JPH10250007A - Water absorbing multilayer sheet and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water absorbing multilayer sheet from which a polyethylene oxide gelling with absorption of water does not swell out and of which the water absorbing capacity does not lower. SOLUTION: In a manufacture of a water absorbing multilayer sheet of which the whole surface of a film constituted mainly of macromolecules of a polyethylene oxide is covered with a film constituted mainly of polyvinyl alcohol and a water absorbing multilayer sheet of which the inner layer is a water absorbing film and the outer layer is a film having properties of a semipermeable membrane, an end face treatment process wherein the film having the properties of the semipermeable membrane is melted and, in this state, made to cover the end face of the water absorbing multilayer sheet is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-absorbent multilayer sheet having been subjected to an edge treatment, and a method for producing the same.

[0002]

2. Related Art and Problems to be Solved by the Invention
Japanese Patent Application Laid-Open No. 6-187068 discloses a water-absorbing sheet obtained by fusing and laminating a sheet of a water-absorbing resin mainly composed of ethylene oxide on a semi-permeable polyvinyl alcohol sheet. Further, it is also disclosed that since the water-absorbing sheet disclosed in the above-mentioned publication is gelled and easily flows when it absorbs water, it is preferable to laminate another sheet on both sides of the water-absorbing resin sheet.

[0003] However, when pressure is applied to the above-mentioned water-absorbing sheet, gelled polyethylene oxide is extruded from the end face of the sheet, and the periphery of the sheet may be stained. To prevent contamination, there is a method to increase the degree of crosslinking of ethylene oxide,
Increasing the degree of crosslinking lowers the water absorption capacity.

Accordingly, an object of the present invention is to provide a water-absorbing multilayer sheet in which polyethylene oxide gelled by water absorption does not protrude from the sheet and does not cause a decrease in water-absorbing ability.

[0005]

The gist of the present invention is a water-absorbing multilayer sheet in which the entire surface of a film mainly composed of a polyethylene oxide polymer is covered with a film mainly composed of polyvinyl alcohol. Further, the gist of the present invention is that the inner layer is a water-absorbing film, and the outer layer is a semi-permeable film. This is a method for producing a water-absorbent multilayer sheet provided with an end face treatment step in which an end face is covered with a semipermeable film. Preferably, the end face treatment step includes a step of cutting the water-absorbing multilayer sheet.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION A description will be given of an end face treatment step of covering an end face of a film mainly composed of a polyethylene oxide polymer with a film mainly composed of polyvinyl alcohol, provided on the upper and lower surfaces of the film.

[0007] The melting point of a water-absorbing film containing a polyethylene oxide-based polymer as a main component is about 60 ° C, and the melting point of a semipermeable membrane film containing a polyvinyl alcohol as a main component is about 190 ° C. Therefore, at a temperature at which the polyvinyl alcohol film is melted, the polyethylene oxide polymer film is melted. Then, when the film of polyvinyl alcohol as the outer layer is pressed with a pressing blade (seal blade), the film of the polyethylene oxide polymer as the inner layer is pushed to the left and right of the pressing blade, and at the same time, while being pushed away, The molten polyvinyl alcohol flows in, and the end surface of the water-absorbent multilayer sheet is covered with a film containing polyvinyl alcohol as a main component.

When the end face treatment step includes a step of cutting the water-absorbent multilayer sheet, the above-mentioned sealing blade and the cutting blade to be cut may be the same or different. If different, the cut surface can be cleaned up by optimizing the width of the seal blade and the width of the cut blade, and the respective temperatures according to the thickness of the water-absorbent multilayer sheet. Usually, the width of the sealing blade is wider than the width of the cutting blade, and the temperature of the cutting blade is higher than the temperature of the sealing blade, so that the cut surface can be cleaned.

For the seal, for example, ultrasonic vibration may be used instead of the seal blade. In particular, to cut a long water-absorbent multilayer sheet into a desired size such as a roll,
By using the ultrasonic vibrator and the cutting blade in the longitudinal direction of the conveyed sheet and using the sealing blade and the cutting blade in the width direction, a beautiful end face can be obtained efficiently.

In the water-absorbing multilayer sheet of the present invention, the water-absorbing film containing a polyethylene oxide polymer as a main component and the semipermeable film containing polyvinyl alcohol as a main component do not need to be bonded on the entire surface. , May be partially attached. Curling can be prevented by partially adhering a part that absorbs moisture and expands to a non-adhered part.

The term "partially adhered" refers to, for example, heat bonding or bonding with an adhesive in a dot, line, or lattice shape. The area to be stuck is suitably about 5 to 50% of the whole. If this area is less than 5%, the sticking strength is insufficient. Is reduced. It is preferable that the attachment is provided so as to be uniformly dispersed throughout.

A water-absorbing film containing a polyethylene oxide-based polymer as a main component will be described. A resin containing polyethylene oxide as a main component shows water solubility or water swelling depending on its composition, but when crosslinked, it is insoluble in water and also shows water absorption. The water-absorbing resin film mainly composed of ethylene oxide in the present invention may be any of these, and can be selected according to the required amount of water absorption and the method of use.

As the semipermeable membrane used in the present invention, polyvinyl alcohol (hereinafter sometimes abbreviated as PVA) is used. The semi-permeable membrane comes to the side that comes into contact with food etc. when used, has a strong affinity for water but is insoluble in water, allows water molecules and odor components to permeate, but has a large molecule umami component Has a semipermeable membrane property that does not allow transmission. Such a film can be obtained, for example, by forming a completely aged PVA. The PVA film may also contain a plasticizer such as glycerin to impart flexibility.

In order to attach the water-absorbing film and the semipermeable film, heat fusion is preferred. As a method of laminating a water-absorbent resin film mainly composed of ethylene oxide on a PVA film used as a semipermeable film, a water-absorbent resin film and a PVA film formed by a method described below, a nip roll, There is a method of thermocompression bonding using a press plate. In this case, the water-absorbent resin film is melted at a low temperature of about 60 to 100 ° C. and fused to the PVA film, so that the PVA film is not adversely affected by heat. As another method, there is a method in which a molten water-absorbent resin is coated on a PVA film while being extruded into a film.

The polyethylene oxide-based polymer constituting the water-absorbing film used in the present invention is not particularly limited, but a repeating unit represented by the following general formula is preferred because of its good thermoformability.

[0016]

Embedded image Where A is

Embedded image When

Embedded image And the additional form is

Embedded image Where x, y and z are each an integer of 1 or more, and a weight ratio calculated from x, y and z, 44 (x + z)
/ (Molecular weight of α-olefin oxide having 3 or more carbon atoms)
y is from 80/20 to 94/6, X is a residue of an organic compound having two active hydrogen groups, Y is a hydrocarbon having 1 or more carbon atoms, R ₂ is a dicarboxylic acid compound residue or a diisocyanate compound. Residue.

This polymer compound is formed by adding ethylene oxide to ethylene glycol, then polymerizing an alkylene oxide, and further reacting a polycarboxylic acid compound formed by addition polymerization of ethylene oxide with a dicarboxylic acid compound or a diisocyanate compound. can do.

The dicarboxylic acid compound is preferably a cyclic dicarboxylic acid compound or a linear dicarboxylic acid compound, and examples thereof include dicarboxylic acids, dicarboxylic anhydrides, and lower alkyl esters of dicarboxylic acids. Examples of the dicarboxylic acid include phthalic acid, isophthalic acid, terephthalic acid, malonic acid, succinic acid, sebacic acid, maleic acid, fumaric acid, adipic acid, and itaconic acid. Also,
Examples of the dicarboxylic anhydride include anhydrides of the various dicarboxylic acids. Further, as the lower alkyl ester of the dicarboxylic acid, methyl ester, dimethyl ester, ethyl ester of the various dicarboxylic acids,
Examples include diethyl ester, propyl ester, dipropyl ester and the like.

Particularly preferred are linear dicarboxylic acids having 12 to 36 carbon atoms and lower alkyl esters thereof. Specific examples of the linear dicarboxylic acid having 12 to 36 carbon atoms include 1,10-decamethylenedicarboxylic acid, 1,14-tetradecamethylenedicarboxylic acid,
Examples thereof include 18-octadecamethylene dicarboxylic acid and 1,32-dotriacontamethylene dicarboxylic acid. Examples of the lower alkyl esters include methyl, ethyl, propyl and dipropyl esters of these dicarboxylic acids. Can be These can be used alone or in combination of two or more. Among them, it is preferable to use the above-mentioned dicarboxylic anhydrides and lower alkyl esters of dicarboxylic acids, particularly from the viewpoint of ease of reaction.

Examples of the diisocyanate compound include 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, and methylene biscyclohexyl diisocyanate (H12MDI). These can be used alone or in combination of two or more.

As a method for producing a film from a resin containing a polyethylene oxide-based polymer as a main component, there are a solution casting method, a melt extrusion method, a calendering method and the like. In the case of a homopolymer of ethylene oxide, a film can be obtained by forming an aqueous solution into a film by a casting method or an extrusion method and drying the film. Also, if the above resin,
A film can be easily formed by melt extrusion molding utilizing good thermoplasticity. In the film, a heat stabilizer, an antioxidant, a colorant, and the like can be contained as needed, as long as the film does not affect food.

In the present invention, the absorbent film may be crosslinked as required. When crosslinking the film, the film can be irradiated with ionizing radiation or ultraviolet rays.
As the ionizing radiation, an electron beam, γ-ray, X-ray, or the like can be used. Irradiation is preferably performed in a substantially oxygen-free state, such as by substituting with an inert gas such as nitrogen.
As a crosslinking method, it is also possible to blend a crosslinking agent into a resin mainly composed of ethylene oxide and carry out thermal crosslinking.

[0023]

EXAMPLES Examples will be described below, but the present invention is not limited to these examples.

Example 1 After addition polymerization of ethylene glycol with ethylene oxide, addition polymerization of butylene oxide was performed, and methyl octadecane-1,18-dicarboxylate was added to polyalkylene oxide obtained by addition polymerization of ethylene oxide. In addition, a transesterification reaction was performed.
The thus obtained polymer compound having a weight average molecular weight of 150,000 is melted by an extruder, extruded at a T-die temperature of 140 ° C. to a thickness of 50 μm, and a water-absorbing film containing a polyethylene oxide-based polymer as a main component is formed. Manufactured.

On both sides of the obtained water-absorbing film, PVA
A film (thickness: 15 μm, glycerin 6% added, fully aged film) was prepared using a partially uneven nip roll at a temperature of 65 ° C., a linear pressure of 3.0 kg / cm, and a take-up speed of 1.5 m / min. Roll crimped. A water-absorbing multi-layer sheet was obtained in which a semi-permeable film mainly comprising polyvinyl alcohol was partially adhered to both sides of a water-absorbing film mainly comprising a polyethylene oxide polymer.

The resulting water-absorbent multilayer sheet is blown on all sides using a sealing blade at the first stage and a cutting blade at the second stage, and is 250 mm long and 350 mm wide, the entire surface of which is covered with polyvinyl alcohol. I got The setting conditions for the seal blade were 4 mm in width, 380 ° C. for 1 second, and the setting conditions for the cutting blade were 30 ° for the cutting edge, 400 ° C. in temperature, 0.
5 sec.

The above-described water-absorbent multilayer sheet whose entire surface was covered with polyvinyl alcohol was immersed in water at 23 ° C. and allowed to stand for 1 hour, so that water was contained in the water-absorbent multilayer sheet.
The polyethylene oxide polymer constituting the inner layer swelled, but the gelled polyethylene oxide did not protrude from the sheet.

(Example 2) The long P used in Example 1 was used.
After sandwiching the long water-absorbent film mainly composed of polyethylene oxide-based polymer used in Example 1 with a VA film (thickness 15 μm, glycerin 6% added, fully aged film), the length was 20 m in the longitudinal direction. / Min while running at a frequency of 20 kHz and an output of 450 W
At the same time, the film was sandwiched between a roller-shaped cutting blade and the film was melted. The cutting edge of the cutting blade was 30 degrees. In the width direction, the first stage is cut with a seal blade and the second stage is cut with a cutting blade.
A sheet having a size of 50 mm and a width of 350 mm and the entire surface of which was covered with polyvinyl alcohol was obtained.

The above-described water-absorbent multilayer sheet whose entire surface was covered with polyvinyl alcohol was immersed in water at 23 ° C. and allowed to stand for 1 hour, so that water was contained in the water-absorbent multilayer sheet.
The polyethylene oxide polymer constituting the inner layer swelled, but the gelled polyethylene oxide did not protrude from the sheet.

[0030]

As described above, according to the present invention, the entire surface of a film mainly composed of a polyethylene oxide polymer is
Provided is a water-absorbent multilayer sheet that has been subjected to an end surface treatment that is covered with a film containing polyvinyl alcohol as a main component, so that water-absorbed and gelled polyethylene oxide does not protrude from the sheet and does not cause a decrease in water-absorbing ability. It is in.

Claims (3)

[Claims] 1. A water-absorbing multilayer sheet, wherein the entire surface of a film mainly composed of a polyethylene oxide polymer is covered with a film mainly composed of polyvinyl alcohol. 2. A method for producing a water-absorbing multilayer sheet in which an inner layer is a water-absorbing film and an outer layer is a semipermeable film, wherein the semi-permeable film is melted while the end face of the water-absorbing multilayer sheet is semipermeable. A method for producing a water-absorbent multilayer sheet, comprising an end face treatment step for covering with a film. 3. The method for producing a water-absorbent multilayer sheet according to claim 2, wherein the end face treatment step includes a step of cutting the water-absorbent multilayer sheet.