Naphthalate polyester filaments, yarns or fibers consisting essentially of a naphthalate polyester which has an intrinsic viscosity of 0.3 to 3.5 and a softening point of at least 200.degree. C, and in which at least 85 mol% of the total recurring units consist of units of the formula ##STR1## wherein n is 4 or 6, and having at least one diffraction peak at a Bragg scattering angle 2.theta. = 16.3.degree. -- 16.7.degree. and/or 2.theta. = 25.3.degree. - 25.8.degree. in their X-ray diffraction. These filaments, yarns or fibers are useful especially as an electrically insulating material, an elastomeric reinforcing material, a fluid filter material, a paper-making canvas and a fastener component material. Of these, filaments, yarns or fibers of poly(tetramethylene 2,6-naphthalate) are prepared by melt-spinning the polymer thereby to form undrawn filaments having a birefringence of at lest 0.01 and a density of not more than 1.300, drawing the undrawn filaments in at least one step at a temperature of at least 60.degree. C. at a total draw ratio of at least 1.8, and then heat-treating the drawn filaments at a temperature higher than the temperature employed in the drawing step and within a range of 100.degree. to 240.degree. C. at constant length, under a restricted shrinkage of not more than 15%, or under a stretch of not more than 15%.

This invention relates to naphthalate polyester filaments, yarns or fibers 
having superior chemical stability. 
In recent years, filaments composed of poly(ethylene-2,6-naphthalate) have 
been proposed as new polyester fibers. The poly(ethylene-2,6-naphthalate) 
filaments have superior mechanical characteristics and thermal stability, 
but their chemical characteristics are not entirely satisfactory. In 
particular, their use in areas requiring chemical stability, for example, 
anti-oxidation, wet heat resistance, or chemical resistance, has been 
limited. 
Accordingly, it is an object of this invention to provide naphthalate 
polyester filaments, yarns or fibers having superior chemical properties 
along with superior mechanical properties and thermal stability. 
The above object of this invention can be achieved in accordance with this 
invention by naphthalate polyester filaments, yarns or fibers consisting 
essentially of a naphthalate polyester which has an intrinsic viscosity of 
0.3 to 3.5 and a softening point of at least 200.degree. C. and in which 
at least 89 mol% of the total recurring units consist of units of the 
following formula 
##STR2## 
wherein n is 4 or 6, and having at least one diffraction peak at a Bragg 
Scattering angle 2.theta. = 16.3.degree. - 16.7.degree., and/or 2.theta. = 
25.3.degree. - 25.8.degree. in their X-ray diffraction. 
The naphthalate polyester used in this invention contains 
tetramethylene-2,6-naphthalate or hexamethylene-2,6-naphthalate units in a 
proportion of at least 85 mol% of the total recurring units of the 
polymer. 
The naphthalate polyester used in this invention is generally prepared by 
reacting naphthalene-2,6-dicarboxylic acid and/or its functional 
derivative with tetramethylene glycol or hexamethylene glycol and/or a 
functional derivative thereof under suitable conditions. In this reaction, 
at least one suitable third component can be added in an amount of not 
more than 15 mol% before completion of the polymerization, thereby to mix 
or copolymerize it with the naphthalate polymer. 
Suitable third components include, for example, dicarboxylic acids such as 
terephthalic acid, isophthalic acid, 2-methylterephthalic acid, 
4-methylisophthalic acid, dichloroterephthalic acid, dibromoterephthalic 
acid, 5-sodiumsulfoisophthalic acid, naphthalate-2,7-dicarboxylic acid, 
diphenyldicarboxylic acid, diphenyl ether dicarboxylic acid, 
diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid or 
sebacic acid, hydroxy acids such as p-.beta.-hydroxyethoxybenzoic acid, 
functional derivatives of these acids, dihydroxy compounds such as 
ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, 
hexamethylene glycol (tetramethylene glycol when the glycol component is 
hexamethylene glycol), decamethylene glycol, neopentylene glycol, 
cyclohexanedimethylol, hydroquinone, bis(.beta.-hydroxyethoxy)benzene, 
bisphenol A, bis(p-hydroxyphenyl)sulfone, bis (p-.beta.-hydroxyethoxy 
phenyl)sulfone, polyoxyethylene glycol, polyoxypropylene glycol, or 
polyoxytetramethylene glycol, or functional derivatives of these dihydroxy 
compounds. A compound having at least three ester-forming functional 
groups, such as glycerine, pentaerythritol, trimethylol propane, 
trimellitic acid, trimesic acid or pyromellitic acid, can also be 
incorporated in such quantities as will maintain the polymer substantially 
linear (that is to say, as will not cause cross-linkage). A monofunctional 
compound such as benzoic acid or naphthoic acid can also be incorporated 
in order, for example, to adjust the degree of polymerization of the 
polymer. 
The naphthalate polyester used in this invention may also contain a 
delusterant such as titanium dioxide, a stabilizer such as phosphoric 
acid, phosphorous acid, phosphonic acid or an ester of any of these, an 
ultraviolet absorbent such as a benzophenone derivative or benzotriazole 
derivative, an anti-oxidant, a lubricant, a pigment or a filler. As the 
filler, other polymers such as polyethylene terephthalate, 
poly(ethylene-2,6-naphthalate), polytetramethylene terephthalate can also 
be used. 
The naphthalate polyester filaments, yarns, or fibers of this invention are 
composed of naphthalate polyesters of relatively high molecular weights, 
that is, naphthalate polyesters having an intrinsic viscosity of 0.3 to 
3.5, preferably 0.35 to 2.0, and a softening point of at least 200.degree. 
C. 
The "intrinsic viscosity", as used in the present application, can be a 
measure of the degree of polymerization of the polymer, and is a value 
measured on an o-chlorophenol solution of the polymer at 35.degree. C. 
If the intrinsic viscosity of the polyester constituting the filaments, 
yarns or fibers of this invention is lower than 0.3, the physical 
properties of the product are deteriorated, and if it is in excess of 3.5, 
the polymer is difficult to spin. 
The "softening point", as used in the present application, is measured as 
follows: The polymer is heat-treated at 100.degree. C. for 1 hour, and 
then set in a penetrometer having a plunger with a diameter of 3 mm and a 
weight of 10.0 g. The temperature is raised at a rate of 6.degree. C./5 
minutes from 140.degree. C., and the temperature at which the plunger has 
penetrated over the distance of 0.5 mm is defined as the softening point 
of the polymer. 
If the softening point of the polymer is lower than 200.degree. C., the 
thermal stability of the filaments is reduced, and the service temperature 
of the filaments is lowered. 
The filaments of this invention range from those having a monofilament 
denier of less than 100 to bristles having a monofilament denier of more 
than 100. 
The shape of the cross-section of the filament of this invention is not 
only a circular shape, but also a non-circular shape such as a triangular, 
cross or trilobal shape. The filaments may also be hollow filaments. 
The filaments, yarns or fibers of this invention have a specific 
crystalline structure characterized by the fact that in a diffraction 
intensity distribution curve in the equatorial direction as determined by 
an X-ray diffraction analysis, they have at least one diffraction peak at 
a Bragg Scattering angle 2.theta. = 16.3.degree. to 16.7.degree. and/or 
2.theta. = 25.3.degree. to 25.8.degree.. The above Bragg Scattering angle 
(2.theta.) is essentially 16.7 and/or 25.6.degree., but for various 
reasons such as influences from a crystal modification having a peak in 
the vicinity of the peak at 2.theta., it may fluctuate between 
16.3.degree. and 16.7.degree., and also between 25.3.degree. and 
25.8.degree., as stated above. 
Before the present invention, British Pat. No. 987,013 proposed 
polytetramethylene naphthalate fibers, but these prior art naphthalate 
fibers are essentially different from the polytetramethylene naphthalate 
filaments, yarns or fibers of this invention in that the X-ray diffraction 
intensity distribution curve does not have a peak at a Bragg Scattering 
angle 2.theta. = 16.3.degree. - 16.7.degree. or 2.theta. = 25.3.degree. - 
25.8.degree.. 
The accompanying drawings are graphic representations showing the 
diffraction intensity distribution curves in the equatorial direction of 
various poly(tetramethylene 2,6-naphthalate) filaments as determined by an 
X-ray diffraction analysis. 
The X-ray diffraction analysis in this invention was performed using an 
apparatus (D-9C, the product of Rigaku Denki Kabushiki Kaisha) under the 
following conditions. 
35 KV, 20 mA, nickel filter 
Divergence slit diameter: 0.15 mm 
Scattering slit: 1.degree. 
Receiving slit 0.4 mm, 
.lambda. = 1.542 A 
FIG. 1 illustrates the diffraction intensity distribution curves of the 
tetramethylene naphthalate polyester filaments of this invention, the 
curves 1, 2 and 3 referring to the filaments obtained in the Examples to 
be given later; 
FIG. 2 illustrates the diffraction intensity distribution curve of the 
poly(tetramethylene-2,6-naphthalate) filaments obtained by the method 
disclosed in British Pat. No. 987,013; and FIG. 3 illustrates the X-ray 
diffraction intensity distribution curve (curve 6) of the hexamethylene 
naphthalate polyester filament of this invention. 
As is clear from curve 1 in FIG. 1, the naphthalate polyester filaments of 
this invention have diffraction peaks at the following three points: 
2.theta. = 16.7.degree., 2.theta. = 23.0.degree., and 2.theta. = 
25.6.degree., and slight shoulders are observed at 2.theta. = 24.1.degree. 
and 2.theta. = 15.3.degree.. Curve 2 shows that the filaments have 
diffraction peaks at the following four points: 2.theta. = 15.3.degree., 
2.theta. = 16.7.degree., 2.theta. = 24.1.degree., and 2.theta. = 
25.6.degree., and at 2.theta. = 23.0.degree., a shoulder is observed. 
Curve 3 shows that the filaments have diffraction peaks at the following 
two points: 2.theta. = 16.3.degree. - 16.7.degree., and 2.theta. = 
25.3.degree. to 25.8.degree.. It can thus be seen that all of the 
filaments have a diffraction peak in at least one of the ranges of 
2.theta. = 16.3.degree. to 16.7.degree., and 2.theta. = 25.3.degree. to 
25.8.degree.. 
On the other hand, as shown in FIG. 2, the naphthalate polyester filaments 
produced by the method disclosed in British Pat. No. 987,013 have 
diffraction peaks only at the two points: 2.theta. = 15.3.degree. and 
2.theta. = 24.1.degree., and have no diffraction peaks at 2.theta. = 
16.3.degree. to 16.7.degree., and 2.theta. = 25.3.degree. to 25.8.degree.. 
As shown in curve 6 of FIG. 3, hexamethylene naphthalate polyester 
filaments have diffraction peaks at 2.theta. = 16.6.degree. and 2.theta. = 
24.4.degree.. 
Owing to the novel crystal structure as mentioned above, the naphthalate 
polyester filaments, yarns or fibers of this invention have higher Young's 
modulus and more superior properties endurable for use at high 
temperatures for prolonged periods of time than the prior art naphthalate 
polyester filaments, for example, those described in British Pat. No. 
987,013, while retaining sufficient tenacity and break elongation. For 
example, tetramethylene naphthalate polyester filaments, yarns or fibers 
having a monofilament denier of less than 100 have a tenacity of at least 
4.5 g/de, preferably 4.8 to 8.0 g/d and a Young's modulus of at least 900 
Kg/mm.sup.2, preferably 1000 to 1500 Kg/mm.sup.2 which are about 50% 
higher than those of the prior art. Furthermore, these fibers have a 
tenacity retention of at least 50% after treatment for 96 hours at 
200.degree. C, and have superior chemical resistance and resistance to 
hydrolysis. Accordingly, these fibers are suitable for use as electrically 
insulating materials of class F, conveyor belt materials or reinforcing 
materials such as tire cords used at high temperatures, or filters for the 
chemical industry. 
Bristlelike tetramethylene naphthalate polyester filaments of this 
invention having a monofilament denier of at least 100 have a tensile 
strength at break of at least 2.5 g/d, preferably at least 2.8 g/d, and a 
period of at least 10 days is required until the tensile strength at 
breakage of the filaments decreases to below 1.0 g/d in water kept at 
120.degree. C. This is superior to the conventional polyester bristlelike 
monofilaments composed of polyethylene terephthalate which decrease in 
their tensile strength at breakage to below 1.0 g/d in 200 hours at the 
longest. 
The bristlelike tetramethylene naphthalate polyester filaments of this 
invention have good chemical resistance, resistance to hydrolysis, 
resistance to wet heat and resistance to oxidation. When these bristlelike 
filaments are allowed to stand in pure water kept at 120.degree. C., the 
time required until their tensile strength at breakage decreases to 1.0 
g/d is at least 10 days, preferably at least 300 hours. These filaments 
also have a tenacity retention of at least 90% after having been allowed 
to stand for 2 weeks in the air kept at 170.degree. C. (the conventional 
bristlelike polyethylene terephthalate monofilaments have a tenacity 
retention of less than 90%), and a tenacity retention of at least 80% 
after having been treated with a 20% aqueous solution of sodium hydroxide 
at 80.degree. C. for 24 hours (the conventional bristlelike polyethylene 
terephthalate monofilaments have a tenacity retention of 40% at most), and 
also have a shrinkage in boiling water of not more than 2.0%, preferably 
not more than 1.5%. Thus, the bristlelike naphthalate polyester filaments 
of this invention have superior resistance to wet heat, resistance to 
oxidation, and resistance to alkali hydrolysis. Accordingly, the 
bristle-like filaments of this invention are suitable for use as a dryer 
canves in a paper-making process, chemical filter nets, materials of 
brushes for chemical cleaning materials and reinforcing materials for 
belts for transporting goods or for power transmission, cable cords, 
reinforcing materials for blade hoses, or fastener component materials. 
The tetramethylene naphthalate polyester filaments (including bristlelike 
monofilaments), yarns and fibers of this invention can also be used in 
combination with other filaments, yarns or fibers (for example, 
polyethylene terephthalate filaments, yarns or fibers, or nylon filaments, 
yarns or fibers). 
The tetramethylene naphthalate polyester filaments, yarns or fibers of this 
invention as described above can be produced by meltspinning a naphthalate 
polyester containing at least 85 mol% of tetramethylene-2,6-naphthalate 
units and having an intrinsic viscosity of 0.3 to 3.5 and a softening 
point of at least 200.degree. C. to form undrawn filaments having a 
birefringence of at least 0.01 and a density of not more than 1.300, 
drawing the filaments at a temperature of at least 60.degree. C., 
preferably 75 to 220.degree. C. at a total draw ratio of at least 1.8, 
preferably 2.5 to 7.0 in at least one step, and then heat-treating the 
drawn filaments at a temperature higher than the drawing temperature and 
within the range of 100.degree. to 240.degree. C., preferably 150.degree. 
to 240.degree. C., at constant length or while allowing a restricted 
shrinkage of not more than 15% or a stretch of not more than 15%. 
The drawing can be performed in two or more steps. In this case, it is 
recommended to perform the first-step drawing at a temperature of 
60.degree. to 150.degree. C. and the second-step drawing at a temperature 
higher than the firststep drawing temperature and within the range of 
100.degree. to 220.degree. C., and adjust the total draw ratio to 2.0 - 
7.0. 
The undrawn filaments can be conveniently obtained by melting the 
tetramethylene naphthalate polyester used in this invention, and extruding 
the molten polymer through a spinneret, while heating the atmosphere near 
the filaments over an area which extends from the underface of the 
spinnerete to a point at least 10 cm apart from it to a temperature of 
200.degree. to 600.degree. C. The resulting undrawn filaments having a 
birefringence of at least 0.01 and a density of not more than 1.300 have 
good drawability, and can be drawn smoothly at a temperature of at least 
60.degree. C. However, it should be noted that the present invention is 
not limited to filaments produced by this method. 
Heating of the atmosphere below the spinneret in this spinning method can, 
for example, be accomplished by providing a heated spinning cell, or 
blowing a heated gas. The heating medium may be air, and in order to 
prevent the heat-deterioration of the filaments, an inert gas such as 
N.sub.2 or CO.sub.2 is effectively used. 
In order to obtain undrawn filaments having good drawability, it is 
necessary to raise the temperature of the atmosphere below the spinneret 
to more than 200.degree. C. When it is raised to more than 600.degree. C., 
no special advantage is brought about, and rather there is an increasing 
danger. Thus, temperatures above this limit are difficult to employ in 
actual operations. 
The spun filaments should be brought into contact with the atmosphere 
heated at 200.degree. to 600.degree. C. in a zone extending from the 
underface of the spinneret to a point at least 10 cm apart from it; 
otherwise, no effect can be obtained. The length of the zone in which the 
atmosphere is to be heated at 200.degree. to 600.degree. C. is dominated 
by other spinning conditions. But if the take-up speed does not exceed 600 
m/min., the length of 10 cm to 100 cm is sufficient. If, however, the 
take-up speed is above 600 m/min. or the temperature of the atmosphere is 
below 300.degree. c., it is sometimes necessary, according to the type of 
polymer, to heat a zone which runs over a distance of 200 cm from the 
spinneret. 
After passing the spun filaments through such a heated atmosphere, the 
filaments are cooled and solidified by a conventional method. 
The above procedure gives rise to undrawn yarns having a relatively low 
degree of crystallinity and good drawability in spite of being highly 
oriented. The degree of crystallinity is measured usually by the density 
method. 
The degree of crystallinity (.alpha.) according to the density method is 
defined by the following equation. 
##EQU1## 
wherein 
dk is the density of the crystalline phase, 
da is the density of the non-crystalline phase, and 
d is the density of a sample. 
This equation (1) can be written as: 
EQU .alpha. = K - K'/d 
wherein 
K and K' are constants. 
The density of the non-crystalline phase of tetramethylene naphthalate 
polyester is difficult to measure since it is difficult to prepare a 
completely amorphous polymer. Furthermore, the density of complete 
crystals of this polymer is not known. 
However, even if the densities of the complete crystalline or amorphous 
phases are not known, it could be judged qualitatively that since the 
degree of crystallinity (.alpha.) is the function of the density (d) of 
the sample, the degree of crystallinity (.alpha.) becomes higher if the 
density (d) is higher. Accordingly, in the present invention, the degree 
of crystallinity is expressed in terms of density. 
Preferably, the naphthalate polyester filaments, yarns or fibers of this 
invention in which the proportion of hexamethylene naphthalate units is at 
least 85 mol% are highly oriented so that their tenacity is at least 2.5 
g/d. 
Bristlelike monofilaments each having at least 100 denier and composed of 
the hexamethylene naphthalate polyester as defined in the present 
invention have superior resistance to wet heat, and when allowed to stand 
in pure water at 120.degree. C., they exhibit a tenacity retention time 
(the time required until the tenacity decreases to 1.0 g/d) of at least 10 
days (at the longest 200 hours in the case of the known polyester 
bristlelike monofilaments composed of polyethylene terephthalate). 
The hexamethylene naphthalate polyester filaments, yarns or fibers of this 
invention having a monofilament denier of less than 100 also exhibit a 
tenacity retention time in pure water at 120.degree. C., of at least 10 
days. 
The above hexamethylene naphthalate polyester filaments, yarns or fibers 
can be prepared by spinning and drawing a polyester containing at least 85 
mol% of hexamethylene-2,6-naphthalate units as a starting material in the 
same way as in the preparation of the known filaments, yarns or fibers. 
The spun filaments can be rapidly cooled in a liquid kept at not more than 
20.degree. C., or they are solidified after being passed at least once 
through a zone extending over a distance of at least 10 cm from the 
spinneret and heated at a temperature of 150.degree. to 600.degree. C. Or 
the spun filaments are solidified in a coagulating bath kept at 50.degree. 
to 200.degree. C. Thus, undrawn filaments having good drawability can be 
obtained. Instead of these, the filaments can also be spun directly into 
the atmospheric air. 
The drawing of the filaments may be performed immediately after the 
spinning step or after the filaments have been wound up. The use of a 
heating medium such as air, an inert gas, steam, or an inert liquid as 
heating means is preferred in the drawing step, because this results in 
good drawing condition, and drawn filaments of uniform properties can be 
obtained. The drawing can be performed either in a single step or in a 
multiplicity of steps. 
The filaments as drawn have sufficient properties, but their properties can 
be further improved if they are heat-treated at a temperature higher than 
the drawing temperature while allowing shrinkage or stretch or at constant 
length. 
The hexamethylene naphthalate polyester filaments, yarns or fibers of this 
invention have superior chemical resistance, resistance to hydrolysis, 
resistance to wet heat, and resistance to oxidation to the conventional 
polyester filaments, yarns or fibers composed of polyethylene 
terephthalate. They are suitable for use in applications which require 
these properties, for example, dryer canvas in a paper-making process, 
filters for chemical liquids, materials of bushes for chemical cleaning, 
reinforcing belt materials for radial tires or belted bias tires, 
materials or reinforcing materials for belts used to transport goods or 
transmit power, cable cords, or reinforcing materials for blade hoses. 
Furthermore, because of the superior abrasion resistance, they are also 
useful as fastener component materials.

The following Examples illustrate the present invention in greater detail. 
In the Examples, the various properties mentioned were measured by the 
following methods. 
Resistance to Wet Heat 
This property is expressed in terms of the period of time which is required 
until the tensile strength at breakage of fibers decreases to 1.0 g/d when 
the fibers are immersed in pure water kept at 120.degree. C. The larger 
this value is, the more superior is the wet heat resistance of the fibers. 
Resistance to Oxidation 
The fibers are exposed to air at 170.degree. C., and after 2 weeks, the 
tenacity retention over the initial tenacity is determined and expressed 
in percent. 
Resistance to Alkali 
This property is expressed by a tenacity retention (%) after a lapse of 24 
hours when the fibers are immersed in a 20% aqueous solution of sodium 
hydroxide at 80.degree. C. 
Intrinsic Viscosity 
Meausred on an o-chlorophenol solution at 35.degree. C. 
Tenacity, Elongation and Young's Modulus 
A tensile test was performed at a tensile speed of 100%/min. using a sample 
having a length of 20 cm. The tenacity is expressed by a value per denier 
of the sample before tensile test. 
Shrinkage in Boiling Water 
The sample filament is immersed in boiling water at 100.degree. C. in a 
free state for 30 minutes. The shrinkage of the filament is expressed in 
percent based on the length before treatment. 
Thermal Stability Test 
The sample filament is treated in an air bath at 200.degree. C. for 96 
hours in a free state. The tenacity retention of the filament is then 
measured. Filaments having a tenacity retention of at least 50% are 
evaluated as serviceable. 
EXAMPLES 1 TO 5 AND COMATIVE EXAMPLE 1 
Poly(tetramethylene-2,6-naphthalate) having an intrinsic viscosity of 0.86 
was melt-spun at a spinning temperature of 280.degree. C from a spinneret 
having 12 circular orifices with a diameter of 0.5 mm, and taken up at a 
rate of 360 m/min. At this time, an area extending over a distance of 100 
cm from the underface of the spinneret was heated at 400.degree. C. The 
spun filaments were passed through this heated atmosphere, and taken up. 
Each of the undrawn filaments was wound through one turn around a pin at 
the various temperatures shown in Table 1, and then heat-set on a plate at 
various temperatures. The properties of the resulting filaments are shown 
in Table 1. The resulting filaments had an intrinsic viscosity of 0.81. 
For comparison, the properties of poly(tetramethylene-2,6-naphthalate) 
filaments produced by the method disclosed in Example 9 of British Pat. 
No. 987,013 are also shown in Table 1. 
Table 1 
__________________________________________________________________________ 
X-ray 
Tempera- Tempera- 
diffrac- Denier 
ture of 
Draw 
ture of 
tion Elonga- 
Young's 
Size (per 
Thermal 
pin ratio 
plate intensity 
Tenacity 
tion modulus 
monofila- 
Stability 
Examples 
(.degree. C) 
(TDR) 
(.degree. C) 
curve* 
(g/d) 
(%) (kg/mm.sup.2) 
ment) 
test 
__________________________________________________________________________ 
1 75 3.1 150 1 5.0 9.5 1250 5.4 Service- 
(constant able 
length) 
2 100 3.4 150 2 6.4 8.2 1340 4.9 " 
(5% 
stretch) 
3 125 2.8 150 1 5.6 10.6 1100 6.0 " 
(5% 
shrinkage) 
4 175 3.0 220 2 5.5 13.9 1000 5.6 " 
(constant 
length) 
5 90 4.8 180 1 5.2 11.4 980 3.5 " 
(constant 
length) 
Com- 
parative Not 
Examples 
90 1.5 185 5 4.2 10.0 750 2.6 Service- 
1 able. 
__________________________________________________________________________ 
*The numerals indicate the numbers attached to the curves in FIGS. 1 and 
2. 
EXAMPLE 6 
Poly(tetramethylene-2,6-naphthalate) having an intrinsic viscosity of 1.2 
was spun at 285.degree. C., and taken up at a rate of 750 m/min. The X-ray 
diffraction intensity distribution of the undrawn filaments obtained was 
similar to curve 4 in FIG. 2. The filaments had an intrinsic viscosity of 
1.02, a monofilament denier of 8.0, a tenacity of 3.6 g/d and an 
elongation of 15.2%, but a Young's modulus of 620 Kg/mm.sup.2 
(comparison). 
The undrawn filaments obtained were drawn to 1.3 times their original 
length by a pin kept at 100.degree. C., and heat set at 180.degree. C. The 
X-ray diffraction intensity distribution curve of the resulting drawn 
filaments was similar to that of curve 5 or FIG. 2. The drawn filaments 
had a monofilament denier of 6.2, a tenacity of 3.9 g/d, an elongation of 
12.5% and a Young's modulus of 750 kg/mm.sup.2. The drawn filments were 
found to be unserviceable by the thermal stability test (comparison). 
When the above undrawn filaments were drawn to 2.4 times their original 
length by a pin kept at 150.degree. C., and then heat treated at 
200.degree. C., the X-ray diffraction intensity distribution curve of the 
filaments became curve 1 of FIG. 1. The drawn filaments had a monofilament 
denier of 3.3, a tenacity of 5.3 g/d, an elongation of 12.9% and a Young's 
modulus of 1000 kg/mm.sup.2, and were found to be serviceable by the 
thermal stability test. 
EXAMPLE 7 
The same undrawn filaments as in Example 1 were wound through five turns 
around a feed roller with a diameter of 90 mm heated at 50.degree. C., and 
then drawn to 3.1 times their original length, and successively heat 
treated at constant length at 200.degree. C. The X-ray diffraction 
intensity distribution curve of the resulting filaments was similar to 
curve 2 in FIG. 1. The filaments had a monofilament denier of 5.4, a 
tenacity of 5.3 g/d, an elongation of 15.9% and a Young's modulus of 1070 
kg/mm.sup.2, and were found to be serviceable by the thermal stability 
test. 
When the filaments were wound through 5 turns around a heated feed roller 
with a diameter of 90 mm at a temperature of 175.degree. C., and drawn, 
they could be drawn only to 1.4 times their original length, and even when 
they were heat-set at 220.degree. C., the X-ray diffraction intensity 
distribution curve of the filaments was similar to curve 5 in FIG. 2. The 
drawn filaments had a monofilament denier of 12, a tenacity of 2.3 g/d, an 
elongation of 46.2% and a Young's modulus of 550 kg/mm.sup.2, and were 
found to be not serviceable by the thermal stability test (comparison). 
EXAMPLE 8 
Poly(tetramethylene 2,6-naphthalate) having an intrinsic viscosity of 0.95 
was spun at 280.degree. C., and wound up at a rate of 360 m/min. The 
undrawn filaments (with an intrinsic viscosity of 0.91) were drawn to 2.5 
times their original length by a pin kept at 90.degree. C., and wound up 
without heat-setting. The X-ray diffraction intensity distribution curve 
of these filaments was similar to curve 3 of FIG. 1. The drawn filaments 
had a monofilament denier of 6.7, a tenacity of 4.6 g/d, an elongation of 
6%, and a Young's modulus of 900 kg/mm.sup.2, and were found to be 
serviceable by the thermal stability test. 
EXAMPLES 9 AND 10 AND COMATIVE EXAMPLE 2 
Poly(tetramethylene-2,6-naphthalate) having various intrinsic viscosities 
as shown in Table 2 was heated at 280.degree. C., and extruded into the 
air through a spinneret having one spinning orifice of a complete circular 
shape. The filament was immediately led into water kept at 20.degree. C. 
to cool and solidify it. Successively, it was drawn at the draw ratio 
shown in Table 2 in a bath of ethylene glycol kept at 70.degree. C. and 
heat-treated at 175.degree. C. at constant length to form a bristlelike 
filament having a denier of 2100 to 2600. The properties of the 
bristlelike filaments were measured, and the results are shown in Table 2. 
Table 2 
__________________________________________________________________________ 
Intrinsic X-ray 
Shrinkage 
[.eta.] of 
viscosity Normal Wet heat 
Alkali 
diffrac- 
in 
naphtha- 
of fila- Normal 
elonga- 
Knot resist- 
resist- 
tion boiling 
late ments as 
Draw 
tenacity 
tion strength 
ance ance 
intensity 
water 
Runs polymer 
extruded 
ratio 
(g/d) 
(%) (g/d) 
(days) 
(%) curve 
(%) 
__________________________________________________________________________ 
Example 
9 0.89 0.83 4.8 4.3 28 3.2 24 93 2 0.7 
Example 
10 0.58 0.54 6.2 5.8 23 3.5 32 91 2 1.3 
Compara 
tive 
Example 
0.28 0.25 5.0 5.1 5.3 1.0 10 85 2 1.1 
__________________________________________________________________________ 
A paper-making canvas was prepared by weaving the bristlelike filaments 
obtained in each of Examples 9 and 10, and used continuously for two 
months in a wet heat zone in a process of producing good quality paper. No 
abnormal phenomenon occurred, and the operability of the canvas was 
stable. 
EXAMPLE 11 
Poly(tetramethylene-2,6-naphthalate) having an intrinsic viscosity of 0.86 
was melted at 280.degree. C. and then extruded into the air through a 
spinneret having one spinning orifice of complete circular shape. 
Immediately then, the filament was led into water kept at 0.degree. C. to 
quench and solidity it. The solidified filament was wound up, then drawn 
at a ratio of 4.6 in a bath of ethylene glycol kept at 70.degree. C. and 
heat-treated at 180.degree. C. at constant length to form a bristlelike 
filament having an intrinsic viscosity of 0.81 and a denier size of 610. 
The X-ray diffraction intensity distribution curve of this filament was 
the same as curve 2 of FIG. 1. 
The properties of this bristlelike filament and those of a commercially 
available polyethylene terephthalate bristle (T-PRN of Hcechst AG, 600 
denier) were measured, and the results are shown in Table 3. 
Table 3 
______________________________________ 
Present Commercially 
invention 
available bristle 
______________________________________ 
Normal strength (g/d) 
5.9 4.3 
Normal elongation (%) 
21 49 
Knot strength (g/d) 
3.5 3.7 
Knot elongation (%) 
12 30 
Wet heat resistance (days) 
30 8 
Resistance to oxidation (%) 
100 88 
Alkali resistance (%) 
92 40 
Shrinkage in boiling water (%) 
1.0 2.4 
______________________________________ 
A paper-making canvas was produced in the same way as in Example 9 using 
each of the bristles shown above. No abnormal phenomenon was seen in the 
canvas produced from the bristle of this invention after continuous use 
for 2 months, whereas in the canvas produced from the commercially 
available bristles, several bristles were seen to break on the 20th day. 
EXAMPLES 12 TO 15 
Bristles of various normal tenacities and elongations and knot strengths 
and elongations were prepared under the same conditions as in Example 11 
except that the drawing conditions were varied as indicated in Table 4. 
The wet heat resistance of each of the bristles was measured. The results 
are shown in Table 4. 
Table 4 
______________________________________ 
Examples 
15 
(compar- 
12 13 14 ison) 
______________________________________ 
Normal strength (g/d) 
6.3 3.6 2.9 2.4 
Normal elongation (%) 
41 31 38 46 
Knot strength (g/d) 
3.8 2.9 2.5 1.9 
Knot elongation (%) 
28 39 32 36 
Wet heat resistance 
45 20 15 7 
(days) 
Drawing temperature 
90/120* 90 90 90 
(.degree. C) 
Draw ratio 6.3 3.2 2.5 1.8 
Denier size (denier) 
450 860 1200 1500 
X-ray diffraction in 
tensity distribution 
1 2 2 4 
curve 
______________________________________ 
*Drawing was done in two steps. The draw ratio was 4.2 in the first step, 
and 1.5 in the second step. 
A rubber belt for transporting goods was produced using the bristlelike 
filament of Example 12 as a reinforcing material, and used for conveying 
wet tows in the step of drying crimped polyester tows. After 20 days' 
continuous operation, no trouble occurred. 
EXAMPLE 16 
Poly(tetramethylene-2,6-naphthalate) having an intrinsic viscosity of 0.92 
was melted at 280.degree. C., and spun through a spinneret having one 
spinning orifice. The atmosphere in a zone extending over a distance of 
100 cm below the spinneret was heated at 450.degree. C. by means of a 
heated cell. The spun filament was passed through this zone, and then 
cooled and solidified in the air. 
The resulting undrawn filaments (with an intrinsic viscosity of 0.87) were 
wound around a heated feed roller at 50.degree. C. and drawn at a ratio of 
3.9, followed by heat-treatment at 180.degree. C. to form a bristle having 
a size of 1000 denier. 
The resulting bristle had a normal tenacity of 4.2 g/d and exhibited a wet 
heat resistance of 28 days. Also, this bristle showed an X-ray diffraction 
intensity distribution curve similar to curve 2 of FIG. 1. When this 
bristle was immersed for 24 hours in sulfuric acid, no change was seen. 
The bristle had a shrinkage in boiling water of 0.6%. 
EXAMPLES 17 AND 18 AND COMATIVE EXAMPLE 3 
Poly(tetramethylene-2,6-naphthalate) having an intrinsic viscosity of 0.88 
was extruded at a spinning temperature of 280.degree. C. using a spinneret 
with 12 orifices each having a diameter of 0.5 mm and a length of 0.9 mm 
at an extrusion rate of 8.0 g/min. The extruded filaments were wound up at 
a rate of 360 m/min. At this time, a heated spinning cell was provided in 
a region extending from 1 cm immediately below the spinneret to 100 cm 
below it so that the temperature of the yarn path was maintained at 
250.degree. C. (Example 17) and 400.degree. C. (Example 18), respectively. 
The birefringence and density of the resulting undrawn filaments, and the 
maximum draw ratio at the time of drawing on a hot pin kept at 100.degree. 
C. are shown in Table 5. For comparison, the above procedure was repeated 
except that the heated spinning cell was not provided. The results are 
also shown in Table 5. 
Table 5 
______________________________________ 
Temperature 
of the 
atmosphere 
Birefrin- 
Density Maximum 
(.degree. C) 
gence (g/dm.sup.3) 
draw ratio 
______________________________________ 
Example 17 
250 0.236 1.2980 3.72 
Example 18 
400 0.226 1.2975 4.10 
Comparative 
Example 3 
* 0.258 1.3015 2.70 
______________________________________ 
*The temperature at a point 0.5 cm below the spinneret was 185.degree. C. 
When the atmosphere below the spinneret was heated to 250.degree. 
-400.degree. C. in Examples 17 and 18, the birefringence of the filaments 
exceeded 0.22 which is about 100 times as high as that of an ordinary 
polyester. Since, however, the density (therefore, degree of 
crystallinity) of the filaments was low, the maximum draw ratio was higher 
than in the case of not heating the atmosphere below the spinneret, and 
undrawn filaments of good quality were obtained. 
EXAMPLE 19 AND COMATIVE EXAMPLE 4 
Poly(tetramethylene-2,6-naphthalate) having an intrinsic viscosity of 0.64 
and having copolymerized therewith 2 mol% of terephthalic acid was spun 
under the same conditions as in Eample 17. The spinning temperature was 
285.degree. C., and instead of providing a heated spinning cell, air 
heated at 300.degree. C. was fed at a speed of 3 meters per second to a 
region measuring 80 cm in length. The filaments were wound up at a rate of 
500 m/min. The resulting filaments had a birefringence of 0.240, a density 
of 1.2985, and a maximum draw ratio at 100.degree. C. of 3.25. 
When heated air was not blown in the above procedure for the sake of 
comparison, the temperature of the atmosphere at a point 0.5 cm below the 
spinneret was about 185.degree. C. At a take-up speed of 500 m/min., the 
filaments broke and could not be wound up. 
EXAMPLE 20 
Poly(hexamethylene-2,6-naphthalate) having an intrinsic viscosity of 0.92 
was melted at 255.degree. C., and then extruded through a spinneret having 
one spinning orifice of a complete circular shape. The spun filaments were 
quenched and solidified in ice water, and successively drawn to 5.2 times 
their original length in a bath of ethylene glycol kept at 50.degree. C. 
The spun filaments had an intrinsic viscosity of 0.88. 
The properties of resulting bristlelike filaments are shown in Table 6 
together with those of commercially available polyethylene terephthalate 
bristles (T-PRN, the product of Hoechst AG). 
Table 6 
______________________________________ 
Commercially 
Invention 
available bristles 
______________________________________ 
Denier size (denier) 
570 600 
Normal tenacity (g/de) 
4.8 4.3 
Normal elongation (%) 
24 49 
Knot strength (g/de) 
2.8 3.7 
Knot elongation (%) 
15 30 
Wet heat resistance (days) 
24 8 
Resistance to oxidation (%) 
100 88 
Resistance to hydrolysis (%) 
93 40 
X-ray diffraction intensity curve 
Curve 6 of 
-- 
Figure 3 
______________________________________ 
EXAMPLE 21 
Bristlelike filaments were prepared in the same way as in Example 20 except 
that the drawing conditions were varied as shown in Table 7. The tenacity, 
elongation, and wet heat resistance of the resulting filaments are shown 
in Table 7. 
Table 7 
______________________________________ 
Run No. 1 2 3 
______________________________________ 
Denier size (denier) 
420 580 630 
Normal tenacity (g/de) 
5.2 3.8 2.5 
Normal elongation (%) 
22 32 35 
Knot strength (g/de) 
3.8 3.0 2.1 
Knot elongation (%) 
16 22 27 
Wet heat resistance (days) 
32 20 9 
X-ray diffraction intensity curve 
Curve 6 Curve 6 Curve 6 
______________________________________ 
EXAMPLE 22 
Poly(hexamethylene-2,6-naphthalate) having an intrinsic viscosity of 0.75 
was melted at 250.degree. C. and spun using a spinneret having one 
spinning orifice. At this time, a heated spinning cell was provided over a 
region extending from immediately below the spinneret to a point 300 cm 
below it, and the filament was passed through the atmosphere within this 
region kept at 300.degree. C., and then cooled and solidified. The 
filament as spun had an intrinsic viscosity of 0.72. 
The undrawn filament was wound through 8 turns around a roller heated at 
40.degree. C., and then drawn to 3.8 times their original length. The 
resulting bristlelike filament had a denier size of 470 denier, a normal 
tenacity of 4.1 g/de and a knot strength of 3.1 g/de. The bristlelike 
filament had a wet heat resistance of 30 days, which indicates superior 
wet heat resistance. 
The X-ray diffraction intensity curve of this bristlelike filament was the 
same as that of curve 6. 
EXAMPLE 23 
Poly(tetramethylene-2,6-naphthalate) was melt-spun at 280.degree. C. 
through a spinneret having 48 circular orifices with a diameter of 0.5 mm 
to form poly(tetramethylene-2,6-naphthalate) filaments. The undrawn 
filaments obtained were drawn to 2.6 times the original length by a pin 
kept at 150.degree. C., and heat-set at 180.degree. C. The properties of 
the filaments had the properties as shown in Table 8. 
These yarns were twisted, sized by means of rollers, and denoted to form a 
warp yarn. On the other hand, a weft yarn was obtained by the steps of 
bobbin take-up, Italian throwing and pirn winding. Using these yarns, a 
woven cloth with a width of 101 cm was prepared. The density of the warp 
and weft at this time was 72 .times. 31/inch. The cloth was boiled in loop 
in hot water kept at 90.degree. to 100.degree. C. to reduce the content of 
the adhering size to less than 0.2%, and then dried by means of rollers at 
a temperature of 115.degree. C. Then, the cloth was passed through a pin 
tenter having a length of 1.5 m at a rate of 20 m/min. at a temperature of 
220.degree. C. under tension (degree of tension 1.01) to heat-treat the 
fabric. At this time, the density of the warp and weft was 74 .times. 
32.5/inch. The properties of the cloth are shown in Table 8. 
Table 8 
______________________________________ 
Properties of the filaments 
Tenacity (g/de) 5.50 
Elongation (%) 14.0 
Young's modulus (kg/mm.sup.2) 
1300 
Shrinkage in boiling water (%) 
2.5 
Shrinkage in dry heat at 180.degree. C. (%) 
3.9 
X-ray diffraction intensity 
curve (Curve 1 of Figure 1) 
Properties of the woven cloth 
Tensile strength (kg/mm.sup.2) 
850 (warp) 
800 (weft) 
Tensile elongation (%) 
15 (warp) 
18 (weft) 
Tensile elasticity (kg/cm.sup.2 .times. 10.sup.2) 
15 (warp) 
13 (weft) 
Elemendorf tear strength (kg) 
above 1.1 (warp) 
above 1.5 (weft) 
______________________________________ 
The heat-treated cloth so obtained was impregnated with a varnish composed 
of a copolymer of methylphenyl siloxane and alkyd (the so-called 
alkyd-modified silicone varnish), dried at 120.degree. C. for 5 minutes, 
and further baked at 200.degree. C. for 25 minutes. The amount of varnish 
impregnated was 2.6 times the amount of the cloth. The properties of the 
varnish-impregnated cloth were measured. Furthermore, the 
varnish-impregnated cloth was deteriorated for 1 week in hot air at 
200.degree. C., and then its properties were measured. The results are 
shown in Table 9. It is seen from the results that the cloth obtained is 
useful as an electrically insulating material having superior thermal 
stability. 
Table 9 
__________________________________________________________________________ 
Value after 
deterioration 
for 7 days at 
Properties Initial value 
200.degree. C. 
__________________________________________________________________________ 
Tensile strength (kg/cm.sup.2) 
(15 cm width) 630 400 
Tensile elongation (%) 
(15 cm width) 13 9.5 
Schopper bending resistance(cycles) 
&gt;10.sup.3 
900 
Mullen bursting strength (kg/cm.sup.2) 
&gt; 8 6 
Volume resistivity (ohms-cm) 
3 .times. 10.sup.15 
3 .times. 10.sup.15 
Dielectric breakdown voltage (KV/mm) 
50 48 
__________________________________________________________________________ 
EXAMPLES 24 AND 25 AND COMATIVE EXAMPLE 5 
Cords of the structures indicated in Table 10 were produced using 
poly(tetramethylene-2,6-naphthalate) filaments having an intrinsic 
viscosity of 0.80, a tenacity of 6.8 g/de, a Young's modulus of 1700 
kg/mm.sup.2, and the same X-ray diffraction intensity curve as curve 1 in 
FIG. 1 (to be abbreviated to C.sub.4 N) and 
poly(hexamethylene-2,6-naphthalate) filaments having an intrinsic 
viscosity of 0.75, a tenacity of 5.7 g/de, a Young's modulus of 1300 
kg/mm.sup.2 and the same X-ray diffraction intensity curve as curve 6 of 
FIG. 3 (to be abbreviated to C.sub.6 N). V-belts were produced using the 
resulting cords as a reinforcing material. Using the belts obtained, an 
operating test was conducted under the following conditions: 
______________________________________ 
Outside diameter of pulley 
60 mm 
Number of rotation 3600 rpm 
Load 50 kg 
______________________________________ 
For comparison, V-belts were prepared in the same manner as above using 
rayon and polyethylene terephthalate (PET) filaments, and an operating 
test was conducted under the same conditions. The results are shown in 
table 10. 
Table 10 
______________________________________ 
Example 
Example Comparative 
24 25 Example 5 
______________________________________ 
Material C.sub.4 N 
C.sub.6 H 
Rayon PET 
Denier/number of 
filaments 1000/3/3 1000/3/3 1100/2/5 
1000/3/3 
Number of twists 
(T/10 cm; Z .times. S) 
10 .times. 15 
10 .times. 15 
10 .times. 27 
10 .times. 15 
Tenacity of belt (kg) 
440 400 310 430 
Tenacity retention 
of belt (%) 97 98 85 75 
Elongation during 
running (%) 0.28 0.35 0.60 1.52 
Durability (index) 
170 180 100 130 
______________________________________ 
The tenacity retention was calculated from the value measured after 72 
hours. The elongation during running was calculated from the value 
measured after 24 hours. The index of durability was calculated on the 
basis that the durability of the rayon cord is 100. 
It is seen from the above results that the belts reinforced with the 
polytetramethylene naphthalate and polyhexamethylene naphthalate cords in 
accordance with this invention have very high tenacity retention, low 
elongation during running, and superior dimensional stability. It is 
thought that these properties are due to the reduced heat build-up during 
running and good thermal stability and wet heat resistance of the cords. 
EXAMPLES 26 AND 27 
Tire fabrics were produced using cords of each of the yarns having the 
properties shown in Table 11. Using the tire fabrics as a carcass 
reinforcing material and a rayon cord as a belt-like reinforcing material, 
radial tires were built. 
Table 11 
______________________________________ 
Example Example 
26 27 
(C.sub.4 H) 
(C.sub.6 N) 
______________________________________ 
Intrinsic viscosity of the yarn 
0.91 0.82 
Total denier (de) 1020 de/ 1010 de/ 
192 fil 192 fil 
Tenacity (g/de) 7.60 5.05 
Elongation (%) 6.7 8.9 
Young's modulus (kg/mm.sup.2) 
1710 1200 
Shrinkage in boiling water (%) 
2.7 2.5 
Shrinkage in dry heat at 180.degree. C (%) 
5.9 4.8 
X-ray diffraction intensity curve 
1 6 
______________________________________ 
The cord for the carcass reinforcing material consisted of two of the above 
yarn in a two ply construction. The twists was 40.sup.S .times. 40.sup.Z 
T/10 cm, and the number of cords (the density of the warp in the fabric) 
was 50/5 cm. The rayon cord used as the belt-like reinforcing material had 
a size of 1650 de/3 fil. The number of twists was 30.sup.S .times. 
30.sup.Z T/10 cm, and the number of cords was 35/5 cm. It was of a four 
ply construction. The size of the tire used was 165 SR 13. The belt-like 
reinforcing material was disposed at an angle of about 15.degree. with 
respect to the circumferential direction of the tire, and the cord as a 
carcass reinforcing material was placed at an angle of 90.degree. with 
respect to the circumferential direction. The properties of the resulting 
radial tires are shown in Table 12. 
Table 12 
______________________________________ 
Properties Properties 
Yarn of of the cords of the tires 
Tire carcass Dry heat Disc 
No. material shrinkage 
fatigue 
Durability 
Uniformity 
______________________________________ 
1 C.sub.4 N 
1.8 80 Good 75 
2 C.sub.6 N 
2.0 82 Good 85 
______________________________________ 
The evaluation of the properties of the above cords and tires was made by 
the following procedures. 
1. Dry heat shrinkage of the cord: Shrinkage (%) of the cord after it has 
been exposed to dry air at 150.degree. C. for 30 minutes while allowing it 
to shrink freely. 
2. Disc fatigue: The fatigue strength of the cord is measured by the method 
defined in JIS L1017 1963. The amount of distortion is expressed by 
tenacity residue ratio [tenacity after fatigue .times. 100/tenacity before 
fatigue (%)] after fatigue for 24 hours under the following conditions: 
extension/compression 7.5%/15%, bend angle 75.degree., speed of rotation 
1800 rpm. 
3. Durability: The tire was driven on a drum at a speed of 80 km/hour under 
a load of 410 kg. The pressure of the air in the tire is 1.9 kg/cm.sup.2. 
When it runs more than 20,000 km without trouble, the evaluation is given 
as "good", and when it cannot run more than 20,000 Km without trouble, the 
evaluation is "bad". 
4. Uniformity: The tire is rotated, and the non-uniformity of the tire in 
the radical direction is detected by the bias of the force (kg) (radial 
force variation). Smaller values (RFV values) show better uniformity. In 
the table, the numerals for uniformity are indices on the basis that the 
RFV value of a polyethylene terephthalate carcass tire is 100. 
EXAMPLE 28 
Poly(tetramethylene-2,6-naphthalate) having an intrinsic viscosity of 0.72 
was melt-spun at 280.degree. C. using a spinneret having one orifice with 
a diameter of 1.5 mm and an L/D ratio of 1.0. The resulting filament was 
drawn to about 4 times its original length at 75.degree. C., and heat-set 
at 180.degree. C. During the filament-making process, no odoriferous gas 
was evolved. The resulting monofilament had 2450 denier, a tenacity of 3.9 
g/d, and elongation of 25%, and a shrinkage in boiling water of 0.9%. The 
monofilament exhibited the same X-ray diffraction intensity curve as curve 
2 of FIG. 1. 
An L-shaped fastener was produced from this monofilament using a 
traverse-equipped disc heated at 100.degree. to 120.degree. C. There was 
scarcely any shrinkage of the monofilament during this operation, and no 
trouble occurred. 
A sliding tab of the zipper was moved up and down and even after 10,000 
cycles, all twenty samples could still be used. 
EXAMPLE 29 
Poly(tetramethylene-2,6-naphthalate) was melt-spun at 280.degree. C. using 
a spinneret having 48 holes each with a diameter of 0.5 mm and a circular 
cross section to form filaments having an intrinsic viscosity of 0.88. The 
undrawn filaments were drawn to 2.6 times their original length by means 
of a pin at 150.degree. C., and heat-set at 180.degree. C. Three kinds of 
drawn filaments having the properties shown in Table 13 were obtained. The 
X-ray diffraction intensity curve of these filaments was the same as curve 
1 of FIG. 1. The chemical properties of these filaments were determined, 
and the results are shown in Table 13. 
Table 13 
______________________________________ 
Properties of the filaments 
Chemical properties 
Wet heat 
Alkali 
Acid 
Young's resist- 
resist- 
resist- 
Tenacity 
Elongation 
modulus ance ance ance 
(g/d) (%) (kg/mm.sup.2) 
(days) (%) (%) 
______________________________________ 
5.50 14.0 1300 30 95 92 
______________________________________ 
A plain weave fabric was produced from these filaments with a warp and weft 
density of 75 .times. 35/inch. It was heat-cut in the shape of a circle 
having a diameter of 30 cm to form a filter. 
A slurry of terephthalic acid having a pH of 1.2 which had been 
precipitated with hydrochloric acid was heated to 80.degree. C. and 
filtered by means of the filter many times. Each time, the filtration was 
performed for 24 hours, and after it, the filter was washed before using 
it next time. After 20 repeated cycles of filtration, the filter was still 
in good condition.