JP7729071B2 - Polyester thick and thin multifilament - Google Patents

Description

The present invention relates to a polyester thick-thin multifilament that has thickness variations in the longitudinal direction of the yarn, can produce a mottled look with a high contrast between light and dark shades, and can produce woven and knitted fabrics with a soft texture.

In recent years, there has been a growing need for woven and knitted fabrics with excellent design features for sportswear and interior applications, and demand is expanding for heathered materials with high contrast between light and dark shades, rich design potential, and a soft texture.

A well-known technique for producing a typical multifilament with a mottled texture is to non-uniformly stretch highly oriented, unstretched polyester multifilament to produce a multifilament with thickness and thinness in the longitudinal direction of the yarn. The thick and thin multifilament obtained in this way has a mottled texture due to the differences in dyeing shade resulting from the thickness and thinness, and is used in woven and knitted clothing applications such as outerwear and casual wear for women and men, as well as interior applications (Patent Document 1).

On the other hand, in order to improve the color development of polyester multifilaments, ionic dyeing sites, such as isophthalic acid components containing metal sulfonate groups, can be copolymerized to obtain thick and thin polyester multifilaments that can be dyed with cationic dyes with excellent color development (Patent Documents 2 to 5).

A method of blending polyester and nylon and dyeing them differently has also been proposed (Patent Document 6). According to this method, polyester and nylon are blended and stretched at a temperature below the two-time transition temperature to form thick and thin spots, resulting in differences in dyeing density and multiple colors achieved by dyeing with different dyes, making it possible to obtain polyester multifilament with a wide range of designs.

Special Publication No. 50-18717 JP 2018-162531 A Japanese Patent Application Laid-Open No. 2003-306830 Japanese Patent Application Laid-Open No. 2006-200064 Japanese Patent Application Laid-Open No. 2004-277956 Japanese Unexamined Patent Publication No. 55-158329

However, while the mottled tones obtained using the methods described in Patent Documents 2 to 5 have excellent color clarity, highly oriented, undrawn multifilaments made using only polymers copolymerized with ionic dyeing sites, such as isophthalic acid components containing metal sulfonate groups, have a short constant stress elongation range elongation, and when unevenly drawn in the subsequent drawing process, the difference in fiber diameter between the thick and thin portions becomes small. This effect is more pronounced in highly oriented, undrawn multifilaments with low single yarn fineness. Therefore, although the resulting cationic dyeable polyester thick-thin multifilaments have excellent color clarity, the resulting mottled tones have low contrast in shade, weakening their characteristics as decorative materials.

In addition, the fiber described in Patent Document 6 is produced by blending polyester and nylon, melt-spinning the blend, and drawing at a low temperature below the secondary transition point to form thick and thin patterns. Because the blending of polyester and nylon reduces the strength of the highly oriented, undrawn multifilament, when the single-fiber fineness is low, spinnability is particularly poor, and single-fiber breakage occurs frequently during spinning, making spinning difficult. Furthermore, to avoid yarn breakage and single-fiber breakage during drawing, drawing must be performed at a low ratio. As a result, the difference in fiber diameter between the thick and thin portions is insufficient, resulting in a low contrast between light and dark shades in the resulting figured pattern.
The present invention aims to provide a polyester thick-thin multifilament yarn which has excellent processability, has thickness and thinness in the yarn longitudinal direction, can express a mottled look with a large contrast in shade, and can give woven or knitted fabrics having a soft texture.

In order to solve the above problems, the present invention employs the following configuration.
(1) A polyester thick/thin multifilament characterized in that it contains 0.6 to 2.5 mol % of an isophthalic acid component containing a metal sulfonate group relative to the total dicarboxylic acid of the polyester, and satisfies the following A to B:
A. Single yarn fineness: 0.40 to 1.2 dtex
B. The average number of fineness fluctuation peaks (N40) in the Worcester waveform resulting from unevenness in the fineness in the longitudinal direction of the multifilament, with a fineness fluctuation rate width of 40% or more from the baseline, is 3 to 17/m
(2) The polyester thick/thin multifilament according to (1), characterized in that the breaking strength is 1.8 to 2.5 cN/dtex and the toughness is 19.0 or more.
(3) A polyester thick-thin multifilament according to (1), characterized in that the Worcester thick-thin unevenness resulting from unevenness in the lengthwise direction of the multifilament is 5 to 16%.
(4) A polyester thick/thin multifilament according to (1), characterized in that the coefficient of variation CV% of the number of fineness fluctuation peaks (N20) having a fineness fluctuation rate width of 20% or more from the fineness fluctuation baseline of the Worcester waveform resulting from fineness unevenness in the longitudinal direction of the multifilament is 12% or less.

The cationic dyeable polyester thick/thin multifilament of the present invention provides woven and knitted fabrics with excellent color clarity when dyed, a large contrast between the darkly and lightly dyed areas in the heathered tone, and a soft texture.

SS curve to explain constant stress elongation region elongation (NDR elongation) FIG. 1 is an explanatory diagram showing a schematic diagram of a non-uniform stretching device used in the examples. Worcester waveform chart and fineness fluctuation peak

The present invention is described in detail below.

The main component of the polyester of the present invention is polyethylene terephthalate obtained by esterifying or transesterifying terephthalic acid or its ester-forming derivative with ethylene glycol or its ester-forming derivative.

The content of the metal sulfonate group-containing isophthalic acid component (SI component) in the polyester thick/thin multifilament of the present invention is 0.6 to 2.5 mol % based on the total carboxylic acid components.
If the SI component content is less than 0.6 mol%, sufficient color clarity cannot be obtained, and the mottled tone also has a low contrast between light and dark. If the SI component content exceeds 2.5 mol%, the multifilament is dyed uniformly regardless of whether it is thick or thin, making the mottled tone less noticeable and reducing the mechanical properties (strength, etc.) of the multifilament. The SI component content is preferably 1.0 to 2.0 mol%.

The polyester thick/thin multifilament of the present invention has a mean value of 3 to 17 peaks/m, preferably 5 to 17 peaks/m, for the fineness fluctuation rate in the longitudinal direction of the multifilament, where the range of fineness fluctuation rate from the baseline of the fineness fluctuation rate in a Worcester waveform chart is 40% or more. If the mean value of N40 is less than 3 peaks/m, the difference in shade between light and dark dyeing is insufficient, and a clear mottled pattern cannot be obtained. Furthermore, if the mean value of N40 exceeds 17 peaks/m, the darkly dyed areas become dominant, the entire fabric appears darkly dyed, and a clear mottled pattern cannot be obtained.

The polyester thick/thin multifilament of the present invention has a single yarn fineness of 0.40 to 1.2 dtex. It is more preferably 1.0 dtex or less, and even more preferably 0.8 dtex or less. If the single yarn fineness is less than 0.4 dtex, the darkly and lightly dyed areas will be finely dispersed, making the heathered pattern less visible and preventing a clear heathered pattern from being obtained. If the single yarn fineness exceeds 1.2 dtex, the bending rigidity will increase when the fabric is made, making it impossible to obtain a soft feel.

A preferred embodiment of the polyester thick/thin multifilament of the present invention has a breaking strength of 1.8 to 2.5 cN/dtex. By keeping the breaking strength within this range, the yarn can be easily passed through post-processing steps, and when dyed into a woven or knitted fabric, the contrast between light and dark hues in the heathered pattern is excellent.

The toughness of the polyester thick/thin multifilament of the present invention is preferably 19.0 or more, more preferably 20.0 or more. The toughness T is expressed by the following formula, where ScN/dtex is the strength of the multifilament and E% is the elongation.
T = S × E ^1/2
If the toughness is 19.0 or more, the fabric strength when made into a woven or knitted fabric is at a level suitable for clothing applications, and the high-level processability is good.

The polyester thick-thin multifilament of the present invention preferably has a Worcester thick-thin pattern resulting from the unevenness of the fineness in the longitudinal direction of the multifilament, of 5 to 16%. By keeping the Worcester thick-thin pattern within this range, a clear figured look can be obtained when the fabric is made. In addition, localization of thick areas that indicate darkly dyed areas is less likely to occur, resulting in good dimensional stability for woven and knitted fabrics.

The polyester thick/thin multifilament of the present invention preferably has a coefficient of variation CV% of 12% or less for the number of fineness fluctuation peaks (N20) at which the fineness fluctuation range from the baseline of the fineness fluctuation rate in a Worcester waveform chart is 20% or more, with respect to the fineness fluctuation rate in the longitudinal direction of the multifilament. It is more preferably 3 to 10%. An N20 CV% of 12% or less means that there is little variation in the frequency of thick/thin irregularities in the longitudinal direction of the multifilament, and when made into a woven or knitted fabric, localization of thick and thin portions is unlikely to occur, resulting in a stable heathered texture. Furthermore, the fabric has excellent fabric strength and dimensional stability.

The specific method for producing the polyester thick/thin multifilament of the present invention is described in detail below.

The polyester thick/thin multifilament of the present invention is obtained by melt-mixing and spinning two types of polyester with different melting points as measured by DSC to obtain a highly oriented, undrawn yarn with a constant stress elongation region elongation (NDR elongation A) of 35 to 70% in the S-S curve. The highly oriented, undrawn yarn is then non-uniformly drawn in a separate process using a friction resistor.

Two types of polyesters with different melting points are used: a polyester obtained by esterifying or transesterifying a dicarboxylic acid or its ester-forming derivative with a diol or its ester-forming derivative (hereinafter referred to as "polyester A"), and a polyester obtained by copolymerizing polyester A with an SI component as a third component (hereinafter referred to as "copolyester B"). This SI component (an isophthalic acid component containing a metal sulfonate group) is preferably 5-sodium dimethyl sulfoisophthalate. The above polyesters A and copolymer polyester B may be copolymerized with a fourth component, or recycled raw materials may be used, as long as the objectives of the present invention are not exceeded. Furthermore, additives such as matting agents, pigments, dyes, antifouling agents, fluorescent brighteners, flame retardants, stabilizers, weather resistance agents, UV absorbers, lubricants, or moisture absorbers may also be added.

From the viewpoint of compatibility, it is preferable that the ratio (Pb/Pa) of the melt viscosity (Pb) of polyester A to the melt viscosity (Pa) of copolymer polyester B be 0.7 to 2.0. By keeping the melt viscosity ratio within this range, the compatibility of the two types of polyester is increased, and the breaking strength and toughness of the polyester thick/thin multifilament of the present invention can be maintained at a high level. Furthermore, yarn breakage is suppressed during spinning of highly oriented undrawn yarn and uneven drawing processing, resulting in excellent operability.

The blend weight ratio of polyester A to copolymer polyester B is 50% by weight or more of polyester A relative to 100% by weight of the total of polyester A and copolymer polyester B. Preferably, it is 55 to 80% by weight. By keeping the polyester A ratio within this range, the NDR elongation A can be maintained for a long period of time, and when non-uniformly stretched in the subsequent stretching process, the difference in fiber diameter between the thick and thin sections becomes large, resulting in a high contrast between light and dark and a clear figured pattern. On the other hand, if the polyester A ratio is less than 50%, the NDR elongation A becomes short, and when non-uniformly stretched in the subsequent stretching process, the difference in fiber diameter between the thick and thin sections becomes small, resulting in a low contrast between light and dark and a clear figured pattern cannot be obtained, which is undesirable.

Methods that can be used to melt-knead and mix polyester A and copolymer polyester B include melting the two types of polyester polymers separately and then melt-kneading them in a mixer, or mixing the two types of polyester polymers in chip form and then melting them.

Furthermore, by combining these methods, it is possible to achieve a compatible system in which copolymer polyester B is evenly dispersed throughout the multifilament, resulting in a highly oriented undrawn yarn with an NDR elongation A of 35-70% in the S-S curve. The polyester thick-thin multifilament obtained by non-uniformly drawing this highly oriented undrawn yarn can have an average value of the fineness fluctuation peak (N40) within the desired range. It also maintains high breaking strength and toughness. More specifically, polyester A and copolymer polyester B are each chipped, weighed, and mixed, then melt-kneaded using an extruder, and further stirred and mixed using a piping mixer. The S-S curve behavior of the fiber obtained by melt-kneading and mixing the two polymers, polyester A and copolymer polyester B, in the above ratio has a longer NDR elongation A than the S-S curve of the highly oriented undrawn yarn of copolymer polyester B alone, and is closer to the S-S curve of the highly oriented undrawn yarn of polyester A alone. As a result, when the fabric is stretched unevenly in the subsequent stretching process, the difference in fiber diameter between the thick and thin sections becomes greater, resulting in a greater contrast between light and dark shades and a clear, figured look.

Furthermore, as the single yarn fineness decreases, the NDR elongation A shifts to a shorter value, so even for highly oriented, undrawn yarns of low single yarn fineness made from copolymer polyester B alone, the NDR elongation A does not appear in the S-S curve, or the range is very narrow. However, by using two types of polymer, polyester A and copolymer polyester B, the NDR elongation A of highly oriented, undrawn yarns can be maintained for a long time, even with a low single yarn fineness. When unevenly drawn in the subsequent drawing process, the difference in fiber diameter between the thick and thin sections becomes large, resulting in a strong contrast between light and dark, and a distinct figured grain.

When melt-kneading, it is preferable to knead the materials firmly using an extruder, and this can be done using known methods such as a single-screw or double-screw extruder.

The pipe mixer used for stirring and mixing after melt kneading is preferably one that repeatedly changes position and divides the material being transported. The elements installed in the pipe to achieve this can be of any known shape, but it is preferable to divide and change position five or more times, as this will allow for robust stirring and mixing of the two types of polyester polymers.

Melt spinning can be carried out using conventional methods. That is, polyester polymer is melted at a temperature of 275-300°C, extruded from a spinneret, and cooled air is blown onto the melt to form threads. After the threads converge, they are entangled with an oil agent and wound into a package to wind up highly oriented, undrawn multifilaments.

The highly oriented undrawn yarn of the present invention is preferably spun at a spinning speed of 2000 to 3200 m/min. A spinning speed of 2000 m/min or higher ensures that the strength of the drawn thick/thin multifilament reaches a practical level, which is advantageous from the standpoint of productivity. Furthermore, a spinning speed of 3200 m/min or lower produces the NDR elongation A shown in Figure 1, resulting in less occurrence of thick/thin variations in the longitudinal direction of the multifilament during the drawing process.

When producing the highly oriented undrawn yarn of the present invention, oiling is carried out using an oiling guide. The amount of spinning oil applied to the highly oriented undrawn yarn is preferably 0.7 to 1.6% by mass. The oiling method is not particularly limited, as long as it is a method that generally applies oil to melt-spun highly oriented undrawn yarn, such as an oiling guide or oiling roller. By keeping the amount of spinning oil applied within this range, it is possible to prevent a decrease in breaking strength and toughness due to friction with the equipment, and it also reduces scum deposition on the yarn running parts of the equipment and prevents excessive adhesion of volatilized oil to the friction resistor, stabilizing the surface condition of the friction resistor and reducing variation in the frequency of thick and thin spots in the longitudinal direction of the multifilament.

The polyester thick-thin multifilament of the present invention is obtained by non-uniformly drawing the highly oriented undrawn yarn at a predetermined drawing ratio using a friction resistor. The non-uniform drawing process can be carried out consecutively to the spinning process, but since the highly oriented undrawn yarn immediately after spinning does not have a clear constant stress elongation region elongation shown as A in Figure 2, it is difficult to form thick and thin multifilaments even with non-uniform drawing. For this reason, it is preferable to first wind the highly oriented undrawn yarn and then non-uniformly draw it.

Figure 2 shows one embodiment of a preferred non-uniformly drawn yarn manufacturing apparatus that can be used in the present invention. In Figure 2, highly oriented undrawn yarn 1 is drawn at a low magnification between feed roller 2 and drawing roller 4 via friction resistor 3 to form thick and thin multifilaments, which are then wound on winder 6.

A cylindrical heat pin is preferred as the friction resistor. By wrapping the highly oriented undrawn yarn around the cylindrical heat pin, the friction resistor can stably grip the running yarn, stabilizing the stick-slip phenomenon and reducing the variation in the frequency of thick and thin spots in the longitudinal direction of the multifilament, and achieving a distinct mottled grain.

The draw ratio is determined by the speed ratio between the feed roller 2 and the stretching roller 4. In order to produce stable thick-thin variations, the draw ratio is preferably 0.80≦α≦1.10 when determined according to the following formula (2). The NDR elongation refers to part A in FIG. 1. When α is 1.10 or less, the frequency of occurrence of thick portions becomes favorable, and when the fabric is made into a dyed fabric, the dark-dyed portions become prominent, resulting in the desired figured tone. Furthermore, when α is 0.80 or more, the strength and toughness of the thick-thin multifilament are at a practical level, and there is little occurrence of thread breakage during advanced processing.
(1 + constant stress elongation region elongation A (%)/100) x α times... (2)
(α: coefficient in stretching ratio)
Furthermore, the polyester thick/thin multifilament of the present invention may be heat-set using a heated roller or the like after being non-uniformly drawn, within the scope of the present invention.

The cross-sectional shape of the filaments that make up the polyester thick/thin multifilament is not particularly limited, and any shape, such as a round cross section, triangular cross section, ellipse, or multi-lobed cross section, can be preferably used.

The present invention will be explained in more detail below with reference to examples. Note that the property values in the examples were determined using the following methods.

(1) Measurement of isophthalic acid components having metal sulfonate groups: The chip and fiber sample were analyzed for elements using a fluorescent X-ray analyzer (ZSX-100e, manufactured by Rigaku Corporation). The amount of S element was calculated by multiplying the molecular weight of the S component.

(2) Melt Viscosity: The chip-like polymer was adjusted to a moisture content of 150 ppm or less using a vacuum dryer, and the melt viscosity was measured using a melt indexer (L225-41 manufactured by Tateyama Scientific Industry Co., Ltd.) at a measurement temperature of 290°C, the same as the spinning temperature, a load of 1000 g, a measurement distance of 2.54 cm, an orifice inner diameter of 0.2095 cm, an orifice length of 0.8000 cm, and a piston diameter of 0.9478 cm, all in a nitrogen atmosphere.

(3) N40
Measurement is carried out for 25 seconds using a Worcester yarn evenness tester described below, and the lowest value of the fineness fluctuation rate in the obtained Worcester waveform chart (corresponding to a yarn length of 10 m) is taken as the baseline (C in Figure 3). A line is drawn at a position (D in Figure 3) that is +40% from the baseline a, and the number of fineness fluctuation peaks having a peak top equal to or higher than line D is counted (Figure 3). The Worcester waveform chart is obtained by using a USTER TESTER UT-4 manufactured by Zellweger, selecting the measurement throttle to be used depending on the total fineness of the yarn, and then measuring for 1 minute under conditions of a yarn speed of 25 m/min and a twist number of 5,000 T/m.

(4) Coefficient of variation of N20 CV%
Measurement is carried out for 25 seconds using the Worcester yarn evenness tester, and the minimum value of the fineness fluctuation rate in the obtained Worcester waveform chart (corresponding to a yarn length of 10 m) is taken as the baseline (C in Figure 3). A line is drawn at a position +20% from the baseline a (E in Figure 3), and the number of fineness fluctuation peaks having a peak top equal to or higher than line E is counted (Figure 3). After counting the number of peaks in a yarn length of 10 m, this measurement is repeated six times, and the average value and coefficient of variation CV% are calculated from the obtained number of peaks. The Worcester waveform chart is under the same conditions as above.

(5) Amount of Spinning Oil Adhesion 10 g of the obtained highly oriented, undrawn multifilament is precisely weighed, and the oil is extracted with 100 ml of methanol. The ratio (mass %) of the extracted amount to the highly oriented, undrawn multifilament is defined as the amount of spinning oil adhering (mass %).

(6) Total fineness and single yarn fineness The false-twisted yarn was wound 100 times on a measuring machine with a frame circumference of 1.0 m at an unwinding tension of 1/11.1 (g/dtex), and the weight was measured using a balance. The weight obtained by multiplying it by 100 was taken as the total fineness. The value obtained by dividing the total fineness by the number of filaments was taken as the single yarn fineness.

(7) Amount of Spinning Oil Adhesion 10 g of the obtained highly oriented, undrawn multifilament is precisely weighed, and the oil is extracted with 100 ml of methanol. The ratio (mass %) of the extracted amount to the highly oriented, undrawn multifilament is defined as the amount of spinning oil adhering (mass %).

(8) S-S curve (breaking strength, breaking elongation, toughness, NDR elongation)
A stress-strain curve was obtained using a TENSILON RTC-1210A manufactured by ORIENTEC (now A&D) Co., Ltd., under conditions of a test length of 200 mm and a tensile speed of 200 mm/min. The strength was calculated by dividing the force at which the yarn broke by the fineness, and the elongation at which the yarn broke was calculated by dividing the elongation by the sample length and multiplying this by 100. Each value was measured at three different samples, and the average value was calculated. Toughness was expressed from the strength and elongation results using the above formula (1). The constant stress elongation region elongation was calculated by reading the elongation at A on the chart shown in Figure 3 obtained in the measurement, measuring six different samples, and calculating the average value.

(9) Color vividness A tubular knitted fabric having a basis weight of 150 g/m2 was prepared using the obtained cationic dyeable polyester thick/fine multifilament and dyed under the conditions described below. The color vividness of the dyed woven/knitted fabric was visually judged by three experienced inspectors, who agreed that the color vividness was "extremely excellent" was given 5 points, "excellent" was given 4 points, "average" was given 3 points, "poor" was given 2 points, and "no color vividness" was given 1 point, with a score of 4 points or more being considered a pass.
[Dyeing conditions]
Dye: Eisen Carotene Blue GLH 0.7% O.W.F.
Dyeing assistant: sodium acetate 0.15g/L
Acetic acid (100%) 0.5 mL/L
Bath ratio: 1:100
Dyeing: After treating at 50°C for 15 minutes, the temperature is increased at a rate of 1.6°C/minute, and the material is treated at 98°C for 20 minutes.

(10) Shade contrast The tubular knitted fabric prepared in the above item (9) was visually judged by three experienced inspectors, and by consensus, the shade contrast was given 5 points for "sufficiently large," 4 points for "large," 3 points for "normal," 2 points for "small," and 1 point for "no shade contrast," with a score of 4 or more being considered a pass.

(11) Variation in heathered pattern The cylindrical knitted fabric prepared in (9) above was visually inspected by three inspectors with five years or more of experience in quality assessment, and by consensus, the heathered pattern was given 5 points for "sufficiently dispersed," 4 points for "dispersed," 3 points for "normal," 2 points for "slightly localized," and 1 point for "localized," with a score of 4 or more being considered a pass.

(12) Soft feel: The cylindrical knitted fabric prepared in (9) above was subjected to a sensory evaluation of its soft feel. Three experienced inspectors jointly scored the soft feel as "extremely excellent" with 5 points, "excellent" with 4 points, "average" with 3 points, "poor" with 2 points, and "not soft" with 1 point, with a score of 4 or more being considered a pass.

(13) Spinning operability When the yarn breakage occurrence rate during spinning was converted to the value when produced using a four-spindle winding machine, the yarn breakage occurrence rate calculated by dividing the number of yarn breakages by the number of spinnings was rated as follows: "less than 1.0 times" was rated as ○○, "1.0 times or more but less than 3.0 times" was rated as ○, "3.0 times or more but less than 5.0 times" was rated as △, and "5.0 times or more" was rated as ×. A level of ○ or more was the target level.

(14) Processing operability When a textured yarn with a winding amount of 3.0 kg was produced using a manufacturing device for unevenly drawn yarn, the fill rate of the textured yarn drum was evaluated as follows: ◯ for "90% or more," ◯ for "85% or more but less than 90%," △ for "80% or more but less than 85%," and × for "less than 80%." A target level is ◯ or more.

(15) Advanced Processing Operability For the operability of advanced processing, when producing a woven or knitted fabric using cationic dyeable polyester thick/thin multifilament, the penalty point rate obtained by dividing the number of yarn breakages by the number of works in progress was rated as follows: "less than 1.0%" is ○○, "1.0% or more but less than 3.0%" is ○, "3.0% or more but less than 5.0%" is △, and "5.0% or more" is ×. ○ or more is the target level.

[Example 1]
Polyester A, which does not contain an isophthalic acid component having a metal sulfonate group (SI component), and copolymer polyester B, which contains an SI component, and which has a melt viscosity ratio (copolymer polyester B/polyester A) at 290°C of 1.3, were weighed so that the proportion of the SI component was 1.6 mol% based on the total dicarboxylic acids. The mixture was melt-kneaded in a single-screw extruder at a kneading temperature of 284°C and mixed through a piping mixer that was divided and changed position 12 times. The mixture was melt-spun using a spinneret with 192 holes at a spinning temperature of 290°C and a spinning speed of 2,000 m/min. After applying 0.85% by mass of spinning oil, the mixture was wound around a drum in two yarn take-up to obtain a highly oriented, undrawn yarn consisting of 96 filaments and a total fineness of 100 dtex.

Next, the highly oriented undrawn yarn was hot-pin drawn using a drawing machine such as that shown in Figure 1, with the temperature of the hot pins 3 set to 80°C and the draw ratio set to 0.95, with the coefficient α in equation (1) being 0.95. The yarn was then taken up by the feed rollers 5 and wound onto a bobbin by the winder 6 to obtain a polyester thick-thin multifilament having 96 filaments and a total fineness of 66 dtex. The resulting polyester thick-thin multifilament had good properties, as shown in Table 1.

[Examples 2 to 5]
Spinning and drawing were carried out in the same manner as in Example 1, except that the blend ratio of copolymer polyester B/polyester A in Example 1 was changed and the ratio of the SI component to the total dicarboxylic acids in the yarn was changed, to obtain polyester thick/thin multifilaments. The properties of the obtained multifilaments are shown in Table 1. As shown in Table 1, the obtained polyester thick/thin multifilaments had good properties.

[Examples 6 to 11]
Spinning and drawing were carried out in the same manner as in Example 1, except that the proportion of the SI component contained in copolymer polyester B, the blend ratio of copolymer polyester B/polyester A, and the proportion of the SI component to all dicarboxylic acids in the yarn were changed, to obtain polyester thick/thin multifilaments. The properties of the obtained multifilaments are shown in Table 2. As shown in Table 1, the obtained polyester thick/thin multifilaments had good properties.

[Examples 12 to 15]
Spinning and drawing were carried out in the same manner as in Example 1, except that the number of holes in the spinneret and the polymer discharge rate used in Example 1 were changed, to obtain polyester thick/thin multifilaments. The properties of the obtained multifilaments are shown in Table 3. As shown in Table 1, the obtained polyester thick/thin multifilaments had good properties.

[Example 16]
Spinning and drawing were carried out in the same manner as in Example 1, except that the number of divisions and position changes of the piping mixer used in Example 1 was changed to 5, to obtain a polyester thick/thin multifilament. The properties of the obtained multifilament are shown in Table 3. As shown in Table 1, the obtained polyester thick/thin multifilament had good properties.

[Examples 17 to 18]
Spinning and drawing were carried out in the same manner as in Example 1, except that the melt viscosity ratio of the polymers used in Example 1 was changed, to obtain polyester thick/thin multifilaments. The properties of the obtained multifilaments are shown in Table 4. As shown in Table 1, the obtained polyester thick/thin multifilaments had good properties.

[Examples 19 to 20]
Spinning and drawing were carried out in the same manner as in Example 1, except that the amount of spinning oil applied was changed, to obtain polyester thick/thin multifilaments. The properties of the obtained multifilaments are shown in Table 4. As shown in Table 1, the obtained polyester thick/thin multifilaments had good properties.

[Examples 21 to 22]
Spinning and drawing were carried out in the same manner as in Example 1, except that the coefficient α in the draw ratio was changed, to obtain a polyester thick/thin multifilament. The properties of the obtained multifilament are shown in Table 4. As shown in Table 1, the obtained polyester thick/thin multifilament had good properties.

[Example 23]
Spinning and drawing were carried out in the same manner as in Example 1, except that after non-uniform drawing in Example 1, heat setting was carried out at 90°C with a heated roller, to obtain a polyester thick/thin multifilament. The properties of the obtained multifilament are shown in Table 4. As shown in Table 1, the obtained polyester thick/thin multifilament had good properties.

[Comparative Example 1]
Spinning and drawing were carried out in the same manner as in Example 1, except that polyester A was not used and only copolymer polyester B, which contained an SI component in which the proportion of isophthalic acid relative to the total dicarboxylic acids was 1.6 mol %, was used, to obtain a polyester thick/thin multifilament. The properties of the obtained multifilament are shown in Table 5. The obtained polyester thick/thin multifilament had a mottled texture with little contrast between light and dark colors and a large degree of variation, making it uncharacteristic as a design material. In addition, the target operability for advanced processing was not achieved.

[Comparative Examples 2 to 4]
Spinning and drawing were carried out in the same manner as in Example 1, except that the blend ratio of copolymer polyester B/polyester A and the ratio of the SI component to the total dicarboxylic acids in the yarn were changed, to obtain polyester thick/thin multifilaments. The properties of the obtained multifilaments are shown in Table 5. The polyester thick/thin multifilaments obtained in Comparative Example 2 lacked color clarity.

The polyester thick-thin multifilament obtained in Comparative Example 3 had a low contrast between light and dark colors and a highly variable heathered pattern, making it uncharacteristic for a design material. Furthermore, the spinning, processing, and advanced processing operability did not achieve the targets.

The polyester thick-thin multifilament obtained in Comparative Example 4 had a low contrast between light and dark shades and a flecked appearance that lacked distinctive features as a decorative material. Furthermore, the spinning, processing, and advanced processing operability did not achieve the targets.

[Comparative Examples 5 to 6]
Spinning and drawing were carried out in the same manner as in Example 1, except that the number of spinneret holes and the polymer discharge rate used in Example 1 were changed, to obtain polyester thick/thin multifilaments. The properties of the obtained multifilaments are shown in Table 5. As shown in Table 5, the polyester thick/thin multifilaments obtained in Comparative Example 5 had a mottled appearance with little contrast between light and dark shades and lacked characteristics as a design material, and the spinning, processing, and advanced processing operability did not achieve the targets.

As shown in Table 5, the polyester thick/thin multifilament obtained in Comparative Example 6 had a low contrast between light and dark shades and a heathered appearance that lacked distinctive features as a decorative material. Furthermore, the resulting fabric lacked a soft feel.

[Comparative Examples 7 to 8]
Spinning and drawing were carried out in the same manner as in Example 1, except that the coefficient α in the draw ratio was changed, to obtain a polyester thick/thin multifilament. The properties of the obtained multifilament are shown in Table 5. As shown in Table 5, the obtained polyester thick/thin multifilament had a small contrast between light and dark shades and a flecked appearance that lacked characteristics as a design material.

[Comparative Example 9]
Spinning and drawing were carried out in the same manner as in Example 1, except that drawing was carried out using a hot roller instead of a friction resistor, to obtain a polyester thick/thin multifilament. The properties of the obtained multifilament are shown in Table 5. The obtained polyester thick/thin multifilament had a flecked pattern with little contrast between light and dark colors and large variations, and was a flecked pattern lacking characteristics as a design material.

[Comparative Example 10]
Spinning and drawing were carried out in the same manner as in Example 1, except that only Polyester A was used, to obtain a polyester thick/thin multifilament. The properties of the obtained multifilament are shown in Table 5. The obtained polyester thick/thin multifilament lacked color development.

1: Highly oriented undrawn yarn 2: Feed roller 3: Friction resistor (heat pin)
4: Stretching roller 5: Feed roller 6: Winder A: NDR elongation B: Elongation to break C: Baseline of Worcester waveform chart D: Line showing a fineness variation rate of +40% from the baseline of the Worcester waveform chart E: Line showing a fineness variation rate of +20% from the baseline of the Worcester waveform chart

Claims (4)

A polyester thick/thin multifilament characterized by containing 0.6 to 2.5 mol % of an isophthalic acid component having a metal sulfonate group relative to the total dicarboxylic acid of the polyester, and satisfying the following A to B:
A. Single yarn fineness: 0.40 to 1.2 dtex
B. The average number of fineness fluctuation peaks (N40) in the Worcester waveform resulting from unevenness in the fineness in the longitudinal direction of the multifilament, with a fineness fluctuation rate width of 40% or more from the baseline, is 3 to 17/m The polyester thick/thin multifilament described in claim 1 has a breaking strength of 1.8 to 2.5 cN/dtex and a toughness of 19.0 or more. The polyester thick-thin multifilament according to claim 1, characterized in that the Worcester thick-thin unevenness resulting from uneven fineness in the longitudinal direction of the multifilament is 5 to 16%. The polyester thick/thin multifilament according to claim 1, characterized in that the coefficient of variation CV% of the number of fineness fluctuation peaks (N20) with a fineness fluctuation rate width of 20% or more from the fineness fluctuation baseline of the Worcester waveform resulting from fineness unevenness in the longitudinal direction of the multifilament is 12% or less.