JPH039235B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a wet-laid nonwoven fabric having a mesh-like sparse structure and a spider web structure in the sparse portions, and a method for producing the same. Traditionally, knitted fabrics, orthogonal nonwoven fabrics, and spunbond nonwoven fabrics have been required to have excellent breathability, high strength, and high toughness for use as reinforcing materials for desiccant packaging, disposable pocket warmer packaging, etc., or for agricultural materials. etc. have been used. For each of the above-mentioned uses, it is further required that there is no deformation of the weave or stitch structure (so-called mesh deviation), and that it is morphologically stable, and knitted fabrics, orthogonal nonwoven fabrics, or spunbond nonwoven fabrics have a low basis weight. This tends to make the structure non-uniform and cause uneven density and strength, so methods such as resin processing have been used to make the structure more dense than necessary, or in the case of coarse fabrics such as cheesecloth. However, such methods are not only uneconomical, but also result in the loss of the coarse, porous structure required for these applications. In addition, for applications such as cheesecloth, it is desirable that the stitches or textures be embedded in single fibers like a spider's web. has fulfilled that role. It is more preferable that such fuzz exists in a fixed manner between the spun yarns constituting the knitted fabric, across stitches and weaves, rather than in a free form. Resin processing, such as that applied during the manufacture of cheesecloth, is effective in fixing fuzz, but has the disadvantage that the spaces in the stitches and textures are filled with resin. Paper having a mesh structure similar to cheesecloth is also known, but its paper strength, particularly its wet strength, is weak and it cannot be used for the above-mentioned purposes. The inventors of the present invention have arrived at the present invention as a result of intensive research to eliminate the above-mentioned drawbacks of conventional knitted fabrics and non-woven fabrics having a rough structure with many voids. An object of the present invention is to provide a high-strength wet-laid nonwoven fabric having a dense structure and a method for producing the same. One of the present invention is a wet-laid nonwoven fabric having a mesh-like sparse structure, in which the area of the dense portion is 20% of the area of the nonwoven fabric.
% or more and 80% or less, and consists of a first component consisting of a fiber-forming polymer (hereinafter sometimes referred to as a high melting point component) and one or more components whose melting point is at least 10°C lower than that of the first component. A second component (hereinafter sometimes referred to as a low melting point component) consisting of a polymer of A wet-laid nonwoven fabric containing composite fibers in an amount of 20% or more of the weight of the nonwoven fabric, whose form is stabilized by heat fusion of the heat-adhesive composite fibers, and which has a spider web structure in its coarse portions. . Another aspect of the present invention is to make paper using a wet method from heat-adhesive fibers made of composite components with a melting point difference of 10°C or more,
Subsequently, the temperature is higher than the melting point of the low melting point component of the heat-adhesive fiber,
In a wet nonwoven fabric manufacturing method in which heat treatment is performed at a temperature below the melting point of a high melting point component, occlusions are distributed in a mesh pattern with a constant density so that the area of the area where the occlusions are present is 20% or more and 80% or less of the total area. A fiber mixture containing a paper wire mesh having openings and heat-adhesive conjugate fibers having a fiber length of at least one-half of the mesh spacing formed in the portions where the closing openings are present in an amount of at least 20% by weight of the entire nonwoven fabric. This is a method for producing a wet-laid nonwoven fabric having a sparse and dense structure and a spider web structure in the coarse portions. In the present invention, any of the paper-making methods commonly used in the production of wet-laid nonwoven fabrics, such as round screen, short screen, inclined fourdrinier, and funnel homer, can be used; In order to achieve this, a wire mesh having closed meshes distributed at a constant density is used as the paper-making wire mesh. As this kind of wire mesh,
For example, one or a certain number of adjacent meshes of an ordinary paper-making wire mesh may be blinded with resin or the like and the closed meshes arranged in a mesh pattern at appropriate intervals can be effectively used. The nonwoven fabric obtained using such a wire mesh is
Fibers concentrate in the openings of the wire mesh as the water flows, so the openings of the wire mesh have a high fiber density and form the skeleton of the thread pattern of the nonwoven fabric mesh, contributing to the strength and preventing blockage of the wire mesh. The fiber density in the mesh area is coarse, creating a mesh pattern that contributes to the breathability of the nonwoven fabric. In the present invention, the area of the high-density portion of the nonwoven fabric (hereinafter sometimes referred to as a dense portion) is limited to 20% or more and 80% or less of the entire area of the nonwoven fabric, and therefore,
The reason why the area of the closed part of the wire mesh used in the paper machine is limited to less than 80% and more than 20% of the area of the wire mesh is as follows.
If the area ratio of dense areas is less than 20%, the strength of the nonwoven fabric will be less than that of a uniform nonwoven fabric with the same basis weight and no coarse structure, and the area ratio of dense areas will be less than 80%.
This is because if it exceeds %, it will only be as strong as a uniform nonwoven fabric with the same basis weight. The heat-adhesive conjugate fibers composed of components with different melting points used in the present invention are used to stabilize the form of the nonwoven fabric by thermally adhering the low-melting-point components of the conjugate fibers through heat treatment after papermaking. The fiber shape of the high melting point component is maintained during the heat treatment, and the resulting nonwoven fabric has higher strength and a better feel than a nonwoven fabric made of monocomponent fibers such as polypropylene or polyethylene. The combination of composite components for such thermally adhesive composite fibers is such that the difference in melting point between the two components is at least 10
℃, preferably 20℃ or higher, and a combination of thermoplastic resins in which at least the high melting point component has fiber-forming properties can be used, but as a preferred example, a combination of a low melting point component of polyethylene and a high melting point component of polypropylene can be used. As other examples, ethylene-vinyl acetate copolymer as a low melting point component, a saponified product of the copolymer with any degree of saponification, or a mixture of these and polyethylene, etc., and polypropylene, polystyrene, etc. as a high melting point component. combinations are shown. The composite structure is a parallel type or sheath-core type structure such that the low melting point component occupies at least a part, preferably one-half or more, of the fiber surface. In the present invention, the fiber length of the thermoadhesive fiber is 2 of the shortest opposite side of the coarse structure (between the dense structures) of the nonwoven fabric.
That's more than 1/2. If the fiber length is one-half or more of the shortest opposite side of the coarse tissue, the fibers present as fuzz in the coarse tissue will be bonded to the fibers in the dense region at the root portion, and to other fluff fibers at the tip, Since the overall morphology is stabilized across the coarse structure, the fibers present as fluff make a greater contribution to the strength of the nonwoven fabric, resulting in a high strength nonwoven fabric while maintaining good air permeability. . The upper limit of the fiber length is limited by the dispersibility of the fibers during paper making, and is generally about 20 to 25 mm. If the fiber length is less than 1/2 of the shortest opposite side of the coarse structure, the amount of fuzz that is fixed across the coarse structure will decrease, resulting in a decrease in the strength of the nonwoven fabric, which is not preferable. The thermoadhesive conjugate fiber can be used alone, but it can also be mixed with other fibers, and in this case, the mixing ratio (weight % of the thermoadhesive conjugate fiber in the mixed fiber) is Must be 20% or more. Other fibers to be mixed with the heat-adhesive composite fibers can be any short fibers that do not lose their fiber shape during heat treatment for heat-adhesion and can be used in wet papermaking, such as pulp. , papermaking rayon, etc. are preferably used. Furthermore, in order to facilitate paper making, fibrous polyvinyl alcohol for paper making, synthetic fiber pulp, etc. may be added.
The reason why the mixing ratio of heat-adhesive composite fibers is set to 20% by weight or more is that non-fibrillar fibers such as heat-adhesive composite fibers do not have entanglement between fibers due to fibrils during paper making, so the mixing ratio of thermoadhesive composite fibers is set to 20% by weight or more. This is because if it is less than that, the nonwoven fabric will not have enough strength due to thermal adhesion, and may be weaker than paper made only of pulp, which is not preferable. The thus obtained wet-laid nonwoven sheet is dried and heat-treated in the next drying step, and becomes the nonwoven fabric of the present invention in which the fibers are fixed by thermal bonding of the heat-adhesive conjugate fibers. The drying and heat treatment are easily carried out by, for example, operating a dryer such as a well-known Yankee dryer at a temperature higher than the melting point of the low melting point component and lower than the melting point of the high melting point component of the heat-adhesive conjugate fiber. The nonwoven fabric of the present invention has a mesh-like dense structure,
It has a spider web structure in its rough parts and has excellent breathability, as well as high strength and toughness. It is also possible to subject the nonwoven fabric of the present invention to secondary processing using a thermal calendar roll or the like for the purpose of further strengthening the thermal adhesion of the thermally adhesive conjugate fibers. The present invention will be explained below with reference to Examples. The evaluation method for nonwoven fabrics is based on JIS L1096 (general textile testing method), and the strength, elongation, and toughness (strength, × elongation)
was measured for two types of samples: one in the running direction (MD) of the paper wire mesh and the other in the direction perpendicular to it (CD). Examples 1 and 2, Comparative Examples 1 to 3 The high melting point component is polypropylene (melting point 165°C),
A mixed fiber of 60% by weight of sheath-core type heat-adhesive composite fiber with a low melting point component of polyethylene (melting point 130℃) and a fineness of 3 denier cut into the specified length shown in the table and 40% by weight of pulp. Uniform network structure shown in Figure 1 (coarse part l ¹ = 9 mm, l ₂ = 12 mm, dense part t ₁ = t ₂ =
The paper is made using a circular mesh paper machine using a wire mesh that has been closed to a density of 3 mm (3 mm, dense area area: 40%), then dried and heat treated in a Yankee dryer at 135°C to a paper weight of 20 g/
Wet-laid nonwoven fabrics having a dense structure of around m ² were obtained (Examples 1 and 2, Comparative Example 1). Furthermore, for comparison, a wet nonwoven fabric with a more uniform texture than similar mixed fibers was obtained using an ordinary wire mesh without closed mesh (Comparative Example 2,
3). The strength and elongation characteristics of these nonwoven fabrics are also shown in the table. From the data of each example above, the fiber length of the thermoadhesive composite fiber is 2 of the shortest distance between opposite sides of the coarse structure (l ₁ = 9 mm).
When the fiber length of the composite fiber is 4.5 mm or less (Comparative Example 1), the strength is lower than that of a nonwoven fabric with a similar fiber composition and a uniform structure (Comparative Example 2), whereas the fiber length of the composite fiber is 4.5 mm.
Example 1, which has a thickness exceeding mm, is superior to Comparative Example 3, which has a uniform structure, in terms of strength, elongation, and toughness. The nonwoven fabric obtained in Example 1 was suitable as a packaging material for disposable hand warmers. The nonwoven fabric of Example 2, which uses composite fibers with a longer fiber length than those of Example 1, has further improved strength, elongation, and toughness, and when this nonwoven fabric is used as cheesecloth, condensed water droplets form spiders in the rough tissue. It showed an excellent effect in that it was caught in the nest-like fuzz and did not fall. Examples 3 to 5, Comparative Examples 4 to 6 The high melting point component is polypropylene (melting point 165°C),
Low melting point component is low density polyethylene (melting point 115℃)
75% by weight and ethylene-vinyl acetate copolymer (melting point
96℃, vinyl acetate content 7.53 mol%) 50% by weight of sheath-core type thermoadhesive composite fiber with a fineness of 3 denier fiber length 10 mm, which is a mixture of 25% by weight of vinyl acetate (vinyl acetate content 7.53 mol%), and 4 denier 7 mm
Mixed fibers consisting of 45% by weight of rayon for papermaking and 5% by weight of vinylon binder for papermaking were mixed to the predetermined coarse part size (l ₁ , l ₂ ) and the width of the dense part (t ₁ ,
Paper is made using circular mesh paper making using a wire mesh that has been crushed in t ₂ ),
Subsequently, it was dried and heat-treated in a Yankee dryer at 115°C to obtain a wet-laid nonwoven fabric having a dense structure with a basis weight of around 18 g/m ² (Examples 3 to 5, Comparative Examples 4 and 5).
Furthermore, a wet nonwoven fabric with a uniform structure was obtained using a similar mixed fiber using a normal wire mesh having no closed mesh (Comparative Example 6). The physical properties of these nonwoven fabrics are shown in the table. From the data of each example above, a nonwoven fabric in which the area of the dense part exceeds 80% is similar to a nonwoven fabric with a uniform structure in terms of strength and elongation, and the effect of the coarse/dense structure does not appear, and the area of the dense part is 20%. It can be seen that those that do not reach this level have low strength. On the other hand, nonwoven fabrics in which the area of dense portions is 20% or more and 80% or less are excellent in strength, elongation, and toughness. Examples 6 and 7, Comparative Examples 7 and 8 The high melting point component is polyethylene terephthalate (intrinsic viscosity 0.65, melting point 260°C), the low melting point component is polyethylene (melting point 130°C), the fineness is 5 denier, the fiber length is 10 mm. Sheath-core type thermoadhesive composite fibers and pulp were blended at the predetermined mixing ratio shown in the table, paper was made using the wire mesh used in Example 1, dried with a Yankee dryer at 135°C, and heat treated to obtain a wet nonwoven fabric. (Examples 6 and 7, Comparative Example 7). Furthermore, for comparison, a paper made only of pulp and having a uniform texture was obtained. The physical properties of these nonwoven fabrics and papers are shown in the table. From these data, it can be seen that the nonwoven fabric with a coarse structure in which the mixing ratio of thermoadhesive composite fibers is less than 20% by weight (Comparative Example 7) is inferior to the paper with a uniform structure made only of pulp (Comparative Example 8), but It can be seen that strength, elongation, and toughness are all improved by increasing the mixing ratio of heat-adhesive composite fibers to 20% by weight or more (Examples 6 and 7). The wet-laid nonwoven fabrics obtained in Examples 6 and 7 had excellent water retention and breathability, and exhibited sufficient performance as packaging materials for protecting the roots of seedlings, but the products of Comparative Examples 7 and 8 were strong, especially wet and strong. was weak and unusable.

【table】

[Table] *1 Toughness = Strength x Elongation

[Brief explanation of the drawing]

FIGS. 1 and 2 are schematic diagrams of the fiber structure of the wet-laid nonwoven fabric of the present invention, which has a mesh-like sparse structure and has a spider web structure in the coarse portions. In the figure, 1 is the dense part, 2 is the coarse part, and 3 is the adhesion state of the fluff fibers that make up the coarse part, l ₁ and l ₂ are the widths of the coarse parts, and t ₁ and t ₂ are the widths of the dense parts. , MD indicates the moving direction of the paper wire mesh, and CD indicates the direction perpendicular to the moving direction.

Claims (1)

[Scope of Claims] 1. A wet-laid nonwoven fabric having a mesh-like sparse and dense structure, in which the area of the dense portion accounts for 20% or more and 80% or less of the area of the nonwoven fabric, and the first component (hereinafter referred to as a high fiber-forming polymer) is composed of a fiber-forming polymer. (sometimes referred to as melting point component) and one or two components whose melting point is at least 10°C lower than that of the first component.
A second component (hereinafter sometimes referred to as a low melting point component) consisting of at least one polymer, and the fiber length is one half of the shortest distance between opposite sides of the coarse structure (between the dense structures).
Heat-adhesive composite fibers that are more than 20% of the weight of the nonwoven fabric
A wet-laid nonwoven fabric comprising the above, whose form is stabilized by heat fusion of the heat-adhesive conjugate fibers, and which has a spider web structure in its coarse portions. 2. A wet process in which thermally adhesive fibers made of composite components with a melting point difference of 10°C or more are made into paper using a wet method, and then heat treated at a temperature higher than the melting point of the low melting point component and lower than the melting point of the high melting point component of the thermally adhesive fiber. In the nonwoven fabric manufacturing method, the area of the part with closed eyes is 20% of the total area.
A paper-making wire mesh having occlusions distributed in a mesh-like manner with a constant density such that the density is 80% or less, and a paper-making wire mesh having a fiber length of at least one-half of the interval between the meshes formed in the area where the occlusions are located. Adhesive Composite Fiber Non-Woven Whole 20
A method for producing a wet-laid nonwoven fabric having a coarse and dense structure and having a spider web structure in the coarse portions, the method comprising using a fiber mixture containing at least % by weight.