JP3170366B2 - Freshness retention sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to packaging of fruits, vegetables, etc.
The present invention relates to a freshness retaining sheet for retaining freshness.

[0002]

2. Description of the Related Art Various freshness preserving sheets for fruits, vegetables and the like have already been proposed. For example, Japanese Patent Publication No. 2-80236 proposes a freshness retaining sheet in which an intermediate layer made of a highly water-absorbing fiber and an outer layer made of a porous nonwoven fabric are integrated with a hydrophobic nonwoven fabric inner layer, which is effective in preventing drainage. Have been. However, the highly water-absorbing fiber described therein is a fiber obtained by hydrolyzing and cross-linking an acrylic fiber, has no high hygroscopicity, and has a low hygroscopic rate. Also preferably 50% by weight
As described above, there is a disadvantage that a large amount of highly water-absorbing fibers is required for the nonwoven fabric.

[0003] In addition, the superabsorbent fibers having a high moisture absorption rate have a large degree of swelling, and when the content of the nonwoven fabric is 50% by weight or more, the air permeability is remarkably reduced, which is not effective in maintaining freshness.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an inexpensive freshness retaining sheet which is effective in preventing drainage of fruits and vegetables and has a high moisture absorption rate.

[0005]

Means for Solving the Problems The present inventors have studied high-absorbency and high-absorbency fibers which have high water absorbency and high water absorbency with respect to water, and have studied the preparation and form thereof to complete the present invention.

That is, the freshness maintaining sheet of the present invention has a multilayer structure.
A freshness maintaining sheet formed of a nonwoven fabric, wherein the first layer is hydrophobic, the second layer is 20 ° C., and the relative humidity is 60%.
10 water-absorbing fibers having a moisture absorption of 15% by weight or more under
, And a non-woven fabric containing 15 to 40% by weight of the heat-sealing fiber.

Preferably, a monomer having a carboxylic acid group, a monomer having a hydroxyl group capable of reacting with the carboxylic acid group to form an ester cross-link, and a monomer having an alkali metal carboxylate are copolymerized and crosslinked by heat. The fiber is made of 1200% by weight or more,
A freshness retaining sheet characterized by containing a highly water-absorbing fiber that absorbs less than 000% by weight of water and has a moisture absorption of 15% by weight or more at 20 ° C. and 60% relative humidity.

As the monomer having a carboxylic acid group of the superabsorbent fiber used in the present invention, for example, acrylic acid (hereinafter abbreviated as "AA"), methacrylic acid, maleic acid and the like are used.

As the monomer having an alkali metal carboxylate, for example, alkali metal salts such as AA, methacrylic acid and maleic acid are used. As the alkali metal, sodium (hereinafter abbreviated as "Na"), potassium and the like are used. The ratio of the monomer having a carboxylic acid group to the monomer having a carboxylic acid alkali metal base is from 1/1 to 1/10. The total of the monomer having a carboxylic acid group and the monomer having a carboxylic acid alkali metal base is reduced from 70% by weight to 99.5% by weight. It is preferably at least 80% by weight. If it is less than 70% by weight, the water absorption of physiological saline is insufficient.

As the monomer having a hydroxyl group, for example, hydroxyethyl methacrylate (hereinafter referred to as "H
EMA ". ), Hydroxypropyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, glyceryl monomethacrylate,
Glyceryl monoacrylate or the like is used.

Each of these monomers may be used in a plurality of types. The monomer having a hydroxyl group is contained in an amount equal to or less than the equivalent of free acrylic acid by 0.5% by weight or more. 0.
If it is less than 5% by weight, crosslinking will be insufficient.

In addition to the above monomers, other vinyl monomers such as vinyl acetate (hereinafter referred to as "V
A ". ), Acrylonitrile and the like may be used. The amount of the monomer for plasticization is preferably 30% by weight or less.

The polymerization method used in the present invention is not particularly limited, but water-based polymerization may be used if the monomer composition is water-soluble. Sodium persulfate, which is generally used, may be used as the polymerization initiator.

The spinning method used in the present invention is preferably a general dry spinning method. In the case of wet spinning, water cannot be used as a coagulant, so it must be used in an organic solvent system.

After the dry spinning, the film is stretched 1.3 times or more with dry heat while remaining 10% by weight or more of moisture, and then subjected to a crosslinking treatment with dry heat. Crimping and cutting are appropriately performed. 1 water
Unless it is stretched 1.3 times or more by dry heat with 0% by weight or more remaining, the fiber strength becomes insufficient. Fibers having a large molecular weight have a large water absorption, but have a large molecular weight, so that they are difficult to be stretched, and the fiber strength is low.

The superabsorbent fiber used in the present invention produced by the above method absorbs at least 1200% by weight of water. It is preferably at least 1800% by weight. If it exceeds 3000% by weight, the fiber strength is reduced. 20 ° C, relative humidity 60
% Is 15% by weight or more.

The method for producing the nonwoven fabric used in the present invention may be a general method. For example, a method of mixing heat-fused fibers by a needle punch method or an air-lay method may be used.

The freshness retaining sheet of the present invention contains 10 to 40% by weight of superabsorbent fibers. More preferably, it is 20 to 40% by weight. If it is less than 10% by weight, practically moisture absorption,
Insufficient water absorption capacity. If it exceeds 40% by weight, the air permeability is significantly reduced.

The density of the nonwoven fabric used for the freshness retaining sheet of the present invention is from 0.02 to 0.06 gr / cm ³ . If the density is less than 0.02 gr / cm ³ , the strength is insufficient,
If it exceeds 6 gr / cm ³ , the hygroscopicity decreases, and the surface of the sheet becomes wet.

The heat-fused fibers used in the present invention are not particularly limited. For example, there are commercially available fibers in which the core is made of polypropylene, the sheath is made of polyethylene, and the core is made of polyester, and the sheath is made of polyethylene. The blending ratio is 15 to 40% by weight. If it is less than 15% by weight, the strength of the nonwoven fabric is insufficient, and if it exceeds 40% by weight, the hand becomes hard.

More preferably, a film is laminated on the side not in contact with the atmosphere for maintaining strength, selectively permeating ethylene gas, and retaining moisture. The film used in the present invention has sufficient strength, and it is preferable to use a selective membrane that allows ethylene gas to permeate but does not allow water vapor to permeate. For example, a silicone-based film is known as a permselective membrane and is preferred.

In the freshness maintaining sheet of the present invention, it is preferable that the first layer is hydrophobic because the inner surface is dry-touched and is not easily drained.

[0023]

EXAMPLES Further details will be described in Examples. In Examples, “%” is “% by weight” unless otherwise specified. The water absorption of physiological saline in the superabsorbent fiber was measured according to DIN 53814, and the composition of the superabsorbent fiber was measured for the content of alkali metal salt by X-ray fluorescence analysis.

The monomer composition was measured by IR on a vacuum-dried sample, and the polymerization rate was measured using an ear-troscan MK5 (TL).
C / FID). The content of the superabsorbent fiber was determined from the dry weight after the other fiber was dissolved and washed. Fiber strength and the like were measured according to JIS L1015.

The moisture absorption of the superabsorbent fiber was determined from the weight after standing in a constant temperature room at room temperature of 20 ° C. and a relative humidity of 60% for one day and night and the absolute dry weight.

Production Example 1 Monomer concentration 15%, polymerization temperature 5 with the polymerization composition shown in Table 1.
Aqueous solution polymerization was carried out at 5 ° C. for 4 hours using sodium persulfate as a polymerization initiator. As a result of measuring the polymerization rate by TLC, there was no peak of the monomer, and thus the polymerization rate was practically 100%. Therefore, the polymerization composition of the obtained polymer coincided with the polymerization charge composition.

Next, the obtained polymer dope is concentrated,
The viscosity was adjusted to near 90 poise at 0 ° C. It was spun into a dry hot nitrogen stream and dried in the same manner as a commonly used dry spinning, and the yarn with 20% of water remaining was stretched 1.5 times at 100 ° C. dry heat. After crimping with a gear crimper, 12
Dry heat cross-linking treatment was performed at 0 ° C. for 5 minutes, and cut to obtain 10 denier, 51 mm superabsorbent fibers. Table 1 shows the moisture absorption and water absorption of the obtained superabsorbent fibers.

The obtained fiber had a mechanical strength of 1 gr / denier or more, and could be mounted on a normal card.

[0029]

[Table 1] Composition No. Sample No. 4 had a high water absorption but lacked crosslinking and was partially dissolved in water. Composition No. 5 was insufficient in moisture absorption and water absorption.

Production Example 2 Composition No. 1 produced in Production Example 1 2 super-absorbent fibers and commercially available core polyester, heat-fused fiber of sheath polyethylene 3 denier 51 mm Commercially available polyester cotton semi-dal 3 denier 51 mm are mixed in the ratio shown in Table 2, and nonwoven fabric is manufactured by a commonly used dry nonwoven method. did. That is, after blending, carding is performed, and a basis weight is set using a 110 ° C. pressure heater roller.
A non-woven fabric of 0 gr / m ² was produced. This nonwoven fabric was used for the second layer. The thickness of the obtained nonwoven fabric was about 0.9 mm. Table 2 shows the mixing ratio of this nonwoven fabric.

[0031]

[Table 2]

Next, commercially available 3 denier 51 mm of heat-bonded fiber of core polyester and sheath polyethylene and 51 mm of commercially available polyester cotton semi-dal 3 denier were mixed at 20% by weight and 80% by weight, and a 50 gr / m ² nonwoven fabric was similarly prepared. Manufactured. The thickness of the obtained nonwoven fabric was about 0.9 mm.
This nonwoven fabric was used for the first layer.

The first layer and the second layer of the nonwoven fabric were overlaid and bonded together by a heated embossing roller to produce a freshness maintaining sheet.

Example 1 Ripe peaches were watered, placed on a net for one minute, and drained. In the state where the surface of the peach is wet, it is wrapped with a two-layer nonwoven fabric freshness maintaining sheet produced in Production Example 2, placed in a cardboard box without any gap, and stored at 20 ° C. for 2 days.
The box was opened and peach drainage was checked, and the results are shown in Table 3.

[0035]

[Table 3]

Example 2 Formulation No. Wrap the ripe peaches in a non-woven freshness maintenance sheet consisting of only one layer from 1 to 4, place them in a cardboard box without any gaps, store at 20 ° C for 2 days, open the box and inspect the peaches for drainage did. No peach drainage occurred in all four types.

Comparative Example 1 A commercially available superabsorbent fiber of the type obtained by hydrolyzing and crosslinking an acrylic fiber was used. The freshness of peach was inspected in the same manner as in Example 1 for a freshness maintaining sheet manufactured by changing only the superabsorbent fiber in the preparation of No. 1. Due to low hygroscopicity, the surface of the peach did not dry and drained.

Comparative Example 2 Compound No. 2 was prepared in the same manner as in Production Example 2. In the preparation of No. 1, the gauge of the heating roller was expanded and the density was adjusted to 0.01 gr / cm ³ to produce a nonwoven fabric consisting of only one layer. However, the strength was insufficient and normal handling was not possible.

Comparative Example 3 Compound No. 3 was prepared in the same manner as in Production Example 2. In the preparation of No. 4, the gauge of the heating roller was narrowed, and the density was adjusted to 0.09 gr / cm ³ to produce a nonwoven fabric consisting of only one layer.
At the time of the freshness retention test, air permeability was poor, and drainage occurred.

Comparative Example 4 A nonwoven fabric consisting of only one layer was produced in the same manner as in Production Example 2 except that the blending amount of the superabsorbent fiber was changed to 10%, and the blending ratio of the heat-fusible fiber was changed to 10% and 50%. .

When the blending amount of the heat-fusible fiber was 10%, the strength of the nonwoven fabric was weak, and when it was 50%, the hand of the nonwoven fabric became too hard.

[0042]

The freshness retaining sheet of the present invention has high moisture absorption and high water absorption, and is effective in preventing drainage of fruits, vegetables and the like.

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) D04H 1/00-18/00 B32B 1/00-35/00 A23B ⁷ /00-7/16

Claims (3)

(57) [Claims] 1. A method for preserving freshness formed from a nonwoven fabric having a multilayer structure.
A supporting sheet, wherein the first layer is hydrophobic and the second layer is 2
10 to 40% by weight of superabsorbent fibers having a hygroscopicity of 15% by weight or more at 0 ° C. and 60% relative humidity;
A freshness retaining sheet comprising a nonwoven fabric containing 5 to 40% by weight. 2. The superabsorbent fiber comprises a monomer having a carboxylic acid group, a monomer having a hydroxyl group capable of reacting with the carboxylic acid group to form an ester crosslink, and a monomer having an alkali metal carboxylate. 2. The freshness preserving sheet according to claim 1, wherein the preserving sheet is a fiber that is polymerized and crosslinked by heat, and is a highly water-absorbing fiber that absorbs physiological saline in an amount of 1200% by weight or more and less than 3000% by weight. 3. The non-woven fabric of the second layer has a density of 0.02 to 0.06 gr / cm ^3.
The freshness retaining sheet as described.