Moisture-absorbing sheet for absolute dryness

Abstract

A moisture-absorbing sheet for absolute dryness, which is for application to adherends having water contents of 2,500 ppm or less, the moisture-absorbing sheet being characterized by comprising a resin layer (A), a moisture-absorbing layer, and a resin layer (B) stacked in this order and also characterized in that the moisture-absorbing layer is formed from a binder resin having a Tg of 0°C or lower, the binder resin is an olefin-based resin, the binder resin contains calcium oxide having a median diameter (D50) of 20 μm or smaller in an amount of 5-20 wt%, the resin layer (A) and the resin layer (B) are each a skin layer or a pressure-sensitive adhesive layer, the resin layer (A) and the resin layer (B) each have a thickness of 3-20 μm, and the moisture-absorbing layer has a thickness of 20-30 μm.

Description

Moisture-absorbing sheet for deep drying

[0001] The present invention relates to a moisture-absorbent sheet, and more particularly to a moisture-absorbent sheet for bone-dry use to be used on an adherend with a low moisture content.

[0002] Conventionally, moisture-absorbing sheets (also called water-absorbing sheets or desiccant sheets) having a moisture-absorbing layer in which a desiccant is dispersed have been widely used for absorbing moisture and preventing moisture. Various layer configurations have been proposed for such moisture-absorbing sheets. Patent Document 1 proposes a moisture-absorbing sheet consisting of a desiccant layer, a moisture-permeable sheet provided on one side of the desiccant, and an adhesive layer provided on the other side of the desiccant layer, and describes that cellophane sheets, acetate sheets, nylon sheets, etc. are used as the moisture-permeable sheet. Patent Documents 2 and 3 also describe desiccant sheets having a moisture-absorbing layer in which a desiccant is dispersed.

[0003] Recently developed electronic devices, such as organic electroluminescence (organic EL) displays, solar cell panels, liquid crystal touch panels, and electronic paper, are sensitive to charge leakage, and therefore the plastic substrates or circuit boards forming these devices must be dried to an extremely low moisture content (bone-dry state). The sheets described in Patent Documents 1 to 3 are known to have a certain moisture-absorbing effect on adherends with high moisture content. However, since the plastic substrates or circuit boards are dried to a certain extent during their manufacturing process, their moisture content is already low, making it difficult to dry adherends with low moisture content, such as plastic substrates or circuit boards, to an bone-dry state.

[0004] Therefore, for products requiring extremely low moisture content, such as plastic substrates or circuit boards, drying has been required by batch processing, in which the products are heated in a nitrogen atmosphere or vacuum environment, such as in a glove box. However, such batch processing has a problem of low processing efficiency because the volume of the glove box is limited and it is not possible to dry a large amount of adherends. In addition, the humidity inside the glove box must be kept extremely low, making it very complicated to create a drying environment. Therefore, a more efficient method for drying plastic substrates, circuit boards, etc., has been desired.

[0005] JP 2006-326838 A JP 2019-177645 A JP 2019-179705 A

[0006] An object of the present invention is to provide a moisture-absorbing sheet for bone-dry use that can dry an adherend having a low moisture content to bone-dry condition.

[0007] The present inventors discovered that a resin film containing calcium oxide as a desiccant can make an adherend with a low moisture content into an absolutely dry state by selecting conditions such as the particle size and concentration of the calcium oxide, and this led to the completion of the present invention.

[0008] According to the present invention, there is provided a moisture-absorbent sheet for bone-dry use, which is used on an adherend having a moisture content of 2500 ppm or less, characterized in that the moisture-absorbent sheet is formed by laminating a resin layer (A), a moisture-absorbent layer, and a resin layer (B) in this order, the moisture-absorbent layer is formed from a binder resin having a Tg of 0°C or less, the binder resin is an olefin-based resin and contains 5 to 20% by weight of calcium oxide having a median diameter (D50) of 20 μm or less, the resin layer (A) and the resin layer (B) are skin layers or adhesive layers, the thicknesses of the resin layer (A) and the resin layer (B) are 3 to 20 μm, and the thickness of the moisture-absorbent layer is 20 to 30 μm.

[0009] The moisture-absorbing sheet of the present invention can preferably adopt the following features: (1) The moisture content of the adherend is 2000 ppm or less, (2) The sheet is held in a roll body in a state adjacent to the adherend or laminated with the adherend via an adhesive layer of 4 μm or less.

[0010] Furthermore, according to the present invention, there is provided an oven-drying method in which the moisture-absorbing sheet for oven-drying is laminated adjacent to the adherend or via an adhesive layer of 4 μm or less, and the sheet is allowed to stand at 23° C. for 7 days, thereby reducing the moisture content of the adherend to 100 ppm or less.

[0011] The moisture-absorbent sheet of the present invention can be used on adherends with low moisture content to dry the adherend to an absolute dry state. Furthermore, the moisture-absorbent sheet of the present invention can be held in a roll, adjacent to the adherend or laminated via an adhesive layer. This allows for higher drying efficiency than batch processing. Furthermore, the moisture-absorbent sheet of the present invention can dry the adherend to an absolute dry state at room temperature, making drying easier than batch processing.

[0012] Figure 1 shows an example of the layer structure of the moisture-absorbent sheet of the present invention. Figure 2 shows an example of the layer structure when the moisture-absorbent sheet of the present invention is bonded to an adherend. Figure 3 shows another example of the layer structure when the moisture-absorbent sheet of the present invention is bonded to an adherend. Figure 4 shows an example of the moisture-absorbent sheet of the present invention bonded to an adherend and rolled up. Figure 5 shows an example of the layer structure when multiple moisture-absorbent sheets of the present invention are bonded to an adherend.

[0013] <Moisture-absorbing sheet 1> As shown in Fig. 1, the moisture-absorbing sheet 1 of the present invention is formed by laminating, in this order, a resin layer (A) 5, a moisture-absorbing layer 3, and a resin layer (B) 7. This moisture-absorbing sheet 1 is formed by laminating the respective layers by co-extrusion.

[0014] The thickness of the moisture-absorbent sheet 1 of the present invention is set to a thickness that achieves the desired amount of water absorption depending on the amount of calcium oxide blended in the moisture-absorbent layer 3, but is generally preferably in the range of 26 to 70 μm, and particularly 30 to 65 μm. If the thickness of the moisture-absorbent sheet 1 is less than 26 μm, the amount of calcium oxide particles will be insufficient, resulting in a decrease in drying properties and a decrease in the strength of the moisture-absorbent sheet 1, making it more susceptible to breakage. On the other hand, if the thickness of the moisture-absorbent sheet 1 is more than 70 μm, the excessive thickness will result in unnecessary increases in costs.

[0015] It is desirable that the thickness variation of the moisture-absorbent sheet 1 of the present invention be within the range of ±6 μm, preferably ±5 μm. In particular, if the variation in the widthwise thickness of the moisture-absorbent sheet 1 exceeds ±6 μm, when the moisture-absorbent sheet 1 is produced in a long roll, variation will occur in the winding pressure in the widthwise direction of the roll, resulting in partial sagging of the moisture-absorbent sheet 1. This is because the partial sagging may cause processing defects such as the introduction of wrinkles when the moisture-absorbent sheet 1 and the adherend 9 are bonded together.

[0016] The moisture-absorbent sheet 1 of the present invention can be colored. When the moisture-absorbent sheet 1 is colored, it can be given a design feature. When forming the resin layer (A), the resin layer (B), and the moisture-absorbent layer described below, a desired pigment can be mixed with the resin forming any one or more layers to obtain a colored moisture-absorbent sheet 1.

[0017] Each layer constituting the moisture-absorbent sheet 1 of the present invention will be described below.

[0018] <Moisture Absorbing Layer 3> The moisture absorbing layer 3 is a layer formed between the resin layer (A) 5 and the resin layer (B) 7. The moisture absorbing layer 3 is formed from a binder resin containing calcium oxide as a desiccant.

[0019] <Calcium oxide> In the present invention, calcium oxide is used as a desiccant. Calcium oxide is a type of chemical desiccant that chemically reacts with water. Calcium oxide is suitable for use as a desiccant because it has moderate water reactivity, stably maintains its granular shape, and is relatively inexpensive. The reaction between calcium oxide and water is expressed by the following formula: CaO + H ２ O → Ca(OH) ２

[0020] The median diameter (D50) of calcium oxide, which serves as a desiccant, is 20 μm or less, preferably 10 μm or less, and more preferably 5 μm or less. This median diameter is measured as a particle size converted into volume by, for example, laser diffraction scattering, and refers to the particle diameter at which the cumulative distribution value is 50%. If the median diameter (D50) of calcium oxide is greater than 20 μm, drying properties are reduced, making it difficult to achieve an absolute dry state for the adherend 9. In addition, there is a risk of particles protruding from the binder resin and transferring to the adherend 9. Furthermore, since calcium oxide is mixed with a resin to form the moisture-absorbing layer 3, it is desirable to select a calcium oxide particle diameter smaller than the thickness of the moisture-absorbing layer 3. This is because if the particles have a diameter larger than the thickness of the moisture-absorbing layer 3, there is a risk that the particles will protrude from the binder resin and be transferred to the adherend 9, as described above, and further problems will arise such as defects being formed in the moisture-absorbing layer 3 or the layer surface becoming rough, preventing the layer from fully exhibiting its original moisture-absorbing function.

[0021] Furthermore, calcium oxide is preferably contained in the moisture-absorbing layer 3 formed by mixing with the binder resin in a range of 5 to 20% by weight, particularly 8 to 18% by weight. If the calcium oxide content is less than 5% by weight, drying properties are reduced, making it difficult to dry the adherend 9. On the other hand, if the calcium oxide content is more than 20% by weight, the particles may aggregate, causing them to protrude from the binder resin and transfer to the adherend 9, or the processability of the sheet itself may be reduced.

[0022] Furthermore, calcium oxide may be surface-treated with a small amount of a surface treatment agent, such as a metal salt of a higher fatty acid such as zinc stearate or calcium stearate, to the extent that its drying properties are not impaired, thereby improving its dispersibility in resins.

[0023] <Binder Resin> In the present invention, a resin having a Tg (glass transition temperature of the resin) of 0°C or lower is used as the resin in which calcium oxide is dispersed, i.e., the binder resin. When the Tg is 0°C or lower, the resin becomes soft and rubbery at room temperature, making the resin more mobile at low temperatures and activating the movement of moisture, thereby improving the drying properties of the moisture-absorbing sheet 1 on the adherend 9. In the present invention, an olefin-based resin is preferably used as such a binder resin having a Tg of 0°C or lower. Furthermore, olefin-based resins are suitable as binder resins because they have a low water content and can fully exhibit the performance of a desiccant.

[0024] In the present invention, calcium oxide, which serves as a desiccant, is dispersed in a resin by melt-kneading the aforementioned amount of calcium oxide with the resin, and the resin composition prepared by melt-kneading is then melt-extruded to form the moisture-absorbing layer 3. Therefore, in forming the moisture-absorbing layer 3, it is possible to form a desiccant masterbatch in advance and then knead it with a binder resin, as in the examples described below, and a base material for the desiccant masterbatch that can be kneaded with the binder resin of the moisture-absorbing layer 3 and molded can be used.

[0025] The thickness of the moisture absorbent layer 3 is set to a thickness that achieves the desired amount of water absorption depending on the amount of calcium oxide blended in the moisture absorbent layer 3, and is generally preferably in the range of 20 to 30 μm, and particularly 22 to 28 μm. If the thickness of the moisture absorbent layer 3 is less than 20 μm, the amount of calcium oxide particles will be insufficient, resulting in poor drying properties. On the other hand, if the thickness of the moisture absorbent layer 3 is greater than 30 μm, unnecessary costs will increase.

[0026] <Resin Layer (A) 5> The resin layer (A) 5 is a layer provided on one surface of the moisture-absorbent sheet 1. The resin layer (A) 5 is a skin layer or an adhesive layer. This resin layer (A) 5 can prevent moisture from penetrating from the outside into the moisture-absorbent layer 3, allowing the moisture-absorbent sheet 1 to maintain its drying function for a long period of time. When the resin layer (A) 5 is a skin layer, a thermoplastic resin is generally used, and for example, a resin such as low-density polyethylene (LDPE) can be used. When the resin layer (A) 5 is an adhesive layer, for example, a resin having adhesive properties such as ethylene-vinyl acetate copolymer (EVA), soft polyolefin (LLDPE), or metallocene polyolefin elastomer can be used.

[0027] The thickness of the resin layer (A) 5 is preferably 3 to 20 μm, and more preferably 5 to 18 μm. If the thickness of the resin layer (A) 5 is less than 3 μm, there is a risk that the calcium oxide particles may protrude and be transferred to the adherend 9. On the other hand, if the thickness of the resin layer (A) 5 is more than 20 μm, when the resin layer (A) 5 is provided on the adherend 9 side, the distance from the adherend 9 increases, resulting in a decrease in drying properties. Furthermore, when the resin layer (A) 5 is provided on the side opposite the adherend 9, the thickness becomes excessive in terms of suppressing moisture permeation from the outside. Furthermore, regardless of the location where the resin layer (A) 5 is provided, if the resin layer (A) 5 is excessively thick, the overall thickness of the moisture-absorbent sheet 1 increases, which may make it difficult to bond the resin layer (A) 5 to the adherend 9 to form the roll body 13 described below.

[0028] <Resin Layer (B) 7> The resin layer (B) 7 is a layer provided on the other surface of the moisture-absorbent sheet 1 (i.e., the surface opposite to the resin layer (A) 5). The resin layer (B) 7 is a skin layer or an adhesive layer. The presence of this resin layer (B) 7 makes it possible to prevent moisture from penetrating from the outside into the moisture-absorbent layer, and the drying function of the moisture-absorbent sheet 1 can be maintained for a long period of time. The same resin types as those used for the resin layer (A) 5 can be used for the skin layer or adhesive layer of the resin layer (B) 7. For the same reasons as for the resin layer (A) 5, the thickness of the resin layer (B) 7 is also preferably 3 to 20 μm, and more preferably 5 to 18 μm.

[0029] <Adherend 9> The moisture-absorbent sheet 1 of the present invention is used to dry the adherend 9. The adherend 9 is characterized by having a moisture content of 2500 ppm or less, preferably 2000 ppm or less. In other words, by using the moisture-absorbent sheet 1 of the present invention, it is possible to dry the adherend 9, which already has a low moisture content, to an absolutely dry state.

[0030] The moisture-absorbent sheet 1 of the present invention can dry the adherend 9 by being adjacent to the adherend 9 or by being laminated via an adhesive layer. FIG. 2 shows the layer structure when the moisture-absorbent sheet 1 is adjacent to the adherend 9, and FIG. 3 shows the layer structure when the moisture-absorbent sheet 1 is laminated to the adherend 9 via an adhesive layer 11. When the moisture-absorbent sheet 1 and the adherend 9 are adjacent to each other, the resin layer (A) 5 or resin layer (B) 7 comes into contact with the adherend 9. The resin layer (A) 5 or resin layer (B) 7 in contact with the adherend 9 is a pressure-sensitive adhesive layer, which bonds the moisture-absorbent sheet 1 to the adherend 9. When the moisture-absorbent sheet 1 and the adherend 9 are laminated via the adhesive layer 11, the moisture-absorbent sheet 1 and the adherend 9 are fixed by the adhesive layer 11. The thickness of this adhesive layer is 4 μm or less, and generally 1 to 3 μm. As the adhesive for forming the adhesive layer 11, an epoxy-based or urethane-based dry laminating adhesive is preferably used.

[0031] 4, the moisture-absorbing sheet 1 of the present invention can also be wound around a core material in a state where it is adjacent to the adherend 9 or laminated via an adhesive layer, and held as a roll 13. By forming it into a roll 13, it is possible to dry the adherend 9 efficiently and in a space-saving manner. When storing the roll 13 for a long period of time, it is preferable to store it in an aluminum bag or the like, deaerate it, and then seal it for storage to prevent moisture from penetrating from the outside.

[0032] It is also possible to use multiple moisture-absorbent sheets 1 of the present invention, sandwiching an adherend 9 between them. For example, as shown in FIG. 5 , sandwiching an adherend 9 between moisture-absorbent sheets 1, such as moisture-absorbent sheet 1-adherend 9-moisture-absorbent sheet 1-adherend 9-moisture-absorbent sheet 1, allows for more efficient drying of the adherend 9 and also has the effect of suppressing moisture penetration from the outside into the adherend. In such cases, the resin layer (A) 5 or resin layer (B) 7 facing the adherend 9 of each moisture-absorbent sheet 1 is an adhesive layer, or an adhesive layer is present between each moisture-absorbent sheet 1 and the adherend 9, thereby bonding and fixing each moisture-absorbent sheet 1 to the adherend 9. Furthermore, by holding the moisture-absorbent sheet 1 and the adherend 9 adjacent to each other or laminated via an adhesive layer of 4 μm or less as a roll 13, a moisture-absorbent sheet 1-adherend 9-moisture-absorbent sheet 1-adherend 9-moisture-absorbent sheet 1 configuration can be naturally created.

[0033] Furthermore, since the moisture-absorbent sheet 1 of the present invention and the adherend 9 are combined to form a roll 13, it is preferable that the adherend 9 also has flexibility.

[0034] The adherend 9 requires extremely low moisture content, such as flexible resin substrates used in organic electroluminescence (EL) and solar cells. Such resin substrates can be widely used as components for electronic device products, such as solar cell modules and organic electroluminescence (EL) products (e.g., organic EL lighting, organic EL displays), and as backsheet components for these products. Such adherends 9 are formed from polyester resins, polyamide resins, polyimide resins, polycarbonate resins, olefin-based resins, cyclic olefin-based resins, etc., and are preferably formed from polyester resins, polyamide resins, olefin-based resins, or cyclic olefin-based resins. Polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) are particularly preferred polyester resins. The thickness of the adherend 9 is generally in the range of 12 to 300 μm, and preferably 30 to 200 μm. Furthermore, such adherends 9 may have metal electrodes, transparent electrodes, refractive index adjustment layers, metal oxide layers, etc.

[0035] <Drying Method> Drying of the adherend 9 using the moisture-absorbent sheet 1 of the present invention does not require a low-humidity environment such as a glove box, making the drying process simple. The room temperature when drying the adherend 9 is generally 18 to 28°C. The relative humidity at this room temperature is 45 to 65% RH. In the present invention, by leaving the adherend 9 standing for at least 7 days under these conditions, the moisture content of the adherend 9 can be reduced to an absolutely dry state of 100 ppm or less, preferably 80 ppm or less, and more preferably 50 ppm or less. For example, the moisture-absorbent sheet of the present invention can be laminated adjacently to the adherend 9 or via an adhesive layer of 4 μm or less to form a roll, and the roll can be left sealed in an aluminum bag at 23°C for 7 days, reducing the moisture content of the adherend 9 to 100 ppm or less.

[0036] The excellent effects of the moisture-absorbing sheet of the present invention will be explained in the following experimental examples.

[0037] <Preparation of Calcium Oxide-Containing Masterbatch> Linear low-density polyethylene (LLDPE) pellets were prepared as the base resin for the calcium oxide-containing masterbatch. Calcium oxide powder was prepared as a chemical desiccant and adjusted to the desired particle size using a grinder. The powder was then mixed with the base resin pellets to prepare calcium oxide (CaO)-containing masterbatch (a) containing 10% by weight of calcium oxide. A calcium oxide-containing masterbatch prepared in the same manner using polypropylene (PP) as the base resin was designated calcium oxide-containing masterbatch (b), a calcium oxide-containing masterbatch prepared in the same manner using ethylene-vinyl acetate copolymer (EVA) as the base resin was designated calcium oxide-containing masterbatch (c), a calcium oxide-containing masterbatch prepared in the same manner using cyclic olefin copolymer (COC) as the base resin was designated calcium oxide-containing masterbatch (d), and a calcium oxide-containing masterbatch prepared in the same manner using polyethylene terephthalate (PET) as the base resin was designated calcium oxide-containing masterbatch (e). Similarly, a zeolite-containing masterbatch was prepared using linear low-density polyethylene (LLDPE) as the base resin and zeolite as the desiccant.

[0038] <Preparation of Adherend> A polyethylene terephthalate (PET) film measuring 10 cm × 10 cm and 100 μm thick was left at 23°C and 50% RH for 7 days to prepare a PET film (A) having a moisture content of 2400 ppm as an adherend. Similarly, a PET film measuring 10 cm × 10 cm and 100 μm thick was left at 23°C and 40% RH for 7 days to prepare a PET film (B) having a moisture content of 1900 ppm as an adherend.

[0039] <Drying Property Test> Each moisture-absorbent sheet prepared in each experimental example described below was cut into three pieces measuring 11 cm x 11 cm. As shown in Figure 5, a laminate was prepared by alternately stacking three moisture-absorbent sheets and two PET film adherends. Either PET film (A) or PET film (B) was used as the adherend. This laminate was placed in an aluminum bag, degassed, and sealed. After storage in this state for 7 days under conditions of 23°C and 50% RH, the moisture content of each adherend film and the presence or absence of any defects in appearance (presence or absence of transfer marks of the desiccant, etc.) were confirmed. The moisture content of each film was measured using a Karl Fischer moisture meter CA-310 (manufactured by Nitto Seiko Analytech Co., Ltd.). The evaporation temperature was set to 200°C. The evaluation criteria for the moisture content of the adherend after drying are shown below.

[0040] <Evaluation criteria for moisture content of adherend> ⊚: 50 ppm or less ◯: More than 50 to 100 ppm χ: More than 100 ppm The moisture content was calculated using the following formula: Moisture content [ppm] = detected moisture amount [μg] / weight of adherend [g] The evaluation criteria for poor appearance are shown below. <Evaluation criteria for appearance> ◯: No poor appearance χ: Poor appearance such as transfer marks of calcium oxide particles When the resin layer (A) or resin layer (B) of the moisture-absorbent sheet facing the adherend was an adhesive layer, the moisture-absorbent sheet and the adherend were fixed by the adhesive layer. When the resin layer (A) or resin layer (B) of the moisture-absorbent sheet facing the adherend was a skin layer, a 3 μm dry lamination adhesive was laminated between the skin layer and the adherend to form an adhesive layer, thereby bonding and fixing the moisture-absorbent sheet to the adherend.

[0041] <Method for Measuring Tg of Binder Resin> The Tg of the binder resin was measured using a viscoelasticity measuring device DMS6100 (manufactured by Seiko Instruments Inc.).

[0042] <Method for measuring median diameter (D50) of calcium oxide particles> The median diameter (D50) of calcium oxide particles was measured using a particle size distribution analyzer SALD-3100 (manufactured by Shimadzu Corporation).

[0043] Experimental Example 1 A calcium oxide-containing masterbatch (a) was prepared as a desiccant-containing masterbatch. Furthermore, low-density polyethylene (LDPE) with a Tg of −100°C was prepared as a binder resin. Low-density polyethylene (LDPE) was also prepared as a resin for forming the skin layer of resin layer (A). A metallocene polyolefin elastomer was also prepared as a resin for forming the adhesive layer of resin layer (B). The binder resin (LDPE) was mixed with the calcium oxide-containing masterbatch (a) so that the desiccant component (CaO) was 10 parts by weight (i.e., 10% by weight) per 90 parts by weight of the resin component, to form a moisture-absorbing layer. The LDPE resin composition for forming resin layer (A), the metallocene polyolefin elastomer resin composition for forming resin layer (B), and the metallocene polyolefin elastomer resin composition for forming resin layer (B) were then introduced into an extruder. A moisture-absorbing sheet was formed by coextrusion so that the resin layer (A) had a thickness of 10 μm, the moisture-absorbing layer had a thickness of 25 μm, and the resin layer (B) had a thickness of 10 μm. The calcium oxide particles contained therein had a median diameter (D50) of 2 μm. A PET film (A) was used as the adherend for the drying property evaluation and appearance evaluation.

[0044] Experimental Example 2 A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that the adherend used for the drying property evaluation and appearance evaluation was a PET film (B).

[0045] <Example 3> A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that the thickness of the resin layer (A) was 3 μm, the thickness of the moisture-absorbing layer was 25 μm, and the thickness of the resin layer (B) was 3 μm.

[0046] <Example 4> A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that the thickness of the resin layer (A) was 20 μm, the thickness of the moisture-absorbing layer was 25 μm, and the thickness of the resin layer (B) was 20 μm.

[0047] Experimental Example 5 A moisture-absorbing sheet was formed in the same manner as in Experimental Example 1, except that the resin layer (B) was a skin layer made of LDPE and having a thickness of 10 μm.

[0048] Experimental Example 6 A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that the thickness of the moisture-absorbent layer was changed to 20 μm.

[0049] Experimental Example 7 A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that the thickness of the moisture-absorbent layer was changed to 30 μm.

[0050] Experimental Example 8 A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that the amount of calcium oxide blended in the moisture-absorbent layer was changed to 5% by weight.

[0051] Experimental Example 9 A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that the amount of calcium oxide blended in the moisture-absorbent layer was changed to 20% by weight.

[0052] Experimental Example 10 A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that the median diameter (D50) of the calcium oxide particles blended in the moisture-absorbent layer was 20 μm.

[0053] <Experimental Example 11> A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that in Experimental Example 1, polypropylene (PP) having a Tg of 0°C was used as the binder resin and calcium oxide masterbatch (b) was used to form the moisture-absorbent layer.

[0054] <Experimental Example 12> A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that the binder resin was an ethylene vinyl acetate copolymer (EVA) having a Tg of −42° C., and the moisture-absorbent layer was formed using calcium oxide masterbatch (c).

[0055] <Experimental Example 13> A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that the thickness of the resin layer (A) was 1 μm, the thickness of the moisture-absorbing layer was 25 μm, and the thickness of the resin layer (B) was 1 μm.

[0056] <Experimental Example 14> A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that the thickness of the resin layer (A) was 10 μm, the thickness of the moisture-absorbing layer was 10 μm, and the thickness of the resin layer (B) was 10 μm.

[0057] Experimental Example 15 A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that the amount of calcium oxide blended in the moisture-absorbent layer was changed to 3% by weight.

[0058] Experimental Example 16 A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that the amount of calcium oxide blended in the moisture-absorbent layer was changed to 30% by weight.

[0059] Experimental Example 17 A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that the median diameter (D50) of the calcium oxide particles blended in the moisture-absorbent layer was 35 μm.

[0060] <Experimental Example 18> A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that in Experimental Example 1, a cyclic olefin copolymer (COC) having a Tg of 80°C was used as the binder resin and a calcium oxide masterbatch (d) was used to form the moisture-absorbent layer.

[0061] <Experimental Example 19> A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that in Experimental Example 1, polyethylene terephthalate (PET) having a Tg of 70°C was used as the binder resin and calcium oxide masterbatch (e) was used to form the moisture-absorbent layer.

[0062] Experimental Example 20 A moisture-absorbent sheet was formed in the same manner as in Experimental Example 1, except that the moisture-absorbent layer was formed using a zeolite-containing masterbatch.

[0063] The samples prepared in Experimental Examples 1 to 20 were evaluated according to the procedures described above, and the results are shown in Table 1.

[0064]

[0065] 1: Moisture-absorbing sheet 3: Moisture-absorbing layer 5: Resin layer (A) 7: Resin layer (B) 9: Adherend 11: Adhesive layer 13: Roll body

Claims

1. A moisture-absorbent sheet for use on an adherend having a moisture content of 2500 ppm or less, the moisture-absorbent sheet being laminated in the order of a resin layer (A), a moisture-absorbent layer, and a resin layer (B), the moisture-absorbent layer being formed from a binder resin having a Tg of 0°C or less, the binder resin being an olefin-based resin, and containing 5 to 20% by weight of calcium oxide having a median diameter (D50) of 20 μm or less, the resin layer (A) and the resin layer (B) being skin layers or adhesive layers, the thicknesses of the resin layer (A) and the resin layer (B) being 3 to 20 μm, and the moisture-absorbent layer being 20 to 30 μm.

2. The moisture-absorbent sheet for bone-dry use according to claim 1, wherein the moisture content of the adherend is 2000 ppm or less.

3. The moisture-absorbent sheet for bone-dry use according to claim 1 or 2, which is held in a roll in a state adjacent to the adherend or laminated via an adhesive layer of 4 μm or less.

4. A method for absolute drying in which the moisture-absorbing sheet for absolute drying according to claim 1 or 2 is laminated adjacent to the adherend or via an adhesive layer of 4 μm or less, and then allowed to stand at 23° C. for 7 days, thereby reducing the moisture content of the adherend to 100 ppm or less.

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