PREPARATION METHOD FOR POLYLACTIC ACID FIBER FILTER ROD WITH GOOD TEMPERATURE RESISTANCE

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This is a 371 application of PCT International Application PCT/CN2023/076472, filed Feb. 16, 2023, which claims priority to Chinese Patent Application 2022111622084, filed Sep. 23, 2022; the disclosures of which are incorporated by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates to the technical field of cigarette preparation, in particular to a preparation method for a polylactic acid fiber filter rod with better temperature resistance.

BACKGROUND ART

Polylactic acid (PLA) is a polymer material synthesized chemically from lactic acid, which is obtained through the fermentation of starch deriving from renewable plant resources. It has excellent recyclability and biodegradability and exhibits the following characteristics that 1. renewable plant resources (corn, wheat, beet, rice, potatoes, sweet potatoes and the like) and organic wastes (corncobs or roots, stems, leaves and peel of other crops) are used as raw materials, so as to get rid of dependence on timber and petroleum resources and meet the requirements of sustainable development; 2. the polylactic acid can be fully bio-degraded, and will be naturally decomposed into water and carbon dioxide over time in natural environments without leading to environmental pollution, and the carbon dioxide produced can be reused through plant photosynthesis, forming a permanent and closed carbon cycling system, making the polylactic acid a veritable “green material”; 3. compared with three major synthetic fibers (dacron, chinlon and arylon), energy consumption is low in production of polylactic acid fibers, making the polylactic acid fibers a polymer material with relatively low resource and environment loads; and 4. the polylactic acid has good processability, and tows can be produced by a melt spinning method typical of thermoplastic resin.

At present, the polylactic acid fibers have been developed for use in fields such as tows for cigarettes, however, the polylactic acid fibers for the tows for cigarettes greatly differ from conventional polylactic acid tows for clothing in performance requirements, for example, the polylactic acid fibers for clothing have to meet the requirements of fiber spinning, knitting and textile printing and dyeing, washing and ironing, have to possess high degree of crystallinity, degree of orientation and mechanical strength, can withstand the temperature of 80-100° C., have to be insoluble and non-swelling in detergent aqueous solutions and dry cleaning solvents, and should exhibit a specific level of hygroscopicity and meanwhile adsorb minimal quantities of other gaseous substances in surroundings. However, the tows for cigarettes should meet the following requirements that (1) filter rods made by the tows for cigarettes are non-toxic and tasteless and high in safety; (2) the tows are high in stability, and can meet the requirements of filter rod forming equipment and filter rod forming processes; (3) the tows have proper rigidity and crimping performance, so as to achieve good elasticity and blooming performance, the filter rods can meet the requirements of certain rigidity, inspiratory resistance and appearance quality after adding a plasticizer or adhesive under the condition of a low tow filling quantity, and the filter rods have a high yield; (4) the tows have enough thermal resistance, and filter tips do not collapse or deform during cigarette smoking; (5) the tows have high filtering efficiency for harmful ingredients in smoke; and (6) sensory quality of the cigarettes is not affected. Thus, it is necessary to develop a special spinning and after-treatment process technology to meet the requirements of use in cigarettes.

For example, the Chinese patent for invention CN111789285A has provided a preparation method of a polylactic acid cooling modified tow filter stick. The preparation method includes the following steps: uniformly mixing polylactic acid master batches, Styrene-Ethylene-Butadiene-Styrene (SEBS) and polypropylene (PP), carrying out online melt polymerization reaction at 140-200° C., carrying out screw extrusion through a screw, cooling, carrying out melt spinning, drafting, crimping, drying, and shaping to obtain polylactic acid tows, and carrying out filter stick molding on a conventional filter stick machine. Compared with a traditional polylactic acid tow filter stick, the polylactic acid cooling modified tow filter stick prepared by the present disclosure has the advantages that the melting point is higher; the thermal resistance is greatly improved, the head shrinking phenomenon is avoided in a heating non-combustion tobacco product, meanwhile, the smoke temperature is remarkably reduced, the problems that the heating non-combustion tobacco product is high in smoke temperature, high in hot pricking feeling and poor in smoking comfort are solved, and the method is suitable for industrial production.

However, the preparation method of the filter stick still has the following problems: the melting point and crystallinity of the PLA are related to the molecular weight of polymers and the content of levolactic acid monomers. When the crystallinity of the PLA is high, its temperature resistance is better, but the high crystallinity easily leads to the formation of crystallization sites. When the tows are formed into the filter stick, the crystallization sites are randomly distributed at different positions of the tows. During the cutting of the filter stick in the rolling and connecting process, the high-speed movement of the filter stick causes differences in force applied by a knife on the crystallization sites and the tows, which easily leads to gap or even breakage of the knife. This results in the frequent shutdown of a cigarette making and plug assembling machine, the uneven cross-section and deformation of the filter stick, and non-compliance with roundness specifications. Additionally, the presence of multiple crystallization sites in the tows also affects specific surface areas of the tows in the filter stick, which significantly affects the filtration efficiency and aroma substances of the filter stick, and meanwhile, the sensory quality of the cigarettes is adversely affected.

Thus, in order to solve the above problems, it is necessary to design a reasonable preparation method for a polylactic acid fiber filter rod with better temperature resistance.

SUMMARY

The objective of the present disclosure is to provide a preparation method for a polylactic acid fiber filter rod with better temperature resistance. The preparation method is simple and convenient. By means of controlling the proportions and preparation of polylactic acid raw materials, so as to obtain sheath-core polylactic acid fibers of a multi-layer structure and improve the uniformity of an inner-layer structure thereof, that is, crystallization distribution in the polylactic acid fibers becomes more uniform, the generation of crystallization sites is reduced, damage to a knife is avoided during the high-speed cutting process, and the prepared polylactic acid fiber filter rod is stable to cut. The crystallinity and the temperature resistance gradually change from inside to outside in the sheath-core polylactic acid fiber tows of the multi-layer structure, such that the whole filter rod has better temperature resistance, and the filter performance of the polylactic acid tows is improved.

In order to achieve the above objectives, the present disclosure provides the following technical solutions:

A preparation method for a polylactic acid fiber filter rod with better temperature resistance includes the following steps:

• • S1: acquiring various polylactic acid raw materials, and acquiring a content of a levo-isomer in each polylactic acid raw material; selecting at least two kinds of up-to-standard polylactic acid raw materials having the content of the levo-isomer being within a predetermined range;
  • S2: selecting an up-to-standard polylactic acid raw material having the highest content of the levo-isomer in step S1 to serve as a first component raw material, and induce crystallization by means of drafting stress when spinning is carried out on the first component raw material, so as to obtain a core component; selecting an up-to-standard polylactic acid raw material having the lowest content of the levo-isomer in step S1 to serve as a second component raw material, and adding glyceryl triacetate to the second component raw material to obtain a sheath component;
  • S3: matching the core component with the sheath component according to a preset proportion, such that an outer side of the core component is coated with the sheath component, so as to form sheath-core polylactic acid fiber tows; and
  • S4: carrying out composite forming on a plurality of sheath-core polylactic acid fiber tows to obtain a polylactic acid filter rod.

As a preference of the present disclosure, in a case that kinds of the up-to-standard polylactic acid raw materials are no less than three, and

• • before carrying out step S3, each of the up-to-standard polylactic acid raw materials, except for the up-to-standard polylactic acid raw materials in step S2, is separately processed, to obtain a transitional component; and
  • during carrying out step S3, the transitional component is placed between the core component and the sheath component to form the sheath-core polylactic acid fiber tows of a multi-layer structure.

As a preference of the present disclosure, in a case that the kinds of other up-to-standard polylactic acid raw materials are no less than two,

• • the processing of other up-to-standard polylactic acid raw materials to obtain the transitional components specifically involves separately processing each of the up-to-standard polylactic acid raw materials to obtain a plurality of transitional components; and
  • when the transitional components are placed between the core component and the sheath component, a specific arrangement is as follows: an outer side of the transitional component having the high content of the levo-isomer is coated with the transitional component having the low content of the levo-isomer.

As a preference of the present disclosure, during carrying out step S3, the core component is matched with the sheath component according to the preset proportion, wherein the composition proportion of the core component to the sheath component ranges from 33:67 to 37:63.

As a preference of the present disclosure, during carrying out step S2, a dispersing agent is added to the first component raw material.

As a preference of the present disclosure, during carrying out step S2, nucleating agents are respectively added to the first component raw material and the second component raw material.

As a preference of the present disclosure, a percentage of the nucleating agent added to the first component raw material to the overall first component raw material is not lower than a percentage of the nucleating agent added to the overall second component raw material to the second component raw material; and

• • a difference between the percentage of the nucleating agent added to the first component raw material to the overall first component raw material and the percentage of the nucleating agent added to the second component raw material to the overall second component raw material does not exceed 5%.

As a preference of the present disclosure, during carrying out step S2, before the core component is obtained by the crystallization of the first component raw material, it is ensured that the first component raw material is dispersed evenly; and

• • during carrying out step S2, before the sheath component is obtained by the addition of the glyceryl triacetate to the second component raw material, it is ensured that the second component raw material is dispersed evenly.

As a preference of the present disclosure, the nucleating agents are added to the plurality of transitional components, and the proportion of the nucleating agent to the transitional component having the low content of the levo-isomer is lower than the proportion of the nucleating agent to the transitional component having the high content of the levo-isomer.

As a preference of the present disclosure, after carrying out step S4, the polylactic acid filter rod is cut using an alloy knife.

The preparation method for the polylactic acid fiber filter rod with better temperature resistance of the present disclosure has the beneficial effects that the preparation method is simple and convenient. By means of controlling the proportions and preparation of the polylactic acid raw materials, so as to obtain the sheath-core polylactic acid fibers of the multi-layer structure and improve the uniformity of the inner-layer structure thereof, that is, crystallization distribution in the polylactic acid fibers becomes more uniform, the generation of crystallization sites is reduced, damage to the knife is avoided during the high-speed cutting process, and the prepared polylactic acid fiber filter rod is stable to cut. The crystallinity and the temperature resistance gradually change from inside to outside in the sheath-core polylactic acid fiber tows of the multi-layer structure, such that the whole filter rod has better temperature resistance, and the filter performance of the polylactic acid tows is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a preparation method for a polylactic acid fiber filter rod with better temperature resistance according to the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The followings are specific embodiments of the present disclosure, the technical solutions of the present disclosure are further described, however, the present disclosure is not limited to these embodiments.

Exemplary embodiments of the present disclosure will be described in detail with reference to the drawings. It should be noted that unless otherwise specified, the relative arrangement of modules and structures illustrated in these embodiments do not limit the scope of the present disclosure.

The following description of at least one exemplary embodiment is actually illustrative merely, and never acts as any limitation to the present disclosure or application or use thereof.

Technologies, methods and systems known to those of ordinary skilled in the related art may not be discussed in detail, but are intended to be a part of the specification of authorization where appropriate.

Embodiment 1: As shown in FIG. 1, a preparation method for a polylactic acid fiber filter rod with better temperature resistance includes the following steps:

• • S1: various polylactic acid raw materials are acquired, and the content of a levo-isomer in each polylactic acid raw material is acquired; at least two kinds of up-to-standard polylactic acid raw materials having the content of the levo-isomer being within a predetermined range are selected;

In this context, a cigarette making plant typically has multiple corresponding suppliers of polylactic acid raw materials. Due to differences in origins, batches, and preparation processes, the properties of the polylactic acid raw materials from different suppliers may vary. To ensure crystallinity, the polylactic acid raw materials with the high content of the levo-isomer (levolactic acid monomer) should be selected.

When each polylactic acid raw material arrives, the content of the levo-isomer thereof is measured, and at least two kinds of up-to-standard polylactic acid raw materials having the content of the levo-isomer being within the predetermined range are selected; and generally, the polylactic acid raw materials having the content of the levo-isomer being 90% or more are selected.

S2: an up-to-standard polylactic acid raw material having the highest content of the levo-isomer in step S1 is selected to serve as a first component raw material, and crystallization is induced by means of drafting stress when spinning is carried out on the first component raw material, so as to obtain a core component, wherein

• • the content of the levo-isomer in the first component raw material is in the range of 95% to 98%, for example, the first component raw material is the polylactic acid raw material having the content of the levo-isomer being 97%, and under such high content of the levo-isomer, the melting point of the first component raw material is also higher; and during the spinning and post-processing process, the low-temperature crystallization is induced by means of the drafting stress, such that the crystallinity of drafted tows is improved, the thermal stability of tow sizes is enhanced, and good crimping and shaping may be realized to ensure that the tows have proper rigidity and crimping performance. Furthermore, the tows have good elasticity and blooming performance, lower thermal shrinkage performance and better thermal resistance.

An up-to-standard polylactic acid raw material having the lowest content of the levo-isomer in step S1 is selected to serve as a second component raw material, and glyceryl triacetate is added to the second component raw material to obtain a sheath component, wherein

• • the content of the levo-isomer in the second component raw material is in the range of 91% to 93%, for example, the second component raw material is the polylactic acid raw material with the content of the levo-isomer being 91%, and the glyceryl triacetate needs to be added to the second component raw material; and under the action of the glyceryl triacetate, the tows swell and bond, and may ultimately be matched with the core component obtained from the first component raw material, such that polylactic acid tows of a sheath-core structure with excellent bonding performance are obtained.

S3: the core component is matched with the sheath component according to a preset proportion, such that an outer side of the core component is coated with the sheath component, so as to form the sheath-core polylactic acid fiber tows; and

• • it should be noted that each polylactic acid fiber tow is the tow of the sheath-core structure.

S4: composite forming is carried out on a plurality of sheath-core polylactic acid fiber tows to obtain a polylactic acid filter rod.

The tows are melted and extruded to a filter through a screw extruder to remove impurities, and are then spun through a trilobal spinneret plate at a certain spinning temperature, the newly spun tows are cooled using a process air-conditioning device, surfaces of the tows are coated with an oiling agent to improve the post-processing performance, and the tows are coiled up at a proper coil-up rate and are then temporarily stored in a tow containing barrel. In the post-spinning process, the pre-spun nascent fibers are bundled, drafted in a water bath at a certain temperature and then enter a crimper for crimping so as to achieve required indicators, such as linear density and crimp number.

In the present disclosure, during carrying out step S2, a dispersing agent is added to the first component raw material, such that large crystallization sites are not easy to form in the polylactic acid fiber tows with high crystallinity, and the generation of the crystallization sites is reduced, thus facilitating cutting.

Moreover, during carrying out step S2, nucleating agents are respectively added to the first component raw material and the second component raw material, such that the polylactic acid fiber tows in the core component and the sheath component are higher in crystallinity, i.e., better in thermal resistance.

In this context, the percentage of the nucleating agent added to the first component raw material to the overall first component raw material is not lower than the percentage of the nucleating agent added to the second component raw material to the overall second component raw material; and

• • a difference between the percentage of the nucleating agent added to the first component raw material to the overall first component raw material and the percentage of the nucleating agent added to the second component raw material to the overall second component raw material does not exceed 5%.

The crystallinity and the temperature resistance gradually change from inside to outside in the sheath-core polylactic acid fiber tows of the multi-layer structure, such that the whole filter rod has better temperature resistance, and the filter performance of the polylactic acid tows is improved.

Finally, it is noted that during carrying out step S2, before the core component is obtained by the crystallization of the first component raw material, it is ensured that the first component raw material is dispersed evenly; and

• • during carrying out step S2, before the sheath component is obtained by the addition of the glyceryl triacetate to the second component raw material, it is ensured that the second component raw material is dispersed evenly.

In carrying out step S3, the core component is matched with the sheath component according to the preset proportion, wherein the composition proportion of the core component to the sheath component ranges from 33:67 to 37:63.

The preparation method for the polylactic acid fiber filter rod with better temperature resistance of the present disclosure is simple and convenient. By means of controlling the proportions and preparation of the polylactic acid raw materials, so as to obtain the sheath-core polylactic acid fibers of the multi-layer structure and improve the uniformity of the inner-layer structure thereof, that is, crystallization distribution in the polylactic acid fibers becomes more uniform, the generation of crystallization sites is reduced, damage to the knife is avoided during the high-speed cutting process, and the prepared polylactic acid fiber filter rod is stable to cut. The crystallinity and the temperature resistance gradually change from inside to outside in the sheath-core polylactic acid fiber tows of the multi-layer structure, such that the whole filter rod has better temperature resistance, and the filter performance of the polylactic acid tows is improved.

Embodiment 2, still as shown in FIG. 1, is only one embodiment of the present disclosure, based on Embodiment 1, in the preparation method for the polylactic acid fiber filter rod with better temperature resistance of the present disclosure, in a case that kinds of up-to-standard polylactic acid raw materials are no less than three, and

• • before carrying out step S3, each of up-to-standard polylactic acid raw materials, except for up-to-standard polylactic acid raw materials in step S2, is separately processed, to obtain a transitional component; and
  • during carrying out step S3, the transitional component is placed between a core component and a sheath component to form sheath-core polylactic acid fiber tows of a multi-layer structure.

Further, in a case that the kinds of other up-to-standard polylactic acid raw materials are no less than two (namely, the kinds of the up-to-standard polylactic acid raw materials are no less than four),

• • the processing of other up-to-standard polylactic acid raw materials to obtain the transitional components specifically involves separately processing each of the up-to-standard polylactic acid raw materials to obtain a plurality of transitional components; and
  • when the transitional components are placed between the core component and the sheath component, a specific arrangement is as follows: an outer side of the transitional component having the high content of a levo-isomer is coated with the transitional component having the low content of the levo-isomer.

Therefore, more layers of sheath-core polylactic acid fiber tows are formed, the number of layers with gradually changed crystallinity in the tows is more, each tow may be effectively ensured to have better elasticity and blooming performance, and the thermal shrinkage performance is lower.

Of course, nucleating agents are added to the plurality of transitional components, and the proportion of the nucleating agent to the transitional component having the low content of the levo-isomer is lower than the proportion of the nucleating agent to the transitional component having the high content of the levo-isomer.

Finally, after carrying out step S4, the polylactic acid fiber filter rod is cut using an alloy knife.

The preparation method for the polylactic acid fiber filter rod with better temperature resistance of the present disclosure is simple and convenient. By means of controlling the proportions and preparation of the polylactic acid raw materials, so as to obtain the sheath-core polylactic acid fibers of the multi-layer structure and improve the uniformity of the inner-layer structure thereof, that is, crystallization distribution in the polylactic acid fibers becomes more uniform, the generation of crystallization sites is reduced, damage to the knife is avoided during the high-speed cutting process, and the prepared polylactic acid fiber filter rod is stable to cut. The crystallinity and the temperature resistance gradually change from inside to outside in the sheath-core polylactic acid fiber tows of the multi-layer structure, such that the whole filter rod has better temperature resistance, and the filter performance of the polylactic acid tows is improved.

The present disclosure is not limited to the above specific implementations, and may have various replacements and changes. Any modification, equivalent replacement, improvement, etc. made to the above implementations according to the technical essence of the present disclosure should fall within the scope of protection of the present disclosure.