JPH0667397B2 - Elastic absorber - Google Patents

Description

TECHNICAL FIELD The present invention relates to an elastic absorber suitable as a hygiene article such as a disposable diaper or a sanitary napkin.

[Conventional technology]

Conventionally, various types of disposable diapers have been proposed, but generally, the basic structure thereof is composed of a liquid-permeable front surface portion, a liquid-impermeable back surface portion, and an absorbing portion interposed therebetween. .

The liquid-permeable surface portion is usually composed of a non-woven fabric or a perforated polyethylene film. The liquid-impermeable back surface is usually made of a synthetic resin film. On the other hand, the absorbing part is composed of a pulp material called crushed pulp or cotton-like pulp and a polymeric water-absorbing agent, and this pulp material and the polymeric water-absorbing agent are encapsulated by a skin material such as tissue paper, and the The molecular water-absorbing agent is stably entrapped.

The diaper is constructed by providing the main body of the diaper including the front surface portion, the back surface portion, and the absorbing portion with an adhesive tape or the like for fixing to the body. The cross-sectional structure of the absorbing portion is as shown in FIGS. In each figure, 1 is a net (nonwoven fabric), 2 is ground pulp, 3 is ground pulp, 3 '.
Is a polymer water-absorbing agent, 4 is thin paper, and 5 is cover stock.

As is apparent from these, the absorbent part of the conventional diaper uses a pulp material such as crushed pulp and a polymer water-absorbing agent, but this one has almost no strength and neither compression recovery rate nor lateral bending recovery amount. Since it is low, the absorbing part is deformed due to the dynamic load of the user or the like, and the usability is deteriorated.

Furthermore, it has the drawback that it contracts when absorbing body fluids,
Further, there is a problem that a step of wrapping the pulp material with the skin material is necessary.

From the viewpoint of the layer structure, a diaper having a single-layer absorbent portion has a poor compression feel and flexibility when the compression recovery rate is increased, and a compression recovery rate is improved when the softness and flexibility are improved. However, there is a drawback that it is difficult to keep the balance.

[Problems to be solved by the invention]

The present invention overcomes the above drawbacks by using a specific heat-adhesive defibrated short fiber as the heat-adhesive defibrated short fiber constituting the upper layer and the lower layer of the elastic absorber or the lower layer. An object of the present invention is to provide an elastic absorber having a good balance of softness, flexibility, compression recovery rate and lateral bending recovery property.

Some of the inventors of the present invention have previously disclosed, in JP-A-61-113810, a thermoadhesive defibrated short fiber made of multilayer films, which replaces the conventional thermoadhesive conjugate fiber by spinning. Proposed. The characteristics of the manufacturing method are as follows.

Multilayer films comprising at least two layers, one layer and the other layer being made of a thermoplastic resin having different melting points, may be slit after stretching or stretched and then slit, and then split to further shorten the fibers. Characterize.

The present inventors have examined elastic absorbers used as hygiene products such as paper diapers and sanitary napkins, and when using the above-mentioned heat-adhesive defibrated short fibers for the absorber, the layer structure and the heat-adhesiveness of the absorber. We conducted a diligent study on high melting point thermoplastic resins and low melting point thermoplastic resins that make up defibrated short fibers. As the thermoplastic resin, the heat-adhesive defibrated short fibers using ethylene-propylene block copolymer can be well blended with the pulp material of the upper layer and the lower layer constituting the elastic absorber, and the blend of the upper layer. If a polymeric water-absorbing agent is laid in the intermediate layer between the product and the blend of the lower layer and heat-treated, a solidified elastic absorber is formed. The process can be simplified because it can be solidified without the use of a skin material such as a taper. Further, in addition to the use of specific heat-bondable defibrated short fibers, the layer structure is not a single layer but at least a three-layer structure. For example, strength is imparted compared to conventional absorbers, and the amount of lateral bending recovery, compressibility, softness, and flexibility are well-balanced and dramatically improved.
As a result, the present invention has been completed based on this finding.

[Means and Actions for Solving Problems]

That is, the elastic absorber of the present invention is composed of a mixture of heat-adhesive defibrated yarn short fibers formed of both upper and lower layers of pulp and thermoplastic resin multilayer films of at least two layers having different melting points, The intermediate layer is an elastic absorber having at least a three-layer structure composed of a polymeric water-absorbing agent, and the layer of the high melting point thermoplastic resin of the thermoadhesive defibrated short fibers of both layers or the lower layer is ethylene-propylene block copolymer The elastic absorber is a united body and is heat-treated to be integrated.

Further, the present invention will be described in detail in comparison with the prior art.

Conventionally, as a thermo-adhesive composite fiber utilizing a difference in melting point, for example, a crystalline polypropylene (m.p165 ° C) is used as a high melting point thermoplastic resin and a polyethylene (m.p125 ° C) is used as a low melting point thermoplastic resin. It is also known to use melt-compound spinning as a composite component.

An example of a cross-sectional model of this thermoadhesive conjugate fiber is shown in FIGS. 7 and 8. In the thermoadhesive conjugate fibers of both figures, the inside is formed by the high melting point thermoplastic resin 6 and the outside is formed by the low melting point thermoplastic resin 7.

Such a thermoadhesive conjugate fiber is usually formed into a web and then subjected to an appropriate heat treatment, that is, a heat treatment at a temperature at which a low melting point thermoplastic resin is melted but a high melting point thermoplastic resin is not melted. The contact portions of the above are fused to form a non-woven fabric or the like.

However, in the above-mentioned melt composite spinning, the die and nozzle structure are complicated, which makes it almost impossible to produce a heat-adhesive composite fiber of three or more components.
It is difficult to change the color of the raw material even in the thermoadhesive conjugate fiber made of the component system.

For this reason, although it has excellent performance as a heat-adhesive conjugate fiber, its range of use has been greatly limited.

Further, it is difficult to make a cotton blend with this heat-adhesive conjugate fiber, and even if the cotton blend can be made, the elastic recovery rate and the bending recovery amount are low.

The present inventors have succeeded in overcoming the above problems when they have obtained a heat-bondable defibrated short fiber by a method different from the conventional melt composite spinning as described above.

That is, the thermally adhesive defibrated short fibers can be easily colored and have a wide variety of colors, and not only two layers but also a multilayer structure of three or more layers can be manufactured.

In addition, there are no dies and nozzle troubles (disassembly, cleaning, etc.) that are common in conventional melt composite spinning. And by changing the die shape, it is possible to manufacture heat-bondable defibrated short fibers that are rich in texture and volume, and without using a binder, etc. It has a feature that the cost is lower than that of the other products. Furthermore, this heat-bondable defibrated short fiber is a heat-bondable defibrated short fiber having an uneven thickness and length, which is different from the conventional melt-composite spinning, and it has a branched structure. There is. Since the pulp used in the absorbing part is also generally non-uniform and has a branched structure, it can be well blended with the heat-bondable defibrated short fibers of the present invention.

Such heat-bondable defibrated short fibers are made of multilayer films.

First, the multilayer films will be described by taking a multilayer film as an example. The multilayer film can be produced from a thermoplastic resin based on various known molding methods such as a calendering method, an extrusion method and a casting method. Of these, the extrusion method based on the inflation method and the T-die method is a preferable method, and specific examples thereof include the co-extrusion method based on the inflation die and the T-die, and the lamination method.

For example, a method of simultaneously extruding thermoplastic resins having different melting points from two or more extruders to form a multi-layer blown film is adopted, whereby a multi-layer film similar to a laminated product can be obtained. There are high melting point and low melting point thermoplastic resins.In the present invention, low melting point thermoplastic resins include low density polyethylene, linear low density polyethylene, high density polyethylene and ethylene-vinyl acetate copolymer. Ethylene-propylene block copolymer is used as the high melting point thermoplastic resin. When the above ethylene-propylene block copolymer is used only in the lower layer, crystalline polypropylene is used as the high melting point thermoplastic resin in the upper layer. These resins may contain antioxidants, matting agents, stabilizers, flame retardants, lubricants, ultraviolet absorbers and the like, if necessary.

The multilayer film comprises at least two layers. Among the thermoplastic resins forming the multilayer film, those having at least one melting point are used for the thermoplastic resin forming at least one of the layers and the thermoplastic resin forming the other layer.

The multilayer film comprises at least one layer of high melting point thermoplastic resin and at least one layer of low melting point thermoplastic resin, and the layer of low melting point thermoplastic resin is exposed on at least one outer surface. The melting point difference between the low-melting point thermoplastic resin and the high-melting point thermoplastic resin is, considering the heat treatment conditions described below, the extrusion conditions of the multilayer film, the stretching conditions in the subsequent step, and the like, if the former melting point is M _P ° C. , The melting point of the latter is M _P ＋ 10 ℃
The above is preferable.

As a specific example of the two-layer structure multilayer film, a low melting point thermoplastic resin is a linear low density polyethylene, and a high melting point thermoplastic resin is an ethylene-propylene block copolymer or crystalline polypropylene. Can be mentioned.
Examples of the multilayer film having a three-layer structure include those having the same low-melting thermoplastic resin laminated on the surface of the high-melting thermoplastic resin of the above-mentioned two-layer structure.

In the present invention, it goes without saying that not only the two-layer structure and the three-layer structure but also four or more layers may be used.
At that time, the multilayer film is configured in consideration of heat treatment conditions at a temperature at which the low melting point thermoplastic resin melts and the high melting point thermoplastic resin does not melt.

When the multilayer film according to the present invention is formed by a T-die or the like, the die lip structure may be flat or a streak die may be used. When a die with a streak is used, the heat-debonding defibrated short fibers according to the present invention can have a texture and a volume feeling.

Fig. 5 shows an example of a cross-sectional model of the heat-adhesive defibrated short fibers when a flat die is used, and Fig. 6 shows a cross-sectional model of the heat-adhesive defibrated short fibers when a streak die is used. An example of each is illustrated. In both figures, 8 and 10 are low melting point thermoplastic resin layers, and 9 is a high melting point thermoplastic resin layer.

The multilayer film according to the invention may then be slit and stretched or slit after stretching. The thickness of the multilayer film before stretching is not particularly limited, but generally 30
It is preferably ˜100 μ.

For stretching the multilayer film, any stretching method such as hot plate, hot roll, or oven may be used. The stretching temperature and the stretching ratio are not particularly limited and may be set to optimum conditions depending on the composition and shape of the multilayer film. However, the strength, feel, volume and the like of webs and non-woven fabrics obtained through the post-process largely depend on the physical properties of the fibrils.

When a preferable example of the stretching temperature and the stretching ratio is shown, for example, when a multilayer film composed of a linear low-density polyethylene and an ethylene-propylene block copolymer is slit in the longitudinal direction and stretched with a hot roll, the stretching temperature is 100 to 130 ℃,
The draw ratio is preferably in the range of 4 to 10 times.

Cleaving is performed after such a step. For example, a stretched film (tape-like material) that is slit is brought into contact with a split roll having a needle standing on the surface, and the roll is rotated in the same direction with respect to the traveling direction of the film. Is a step of making the fiber shape, and the final fiber diameter is determined by the lead and pitch of the split roll needle.

The average fineness of the obtained defibrated yarn (split yarn) is considered in consideration of blending with pulp in the subsequent process and shortening of fiber.
It is suitable that it is fibrillated to 100d or less.

This is because not only the joint strength of the elastic absorber after heat fusion decreases when it exceeds 100 d, but also the compression recovery rate becomes about 60%, which is not much different from the conventional disposable diaper absorber.

After forming the defibrated yarn, the continuous fiber is then shortened by using a cutter or the like to obtain the heat-bondable defibrated yarn short fiber according to the present invention. The length of the short fibers is not unconditionally determined and is appropriately selected.

Simultaneously with the shortening of the fibers, for example, sheet pulp is crushed and mixed with the above-mentioned short fibers to obtain a mixed cotton (web).

FIG. 1 is a cross-sectional model showing an example of the elastic absorber of the present invention, in which the upper and lower layers are crushed pulp 11 and heat-bondable defibrated yarn short fibers.
A mixture of 12 (cotton blend) and an intermediate layer having a sandwich structure composed of a polymer water-absorbing agent 13 are integrated by heat treatment.

In the present invention, the thermoplastic resin having a high melting point, which is one of the components constituting the thermoadhesive defibrated short fibers, has an ethylene-propylene rubber content of 4 to 10 wt% in both upper and lower layers or the lower layer of the elastic absorber. % Ethylene-propylene block copolymer is preferred. When the content of ethylene-propylene rubber is within this range, the amount of lateral bending recovery of the elastic absorber is improved.

When the ethylene-propylene rubber content of the ethylene-propylene block copolymer is less than 4% by weight, the amount of lateral bending recovery is weak and the intended purpose cannot be achieved. Also,
When the content of ethylene-propylene rubber in the ethylene-propylene block copolymer exceeds 10% by weight, the heat shrinkage rate becomes large and problems occur in the shape and physical properties of the elastic absorber.

As for the basis weight of the elastic absorber, the ratio of the basis weight of the upper layer to the basis weight of the lower layer is 0.1 to 1: 1 and preferably 0.3 to 1: 1 and more preferably 0.5 to 1: 1. This is because the upper layer has a feeling of texture and volume, and when it comes into contact with body fluid, it immediately shifts to the lower layer, which is necessary for providing a smooth feeling of use. When the basis weight of the upper layer is smaller than 0.1, the upper layer becomes extremely sticky when absorbing body fluid. Further, if the weight per unit area of the upper layer is greater than 1, there is a problem that the water drawability is poor.

In the present invention, the composition ratio of each layer of the elastic absorber is such that the heat-adhesive defibrated short fibers are 70 to 95% (weight basis) in the upper layer and 20 in the lower layer.
-60%, crushed pulp 5-30% in the upper layer, 40-80% in the lower layer
In particular, the ratio of the heat-bondable defibrated short fibers and pulp in the lower layer is 40:60, preferably 50:50. The heat-bondable defibrated yarn short fiber / pulp ratio of the entire elastic absorber is 40 to 70
/ 30 to 60, and 63.5 / 36.5 is particularly suitable. The ratio of the heat-adhesive defibrated yarn short fibers / pulp / polymer water-absorbing agent in the total absorber composition ratio is 30-60% for the heat-adhesive defibrated yarn short fibers, 15-45% for the pipe, and the polymer water-absorbing agent. A range of 15-30% is suitable.

The polymer water-absorbing agent used in the present invention preferably has an absorption capacity [water absorption amount (g) / water-absorbing agent (g)] of 500 to 1000, and a polysodium acrylate crosslinked product, acrylic acid and vinyl acetate Saponified polymer, potassium polyacrylate crosslinked product, starch-acrylic acid graft polymer,
Is preferred. A particle size of 10 to 1000 μ, particularly 100 to 500 μ is preferable in terms of availability and handling.

The pulp used in the present invention may be of any type as long as it is a natural fiber. Mechanical pulp is a typical example,
Wood pulps such as chemical mechanical pulps, semi-chemical pulps, and chemical pulps are mentioned, and it is desirable to crush and use these pulps.

After forming a sandwich structure in which the upper layer and the lower layer are made of a mixture of thermally adhesive defibrated short fibers and pulp and the intermediate layer is made of a polymeric water absorbing agent, the sandwich structure is heat-treated. This heat treatment is performed, for example, using a hot air circulation type oven at a temperature at which the low melting point thermoplastic resin constituting the heat-bonding defibrated short fibers is melted but the high melting point thermoplastic resin is not melted. By this heat treatment, the low-melting thermoplastic resins of the heat-adhesive defibrated short fibers in both upper and lower layers are bonded to each other, and the whole becomes an elastic absorber.

The elastic absorber of the present invention is not limited to the above,
If at least the pulp and the heat-bondable unwound short fibers are mixed, a layer structure of more than 3 layers can be adopted in combination with the polymer water-absorbing agent.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. Prior to that, the physical property evaluation methods applied to the examples and comparative examples will be described.

1. Apparent thickness [ν] mm 2. Unit weight [M] g / m ² 3. Sheet joining strength [St] kg / 25 mm Dry & Wet st: 25 mm width, chuck distance 10 cm, pulling speed 200 mm / min Average strength 4. Flexure recovery amount [angle] The sample was bent 10 cm × 10 cm × 10 cm, and 30 cc of artificial urine was added to this.
Is evenly dispersed, bent and held for 3 minutes, and the amount of recovery is measured 1 minute after opening.

5.Compression recovery rate Dry & Wet 1V3: 1min, 3g / cm 2 initial load at height 1V40: 1min, 40g / cm ² after the load holding height 2V3: 1V40 After measurement, 1min between 3 g / cm at ² load after standing between 5min Final height Example 1 Linear low density polyethylene (LLDPE, melting point 120 ° C, density on both sides of crystalline polypropylene (PP, melting point 163 ° C, MFR3.0)
0.92, MFR1.2) was placed and coextruded by the T-die method to obtain a three-layer film having a thickness of 50 μm. Then, this three-layer film was uniaxially stretched at a temperature of 103 ° C. to obtain a thickness of LLDPE (6 μ) /
A three-layer film of PP (10μ) / LLDPE (6μ) was molded. Also, the same LLDPE as in Example 1 was placed on both sides of an ethylene-propylene block copolymer (content of ethylene-propylene rubber: 10% by weight, melting point: 160 ° C, MFR1.3) by the same method as described above, and coextrusion was performed. , Thickness is LLDPE (10μ) /
Ethylene-propylene block copolymer (30μ) / LLDP
A three layer film of E (10μ) was molded. The three-layer film was stretched at a temperature of 103 ° C. and the thickness was LLDPE (6μ) / ethylene-propylene block copolymer (10μ) / LLDPE (6
μ) was obtained.

Subsequently, each film was defibrated by a conventional method to obtain a defibrated yarn having a single yarn fineness of 12d and a latter of 20d. The defibrated yarn was cut into short fibers by a cutter, and the short fibers were mixed with pulp that had been previously crushed to obtain a web.

Next, an elastic absorber as shown in FIG. 1 was manufactured by using the web and the polymeric water absorbing agent in the following manner.

First, the upper web is a defibrated yarn with a single yarn fineness of 12d, and the lower web is a defibrated yarn with a single yarn fineness of 20d. Acid graft polymer powder (average particle size
300μ, absorption capacity 800) were dispersed. At that time, pulp /
The composition ratio of the heat-bondable defibrated short fibers is 14/86 in the upper layer and in the lower layer
50/50, the composition ratio of the entire elastic absorber was pulp / heat-adhesive defibrated short fiber / polymer water-supplier 27.2 / 47.4 / 25.4, and the weight ratio of the upper layer / lower layer was 0.6 / 1. .

Put the obtained three-layer structure in a hot air circulation type oven,
An elastic absorber was manufactured by heat treatment at 5 ° C for 5 minutes.

This elastic absorber had good softness and flexibility, and was particularly excellent in bending recovery, and was highly elastic as a whole.

Example 2 An elastic absorber was produced in the same manner as in Example 1 except that the content of ethylene-propylene rubber in the ethylene-propylene block copolymer of the thermally adhesive defibrated short fibers in the lower layer was 4% by weight. This elastic absorber was excellent in softness and flexibility, and was particularly excellent in bending recovery, and thus was excellent in elasticity as a whole.

The results of measuring the characteristics of the elastic absorbers of Examples 1 and 2 are shown in Table 1.

[Effects of the Invention] 1) The elastic absorber of the present invention is capable of satisfactorily blending the heat-adhesive defibrated short fibers, which is one of the constituents, with the crushed pulp, and simultaneously includes the polymeric water-absorbing agent. Since it can be incorporated, the upper layer is rich in softness and flexibility, the surface is hard to be wet, and the whole is elastic and has a good water retention effect.

2) According to the present invention, a homogenized sheet-like material (mat) is obtained by heat-treating the above blend,
It is possible to fix crushed pulp and a polymeric water absorbing agent.

Therefore, the step of wrapping the pulp with a skin material such as tissue paper, which has been conventionally required, becomes unnecessary, and the step in manufacturing the elastic absorber can be remarkably simplified.

3) The elastic absorber of the present invention is high in strength, has an excellent amount of bending recovery, is comfortable to use as a disposable diaper both before and after urination, and hardly deforms due to lateral bending recovery.

4) In the elastic absorber of the present invention, the swelling free space of the crushed pulp and the polymer water-absorbing agent is expanded, so that the absorption capacity per unit weight is increased, and for example, in the case of a paper diaper, it is possible to reduce its weight, and it is possible to greatly reduce the weight. The cost can be reduced.

5) Therefore, the elastic absorber of the present invention can exhibit high commercial value as sanitary napkins and other sanitary products, not limited to disposable diapers.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an elastic absorber showing an embodiment of the present invention, FIGS. 2 to 4 are sectional views of an absorbent portion of a conventional paper diaper, and FIG. 5 is a thermal adhesive solution according to the present invention. FIG. 6 is a cross-sectional view showing an example of a model of short fiber, FIG. 6 is a cross-sectional view showing another example of a model of the same short fiber, FIG. 7 is a cross-sectional view showing an example of a conventional composite fiber, and FIG. FIG. 6 is a cross-sectional view showing another example of the composite fiber of FIG. 1 ... Net, 2 ... Ground pulp, 3 ... Ground pulp,
3 '... Polymer water-absorbing agent, 4 ... Thin paper, 5 ... Coverstock, 6 ... High melting point thermoplastic resin layer, 7 ... Low melting point thermoplastic resin layer, 8 ... Low melting point thermoplastic Resin layer, 9 ...
… High melting point thermoplastic resin layer, 10 …… Low melting point thermoplastic resin layer, 11 …… Pulverized pulp, 12 …… Thermal adhesive defibrated short fibers, 13 …… Polymer water absorbing agent.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location 2119-3BD

Claims (2)

[Claims] 1. An upper layer and a lower layer both are made of a mixture of pulp and thermoadhesive defibrated short staple fibers formed from at least two layers of thermoplastic resin multi-layered films having different melting points, and the intermediate layer is high. An elastic absorber having at least a three-layer structure composed of a molecular water-absorbing agent, wherein the layer of the high melting point thermoplastic resin of the thermoadhesive defibrated short fibers of both layers or the lower layer is an ethylene-propylene block copolymer, The elastic absorber is characterized in that the elastic absorber is heat-treated and integrated. 2. A thermoadhesive defibrated filament short fiber formed from at least two layers of thermoplastic resin multilayer films having different melting points comprises at least one layer of high melting point thermoplastic resin and low melting point thermoplastic resin. Multi-layered films comprising at least one layer, in which the low melting point thermoplastic resin layer is exposed on at least one outer surface, are stretched after slitting or slit after stretching, and then split, and further made into short fibers. The elastic absorber according to claim (1).