JP2004176021A - Water-absorptive and moisture-absorptive and releasing molded product and its preparation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a three-dimensional molded product which exhibits high water-absorption and moisture-absorption and release; and its preparation method. <P>SOLUTION: The molded product comprises being at least partly provided with a composite which is comprised of a plant fiber and a high water-absorptive material unified with a binder resin. The molded product has strength enough to keep the three-dimensional form and exhibits high water-absorption and moisture-absorption and release. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to, for example, molding of containers and trays, and more particularly to a molded article having water absorption and moisture absorption / desorption properties, and a method for producing the same.
[0002]
[Prior art]
For example, a material having high water absorbing performance is required for a disposable diaper, a water stopping material, a dehumidifying material, a water retaining sheet, and the like, and various high water absorbing materials are known.
Above all, the water-absorbing fiber "Bel Oasis" (manufactured by Kanebo Co., Ltd.) is widely known as an excellent fiber exhibiting a high water absorption and a high hygroscopicity (for example, see Patent Documents 1 and 2).
[0003]
[Patent Document 1]
Japanese Patent No. 3154286 [Patent Document 2]
Japanese Patent No. 3170366
[Problems to be solved by the invention]
However, such a water-absorbing fiber does not have high strength, especially at the time of absorbing water, and may have a low strength for maintaining its shape, such as a nonwoven fabric, a knitted fabric, a futon, a filter, or the like, as an application form. It is difficult to apply to a molded product that needs to maintain a three-dimensional shape, such as a container, in a limited form.
[0005]
The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide a molded article exhibiting high water absorption and high moisture absorption / desorption properties, and a method for producing the same.
[0006]
[Means for Solving the Problems]
The molded article of the present invention is characterized by comprising at least a part of a composite material in which a vegetable fiber and a superabsorbent material are integrated with a binder resin.
Preferably, the pulp fiber is used as the plant fiber, and the fibrous material is used as the superabsorbent material. In particular, a crosslinked sodium polyacrylate fiber is desirable as the superabsorbent material.
Further, the composite material is desirably layered, and preferably has a multilayer structure as a molded body, and at least one of the layers is a layer made of the composite material.
The molded article of the present invention can be applied to a wide variety of shapes, particularly containers.
The method for producing a molded article of the present invention includes a step of mixing a vegetable fiber, a superabsorbent material, and a binder resin by a dry method, applying a heat treatment to melt the binder resin, fusing, and integrating. It is a feature.
The binder resin used for the mixing is desirably a fibrous resin.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
The molded article of the present invention is at least partially formed of a composite material in which a vegetable fiber and a superabsorbent material are integrated with a binder resin.
As the plant fiber, for example, herbaceous fiber such as hardwood, conifer, rice, and reed is suitable. As a usage form, used paper can be used in addition to pulp fiber, deinked pulp (DIP) derived from used paper, and the like. Further, not only vegetable fibers, but also fibers containing materials such as synthetic fibers may be used in combination, if necessary, and may contain additives such as sizing agents used in ordinary wet papermaking. Absent.
This plant fiber serves as a main component of the composite material in the present invention, and maintains the strength as a molded article.
In addition, since it is a vegetable fiber, not only does the molded body exhibit bulkiness and enables a lightweight, thick molded body, but also has water permeability and air permeability, and water attached to the surface. Can be quickly led to the internal water-absorbing material, moisture can be taken into the water-absorbing material, and conversely, moisture can be released from the water-absorbing material to the outside.
[0008]
As the superabsorbent material of the present invention, those widely known as superabsorbent materials can be applied. For example, polyacrylate resin, starch-acrylate graft polymer, vinyl acetate copolymer, maleic anhydride copolymer, vinyl alcohol copolymer, A-type silica gel and B-type silica gel as inorganic materials And natural materials include vegetable materials such as pulp and cotton. In particular, those having a water absorption of 10 g / g or more are preferable.
Examples of commercially available superabsorbent resins include, in powder form, "AQUALIC" (Nippon Shokubai), "Alonzap" (TOA Gosei), "AQUA RESERVE" (Nippon Synthetic Chemical), and "AQUAKEEP" (Sumitomo). Refinement). In the fibrous form, there are "Lanseal" (Toyobo), "Bell Oasis" (Kanebo synthetic fiber) and the like.
Above all, "BELL OASIS", which is obtained by directly spinning and cross-linking a sodium acrylate polymer, has high water absorption performance (80 times its own weight (under physiological saline: 45 times its own weight)) and high moisture absorption performance ( Under a relative humidity of 90%, it has a moisture absorption rate of 150% by mass. Under the condition of a relative humidity of 90%, it exhibits a moisture absorption capacity of about 7 times that of cotton and about 2 times that of B-type silica gel. It absorbs water quickly due to its large surface area and does not easily release moisture when pressure is applied. In addition, it has excellent durability performance which does not deteriorate even when water absorption and moisture absorption are repeated. Furthermore, light resistance is high, and deterioration of water absorption performance due to light is not observed. It also has chemical resistance to various organic solvents (acetone, benzene, alcohol, etc.). Further, the heat resistance is 150 ° C. or higher, and the decrease in water absorption / humidity performance due to heat is small. Furthermore, in addition to having excellent flame retardancy (oxygen index LOI = 42, Disaster Prevention Association Certified Code A-21), it also has a deodorizing function, particularly a deodorizing property against ammonia. Furthermore, the calorie during combustion is low (4200 cal / g), and it is easy to incinerate and environmentally friendly.
The superabsorbent material can be of various forms, such as fibrous or powdery, as long as it does not hinder moldability, but if it is fibrous, it can be more entangled with plant fibers and reliably prevent falling off It is preferable that the material be fibrous, since it can maintain good permeability without impairing the capillary action even after absorbing and swelling the liquid.
In the case of a fibrous material, a material within a range of 2.0 to 12.0 dtex and a fiber length of 2.0 to 7.0 mm so as not to hinder mixed fusion and to prevent excessive precipitation on the surface. Is preferred.
[0009]
As the binder resin, various thermoplastic resins can be used, depending on the compatibility with the plant fiber and the superabsorbent material, the use of the molded article, and the like. In particular, a material having a low melting point is preferable from the viewpoint of facilitating fusion bonding, and a polyolefin, particularly, polyethylene, or polylactic acid is suitable.
It is desirable that the binder resin be in a fibrous form before melting in that the binder resin is more likely to be entangled with the plant fiber and the like and is reliably prevented from falling off. In the case of a fibrous form, a fiber having a length before melting of 1 to 25 mm is preferable in terms of strength, moldability, and the like. For the same reason, 0.5 to 50 dtex is preferable.
Further, as the binder resin, it is sufficient that at least the surface has heat-fusibility, and a composite fiber such as a core-sheath type may be used. For example, the inside may not be a thermoplastic resin, but may be resin fibers composed of vegetable fibers, chemical fibers, or the like, or may contain additives such as surfactants. Further, by using a composite fiber using materials having different melting points and melting only the resin having a lower outer melting point at the time of fusion, a molded article having higher strength can be obtained.
Due to the presence of this binder resin, the plant fiber and the highly water-absorbing material are integrated into a three-dimensional molded body that retains its shape while exhibiting functions such as water absorption and moisture absorption and desorption by the highly water-absorbing material. Can be formed.
[0010]
The proportion in the composite material is preferably 20 to 85% by mass of the plant fiber, 5 to 50% by mass of the super absorbent material, and 10 to 30% by mass of the binder resin. The more appropriate ratio of these depends on the use of the molded article. However, when the amount of the vegetable fiber is 50 to 80% by mass, the molded article has excellent strength, sufficient air permeability, liquid permeability, and the like. Become. Further, when the superabsorbent material is 10 to 40% by mass, high water absorption and moisture absorption / desorption properties are exhibited, and when the binder resin is 10 to 30% by mass, plant fibers and superabsorbent materials are used. They can be reliably integrated without hindering each function.
[0011]
Other components may be incorporated into the composite material without departing from the spirit of the present invention. For example, if necessary, various known additives, that is, antioxidants, plasticizers, lubricants, various stabilizers, antiblocking agents, antistatic agents, dyes, pigments, weather resistance stabilizers, antistatic agents, Antifogging agents, slip agents, leveling agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, silane coupling agents, deodorants, fragrances, inorganic fillers, organic fillers, surface-organized inorganic fillers, etc. It is possible to add inorganic and organic fillers.
[0012]
The molded article of the present invention is molded using the above-described composite material, and the composite material is used for all or a part of the molded article.
The shape as a molded body is shaped according to the purpose, and various three-dimensional molded bodies are applied in addition to the flat shape as shown in FIG. For example, in the container 28 illustrated in FIG. 4, a composite material is used for both the container body 30 and the lid 32, and the composite material is also used in the tray illustrated in FIG.
The entire plate-shaped molded body 10 shown in FIG. 1 is molded only with the above-described composite material. Therefore, it exhibits a water absorbing function throughout.
The flat molded body 12 shown in FIG. 2 includes a layer 14 made of a composite material in which plant fibers and a superabsorbent material are integrated with a binder resin, and a layer 16 having voids in which plant fibers are integrated with a binder resin. It has a two-layer structure.
The flat molded body 18 shown in FIG. 3 is obtained by integrating a portion 20 made of a composite material in which plant fibers and a superabsorbent material are integrated with a binder resin, and the plant fibers formed therearound with a binder resin. It has a two-layer structure of a layer 24 composed of the portion 22 and a thermoplastic resin layer 26, in which the composite material is unevenly distributed.
As described above, in the molded article of the present invention, it is sufficient that the above-described composite material is provided at least in part, and, of course, a multilayer structure having three or more layers may be used. By using the composite material and another material in this way, it is possible to design strength physical properties, form retention, surface condition, and the like according to the intended use.
For example, if the composite material absorbs too much water, it gels and reduces the adhesion between the fibers, and at the same time, the surface shape tends to be deformed. However, as shown in FIG. By doing so, the layer made of a material other than the composite material functions as a support, improves shape retention, buckling resistance, and tensile strength, and can suppress deformation due to swelling.
Also, when press-molding with a metal mold in the manufacturing process, it is easier to remove the mold because the mold releasability is improved when molded together with another layer than when the composite is used alone.
Further, for example, in a case where direct contact of the composite material with the food is avoided in a use such as a food container or the like, a coating layer made of a material that does not cause any trouble may be formed on the surface.
[0013]
Further, the molded article of the present invention has a feature that it can be applied to a molded article having a more complicated shape. For example, in the container 28 shown in FIG. 4, both the container body 30 and the lid 32 are made of the above-described composite material. That is, in each of the container body 30 and the lid 32, a three-layer structure in which the composite material layer 34 made of the above-described composite material is sandwiched by the water-resistant layer 38 and the permeable layer 36 obtained by integrating plant fibers with a binder resin. Of structure.
In such a container 28, for example, when an object having moisture is accommodated in the container 28 and sealed with the lid 32, moisture that has permeated or volatilized from the contents is transmitted through the container body 30 and the lid 32. The light passes through the layer 36 and is absorbed by the composite material layer 34 of the container body 30 and the lid 32. Therefore, it is possible to prevent water droplets due to dew condensation or the like from adhering to the inner surfaces of the container body 30 and the lid 32, and to prevent partial wetting of the contents. Further, since the superabsorbent material releases moisture so as to maintain an arbitrary equilibrium state, the inside of the container 28 is kept at a constant humidity, and extreme drying can be prevented. Therefore, for example, even when the content is a cake or the like, good quality can be maintained.
In addition, since the composite material layer 34 is not exposed on the surface, surface deformation due to water absorption and surface stickiness due to moisture absorption can be suppressed.
Further, since the water-resistant layer 38 is provided on the outside of the container body 30 and the lid 32, the container does not absorb moisture from the outside, and the water resistance is maintained, so that the container is easy to use. improves.
Therefore, although there is an advantage of simplicity of manufacture in the case of a single-layer structure, by forming the above-described multilayer structure, different functions are exerted on each of them, and a more excellent molded article with high added value is obtained. be able to.
[0014]
The tray 40 shown in FIG. 5 is formed by laminating a water-absorbing layer 44 made of the above-described composite material and a permeable layer 46 in which plant fibers are integrated with a binder resin on a substrate 42 made of a thermoplastic resin such as polystyrene. The liquid such as water spilled on the permeable layer 46 quickly penetrates the permeable layer 46 and is absorbed by the water absorbing layer 44, so that accumulation of the liquid on the tray 40 can be prevented.
[0015]
In the method for producing a molded article of the present invention, the composite material is molded using the above-described composite material. In molding the composite material, the plant fiber, the superabsorbent material, and the binder resin, which are constituents thereof, are mixed by a dry method. Then, a step of subjecting the binder resin to heat treatment to melt, fuse and integrate the binder resin is provided.
Specifically, for example, as shown in FIG. 6, pulp fibers, a fibrous binder resin, and a fibrous high-absorbency material that have been sufficiently defibrated are supplied to the kneading rotor 56 from three hoppers 50, 52, and 54. These are mixed and sprinkled on a belt conveyor 58 to form a web 60. At this time, as the belt conveyor 58 to be used, a forming conveyor in which the conveyor belt has a mesh shape is preferable, and a sheet having a more uniform thickness can be obtained by suction from below. In the illustrated example, the plant fiber, the superabsorbent material and the binder resin are simultaneously mixed.However, the present invention is not limited to this. For example, a mixture in which the superabsorbent material and the binder resin are mixed in advance and the vegetable fiber are mixed. Mixing may be performed, or a sheet made of a mixture of vegetable fibers and a binder resin may be coated with a highly absorbent material to which an adhesive has been added.
[0016]
After that, heat treatment is performed to melt the binder resin. In order to perform the heat treatment, as shown in FIG. The heating device 62 in the illustrated example blows hot air downward from above onto the web 60 on the mesh conveyor 58. Depending on the type of the binder resin, for example, if the binder resin is polyethylene, 120 is used. Hot air heated to ~ 160 ° C is blown. In addition, as a heating device, for example, a device using infrared rays or an electron beam can be used. However, a heating device using hot air easily transfers heat to the inside of the web, and is excellent in productivity.
Further, it is desirable to use a pressure treatment in combination with the heat treatment, and a nip roll or the like may be employed. If heat press molding is performed, heat treatment, pressure treatment, and shaping can be performed simultaneously.
By performing such a heat treatment, the binder resin is melted, and then cooled and solidified, whereby the vegetable fibers and the superabsorbent material are fused and integrated to produce a sheet-shaped molded body as shown in FIG. Is done. Such a molded article can be wound and provided for storage and transportation, depending on the thickness.
In the present invention, it is important to use such a dry method. That is, conventionally, in general, in a molding method using plant fiber as a material, a so-called wet process in which a plant fiber is dispersed in water, the slurry is filtered through a net having a specific shape, and then dried to form a molded product. A molding method called a pulp molding method is usually used. However, if a highly water-absorbing material such as PAA-Na fiber is mixed in the slurry, the water in the slurry is taken in, and proper molding cannot be performed. Even if the shaping can be performed satisfactorily, a greater amount of time and energy is spent in the drying process than in the conventional wet method, which may cause a cost increase.
However, in the present invention, by using the binder resin, the dry fiber-laying method can be used, and a high water-absorbing material can be mixed to form well.
[0017]
In the case of a laminate as shown in FIG. 2, a predetermined material is laminated before the above-mentioned heat treatment is performed, and a heat treatment is performed in that state to be integrated, or after each layer is separately manufactured, Various known means such as combining can be applied. Similarly, a molded article as shown in FIG. 3 can be appropriately manufactured by applying various known means.
Then, by performing secondary molding using the obtained sheet-shaped molded body, molded bodies having various shapes can be manufactured. The secondary molding method is not particularly limited, either, and a vacuum molding method such as straight molding or drape molding is suitable. By applying such a molding method, a three-dimensional molded body such as the container body 30, the lid 32, and the tray 40 as shown in FIGS.
In addition, a bag-shaped molded body can be obtained by laminating two three sides of a sheet-shaped molded body as shown in FIGS.
Also in the multilayering means, in addition to three-dimensional molding using a multilayer sheet, after forming one of the layers, it can be multilayered by painting or the like. For example, in the case of the container body 30 as shown in FIG. 4, after forming the composite material layer 34 and the permeable layer 36 in a two-layer structure, the water-resistant layer 38 is coated by, for example, a method of spray coating an aqueous emulsion, or a resin coating by vacuum forming. The film can be formed by a method such as the above method, a method of forming a film by powder electrostatic coating and heat treatment, or the like.
It is also possible to produce a molded article such as a tray without undergoing secondary molding, for example, as described in JP-A-2001-232611, a mixture of each raw material such as plant fiber A desired molded product can also be manufactured by directly supplying it onto a predetermined mold and performing hot press molding.
[0018]
The molded article of the present invention can be applied to a wide variety of applications. In particular, trays and bags for heating and cooking by a microwave oven such as a drip sheet (laying sheet) for absorbing the moisture of fresh food, a tray for fresh fish or raw meat, a meat bun, and the like. If applied to the inside of a lunch box, a confectionery container, a pet breeding box, a container for chilled transportation, etc. This is extremely useful, for example, when applied to a flowerpot or the like, the number of times of watering can be reduced.
[0019]
【Example】
A fluff pulp prepared by fibrillating conifer-derived bleach kraft pulp (NBKP) was prepared as a plant fiber.
As the binder resin, resin fibers having a core-sheath structure (core / sheath = polypropylene (hereinafter referred to as PP) / polyethylene (hereinafter referred to as PE)) were prepared.
Then, the fluff pulp and the resin fiber are mixed (mass ratio: 9: 1), formed into a web (specific gravity: about 400 g / m ² , thickness: 5 to 6 mm) by an airlaid method as a dry process. The pulp mat was prepared by exposure to an oven having a melting point of 130 ° C. or more and a melting point of PP (160 ° C.) or less.
Further, sodium polyacrylate fiber (copolymer) comprising 78 mol% of acrylic acid (75% is neutralized as a sodium salt), 20 mol% of methyl acrylate and 2 mol% of hexapropylene glycol monomethacrylate ( PAA-NA fiber). Then, the same fluff pulp and resin fiber and PAA-NA fiber as above are mixed (mass ratio 6: 2: 2), and pulp mat (specific gravity: about 400 g / m ² , thickness: (Approximately 5 mm).
The obtained two types of pulp mats are superimposed, a pulp mat made of a composite material is arranged on the female mold side of the hot press mold, and pressed by the opposing male mold to perform hot press molding. A molded body having the shape of the container body shown in FIG. In the hot press molding, the mold temperature was set to 160 ° C. or more, which is the melting point of PP, in order to melt PP, which is the core of the resin fiber.
Then, an aqueous acrylic emulsion was wet-spray-coated on the outside of the layer made of the composite material to manufacture a container body 30 provided with a water-resistant layer 38 as shown in FIG.
[0020]
【The invention's effect】
The molded article of the present invention has sufficient strength to maintain a three-dimensional shape, and exhibits high water absorption and high moisture absorption / release properties.
ADVANTAGE OF THE INVENTION According to the manufacturing method of the molded object of this invention, a molded object which has various shapes easily, in a short time and at low cost, and which exhibits high water absorption and moisture absorption / desorption can be produced.
Therefore, according to the present invention, a drip sheet (sheet spread), a tray for fresh fish or raw meat, a tray or bag for heating and cooking with a microwave such as a meat bun, etc. It is extremely useful for a lunch box, a confectionery container, a pet breeding box, an inner wall material of a chilled transport container, etc., which are required to keep the water content constant, a flower pot, etc., which require high water retention.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an example of a molded article of the present invention.
FIG. 2 is a cross-sectional view showing one example of a molded article of the present invention.
FIG. 3 is a cross-sectional view showing one example of a molded article of the present invention.
FIG. 4 is a cross-sectional view showing one example of a molded article of the present invention.
FIG. 5 is a cross-sectional view showing one example of a molded article of the present invention.
FIG. 6 is a process chart illustrating an example of a method for manufacturing a molded article according to the present invention. FIG. 7 is a process chart illustrating an example of a method for manufacturing a molded article according to the present invention.
10 molded body 12 molded body 18 molded body 34 composite material layer

Claims (9)

A molded article characterized by comprising at least a part of a composite material in which a vegetable fiber and a superabsorbent material are integrated with a binder resin. The molded article according to claim 1, wherein the plant fiber is a pulp fiber. The molded article according to claim 1, wherein the superabsorbent material is fibrous. The molded product according to any one of claims 1 to 3, wherein the superabsorbent material is a crosslinked sodium polyacrylate fiber. The molded product according to any one of claims 1 to 4, wherein the composite material is a layer. The molded article according to claim 5, having a multilayer structure, at least one of which is a layer made of the composite material. The molded article according to any one of claims 1 to 6, wherein the molded article is in a container shape. A method for producing a molded article, comprising a step of mixing a vegetable fiber, a superabsorbent material, and a binder resin by a dry method, subjecting the mixture to heat treatment, and melting, fusing, and integrating the binder resin. The method for producing a molded article according to claim 8, wherein the binder resin to be mixed is fibrous.

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