Pet waste fiber-derived polyester resin pellet for fiber, and method for producing the same

Abstract

To provide a PET waste fiber-derived polyester resin pellet which is suitable for a fiber.SOLUTION: A PET waste fiber-derived polyester resin pellet for a fiber contains PET and a chain extender, wherein the number of fine domains, which are dispersed in a PET matrix in a pellet and are composed of a chain extender having a major axis of 0.01 μm or more and 0.20 μm or less, is 5 or more and 50 or less per square μm of a resin cross section, MFR of a pellet, which does not have a large domain having a major axis of 0.50 μm or more and is evaluated by a method described in JIS K 7210-1, is 50 g / 10 min or more and 150 g / 10 min or less, under the conditions of a measurement temperature of 285°C and a measurement load of 2.16 kgf, and a limiting viscosity number (η) is 0.50 or more and 0.75 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to polyester resin pellets for fiber derived from PET (polyethylene terephthalate) waste fibers and a manufacturing method thereof. More specifically, the present invention relates to pre-consumer recycled polyester resin pellets obtained by remelting and filtering waste PET fiber material recovered from any pre-consumer process, such as melt spinning, false twisting and other yarn processing, twisting, weaving / knitting preparation, weaving / knitting, and nonwoven fabric manufacturing, and a manufacturing method thereof. PET waste fibers include long fibers (filaments), short fibers (staple fibers), and long-fiber nonwoven fabrics (spunbond, meltblown, etc.). [Background technology]

[0002] Polyester resin is a general-purpose resin used in a wide range of fields, including fibers, films, and resin molded products. It boasts excellent heat and chemical resistance and is relatively inexpensive, making it one of the general-purpose resins for which production and demand are expected to continue to grow. However, as production and demand expand, the amount of waste disposal continues to increase, and recycling methods must be considered worldwide, taking into account recent issues such as sustainability, SDGs, and the problem of marine microplastics.

[0003] Recycling of PET bottles has already taken root in Japan, with over 90% of the market volume being collected and reused through one of three methods: material recycling, feedstock recycling, or energy recovery. Recently, beverage manufacturers have also been promoting bottle-to-bottle recycling and circular economy initiatives, accelerating this trend. In the textile industry, bottle-to-fiber has long been the primary method of polyester recycling. However, as bottle-to-bottle recycling has accelerated, the supply of recovered PET bottles, the raw material, has fallen short of fiber demand, threatening the quantitative stability of production and the sustainability of product prices. It is now time to seriously consider fiber-to-fiber recycling.

[0004] The raw fibers used in fiber-to-fiber recycling can be broadly divided into pre-consumer materials, such as fiber scraps, discharged waste, and resin waste generated in spinning factories, textile waste from weaving and knitting factories and false twisting factories, discarded fabric from dyeing factories, and textile waste such as offcuts from sewing factories, and post-consumer materials, primarily used garments such as used clothing collected or discarded from consumers. This invention relates to recycled polyester resins used as pre-consumer materials. Note that pre-consumer recycling in this context refers to recycling recycled materials into completely different products, rather than recycling them in the same process where waste is generated. This is an extremely important initiative for reducing waste from each factory and achieving zero emissions.

[0005] In light of these current circumstances and background, various proposals have been made. For example, Patent Documents 1 and 2 propose a method of using recycled polyester resin, consisting of polyester waste generated in the virgin chip manufacturing process and / or film manufacturing process, as a raw material, remelting and pelletizing the resin, and then subjecting the resin to high-temperature solid-state polymerization under vacuum to obtain polyester fibers with high intrinsic viscosity and high elongation at break. While this method makes it possible to obtain high-strength polyester fibers suitable for industrial material applications, the intrinsic viscosity is too high for clothing applications, resulting in problems such as poor flexibility, drapeability, and ability to follow bending deformation when woven and knitted using the fibers.

[0006] Furthermore, Patent Document 3 proposes a method for obtaining a high-viscosity, high-molecular-weight polyester by blending the starting materials, recycled polyester polymer, with an alkylene diol, followed by heat melting, cracking, filtration, re-pelletization, and solid-state polymerization. In this method, the molecular weight is reduced by the cracking step, but the reduced melt viscosity makes it easier to remove impurities, and the degree of polymerization can be controlled by the subsequent solid-state polymerization to obtain the target physical properties. However, this recycling consumes a lot of heat energy and electricity, even if it is not as efficient as feedstock recycling, which returns the polyester monomer or the main polyester raw material, and therefore it is not necessarily an appropriate or sustainable method.

[0007] Furthermore, Patent Document 4 proposes a method of recovering, remelting, and pelletizing polyester sheets for magnetic recording media such as floppy disks, and then melt-spinning the resulting multifilament. While this method is effective as a means of recycling materials that would otherwise be incinerated, it not only has drawbacks in terms of consumer performance, such as insufficient practical strength and coloring of the multifilament, but also introduces a large amount of impurities, which is likely to significantly impair spinning performance. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-100087 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-250811 [Patent Document 3] Special table 2010-513571 publication [Patent Document 4] Japanese Patent Application Publication No. 7-316921 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention was made in response to the problems of the conventional technology, and its object is to provide polyester resin pellets derived from PET waste fibers that are suitable for use in fibers, a method for producing the same, fibers made from the pellets, and fiber structures (woven fabrics, knitted fabrics, nonwoven fabrics, etc.) made from the fibers. [Means for solving the problem]

[0010] As a result of extensive research to achieve the above object, the inventors have discovered that recycled pellets of polyester resin having properties suitable for fiber use can be obtained by melt-kneading waste PET fiber and a chain extender in a melt extruder under specific conditions, leading to the completion of the present invention.

[0011] The present invention was completed based on the above findings and has the following features (1) to (7). (1) A polyester resin pellet for fiber derived from waste PET fibers, which contains PET and a chain extender, characterized in that the number of microdomains consisting of the chain extender with a major axis of 0.01 μm or more and 0.20 μm or less dispersed in the PET matrix in the pellet is 5 to 50 per square μm of the resin cross section, and no large domains with a major axis of 0.50 μm or more are formed; the melt flow rate (MFR) of the pellet evaluated by the method described in JIS K7210-1 is 50 g / 10 min to 150 g / 10 min at a measurement temperature of 285°C and a measurement load of 2.16 kgf, and the intrinsic viscosity [η] is 0.50 to 0.75. (2) The polyester resin pellets for fiber made from waste PET fibers according to (1), characterized in that the chain extender is an epoxy-based chain extender. (3) The polyester resin pellets for fiber made from PET waste fiber according to (1), characterized in that the chain extender is a polymer compound represented by the following general structural formula: JPEG2025160719000002.jpg54166In the formula, R1 to R5 are hydrogen, a methyl group, or an alkyl group; R6 is an alkyl group; and x, y, and z are integers of 1 to 20. (4) Polyester resin pellets for fiber made from PET waste fiber according to (1), containing organic nitrogen in the range of 200 ppm to 2000 ppm. (5) Fibers characterized by using polyester resin pellets for fibers derived from waste PET fibers according to any one of (1) to (4). (6) A fiber structure characterized by using the fiber according to (5). (7) A method for producing polyester resin pellets for fiber derived from PET waste fibers according to any one of (1) to (4), characterized in that the molten polymer temperature in the cylinder barrel of the melt extruder is set to 275 to 315°C, the L / D (length / diameter ratio) of the melt extruder screw is set to 15 to 50, and the compression ratio of the melt extruder is set to 3 / 1 to 5 / 1, and the PET waste fibers and the chain extender are melt-kneaded together in the melt extruder. [Effects of the Invention]

[0012] According to the present invention, polyester fiber waste materials such as fiber scraps, resin scraps, nonwoven fabric scraps, and effluent waste, which have traditionally been incinerated as industrial waste or thermally recovered through thermal recycling (energy recovery), can be regenerated into fiber raw material pellets and even fiber structures. Furthermore, the manufacturing method of the present invention is based on material recycling (mechanical recycling), which does not require the use of organic solvents for dissolution or the high energy consumption of heat or electricity, as in chemical recycling (feedstock recycling). This makes it possible to regenerate raw materials using a more environmentally friendly, efficient, economical, and sustainable recycling method. By effectively utilizing the pellet resin derived from PET waste fiber of the present invention, as well as fibers and fiber structures made from it, we can move one step closer to achieving zero emissions. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a TEM photograph (magnification: 5000 times) of the cross section of the PET resin pellet obtained in Example 1. [Figure 2] FIG. 2 is a TEM photograph (magnification: 10,000 times) of the cross section of the PET resin pellet obtained in Example 1. [Figure 3] FIG. 3 is a TEM photograph (magnification: 5000 times) of the cross section of the PET resin pellet obtained in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0014] The polyester resin pellets for fiber of the present invention are obtained by melt-kneading PET waste fibers and a chain extender together under specific conditions. The pellets are characterized by having 5 to 50 microdomains of chain extender with major axes of 0.01 μm to 0.20 μm dispersed in the PET matrix, per square μm of resin cross section, with no large domains of major axes of 0.50 μm or more. The microdomains are derived from the chain extender, and the chain extension reaction proceeds at the contact interface with the polyethylene terephthalate matrix resin, while the interior of the domains is an agglomeration of unreacted, deactivated chain extender. As described above, the chain extension reaction of polyethylene terephthalate proceeds at the interface between the domains and the polyethylene terephthalate matrix resin. Therefore, it is desirable to keep the domain size as small as possible and finely disperse the domains to increase the contact area at the contact interface and to achieve uniform dispersion without uneven distribution.

[0015] Figures 1 and 2 are cross-sectional photographs of polyester resin pellets derived from PET waste fibers of the present invention, at magnifications of 5,000x and 10,000x, respectively. Numerous microdomains can be seen in the cross-sections. In each photograph, the microdomains are slightly darker in color than the polyethylene terephthalate matrix resin and appear to be dispersed in an irregular shape. Figure 3 is a cross-sectional photograph of polyester resin pellets derived from PET waste fibers that does not contain a chain extender, and no microdomains are present.

[0016] The polyester resin pellets for fiber of the present invention are recycled from pre-consumer raw materials derived from PET waste fibers. Therefore, the raw materials are subjected to hydrolysis by heating and melting to some extent. To reuse the raw materials for fiber applications, the inventors considered it necessary to subject the raw materials to solid-state polymerization or to use a chain extender to improve the melt viscosity.

[0017] The former solid-state polymerization method requires initial capital investment, long processing times, and high running costs. Therefore, it has been found that the latter method, using a chain extender to improve melt viscosity, is practically preferable. However, excessive use of chain extender increases the domain size resulting from chain extender-related reactions, leading to reduced productivity due to gelation and filter clogging. Therefore, the amount used must be appropriately adjusted. Specifically, the amount of chain extender used relative to the PET waste fiber is preferably 0.5-4% by mass, more preferably 0.8-3.5% by mass. Furthermore, it is necessary to achieve fine and uniform domain size and dispersion; failure to do so may result in poor physical properties after fiberization.

[0018] As a result of the inventor's investigation into these points, it was found that by controlling the size and dispersion state of the microdomains consisting of the chain extender dispersed in the PET matrix in the resin pellets so that the size of the microdomains with a major axis of 0.01 μm or more and 0.20 μm or less, and so that the number of domains with a size of 0.01 μm or more and 0.20 μm or less is 5 to 50 per square μm of the resin cross section, and by suppressing the formation of large domains with a major axis of 0.50 μm or more, the physical properties and mechanical strength when used as a fiber can be maintained without any problems.

[0019] The greater the difference in melt viscosity between the polyester resin matrix and the chain extender, the more difficult it is to reduce the domain size and control the uniform dispersion. Typically, the polyester resin matrix has a higher viscosity than the chain extender. To disperse a low-viscosity chain extender in a high-viscosity polyester resin, adjusting various conditions, such as the combination of screw elements in the melt extruder, barrel temperature, and rotation speed, creates a shear, elongation, and dispersion effect, which reduces the size of the chain extender domains and allows for more uniform dispersion.

[0020] Since the chain extension reaction proceeds at the contact interface between the polyester resin and the microdomains, the chain extension reaction can be efficiently promoted by forming microdomains and increasing the contact area between the polyester resin and the chain extender. The domains should be maintained as discontinuous rod-like particles aligned parallel to the longitudinal direction of the extruded strands and pellets, and by further inducing shear deformation and elongation deformation, they can be made to resemble ideal spherical particles. Thus, controlling the size and dispersion state of the domains is important.

[0021] The cross-sectional shape of the microdomains is irregular, and can take on a variety of shapes, including oval, cloud-like, and circular. However, domains with a major axis significantly exceeding 0.20 μm, such as 0.50 μm or larger, indicate that the chain extender is not uniformly dispersed but is unevenly distributed and undergoes molecular association. This creates large gaps during the uniaxial deformation process of spinning and drawing, which can lead to fiber breakage and other undesirable physical properties. Furthermore, if there are fewer than five microdomains with a major axis of 0.01 μm or larger but less than 0.20 μm per square μm of resin cross section, i.e., if the amount of chain extender added is too small, the thickening effect is poor, the melt viscosity remains low, and stretchability and spinnability are impaired. Furthermore, if the number of microdomains of the same size exceeds 50 per square micrometer of the resin cross section, the thickening effect will be too great, the melt viscosity will be high, and the filter back pressure will be large, which may also hinder the operability in spinning drawability, and this is not preferable.

[0022] Furthermore, it is important that large domains with a major axis of 0.50 μm or more are not formed. If large domains are formed, the chain extension reaction will not proceed efficiently, and if they are unevenly distributed, not only will this lead to a decrease in the physical strength of the resulting yarn, but it will also cause problems such as impaired dye levelness when dyed. Furthermore, there is a concern that this will significantly deteriorate operability and quality, such as yarn breakage during melt spinning and single yarn breakage and fluff, which is undesirable. It is therefore necessary to uniformly disperse an appropriate amount of domains without the presence of excessively large domains.

[0023] The size and dispersion of microdomains can be easily controlled by adjusting the type and combination of screw elements in the melt extruder, the rotation speed, the barrel temperature of the melt extruder, and, in the case of multi-screw extruders, the kneading conditions, such as intermeshing counter-rotating (counter-rotating), intermeshing co-rotating (co-rotating), non-intermeshing counter-rotating (counter-rotating), intermeshing self-wiping co-rotating (co-rotating), and the kneading elements (forward, reverse, orthogonal). Excessive domain size and number per unit area can lead to poor operability due to intermolecular association, aggregation, and gelation, as well as to poor physical properties of resin molded products such as fibers. By controlling the size and number to a certain level, operating conditions that satisfy both operability and physical properties can be achieved. Specifically, the melt extruder barrel temperature can be appropriately adjusted to adjust the molten polymer temperature to a range of 275–315°C, the length / diameter ratio (L / D) of the melt extruder screw to 15–50, and the compression ratio of the melt extruder to 3 / 1–5 / 1. If these conditions are not met, it becomes difficult to control the above-mentioned minute domains to an appropriate size and dispersion state.

[0024] The melt flow rate (MFR) of the polyester resin pellets obtained by the above method can be evaluated by the method described in JIS K7210-1 (ISO1133-1). When evaluated under conditions of a measurement temperature of 285°C and a measurement load of 2.16 kgf, the MFR is 50 g / 10 min to 150 g / 10 min, preferably 70 g / 10 min to 120 g / 10 min. A high viscosity range of less than 50 g / 10 min is suitable for industrial material applications such as polyester tire cord and blow-molded applications such as PET bottles, but is too viscous for general clothing applications, resulting in a stiff texture of the resulting fabric. Conversely, a viscosity exceeding 150 g / 10 min is too low, resulting in poor fiber strength and a tendency to induce spun yarn breakage, hindering operability. The MFR varies depending on the type and amount of chain extender used, the size and dispersion state of the microdomains formed by the chain extender, the barrel temperature and residence time of the melt extruder, and other factors, and can be controlled by appropriately setting these factors.

[0025] The intrinsic viscosity [η] of the polyester resin pellets for fiber of the present invention is in the range of 0.50 to 0.75, more preferably 0.55 to 0.70. If the intrinsic viscosity [η] is below this range, the melt viscosity during fiber melt spinning is low, resulting in poor spinnability and impaired operability. Furthermore, the physical properties of the finished fiber, such as strength and elongation, remain low, making it difficult to produce a fiber suitable for general consumption. While fibers with an intrinsic viscosity [η] exceeding 0.75 are expected to be used as high-strength fibers for industrial applications, etc., the polyester resin pellets for fiber of the present invention are derived from pre-consumer raw materials, and therefore, increasing the intrinsic viscosity [η] requires further increasing the chain extender concentration. Increasing the chain extender concentration not only increases costs but also causes pressure increases, such as gelation in polymer piping. Furthermore, the formation of many chain extender-derived domains increases the likelihood of operational problems, such as yarn breakage, during melt spinning and drawing. The intrinsic viscosity also varies depending on the type and amount of chain extender used, the size of the microdomains formed by the chain extender, the dispersion state, the barrel temperature and residence time of the melt extruder, etc., and can be controlled by appropriately setting these factors.

[0026] The oligomers formed in polyethylene terephthalate (PET) are separated into linear and cyclic oligomers. Linear oligomers are compatible with PET, but cyclic oligomers are not. The cyclic trimer of PET, which accounts for more than 50% of the total mass of oligomers produced (roughly equivalent to about 1% by mass), has a higher melting point of 320°C than PET, is not compatible with PET, and is prone to sublimation, causing various problems during processing, such as the generation of white powder.

[0027] The mass ratio (C-OLG / L-OLG) of linear oligomers (L-OLG) containing linear dimers to linear tetramers and cyclic oligomers (C-OLG) containing cyclic dimers to cyclic decamers is preferably 0.032 to 0.055, more preferably 0.040 to 0.050. If the C-OLG / L-OLG ratio exceeds the above range, the amount of cyclic oligomers increases excessively, which can cause problems with operability and quality, such as the generation of white powder and scum in the process. If the ratio is below the above range, the amount of linear oligomers increases excessively, which can cause problems such as reduced physical strength and reduced heat resistance.

[0028] In the case of polyethylene terephthalate, repeated remelting by heating tends to decrease the amount of cyclic oligomers and increase the amount of linear oligomers, but repeated remelting by heating accelerates hydrolysis, increasing the amount of monomer components such as terephthalic acid (TPA), monohydroxyethyl terephthalate (MHET), and bishydroxyethyl terephthalate (BHET), which can lead to defects such as yellowing and discoloration. The mass ratio (C-OLG / L-OLG) of linear oligomers (L-OLG) to cyclic oligomers (C-OLG) varies depending on the cylinder barrel temperature, residence time, compression ratio, etc. of the melt extruder, and can be controlled by appropriately setting these.

[0029] The total oligomer content, which is the sum of the linear and cyclic oligomers, is preferably in the range of 1.0% to 1.6% by mass, and more preferably 1.1% to 1.5% by mass, in the polyester resin. While the lower the total oligomer content, the better, it is difficult to control the total oligomer content to less than 1.0% by mass, even in virgin PET obtained by transesterification and polycondensation of ethylene glycol and terephthalic acid in a 1:1 molar ratio. Furthermore, a content exceeding 1.6% by mass is undesirable because it can result in the generation of white powder or scum, coloration, and a decrease in physical strength.

[0030] Furthermore, the amount of carboxyl end groups in the polyester resin is preferably 10 eq. / ton to 40 eq. / ton, more preferably 10 eq. / ton to 35 eq. / ton, and even more preferably 10 eq. / ton to 30 eq. / ton. A carboxyl end group amount below this range, i.e., ideally progressing polycondensation with little thermal hydrolysis, is technically difficult to achieve with recycled polyester pellets. Furthermore, if the amount exceeds 40 eq. / ton, thermal hydrolysis progresses to an advanced state, making it difficult to maintain practical physical strength. The heterocycle of the chain extender is thought to react one-to-one with the carboxyl groups of polyethylene terephthalate. Therefore, by reducing the size of the microdomains of the chain extender and dispersing them more uniformly without uneven distribution, the interfacial area with the polyethylene terephthalate matrix resin is increased, further accelerating the chain extension reaction.

[0031] Furthermore, the amount of diethylene glycol in the polyester resin is preferably 0.05 mol% to 1.20 mol%, more preferably 0.10 mol% to 1.00 mol%, and even more preferably 0.20 mol% to 0.80 mol%. Diethylene glycol is a by-product of the ester exchange and polycondensation reaction of PET. A content exceeding 1.20 mol% is undesirable because it reduces physical properties such as mechanical strength and can cause the resin itself to turn yellow. While a lower amount of diethylene glycol is preferable, because it is a by-product, controlling it to less than 0.05 mol% is extremely difficult and unrealistic in the present invention, which uses recycled raw materials.

[0032] The polyester resin pellets for fiber of the present invention are intermolecularly crosslinked with a chain extender. The chain extender is preferably one that intermolecularly crosslinks the carboxyl groups that make up PET and contains multiple three- to six-membered heterocyclic rings in its molecular structure, such as ethylene oxide, aziridine, ethyleneimine, oxazoline, triazine, oxetane, imidazole, pyrazole, or tetrahydrofuran, and known chain extenders can be used in combination. In particular, those containing cyclic ethers such as ethylene oxide, oxetane, and tetrahydrofuran are preferred, and those containing ethylene oxide, especially bifunctional epoxides, and multifunctional epoxides with three or more functional groups are even more preferred.

[0033] The chain extender is preferably an epoxy-based chain extender, and in particular, it is desirable for it to be a polymer compound having a plurality of epoxy groups in its molecular structure, which is represented by the following general structural formula: JPEG2025160719000003.jpg54166In the formula, R1 to R5 are hydrogen, a methyl group, or an alkyl group; R6 is an alkyl group; and x, y, and z are integers of 1 to 20.

[0034] The weight-average molecular weight of the chain extender is preferably about 5,000 to 10,000. In the case of epoxy-based chain extenders, the epoxy equivalent (weight value; molecular weight / number of epoxy functional groups) is in the range of 200 g / mol to 500 g / mol, preferably 250 g / mol to 480 g / mol. The higher the epoxy equivalent of the epoxy-based chain extender, the lower the possibility of gel formation, but it is preferable to increase the amount used to achieve the thickening effect of the chain extender. Chain extenders with a low epoxy equivalent have a large number of epoxy functional groups, so they are more likely to form a three-dimensional crosslinked structure.

[0035] Fiber spinning and drawing involves uniaxial thermal deformation in the fiber axis direction, so a three-dimensional crosslinked structure makes it difficult for the material to follow the deformation, resulting in thread breakage and reduced operability and yield. If a chain extender with an epoxy equivalent of less than 200 g / mol is used, thread breakage is likely to occur, and even a small amount can form a gel due to three-dimensional crosslinking, which can easily cause a deterioration in operability. Conversely, if the amount exceeds 500 g / mol, the thickening effect cannot be expected unless the amount is increased, resulting in extremely high production costs. Chain extenders are not limited to a single type; multiple types can be used in combination.

[0036] Known chain extenders for polyesters include those containing difunctional aromatic acid anhydrides, such as pyromellitic dianhydride (PMDA), as the active ingredient. Examples include oxazoline or caprolactam chain extenders, chain extenders with glycidyl terminal groups, and epoxy chain extenders, with epoxy chain extenders being particularly preferred. Because these chain extenders have low melting points and tend to stick, they can be pelletized into master batches and melt-kneaded. It is also possible to use multiple epoxides with different numbers of functional groups in combination.

[0037] The matrix base polymer used in the masterbatch is preferably a polyester resin with a melt viscosity similar to that of recycled PET, but is not limited to polyester resins as long as it is compatible with PET. The chain extender may also be microencapsulated. In the case of microcapsules, the reaction is triggered by the destruction of the capsules due to physical shear force or heat during kneading, and the chain extension reaction is initiated by the expansion and liquefaction of the encapsulated chain extender components, which then exude. Generally, due to the difference in viscosity between the molten base polymer and the chain extender, dispersion and mixing are difficult, and the chain extender domains tend to be large and unevenly distributed. However, in the present invention, it is important to keep the domain size small and uniformly dispersed.

[0038] The amount of epoxy chain extender used varies depending on the epoxy equivalent weight and the physical strength of the polyester resin, but is preferably formulated to be 0.5 to 4.0 mass% and more preferably 0.8 to 3.5 mass% based on the total mass of the PET. The epoxy chain extender preferably contains an aromatic and / or aliphatic segment having at least two epoxy groups and a non-epoxy functional group, and is prepared by polymerizing at least one epoxy-functional (meth)acrylic monomer with a non-functional (meth)acrylic acid and / or styrene monomer. Here, (meth)acrylic is defined to include both acrylic and methacrylic monomers. Therefore, examples of epoxy-functional (meth)acrylic monomers include both acrylates and methacrylates. Examples of these monomers include, but are not limited to, those containing 1,2-epoxy groups, such as glycidyl acrylate and glycidyl methacrylate. Other suitable epoxy-functional monomers include allyl glycidyl ether, glycidyl ethacrylate, and glycidyl itaconate.

[0039] Suitable non-functional acrylate and methacrylate monomers for use in epoxy chain extenders include methyl acrylate, ethyl acrylate, normal propyl acrylate, isopropyl acrylate, normal butyl acrylate, cis-butyl acrylate, isobutyl acrylate, tertiary butyl acrylate, normal amyl acrylate, isoamyl acrylate, normal hexyl acrylate, 2-ethylbutyl acrylate, isobornyl acrylate, normal octyl acrylate, 2-ethylhexyl acrylate, normal decyl acrylate, cyclopentyl acrylate, cyclohexyl acrylate, and methylcyclohexyl acrylate. Examples of suitable acrylate and methacrylate monomers include, but are not limited to, methyl methacrylate, ethyl methacrylate, normal propyl methacrylate, isopropyl methacrylate, normal butyl methacrylate, secondary butyl methacrylate, isobutyl methacrylate, tertiary butyl methacrylate, normal amyl methacrylate, isoamyl methacrylate, normal hexyl methacrylate, 2-ethylbutyl methacrylate, methylcyclohexyl methacrylate, cinnamyl methacrylate, crotyl methacrylate, cyclopentyl methacrylate, cyclohexyl methacrylate, 2-ethoxyethyl methacrylate, and isobornyl methacrylate. Particularly suitable are non-functional acrylate and methacrylate monomers, including methyl methacrylate, normal butyl acrylate, normal butyl methacrylate, isobutyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, isobornyl acrylate, and isobornyl methacrylate, and combinations thereof. Additionally, styrene monomers include, but are not limited to, styrene, alpha-methylstyrene, vinyltoluene, para-methylstyrene, tertiary-butylstyrene, orthochlorostyrene, vinylpyridine, and mixtures thereof.

[0040] The chain extender can be fed from any location in the melt extruder. This feeding can be carried out by known methods such as side feeder or tandem. As for the screws of the melt extruder, in addition to single-screw, twin-screw, triple-screw, or other multi-screw types, multi-screws can be suitably used. In addition to the chain extender, flame retardants, organic pigments, inorganic pigments, matting agents, smoothing agents, UV absorbers, antioxidants, heat stabilizers, radical scavengers, and other additives can be added as appropriate depending on the intended use and purpose of the final product. For addition and kneading, twin-screws are preferred, but single-screw screws with high kneading efficiency, such as Dulmage, Maddock, and double-flight types, can also be used. In particular, recycled resin pellets obtained by remelting and pelletizing waste textile materials have a reduced intrinsic viscosity (intrinsic viscosity) due to hydrolysis. Therefore, a radical scavenger can be kneaded into the resin pellets in addition to the chain extender. Examples of known radical scavengers include hindered phenol, hindered amine, and semi-hindered phenol stabilizers.

[0041] The polyester resin pellets for fiber of the present invention preferably contain organic nitrogen at a concentration of 200 ppm to 2000 ppm, more preferably 300 ppm to 1500 ppm. The organic nitrogen is derived from the chain extender. In particular, when the chain extender is polymerized using epoxy-functional (meth)acrylic monomers and non-functional (meth)acrylic acid and / or styrene monomers as main structural units, the molecular skeleton contains nitrogen. There is a correlation between the amount of chain extender added and the organic nitrogen content, and increasing the amount also increases the organic nitrogen content. If the organic nitrogen content is less than 200 ppm, intermolecular crosslinking between the chain extender and carboxyl groups is insufficient, resulting in poor mechanical and thermal properties of the polyester resin. Furthermore, if the organic nitrogen content is significantly greater than 2000 ppm, the viscosity increase caused by the promotion of intermolecular crosslinking can easily lead to deterioration in operability, such as an increase in polymer discharge pressure during melt spinning. As described above, by controlling the organic nitrogen content, it becomes possible to control the thickening effect of the resin melt, that is, the melt viscosity, which can contribute to improvements in physical properties, operability, and yield.

[0042] The polyester resin pellets for fiber of the present invention can be produced using a known melt extruder. The process outlines the following: Raw material polyester fiber waste, such as fiber scraps, nonwoven fabric scraps, and effluent, is shredded using a shredder, then further shredded, reduced in volume, dehydrated, and dried using a cutter compactor. The resulting material is then introduced into a heated melt extruder, where it is melted, degassed, pressurized, filtered, and weighed. The resulting molten strand is then discharged from the die outlet, immediately cooled in a cooling water tank, cut into pellets using a strand cutter, and dehydrated and dried to obtain recycled pellets. Contaminants are captured using a wire mesh or sintered metal filter, resulting in clean resin pellets.

[0043] The filter screen used for filtration is attached to a breaker plate. High levels of contamination in the molten polymer can easily clog the filter, increasing backpressure. Therefore, to maintain appropriate backpressure, it is desirable to install a screen changer or screen backwashing device. It is desirable to use a slightly coarse primary filter and a fine secondary filter for efficient filtration. Various wire mesh weaves (plain weave, twill weave, plain tatami weave, twill tatami weave, etc.), wire diameters, and filtration diameters can be used. It is preferable to combine filter media appropriately depending on the cleanliness of the waste textile material being fed. Suitable wire meshes for use are those with a mesh size of 200 to 800 for plain and twill weaves, and those with a mesh size of 50 to 300 (vertical and horizontal) or 500 to 4000 (horizontal and vertical).

[0044] Furthermore, since wire mesh filters cannot completely capture fine contaminants, it is effective to combine filtration with a sintered metal filter. A preferred example of a sintered metal filter is the Naslon (registered trademark) filter manufactured by Nippon Seisen Co., Ltd. Sintered filters cannot be reused by backwashing, and must be replaced with a new one each time they become clogged. For wire mesh filters, if the machine is equipped with an automatic screen backwashing device, the polymer flow can be reversed to clean the wire mesh filter before it becomes clogged, allowing for continuous production without replacing the wire mesh filter.

[0045] The filtration diameter of the sintered metal filter is preferably 5 μmφ or more and 100 μmφ or less, more preferably 10 μmφ or more and 80 μmφ or less, and even more preferably 15 μmφ or more and 40 μmφ or less. A filtration diameter of less than 5 μmφ allows for the capture of finer contaminants, but the filter becomes clogged in a short time, which is not desirable in terms of running costs and availability. Conversely, a filtration diameter exceeding 100 μmφ may not allow the capture of finer contaminants, which may impair the processability and operability of subsequent processes.

[0046] The L / D (length / diameter ratio) of the melt extruder screw is preferably in the range of 15 to 50, more preferably 20 to 45, and even more preferably 20 to 40. If the L / D is less than 15, the screw will be too short, shortening the melting, degassing, and metering zones, increasing the likelihood of problems such as pellet entrapment. If the screw is too long, with an L / D of more than 50, the thermal history will be large, and hydrolysis will progress, increasing the likelihood of a decrease in molecular weight, etc.

[0047] It is also desirable to provide a vent zone in the melt extruder and evacuate it by vacuuming to actively expel gases and volatile components generated by moisture and heat. Having multiple vent zones, rather than just one, is highly effective in terms of operability and quality. It is desirable to use different types of screw elements for each area. For example, by narrowing the screw helical pitch or tapering the groove depth, it is possible to adjust the compression ratio for each area, and kneading elements can be used to improve the kneading effect. It is also effective to install a polymer gear pump downstream of the extruder to suppress discharge pressure pulsations (surging) and stabilize the discharge of strands.

[0048] As a means of controlling the size and dispersion state of the microdomains, it is desirable to set the compression ratio of the melt extruder to a high value of 3 / 1 to 5 / 1. Because the polyester fiber waste materials used as feedstock, such as fiber scraps, nonwoven fabric scraps, and discharged waste, have a high bulk density, unless the compression ratio is increased, the state of the strand extruded from the die of the melt extruder will not be stable, which could result in problems such as surging.

[0049] It is preferable to set the appropriate compression ratio within the above range depending on the bulk specific gravity (bulk density) of the waste fiber material being fed. It is preferable to increase the compression ratio for materials with a high bulk specific gravity and decrease the compression ratio for materials with a low bulk specific gravity. If the compression ratio is less than 3 / 1, the discharge of the strands may become unstable, making stable operation impossible. Furthermore, if the compression ratio is higher than 5 / 1, the filter back pressure may become high, which may lead to unstable operation, such as venting. It is preferable to set an appropriate compression ratio depending on the condition of the waste fiber material being fed.

[0050] The barrel temperature of the extruder must be set taking into consideration heat generation due to shear, since the polymer temperature is increased by the shear stress of the molten polymer. In the case of PET, the polymer temperature is preferably controlled to 275°C or higher and 315°C or lower, more preferably 310°C or lower, and even more preferably 300°C or lower, in order to suppress hydrolysis. The barrel temperature is preferably set to about 230 to 290°C, and it is preferable to fine-tune it while checking the polymer temperature.

[0051] The polymer gear pump is preferably installed between the screen changer and the die, just before the extruder and screen changer pass through to the die. The strands discharged from the die are cooled in a cooling water tank and then shredded with a strand cutter. Resin pellets can be obtained using either the strand-cutting method, in which the strands are cooled in a cooling water tank and then shredded with a strand cutter, or the water-cooled hot-cut method. The shredded resin pellets are introduced into a vibrating screen and classified, then passed through a dehydration / drying device and a fines removal device, before being air-fed into flexible container bags or other containers to produce the final product. The cooling water introduced into the cooling water tank can be either parallel flow or counter flow to the strand flow direction, but counter flow is preferred for cooling efficiency. It is also preferable to install a partition in the cooling water tank to further increase cooling efficiency.

[0052] The temperature of the water introduced into the cooling water tank (water temperature) is preferably 5 to 30°C, more preferably 7 to 20°C, and even more preferably 10 to 15°C. The bath temperature rises depending on the heat carried over by the strand, but it is desirable to ensure the capacity of the cooling water tank so that the bath temperature is approximately 30 to 40°C. If the polymer discharge hole opened in the die is a round hole, the shape of the pellets will be cylindrical or elliptical. There are no particular limitations on the size of the pellets, but a diameter and length of approximately 1 to 6 mm are preferred.

[0053] The polyester resin pellets produced as described above can be processed into continuous filament fibers, staple fibers, and continuous spunbonded nonwoven fabrics using conventional melt spinning methods. Continuous filament fibers include known forms such as raw silk obtained by direct spinning (spin draw), raw silk obtained by off-line spinning, false-twisted yarn obtained by draw-twisting partially oriented yarns, blended yarn obtained by high-pressure air entanglement of raw silk or false-twisted yarns, and Taslan-textured yarn obtained by high-pressure fluid disturbance of raw silk or false-twisted yarns (Taslan was formerly a registered trademark of DuPont). Furthermore, staple fibers can be spun into yarns using known spinning methods, such as ring spinning, open-end spinning, and the Vortex method (Vortex is a registered trademark of Murata Machinery Co., Ltd.). Staple fibers can also be processed into short-fiber nonwoven fabrics using known methods, such as thermal bonding, chemical bonding, stitch bonding, needle punching, water jet punching, air-laid, and flash spinning. [Example]

[0054] The effects of the present invention will be demonstrated below by way of examples, but the present invention is not limited to these examples. Note that the property values ​​in the text and examples are evaluated based on the following evaluation methods. [Evaluation method] (Melt flow rate (MFR)) According to the method described in JIS K7210-1 Method A (mass measurement method), MFR (g / 10 min) was measured using a Yasuda Seiki Seisakusho melt flow index tester No. 120-FWP-W model at a test temperature of 28°C and a nominal load of 2.16 kg using PET pellet samples that had been pre-treated and dried at 135°C for 12 hours, with the average value of 5 trials taken as the measured value.

[0055] (Intrinsic viscosity number) The polyester resin was dissolved in a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (60 / 40 (weight ratio)), and the intrinsic viscosity (cm) was measured by the four-point dilution method using an Ubbelohde viscometer placed in a thermostatic water bath at 30°C (30±2°C). 3Further explanation of the intrinsic viscosity is given below. The intrinsic viscosity of a polymer depends on its molecular weight, and is given by the Mark-Houwink-Sakurada equation [η] = KM α The viscosity of the polymer solution is η and the viscosity of the solvent is η s , where c is the unit concentration of the polymer, the reduced viscosity η red is η red =[(η-η s ) / η s ] / c, and the intrinsic viscosity [η] can be expressed as the reduced viscosity η red can be calculated by extrapolating the polymer concentration c so that c → 0. Experimentally, the intrinsic viscosity [η] can be calculated from the time it takes for a fluid to flow down the capillary of an Ubbelohde viscometer. The flow time of the polymer solution is t, and the flow time of the solvent is t. s When this is done, the reduced viscosity η red is calculated by using the flow time t and polymer concentration c, red =(t-t s ) / t s It can be shown in c.

[0056] (carboxyl end group amount) Following the method described in ASTM D7409, 1.0 g of PET pellets were pre-dried at 135°C for 12 hours and weighed into a 50 ml Erlenmeyer flask. 20 ml of ortho-cresol was added, and the solution was heated to a boil under reflux with stirring until the pellets were completely dissolved. The resulting solution was cooled to room temperature, and 35 ml of chloroform and 0.04 ml of bromophenol blue were added and stirred. The solution was then titrated with 0.1 mol / L potassium hydroxide ethanol solution. The measured value was the average of five titration runs.

[0057] (PET oligomer content) Approximately 0.05 g of the sample (PET pellets) was weighed and dissolved in 1.5 mL of a 2:3 volumetric mixture of hexafluoroisopropanol (HFIP) and chloroform. After adding 10 mL of chloroform, 5 mL of methanol was added to the resulting solution to precipitate the polymer. After filtration, the solution was concentrated to dryness, and N,N-dimethylformamide (DMF) was added. The filtrate was subjected to high-performance liquid chromatography (HPLC) analysis. The HPLC used was a Shimadzu Nexera XR column with an Imtakt Cadenza CD-C18 3 μm 2 × 150 mm column. The mobile phases used were 0.1% formic acid aqueous solution (mobile phase A) and acetonitrile (mobile phase B). The conditions for analysis were a flow rate of 0.4 mL / min, a column temperature of 45 °C, an injection volume of 5 μL, and a detection wavelength of 258 nm. The amount of PET oligomers contained was quantified from the obtained chromatogram. The quantitative value of linear PET oligomers was calculated in terms of BHET, and the quantitative value of cyclic PET oligomers was calculated in terms of PET cyclic trimer (CT).

[0058] (amount of diethylene glycol) The DEG content (mol%) was determined according to the method described in "Analysis of Glycols in Polyethylene Terephthalate" (co-authored by Akira Mifune and Susumu Ishida) published in Industrial Chemistry Journal, Vol. 65, No. 5 (1962), pp. 824-826. The average value of five trials was used as the measured value.

[0059] (Transmission electron microscope (TEM) observation and determination of the number of microdomains) Using a cryomicrotome, frozen sections of the analytical sample (PET pellets) were prepared, stained in RuO4 vapor for 30 minutes, and then carbon-deposited to prepare the specimen for TEM observation. Using a JEOL JEM-2100 transmission electron microscope at an accelerating voltage of 200 kV, cross-sections were observed and photographed. The number of domains was determined by counting the number of microdomains with major axes of 0.01 μm to 0.20 μm dispersed within a 10 μm square field of view on the resin cross section using photographs magnified 5000 times. The average of the counted values ​​over 20 fields was converted to units of (locations / μm squared) and used as the measurement value.

[0060] (organic nitrogen measurement) Measurements were performed using an evaluation method based on the Pregl-Dumas method. Using a J Science Labs Microcoder JM-11 organic trace element analyzer, 10 mg of resin pellets were gasified at a combustion furnace temperature of 1000°C, passed through an oxidation furnace at 800°C, and a reduction furnace at 650°C, and the resulting nitrogen gas (N2) was quantified using a thermal conductivity detector (TCD). The gas flow rates during combustion were He gas 200 ml / min and O2 gas 15 ml / min.

[0061] (filter back pressure rise coefficient) As a pre-treatment for the test, PET pellets were dried at a drying temperature of 135°C for 12 hours while rotating to prevent sticking, and then melt-extruded from a single-hole nozzle under conditions of an extruder temperature of 285°C, a filter filtration diameter of 20 μmφ, and a discharge rate of 6 g / min. The back pressure increase (pressure increase) versus elapsed time was plotted every 30 minutes, and the nozzle pressure increase coefficient was calculated according to the following formula (1). The average of two trials was used as the measured value. Filter back pressure rise coefficient K * =(ΔP / T) / (Q / S)...Equation (1) where ΔP is the back pressure increase value (MPa) and T is the time (Hr). Also, Q is the discharge rate (Kg / Hr), and 6g / min × 60min / Hr ÷ 1000 (g / Kg) = 0.36 is substituted, and S is the filter area (cm 2 ) and substitute 0.7cm × 0.7cm × π ≒ 15.39. T (Hr) is usually set to an evaluation time of 4 hours, but if there is a lot of impurities and clogging occurs quickly, the test is stopped midway for work safety reasons, and the filter pressure rise coefficient K * Ask for.

[0062] (fineness) The evaluation was carried out by the correct fineness method B (simple method) described in JIS L1013 8.3.1. The average value of 10 trials was taken as the measured value. (Tensile strength and elongation) Evaluation was carried out in accordance with the standard time test described in JIS L1013 8.5.1. The average value of 10 trials was used as the measured value.

[0063] (Stretching / stretching rate) Evaluation was carried out in accordance with Method C (simple method) described in JIS L1013 8.11. The average value of 10 trials was taken as the measured value. (Stretch recovery rate) The evaluation was carried out in accordance with the method described in JIS L1013 8.12. The average value of 10 trials was taken as the measured value. (Dimensional change rate in hot water) The skein dimensional change rate was evaluated according to JIS L1013 8.18.1 (Method A). The average value of 10 trials was used as the measured value.

[0064] (Residual strain rate of circular knit fabric) Residual strain was evaluated according to JIS L1096 8.16.2 D method (repeated constant elongation method). The grip spacing was set to 200 mm, the constant elongation was set to 50% in both the wale direction and the course direction, and the measurement was repeated 5 times. The average value of 10 trials was taken as the measured value.

[0065] Example 1 Cut offcuts of Toyobo MC's polyester spunbond "Ekure®" were introduced into a twin-screw melt extruder and melted, filtered, and pelletized. BASF's Joncryl® ADR4400 (weight-average molecular weight = 7100, glass transition temperature = 65°C, epoxy equivalent = 485 g / mol) was added as an epoxy chain extender at 2% by mass. Contaminants were filtered through a 600-mesh filter. The strands were discharged and cooled in a cooling water bath. They were then shredded using a strand cutter, dehydrated, and dried to obtain PET resin pellets. The molten polymer temperature in the melt extruder barrel was set to 285°C, the length / diameter ratio (L / D) of the melt extruder screw was set to 30, and the compression ratio of the melt extruder was set to 4 / 1. The properties of the resulting PET resin pellets are shown in Table 1. Cross-sectional TEM images of the PET resin pellets (magnifications of 5000x and 10000x) are shown in Figures 1 and 2, respectively.

[0066] The obtained PET resin pellets were stirred and dried at 135°C for 24 hours under a dry nitrogen purging condition, and then 100% of the PET resin pellets were used to obtain a 138 decitex, 36 filament polyester multifilament partially oriented yarn (POY) using a 36-hole round cross-section spinning nozzle at a melt extrusion temperature of 285°C, a nozzle surface temperature of 290°C, and a spinning take-up speed of 3200 m / min.

[0067] The resulting polyester multifilament partially oriented yarn (POY) was subjected to a draw-twisting process using an AIKI Liotech TH-212 draw-twisting machine at a primary heater temperature of 190°C, a secondary heater temperature set to room temperature (OFF), a draw ratio of 1.65, and a processing speed of 100 m / min to produce an 84 dtex, 36-filament draw-twisted yarn (DTY). The number of twists was 3,400 / m, and the spinner used was an Awa Spindle Co., Ltd. eccentric sapphire pin with a diameter of 2.5 mm. Two types of twist directions were used: Z twist (Z→S) and S twist (S→Z). The properties of the resulting DTY are shown in Table 1.

[0068] The resulting drawn false-twisted yarn (DTY) was used 100% of the time, with the false-twist direction alternating between one Z-twist and one S-twist. A polyester knitted fabric (grey) was knitted using a PAILUNG PLKS3B single-knit knitting machine. The knitting machine specifications were a 26-inch diameter, a 22-gauge needle density, and 78 yarn feeders. A 32-course x 27-wale jersey knit was knitted using the knitting machine. The resulting knitted fabric was dry-heat set at 160°C with overfeed in the wale direction, followed by opening and rewinding. The properties of the resulting knitted fabric are shown in Table 1. The resulting knitted fabric had no skew, good handleability, and moderate stretch kickback properties, resulting in a fabric that was resistant to problems such as moiré and wrinkles. When this knitted fabric was used as a backing material for motorcycle seats, the fabric deformed to fit the fine curves, resulting in a beautiful seating surface without wrinkles or distortion.

[0069] Example 2 Cut off pieces of polyester spunbond "Ekure (registered trademark)" manufactured by Toyobo MC Co., Ltd. were used and introduced into a twin-screw melt extruder, where they were melted, filtered, and pelletized. PET resin pellets were obtained in the same manner as in Example 1, except that an epoxy chain extender, BASF's Joncryl (registered trademark) ADR4368-C (weight average molecular weight = 6800, glass transition temperature = 54°C, epoxy equivalent = 285 g / mol), was mixed in an amount of 1% by mass with the cut off pieces. The property values ​​of the obtained PET resin pellets are shown in Table 1.

[0070] The obtained PET resin pellets were stirred and dried at 135°C for 24 hours under a dry nitrogen purging condition, and then 100% of the PET resin pellets were used to obtain a 138 decitex 24 filament polyester multifilament partially oriented yarn (POY) using a 24-hole round cross-section spinning nozzle at a melt extrusion temperature of 285°C, a nozzle surface temperature of 290°C, and a spinning take-up speed of 3200 m / min.

[0071] The resulting polyester multifilament partially oriented yarn (POY) was subjected to a draw-twisting process using an AIKI Liotech TH-212 draw-twisting machine at a primary heater temperature of 195°C, a secondary heater temperature set to room temperature (OFF), a draw ratio of 1.65, and a processing speed of 100 m / min to produce an 84 dtex, 24 filament, draw-twisted yarn (DTY). The number of twists was 3,400 / m, and the spinner used was an Awa Spindle Co., Ltd. eccentric sapphire pin with a diameter of 2.5 mm. Two types of twist directions were used: Z twist (Z→S) and S twist (S→Z). The properties of the resulting DTY are shown in Table 1.

[0072] The resulting drawn false-twisted yarn (DTY) was used 100% of the time, with the false-twist direction alternating between one Z-twist and one S-twist. A polyester knitted fabric (grey) was knitted using a PAILUNG PLKS3B single-knit knitting machine. The knitting machine specifications were a 26-inch diameter, a 22-gauge needle density, and 78 yarn feeders. A 32-course x 27-wale jersey knit was knitted using the knitting machine. The resulting knitted fabric was dry-heat set at 160°C with overfeed in the wale direction, followed by opening and rewinding. The properties of the resulting knitted fabric are shown in Table 1. The resulting knitted fabric had no skew, good handleability, and moderate stretch kickback properties, resulting in a fabric that was resistant to problems such as moiré and wrinkles. When this knitted fabric was used as a backing material for motorcycle seats, the fabric deformed to fit the fine curves, resulting in a beautiful seating surface without wrinkles or distortion.

[0073] Example 3 Cut off pieces of polyester spunbond "Ekure (registered trademark)" manufactured by Toyobo MC Co., Ltd. were used and introduced into a Dulmage screw-type single-screw melt extruder, where they were melted, filtered, and pelletized. PET resin pellets were obtained in the same manner as in Example 1, except that an epoxy chain extender, Joncryl (registered trademark) ADR4400 manufactured by BASF (weight average molecular weight = 7100, glass transition temperature = 65°C, epoxy equivalent = 485 g / mol), was mixed in an amount of 3% by mass with the cut off pieces. The property values ​​of the obtained PET resin pellets are shown in Table 1.

[0074] The obtained PET resin pellets were stirred and dried at 135°C for 24 hours under a dry nitrogen purging condition, and then 100% of the PET resin pellets were used to obtain a 138 decitex, 36 filament polyester multifilament partially oriented yarn (POY) using a 36-hole round cross-section spinning nozzle at a melt extrusion temperature of 285°C, a nozzle surface temperature of 290°C, and a spinning take-up speed of 3200 m / min.

[0075] The resulting polyester multifilament partially oriented yarn (POY) was subjected to a draw-twisting process using an AIKI Liotech TH-212 draw-twisting machine at a primary heater temperature of 195°C, a secondary heater temperature set to room temperature (OFF), a draw ratio of 1.65, and a processing speed of 100 m / min to obtain an 84 dtex, 36-filament draw-twisted yarn (PTY). The number of twists was 3,400 / m, and the spinner used was an Awa Spindle Co., Ltd. eccentric sapphire pin with a diameter of 2.5 mm. Two types of twist directions were used: Z twist (Z→S) and S twist (S→Z). The properties of the resulting DTY are shown in Table 1.

[0076] The resulting drawn false-twisted yarn (DTY) was used 100% of the time, with the false-twist direction alternating between one Z-twist and one S-twist. A polyester knitted fabric (grey) was knitted using a PAILUNG PLKS3B single-knit knitting machine. The knitting machine specifications were a 26-inch diameter, a 22-gauge needle density, and 78 yarn feeders. Using this knitting machine, a 32-course x 27-wale jersey knit was knitted. The resulting knitted fabric was dry-heat set at 160°C with overfeed in the wale direction, followed by opening and rewinding. The properties of the resulting knitted fabric are shown in Table 1. The resulting knitted fabric had no skew, good handleability, and moderate stretch kickback properties, resulting in a fabric that was resistant to problems such as moiré and wrinkles. When this knitted fabric was used as a backing material for motorcycle seats, the fabric deformed to fit the fine curves, resulting in a beautiful seating surface without wrinkles or distortion.

[0077] (Comparative Example 1) PET resin pellets were obtained in the same manner as in Example 1, with the exception that no chain extender was used. The properties of the obtained PET resin pellets are shown in Table 1. A cross-sectional TEM photograph (magnification: 5000 times) of the PET resin pellets is shown in Figure 3.

[0078] The obtained PET resin pellets were stirred and dried at 135°C for 24 hours under a dry nitrogen purging condition, and then 100% of the PET resin pellets were used to obtain a 138 decitex 24 filament polyester multifilament partially oriented yarn (POY) using a 24-hole round cross-section spinning nozzle at a melt extrusion temperature of 280°C, a nozzle surface temperature of 285°C, and a spinning take-up speed of 2600 m / min.

[0079] The resulting polyester multifilament partially oriented yarn (POY) was subjected to a draw-twisting process using an AIKI Liotech TH-212 draw-twisting machine at a primary heater temperature of 185°C, a secondary heater temperature set to room temperature (OFF), a draw ratio of 1.65, and a processing speed of 100 m / min to obtain an 84 dtex, 24 filament, draw-twisted yarn (DTY). The number of twists was 3,400 / m, and the spinner used was an Awa Spindle Co., Ltd. eccentric sapphire pin with a diameter of 2.5 mm. Two types of twist directions were used: Z twist (Z→S) and S twist (S→Z). The properties of the resulting DTY are shown in Table 1.

[0080] The resulting drawn false-twisted yarn (DTY) was used 100% of the time, with the false-twist direction alternating between one Z-twist and one S-twist. A polyester knitted fabric (grey) was knitted using a PAILUNG PLKS3B single-knit knitting machine. The knitting machine specifications were a 26-inch diameter, a 22-gauge needle density, and 78 yarn feeders. A 32-course x 27-wale jersey knit was knitted using the knitting machine. The resulting knitted fabric was dry-heat set at 160°C with overfeed in the wale direction, followed by opening and rewinding. The properties of the resulting knitted fabric are shown in Table 1. The resulting knitted fabric had no skew and good handleability, but exhibited poor stretch kickback. When we tried to use this knitted fabric as a backing material for motorcycle seats, the yarn had poor strength and elongation, and yarn breakage and runs occurred on small curves, making it unsuitable for use.

[0081] (Comparative Example 2) Resin pellets were obtained in the same manner as in Example 2, except that the amount of epoxy chain extender Joncryl ADR4368-C (weight average molecular weight = 6800, glass transition temperature = 54°C, epoxy equivalent = 285 g / mol) manufactured by BASF was changed to 5 mass% relative to the cut off material. However, the viscosity of the strands extruded from the twin-screw melt extruder die was too high, and it could not be said that the extrusion state was stable. The property values ​​of the obtained PET resin pellets are shown in Table 1.

[0082] The obtained PET resin pellets were stirred and dried at 135°C for 24 hours under a dry nitrogen purging condition, and then an attempt was made to spin a 138 decitex 24 filament polyester multifilament partially oriented yarn (POY) using 100% of the PET resin pellets at a melt extrusion temperature of 285°C, a nozzle surface temperature of 290°C, a round cross-section 24-hole nozzle, and a spinning take-up speed of 3200 m / min. However, the filter back pressure rose significantly, making it impossible to spin the POY stably, and production of the POY was abandoned.

[0083] [Table 1]

[0084] Example 4 Except for setting the molten polymer temperature in the melt extruder cylinder to 275°C, PET resin pellets, POY, DTY, knitted fabric, and seating sheet were obtained in that order in the same manner as in Example 1. The finally obtained seating sheet was as good as in Example 1.

[0085] Example 5 Except for setting the molten polymer temperature in the melt extruder cylinder to 300°C, PET resin pellets, POY, DTY, knitted fabric, and seating sheet were obtained in that order in the same manner as in Example 1. The finally obtained seating sheet was as good as in Example 1.

[0086] (Comparative Example 3) PET resin pellets, POY, DTY, knitted fabric, and seating sheet were obtained in the same order as in Example 1, except that the molten polymer temperature in the melt extruder cylinder was set to 265°C. The polymer melt viscosity in the melt extruder cylinder was high, the domain size of the chain extender increased, and localized segregation was observed. This resulted in poor physical properties and quality, such as a deterioration in the operability of POY and DTY and frequent occurrence of single-yarn breakage and fluff. Furthermore, the knitted fabric and seating sheet were found to have insufficient strength, making them undesirable.

[0087] Comparative Example 4 PET resin pellets, POY, DTY, knitted fabric, and seating sheet were obtained in the same order as in Example 1, except that the molten polymer temperature in the melt extruder cylinder was set to 325°C. The polymer melt viscosity in the melt extruder cylinder was low, and the chain extender domain size and dispersion state were good. However, the chain extender was deactivated at high temperature, and the expected thickening effect could not be achieved. As a result, problems such as a deterioration in the operability of POY and DTY and frequent occurrence of single yarn breakage and fluffing were observed. Furthermore, the knitted fabric and seating sheet were found to have insufficient strength, and both the quality and physical properties were unsatisfactory.

[0088] Example 6 PET resin pellets, POY, DTY, knitted fabric, and seat sheet were obtained in this order in the same manner as in Example 1, except that the L / D (length / diameter ratio) of the melt extruder screw was set to 16. The finally obtained seat sheet was as good as in Example 1.

[0089] Example 7 PET resin pellets, POY, DTY, knitted fabric, and seat sheet were obtained in this order in the same manner as in Example 1, except that the L / D (length / diameter ratio) of the melt extruder screw was set to 45. The finally obtained seat sheet was as good as in Example 1.

[0090] (Comparative Example 5) PET resin pellets, POY, DTY, knitted fabric, and seating sheet were obtained in that order in the same manner as in Example 1, except that the L / D (length / diameter ratio) of the melt extruder screw was set to 10. Due to insufficient mixing and dispersion of the molten polymer and chain extender in the melt extruder cylinder, the domain size of the chain extender increased, and localized segregation was also observed. Furthermore, poor quality was confirmed, such as a deterioration in the operability of POY and DTY and frequent occurrence of single yarn breakage and fluff, and the physical strength was also low. The knitted fabric and seating sheet also showed insufficient strength and poor appearance, making them undesirable.

[0091] (Comparative Example 6) PET resin pellets, POY, DTY, knitted fabric, and seating sheet were obtained in that order in the same manner as in Example 1, except that the L / D (length / diameter ratio) of the melt extruder screw was set to 60. The residence time in the melt extruder cylinder was long, and the domain size and dispersion state of the chain extender were good, but at the same time, hydrolysis of the PET resin also progressed excessively, resulting in problems such as a deterioration in the operability of POY and DTY and frequent occurrence of single yarn breakage and fluff. Furthermore, the knitted fabric and seating sheet were found to have insufficient strength, and neither the quality nor the physical properties were satisfactory.

[0092] Example 8 Except for changing the compression ratio of the melt extruder to 3.3 / 1, PET resin pellets, POY, DTY, knitted fabric, and seat sheet were obtained in that order in the same manner as in Example 1. The finally obtained seat sheet was as good as in Example 1.

[0093] Example 9 Except for changing the compression ratio of the melt extruder to 4.5 / 1, PET resin pellets, POY, DTY, knitted fabric, and seat sheet were obtained in that order in the same manner as in Example 1. The finally obtained seat sheet was as good as in Example 1.

[0094] (Comparative Example 7) An attempt was made to produce PET resin pellets in the same manner as in Example 1, except that the compression ratio of the melt extruder was set to 2 / 1. Due to insufficient degassing caused by the low compression ratio of the melt extruder, the resin strands became air-trapped (air-trapped state), and the production operability of the resin pellets was poor. POY spinning was attempted using the resin pellets, but stable operation was not possible, so production was abandoned.

[0095] (Comparative Example 8) Except for changing the compression ratio of the melt extruder to 6 / 1, an attempt was made to produce PET resin pellets in the same manner as in Example 1. After the melt extruder, a molten strand was discharged from the die, but the discharge state was extremely unstable, resulting in an extremely dangerous situation in terms of operational safety, so production was abandoned. [Industrial Applicability]

[0096] The polyester resin pellets for fiber of the present invention are recycled from polyester scraps that would normally be disposed of as industrial waste, and are used as a new raw material for fiber applications. This is material recycling, and although the color and physical strength are inferior to feedstock recycling, it is possible to reduce GHG emissions and energy costs during recycling. Furthermore, viscosity adjustment using a chain extender also has the advantage of reducing initial investment and running costs compared to solid-state polymerization (SSP). The polyester resin pellets for fiber of the present invention are suitable for use in textile materials such as automotive seat linings, door trims, and ceiling linings, in addition to general clothing applications, and have high industrial applicability.

Claims

1. The polyester resin pellets for fiber derived from PET waste fibers contain PET and a chain extender, characterized in that the number of microdomains consisting of the chain extender and having a major axis of 0.01 μm or more and 0.20 μm or less dispersed in the PET matrix in the pellets is 5 to 50 per square μm of the resin cross section, and no large domains with a major axis of 0.50 μm or more are formed; the melt flow rate (MFR) of the pellets evaluated by the method described in JIS K7210-1 is 50 g / 10 min to 150 g / 10 min at a measurement temperature of 285°C and a measurement load of 2.16 kgf, and the intrinsic viscosity [η] is 0.50 to 0.

75.

2. 2. The polyester resin pellets for fiber made from PET waste fibers according to claim 1, wherein the chain extender is an epoxy-based chain extender.

3. 2. The polyester resin pellets for fiber made from PET waste fiber according to claim 1, wherein the chain extender is a polymer compound represented by the following general structural formula: In the formula, R １ ~R ５ is hydrogen, a methyl group, an alkyl group, R ６ is an alkyl group, and x, y, and z are integers from 1 to 20.

4. 2. The polyester resin pellets for fiber made from waste PET fibers according to claim 1, which contain organic nitrogen in the range of 200 ppm to 2000 ppm.

5. A fiber characterized by using the polyester resin pellets for fiber derived from PET waste fiber according to any one of claims 1 to 4.

6. A fiber structure comprising the fiber according to claim 5.

7. 5. The method for producing polyester resin pellets for fiber derived from PET waste fibers according to any one of claims 1 to 4, characterized in that the PET waste fibers and the chain extender are melt-kneaded together in the melt extruder by setting the temperature of the molten polymer in the cylinder barrel of the melt extruder to 275 to 315°C, the L / D (length / diameter ratio) of the melt extruder screw to 15 to 50, and the compression ratio of the melt extruder to 3 / 1 to 5 / 1.

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