A hot-melt composite fiber, its preparation method and fiber web

Abstract

This application relates to the field of air purification technology, and particularly to a heat-meltable composite fiber, which includes a core layer and a skin layer. The skin layer wraps around the outer surface of the core layer. The material composition of the core layer includes polypropylene I, and the material composition of the skin layer includes polypropylene II and a hydrogenated styrene-butadiene block copolymer. The melting point of polypropylene II in the skin layer is 30°C - 40°C lower than the melting point of polypropylene I in the core layer. The skin layer of the heat-meltable composite fiber in this application is made of a blend melt of SEBS-modified polypropylene, which has better fluidity and good transparency than a single-component polypropylene melt. This application also stipulates that the melting point of polypropylene II in the skin layer is 30°C - 40°C lower than the melting point of polypropylene I in the core layer, which can ensure that the physical properties of the core layer remain unchanged when the skin layer components melt during heating and pressing, so that the fiber has a certain strength and elasticity, and at the same time can achieve the adhesion between fibers, which is beneficial to the processing and forming of the fiber web.

Description

Technical Field

[0001] The present application relates to the field of air purification technology, and in particular to a heat-fusible composite fiber and a preparation method and a fiber web thereof. Background Art

[0002] Heat-fusible composite fibers are usually made of low-melting-point resin as the sheath component and high-melting-point resin as the core component. They can be formed into a fiber web by carding and other processing methods, and then the sheath component is melted by heating and pressurizing to bond the fiber intersection points. Heat-fusible composite fibers are widely used because they do not require the use of adhesives and have high production speeds.

[0003] The heat-fusible composite fiber composed of a low-melting-point polypropylene (co-polypropylene, co-PP) sheath component and a polypropylene (polypropylene, PP) core component has attracted people's attention because both the components constituting the sheath and the core contain polypropylene components, and there is a strong affinity between the sheath component and the core component in the composite fiber. However, in the existing co-PP / PP heat-fusible composite fibers, when hot air bonding is performed by hot air bonding, the temperature of hot air bonding generally does not exceed the melting temperature of the polypropylene core layer in order to prevent fiber deformation. However, when a relatively low temperature is used for hot melt bonding in the production of monofilaments, due to the fast production rate, the polypropylene in the skin layer does not have time to melt and bond, which easily leads to the problem of low bonding strength of the fiber web. Summary of the invention

[0004] The present application provides a heat-fusible composite fiber and a preparation method thereof and a fiber web, which are used to solve the problems of poor bonding performance and unsatisfactory transparency of existing heat-fusible composite fibers.

[0005] According to a first aspect of the present application, the present application provides a heat-fusible composite fiber, comprising:

[0006] The core layer comprises polypropylene I;

[0007] A skin layer, wrapped around the outer surface of the core layer; the material composition of the skin layer includes polypropylene II and hydrogenated styrene-butadiene block copolymer;

[0008] The melting point of the polypropylene II in the skin layer is 30° C. to 40° C. lower than the melting point of the polypropylene I in the core layer.

[0009] In a possible design, the mass ratio of the skin layer to the core layer is 1:2-1:1.

[0010] In a possible design, in the skin layer, the weight ratio of the polypropylene II to the hydrogenated styrene-butadiene block copolymer is 4:1-9:1.

[0011] In a possible design, the melt index of the polypropylene I is 3 g / 10 min - 15 g / 10 min; preferably, the melt index of the polypropylene I is 3 g / 10 min - 8 g / 10 min;

[0012] In a possible design, the melting point of the polypropylene I is 160°C - 170°C.

[0013] In a possible design, the polypropylene I is a homopolypropylene.

[0014] In a possible design, in the skin layer, the melt index of the polypropylene II is 3 g / 10 min - 5 g / 10 min, and the melt index of the hydrogenated styrene-butadiene block copolymer is 10 g / 10 min - 30 g / 10 min.

[0015] In a possible design, the diameter of the heat-melt composite fiber is 0.05 mm - 0.06 mm.

[0016] In a possible design, the material components of the skin layer and the core layer each independently further include a lubricant, and the lubricant is selected from one or more of fatty acid amide compounds, fatty acid compounds, paraffin and hydrocarbon resins, siloxane compounds, polysiloxane polymers, fluorine compounds, copolymers of tetrafluoroethylene and propylene, and copolymers of vinylidene fluoride and hexafluoropropylene;

[0017] In a possible design, the lubricant is selected from fatty acid amide compounds.

[0018] In a possible design, in the core layer, the content of the fatty acid amide compound is 0.05% - 1% of the weight of the polypropylene I.

[0019] In a possible design, in the skin layer, the content of the fatty acid amide compound is 0.05% - 1% of the weight of the polypropylene II.

[0020] According to the second aspect of the present application, the present application also provides a method for preparing the above heat-melt composite fiber, including the following steps:

[0021] After the skin layer material components containing polypropylene II and hydrogenated styrene-butadiene block copolymer are melt-extruded by a first screw, they enter a first metering pump for precise metering, and then enter the skin layer channel of a skin-core spinning double-channel composite die head;

[0022] After the core layer material components containing polypropylene I are melt-extruded by a second screw, they enter a second metering pump for precise metering, and then enter the core layer channel of the skin-core spinning double-channel composite die head;

[0023] After passing through their respective channels, the cortical material component and the core material component are compounded into fibers with a skin-core structure on a spinneret plate with multiple spinneret holes; the fibers with a skin-core structure are then extruded through the spinneret plate to obtain multiple primary spun fibers with a skin-core structure;

[0024] The primary spun fibers enter a cooling water tank for cooling, and each fiber is separated after entering its respective silk path in the cooling water tank; the separated spun fibers are stretched by a first-stage water bath with a draw roll and are stretched by hot air in a hot box; after stretching, each spun fiber is wound into a cake separately to obtain the heat-melt composite fiber;

[0025] The draw ratio of the first-stage water bath stretching is 4 to 8 times, and the water temperature of the water bath is 80°C to 95°C; the draw ratio of the hot air stretching is 1.1 to 1.5 times, and the hot air temperature is 85°C to 95°C.

[0026] According to the third aspect of the present application, the present application further provides a fiber web, which is prepared from the above heat-melt composite fiber.

[0027] Advantages of the present application:

[0028] A heat-meltable composite fiber of the present application includes a core layer and a skin layer. The skin layer wraps around the outer surface of the core layer. The material composition of the core layer includes polypropylene I, and the material composition of the skin layer includes polypropylene II and a hydrogenated styrene-butadiene block copolymer. Considering the hot air bonding process, in order to keep the core layer PP from deforming during hot air bonding, the temperature of hot air bonding should not be higher than the melting point of the core layer PP. Considering the need for the skin layer to melt and bond, the melting point of polypropylene II in the skin layer is 30°C - 40°C lower than the melting point of polypropylene I in the core layer, so that the skin layer can melt during bonding. The heat-meltable composite fiber of the present application includes a core layer and a skin layer wrapped around the outside of the core layer. Both the core layer and the skin layer contain polypropylene components, making the core layer and the skin layer have a strong affinity and not easily delaminate. The material composition of the skin layer includes PP and SEBS. SEBS is a linear triblock copolymer with a middle elastic block, having good stability and aging resistance, good temperature resistance, compression set resistance, and excellent mechanical properties; SEBS and PP have good compatibility. After adding polypropylene, the crystallinity of polypropylene is destroyed, making the crystallization of PP finer; SEBS reduces the melting temperature of polypropylene, enabling polypropylene to melt at a lower temperature. At the same time, the prepared blend melt has better fluidity and tensile properties than a single-component polypropylene melt. The good fluidity and stretchability can also ensure the spinnability of the heat-meltable composite fiber. The heat-meltable composite fiber of the present application also stipulates that the melting point of polypropylene II in the skin layer is 30°C - 40°C lower than the melting point of polypropylene I in the core layer. In the production of hot bonding of the fiber web, it can ensure that the physical properties of the core layer remain unchanged when the skin layer components melt during heating and pressing under conditions lower than and close to the melting temperature of the core layer, so that the fiber has a certain strength and elasticity. At the same time, the skin layer melts to achieve bonding between the fibers, which is beneficial to the processing and forming of the fiber web.

[0029] It should be understood that the above general description and the following detailed description are only exemplary and do not limit the present application. Brief Description of the Drawings

[0030] Figure 1 It is a schematic structural diagram of a heat-meltable composite fiber provided by an embodiment of the present application.

[0031] The accompanying drawings here are incorporated into the specification and constitute a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application. Detailed Embodiments

[0032] The following are the preferred embodiments of the embodiments of the present application. It should be noted that for those of ordinary skill in the art, without departing from the principles of the embodiments of the present application, several improvements and refinements can still be made, and these improvements and refinements are also regarded as the protection scope of the embodiments of the present application.

[0033] In a first aspect, the present application provides a heat-meltable composite fiber, comprising:

[0034] a core layer; the material composition of the core layer includes polypropylene I;

[0035] a skin layer, wrapped around the outer surface of the core layer; the material composition of the skin layer includes polypropylene II and a hydrogenated styrene-butadiene block copolymer;

[0036] The melting point of polypropylene II in the skin layer is 30°C - 40°C lower than the melting point of polypropylene I in the core layer.

[0037] In the above solution, the heat-meltable composite fiber of the present application includes a core layer and a skin layer wrapped around the core layer. Both the core layer and the skin layer contain polypropylene components, so that there is a strong affinity between the core layer and the skin layer, and delamination is not likely to occur. The material composition of the skin layer includes PP and a hydrogenated styrene-butadiene block copolymer (Styrene ethylene / butenestyrene, SEBS). SEBS is a linear triblock copolymer with a middle elastic block, having good stability and aging resistance, good temperature resistance, compression set resistance and excellent mechanical properties. The blend melt made of SEBS-modified low-melting-point polypropylene has a lower melting point and better fluidity than the melt of single-component low-melting-point polypropylene. At the same time, the blend also has good toughness, impact elasticity and tensile properties. The good toughness and impact elasticity make the skin layer of the heat-meltable composite fiber not easily break when subjected to external force, better protecting the core layer. The good fluidity and stretchability can also ensure the spinnability of the heat-meltable composite fiber. The heat-meltable composite fiber of the present application also defines that the melting point of polypropylene II in the skin layer is 30°C - 40°C lower than the melting point of polypropylene I in the core layer. The skin layer has good toughness and elasticity. In the production of the fiber web, it can ensure that the physical properties of the core layer remain unchanged when the skin layer components are melted during heating and pressing, so that the fiber has a certain strength and elasticity, and at the same time, fiber-to-fiber adhesion can be achieved, which is beneficial to the processing and forming of the fiber web.

[0038] The following details this solution:

[0039] In some embodiments, the mass ratio of the skin layer to the core layer is 1:2 - 1:1; preferably, the mass ratio of the skin layer to the core layer is 2:3 - 1:1.

[0040] Understandably, by defining the mass ratio of the skin layer to the core layer, it is possible to ensure that the heat-meltable composite fiber has a low-temperature thermal adhesion and ideal strength. If the mass ratio of the skin layer to the core layer is lower than 1:2, the heat-meltable composite fiber produced will have insufficient thermal adhesion and cannot achieve the purpose of low-temperature bonding. If the mass ratio of the skin layer to the core layer is higher than 1:1, the strength of the heat-meltable composite fiber produced will be insufficient, and the single-filament fiber strength greater than 3.5 cN / dtex required by the regulations cannot be achieved. The woven wire mesh is prone to breakage under external forces.

[0041] In some embodiments, in the skin layer, the weight ratio of polypropylene II to the hydrogenated styrene-butadiene block copolymer is 4:1 - 9:1.

[0042] Optionally, in the skin layer, the weight ratio of polypropylene II to the hydrogenated styrene-butadiene block copolymer can be 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, or 9:1, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0043] Understandably, by defining the weight ratio of polypropylene II to the hydrogenated styrene-butadiene block copolymer in the skin layer, the skin layer can not only meet the spinning requirements and maintain the transparency of co-PP, but also have good heat-melt bonding effect.

[0044] In some embodiments, in the core layer, the melt index of polypropylene I is 3 g / 10 min - 15 g / 10 min. It should be noted that the melt index is a value representing the fluidity of a plastic material during processing. It is formulated by the American Society for Testing and Materials (ASTM) according to the method commonly used by DuPont Company in the United States to identify the properties of plastics. The test method is as follows: First, melt the plastic pellets into a plastic fluid, and then measure the number of grams (g) flowing out through a round tube with a diameter of 2.1 mm within a certain time, at a certain temperature and pressure (the standards for various materials are different). The larger the value, the better the processing fluidity of the plastic material, and vice versa.

[0045] Optionally, in the core layer, the melt index of polypropylene I can be 3 g / 10 min, 4 g / 10 min, 5 g / 10 min, 6 g / 10 min, 7 g / 10 min, 8 g / 10 min, 9 g / 10 min, 10 g / 10 min, 11 g / 10 min, 12 g / 10 min, 13 g / 10 min, 14 g / 10 min, or 15 g / 10 min, etc. Of course, it can also be other values within the above range, which are not limited herein. Preferably, in the core layer, the melt index of polypropylene I is 3 g / 10 min - 8 g / 10 min.

[0046] Understandably, by specifically defining the melt index of polypropylene I, the core layer can have appropriate processing fluidity, which is more conducive to the processing and forming of the heat-fusible composite fiber.

[0047] In some embodiments, the melting point of polypropylene I is 160°C - 170°C.

[0048] Optionally, the melting point of polypropylene I can be 160°C, 161°C, 162°C, 163°C, 164°C, 165°C, 166°C, 167°C, 168°C, 169°C or 170°C, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0049] Understandably, by specifically defining the melting point of polypropylene I, the core layer is not easily melted, so as to ensure the morphology of the heat-fusible composite fiber.

[0050] In some embodiments, polypropylene I is homopolypropylene. Polypropylene II is copolymerized polypropylene.

[0051] Understandably, homopolypropylene is polymerized from a single polypropylene monomer, and the molecular chain does not contain ethylene monomers. The molecular chain has a high degree of regularity and good high-temperature resistance. As the material component of the core layer, it can endow the core layer with high-temperature resistance. The blend melt made of SEBS-modified low-melting copolymerized polypropylene has a lower melting temperature, better fluidity and can maintain good transparency than the melt of single-component low-melting copolymerized polypropylene. At the same time, the blend also has good toughness, impact elasticity and tensile properties. The good toughness and impact elasticity make the skin layer of the heat-fusible composite fiber not easily break when subjected to external force, better protecting the core layer. The good fluidity and stretchability can also ensure the spinnability of the heat-fusible composite fiber.

[0052] In some embodiments, in the skin layer, the melt index of polypropylene II is 3 g / 10 min - 5 g / 10 min, and the melt index of the hydrogenated styrene-butadiene block copolymer is 10 g / 10 min - 30 g / 10 min.

[0053] Optionally, in the skin layer, the melt index of polypropylene II can be 3 g / 10 min, 3.5 g / 10 min, 4 g / 10 min, 4.5 g / 10 min, 5 g / 10 min, etc. Of course, it can also be other values within the above range, which are not limited herein. The melt index of the hydrogenated styrene-butadiene block copolymer can be 10 g / 10 min, 12 g / 10 min, 15 g / 10 min, 18 g / 10 min, 20 g / 10 min, 23 g / 10 min, 25 g / 10 min, 28 g / 10 min or 30 g / 10 min, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0054] Understandably, by specifically defining the melt indices of polypropylene II and the hydrogenated styrene-butadiene block copolymer, the skin layer can have appropriate processing fluidity, which is more conducive to the processing and forming of the heat-fusible composite fiber.

[0055] In some embodiments, the diameter of the heat-fusible composite fiber is 0.05 mm - 0.06 mm.

[0056] Optionally, the diameter of the heat-fusible composite fiber can be 0.05 mm, 0.051 mm, 0.052 mm, 0.053 mm, 0.054 mm, 0.055 mm, 0.056 mm, 0.057 mm, 0.058 mm, 0.059 mm or 0.06 mm, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0057] In some embodiments, the material components of the skin layer and the core layer each independently further include a lubricant, and the lubricant is selected from one or more of fatty acid amide compounds, fatty acid compounds, paraffin waxes and hydrocarbon resins, siloxane compounds, polysiloxane polymers, fluorine compounds, copolymers of tetrafluoroethylene and propylene, and copolymers of vinylidene fluoride and hexafluoropropylene.

[0058] In some embodiments, the lubricant is selected from fatty acid amide compounds; in the core layer, the content of the fatty acid amide compound is 0.05% - 1% by weight of polypropylene I; in the skin layer, the content of the fatty acid amide compound is 0.05% - 1% by weight of polypropylene II.

[0059] Preferably, in the core layer, the content of the fatty acid amide compound is 0.1% - 0.5% by weight of polypropylene I; in the skin layer, the content of the fatty acid amide compound is 0.1% - 0.5% by weight of polypropylene II.

[0060] Understandably, adding a lubricant to the skin layer and the core layer can increase the fluidity of the skin layer and the core layer in the molten state, which is beneficial to the processing and forming of the heat-fusible composite fiber and the processing and forming of the fiber web prepared from the heat-fusible composite fiber.

[0061] In some embodiments, the material components of the skin layer and the core layer each independently further include a color paste, and the color paste can be prepared from pigments of different colors, so that the skin layer and the core layer present different colors to achieve different aesthetic effects.

[0062] In a second aspect, the present application further provides a method for preparing the above-mentioned heat-fusible composite fiber, including the following steps:

[0063] After the skin material composition containing polypropylene II and hydrogenated styrene-butadiene block copolymer is melt-extruded by the first screw, it enters the first metering pump for accurate metering, and then enters the skin channel of the skin-core spinning double-channel composite die head;

[0064] After the core material composition containing polypropylene I is melt-extruded by the second screw, it enters the second metering pump for accurate metering, and then enters the core channel of the skin-core spinning double-channel composite die head;

[0065] After passing through their respective channels, the skin material composition and the core material composition are compounded into fibers with a skin-core structure on a spinneret plate with multiple spinneret holes; the fibers with a skin-core structure are then extruded through the spinneret plate to obtain multiple nascent spun fibers with a skin-core structure;

[0066] The nascent spun fibers enter a cooling water tank for cooling, and each fiber is separated after entering its respective silk channel in the cooling water tank; the separated spun fibers are stretched by a primary water bath of a drafting roller and hot air stretched in a hot box; after stretching, each spun fiber is wound into a cake separately to obtain heat-meltable composite fibers;

[0067] The stretching multiple of the primary water bath is 4 to 8 times, and the water temperature of the water bath is 80°C to 95°C; the stretching multiple of the hot air stretching is 1.1 to 1.5 times, and the hot air temperature is 85°C to 95°C.

[0068] Optionally, the stretching multiple of the primary water bath can be 4 times, 4.5 times, 5 times, 5.5 times, 6 times, 6.5 times, 7 times, 7.5 times or 8 times, etc. Of course, it can also be other values within the above range, which are not limited here. The water temperature of the water bath can be 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C or 95°C, etc. Of course, it can also be other values within the above range, which are not limited here. The stretching multiple of the hot air stretching can be 1.1 times, 1.2 times, 1.3 times, 1.4 times or 1.5 times, etc. Of course, it can also be other values within the above range, which are not limited here. The hot air temperature can be 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, 94°C or 95°C, etc. Of course, it can also be other values within the above range, which are not limited here.

[0069] In the above solution, the preparation method of the present application uses a two-component composite spinning production line equipped with a skin-core type component to produce composite fibers with a skin-core structure, and through improving and controlling conditions such as the cooling air speed, cooling temperature, cooling humidity, spinning temperature and spinning speed in the preparation process, the heat-meltable composite fibers prepared have good spinnability.

[0070] In the third aspect, the present application also provides a fiber web, which is prepared from the above heat-meltable composite fibers.

[0071] The embodiments of the present application will be further described below with multiple examples. Among them, the embodiments of the present application are not limited to the following specific examples. Within the scope of protection, appropriate changes can be made for implementation.

[0072] Example 1

[0073] This example provides a heat-meltable composite fiber with a diameter of 0.05 mm. As Figure 1 shown, the heat-meltable composite fiber is composed of a skin layer 2 and a core layer 1 coated within the skin layer 2, and the weight ratio of the skin layer 2 to the core layer 1 is 1:1. The skin layer 2 is prepared from a mixed raw material of co-PP and SEBS with a weight ratio of 9:1, and the core layer 1 is prepared from PP raw material. The interface of this heat-meltable composite fiber is circular and it is in a fibrous shape as a whole.

[0074] Among them, the melt index of co-PP is 3 - 5 g / 10 min, the melting point is 135 °C, the melt index of SEBS is 10 - 30 g / 10 min, and the density is 0.91 g / cm 3 ³; the melt index of PP is 3 - 5 g / 10 min, and the melting point is 168 °C. The melting point of co-PP in the skin layer is 33 °C lower than the melting point of PP in the core layer.

[0075] The preparation method of the heat-meltable composite fiber in this example includes the following steps:

[0076] S1. After uniformly mixing the skin layer material components co-PP and SEBS according to a ratio of 9:1, melt-extrude them through a first screw, then enter a first metering pump for precise metering, and then enter the skin layer channel of a skin-core spinning double-channel composite die head in the skin layer channel;

[0077] S2. After melt-extruding the core layer material component PP through a second screw, enter a second metering pump for precise metering, and then enter the core layer channel of the skin-core spinning double-channel composite die head;

[0078] S3. After the skin layer material components and the core layer material components pass through their respective channels, enter a composite spinning assembly for spinning, and are compounded into fibers with a skin-core structure on a spinneret plate with multiple spinneret holes; the fibers with a skin-core structure are then extruded through the spinneret plate to obtain multiple primary spun fibers with a skin-core structure;

[0079] The primary spun fibers enter a cooling water tank for cooling, and in the cooling water tank, each fiber enters its respective silk channel and then gets separated; the separated spun fibers are subjected to primary water bath stretching by a drafting roller and hot air stretching in a hot box; after stretching, each spun fiber is wound into a cake separately to obtain the heat-meltable composite fiber.

[0080] During the spinning process, the spinning temperature of the skin layer is 245 °C, and the spinning temperature of the core layer is 245 °C; during the cooling process, the temperature of the cold water tank is 30 °C; during the first-stage water bath drawing process, the water bath drawing temperature is 95 °C, and the drawing ratio is 6 times; during the hot box drawing process, the oven temperature is 90 °C, and the oven drawing ratio is 0.95 times.

[0081] The fineness of the heat-meltable composite fiber prepared in this example is 120 dtex, its breaking strength is ≥ 3.9 CN / dtex, and its elongation at break is between 30% and 45%.

[0082] Example 2

[0083] The diameter of the heat-meltable composite fiber described in this example is 0.05 mm. Among them, the mass ratio of the skin layer to the core layer is 1:2, and the skin layer is prepared from a mixed raw material of co-PP and SEBS with a weight ratio of 9:1.

[0084] The preparation method of the heat-meltable composite fiber in this example is the same as that in Example 1.

[0085] The fineness of the heat-meltable composite fiber prepared in this example is 125 dtex, its breaking strength is ≥ 4.9 CN / dtex, and its elongation at break is between 20% and 35%.

[0086] Example 3

[0087] The diameter of the heat-meltable composite fiber described in this example is 0.05 mm. Among them, the mass ratio of the skin layer to the core layer is 2:3, and the skin layer is prepared from a mixed raw material of co-PP and SEBS with a weight ratio of 4:1.

[0088] The preparation method of the heat-meltable composite fiber in this example is the same as that in Example 1.

[0089] The fineness of the heat-meltable composite fiber prepared in this example is 113 dtex, its breaking strength is ≥ 4.3 CN / dtex, and its elongation at break is between 30% and 40%.

[0090] Example 4

[0091] The diameter of the heat-meltable composite fiber described in this example is 0.05 mm. Among them, the mass ratio of the skin layer to the core layer is 1:2, and the skin layer is prepared from a mixed raw material of co-PP and SEBS with a weight ratio of 4:1.

[0092] The fineness of the heat-meltable composite fiber prepared in this example is 115 dtex, its breaking strength is ≥ 5.0 CN / dtex, and its elongation at break is between 25% and 35%.

[0093] Example 5

[0094] Compared with Example 1, the difference is that the melting point of co-PP is 130°C, the melting point of PP is 160°C, and the melting point of co-PP in the skin layer is 30°C lower than that of PP in the core layer.

[0095] The diameter of the heat-meltable composite fiber described in this example is 0.05 mm. Among them, the mass ratio of the skin layer to the core layer is 1:1, and the skin layer is prepared from a mixed raw material of co-PP and SEBS with a weight ratio of 4:1.

[0096] The fineness of the heat-meltable composite fiber prepared in this example is 115 dtex, its breaking strength ≥ 5.0 CN / dtex, and the elongation at break is between 25% and 35%.

[0097] Example 6

[0098] Compared with Example 1, the difference is that the melting point of co-PP is 128°C, the melting point of PP is 168°C, and the melting point of co-PP in the skin layer is 40°C lower than that of PP in the core layer.

[0099] The diameter of the heat-meltable composite fiber described in this example is 0.05 mm. Among them, the mass ratio of the skin layer to the core layer is 1:1, and the skin layer is prepared from a mixed raw material of co-PP and SEBS with a weight ratio of 4:1.

[0100] The fineness of the heat-meltable composite fiber prepared in this example is 115 dtex, its breaking strength ≥ 5.0 CN / dtex, and the elongation at break is between 25% and 35%.

[0101] To further illustrate the excellent properties of the heat-meltable composite fiber of the present invention, the inventor also conducted a large number of comparative experiments. Due to space limitations, only some targeted comparative experimental examples are listed below.

[0102] Comparative Example 1

[0103] Compared with Example 1, the difference is that the skin layer in the heat-meltable composite fiber is only made of co-PP.

[0104] Comparative Example 2

[0105] Compared with Example 1, the difference is that the weight ratio of the skin layer to the core layer is 3:2.

[0106] Comparative Example 3

[0107] Compared with Example 3, the difference is that the weight ratio of the skin layer to the core layer in the heat-meltable composite fiber is 1:3.

[0108] Comparative Example 4

[0109] Compared with Example 3, the difference lies in that the cortex is prepared from a mixed raw material of co-PP and SEBS with a weight ratio of 7:3.

[0110] Comparative Example 5

[0111] Compared with Example 1, the difference lies in that the melting point of co-PP is 140, the melting point of PP is 165, and the melting point of co-PP in the cortex is 25 °C lower than the melting point of PP in the core layer.

[0112] Take 10 samples from Examples 1 to 6 and Comparative Examples 1 to 5 respectively, conduct mechanical property tests with reference to GBT_9997-1988, and take the average value. The results are shown in Table 1:

[0113] Weave the obtained heat-meltable composite fibers into a filter screen, and the obtained filter screen is subjected to hot air bonding for 25 s in a hot air oven at 95 °C. Apply an external force to the bonded wire mesh manually to stretch the filter screen, and observe the bonded part of the wire mesh to evaluate the bonding strength and bonding effect. If there is no displacement of the wire mesh during external stretching, it is judged that the bonding property is good. If there is displacement, it means that this part is not bonded. If there is a small amount of displacement, it means that the bonding effect is poor. The obtained evaluation results are shown in Table 1:

[0114] Table 1 Comparison table of the properties of the heat-meltable composite fibers of Examples 1 to 6 and Comparative Examples 1 to 5

[0115]

[0116] It can be seen from the data in Table 1 that the heat-meltable composite fibers of the present application are significantly superior to co-PP core-shell composite fibers (Comparative Examples 1 to 5) in terms of dimensional stability and strength.

[0117] The blend melt made of SEBS-modified low-melting co-PP has better fluidity, better adhesiveness, and can maintain good transparency than single-component co-PP.

[0118] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A fibrous web, characterized in that, Comprising heat-meltable composite fibers, the heat-meltable composite fibers comprising: A core layer; the material composition of the core layer includes polypropylene I; A skin layer, wrapped around the outer surface of the core layer; the material composition of the skin layer includes polypropylene II and a hydrogenated styrene-butadiene block copolymer; The melting point of the polypropylene II in the skin layer is 30°C - 40°C lower than the melting point of the polypropylene I in the core layer, and the melting point of the polypropylene I is 160°C - 170°C; In the skin layer, the weight ratio of the polypropylene II to the hydrogenated styrene-butadiene block copolymer is 4:1 - 9:1; The mass ratio of the skin layer to the core layer is 1:2 - 1:

1.

2. The fibrous web according to claim 1, characterized in that, The melt index of the polypropylene I is 3 g / 10 min - 15 g / 10 min.

3. The fibrous web according to claim 2, characterized in that, The polypropylene I is a homopolypropylene.

4. The fibrous web according to claim 1, characterized in that, In the skin layer, the melt index of the polypropylene II is 3 g / 10 min - 5 g / 10 min, and the melt index of the hydrogenated styrene-butadiene block copolymer is 10 g / 10 min - 30 g / 10 min.

5. The fibrous web according to claim 1, characterized in that, The diameter of the heat-meltable composite fiber is 0.05 mm - 0.06 mm.

6. The fibrous web according to claim 1, characterized in that, The material composition of the skin layer and the material composition of the core layer each independently further include a lubricant, and the lubricant is selected from one or more of fatty acid amide compounds, fatty acid compounds, paraffin and hydrocarbon resins, siloxane compounds, polysiloxane polymers, fluorine compounds, copolymers of tetrafluoroethylene and propylene, and copolymers of vinylidene fluoride and hexafluoropropylene.

7. A method for preparing the fibrous web according to any one of claims 1-6, characterized in that, Including the preparation of heat-meltable composite fibers, the preparation method of the heat-meltable composite fibers includes the following steps: After the skin layer material composition containing polypropylene II and a hydrogenated styrene-butadiene block copolymer is melt-extruded through a first screw, it enters a first metering pump for precise metering, and then enters the skin layer channel of a skin-core spinning double-channel composite die head; After the core layer material composition containing polypropylene I is melt-extruded through a second screw, it enters a second metering pump for precise metering, and then enters the core layer channel of the skin-core spinning double-channel composite die head; After passing through their respective channels, the skin layer material composition and the core layer material composition are compounded on a spinneret plate with multiple spinneret holes into fibers with a skin-core structure; The fibers with a skin-core structure are then extruded through the spinneret plate to obtain multiple primary spun fibers with a skin-core structure; The primary spun fibers enter a cooling water tank for cooling, and each fiber is separated after entering its respective filament channel in the cooling water tank; The separated spun fibers are subjected to first-stage water bath stretching by a draw roll and hot air stretching in a hot box; After stretching, each spun fiber is wound into a cake separately to obtain the heat-meltable composite fiber; The magnification of the first-stage water bath stretching is 4 to 8 times, and the water bath water temperature is 80°C to 95°C; the magnification of the hot air stretching is 1.1 to 1.5 times, and the hot air temperature is 85°C to 95°C.

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