JPH06158500A - Freshness retaining sheet - Google Patents

Abstract

PURPOSE:To obtain a freshness retaining sheet capable of packaging a fruit, a vegetable, etc., and retaining the freshness by laminating and integrating water absorbing nonwoven fabric containing highly water absorbing fiber and thermally fusible fiber with hydrophobic nonwoven fabric. CONSTITUTION:A monomer having carboxylic acid group such as acrylic acid is copolymerized with a monomer having hydroxyl group such as hydroxyethyl methacrylate and a monomer having an alkali metallic carboxylate such as sodium acrylate and the resultant copolymer is then dry spun, dry hot drawn and dry heat-treated to cross-link the copolymer with esters. Thereby, highly water absorbing fiber capable of absorbing water of >=1200 and <300wt.% physiologically saline solution and >=15wt.% hygroscopicity at 20 deg.C and RH <=60% is obtained. The resultant highly water absorbing fiber in an amount of 10-40wt.% and thermally fusible fiber in an amount of 15-40wt.% are used to form water absorbing nonwoven fabric having 0.02-0.06g/cm<2> density. Polyester-based hydrophobic nonwoven fabric as the first layer is laminated on the water absorbing nonwoven fabric as the second layer, joined and integrated with a heated embossing roller to afford this sheet having a multilayered structure.

Description

Detailed Description of the Invention

[0001]

The present invention relates to packaging fruits, vegetables and the like,
The present invention relates to freshness retaining sheets that retain freshness.

[0002]

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

Further, the highly water-absorbent fiber having a high moisture absorption rate has a large swelling degree, and when the content of the nonwoven fabric is 50% by weight or more, the air permeability is remarkably lowered, and it is not effective for keeping freshness.

[0004]

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

[0005]

Means for Solving the Problems The inventors of the present invention have completed the present invention by studying the formulation and morphology of the highly hygroscopic and highly water-absorbent fibers which have high water absorbency and high hygroscopicity.

That is, the freshness keeping sheet of the present invention is characterized by comprising a non-woven fabric containing 10 to 40% by weight of highly water-absorbent fibers and 15 to 40% by weight of heat-sealing fibers.

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-linking bond, and a monomer having an alkali metal carboxylic acid base are copolymerized and cross-linked by heat. Fiber, and physiological saline more than 1200% by weight, 3
A freshness-maintaining sheet comprising a highly water-absorbent fiber which absorbs less than 000% by weight and has a hygroscopicity of 15% by weight or more at 20 ° C. and a relative humidity of 60%.

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

As the monomer having a carboxylic acid alkali metal base, for example, an alkali metal salt of AA, methacrylic acid, maleic acid, etc. is used. As the alkali metal, sodium (hereinafter abbreviated as “Na”), potassium or the like is used. The ratio of the monomer having a carboxylic acid group to the monomer having an alkali metal carboxylate base is from 1/1 to 1/10. The total amount of the monomer having a carboxylic acid group and the monomer having an alkali metal carboxylate is 70% by weight to 99.5% by weight. It is preferably 80% by weight or more. If it is less than 70% by weight, the water absorption rate of physiological saline is insufficient.

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

Each of these monomers may be used in plural types. The monomer having a hydroxyl group is contained in an amount of 0.5% by weight or more in an amount equal to or less than that of free acrylic acid. 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
It is abbreviated as "A". ), Acrylonitrile or the like may be used. The amount of the monomer for plasticizing is preferably 30% by weight or less.

The polymerization method used in the present invention is not particularly limited, but if the monomer composition is water-soluble, water-based polymerization may be carried out. As the polymerization initiator, generally used sodium persulfate or the like may be used.

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

After the dry spinning, the film is stretched 1.3 times or more by dry heat with 10% by weight or more of water remaining, and then crosslinked by dry heat. Appropriate crimping and cutting. Water is 1
Unless 0% by weight or more remains, the strength of the fiber becomes insufficient unless it is drawn by 1.3 times or more by dry heat. A fiber having a large molecular weight has a large water absorption amount, but on the other hand, since the fiber has a large molecular weight, it is difficult to stretch and the fiber strength becomes low.

The superabsorbent fiber used in the present invention produced by the above method absorbs 1200% by weight or more of water. It is preferably 1800% by weight or more. If it exceeds 3000% by weight, the fiber strength will decrease. 20 ° C, relative humidity 60
% Is a highly hygroscopic fiber having a hygroscopicity of 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 the heat-sealing fibers by a needle punch method or an air lay method may be used.

The freshness keeping sheet of the present invention contains 10 to 40% by weight of super absorbent fiber. It is more preferably 20 to 40% by weight. If it is less than 10% by weight, it will absorb moisture practically.
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 keeping sheet of the present invention is 0.02 to 0.06 gr / cm ³ . If the density is less than 0.02 gr / cm ³ , the strength is insufficient, and 0.0
If it exceeds 6 gr / cm ³ , the hygroscopicity decreases and the surface of the sheet becomes wet.

The heat-sealing fiber used in the present invention is not particularly limited. For example, commercially available fibers include a polypropylene core, a sheath composite of polyethylene, a core polyester, and a sheath composite fiber. 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 texture becomes hard.

More preferably, a film is laminated on the side not exposed to the atmosphere for strength retention, selective permeation of ethylene gas and water retention. The film used in the present invention has a sufficient strength, and it is preferable to use a selective membrane that is permeable to ethylene gas but impermeable to water vapor. For example, a silicone-based film is known as a selectively permeable membrane and is preferable.

In the freshness keeping sheet of the present invention, it is preferable that the first layer is hydrophobic because the inner surface has a dry touch and is less likely to be drained.

[0023]

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

Further, the monomer composition was measured by IR in a vacuum-dried sample, and the polymerization rate was calculated by Eartroscan MK5 (TL
C / FID). The content of the super absorbent fiber was determined from the dry weight after dissolving other fibers and washing. Fiber strength and the like were measured according to JIS L 1015.

The moisture absorption rate of the highly water-absorbent fiber was determined from the weight after standing overnight in a thermostatic chamber at room temperature of 20 ° C. and relative humidity of 60% and the absolute dry weight.

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

Next, the obtained polymer dope was concentrated and
The viscosity was adjusted to near 90 poise at 0 ° C. In the same manner as dry spinning generally used, the yarn was spun in a dry nitrogen stream and dried, and the yarn containing 20% of water was drawn 1.5 times at 100 ° C. in dry heat. 12 after crimping with gear crimper
Dry heat crosslinking treatment was carried out at 0 ° C. for 5 minutes and cut to obtain 10 denier and 51 mm super absorbent fiber. Table 1 shows the moisture absorption rate and water absorption rate of the obtained super absorbent fibers.

The mechanical strength of the obtained fiber was 1 gr / denier or more, and it could be mounted on an ordinary card.

[0029]

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

Production Example 2 Composition No. produced in Production Example 1 2 super absorbent fiber and commercially available core polyester, sheath polyethylene heat fusion fiber 3 denier 51 mm commercially available polyester cotton semi-dall 3 denier 51 mm were blended in the ratio shown in Table 2, and a non-woven fabric was produced by a commonly used dry non-woven fabric method. did. That is, after blending, carding and weighting with a pressure heater roller at 110 ° C 5
A non-woven fabric of 0 gr / m ² was produced. This non-woven fabric was used for the second layer. The thickness of the obtained non-woven fabric was about 0.9 mm. The blending ratio of this non-woven fabric is shown in Table 2.

[0031]

[Table 2]

Next, commercially available core polyester and sheath polyethylene heat-sealing fibers 3 denier 51 mm Commercial polyester polyester semi-dial 3 denier 51 mm was compounded at 20% by weight and 80% by weight, and a nonwoven fabric of 50 gr / m ² was similarly prepared. Manufactured. The thickness of the obtained non-woven fabric was about 0.9 mm.
This non-woven fabric was used for the first layer.

The first layer and the second layer of non-woven fabric were overlaid and bonded to each other with a heating embossing roller to produce a freshness-keeping sheet.

Example 1 Ripe peaches were sprinkled with water, placed on a net for 1 minute and drained. Wrap the surface of the peach in a freshness-preserving sheet made of the two-layered non-woven fabric produced in Production Example 2 and put it in a cardboard box with no gaps, and store it at 20 ° C. for 2 days.
The box was opened, and the peach was examined for water loss. The results are shown in Table 3.

[0035]

[Table 3]

Example 2 Formulation No. Wrap a ripe peach in a non-woven fabric freshness-preserving sheet consisting of 1 to 4 layers, put it in a cardboard box with no gaps, store at 20 ° C for 2 days, and then open the box to inspect the peach for water loss. did. No peach water loss occurred in all four species.

Comparative Example 1 A commercially available highly water-absorbent fiber of a type obtained by hydrolyzing and cross-linking acrylic fiber was used, and the compounding No. In the same manner as in Example 1, the freshness-retaining sheet produced by changing only the highly water-absorbent fiber in the preparation of No. 1 was tested for the water loss condition of the peach. Due to its low hygroscopicity, the surface of the peach did not dry, causing water loss.

Comparative Example 2 Preparation No. 2 was carried out in the same manner as in Production Example 2. With the preparation of No. 1, the gauge of the heating roller was widened and the density was adjusted to 0.01 gr / cm ³ to produce a nonwoven fabric consisting of only one layer, but the strength was insufficient and it could not be handled normally.

Comparative Example 3 In the same manner as in Production Example 2, compound No. Although the gauge of the heating roller was narrowed and the density was adjusted to 0.09 gr / cm ³ with the formulation of 4, a non-woven fabric consisting of only one layer was produced.
During the freshness retention test, the air permeability was poor and water loss occurred.

Comparative Example 4 In the same manner as in Production Example 2, the amount of highly water-absorbent fibers mixed was changed to 10% and the amount of heat-sealing fibers was changed to 10% and 50%, respectively, to produce a nonwoven fabric having only one layer. .

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

[0042]

The freshness keeping sheet of the present invention has high hygroscopicity and high water absorption, and is effective in preventing water loss of fruits and vegetables.

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location A23B 7/148 9281-4B B32B 5/26 7016-4F 27/12 7258-4F

Claims (5)

[Claims] 1. A freshness-keeping sheet comprising a non-woven fabric containing 10 to 40% by weight of highly water-absorbing fibers and 15 to 40% by weight of heat-sealing fibers. 2. 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-linking bond, and a monomer having an alkali metal carboxylic acid base are copolymerized and cross-linked by heat. Characterized in that it contains a highly water-absorbent fiber which absorbs 1200% by weight or more and less than 3000% by weight of physiological saline and has a hygroscopicity of 15% by weight or more at 20 ° C. and 60% relative humidity. The freshness preservation sheet according to claim 1. 3. The freshness-retaining sheet according to claim 1, wherein one side of the sheet is laminated with a silicone-based film that selectively permeates ethylene gas. 4. The freshness keeping sheet according to claim 1, wherein the density of the non-woven fabric containing the super absorbent fiber is 0.02 to 0.06 gr / cm ³ . 5. The freshness-retaining sheet according to claim 1, wherein the non-woven fabric forms a multilayer structure, the first layer is hydrophobic, and the second layer is water-absorbent.