JPH0367652A - Preparation of absorbent - Google Patents

Abstract

PURPOSE:To simply obtain an absorbing material wherein only a surface layer is a liquid permeable skin layer by applying heat treatment to a laminate wherein a surface layer is provided to one surface of an absorbing layer composed of a specific mixture and the content of the hydrophilized staple fiber in the surface layer is larger than that in the absorbing layer at the m.p. of the hydrophilized staple fiber or higher. CONSTITUTION:A surface layer is provided to at least one surface of an absorbing layer. The absorbing layer has a basis wt. larger than that of the surface layer and is composed of wood pulp alone or a mixture of wood pulp and 40 wt.% or less of a hydrophilized staple fiber. The surface layer has a basis wt. of 1- 100g/m<2> and is composed of a mixture consist of the hydrophilized staple fiber and 70 wt.% or less of wood pulp. A laminate wherein the hydrophylized staple fiber content of the surface layer is larger that of the absorbing layer is heat-treated at the m.p. of the hydrophilized staple fiber or higher.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing an absorbent body, and more specifically, it relates to a method for manufacturing an absorbent body, and more specifically, a method for manufacturing an absorbent body from an absorbent layer rich in wood pulp and a skin layer rich in hydrophilized short fibers. The present invention relates to a method for easily manufacturing an aqueous liquid absorbent body formed from a surface layer of the present invention by simply carrying out a single heat treatment.

(Prior art and its problems) Absorbent materials used as disposable diapers, sanitary napkins, medical sponges, wound dressing bats, etc. are made from compositions of natural pulp such as wood pulp and synthetic pulp such as polyolefin pulp. It is well known that the body is manufactured.

In this case, natural pulp absorbs water-based liquids well, but if it is used alone, the strength after liquid absorption is weak and the absorbent material becomes unstable, so by blending synthetic pulp, this disadvantage cannot be compensated for. By utilizing the heat-melting properties of synthetic pulp, it is possible to appropriately heat-seal the entire absorbent body, making it possible to create an absorbent body that takes advantage of the respective properties.

It is also known that such an absorbent body is wrapped or laminated with tissue paper, nonwoven fabric, film, or sheet. The lamination/packaging method involves applying an adhesive to at least one surface of the absorbent body made of a composition of natural pulp and synthetic pulp, and then pressing tissue paper, nonwoven fabric, film, or sheet with a pressure roll, etc. They are integrated by adhesion, or by pressing the absorber and film with a hot roll or by blowing hot air onto them.

However, these manufacturing methods are difficult to handle when using adhesives, and even when blowing hot air to integrate, the surface layer cannot be formed to maintain appropriate air permeability. There are problems such as technical difficulties.

Furthermore, by pasting a resin film or sheet such as polyvinyl alcohol on which a skin layer has been formed in advance on at least one surface of the absorbent layer made of a composition of natural pulp and synthetic pulp, an absorbent body with a skin layer formed on the surface is obtained. Although this method is also known, this method also has the problem that pasting the skin layer is cumbersome and the efficiency of one operation is reduced.

(Object of the invention) Therefore, the object of the present invention is to simply perform a simple heat treatment.
An object of the present invention is to provide a method for manufacturing an absorbent body in which a liquid-permeable skin layer is formed on at least one surface of an absorbent layer.

(Means for solving the problem) According to the present invention, there is provided a method for producing an absorbent body comprising a laminate having a surface layer on at least one surface of the absorbent layer, wherein the absorbent layer has a basis weight larger than that of the surface layer. The surface layer is made of wood pulp alone or a mixture of wood pulp and hydrophilized short fibers of not more than 40%, and the surface layer has a basis weight of 1 to 100 g7m"
The laminate is made of a mixture of hydrophilized short fibers and 70% by weight or less of wood pulp, and the content of the hydrophilized short fibers in the surface layer is higher than that of the absorbent layer. Provided is a method for producing an absorbent body whose surface layer is a liquid-permeable skin layer, which is characterized by heat treatment at a temperature equal to or higher than the melting point of short fibers.

That is, according to the present invention, the absorbent layer is made rich in wood pulp, the surface layer formed on at least one side thereof is made rich in hydrophilic short fibers, and the basis weights of the two are made different, thereby making the absorbent layer hydrophilic. It is possible to easily produce an absorbent body in which only the surface layer is a liquid-permeable skin layer simply by heat-treating the short fiber at a temperature higher than its melting point.

(Description of preferred embodiments) Surface layer 1 The surface layer of the absorbent body of the present invention contains 70% by weight of hydrophilic short fibers.
A suitable liquid-permeable skin layer is formed by a mixture with the following wood pulp, and the mixture contains 40 to 95% by weight of hydrophilic short fibers and 5 to 60% by weight of wood pulp. Furthermore, it is preferable that this surface layer has a basis weight of 1 to 1 g/s", preferably 10 to 50 g/s. , the skin layer is too thin to provide the required strength, and 100
If it exceeds "g/m", the skin layer becomes too thick, which not only slows down the rate of absorption of aqueous liquids, but also makes it impractical.

As the hydrophilic short fibers, thermoplastic resin fibers, for example,
Polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-1-butene copolymer, ethylene-
Polyolefin resins made of one or more a-olefins such as 4-methyl-1-pentene copolymer are melt-spun using various methods, and then short fibers and films obtained by cutting are opened. Examples include split yarn obtained by spinning or synthetic pulp obtained by the flash spinning method disclosed in Japanese Patent Publication No. 52-47049, and among these, synthetic pulp is most preferably used.

Hydrophilic short fibers having an average fiber length of 0.1 to 10 mm and an average mjl diameter of 1 to 30 μm are preferably used.

Various synthetic resins can be used as the synthetic pulp, such as polyolefin, polyester, polyamide, polycarbonate, ionomer, polysulfone,
polyphenyleneether, poly(meth)acrylate,
Examples include poly(meth)acrylate, polyester ether, polyvinyl formal, etc. Among them, polyethylene obtained by flash spinning, polypropylene, ethylene-propylene copolymer, ethylene-1-butene copolymer, ethylene- A fine fibrous material of a polyolefin resin made of one or more a-olefins such as 4-methyl-1-pentene copolymer is preferably used.

Since this synthetic pulp is a hydrophobic material, it is necessary to make the surface hydrophilic.

Short wire method The short fibers mentioned above are those whose surfaces have been made hydrophilic with a surfactant. Methods for making short fibers hydrophilic include a method in which the short fibers are made into a slurry mixture of water containing a nonionic surfactant and then dehydrated, or a method in which polypropylene glycol with a molecular weight of 200 to 1,000 is applied to the surface of the short fibers. Examples include a method of adhesion, but in the former, the HLB of the nonionic surfactant is 2.
0 to 20, and 0 on the surface of the short fibers.
．． Those to which 1 to 5% by weight of a nonionic surfactant are attached exhibit particularly excellent hydrophilicity, resulting in hydrophilized short fibers with excellent absorption performance.

In addition, when these short fibers are obtained by the flash spinning method as disclosed in the above-mentioned Japanese Patent Publication No. 52-47049, the final stage of production is in the state of water slurry, so parent wood treatment is carried out at this stage. It is also economically advantageous to do so.

The polypropylene glycol used in the latter method has a molecular weight of 200 to 10,000, preferably 400 to 6,000, and is obtained by combining propylene oxide in a conventional manner.

The molecular weight of polypropylene glycol is a value determined by gel permeation chromatography, and is calculated from the comparison of the OH value of a standard polypropylene glycol with a known OH value and a sample polypropylene glycol.
From the viewpoint of the effect of imparting hydrophilicity, it is selected from those in the above molecular weight range.

Furthermore, this surface layer may contain 1 to 50% by weight, preferably 5 to 30% by weight, of short fibers with a high melting point for reinforcement, if necessary.

High melting point short fibers mean synthetic resin short fibers that have a higher melting point than hydrophilic short fibers or are infusible, and the difference in melting point from the hydrophilic short fibers is 5°C or more, preferably 20°C. The above is preferable.

Examples of raw materials for such high melting point short fibers include polypropylene, nylon (polyamide), phenol resin, polyimide resin, polyethylene terephthalate resin,
Examples include polybutylene terephthalate resin and poly-4-methyl-1-pentene, particularly polypropylene, polyethylene terephthalate, and poly-4-methyl-1
- Pentene is preferably used.

Furthermore, if the form of the fiber is called composite fiber,
It can provide various characteristics. Such examples include, for example, PP/L D PE, PP/EVA as core/skin.
, high melting point polyester/low melting point polyester, high melting point nylon/low melting point nylon, and PET/PE.

The high melting point short fibers are: l) Fiber length: 0.5 to 50 mm 21 m fiber diameter: O'' to 20 d 3) Young's modulus = 70 to 3000 kgf/m+n2
Those within this range are preferably used.

The absorbent layer constituting the absorbent body of the present invention is made of wood pulp alone,
Alternatively, a mixture of wood pulp and hydrophilized short fibers of 40% by weight or less, preferably wood pulp alone, or a mixture of wood pulp and hydrophilized short fibers of 30% by weight or less is used, and this absorbent layer is made of It is necessary to use a basis weight larger than that of the surface layer. By using a surface layer whose basis weight is smaller than the basis weight of the absorbent layer, and by laminating these and heat-treating them, only the surface layer becomes a liquid-permeable skin layer, which improves the absorption performance integrated with the absorbent layer. This results in the formation of an excellent absorbent body.

Wood pulp is pulp made from plant fibers, including wood pulp obtained by mechanically or chemically crushing wood, as well as original natural fibers such as cotton, or recycled staple fibers such as rayon. is used.

The proportion of hydrophilic short fibers mixed into the wood pulp is 40% by weight.
Exceeding this is not preferable because bulkiness and absorption capacity are lost.

For this absorbent layer, short fibers, particularly bent short fibers with a high melting point that have been made hydrophilic, are suitably used in order to impart bulkiness as required.

Furthermore, a superabsorbent polymer such as alkaline acid grafted starch can be appropriately blended into the absorbent layer.

The absorbent body of the present invention can be used for disposable diapers, sanitary napkins,
It is used in medical sponges, wound pads, etc., and is generally used in the form of a sheet, but depending on the purpose, it can also be used in other shapes such as a block or rod. If it is in sheet form, an exterior material with low water retention or a backing material that is impervious to water may be laminated as necessary.

A feature of the present invention is that the surface layer is laminated on at least one surface of the absorbent layer, and the surface layer is heat-treated at a temperature equal to or higher than the melting point of the synthetic pulp.

The heat treatment method includes, for example, applying hot air to the laminate or passing hot air through it, or using an air oven, an infrared heater, etc. in a heated atmosphere such as a hot wire width pair to heat the synthetic pulp. Although a method of processing at a temperature higher than the melting point for a required period of time is exemplified, it is preferable to use a through-drying method in which hot air is blown through from the surface layer side of the laminate.

In addition, in forming the absorbent layer in the present invention and a surface layer on at least one surface of the absorbent layer, it is desirable to employ an air lay method.

The air lay method is a method that uses air instead of water to disperse pulp fibers.
r method, 5can-11eb Drum 5yste
-Three basic processes are known, called ``Kamiba Gikyo Kyokai'' Vol. 41, No. 2, pages 18 to 24, of which the absorbent layer and surface layer are formed. As a result, it is possible to obtain a laminate in which the boundary between the absorbent layer and the surface layer is continuously integrated, and in the absorber thus obtained, liquid is quickly absorbed through the surface layer, and peeling at the interface is prevented. The result is an absorber with a porous structure that does not cause liquid formation and has excellent liquid permeability.

(Effects of the Invention) According to the present invention, a high-strength absorbent body with a skin layer formed on the surface can be produced by simply heat-treating the laminate having the specific layer structure above the melting point of the hydrophilic short fibers. It is easy to manufacture and the skin layer has the characteristic of being liquid permeable.

(Example) Hereinafter, the present invention will be explained in detail with reference to Examples.

Example 1 Wood pulp: NBSP (manufactured by Yamaba Kokusaku Pulp ■) Synthetic pulp: Polyethylene synthetic pulp produced by flash spinning, the surface of which was treated with a nonionic surfactant (average fiber length 1 .2am) Surface layer The above-mentioned wood pulp and synthetic pulp were each mixed in an amount of 1°β.
A total of 20 g was thoroughly mixed in an LO4 pulper (10 g of water) and then dehydrated in a hand paper machine to obtain a blend sheet.

This blend sheet is air-dried at room temperature and then pulverized and defibrated using a Hammer Milk Eve pulverizer to obtain a flocculent material.

豐豐贴18g of the wood pulp and 2g of synthetic pulp are mixed in the same manner to obtain a flocculent material.

Next, 300g/m2 of the cotton-like material for forming the absorbent layer
After forming an absorbent sheet of 50 g/m" on top of the absorbent sheet using a floc air-lay method for forming a surface layer, and pressing with a load of 0.5 kg/cn+",
Heat treatment was performed at 150° C. for 5 minutes in a hot air circulation type dryer.

The thus obtained absorbent body had a liquid-permeable skin layer with a smooth surface layer, and when 5 cc of 20° C. water was dropped onto it, the entire amount was instantly absorbed.

Example 2 The composition of the surface layer was 6 g of wood pulp and 14 g of synthetic pulp, and the composition of the absorbent layer was 16 g of wood pulp, 4 g of synthetic pulp.
An absorbent body was produced in the same manner as in Example 1 except that the absorbent material was changed to g. The absorbent body thus obtained had a skin layer with a smooth surface layer, and was extremely strong compared to the absorbent layer.

Also, when 5 cc of 20°C water was dropped into this absorber, the entire amount was instantly absorbed.

Example 3 A flocculent material was prepared in the same manner as in Example 1, except that the composition of the first layer and the third layer was 6 g of wood pulp and 14 g of synthetic pulp, and the composition of the second layer was 18 g of wood pulp and 2 g of synthetic pulp. I got it.

Next, the first and third layers were coated at 30 g/m", and the second layer was coated at 4 g/m".
00 g/w'' basis weight, the third layer, second layer, and -th layer were laminated in this order, and the spacing between two Teflon IM-covered heating plates was set to 5ffII11, and the laminated web was sandwiched between them.
Heat treatment was performed at 50°C for 2 minutes.

The absorbent material thus obtained had strong and smooth skin layers on both sides and exhibited excellent liquid absorbency.

Since the absorbent body having skin layers on both sides has sufficient strength by itself, it can be used without requiring backing with a film or nonwoven fabric.

Comparative Example The composition of the surface layer was 16 g of wood pulp and 4 g of synthetic pulp, and the composition of the absorbent layer was 14 g of wood pulp and 6 g of synthetic pulp.
An absorbent body was produced in the same manner as in Example 1, except that the basis weight of the surface layer was 60 g/m2 and the basis weight of the absorbent layer was 300 g/11''.

The absorbent material obtained in this way had fluff on the surface, but the entire absorbent web was almost uniform and no skin layer was formed on the surface.

Claims (3)

[Claims] (1) A method for producing an absorbent body comprising a laminate having a surface layer on at least one surface of the absorbent layer, wherein the absorbent layer is made of wood pulp alone or wood pulp with a basis weight larger than that of the surface layer, or wood pulp and 40% by weight. % or less of hydrophilized short fibers, and the surface layer has a basis weight of 1 to 100 g/m^2.
A laminate consisting of a mixture of hydrophilized short fibers and 70% by weight or less of wood pulp, and in which the surface layer has a higher hydrophilized short fiber content than the absorbent layer, is made of hydrophilized short fibers. A method for producing an absorbent body whose surface layer is a liquid-permeable skin layer, characterized by heat treatment at a temperature equal to or higher than the melting point. (2) The manufacturing method according to claim (1), wherein the hydrophilized short fibers are synthetic pulp. (3) The manufacturing method according to claim (1), wherein the absorbent layer and the surface layer are formed by an air lay method.