JP2006326838A - Hygroscopic sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hygroscopic sheet having high hygroscopicity capable of being installed in a narrow space without becoming bulky. <P>SOLUTION: The hygroscopic sheet 10 is constituted of a moisture absorbable sheet 11, the desiccant layer 12 formed on the surface of the moisture permeable sheet 11 and the pressure-sensitive adhesive layer 13 formed on the surface of the desiccant layer 12. The desiccant layer 12 is constituted of a desiccant and a binder resin for fixing the desiccant. As the desiccant, a substance causing a irreversible chemical reaction with respect to moisture, stable in a solution of the binder resin and acquired inexpensively is preferable and particles comprising calcium oxide can be used suitably. As the moisture permeable sheet 11, a sheet permitting the permeation of moisture and hardly permeable to carbon dioxide is preferable and a cellophane sheet is preferably used. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to precision instruments and parts thereof (organic EL elements, semiconductor devices, etc.), musical instruments (piano, etc.), pharmaceuticals (tablets, etc.), foodstuffs (dry noodles, salt, etc.), clothing, shoes, etc. The present invention relates to a hygroscopic material suitable for moisture absorption and moisture prevention of articles whose efficacy, flavor and texture are deteriorated, particularly a sheet-like hygroscopic material (referred to as “moisture absorbent sheet”).

  A hygroscopic material in which a desiccant such as silica gel or zeolite is contained in a bag made of a breathable sheet is used for moisture absorption and moisture prevention of precision instruments and parts thereof, pharmaceuticals, foodstuffs, musical instruments and the like (Patent Document 1, 2). For example, there is a bag in which a desiccant is enclosed in a bag formed by stacking two breathable sheets made of synthetic fibers. In such a hygroscopic material, since the desiccant is only put in the bag, almost all of the added desiccant can contribute to moisture prevention and moisture absorption, but if the posture of the hygroscopic material is changed, the desiccant moves. It is difficult to keep the shape of the hygroscopic material, in particular, the thickness, not only bulky, but also to arrange such a hygroscopic material in a narrow space to prevent moisture or moisture absorption in this space. .

  Further, in order to absorb (or prevent moisture) the article, there is a hygroscopic material in which a desiccant is disposed on the inner surface of a container for housing the article (see Patent Documents 3, 4, and 5). For example, in an organic EL display, an organic molecule reacts with oxygen and moisture (humidity) and deteriorates to shorten the lifetime of the display. Therefore, a transparent electrode layer such as ITO, an organic EL light emitting layer, and a counter electrode layer are formed on a glass substrate. Is disposed on the inner surface of the lower portion of the sealing cap that seals the organic EL laminate. As this desiccant, particles such as anhydrous calcium sulfate of 20 μm to 200 μm are used, and the desiccant is adhered and held on the adhesive layer formed on the lower inner surface of the sealing cap having a depth of about 0.4 mm. It is covered with a breathable sheet made of synthetic fiber having a thickness of 20 μm to 200 μm. However, when adhering the particulate desiccant, the excess desiccant is simply shaken off, so that the desiccated desiccant remains attached to the inner surface of the sealing cap. When the organic EL laminated body is sealed, the desiccant adhering to the sealing cap drops and floats, and adheres to the organic EL laminated body, thereby contaminating the organic EL laminated body.

Furthermore, there is a hygroscopic material in which a desiccant is kneaded into a bag or wrapping paper for storing articles (see Patent Document 6). For example, there is a sheet material made of a thermoplastic resin kneaded with a desiccant. In such a sheet material, the thickness can be set to 60 μm to 200 μm. However, if the amount of the desiccant kneaded into the thermoplastic resin is increased, the bag becomes brittle, so that a large amount of desiccant cannot be kneaded. High hygroscopicity cannot be obtained. Moreover, since only the desiccant located on the surface portion of the sheet material only contributes to moisture prevention and moisture absorption, high hygroscopicity cannot be obtained.
JP 2000-188367 A JP 2000-202011 A JP 2001-185349 A JP 2001-23507 A JP-A-10-34791 JP-A-10-272168 Organic EL displays, nanoelectronics, future issues and prospects, http: // www. nanoelectronics. jp / kaitai / oel / 7. htm

  Accordingly, an object of the present invention is to provide a hygroscopic sheet having high hygroscopicity that can be installed without being bulky in a narrow space and does not drop the desiccant.

  The moisture absorbent sheet of the present invention that achieves the above object is composed of a moisture permeable sheet, a desiccant layer formed on the surface of the moisture permeable sheet, and an adhesive layer formed on the surface of the desiccant layer.

  The desiccant layer is composed of a desiccant and a binder resin that fixes the desiccant, and particles made of calcium oxide are used as the desiccant. In addition, a sheet having permeability to moisture (permeating moisture) is used as the moisture permeable sheet, and a cellophane sheet, an acetate sheet, or a nylon sheet is used as the sheet that transmits moisture. Preferably, as the moisture permeable sheet, a sheet having permeability to moisture and hardly permeable to carbon dioxide gas (not easily permeable to carbon dioxide gas) is used, and a cellophane sheet is preferably used as this sheet. The

  The hygroscopic sheet of the present invention moisture-proofs an article by adhering the pressure-sensitive adhesive layer to the article or the package of the article.

  Since the present invention is configured as described above, the hygroscopic material can be installed without being bulky in a narrow space, and the desiccant is not dropped off. Moreover, a high hygroscopicity can be exhibited for a long time while being a thin sheet.

  As shown in FIG. 1, the moisture absorbent sheet 10 of the present invention includes a moisture permeable sheet 11, a desiccant layer 12 formed on the surface of the moisture permeable sheet 11, and an adhesive layer 13 formed on the surface of the desiccant layer 12. Consists of

  The desiccant layer 12 includes a desiccant and a binder resin that fixes the desiccant. As the binder resin, a binder resin such as polyester or polyurethane is used.

As the desiccant, those which cause an irreversible chemical reaction with moisture, are stable in a binder resin solution and can be obtained at low cost, and particles made of calcium oxide are preferably used. The average particle diameter of the particles made of calcium oxide is in the range of 0.1 μm to 50 μm.

A sheet having permeability to moisture is used as the moisture-permeable sheet, and a cellophane sheet, an acetate sheet, or a nylon sheet having a thickness in the range of 10 μm to 100 μm is used as the sheet that transmits moisture.

Calcium oxide reacts with water to form calcium hydroxide, but further reacts in the presence of carbon dioxide gas to form calcium carbonate, releasing water, and its drying power (moisture absorption capacity) is impaired. For this reason, preferably, a sheet that is permeable to moisture and hardly permeable to carbon dioxide gas is used as the moisture-permeable sheet 11, and the thickness is preferably in the range of 10 μm to 100 μm. A certain cellophane sheet is used. As shown in Table 1 below, the cellophane sheet has the lowest oxygen permeability compared to the acetate sheet and the nylon sheet, and is therefore considered to have the property of being hardly permeable to carbon dioxide gas. Because.

<Example> The moisture absorption sheet of the Example was manufactured. Calcium oxide (90 parts by weight), 30 wt% polyurethane resin solution (72 parts by weight), methyl ethyl ketone (9 parts by weight), and anone (1 part by weight) were charged into a pot mill and dispersed (48 hours). After dispersion, 75 wt% isocyanate (3 parts by weight) is added to produce a paint, and a comma coater is applied to the surface of a cellophane sheet (thickness 20 μm) (permeate moisture but hardly permeate carbon dioxide). It was applied and dried to form a desiccant layer on the surface of the cellophane sheet. The paint was applied to the surface of the cellophane sheet so that the thickness of the desiccant layer after drying the paint was 80 μm.

Next, an acrylic pressure-sensitive adhesive is applied to the surface of the release sheet and dried to form a pressure-sensitive adhesive layer having a thickness of 20 μm on the surface of the release sheet. The surface of this pressure-sensitive adhesive layer is the surface of the desiccant layer. The moisture absorbent sheet of the example with a release sheet was manufactured (ie, laminated) (the thickness excluding the pressure-sensitive adhesive layer was 100 μm).

<Comparative example> The moisture absorption sheet of the comparative example was manufactured. The same paint as that of the above example was applied to the surface of a 24 μm thick polyethylene terephthalate (PET) sheet (used as a base sheet) using a comma coater, dried, and then dried onto the surface of the polyester sheet. A layer was formed. The paint was applied to the surface of the polyester sheet so that the thickness of the desiccant layer after drying the paint was 80 μm.

Next, an acrylic pressure-sensitive adhesive is applied to the surface of the release sheet and dried to form a pressure-sensitive adhesive layer having a thickness of 20 μm on the surface of the release sheet. A comparative moisture-absorbing sheet with a release sheet was produced by pasting (that is, laminating) (the thickness excluding the adhesive layer was 104 μm).

<Comparative test> The moisture absorbing sheets with release sheets of the examples and comparative examples were cut into test pieces having a size of 6 cm x 6 cm, each release sheet was peeled off, and each test piece was put in a petri dish, and 80% The specimens were left in a constant temperature and humidity chamber with relative humidity, and the moisture absorption rates of these test pieces were compared.

<Test Results> Table 2 below shows the time-series weight changes and moisture absorption rates of the test pieces of the moisture absorbent sheets of Examples and Comparative Examples. Here, the moisture absorption rate was calculated using Equation 1 below.

  About the difference in the structure of the moisture absorption sheet of an Example and a comparative example, in the moisture absorption sheet of an Example, the desiccant layer is covered with the cellophane sheet which permeate | transmits a water | moisture content but cannot permeate | transmit a carbon dioxide gas easily. On the other hand, in the hygroscopic sheet of the comparative example, the desiccant layer is directly exposed to the outside air.

Theoretically, the moisture absorption of the calcium oxide used as the desiccant with respect to moisture is about 32%. When the comparative test results in Table 2 are analyzed based on the theoretical value of the moisture absorption rate, the calcium oxide in the desiccant layer absorbs moisture in both the moisture absorbent sheet of the example and the comparative example. However, in the hygroscopic sheet of the comparative example, the calcium oxide in the desiccant layer comes into contact with a large amount of carbon dioxide in the outside air as compared with the example. For this reason, in the moisture absorbent sheet of the comparative example, the calcium oxide in the desiccant layer not only absorbs moisture, but also reacts in a larger amount with carbon dioxide in the outside air than in the example to become calcium carbonate. This releases more water. As a result, as shown in Table 2 above, the moisture absorption rate of the moisture absorbent sheet of the comparative example is higher than that of the example. That is, the moisture absorbing sheet of the example has a smaller amount of calcium oxide that reacts with carbon dioxide gas to become calcium carbonate than the comparative example (that is, the amount of calcium oxide that functions as a desiccant is larger). From this, the high hygroscopicity of calcium oxide used as a desiccant can be exhibited relatively stably for a long time.

Further, in the moisture absorbent sheet of the example, since the desiccant layer is covered with a cellophane sheet (moisture permeable sheet), the edge part of the desiccant layer is slightly deformed in a wave shape, and the desiccant does not fall off. It was. However, in the hygroscopic sheet of the comparative example, the desiccant was dropped.

FIG. 1 is a cross-sectional view of the moisture absorbent sheet of the present invention.

Explanation of symbols

10 ... Hygroscopic sheet 11 ... Moisture permeable sheet 12 ... Desiccant layer 13 ... Adhesive layer

Claims (6)

A moisture absorbing sheet,
Moisture permeable sheet,
A desiccant layer formed on the surface of the moisture-permeable sheet, and an adhesive layer formed on the surface of the desiccant layer,
Hygroscopic sheet consisting of. The moisture absorbent sheet according to claim 1,
The desiccant layer is
A desiccant and a binder resin for fixing the desiccant;
Consisting of
As the desiccant, particles made of calcium oxide are used.
However, a hygroscopic sheet. The moisture absorbent sheet according to claim 1,
As the moisture permeable sheet, a sheet having permeability to moisture is used.
However, a hygroscopic sheet. The moisture absorbent sheet according to claim 3,
Cellophane sheet, acetate sheet, or nylon sheet is used as the sheet.
However, a hygroscopic sheet. The moisture absorbent sheet according to claim 1,
As the moisture permeable sheet, a sheet having permeability to moisture and hardly permeable to carbon dioxide gas is used.
However, a hygroscopic sheet. The moisture absorbent sheet according to claim 5,
A moisture absorbing sheet where a cellophane sheet is used as the sheet.

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