JPH0160577B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a bulky nonwoven fabric with excellent flexibility and a method for producing the same. [Prior Art] Parallel type or sheath-core type polypropylene thermoadhesive conjugate fiber consisting of two components with different melting points, in which the component with the lower melting point occupies a considerable portion of the fiber surface, for example, more than half, and the same. It has been many years since non-woven fabrics using these materials were known, and various improvements have been made during that time. The main improvements in these improvements are as disclosed in, for example, Japanese Patent Publication No. 52-12830, Japanese Patent Application Publication No. 58-136867, and Japanese Patent Application Publication No. 180614/1980, etc., in heat treatment when processing into nonwoven fabrics. The aim was to improve the shrinkage properties, the strength and bulkiness of the obtained nonwoven fabric, and although some results were obtained, the bulkiness was not sufficient. [Problems to be Solved by the Invention] As described above, sufficient results have not been obtained in improving the bulkiness of nonwoven fabrics obtained by heat treating polypropylene thermoadhesive conjugate fibers. Under these circumstances, there is a problem that for some uses, such as paper diapers and sanitary materials, it is not possible to meet the demands of further improving the bulkiness and therefore the softness of nonwoven fabrics when processed. Improvement was strongly desired. [Means for Solving the Problems] As a result of intensive research aimed at solving the above-mentioned problems and providing a bulky nonwoven fabric with excellent flexibility, the present invention has been made to solve the above problems. By configuring and using heat-adhesive composite fibers to impart properties and heat-adhesive properties through the sheath, the resulting nonwoven fabric has sufficient bulk and a soft texture. The present invention was completed by determining that the present invention also has the following properties. That is, one of the present inventions has a parallel composite structure consisting of core components of two types of polypropylene polymers, the composite ratio of which is 1:2 to 2:1, and the Q value of one of the core components (here Q=weight average molecular weight/
The core component has a number average molecular weight (number average molecular weight) of 6 or more and the Q value of the other core component is 5 or less, and a polyethylene polymer sheath component whose melting point is 20°C or more lower than the lower melting point of the above two core components. The heat-adhesive composite fiber contains at least 30% by weight of heat-adhesive composite fibers consisting of a sheath covering the core in a proportion of 25 to 55% by weight based on the total amount of the core. A nonwoven fabric characterized in that it is stabilized by adhesion between fibers without the formation of nodal aggregates made of sheath components in the sheath portion of the fibers (hereinafter referred to as the first invention). ). Another aspect of the present invention is to use two types of polypropylene polymers separately for two types of core components, and a polyethylene type polymer whose melting point is 20°C or more lower than the lower melting point of the above two types of polypropylene polymers. are used for each of the sheath components, composite spinning is carried out, and 2
It has a parallel composite structure consisting of seed core components, the composite ratio is 1:2 to 2:1, and the Q value of one core component (here, Q = weight average molecular weight / number average molecular weight) is 6. A composite structure in which the other core component has a Q value of 5 or less, and the core component is covered with a sheath component at a ratio of 25 to 55% by weight based on the total amount of the core component. An undrawn yarn is obtained, and the composite undrawn yarn is stretched at a stretching temperature from room temperature to 130° C. without heat treatment or cooling treatment under no tension prior to stretching, and the total stretching ratio is increased by one step or more from 1.3 to 9 times. A web containing at least 30% by weight of the heat-adhesive conjugate fiber is prepared by stretching in the drawing step of 30% by weight, and the melting point of the sheath component is higher than that of the lower of the two core components. This invention relates to a method for producing a nonwoven fabric characterized by heat treatment at a temperature lower than its melting point (hereinafter sometimes referred to as the second invention). [Specific explanation of the structure of the first invention] The structure of the first invention will be specifically explained below. First, the heat-adhesive conjugate fiber used in the nonwoven fabric according to the present invention will be explained with reference to the drawings. FIG. 1, FIG. 2, and FIG. 3 are sectional views each schematically showing the cross-sectional configuration of the heat-adhesive conjugate fiber used in the present invention. In the drawings, reference numeral 1 denotes a core, which has a parallel composite structure composed of core segments 1a and 1b each made of core components of two types of polypropylene polymers. The parallel composite structure of the core 1 has various aspects. For example, a cross-sectional structure in which a circle is divided into two semicircles by the diameter as shown in Fig. 1, or a cross-sectional structure in which one core segment band 1a is divided into two semicircles by its diameter, or most of the circumference of one core segment band 1a is left aside and most of it is divided into two half circles as shown in Fig. 2. There is a cross-sectional structure surrounded by the band 1b, and in reality, in many cases, the cross-sectional structure is intermediate between the above two extremes. Further, the structure may be such that the core portion 1 is eccentric in the fiber cross section as shown in FIG. A typical polypropylene polymer is crystalline polypropylene, but propylene and a small amount of ethylene, butene-1, pentene-1
It may also be a copolymer with an α-olefin other than propylene such as, for example, propylene, and in that case, the comonomer component is preferably 40% by weight or less. Two types of such polypropylene polymers are used as the core components of the core segments 1a and 1b, respectively, but they differ in Q value, and the core component of one of the core segments 1a (hereinafter referred to as 1a
The Q value of the core component (hereinafter sometimes abbreviated as component 1b) of the other core segment band 1b is 6 or more and general-purpose polypropylene is 5. Below, preferably 3 to 5. Here, the Q value is a numerical value representing the molecular weight distribution of the polymer, and is expressed by the following formula: Q=w/n (where w is the weight average molecular weight and is the number average molecular weight). Further, the composite ratio of core components 1a and 1b constituting the core portion 1 is 1:2 to 2:1. In this way, core 1 has a different Q value from the 1a component.
By forming a parallel composite structure with the 1b component,
In addition to imparting actual crimp to the composite fiber, the latent crimp is brought to the surface through heat treatment, thereby making it bulky. 2 is a sheath part made of a polyethylene polymer whose melting point is 20°C or more lower than the lower melting point of the two core components of core part 1, that is, component 1a and component 1b (if there is no difference in melting point, the melting point is the same). It consists of a sheath component. Examples of such polyethylene polymers include polyethylene and ethylene-vinyl acetate copolymers (ethylene content: 98 to 60% by weight). Further examples of polyethylene include low density polyethylene, medium density polyethylene and high density polyethylene. A sheath-core type composite structure is constructed by covering the core 1 with the sheath 2, and the proportion of the sheath 2 is larger than that of the core 1.
and 25 to 55% by weight based on the total amount. If the proportion of this sheath part 2 is less than 25% by weight, the strength of the resulting nonwoven fabric will be too low, causing a practical problem, and if it exceeds 55% by weight, it will interfere with the crimp development of the core part 1, resulting in composite fibers. This results in insufficient crimp and poor bulkiness. The sheath portion 2 is made of a polyethylene polymer with a low melting point as described above, and forms a portion where fibers are bonded, that is, an interfiber bonding portion, similar to conventional heat-adhesive sheath-core composite fibers. . Even if the heat-adhesive composite fiber is composed of the same components as the core part 1 and the sheath part 2, the manufacturing process is different from the manufacturing process according to the present invention described below. As disclosed in JP-A No. 63-105161, there are cases in which knot-shaped aggregates of sheath components are formed at many locations in the sheath, but the composite constituting the nonwoven fabric according to the present invention Such knot-like aggregates are not formed in the fibers. The fineness of the heat-adhesive conjugate fiber is not particularly limited, but in the case of a nonwoven fabric used for applications in which texture is important, a denier of 0.7 to 7 is appropriate. The nonwoven fabric according to the present invention may contain the above heat-adhesive conjugate fibers alone or contain at least 30% by weight of other fibers such as rayon, cotton, hemp, polyamide fibers, etc.
It is mixed with polyester fibers, acrylic fibers, etc., and forms a nonwoven fabric structure by the interfiber bonding parts of the sheath part 2 of the heat-adhesive conjugate fibers. [Specific explanation of the structure of the second invention] In manufacturing the nonwoven fabric according to the invention, first, heat-adhesive composite fibers are manufactured as follows. That is, three types of polymers are prepared: two types of polypropylene polymers for the core component and a polyethylene polymer for the sheath component as explained in the configuration of the first invention. Regarding the polypropylene polymer for the core component, melt fluorate (MFR) is used as a polypropylene polymer for the 1a component with a Q value of 6 or more.
It may be indicated by According to condition 14 of Table 1 of JIS K7210. The same applies hereinafter) is preferably 4 to 40, and as a polypropylene polymer for component 1b having a Q value of 5 or less, a melt fluorate is preferably 4 to 60. A polypropylene polymer having a Q value of 5 or less can also be produced by the following method using a polypropylene polymer having a Q value greater than 5 as a raw material polymer. That is, one method is
Organic peroxide compounds that generate peroxide when heated to a temperature higher than the melting point of the raw material polymer, such as t-butyl hydroperoxide, cumain hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, etc. This is a method of adding and mixing 0.01 to 1.0% by weight of 0.01 to 1.0% by weight to a raw material polymer, followed by melt extrusion using an extruder and granulation. Alternatively, a method may be used in which melt extrusion and granulation are repeated several times at high temperature without adding the organic peroxide compound. In this way, the Q value becomes a little smaller due to melt extrusion, so as a polymer before composite spinning, the Q value of the polymer for component 1a should be slightly larger than 6, and the Q value of the polymer for component 1b should be slightly larger than 6. may be slightly larger than 5. Polyethylene polymers are also referred to as meltoids (MI).JIS K7210
According to condition 4 in Table 1. ) is preferably 2 to 50. Once the three types of polymers are prepared, they are individually fed to three extruders and melt extruded.
Each is led via a separate gear pump to a known suitable composite spinning die. As a known composite spinning die that can spin three polymer components into a cross-sectional structure similar to that of the heat-adhesive composite fiber according to the present invention, for example, the composite spinneret described in Japanese Patent Publication No. 44-29522 A spinning nozzle can be used. When introducing the above three types of polymers into such a composite spinning nozzle, the amount of each polymer for core component 1a and core component 1b is set at a predetermined composite ratio in the range of 2:1 to 1:2. In addition, the pumping amount of each gear pump is adjusted so that the amount of polymer for the sheath component becomes a predetermined ratio in the range of 25 to 55% by weight based on the total amount of the polymer in the core 1. The thus obtained composite undrawn yarn having a predetermined cross-sectional structure is drawn in one step or in multiple steps. The stretching temperature is from room temperature (15 to 40°C) to 130°C. In multi-stage drawing, it is usually better to set the first-stage drawing temperature lower than the second-stage drawing temperature, and in the case of single-stage drawing, it is better to use a relatively low drawing temperature at or near room temperature to improve the latent winding of the resulting composite fiber. This is preferred because it increases shrinkage. Generally, heat is generated during stretching, so the first stage of stretching is preferably performed at a low temperature within a specified range, for example, while passing through water maintained at room temperature, or in a room maintained at room temperature with cooling water, etc. It is preferable to do so. In addition, the stretching ratio is 1.3 to 9 times, especially 1.5 to 9 times, expressed as a total stretching ratio, including the case of multi-stage stretching.
Six times is preferred. In the above-mentioned drawing step, the composite undrawn yarn is not subjected to heat treatment under no tension prior to drawing and then cooled to room temperature, as disclosed in JP-A-63-105161. By not performing at least the heat treatment and cooling treatment under non-tension conditions as described above prior to stretching, the maximum stretching ratio (when the yarn begins to break) is When the drawing is carried out at less than 90% of the drawing ratio (drawing ratio), the sheath portion of the drawn composite fiber is more completely formed into knot-like agglomerations of sheath components by heat treatment as disclosed in JP-A-63-105161. No agglomerate-forming parts are formed. By carrying out the process at the temperature and stretching ratio as described above, it is possible to obtain three-dimensional crimp that increases the fiber strength and lowers the shrinkage rate of the resulting nonwoven fabric to increase its bulk. Once the stretching is completed, it is dried if necessary and, depending on the application, it can be left as is or cut into a predetermined length. From the viewpoint of processing efficiency, it is usually preferable to draw the undrawn yarn by collecting the undrawn yarn into tows of tens of thousands to millions of deniers. A web consisting of the heat-adhesive conjugate fiber obtained in this way alone or mixed with the above-mentioned other fibers so as to contain at least 30% by weight is prepared, and this web is sheathed with the heat-adhesive conjugate fiber. The nonwoven fabric according to the present invention is obtained by heat treatment at a temperature higher than the melting point of the two core components and lower than the lower melting point of the two core components. [Effect] The heat-adhesive composite fiber used in the nonwoven fabric according to the present invention has a parallel composite structure in which the core uses polypropylene polymers with different Q values, and the melting point is higher than that of the core component polymer. It has a composite structure in which the core is covered with a polyethylene polymer sheath that is lower than the core. Therefore, a nonwoven fabric obtained by heat-treating a web containing such heat-adhesive conjugate fibers at a predetermined temperature is a sufficiently bulky and very stable nonwoven fabric. The reason for this is that, although the composite fibers that make up this nonwoven fabric generally have a sheath-core structure that causes little crimp, the core has a parallel composite structure, which causes apparent crimp to occur even before heat treatment. The latent crimp is brought to light by the heat treatment, and the crimp is sufficiently large and has a gentle three-dimensional crimp form, making the nonwoven fabric sufficiently bulky, and the entire cross-sectional structure of the fiber is Because of the sheath-core structure, the thermal adhesion is sufficient, and the nonwoven fabric structure formed by the interfiber thermal bonding portions is extremely stable. Therefore, the nonwoven fabric according to the present invention has sufficiently improved bulk, which has been a problem in the past, and has a soft texture although no knot-like aggregates made of sheath components are formed in the sheath portion. It also has the following. [Examples and Comparative Examples] The present invention will be explained in more detail below using Examples and Comparative Examples. Examples 1 to 12, Comparative Examples 1 to 5 (i) Production of heat-adhesive conjugate fiber Eight types of polypropylene a, b, shown in Table 1
C, d, e, f, g, and h and two types of polyethylene polymers i and j are used in various combinations shown in Table 2 to produce components 1a and 1b, each consisting of two types of polypropylene. A composite fiber having a core having a parallel composite structure covered with a sheath made of one type of polyethylene polymer was manufactured by subjecting it to composite spinning and drawing as follows. A spinneret with a hole diameter of 1.0 mmφ and 120 holes was used, and the composite ratio of component 1a and component 1b constituting the core was 1:1, and the ratio of the sheath to the total amount of the core and sheath was The proportion was varied from 33.3 to 66.7% by weight, and the spinning temperature (polymer temperature just before spinning)
Polypropylene is heated at 260℃ for both 1a and 1b components.
So, the polyethylene polymer is spun at 220℃ and has a density of 11d/f (denier per filament).
An undrawn yarn was obtained. The undrawn yarn was drawn into a tow of about 90,000 denier. Three stages of stretching rolls were used for stretching. One-stage stretching was performed by passing the tow through a first stretching roll and a second-stage stretching roll, and two-stage stretching was performed by passing the tow through a third stretching roll following the first-stage stretching. Regarding the stretching temperature, it is specified that the first-stage stretching temperature (the stretching temperature in the case of one-stage stretching is the same) is the same as the temperature of the first stretching roll, and the second-stage stretching temperature is the same as the temperature of the second stretching roll. . In this manner, the tow is first passed through a 0.2% surface finisher bath at 21°C, then passed through a first draw roll at 26°C, a second draw roll at 80°C, and a third draw roll at 28°C. Two-stage stretching (Example 1~
9. Comparative Examples 1 to 5) or one-stage stretching (Examples 10 to 12) with the temperature of the second stretching roll set at 70°C without using the third stretching roll, and then the temperature was higher than room temperature. , cooled to room temperature. The strength and elongation of each heat-adhesive conjugate fiber thus obtained was measured, and the crimp shape was also examined. (ii) Production of a nonwoven fabric made of each heat-adhesive conjugate fiber alone Each heat-adhesive conjugate fiber obtained in the previous section (i) is passed through a carding machine twice to form a web with a basis weight of 100 g/m ² .
Each web was placed in a hot air circulation dryer at 145° C. for 5 minutes to non-woven, and then cooled to room temperature. The bulk of the obtained nonwoven fabric was tested. The results are shown in Table 2. Examples 13 to 17, Comparative Examples 6 to 7 Manufacture of nonwoven fabrics consisting of mixed fibers with other fibers having different contents of heat-adhesive conjugate fibers The heat-adhesive conjugate fibers obtained in Example 3 (2.9 d /
f) cut into 64 mm and 2d x 51 mm of rayon were mixed in the proportions shown in Table 3, and Example 1 was prepared.
A nonwoven fabric having a basis weight of approximately 100 g/m ² was produced in the same manner as in Example 12, and the bulk and texture of the nonwoven fabric were tested, and the strength and elongation of the nonwoven fabric was also measured. The results are shown in Table 3. In addition, Example 17 is a nonwoven fabric manufactured in the same manner as above except that 100% of the heat-adhesive composite fiber obtained in Example 3 was used and no other fibers were used, and the same test was performed as above. The results are also listed in Table 3. The above test methods are shown below. Fiber strength and elongation: According to JIS L1015 7.7. Crimp shape: After heating to 145°C for 5 minutes, visually determine whether it is two-dimensional crimp or three-dimensional crimp. Bulkyness of non-woven fabric: Cut each non-woven fabric into 20cm x 20cm pieces.
The bulkiness value (mm) is calculated by calculating the thickness of each nonwoven fabric from the thickness of the entire nonwoven fabric, which is measured by stacking the nonwoven fabrics and placing cardboard on top. Strength and elongation of non-woven fabric: Five 20 cm x 5 cm test pieces were cut from the non-woven fabric with the 20 cm sides along the flow direction on the carding machine, and each was tested using an autograph tensile strength tester at a gripping interval of 100 mm and a tensile speed. The breaking strength and elongation are determined under the condition of 100 mm/min, and the average value of 5 sheets is taken.

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[Table] From Table 2, the following various things can be seen regarding the relationship between the structure of the thermoadhesive conjugate fibers constituting the nonwoven fabric and the nonwoven fabric. That is, from Examples 1 to 12 and Comparative Examples 1 to 4, if the Q values of the two types of core components of the heat-adhesive composite fiber are within the range specified in the present invention, other configurations are acceptable according to the present invention. It can be seen that the three-dimensional crimp is sufficiently expressed and the bulk of the nonwoven fabric is excellent, provided that the above conditions are satisfied. Also, Example 6~
12 and Comparative Example 5, the nonwoven fabric produced by obtaining composite fibers by the method of the present invention is superior in both the expression of three-dimensional crimp and the bulk of the nonwoven fabric, whereas the proportion of the sheath portion is superior to that obtained by the method of the present invention. When using composite fibers obtained under conditions other than the above, the raw material polymer may be the same or different from the raw material polymer of the composite fiber used for the nonwoven fabric obtained by the method of the present invention. It can be seen that it is inferior in various characteristics. Furthermore, from a comparison of Comparative Examples 6 to 7 and Examples 13 to 17 in Table 3, it is clear that the thermal adhesive composite fiber used in the present invention is present in an amount of 30% by weight or more in the mixed fiber with other fibers such as rayon. If used, the texture, bulk,
It can be seen that a nonwoven fabric with excellent strength can be obtained. It should be noted that in each of the Examples as well as in each Comparative Example, no knot-shaped agglomerated portions were formed in the sheath portion of the composite fiber.

[Brief explanation of drawings]

FIG. 1, FIG. 2, and FIG. 3 are sectional views each schematically showing the cross-sectional configuration of the heat-adhesive conjugate fiber used in the present invention. 1...Core part, 1a... Core segment band, 1b... Core segment band, 2... Sheath part.

Claims (1)

[Claims] 1. It has a parallel composite structure consisting of core components of two types of polypropylene polymers, and the composite ratio thereof is 1:2.
~2:1, and the core has a melting point above the Q value of one core component (here, Q = weight average molecular weight/number average molecular weight) of 6 or more and the Q value of the other core component of 5 or less. It consists of a polyethylene polymer sheath component whose melting point is 20°C or more lower than the melting point of the lower of the two core components, and covers the core at a ratio of 25 to 55% by weight based on the total amount with the core. It contains at least 30% by weight of heat-adhesive conjugate fibers consisting of a sheath part, and the fibers are bonded together without forming knot-like aggregates made of the sheath component in the sheath part of the heat-adhesive conjugate fibers. A nonwoven fabric characterized by being stabilized by 2. The nonwoven fabric according to claim 1, wherein the polypropylene polymer of at least one of the two types of core components of the heat-adhesive conjugate fiber is polypropylene. 3. The nonwoven fabric according to claim 1, wherein the polypropylene polymer of at least one of the two types of core components of the heat-adhesive conjugate fiber is a copolymer of propylene and a small amount of α-olefin other than propylene. 4. The nonwoven fabric according to any one of claims 1 to 3, wherein the polyethylene polymer of the sheath component of the heat-adhesive conjugate fiber is polyethylene. 5. The nonwoven fabric according to any one of claims 1 to 3, wherein the polyethylene polymer of the sheath component of the heat-adhesive composite fiber is an ethylene-vinyl acetate copolymer with an ethylene content of 98 to 60% by weight. . 6 Separately 2 types of polypropylene polymers
Two types of core components are obtained by composite spinning using a polyethylene polymer whose melting point is at least 20°C lower than the lower melting point of the two types of polypropylene polymers mentioned above for the seed core component and for the sheath component. It has a parallel composite structure consisting of a composite ratio of 1:2 to
2:1 and the Q value of one core component (here Q
= weight average molecular weight / number average molecular weight) is 6 or more and the Q value of the other core component is 5 or less.
A composite undrawn yarn having a structure in which the core is coated at a ratio of 55% by weight is obtained, and the composite undrawn yarn is heated from room temperature to 130°C without heat treatment and cooling treatment under no tension prior to stretching. A thermoadhesive conjugate fiber is produced by stretching it in one or more stretching steps at a total stretching ratio of 1.3 to 9 times at a stretching temperature, and a web containing at least 30% by weight of the thermoadhesive conjugate fiber is prepared, and a sheath component is prepared. A method for producing a nonwoven fabric, the method comprising heating at a temperature higher than the melting point of the lower one of the two core components and lower than the melting point of the lower one of the two core components.