JP7577271B2 - Polyester splittable composite fiber, woven/knitted fabric, and method for producing the same - Google Patents

Description

The present invention relates to a polyester-based splittable composite fiber that is made in part from recycled polyester resin containing recycled polyester raw materials derived from used polyester products and unused polyester generated in the process of manufacturing polyester products, and in which an easily alkali-soluble component is split into multiple pieces by an easily alkali-soluble component. The present invention also relates to a woven or knitted fabric that contains fibers made of the above-mentioned recycled polyester resin.

Polyethylene terephthalate (PET) has a high melting point, is resistant to chemicals, and is relatively low cost, so it is widely used in fibers, films, plastic bottles, and other molded products. The production of waste is unavoidable during the manufacturing and processing stages of these polyester products, and in many cases, it is disposed of after use. However, when incinerated, high heat is generated, which causes significant damage to the incinerator and shortens its lifespan. On the other hand, if it is not incinerated, it will remain semi-permanently as it does not decompose.

In recent years, it has become a problem that plastics are a major cause of marine pollution, with a worldwide movement to reduce the use of plastics and switch to biodegradable plastics. Plastics are a major cause of marine pollution, and in recent years, plastics have been found to be harmful to marine ecosystems. Plastics are a major cause of marine pollution, and in recent years, plastics have been found to be harmful to marine ecosystems.
From the viewpoint of such environmental problems, various methods of recycling are being carried out to reuse resources. Regarding polyester products such as PET, in addition to the method of recycling polyester waste generated in the manufacturing process, a method of collecting products that were once on the market and then discarded and reusing them as raw materials is being considered. In particular, in recent years, textile products that have been given the Eco Mark, which is certified as having achieved a certain recycling rate, have become widespread.

Various methods have been proposed for recycling polyester raw materials, such as polyester waste generated in the manufacturing process or recovered used polyester products.
For example, there have been proposed a method of adding methanol to PET scraps to decompose them into dimethylene terephthalate (hereinafter sometimes referred to as "DMT") and ethylene glycol (hereinafter sometimes referred to as "EG") (Patent Document 1), a method of adding EG to PET scraps to depolymerize them, and then adding methanol to recover DMT (Patent Document 2), a method of depolymerizing PET scraps with EG to form oligomers, which are then used in a polycondensation reaction (Patent Document 3), and the like.

Incidentally, impurities that can become a problem when recycling PET bottles or the like that have already been made into products include, in addition to the various additives added to the polyester resin, those attached to the bottle body, such as a) caps (aluminum, polypropylene, polyethylene), b) inner plugs, c) liners (polypropylene, polyethylene), d) labels (paper, resins such as polystyrene, ink), e) adhesives, f) printing inks, etc.
Generally, as a pretreatment for the recycling process, the collected PET bottles are put through a vibrating sieve to remove sand, metal, etc. The PET bottles are then washed, and the colored bottles are separated, followed by coarse crushing. Labels, etc. are then removed by wind separation. Furthermore, aluminum pieces originating from the caps, etc. are removed, and the PET bottle pieces are finely crushed. Components such as adhesives, proteins, and mold are removed by high-temperature alkaline washing, and different components such as polypropylene and polyethylene are separated based on differences in specific gravity.
However, even if these steps are carried out, it is difficult to completely separate and remove non-polyester resins, particularly polypropylene, polyethylene, polystyrene, etc., from the PET resin.
For example, even if an attempt is made to produce a recycled polyester resin using the recycling methods described in Patent Documents 1 to 4, it is difficult to obtain a product having the same quality as virgin polyester resin because the foreign matter derived from non-polyester resin cannot be sufficiently removed and the amount of foreign matter mixed in cannot be sufficiently reduced. If the amount of foreign matter mixed in is not sufficiently reduced, the pressure rise rate of the filtration filter in the spinning process or film-forming process is high, long-term continuous operation is not possible, and processing operability is very poor. Moreover, the methods described in Patent Documents 1 to 3 require a large amount of cost for the installation, operation, maintenance, etc. of the recovery device, and there is room for improvement in terms of practicality.

The invention described in Patent Document 4 describes a method in which polyester waste is depolymerized with ethylene glycol, filtered through a filter with an average mesh size of 10 to 50 μm, and then repolymerized. It is disclosed that the obtained recycled polyester resin has a small amount of foreign matter mixed in and is excellent in operability during processing.
However, even with this method, the above-mentioned foreign matter derived from the non-polyester resin cannot be sufficiently removed, and the amount of the foreign matter mixed in cannot be sufficiently reduced.
As described above, a recycled polyester resin that can sufficiently remove not only various inorganic substances but also foreign matter derived from non-polyester resins, and that can produce various products similar to those produced from virgin polyester resins and that can produce high-quality products has not yet been obtained.

In particular, when polyester resin is used for melt spinning to obtain fibers, the amount of foreign matter mixed in has a significant impact on productivity. The more complex the shape of the fiber is and the finer the fiber is, the greater the influence of foreign matter becomes, making production difficult and resulting in poor mechanical properties of the fiber.

Special Publication No. 42-8855 Japanese Unexamined Patent Publication No. 48-62732 Japanese Unexamined Patent Publication No. 60-248646 JP 2005-171138 A

The present invention aims to solve the above problems and provide a splittable composite fiber made at least in part from recycled polyester resin that contains a high proportion of recycled polyester raw materials derived from used polyester products and unused polyester generated in the process of manufacturing polyester products, and which has mechanical properties similar to those of virgin polyester resin alone and can be obtained with good productivity.

The present inventors conducted extensive research to solve the above problems and arrived at the present invention.
That is, the present invention relates to the following (1) to (3).
(1) A conjugate fiber having a polyester resin A which is a component hardly soluble in alkali and a polyester resin B which is a component easily soluble in alkali, in which the polyester resin A is divided into a plurality of pieces by the polyester resin B in the cross-sectional shape of the fiber, and having a single yarn fineness of 5.0 dtex or less , wherein the polyester resin A is 40% by mass or more of a recycled polyester resin containing a component derived from at least one recycled polyester raw material of a) used polyester products and b) polyester waste generated in a process for producing a polyester resin or a polyester product, and the recycled polyester resin (polyester resin A) has a diethylene glycol content of 4 mol% or less, a carboxyl end group concentration of 30 equivalents/t or less , and an average pressure rise rate of 0.6 MPa/h or less when the total amount of all glycol components is taken as 100 mol%. Here, the average pressure rise rate is a value calculated by the following procedure: a pressure rise tester including an extruder and a pressure sensor is used, a stainless steel filter (nominal mesh size: 1400 mesh, weave: twill weave, vertical mesh: 165 mesh, horizontal mesh: 1400 mesh, vertical line diameter: 0.07 mm, horizontal line diameter: 0.04 mm, filtration grain size: 12 μm) is set at the tip of the extruder, polyester resin is melted at 300° C. in the extruder, and the melt is extruded from the filter at a discharge rate of 29.0 g/min. The pressure value at the start of extrusion is defined as the "initial pressure value (MPa)", and the pressure value at the time of continuous extrusion for 12 hours thereafter is defined as the "final pressure value (MPa)". The average pressure rise rate is calculated based on these pressure values by the following calculation formula A:
Average pressure rise rate (MPa/h)=(final pressure value-initial pressure value)/12...A) .
(2) A woven or knitted fabric containing a) a used polyester product and b) a fiber made of a recycled polyester resin (polyester resin A) containing 40% by mass or more of a component derived from at least one recycled polyester raw material of polyester waste generated in a process for producing a polyester resin or a polyester product, wherein the polyester resin A has a diethylene glycol content of 4 mol% or less, a carboxyl end group concentration of 30 equivalents/t or less, and an average pressure rise rate of 0.6 MPa/h or less when the total amount of all glycol components is taken as 100 mol% (wherein the average pressure rise rate is a value calculated by the following procedure: using a pressure rise tester including an extruder and a pressure sensor, A stainless steel filter (nominal mesh size: 1400 mesh, weave: twill weave, vertical mesh: 165 mesh, horizontal mesh: 1400 mesh, vertical line diameter: 0.07 mm, horizontal line diameter: 0.04 mm, filtration particle size: 12 μm) was set at the tip of an extruder, polyester resin was melted at 300° C. in the extruder, and the melt was extruded from the filter at a discharge rate of 29.0 g/min. The pressure value at the start of extrusion was defined as the "initial pressure value (MPa)" and the pressure value at the time of continuous extrusion for 12 hours thereafter was defined as the "final pressure value (MPa)." Based on these pressure values, the average pressure rise rate was calculated using the following calculation formula A:
Average pressure rise rate (MPa / h) = (final pressure value - initial pressure value) / 12 ... A),
and wherein the single yarn fineness of the fiber made of the polyester resin A is 1.0 dtex or less.
(3) A method for producing a woven or knitted fabric according to (2), comprising the steps of: obtaining a green fabric by weaving or knitting the polyester-based splittable composite fiber for woven or knitted fabrics according to (1); and subjecting the green fabric to an alkali weight reduction treatment to elute the polyester resin B, thereby splitting and splitting the polyester resin A portion.

In the polyester splittable conjugate fiber of the present invention (hereinafter sometimes referred to as the conjugate fiber of the present invention), the recycled polyester resin used as the polyester resin A, which is a component hardly soluble by alkali, contains little foreign matter and has a carboxyl end group concentration and a diethylene glycol content that satisfy specific ranges, so that in the process of obtaining fibers by melt spinning, long-term continuous operation is possible even for fibers with complex cross-sectional shapes, and products can be obtained with good productivity. Furthermore, the conjugate fiber of the present invention has mechanical property values similar to those of fibers using virgin polyester resins, and can be suitably used in various fields and applications such as various clothing and industrial fields.
The woven or knitted fabric of the present invention contains fine fibers made of the recycled polyester resin, and therefore has mechanical properties similar to those of fabrics made using virgin polyester resin, and is also excellent in flexibility and density.

FIG. 1 is a schematic diagram showing one embodiment of a cross section of a conjugate fiber (single fiber) of the present invention.

The present invention will be described in detail below.
The conjugate fiber of the present invention contains polyester resin A, which is a component that is hardly soluble in alkali, and polyester resin B, which is a component that is easily soluble in alkali.

The polyester resin A, which is the poorly alkali-soluble component of the present invention, is a recycled polyester resin containing a component derived from at least one recycled polyester raw material, i.e., a) used polyester product and b) unused polyester generated in the process of producing a polyester product.
The above-mentioned used polyester products (a) include, for example, polyester molded products (including fibers) that were once distributed on the market and then collected after use, etc. Representative examples thereof include containers such as PET bottles and packaging materials.
The unadopted polyester generated in the process of manufacturing the polyester product of b) above is polyester that has not been commercialized. Examples of such unadopted polyester include resin pellets that do not meet the specifications, materials that are no longer needed during molding, pieces cut during molding, scraps generated during molding or processing, cut-up pieces of transitional products generated when the brand is changed, cut-up pieces of prototypes or defective products, etc.
The above a) and b) are not limited in terms of their form, and may be pelletized by further processing such as crushing and cutting as necessary, or may be melted and pelletized.
The recycled polyester raw materials a) and b) may be either crystalline or amorphous. Therefore, for example, pellets of amorphous polyester waste that have not been heat-treated, crystalline pellets that have been heat-treated, or a mixture of crystalline pellets and amorphous pellets can be used. In the present invention, it is preferable to use crystalline recycled polyester raw materials, particularly for the purpose of preventing the pellets from fusing together during charging into the can or during the depolymerization reaction. Therefore, materials a) or b) that have been crystallized by heat treatment (crystallized pellets, etc.) can be suitably used.

The polyester resin A of the present invention preferably contains 40% by mass or more of the recycled polyester raw material, and more preferably 50% by mass or more. If the content of the recycled polyester raw material is less than 40% by mass, the objective of considering environmental issues cannot be achieved. There is no particular upper limit to the content of the recycled polyester raw material, but according to the manufacturing method of polyester resin A described below, it is possible to easily obtain polyester resin A with a recycled polyester raw material content of 40 to 80% by mass.

The polyester resin A of the present invention has the characteristic values of a diethylene glycol content of 4 mol% or less and a carboxyl end group concentration of 30 equivalents/t or less when the total amount of all glycol components is 100 mol%.

In the polyester resin A of the present invention, when the total amount of all glycol components is 100 mol%, the diethylene glycol content is 4 mol% or less, and preferably 3.5 mol% or less. In particular, in the polyester resin A obtained by the manufacturing method described later, ethylene glycol is used as one of the raw materials, and diethylene glycol may be generated as a by-product. The polyester resin A has a small amount of diethylene glycol as a by-product, and has excellent crystallinity due to the diethylene glycol content of 4 mol% or less. For this reason, melt spinning can be performed with good operability like virgin polyester, and it is possible to obtain a composite fiber with a complex cross-sectional shape in which the polyester resin A is divided into multiple pieces by the polyester resin B as shown in Figure 1 described later. It is also possible to obtain a composite fiber with excellent mechanical properties such as strength and elongation. The lower limit of the diethylene glycol content can be, for example, about 0.5 mol%, but is not limited thereto.

The polyester resin A of the present invention has a carboxyl end group concentration of 30 equivalents/t or less, preferably 25 equivalents/t or less, and most preferably 20 equivalents/t or less. By making the carboxyl end group concentration 30 equivalents/t or less, the polyester resin A has excellent thermal stability, and therefore can be melt spun with good operability like virgin polyester. Therefore, it is possible to obtain a composite fiber with a complex cross-sectional shape in which the polyester resin A is divided into a plurality of pieces by the polyester resin B, as shown in FIG. 1 described later. It is also possible to obtain a composite fiber with excellent mechanical properties such as strength and elongation.
The lower limit of the carboxyl end group concentration can be, for example, about 5 equivalents/t, but is not limited to this.

When the diethylene glycol content of the polyester resin A of the present invention exceeds 4 mol % or the carboxyl end group concentration exceeds 30 equivalents/t, the crystallinity and thermal stability of the polyester resin A are inferior, and it is not possible to efficiently obtain a composite fiber with a complex cross-sectional shape in which the polyester resin A is divided into multiple pieces by the polyester resin B through melt spinning. In other words, it is not possible to obtain a cross-sectional shape in which the polyester resin A has a uniform shape and size as shown in Figure 1. For this reason, the fibers made of the polyester resin A obtained by subjecting the polyester resin B to an alkali weight reduction treatment from such a composite fiber will have variations in shape and size.

The polyester resin A of the present invention preferably has an average pressure rise rate of 0.6 MPa/h or less, as measured by the following method. Among them, it is preferably 0.5 MPa/h or less, and more preferably 0.4 MPa/h or less. The average pressure rise rate in the present invention is an index of the amount of foreign matter derived from various inorganic substances or foreign matter derived from non-polyester resins, and the smaller the average pressure rise rate, the smaller the amount of foreign matter. By having an average pressure rise rate of 0.6 MPa/h or less, melt spinning can be performed with good productivity like virgin polyester, and it is also possible to produce fibers with excellent mechanical properties such as strength and elongation. The lower limit of the average pressure rise rate can be, for example, about 0.01 MPa/h, but is not limited thereto.
The average pressure rise rate is measured using a pressure rise tester including an extruder and a pressure sensor. A stainless steel filter (nominal mesh size: 1400 mesh, weaving: twill weave, vertical mesh: 165 mesh, horizontal mesh: 1400 mesh, vertical line diameter: 0.07 mm, horizontal line diameter: 0.04 mm, filtration grain size: 12 μm) is set at the tip of the extruder, polyester resin is melted at 300° C. in the extruder, and the melt is extruded from the filter at a discharge rate of 29.0 g/min. The pressure value at the start of extrusion is defined as the "initial pressure value (MPa)" and the pressure value at the time of continuous extrusion for 12 hours thereafter is defined as the "final pressure value (MPa)". The average pressure rise rate is calculated based on these pressure values using the following calculation formula A.
Average pressure rise rate (MPa / h) = (final pressure value - initial pressure value) / 12) ... A)

The polyester resin A of the present invention is not particularly limited in type, but it is preferable to use polyethylene terephthalate (PET) mainly composed of ethylene terephthalate units. The content of PET in the polyester resin A of the present invention is preferably 70% by mass or more, more preferably 80% by mass or more, and further preferably 90 to 100% by mass.
In particular, in the manufacturing method of polyester resin A described later, PET, which is usually a polycondensation product of ethylene glycol and terephthalic acid, can be obtained, but when components other than ethylene glycol and terephthalic acid are present in the recycled polyester raw material, polyester resins other than PET may be produced by the polycondensation reaction. For this reason, the polyester resin A may contain, in addition to the main component PET, the following components as acid components or glycol components copolymerized therein. Two or more of these components may be included.

Examples of the acid component include isophthalic acid, phthalic acid, phthalic anhydride, naphthalenedicarboxylic acid, adipic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, dodecanedioic acid, dimer acid, trimellitic anhydride, trimellitic acid, pyromellitic acid, 1,4-cyclohexanedicarboxylic acid, sebacic acid, dimer acid, etc. Examples of the glycol component include neopentyl glycol, 1,4-butanediol, 1,2-propylene glycol, 1,5-pentanediol, 1,3-propanediol, 1,6-hexamethylenediol, diethylene glycol, 1,4-cyclohexanedimethanol, dimer diol, butylethylpropanediol, (2-methyl-1,3-propanediol, trimethylolpropane, glycerin, pentaerythritol, ethylene oxide adducts of bisphenol A or bisphenol S, etc.

For the polyester resin B, which is the alkali-soluble component of the present invention, it is preferable to use polyethylene terephthalate (PET) mainly composed of ethylene terephthalate units, in view of alkali solubility, divisibility, spinnability, etc. In order to increase the dissolution rate by alkali weight reduction treatment, it is preferable to copolymerize the polyester resin B with an aromatic dicarboxylic acid component having a sulfonate group in the dicarboxylic acid component. As an aromatic dicarboxylic acid component containing a sulfonate group, 5-sodium sulfoisophthalic acid is suitable. The amount of copolymerization is appropriately selected depending on the difference in alkali dissolution rate between polyester resin A and polyester resin B, but it is preferable to set it to 0.1 to 10.0 mol%, and it is preferable to keep the amount of copolymerization as small as possible in terms of spinning operability and cost.

Furthermore, it is preferable that the polyester is copolymerized with polyalkylene glycol having an average molecular weight of 1000 to 10000. Polyalkylene glycol dissolves quickly in an alkali in polyester, cutting the molecular chains of the polyester and generating voids on the surface to increase the surface area, thereby accelerating the dissolution rate. It is preferable that the amount of polyalkylene glycol copolymerized in the polyester is 1 to 20% by mass.

In addition, modifiers (for example, matting agents, stabilizers, flame retardants, or colorants) may be added to the polyester resin A and polyester resin B described above, as long as the effects of the present invention are not impaired. In addition, various functional components (for example, cationic dye-dyeable components or heat-shrinkable components) may be copolymerized or mixed and contained.

In the cross-sectional shape of the composite fiber of the present invention, polyester resin A, which is a component that is difficult to dissolve in alkali, is divided into multiple pieces by polyester resin B, which is a component that is easily dissolved in alkali. The composite fiber of the present invention is split and split by dissolving all or part of the polyester resin B when subjected to an alkali weight reduction treatment.

Next, the arrangement of polyester resin A and polyester resin B in the conjugated fiber of the present invention will be described. In the cross section of the constituting single fiber of the present invention cut perpendicularly to the longitudinal direction, polyester resin A is divided into a plurality of pieces by polyester resin B. Figures 1(a) to (d) are schematic diagrams showing embodiments of the cross-sectional shape of a single fiber of such conjugated fiber, in which 1 is polyester resin A, 2 is polyester resin B, and 3 is a hollow portion.
FIG. 1(a) shows a fiber having a hollow portion 3 near the center, with 20 flat segments made of polyester resin A radially arranged around the hollow portion.
FIG. 1(b) shows eight roughly triangular segments made of polyester resin A arranged radially.
FIG. 1(c) shows 19 circular segments made of polyester resin A arranged in an array.
FIG. 1(d) shows ten flat segments made of polyester resin A arranged radially.

In the composite fiber of the present invention, in order to easily peel off each segment during the alkali weight reduction treatment and subsequent processes and to achieve a high degree of division, it is preferable that the multiple segments of polyester resin A exist in an independent state without contacting other segments due to polyester resin B, as shown in Figure 1.

The number of segments of polyester resin A in the composite fiber of the present invention is not particularly limited, but taking into consideration the spinnability, ease of spinneret preparation, and the productivity of ultrafine fibers, it is preferable to have 2 to 60 segments, and more preferably 4 to 30 segments. The shape of the segments is not particularly limited, and as shown in Figure 1, they can be flat, approximately triangular, round, etc., and according to the composite fiber of the present invention, the ultrafine fibers made of polyester resin A that are finally obtained can have various shapes.

In other words, the composite fiber of the present invention is split by alkali weight reduction treatment, but when alkali weight reduction treatment is performed, polyester resin B is dissolved, and each segment of polyester resin A is separated to obtain an ultrafine fiber.

The volumetric composite ratio of polyester resin A to polyester resin B is preferably 60/40 to 95/5, taking into consideration the single yarn fineness of the composite fiber, the number of divisions, the single yarn fineness of the ultrafine fiber after the division process, etc., and is preferably 75/25 to 85/15. Within this range, polyester resin A can be easily divided by the alkaline reduction treatment, and the amount of polyester resin B eluted by the alkaline solution is small, making it economical. In addition, the fabric obtained after the alkaline reduction treatment has little loosening of the structure, and the occurrence of structure misalignment can be suppressed, so a high-density fabric with excellent texture can be obtained.

The ultrafine fibers made of polyester resin A obtained after such splitting must have a single-filament fineness of 1.0 dtex or less, preferably 0.5 dtex or less, and more preferably 0.2 dtex or less. If the ultrafine fibers are 0.5 dtex or less, the resulting fiber structure will be more flexible and dense, and will be suitable for polishing and cleaning performance. In addition, taking into consideration spinnability and ease of spinneret production, the single-filament fineness is preferably 0.01 dtex or more.

The composite fiber of the present invention may be either a highly oriented undrawn yarn (POY) or a drawn yarn (FDY).
The single fiber fineness of the conjugated fiber of the present invention is not particularly limited, but considering the number of segments of the polyester resin A as described above and the single fiber fineness of the ultrafine fiber obtained after splitting, it is preferably 1 to 5.0 dtex.
The composite fiber of the present invention may be either a multifilament or a monofilament, but is preferably a multifilament, and preferably has a total fineness of 40 to 130 dtex.

The composite fiber of the present invention uses a recycled polyester resin that satisfies the above-mentioned characteristic values as polyester resin A, and therefore has performance equivalent to that of virgin polyester resin. For this reason, the strength of the composite fiber of the present invention is preferably 2.0 cN/dtex or more in the case of POY, and more preferably 2.4 cN/dtex or more. In the case of FDY, it is preferably 3.0 cN/dtex or more, and more preferably 3.5 cN/dtex or more. In addition, the elongation of the composite fiber of the present invention is preferably 90 to 140% in the case of POY, and more preferably 100 to 130%. In the case of FDY, it is preferably 25 to 55%, and more preferably 30 to 50%. By satisfying the above strength and elongation, woven fabrics and knitted fabrics can be obtained with good operability without thread breakage during weaving and knitting.

Next, the woven or knitted fabric of the present invention is a woven or knitted fabric which contains, at least in part, fibers made of the polyester resin A described above.
The content of the fiber made of polyester resin A in the woven or knitted fabric of the present invention is preferably 25% by mass or more, and more preferably 35% by mass or more. As a fiber that can be used as a fiber other than the fiber made of polyester resin A, polyester fibers are preferable, and those having the same fineness as the conjugate fiber of the present invention or those having a fine fineness can be used. Also, those having high shrinkage can be used.

The woven or knitted fabric of the present invention can be obtained by subjecting the woven or knitted fabric obtained by weaving or knitting a part of the composite fiber of the present invention to an alkali weight reduction treatment, dissolving the polyester resin B in the composite fiber of the present invention, and splitting the polyester resin A part. The details of the manufacturing method will be described later.

The woven and knitted fabrics of the present invention are not particularly limited in terms of weave. Examples of woven fabrics include woven, twill, satin, dobby, and double weave. The knitted fabrics of the present invention are also not particularly limited in terms of weave, and examples include circular knits such as plain jersey, smooth, rib, and pique, and warp knits such as single tricot and half tricot.

Next, a method for producing the polyester resin A, which is a recycled polyester resin, will be described. In the method for producing the polyester resin A of the present invention, it is important to carry out the steps (1) to (5) in this order.
(1) A slurry of ethylene glycol and terephthalic acid is added to obtain ethylene terephthalate oligomers.
(2) Ethylene glycol is added to the oligomer obtained in (1).
(3) The recycled polyester raw material is added to the oligomer obtained in (2) to which ethylene glycol has been added under normal pressure while stirring, so that the molar ratio of total glycol components/total acid components becomes 1.08 to 1.35, and depolymerization is performed under heat treatment conditions of 245 to 280° C.
(4) The depolymerized polymer obtained in (3) is passed through a metal filter having a filtration grain size of 10 to 25 μm to filter out foreign matter.
(5) A polymerization catalyst is added to the depolymerized product obtained in (4) after filtering out foreign matter, and a polycondensation reaction is carried out at a temperature of 260° C. or higher and a reduced pressure of 1.0 hPa or lower.

First, in the step (1), a slurry of ethylene glycol and terephthalic acid is added as a preliminary step to depolymerize the recycled polyester raw material [a) used polyester products and b) at least one of unused polyesters generated in the process of manufacturing polyester products] to obtain an esterification reaction product (ethylene terephthalate oligomer). The amount of the ethylene terephthalate oligomer is preferably 0.20 to 0.80% by mass, more preferably 0.30 to 0.70% by mass, of the finally obtained recycled polyester resin (100% by mass).
If the amount of ethylene terephthalate oligomer is less than the above range, the recycled polyester raw material is likely to block with itself when the recycled polyester raw material is added in step (3), which is undesirable because it places an excessive load on the mixer.
On the other hand, if the amount of ethylene terephthalate oligomer is more than the above range, no particular problem occurs in the depolymerization reaction, but the recycling rate of the finally obtained recycled polyester resin is undesirably low.

In the step (2), ethylene glycol is added to the ethylene terephthalate oligomer obtained in the step (1).
In order to sufficiently advance the depolymerization reaction in the step (3), the amount of ethylene glycol added is preferably 5 to 15 mass % relative to 100 mass % of the ethylene terephthalate oligomer, and more preferably 10 to 15 mass %. If the amount of ethylene glycol added exceeds 15 mass %, the ethylene terephthalate oligomer tends to solidify in the reactor, which may make it impossible to continue the subsequent reaction, and this is not preferable.
When ethylene glycol is added to the ethylene terephthalate oligomer, it is preferable to uniformize the temperature of the contents while rotating the stirrer before adding the ethylene glycol, in order to prevent the oligomer from solidifying.

In the step (3), the recycled polyester raw material is added with stirring to the oligomer obtained in the step (2) to which ethylene glycol has been added, so that the molar ratio of total glycol components/total acid components is 1.08 to 1.35, and depolymerization is carried out under heat treatment conditions of 245 to 280°C.
In the production method of the present invention, this step is important. That is, in conventional methods using recycled polyester raw materials, depolymerization is carried out using only the recycled polyester raw materials, but in the present invention, the recycled polyester raw materials are depolymerized in the presence of ethylene terephthalate oligomer and ethylene glycol, and the recycled polyester raw materials are charged with all components, oligomer, ethylene glycol, and recycled polyester raw materials, in such a way that the molar ratio of total glycol components/total acid components is 1.08 to 1.35, and depolymerization is carried out. The molar ratio of total glycol components/total acid components is preferably 1.10 to 1.33, more preferably 1.12 to 1.30.
By carrying out the above-mentioned steps (1) to (3), not only various inorganic substances but also foreign substances derived from non-polyester resins are efficiently precipitated, so that these foreign substances can be filtered out without fail in the step (4). In the polycondensation reaction in the step (5), it becomes possible to obtain a recycled polyester resin having a diethylene glycol content and a carboxyl end group concentration that are not more than a specific amount as characteristic values of the present invention, and having a small amount of foreign substances mixed in.
In the production method of the present invention, it is preferable that the above-mentioned depolymerization reaction does not decompose the recycled polyester raw material into monomers, but into oligomers having a repeating unit of about 5 to 20. By controlling in this way, not only various inorganic substances but also foreign substances derived from non-polyester resins are efficiently precipitated, so that it is possible to remove a larger amount of foreign substances.
If the molar ratio of total glycol components/total acid components during the depolymerization reaction is outside the above range, the resulting recycled polyester resin will not satisfy at least one of the carboxyl end group concentration and diethylene glycol content specified in the present invention, and will have a high average pressure rise rate. This is because, when the molar ratio of total glycol components/total acid components during the depolymerization reaction is outside the above range, the precipitation of various inorganic substances and foreign substances derived from non-polyester resins is not efficiently carried out, and these foreign substances cannot be filtered out completely in the step (4), and the foreign substances precipitate after the polycondensation reaction in the step (5), resulting in a recycled polyester resin with a high average pressure rise rate.

The reactor used in the production method of the present invention may be a commonly used esterification reactor without any particular problem in terms of volume and shape of the stirring blades. However, in order to efficiently advance the depolymerization reaction, it is preferable that the reactor has a structure equipped with a distillation column that does not distill ethylene glycol outside the system.
When the recycled polyester raw material is charged, it is preferable to carry out the charging under normal pressure while stirring, and it is more preferable to charge it in a state where it is purged with a small amount of inert gas (generally nitrogen gas is used).

The reaction temperature during depolymerization in the step (3) is preferably set at an internal temperature of the reactor in the range of 245 to 280° C., and more preferably set at an internal temperature in the range of 255 to 280° C. If the reaction temperature during depolymerization is less than 245° C., the reaction product solidifies, the operability deteriorates, and even if a recycled polyester resin is obtained, the diethylene glycol content and the carboxyl end group concentration become too high. If the reaction temperature exceeds 280° C., the diethylene glycol content and the carboxyl end group concentration of the obtained recycled polyester resin become too high.
The depolymerization reaction time (the reaction time from the end of the introduction of the recycled polyester raw material) is preferably within 4 hours, and from the viewpoints of suppressing the amount of diethylene glycol as a by-product and suppressing deterioration in the color tone of the polyester, it is more preferably within 2 hours.

In the step (4), the depolymerized product from the step (3) is passed through a metal filter having a filtration particle size of 10 to 25 μm to filter out foreign matter. As described above, by carrying out the depolymerization reaction under the conditions of the step (3), not only various inorganic substances but also foreign matter derived from non-polyester resins is efficiently precipitated, and therefore, by passing the depolymerized product through a metal filter having a filtration particle size of 10 to 25 μm, the precipitated foreign matter can be filtered out to obtain a depolymerized product with a small amount of foreign matter mixed in.
If a metal filter with a filtering particle size of more than 25 μm is used, foreign matter in the polymer cannot be sufficiently removed, and the resulting recycled polyester resin contains a large amount of foreign matter. Therefore, when such a resin is used for spinning, the nozzle pack is pressurized and yarn breakage occurs. On the other hand, if a metal filter with a filtering particle size of less than 10 μm is used, clogging due to foreign matter is likely to occur, and the filter life is shortened, which is disadvantageous in terms of cost and also deteriorates operability.

The metal filters that can be used in step (4) of the present invention can be general-purpose filters, but examples include screen changer filters, leaf disk filters, and candle-type sintered filters.

In the manufacturing method of the present invention, a polymerization catalyst is added to the depolymerization product obtained after the foreign matter filtration through the above step (4), and a polycondensation reaction is carried out at a temperature of 260° C. or higher and a reduced pressure of 1.0 hPa or lower. As the polymerization catalyst, for example, one or more of germanium, antimony, titanium, and cobalt compounds can be used, but preferably a germanium or antimony compound is used. Furthermore, when the transparency of the resulting recycled polyester resin is important, it is preferable to use a germanium compound. Examples of germanium or antimony compounds include oxides, inorganic acid salts, organic acid salts, halides, and sulfides thereof. It is preferable to use 5×10 ⁻⁵ mol/unit or more of these polycondensation catalysts per mole of the acid component of the polyester resin to be produced, and more preferably 6×10 ⁻⁵ mol/unit or more.
In addition, since the polymerization catalyst contained in the recycled polyester raw material may also act as a catalyst during the polycondensation reaction, it is preferable to take into consideration the amount and type of the polymerization catalyst contained in the recycled polyester raw material when adding the polymerization catalyst in step (4).

During the polycondensation reaction, a fatty acid ester, a hindered phenol-based antioxidant, or a phosphorus compound may be added in addition to the above-mentioned polymerization catalyst.
Specific examples of fatty acid esters include beeswax (a mixture mainly composed of myricyl palmitate), stearyl stearate, behenyl behenate, stearyl behenate, glycerin monopalmitate, glycerin monostearate, glycerin distearate, glycerin tristearate, pentaerythritol monopalmitate, pentaerythritol monostearate, pentaerythritol distearate, pentaerythritol tristearate, pentaerythritol tetrastearate, dipentaerythritol hexastearate, etc. Among these, glycerin monostearate, pentaerythritol tetrastearate, and dipentaerythritol hexastearate are preferred.

Hindered phenol antioxidants include 2,6-di-t-butyl-4-methylphenol, n-octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane, tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, 4,4'-butylidenebis-(3-methyl-6-t-butylphenol), triethyl Examples of compounds that can be used include ethylene glycol-bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate] and 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1'-dimethylethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane, but in terms of effectiveness and cost, tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane is preferred.

Phosphorus compounds that can be used include phosphorous acid, phosphoric acid, trimethyl phosphite, triphenyl phosphite, tridecyl phosphite, trimethyl phosphate, tridecyl phosphate, and triphenyl phosphate.

Then, in the polycondensation reaction tank, the polycondensation reaction is carried out at a temperature of 260° C. or higher and under a reduced pressure of 1.0 hPa or lower. If the polycondensation reaction temperature is lower than 260° C. or the pressure during the polycondensation reaction exceeds 1.0 hPa, the polycondensation reaction time becomes long, resulting in poor productivity.
The polycondensation reaction temperature is more preferably 270° C. or higher. However, if the polycondensation reaction temperature is too high, the polymer is colored due to thermal decomposition, the color tone is deteriorated, and the amount of terminal groups (COOH) is also increased due to thermal decomposition. Therefore, in the present invention, the upper limit of the polycondensation reaction temperature is preferably 285° C. or lower.

The intrinsic viscosity of the polyester resin A of the present invention obtained by the above polycondensation reaction is preferably 0.38 to 0.70 dl/g, taking into consideration melt spinning.

Next, a method for producing the composite fiber of the present invention will be described.
The following is an embodiment of a manufacturing method in which the conjugate fiber of the present invention is FDY, and melt spinning can be performed using a normal conjugate spinning device. In melt conjugate spinning of FDY of the present invention, polyester resin B is spun from a spinneret so as to divide polyester resin A. Specifically, polyester resin A and polyester resin B are prepared, and after being separately melted, they pass through separate pipes and flow into a spinneret pack. The polymers flowing into the pack are joined by the spinneret, and are combined into a split fiber type, orange type, sea island type, or other form by a known technique and discharged from the spinneret. In this case, it is appropriate to perform spinning under conditions of a spinning temperature of 280 to 295°C and a spinning speed of 3000 to 3600 m/min. After spinning, the polymer discharged from the spinneret is cooled and solidified, and an oil agent is applied, and then the conjugate fiber of the present invention (FDY) is obtained by drawing and heat treating at a drawing temperature of 70 to 90°C, a draw ratio of 1 to 2 times, and a heat treatment temperature of 140 to 170°C.

Next, the method for producing the woven or knitted fabric of the present invention will be described.
The woven or knitted fabric of the present invention can be obtained, for example, by subjecting a grey fabric obtained through processes such as weaving and knitting using the conjugate fiber of the present invention obtained by the above-mentioned production method to an alkali weight reduction treatment.
The alkali weight loss treatment may be carried out by a conventionally known method. In the case of a splittable composite fiber as shown in FIG. 1(a), the amount of dissolution and removal by the alkali solution, i.e., the weight loss, is preferably about 15 to 30% by mass, and more preferably about 20 to 25% by mass. If the weight loss rate is less than 15% by mass, the splittable composite fiber is not sufficiently split and the woven or knitted fabric tends not to have a good feel. If the weight loss rate exceeds 30% by mass, the splittable fiber is satisfactorily split, but the ultrafine fibers are also slightly dissolved, and the strength of the resulting woven or knitted fabric tends to decrease.
The conditions for the alkali dissolution treatment are those generally used in the weight reduction process of polyester fiber structures, and include, for example, a method using a 0.5% to 5.0% aqueous sodium hydroxide solution, more preferably 1.0% to 3.0%, and particularly preferably 1.0% to 2.0%. The treatment temperature is preferably 85°C to 100°C, and more preferably 90°C to 98°C.

The present invention will now be described in more detail with reference to the following examples, in which the various property values and the like are measured and evaluated as follows:
(a) Intrinsic Viscosity The intrinsic viscosity was measured using a mixture of equal masses of phenol and tetrachloroethane as a solvent at a concentration of 0.5 g/dl and a temperature of 20°C.
(b) Composition of Polyester Resin A polyester resin was dissolved in a mixed solvent of deuterated hexafluoroisopropanol and deuterated chloroform in a volume ratio of 1/20, and 1H-NMR was measured using a JEOL LA-400 NMR apparatus. The type and content of copolymerization components were determined from the integrated intensity of the proton peak of each component in the obtained chart.
(c) Carboxyl End Group Concentration 0.1 g of the resulting recycled polyester resin was dissolved in 10 ml of benzyl alcohol, 10 ml of chloroform was added to the solution, and the solution was titrated with a 1/10 N potassium hydroxide benzyl alcohol solution to determine the carboxyl end group concentration.
(d) Average pressure rise rate measured by pressure rise tester. Measured by the above-mentioned method.

(e) Strength of splittable composite fiber: Measured according to JIS L-1013 using an autograph DSS-500 manufactured by Shimadzu Corporation at a gripping distance of 25 cm and a pulling speed of 30 cm.
(f) Elongation of splittable composite fiber: According to JIS L-1013, measurement was performed using an autograph DSS-500 manufactured by Shimadzu Corporation at a gripping distance of 25 cm and a pulling speed of 30 cm.
(g) Single yarn fineness (dtex) of splittable composite fiber
Measurement was performed according to JIS L-1013 8.3.1B method.

(h) Spinnability The state of yarn breakage during melt spinning in obtaining POY was evaluated on the following three-level scale based on the number of yarn breakages per spindle when melt spinning was carried out continuously for 24 hours.
○: The number of thread breakages was 0.
△: The thread broke once or twice.
x: The thread broke three or more times.
(i) Stretchability The state of yarn breakage during drawing of POY was evaluated according to the number of breaks (total number) when drawing was performed continuously for 10 hours using 100 spindles, and the result was rated into the following three-level scale.
○: The number of cuts was 0 to 1.
△: The number of cuts was 2 to 4.
×: The number of breaks was 5 or more.
(j) Fabric nap (raised feel, texture)
The resulting woven fabric was evaluated for nap feel based on the following criteria.
◯: The nap feeling is good.
△: The feeling of standing hair is normal.
×: The feeling of standing up is insufficient.
(k) Softness of Woven Fabric The softness of the obtained woven fabric was evaluated by touch according to the following criteria.
○: Feels soft to the touch.
△: Feels normal to the touch.
×: Feels hard to the touch.

[Production of recycled polyester resin]
Recycled polyester resin A
A slurry of terephthalic acid (TPA) and ethylene glycol (EG) (TPA/EG molar ratio = 1/1.6) was supplied to an esterification reactor and reacted under conditions of a temperature of 250°C and a pressure of 50 hPa to obtain an ethylene terephthalate oligomer (number average degree of polymerization: 5) with an esterification reaction rate of 95%.
45.0 parts by mass of ethylene terephthalate oligomer was charged into the esterification reactor, and then 10.0 parts by mass of ethylene glycol was charged while the agitator of the esterification reactor was rotating. When the internal temperature of the esterification reactor (hereinafter referred to as "ES can") stopped decreasing, 55.0 parts by mass of recycled polyester raw material (pellet-shaped polyester waste generated in the process of producing polyester resin) was charged in a fixed amount over about 2 hours via a rotary valve. At this time, the recycled polyester raw material was charged so that the molar ratio of total glycol components/total acid components (hereinafter sometimes referred to as "G/A") was 1.20.
Thereafter, a depolymerization reaction was carried out for 1 hour under heat treatment conditions at 270° C. Then, the obtained depolymerization product was pressure-fed to a polycondensation reactor (hereinafter referred to as a PC can) with a candle filter having an opening of 20 μm set between the esterification reactor and the polycondensation reactor, and then antimony trioxide was added as a polymerization catalyst at 1.0×10 ⁻⁴ mol/unit and EG slurry of titanium dioxide at 0.20 mass %, and the PC can was decompressed and, 60 minutes later, a melt polymerization reaction was carried out at a final pressure of 0.5 hPa and a temperature of 275° C. for 4 hours to obtain a recycled polyester resin A (intrinsic viscosity: 0.64).

Recycled polyester resin B
In the same manner as in the case of the recycled polyester resin A, an ethylene terephthalate oligomer (number average degree of polymerization: 5) having an esterification reaction rate of 95% was obtained.
30.0 parts by mass of ethylene terephthalate oligomer was charged into the ES can, and then 7.0 parts by mass of ethylene glycol was added while the agitator of the ES can was rotating. When the internal temperature of the ES can stopped decreasing, 70.0 parts by mass of recycled polyester raw material (same as in Example 1) was added in a fixed amount over about 2 hours via a rotary valve.
At this time, the recycled polyester raw material was charged so that G/A was 1.10. Then, a depolymerization reaction was carried out for 1 hour under heat treatment conditions at 270° C. Then, the obtained depolymerization was pressure-fed to a PC can with a candle filter having an opening of 20 μm set between the ES can and the PC can, and then antimony trioxide was added as a polymerization catalyst to a concentration of 1.0×10 ⁻⁴ mol/unit. After 60 minutes of reducing the pressure in the PC can, a melt polymerization reaction was carried out at a final pressure of 0.5 hPa and a temperature of 275° C. for 5 hours to obtain a recycled polyester resin B (intrinsic viscosity: 0.65).

Recycled polyester resin C
An ethylene terephthalate oligomer (number average degree of polymerization: 5) with an esterification reaction rate of 95% was obtained in the same manner as in Example 1. 45.0 parts by mass of the ethylene terephthalate oligomer was charged into an ES can, and then 7.0 parts by mass of ethylene glycol was added while the agitator of the ES can was rotating. When the internal temperature of the ES can stopped decreasing, 55.0 parts by mass of recycled polyester raw material (PET bottles crushed or remelted and pelletized) was added in a fixed amount over about 2 hours via a rotary valve.
At this time, the recycled polyester raw material was charged so that G/A was 1.16. Then, a depolymerization reaction was carried out for 1 hour under heat treatment conditions at 270°C. Then, the obtained depolymerization was pressure-fed to a PC can by setting a candle filter with an opening of 20 μm between the ES can and the PC can, and then antimony trioxide was added as a polymerization catalyst at 1.0×10 ⁻⁴ mol/unit and EG slurry of titanium dioxide at 0.40 mass%, and the PC can was decompressed and melt polymerization reaction was carried out at a final pressure of 0.5 hPa and a temperature of 275°C for 4 hours after 60 minutes to obtain a recycled polyester resin C (intrinsic viscosity: 0.64).

Recycled polyester resin D
In the same manner as in Example 1, an ethylene terephthalate oligomer (number average degree of polymerization: 5) having an esterification reaction rate of 95% was obtained.
45.0 parts by mass of ethylene terephthalate oligomer was charged into the ES can, and then 10.0 parts by mass of ethylene glycol was added while the agitator of the ES can was rotating. When the internal temperature of the ES can stopped decreasing, 55.0 parts by mass of recycled polyester was added in a fixed amount over about 2 hours via a rotary valve. At this time, the recycled polyester raw material (same as in Example 1) was added so that the G/A was 1.20.
Thereafter, a depolymerization reaction was carried out for 1 hour under heat treatment conditions at 270° C. Then, the obtained depolymerization product was pressure-fed into a PC can through a candle filter with a mesh size of 25 μm set between the ES can and the PC can, and then antimony trioxide was added as a polymerization catalyst at 1.0×10 ⁻⁴ mol/unit, cobalt acetate at 0.5×10 ⁻⁴ mol/unit, and EG slurry of titanium dioxide at 0.05 mass %. The PC can was decompressed, and after 60 minutes, a melt polymerization reaction was carried out at a final pressure of 0.5 hPa and a temperature of 280° C. for 3 hours to obtain a recycled polyester resin D (intrinsic viscosity: 0.56).

Recycled polyester resin E
In the same manner as in the case of the recycled polyester resin A, an ethylene terephthalate oligomer (number average degree of polymerization: 5) having an esterification reaction rate of 95% was obtained.
30.0 parts by mass of ethylene terephthalate oligomer was charged into an ES can, and then 2.5 parts by mass of ethylene glycol was added while the agitator of the ES can was rotating. When the internal temperature of the ES can stopped decreasing, 70.0 parts by mass of recycled polyester was added in a fixed amount over about 2 hours via a rotary valve. At this time, the recycled polyester raw material (same as in Example 1) was added so that the G/A was 1.06.
Thereafter, a depolymerization reaction was carried out for 1 hour under heat treatment conditions at 270° C. Then, the obtained depolymerization product was pressure-fed into a PC can through a candle filter with a mesh size of 20 μm set between the ES can and the PC can, and then antimony trioxide was added as a polymerization catalyst at 1.0×10 ⁻⁴ mol/unit, cobalt acetate at 0.5×10 ⁻⁴ mol/unit, and EG slurry of titanium dioxide at 0.40 mass %. The PC can was decompressed, and after 60 minutes, a melt polymerization reaction was carried out at a final pressure of 0.5 hPa and a temperature of 275° C. for 4 hours to obtain a recycled polyester resin E (intrinsic viscosity: 0.64).

Recycled polyester resin F
In the same manner as in the case of the recycled polyester resin A, an ethylene terephthalate oligomer (number average degree of polymerization: 5) having an esterification reaction rate of 95% was obtained.
50.0 parts by mass of ethylene terephthalate oligomer was charged into an ES can, and then 19.0 parts by mass of ethylene glycol was added while the agitator of the ES can was rotating. When the internal temperature of the ES can stopped decreasing, 50.0 parts by mass of recycled polyester was added in a fixed amount over about 2 hours via a rotary valve. At this time, recycled polyester raw material (same as in Example 1) was added so that G/A was 1.36.
Thereafter, a depolymerization reaction was carried out for 1 hour under heat treatment conditions at 270° C. Then, the obtained depolymerization product was pressure-fed into a PC can through a candle filter with a mesh size of 20 μm set between the ES can and the PC can, and then antimony trioxide was added as a polymerization catalyst at 1.0×10 ⁻⁴ mol/unit, cobalt acetate at 0.5×10 ⁻⁴ mol/unit, and EG slurry of titanium dioxide at 0.40 mass %. After 60 minutes of reducing the pressure of the PC can, a melt polymerization reaction was carried out at a final pressure of 0.5 hPa and a temperature of 275° C. for 4 hours to obtain a recycled polyester resin F (intrinsic viscosity: 0.64).

Virgin polyester resin A slurry of terephthalic acid (TPA) and ethylene glycol (EG) (TPA/EG molar ratio = 1/1.6) was supplied to an esterification reactor and reacted under conditions of a temperature of 250°C and a pressure of 50 hPa to obtain an ethylene terephthalate oligomer (number average degree of polymerization: 5) with an esterification reaction rate of 95%.
100.0 parts by mass of ethylene terephthalate oligomer was charged into a PC can, and 1.0 × 10 ^-4 mol/unit of antimony trioxide as a polymerization catalyst and 0.20 mass% of EG slurry of titanium dioxide were added thereto. The PC can was reduced in pressure, and after 60 minutes, a melt polymerization reaction was carried out at a final pressure of 0.5 hPa and a temperature of 275°C for 3 hours to obtain a virgin polyester resin (intrinsic viscosity 0.46).

The properties of recycled polyester resins A to F and virgin polyester resin are shown in Table 1.

As is clear from Table 1, the recycled polyester resins A to D obtained by carrying out the above-mentioned steps (1) to (5) in order had carboxyl terminal group amounts and diethylene glycol contents within the ranges specified in the present invention, and also had low average pressure rise rates.
On the other hand, in the case of the recycled polyester resin E, since the G/A ratio during the depolymerization reaction in the above-mentioned step (3) was low, the concentration of carboxyl terminal groups was high and the average pressure increase rate was also high.
In the case of the recycled polyester resin F, since the G/A ratio during the depolymerization reaction in the above-mentioned step (3) was high, the diethylene glycol content was high and the average pressure increase rate was also high.

Example 1
The polyester resin A was recycled polyester resin A, and the polyester resin B was copolymerized with 2.5 mol% of 5-sodium sulfoisophthalic acid (SIP-Na) and 12.0 mass% of polyethylene glycol (PEG) having an average molecular weight of 8000, and had an intrinsic viscosity of 0.72. The composite mass ratio of polyester resin A/B was 81.2/18.8, and the spinning temperature was 288° C., the discharge rate was 36 g/min, and the spinning was performed using a composite spinning device equipped with a spinneret having 48 spinning holes designed so that polyester resin B divides polyester resin A into 8. The spun yarn was cooled, oiled, and wound up at a speed of 3100 m/min to obtain POY of 120 dtex/48 filaments. Next, this POY was stretched 1.56 times through a heating roller at 84° C. and further heat-treated on a heat plate at 153° C. to obtain a splittable conjugate fiber (FDY) of 75 dtex/48 filaments. The resulting splittable conjugate fiber had a strength of 3.45 cN/dtex and an elongation of 37.9%, and the cross-sectional shape of each single fiber was as shown in FIG. 1(b).
The resulting splittable conjugate fiber was false-twisted at 175°C and 3000 twists/m using a commercially available false-twisting machine, and a plain weave fabric with a green density of 145 warp/2.54 cm and 95 weft/2.54 cm was woven using this textured yarn as the warp and weft. The resulting plain weave fabric was subjected to an alkali weight reduction treatment in the dyeing process under conditions of 20 g/L caustic soda, a bath ratio of 1:30, and a temperature of 98°C, whereby polyester resin B was dissolved and removed from the splittable conjugate fiber in the fabric, and the fabric was split into ultrafine fibers made of polyester resin A. A conventional finishing process was then performed to obtain a woven fabric.

Example 2
A composite fiber of the present invention (75 dtex/48 filaments) was obtained in the same manner as in Example 1, except that recycled polyester resin B was used instead of polyester resin A. Further, a woven fabric was obtained by weaving and carrying out an alkali weight reduction treatment in the same manner as in Example 1.

Example 3
A composite fiber of the present invention (75 dtex/48 filaments) was obtained in the same manner as in Example 1, except that recycled polyester resin C was used instead of polyester resin A. Further, a woven fabric was obtained by weaving and carrying out an alkali weight reduction treatment in the same manner as in Example 1.

Example 4
A composite fiber of the present invention (75 dtex/48 filaments) was obtained in the same manner as in Example 1, except that recycled polyester resin D was used instead of polyester resin A. Further, a woven fabric was obtained by weaving and carrying out an alkali weight reduction treatment in the same manner as in Example 1.

Comparative Example 1
A polyester splittable composite fiber 75 dtex/48 filaments was obtained in the same manner as in Example 1, except that the recycled polyester resin E was used instead of the polyester resin A. Further, a woven fabric was obtained by weaving and carrying out an alkali weight reduction treatment in the same manner as in Example 1.

Comparative Example 2
A polyester splittable composite fiber 75 dtex/48 filaments was obtained in the same manner as in Example 1, except that the recycled polyester resin F was used instead of the polyester resin A. Further, a woven fabric was obtained by weaving and carrying out an alkali weight reduction treatment in the same manner as in Example 1.

Reference Example 1
A polyester splittable composite fiber of 78 dtex/48 filaments was obtained in the same manner as in Example 1, except that a virgin polyester resin was used as the polyester resin A. Further, a woven fabric was obtained by weaving and carrying out an alkali weight reduction treatment in the same manner as in Example 1.

As is clear from Table 2, the polyester splittable conjugate fibers obtained in Examples 1 to 4 were able to be easily spun into conjugate fibers having a complex cross-sectional shape in which polyester resin A was split into multiple pieces by polyester resin B, as shown in Figure 1(b). In addition, the yarn properties were comparable to those of fibers made from virgin polyester resin, and fibers with no practical problems were obtained. In addition, the texture of the woven fabrics obtained in Examples 1 to 4 after alkali weight reduction treatment was comparable to that of fibers made from virgin polyester resin in terms of both nap feel and softness, since the fibers made from polyester resin A obtained by alkali weight reduction treatment were uniform in shape and size.
On the other hand, the polyester splittable composite fiber obtained in Comparative Example 1 had poor spinnability due to the high concentration of carboxyl end groups in the recycled polyester resin used, and the cross-sectional shape of the composite fiber could not be made to have a cross-sectional shape with uniform individual shapes and sizes as shown in Figure 1 (b) for polyester resin A. In addition, the yarn properties were low in strength and elongation. In addition, the texture of the obtained woven fabric after the alkali weight reduction treatment was poor in nap feeling due to the variation in shape and size of the fibers made of polyester resin A obtained by the alkali weight reduction treatment.
The polyester-based splittable conjugate fiber obtained in Comparative Example 2 had poor stretchability because the regenerated polyester fiber used contained a high diethylene glycol content, and the cross-sectional shape of the conjugate fiber could not be made to have a uniform cross-sectional shape and size of each fiber as shown in Fig. 1(b) for polyester resin A. In addition, the texture of the obtained woven fabric after alkali weight reduction treatment was inferior in softness because the shape and size of the fibers made of polyester resin A obtained by alkali weight reduction treatment varied.

1. Polyester resin A
2 Polyester resin B
3. Hollow section

Claims (3)

A conjugated fiber having a polyester resin A which is a component hardly soluble in alkali and a polyester resin B which is a component easily soluble in alkali, in which the polyester resin A is divided into a plurality of pieces by the polyester resin B in the cross section of the fiber, and having a single yarn fineness of 5.0 dtex or less , wherein the polyester resin A is a recycled polyester resin containing 40 mass % or more of a component derived from at least one recycled polyester raw material, which is a) used polyester product and b) polyester waste generated in a process for producing a polyester resin or a polyester product, and the recycled polyester resin (polyester resin A) has a diethylene glycol content of 4 mol % or less, a carboxyl terminal group concentration of 30 equivalents/t or less , and an average pressure rise rate of 0.6 MPa/h or less when the total amount of all glycol components is taken as 100 mol % (in particular, The average pressure rise rate is a value calculated by the following procedure: a pressure rise tester including an extruder and a pressure sensor is used, a stainless steel filter (nominal mesh size: 1400 mesh, weave: twill weave, vertical mesh: 165 mesh, horizontal mesh: 1400 mesh, vertical line diameter: 0.07 mm, horizontal line diameter: 0.04 mm, filtration grain size: 12 μm) is set at the tip of the extruder, polyester resin is melted at 300° C. in the extruder, and the melt is extruded from the filter at a discharge rate of 29.0 g/min. The pressure value at the start of extrusion is defined as the "initial pressure value (MPa)", and the pressure value at the time of extrusion for 12 hours thereafter is defined as the "final pressure value (MPa)". The average pressure rise rate is calculated based on these pressure values by the following calculation formula A:
Average pressure rise rate (MPa/h)=(final pressure value-initial pressure value)/12...A) . a) used polyester products; and b) a woven or knitted fabric containing fibers made of recycled polyester resin (polyester resin A) containing 40% by mass or more of a component derived from at least one recycled polyester raw material of polyester waste generated in a process for producing polyester resin or polyester products, wherein the polyester resin A has a diethylene glycol content of 4 mol% or less, a carboxyl end group concentration of 30 equivalents/t or less, and an average pressure rise rate of 0.6 MPa/h or less when the total amount of all glycol components is taken as 100 mol% (wherein the average pressure rise rate is a value calculated by the following procedure: a pressure rise tester including an extruder and a pressure sensor is used to test the extruder. A stainless steel filter (nominal mesh size: 1400 mesh, weave: twill weave, vertical mesh: 165 mesh, horizontal mesh: 1400 mesh, vertical line diameter: 0.07 mm, horizontal line diameter: 0.04 mm, filtration particle size: 12 μm) was set at the tip of an extruder, polyester resin was melted at 300° C. in an extruder, and the melt was extruded from the filter at a discharge rate of 29.0 g/min. The pressure value at the start of extrusion was defined as the "initial pressure value (MPa)" and the pressure value at the time of continuous extrusion for 12 hours thereafter was defined as the "final pressure value (MPa)." Based on these pressure values, the average pressure rise rate was calculated using the following calculation formula A:
Average pressure rise rate (MPa / h) = (final pressure value - initial pressure value) / 12 ... A),
and wherein the single yarn fineness of the fiber made of the polyester resin A is 1.0 dtex or less. A method for producing a woven or knitted fabric according to claim 2,
A step of obtaining a green fabric by weaving or knitting the polyester-based splittable conjugate fiber for woven or knitted fabrics according to claim 1;
and subjecting the grey fabric to an alkali weight reduction treatment to elute the polyester resin B, thereby splitting and splitting the polyester resin A portion.