Method for Producing Multifilament

One or more embodiments of the present invention relate to a method for producing a multifilament.

In recent years, plastic wastes have imposed heavy burdens on the global environment, such as harmful effects on ecosystems, generation of harmful gas during combustion of the plastic wastes, and global warming due to a large amount of heat generated by the combustion of the plastic wastes. Biodegradable plastics are the materials that can address the above, and the development of biodegradable plastics has been actively ongoing.

Among such biodegradable plastics, carbon dioxide that is generated when a biodegradable plastic obtained using a plant-derived raw material is combusted originally exists in the air. Therefore, combusting such a biodegradable plastic does not cause an increase in carbon dioxide in the atmosphere. This is called carbon neutrality. Importance is given to carbon neutrality under the Kyoto Protocol, which specifies carbon dioxide reduction goals, and active use of carbon neutrality is desired.

Nowadays, in terms of biodegradability and carbon neutrality, aliphatic polyester resins are attracting attention as biodegradable plastics that are microbially produced using plant-derived raw materials as carbon sources. Attention has been directed particularly to polyhydroxyalkanoate resins.

Patent Literature 1 discloses a method for producing a multifilament containing a poly(3-hydroxybutyrate) resin.

Specifically, the production method described in Patent Literature 1 includes the steps of: heating a resin composition containing a poly(3-hydroxybutyrate) resin to a temperature that is not lower than the melting point of the resin composition and that is not higher than the thermal decomposition temperature of the resin composition and discharging the heated resin composition from a spinning nozzle; applying an air flow to the resin composition discharged from the spinning nozzle, which includes 80 holes, the air flow having a temperature that is not lower than the glass transition temperature of the resin composition and that is not higher than the crystallization temperature of the resin composition; and obtaining a multifilament by drawing, with a roll, the resin composition to which the air flow has been applied.

Patent Literature 1 further describes that the cooling effect that is obtained in a case where the speed of the air flow is less than 0.1 m/s is too small.

PTL 1: WO 2021/206154

Here, for the purpose of increasing the productivity of the multifilament containing the poly(3-hydroxybutyrate) resin and having a small average value of the fineness of single filaments, an attempt was made to increase the roll speed at the time of hauling off the filamentous resin composition by a haul-off roll. However, before being hauled off by the haul-off roll, filament breakage would occur, or fusion of single filaments to each other in the obtained multifilament would occur, and for these reasons, the multifilament could not be obtained with high productivity.

In view of the above, a method to increase the productivity of a multifilament containing a poly(3-hydroxybutyrate) resin and having a small average value of the fineness of single filaments is provided.

One or more embodiments of the present invention relate to a method for producing a multifilament including 50 or more single filaments by melt spinning, the method including the steps of: (A) obtaining 50 or more raw filaments in a molten state by discharging a composition including a poly(3-hydroxyalkanoate) resin from a spinning nozzle; and (B) cooling the raw filaments by blowing gas onto the raw filaments in the molten state. The spinning nozzle includes a nozzle surface including 50 or more discharge holes. The nozzle surface is segmented into a central region and a peripheral region surrounding the central region. An outer edge of the central region and an outer edge of the peripheral region are similar in shape to each other and share a same area centroid. A similarity ratio between the outer edge of the central region and the outer edge of the peripheral region is 1:2. The number of discharge holes present in the peripheral region exceeds 75% of the number of discharge holes present on the nozzle surface. A temperature of the gas is from (Tc-45) to (Tc-20)° C. [Tc is a crystallization temperature of the composition including the poly(3-hydroxyalkanoate) resin]. A speed of the gas is 0.01 m/s or greater and less than 0.10 m/s. An average value of fineness of the single filaments is from 3.0 dtex to 15.0 dtex.

One or more embodiments of the present invention make it possible to increase the productivity of a multifilament containing a poly(3-hydroxybutyrate) resin and having a small average value of the fineness of single filaments.

Hereinafter, one or more embodiments of the present invention are described with reference to the accompanying drawings.

A method for producing a multifilament according to the present embodiment is a method for producing a multifilament including 50 or more single filaments by melt spinning.

The method for producing a multifilament according to the present embodiment includes the steps of: (A) obtaining 50 or more raw filaments in a molten state by discharging a composition including a poly(3-hydroxyalkanoate) resin (this composition is hereinafter also referred to as “raw material composition”) from a spinning nozzle; and (B) cooling the raw filaments by blowing gas onto the raw filaments in the molten state.

The spinning nozzle includes a nozzle surface including 50 or more discharge holes.

The nozzle surface is segmented into a central region and a peripheral region surrounding the central region.

The outer edge of the central region and the outer edge of the peripheral region are similar in shape to each other and share the same area centroid.

The similarity ratio between the outer edge of the central region and the outer edge of the peripheral region is 1:2.

The number of discharge holes present in the peripheral region exceeds 75% of the number of discharge holes present on the nozzle surface.

The temperature of the gas is from (Tc-45) to (Tc-20)° C. [Tc is the crystallization temperature of the composition including the poly(3-hydroxyalkanoate) resin].

The speed of the gas is 0.01 m/s or greater and less than 0.10 m/s.

The average value of the fineness of the single filaments is from 3.0 dtex to 15.0 dtex.

The method for producing a multifilament according to the present embodiment further includes the step (C) of obtaining the multifilament by hauling off, by a haul-off roll, the raw filaments that have been cooled in the step (B).

The aforementioned Patent Literature 1 (WO 2021/206154) describes that “in a case where the speed of the air flow applied onto the resin composition discharged from the spinning nozzle is less than 0.1 m/s, the obtained cooling effect is too small, and for this reason, the speed of the air flow may be 0.1 m/s or greater.” On the other hand, in the present embodiment, the speed of the gas in the step (B) is 0.01 m/s or greater and less than 0.10 m/s.

In a case where the discharge holes are arranged uniformly on the nozzle surface with the similarity ratio of 1:2, the ratio of the number of discharge holes present in the peripheral region to the number of discharge holes present on the nozzle surface (this ratio is hereinafter also referred to as “presence ratio”) is 75%. On the other hand, in the present embodiment, the presence ratio exceeds 75%, which means that the discharge holes are distributed in a non-uniform manner such that the discharge holes are present more densely in the peripheral region than in the central region.

The present embodiment makes it possible to increase the productivity of the multifilament containing the poly(3-hydroxybutyrate) resin and having a small average value (from 3.0 dtex to 15.0 dtex) of the fineness of the single filaments.

The reason for this is considered as follows.

Specifically, since the discharge holes are non-uniformly distributed such that the discharge holes are more densely present in the peripheral region, in the step (B), in a bundle of raw filaments, sufficient cooling of the raw filaments positioned at the inner side, which are cooled less easily than the raw filaments positioned at the outer side, is facilitated. Consequently, even though the speed of the gas is less than 0.10 m/s, the time during which the raw filaments are in the molten state can be shortened, and breakage of the raw filaments is less likely to occur. Moreover, in the bundle of raw filaments, cooling unevenness between the outer raw filaments and the inner raw filaments is suppressed; variation in the fineness of the raw filaments is suppressed; and the number of excessively thin raw filaments is reduced, and thereby breakage of the raw filaments is less likely to occur.

Furthermore, since the speed of the gas is less than 0.10 m/s, after the raw filaments are discharged from the spinning nozzle and before the raw filaments are hauled off by the haul-off roll, heat can be suitably removed from the raw filaments while suppressing the temperature of the raw filaments from dropping to fall within a crystallization temperature range (e.g., 50 to 80° C.). Consequently, crystallization of the raw filaments can be suppressed, and the raw filaments are rendered in a state of having excellent flexibility (i.e., easily deformable state), so that breakage of the raw filaments is less likely to occur when the raw filaments are hauled off by the haul-off roll.

Since breakage of the raw filaments is less likely to occur, the spinning speed (i.e., the speed of the haul-off roll) can be increased, which makes it possible to increase the productivity of the multifilament.

The raw material composition contains a polymer component and an additive.

The polymer component includes the poly(3-hydroxyalkanoate) resin.

The polymer component may contain another polymer in addition to the poly(3-hydroxyalkanoate) resin.

The poly(3-hydroxyalkanoate) resin is a polyester containing a 3-hydroxyalkanoic acid as a monomer.

Specifically, the poly(3-hydroxyalkanoate) resin is a resin including the 3-hydroxyalkanoic acid as a structural unit.

The poly(3-hydroxyalkanoate) resin is a biodegradable polymer.

It should be noted that being “biodegradable” in the present embodiment means being able to be decomposed into low molecular weight compounds by microorganisms in a natural environment. Being biodegradable or not can be determined based on tests suited for different environments. Specifically, for example, ISO 14855 (compost) and ISO 14851 (activated sludge) are suited for an aerobic condition, and ISO 14853 (aqueous phase) and ISO 15985 (solid phase) are suited for an anaerobic condition. Also, biodegradability by microorganisms in seawater can be evaluated by biochemical oxygen demand measurement.

The poly(3-hydroxyalkanoate) resin includes a homopolymer and/or a copolymer.

The poly(3-hydroxyalkanoate) resin may include a structural unit expressed by an equation (1) shown below.

(In the above equation (1), R is an alkyl group represented by CH, and p is an integer from 1 to 15. )

The poly(3-hydroxyalkanoate) resin may be a resin including 3-hydroxybutyrate as a structural unit (i.e., a poly(3-hydroxybutyrate) resin).

It should be noted that the poly(3-hydroxybutyrate) resin includes a homopolymer and/or a copolymer.

Examples of the poly(3-hydroxyalkanoate) resin including 3-hydroxybutyrate as a structural unit include P3HB, P3HB3HH, P3HB3HV, P3HB4HB, poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate).

P3HB herein means poly(3-hydroxybutyrate) as a homopolymer.

P3HB3HH herein means poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

P3HB3HV herein means poly(3-hydroxybutyrate-co-3-hydroxyvalerate).

P3HB4HB herein means poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

It should be noted that P3HB has a function to facilitate crystallization of P3HB itself and crystallization of the poly(3-hydroxyalkanoate) resin other than P3HB. Accordingly, the poly(3-hydroxyalkanoate) resin may include P3HB.