knobs less than 15 per 10 meters.

The invention will be further explained by referring to the following examples.

The final or thermally stretched polyxyleneadipamide fibers (MXD-6 fibers) of this invention have a strength of about 1-3 g./d. higher than that of unstretched filaments.

EXAMPLE 1 An MXD6 polymer of an average molecular weight of 21,000 obtained from a mixed pand m-xylylenediamine containing 15 mol percent paraxylylenediamine was melt-spun at a spinning temperature of 285 C. and a take-up velocity of 600 m./min. The rate of extrusion through the spinning orifices Was 14.5 g./mm. /min. The freshly extruded filaments were cooled with air of a velocity of 0.5 m./ sec. On the cooled filaments was deposited water in an amount of 2.5% by oiling. The unstretched filaments were then directly brought into contact with heated pins (at C.) and a hot plate (at 180 C.) to stretch the same 3.5 times the original length and finally taken up at a velocity of 2100 m./min. to obtain MXD-6 fibers. The properties of the unstretched filaments taken in the course of this step were as follows:

Birefringence 3.0 1O

Strength 397 g./d.

Deniers 22.5 d./24 filaments. Breaking strength 6.1 g./d.

The breaking strength of the stretched filaments was 7.0 g./ d. and the breaking elongation was 23 EXAMPLE 2.

A mixture of 35 parts of nylon salt (of meta-xylylenediamine and adipic acid), 0.2 mol percent (based on the nylon salt) of adipic acid (viscosity stabilizer) and 65 parts of water was charged into an autoclave. The temperature was elevated, and water was removed over about 2 hours while keeping the internal pressure under 4 kg./cm. at 140 C. and then the temperature was elevated to 260 C. The reaction was conducted for 1 hour while keeping the internal pressure under kg./cm. at the internal temperature of 260 C. Then the pressure was gradually decreased to atmospheric in 2 hours. Thereafter the polymer was discharged while feeding super-heated steam.

The properties of the resulting polymer were as follows:

= Concentration of terminal amino groups.

EXAMPLE 3 The properties of various polymers obtained by repeating substantially the same polymerizing operation by means of the autoclave used in Example 2 are shown as follows:

Extent [N112] oi Whlteness 10- mol/g. reaction mu (Ts/T100) The water in the aqueous solution of the nylon salt was removed. and then the pressure was gradually reduced to 2 mm. Hg in about 1.6 hours; Under this pressure the reactlon was conducted for 45 minutes.

It will be apparent from the above that the whiteness of the polymer is influenced by the extent of reaction rather than by the 1 value.

EXAMPLE 4 An aqueous solution consisting of 30 parts of metaxylylenediammonium adipate and 100 parts of water was charged into an autoclave. At the same time a phosphorus compound and 1 mol percent (based on the nylon salt) adipic acid (viscosity stabilizer) were added thereto. Then the temperature was gradually elevated to 180 C. to discharge water. Then the temperature was further elevated to 265 C. to drive out substantially all water. The pressure was gradually reduced to 100 mm. Hg under which pressure the heating was continued for 30 minutes to complete the polycondensation reaction. The resulting polyamide (MXD6 polymer) was discharged out of the bottom of the autoclave and was quenched in water bath and cut into chips in the usual manner. The intrinsic viscosity of the polymer was somewhat diiferent depending on the content of the phosphorus compound but was about 1.0 in general. The polymer chips were remelted in a nitrogen gas stream and were heated for 1 hour. The relations of the whitness and the kind and content of the phosphorus compound are summarized in the following table.

whiteness Content Chip after heat Phosphorus compound (p.p.m.) whiteness treated Mn(H POz)2. 0.80 0. 60 MI1(H2PO2)2.- 270 0. 81 0. 62 M11(HzP02)2- 540 0. 84 0. 70 NaHzPOz- 37 0. 77 0. 54 N aHzPOz 360 0. 87 0. 68 NaHzPO 720 0. 89 0. 77 NaHzP z 1, 450 0. 93 0. 84 Ca(H2PO2 33 0. 77 0. 52 Ca(HzPO2)z. 330 0. 88 0. 67 Ca(HgPO2)2 660 0. 88 0. 68 Ca(H2PO2)2 1, 320 0. 84 0. 71 N 0 addition 0. 60 0. 30

As clear from the above table, even if phosphoric acids and phosphorous acids are added, the whitness of the polymer is substantially the same as in the case Without additive, and the whiteness is greatly reduced when heated. In contrast thereto, when hypophosphorus acids are added, MXD-6 polymers with a whitness of more than 0.7 are obtained, and decrease in the whitness by heating is low; By the way, the contents of the various phosphorus compounds given in the above table are values calculated as phosphoric acid radical (H PO phosphorous -acid radical (H PO and hypophosphorous acid radical (H PO EXAMPLE 5 The water content in the chips of each of 5 kinds of polymers (X=0) shown in Table 1 was made 0.01 or 0.25% and the polymer was melt-spun under the following conditions:

Spinning temperature C 275 Take-up speed m./min 400 Blow air speed m./sec 0.5

The unstretched filaments were stretched 3.5 times the initial length on stretching pins heated to 80 C. The

properties of the filaments thus obtained are listed in Table 2.

* Viscosity stabilizer: adipic acid.

EXAMPLE 8 -Polymetaxylyleneadipamide (1 .=2.3) chips were melt-spun in the same manner as in Example 7 at 265 C. except that the water content was varied. The unstretched filaments were hot-stretched in the same manner as in Example 7. The properties of the stretched filaments are shown in the following table.

Water content in chips Whiteness (percent) 65 68 76 83 83 Gel content 25 13 0.5 0. 1 0. 1 Specific fluorescent intensity 0. 08 0. 0. 04 0. 02 0. 02 Number of yarn breakages (times/kg.) 28. 9 6. 8 0. 16 0. 05 0. 04

1 Impossible to spin due to foaming.

TABLE 2 Water Number of Number of Specific content yarn breakage/ knobs/ m. fluoresi kg. m in stretched Whiteness Gel content cent N o chips stretching filaments (percent) 1 (mg/kg.) 1 intensity 3 1 Measured by I IS L-1073 (ludd method) 2 Amount (mg) of the polymer insoluble in formic acid, in which 1 kg. of the stretched filaments is dissolved.

quinine sulfate dissolved in 1 liter of 0.1 N H2304.

It will be noted from Table 2 that the number of yarn breakages at the time of stretching and the number of knobs/1O m. in the resulting filaments have correlations with the gel content (and hence fluorescent intensity).

EXAMPLE 6 The polymers Nos. 2 and 5 in Example 5 were prepared in the same manner but adding sodium hypophosphite in such an amount that the hypophosphorous acid radical (H PO will be 100 p.p.m. based on the polymer. The whiteness (Ts/ T100) of the resulting polymers was 0.83 in No.2 and 0.70 in No. 5.

EXAMPLE 7 What We claim is:

1. A process for producing polyxylyleneadipamide fibers which comprises extruding a molten polymer of adipic acid and a xylylenediamine selected from the group consisting of meta-xylylenediamine and a diamine mixture of meta-xylylenediamine with less than 30 mols percent of para-Xylylenediamine, said polymer containing at least one hydroxyl compound selected from the group consisting of water and non-volatile alcohols in an amount of 0.05- 0.7 mol per kg. of the polymer, through spinning orifices, quenching the extruded filaments to form unstretched filaments, stretching the unstretched filaments 3 to 5 times their original length at to C. while maintaining a water content in the unstretched filaments of less than 4% said unstretched filaments having a birefringence value (An) satisfying the formula wherein X is the molar percentage of para-xylylenediamine in the diamine mixture.

2. The process as claimed in claim 1, wherein the molten polymer to be extruded contains at least one hypophosphorous compound selected from the group consisting of hypophosphorous acid and sodium, potassium,

Ethylene glycol (percent) 13 calcium, zinc, aluminum, manganese and cobalt salts thereof, in an amount of -1000 p.p.m. as hypophosphorous acid radical (H PO 3. The process as claimed in claim 1 wherein the birefringence (An) is controlled in accordance with the formula wherein V is the take-up velocity (m./min.) of the unstretched filaments, Q is the rate (g./mm. /min.) of extrusion of the molten polymer, V/Q is 12 to 120, Mn is the average molecular weight of the polymer and falls within the range 15,000-30,000, and T is as defined in claim 2.

4. The process as claimed in claim 1, wherein the polymer to be extruded has a relative viscosity satisfying the formula wherein n is the relative viscosity of the polymer as measured at 25 C. in respect to a solution of 1 g. of the polymer dissolved in 100 ml. of 96% sulfuric acid, and r is the mol ratio of the nylon salt components in the polymer, and is defined by the formula Mol number of nylon salt components M01 number of M01 number of nylon salt +viscosity components stabilizer 5. A process as claimed in claim 1 wherein the freshly extruded hot filaments are quenched with a cooling gas at a speed of at least 0.5 m./sec. but less than 1 m./sec.

6. A process as claimed in claim 4, wherein the polymer further satisfies the formula:

.TS/TIOOZOJO wherein Ts is the area below a transmission curve plotted against a wave length of 340-800 III/L as measured in a quartz cell of 10 mm. thickness in respect to a polyxyleneadipamide polymer solution having a concentration of 20 g./ ml. in formic acidsolvent, and T100 is the area above the transmission curve.

7. A process as claimed in claim 1 wherein the melt spinning temperature (T, C.) satisfies the formula wherein X is as defined in claim 1.

References Cited UNITED STATES PATENTS JULIUS FROME, Primary Examiner I. H. WOO, Assistant Examiner US. Cl. X.R. 26078; 264-211

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