Hygroscopic sheet for absolute dry

Abstract

To provide a hygroscopic sheet for absolute dry which dries adherend having a low moisture content to an absolute dry state.SOLUTION: A hygroscopic sheet for absolute dry is a hygroscopic sheet used in adherend having a moisture content of 2,500 ppm or less, wherein the hygroscopic sheet is formed by stacking a resin layer (A), a hygroscopic layer, and a resin layer (B) in this order, the hygroscopic layer is formed of a binder resin having Tg of 0°C or lower, the binder resin is an olefinic resin, 5 to 20 wt.% of calcium oxide having a median diameter (D50) of 20 μm or less is contained in the binder resin, 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 hygroscopic layer is 20 to 30 μm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a hygroscopic sheet, and more particularly to a completely dry hygroscopic sheet used for an adherend with a low water content.

Background Art

[0002] Conventionally, a hygroscopic sheet (also called a water-absorbing sheet or a desiccant sheet) having a hygroscopic layer in which a desiccant is dispersed has been widely used for moisture absorption and moisture prevention. As such a hygroscopic sheet, those having various layer structures have been proposed. In Patent Document 1, a hygroscopic sheet including a desiccant layer, a moisture-permeable sheet provided on one surface of the desiccant, and an adhesive layer provided on the other surface of the desiccant layer is proposed, and it is described that a cellophane sheet, an acetate sheet, a nylon sheet, etc. are used as the moisture-permeable sheet. Further, Patent Documents 2 and 3 describe a desiccant sheet including a hygroscopic layer in which a desiccant is dispersed.

[0003] By the way, electronic devices such as organic electroluminescence (organic EL) displays, solar cell panels, liquid crystal touch panels, and electronic papers developed in recent years dislike charge leakage, so the plastic base material or circuit board forming their circuit boards, etc., needs to be dried to an extremely low water content (completely dry state). The sheets described in Patent Documents 1 to 3 show a certain moisture absorption effect on an adherend with a high water content. However, since the plastic base material or circuit board is dried to a certain extent in these manufacturing processes and the water content is already small, it has been difficult to dry an adherend with a low water content such as a plastic base material or a circuit board to a completely dry state.

[0004] Therefore, for products that require an extremely low water content, such as plastic substrates or circuit boards, drying had to be performed by batch processing under a nitrogen atmosphere, such as inside a glove box, or under a vacuum environment by heating. However, in such batch processing, there is a limit to the volume of the glove box, and a large number of adherends cannot be dried, resulting in a problem of low processing efficiency. In addition, it is necessary to make the humidity inside the glove box an extremely low humidity environment, and the construction of the drying environment is very complicated. Therefore, a more efficient method for making a plastic substrate or a circuit board, etc. in an absolutely dry state is required.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a moisture-absorbing sheet for absolute drying that dries an adherend with a low water content to an absolutely dry state.

Means for Solving the Problems

[0007] The present inventors have found that in a resin film containing calcium oxide as a desiccant, by selecting conditions such as the particle size and concentration of the calcium oxide, an adherend with a low water content can be brought into an absolutely dry state, and have thus completed the present invention.

[0008] According to the present invention, there is provided a moisture-absorbing sheet for use on an adherend having a water content of 2500 ppm or less, The hygroscopic sheet is laminated in the order of a resin layer (A), a moisture absorption layer, and a resin layer (B). The moisture absorption layer is formed from a binder resin having a Tg of 0°C or lower. The binder resin is an olefin resin and contains 3 to 20% by weight of calcium oxide having a median diameter (D50) of 20 μm or less in the binder resin. 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. There is provided a moisture-free hygroscopic sheet characterized in that the thickness of the moisture absorption layer is 20 to 30 μm.

[0009] In the hygroscopic sheet of the present invention, the following embodiments can be preferably adopted. (1) The water content of the adherend is 2000 ppm or less. (2) It is held as a roll body in a state of being laminated adjacent to the adherend or via an adhesive layer of 4 μm or less.

[0010] Further, according to the present invention, there is provided a moisture-free method of reducing the water content of the adherend to 100 ppm or less by laminating the moisture-free hygroscopic sheet adjacent to the adherend or via an adhesive layer of 4 μm or less and allowing it to stand at 23°C for 7 days.

Effects of the Invention

[0011] By using the hygroscopic sheet of the present invention for an adherend having a low water content, the adherend can be dried to a moisture-free state. Further, the hygroscopic sheet of the present invention can be held as a roll body in a state of being laminated adjacent to the adherend or via an adhesive layer. Thereby, the drying efficiency is higher than that of batch processing. Furthermore, since the hygroscopic sheet of the present invention can make the adherend moisture-free at room temperature, it can be dried more simply than batch processing.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0013] <Hygroscopic sheet 1> As shown in FIG. 1, the hygroscopic sheet 1 of the present invention is laminated in the order of a resin layer (A) 5, a hygroscopic layer 3, and a resin layer (B) 7. This hygroscopic sheet 1 is formed by laminating each layer by coextrusion.

[0014] The thickness of the hygroscopic sheet 1 of the present invention is set to a thickness such that the target water absorption amount is achieved according to the amount of calcium oxide incorporated in the hygroscopic layer 3. Generally, it is preferably in the range of 26 to 70 μm, particularly 30 to 65 μm. When the thickness of the hygroscopic sheet 1 is less than 26 μm, the amount of calcium oxide particles is insufficient, the drying property deteriorates, and the strength of the hygroscopic sheet 1 decreases, making it easy to break. On the other hand, when the thickness of the hygroscopic sheet 1 is greater than 70 μm, unnecessary costs increase due to the excessive thickness.

[0015] The thickness variation of the hygroscopic sheet 1 of the present invention is desirably within the range of ±6 μm, preferably ±5 μm. In particular, when the thickness variation in the width direction of the hygroscopic sheet 1 exceeds ±6 μm, when the hygroscopic sheet 1 is manufactured as a long roll, variations occur in the winding pressure in the roll width direction, and as a result, partial sagging occurs in the hygroscopic sheet 1. This is because such partial sagging may cause processing defects such as wrinkles being mixed in when the hygroscopic sheet 1 and the adherend 9 are bonded together.

[0016] The hygroscopic sheet 1 of the present invention can be colored. When colored, it can be given a design property. When forming the resin layer (A), the resin layer (B), and the hygroscopic layer described later, a colored hygroscopic sheet 1 can be obtained by mixing a desired pigment into the resin for forming any one layer or a plurality of layers.

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

[0018] <Hygroscopic layer 3> The hygroscopic layer 3 is a layer formed between the resin layer (A) 5 and the resin layer (B) 7. The hygroscopic layer 3 is formed from a binder resin containing calcium oxide which is a drying material.

[0019] <Calcium oxide> In the present invention, calcium oxide is used as the drying material. Calcium oxide is a kind of chemical drying material that chemically reacts with water. Calcium oxide is suitably used as a drying material because it has an appropriate water reactivity, its granular shape is stably maintained, and it is relatively inexpensive. The reaction formula between calcium oxide and water is represented by the following formula. CaO + H2O → Ca(OH)2

[0020] The median diameter (D50) of calcium oxide, which is a desiccant, is 20 μm or less, preferably 10 μm or less, and more preferably in the range of 5 μm or less. This median diameter is measured as the particle diameter in terms of volume by, for example, the laser diffraction scattering method, and is the particle diameter at which the value of the cumulative distribution becomes 50%. When the median diameter (D50) of calcium oxide is greater than 20 μm, the drying property deteriorates, making it difficult to bring the adherend 9 to an absolutely dry state. In addition, there is a risk that particles will protrude from the binder resin and the particles will be transferred to the adherend 9. In addition, since calcium oxide is mixed with a resin and formed into the moisture absorption layer 3, it is desirable to select calcium oxide having a particle diameter smaller than the thickness of the moisture absorption layer 3. If particles having a particle diameter larger than the thickness of the moisture absorption layer 3 are included, there is a risk that particles will protrude from the binder resin and the particles will be transferred to the adherend 9 as described above. Furthermore, problems such as defects occurring in the moisture absorption layer 3 or the surface of the layer becoming rough will occur, and the moisture absorption function, which is the original function of the layer, cannot be sufficiently exhibited.

[0021] Moreover, it is preferable that calcium oxide is contained in the moisture absorption layer 3 formed by mixing with a binder resin in the range of 5 to 20% by weight, particularly 8 to 18% by weight. When the content of calcium oxide is less than 5% by weight, the drying property deteriorates, making it difficult to bring the adherend 9 to an absolutely dry state. On the other hand, when the content of calcium oxide is greater than 20% by weight, there is a risk that particles will protrude from the binder resin due to aggregation of the particles and the particles will be transferred to the adherend 9, and there is also a risk that the processability of the sheet itself will deteriorate.

[0022] In addition, calcium oxide may be surface-treated with a small amount of a surface treatment agent, such as a higher fatty acid metal salt such as zinc stearate or calcium stearate, within a range where its drying property is not impaired, to enhance its dispersibility in the resin.

[0023] <Binder resin> In the present invention, as the resin in which calcium oxide is dispersed, that is, the binder resin, a resin having a glass transition temperature (Tg) of 0 °C or lower is used. When the Tg is 0 °C or lower, the resin becomes soft and rubbery at room temperature, the resin moves easily at low temperatures, the movement of moisture is activated, and the drying property of the hygroscopic sheet 1 with respect to the adherend 9 is improved. In the present invention, an olefin-based resin is preferably used as such a binder resin having a Tg of 0 °C or lower. In addition, the olefin-based resin is also suitable as a binder resin because the water content of the resin itself is small and the performance of the desiccant can be sufficiently exhibited.

[0024] In the present invention, the dispersion of calcium oxide, which is a desiccant, in the resin is carried out by melt-kneading the above-described amount of calcium oxide with the above resin. However, the resin composition prepared by melt-kneading forms the moisture-absorbing layer 3 by melt extrusion. Therefore, in the formation of the moisture-absorbing layer 3, as in the examples described later, it is possible to previously form a desiccant masterbatch and then knead it with the binder resin. As the base material of the desiccant masterbatch, one that can be kneaded and molded with the binder resin of the moisture-absorbing layer 3 can be used.

[0025] The thickness of such a moisture-absorbing layer 3 is set to a thickness such that the target water absorption amount is achieved according to the amount of calcium oxide contained in the moisture-absorbing layer 3. Generally, it is preferably in the range of 20 to 30 μm, particularly 22 to 28 μm. If the thickness of the moisture-absorbing layer 3 is less than 20 μm, the amount of calcium oxide particles is insufficient and the drying property deteriorates. On the other hand, if the thickness of the moisture-absorbing layer 3 is greater than 30 μm, unnecessary costs increase.

[0026] <Resin layer (A) 5> The resin layer (A) 5 is a layer provided on one surface of the hygroscopic sheet 1. The resin layer (A) 5 is a skin layer or an adhesive layer. By this resin layer (A) 5, moisture permeation from the outside to the moisture-absorbing layer 3 can be prevented, and the drying function of the hygroscopic sheet 1 can be maintained over a long period. When the resin layer (A) 5 is used as the skin layer, generally, a thermoplastic resin or the like is applicable, and for example, a resin such as low-density polyethylene (LDPE) can be used. When the resin layer (A) 5 is used as the adhesive layer, for example, a resin having adhesiveness such as ethylene-vinyl acetate copolymer (EVA), soft polyolefin (LLDPE), metallocene polyolefin-based elastomer, etc. can be used.

[0027] The thickness of the resin layer (A) 5 is preferably 3 to 20 μm, 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 calcium oxide particles will protrude and transfer to the adherend 9. On the other hand, if the thickness of the resin layer (A) 5 is greater than 20 μm, when the resin layer (A) 5 is provided on the side of the adherend 9, the distance from the adherend 9 becomes large, so the drying property deteriorates. Also, when the resin layer (A) 5 is provided on the side opposite to the adherend 9, in suppressing moisture permeation from the outside, it becomes an excessive thickness. Further, no matter where the resin layer (A) 5 is provided, if the thickness of the resin layer (A) 5 is excessive, the thickness of the entire hygroscopic sheet 1 becomes thick, so there is also a possibility that it will be difficult to form a roll body 13 by laminating with the adherend 9 as described later.

[0028] <Resin layer (B) 7> The resin layer (B) 7 is a layer provided on the other surface of the hygroscopic sheet 1 (that is, the surface opposite to the resin layer (A) 5). The resin layer (B) 7 is a skin layer or an adhesive layer. Due to the presence of this resin layer (B) 7, moisture permeation from the outside to the hygroscopic layer can be prevented, and the drying function of the hygroscopic sheet 1 can be maintained over a long period. As the skin layer or the adhesive layer of the resin layer (B) 7, the same resin types as those of the resin layer (A) 5 can be used. For the same reason as that of the resin layer (A) 5, the thickness of the resin layer (B) 7 is preferably 3 to 20 μm, more preferably 5 to 18 μm.

[0029] <Adherend 9> The moisture-absorbing sheet 1 of the present invention is used for drying the adherend 9. The adherend 9 is characterized in that the water content is 2500 ppm or less, preferably 2000 ppm or less. That is, by using the moisture-absorbing sheet 1 of the present invention, it is possible to dry the adherend 9, which already has a low water content, to an absolutely dry state.

[0030] The moisture-absorbing sheet 1 of the present invention can dry the adherend 9 by being laminated adjacent to the adherend 9 or via an adhesive layer. Fig. 2 shows the layer structure when the moisture-absorbing sheet 1 is adjacent to the adherend 9, and Fig. 3 shows the layer structure when the moisture-absorbing sheet 1 is laminated by being bonded to the adherend 9 by the adhesive layer 11. When the moisture-absorbing sheet 1 and the adherend 9 are adjacent, the resin layer (A) 5 or the resin layer (B) 7 will contact the adherend 9. Since the contacting resin layer (A) 5 or resin layer (B) 7 is an adhesive layer, the moisture-absorbing sheet 1 and the adherend 9 are bonded together. When the moisture-absorbing sheet 1 and the adherend 9 are laminated via the adhesive layer 11, the adhesive layer 11 fixes the moisture-absorbing sheet 1 and the adherend 9. The thickness of this adhesive layer is 4 μm or less, and generally 1 - 3 μm. In addition, as the adhesive for forming the adhesive layer 11, an epoxy-based or urethane-based dry lamination adhesive is preferably used.

[0031] Also, as shown in Fig. 4, the moisture-absorbing sheet 1 of the present invention can also be wound around a core material in a state of being laminated adjacent to the adherend 9 or via an adhesive layer, and held as a roll body 13. By making it into a roll body 13, the drying of the adherend 9 can be efficiently carried out in a space-saving manner. When storing the roll body 13 for a long time, in order to prevent moisture penetration from the outside, it is preferably put into an aluminum bag or the like, degassed, sealed, and stored.

[0032] It is also possible to use a plurality of the hygroscopic sheets 1 of the present invention with the adherend 9 sandwiched therebetween. For example, as shown in FIG. 5, by sandwiching the adherend 9 with the hygroscopic sheets 1 as in hygroscopic sheet 1 - adherend 9 - hygroscopic sheet 1 - adherend 9 - hygroscopic sheet 1, the drying of the adherend 9 can be performed more efficiently, and there is also an effect of suppressing moisture permeation from the outside to the adherend. In such a case, in each hygroscopic sheet 1, the resin layer (A) 5 or the resin layer (B) 7 facing the adherend 9 is an adhesive layer, or an adhesive layer exists between each hygroscopic sheet 1 and the adherend 9, so that each hygroscopic sheet 1 and the adherend 9 are bonded and fixed. Further, by holding the hygroscopic sheet 1 and the adherend 9 in a laminated state adjacent to each other or via an adhesive layer of 4 μm or less as a roll body 13, the configuration of hygroscopic sheet 1 - adherend 9 - hygroscopic sheet 1 - adherend 9 - hygroscopic sheet 1 can be naturally formed.

[0033] Also, from the point of making the hygroscopic sheet 1 of the present invention and the adherend 9 into a roll body 13 in a combined state, it is preferable that the adherend 9 also has flexibility.

[0034] The adherend 9 is required to have an extremely low water content, and examples thereof include flexible resin substrates used for organic ELs and solar cells. Such resin substrates can be widely used as members of electronic device products, for example, solar cell modules and organic EL products (organic EL lighting, organic EL displays, etc.), and as backsheet members thereof. Such an adherend 9 is formed of a polyester resin, a polyamide resin, a polyimide resin, a polycarbonate resin, an olefin resin, a cyclic olefin resin, etc., and is preferably formed of a polyester resin, a polyamide resin, an olefin resin, or a cyclic olefin resin. As the polyester resin, polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) are particularly preferable. The thickness of the adherend 9 is generally preferably in the range of 12 to 300 μm, particularly 30 to 200 μm. In addition, such an adherend 9 may have a metal electrode, a transparent electrode, a refractive index adjustment layer, a metal oxide layer, and the like.

[0035] <Drying method> Since the drying of the adherend 9 using the hygroscopic sheet 1 of the present invention does not need to be carried out in a low humidity environment by a glove box or the like, the drying process is simple. The room temperature when drying the adherend 9 is generally 18 to 28°C. Also, the relative humidity at this room temperature is 45 to 65%RH. In the present invention, under such conditions, by standing still for at least 7 days, the water content of the adherend 9 can be brought to an absolutely dry state of 100 ppm or less, preferably 80 ppm or less, more preferably 50 ppm or less. For example, the hygroscopic sheet of the present invention is laminated with the adherend 9 adjacent thereto or via an adhesive layer of 4 μm or less to form a roll body, sealed in an aluminum bag, and left standing at 23°C for 7 days, whereby the water content of the adherend 9 can be reduced to 100 ppm or less.

Examples

[0036] The excellent effects of the hygroscopic sheet of the present invention will be described in the following experimental examples.

[0037] <Preparation of calcium oxide-containing masterbatch> Linear low-density polyethylene (LLDPE) pellets were prepared as the base resin of the calcium oxide-containing masterbatch. Calcium oxide powder was prepared as a chemical desiccant, adjusted to a desired particle size using a pulverizer, and kneaded with the base resin pellets to prepare a calcium oxide (CaO)-containing masterbatch (a) having a calcium oxide content of 10% by weight. A calcium oxide-containing masterbatch prepared in the same manner using polypropylene (PP) as the base resin was designated as 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 as 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 as 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 as calcium oxide-containing masterbatch (e). Also, a zeolite-containing masterbatch was prepared in the same manner using linear low-density polyethylene (LLDPE) as the base resin and zeolite as the desiccant.

[0038] <Preparation of adherend> A polyethylene terephthalate (PET) film with a size of 10 cm × 10 cm and a thickness of 100 μm was left standing at 23°C and 50% RH for 7 days to prepare a PET film (A) with a water content of 2400 ppm as the adherend. Similarly, a PET film with a size of 10 cm × 10 cm and a thickness of 100 μm was left standing at 23°C and 40% RH for 7 days to prepare a PET film (B) with a water content of 1900 ppm as the adherend.

[0039] <Drying property test> Each hygroscopic sheet prepared in each of the following experimental examples was cut into three pieces with a size of 11 cm × 11 cm. As shown in Figure 5, a laminate was prepared by alternately stacking three hygroscopic sheets and two adherend PET films. Either PET film (A) or PET film (B) was used as the adherend. This laminate was put into an aluminum bag, degassed, and sealed. After storing it under the conditions of 23°C and 50% RH for 7 days, the water content of each film as the adherend and the presence or absence of appearance defects (such as the presence or absence of transfer marks of the desiccant) were confirmed. The measurement of each moisture content was performed using a Karl Fischer moisture meter CA-310 (manufactured by Nitto Seiko Analytic Co., Ltd.). The vaporization temperature was set at 200 °C. The evaluation criteria for the water content of the adherend after drying are shown below.

[0040] <Evaluation Criteria for Water Content of Adherend> ◎: 50 ppm or less 〇: Exceeding 50 and 100 ppm or less ×: Exceeding 100 ppm In addition, the water content was calculated from the following formula. Water content [ppm] = Detected moisture content [μg] / Weight of adherend [g] Also, the evaluation criteria for appearance defects are shown below. <Evaluation Criteria for Appearance> 〇: No appearance defects ×: Appearance defects such as transfer marks of calcium oxide particles In addition, when the resin layer (A) or resin layer (B) of the hygroscopic sheet facing the adherend is an adhesive layer, the adherend and the hygroscopic sheet were fixed by the adhesive layer. When the resin layer (A) or resin layer (B) of the hygroscopic sheet facing the adherend is a skin layer, a 3-μm dry laminate adhesive was laminated between the skin layer and the adherend to form an adhesive layer, and the adherend and the hygroscopic sheet were bonded and fixed.

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

[0042] <Measurement Method for Median Diameter (D50) of Calcium Oxide Particles> Using a particle size distribution measuring device SALD-3100 (manufactured by Shimadzu Corporation), the median diameter (D50) of calcium oxide particles was measured.

[0043] <Experimental Example 1> Calcium oxide-containing masterbatch (a) was prepared as a desiccant-containing masterbatch, and further, low-density polyethylene (LDPE) with a Tg of -100 °C was used as a binder resin, low-density polyethylene (LDPE) was used as a resin for forming the skin layer of resin layer (A), and a metallocene polyolefin-based elastomer was prepared as a resin for forming the adhesive layer of resin layer (B). The above binder resin (LDPE) was mixed with a calcium oxide-containing masterbatch (a) so that the desiccant component (CaO) was 10 parts by weight (i.e., 10% by weight) with respect to 90 parts by weight of the resin component to obtain a resin composition for forming a moisture-absorbing layer. LDPE, which is a resin composition for forming resin layer (A), and a metallocene polyolefin-based elastomer, which is a resin composition for forming resin layer (B), were charged into an extruder. A moisture-absorbing sheet was formed by coextrusion so that the thickness of resin layer (A) was 10 μm, the thickness of the moisture-absorbing layer was 25 μm, and the thickness of resin layer (B) was 10 μm. In addition, the median diameter (D50) of the calcium oxide particles contained above was 2 μm. A PET film (A) was used as the adherend for dryness evaluation and appearance evaluation.

[0044] <Experimental Example 2> In Experimental Example 1, a moisture-absorbing sheet was formed in the same manner as in Experimental Example 1, except that the adherend used for dryness evaluation and appearance evaluation was a PET film (B).

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

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

[0047] <Experimental Example 5> In Experimental Example 1, a hygroscopic sheet was formed in the same manner as in Experimental Example 1, except that the resin layer (B) was a 10-μm-thick skin layer formed of LDPE.

[0048] <Experimental Example 6> In Experimental Example 1, a hygroscopic sheet was formed in the same manner as in Experimental Example 1, except that the thickness of the moisture-absorbing layer was 20 μm.

[0049] <Experimental Example 7> In Experimental Example 1, a hygroscopic sheet was formed in the same manner as in Experimental Example 1, except that the thickness of the moisture-absorbing layer was 30 μm.

[0050] <Experimental Example 8> In Experimental Example 1, a hygroscopic sheet was formed in the same manner as in Experimental Example 1, except that the calcium oxide content in the moisture-absorbing layer was 5% by weight.

[0051] <Experimental Example 9> In Experimental Example 1, a hygroscopic sheet was formed in the same manner as in Experimental Example 1, except that the calcium oxide content in the moisture-absorbing layer was 20% by weight.

[0052] <Experimental Example 10> In Experimental Example 1, a hygroscopic sheet was formed in the same manner as in Experimental Example 1, except that the median diameter (D50) of the calcium oxide particles incorporated in the moisture-absorbing layer was 20 μm.

[0053] <Experimental Example 11> In Experimental Example 1, a hygroscopic sheet was formed in the same manner as in Experimental Example 1, except that the binder resin was polypropylene (PP) with a Tg of 0°C, and the moisture-absorbing layer was formed using calcium oxide masterbatch (b).

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

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

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

[0057] <Example 15> In Example 1, a hygroscopic sheet was formed in the same manner as in Example 1, except that the calcium oxide content in the moisture absorption layer was 3% by weight.

[0058] <Example 16> In Example 1, a hygroscopic sheet was formed in the same manner as in Example 1, except that the calcium oxide content in the moisture absorption layer was 30% by weight.

[0059] <Example 17> In Example 1, a hygroscopic sheet was formed in the same manner as in Example 1, except that the median diameter (D50) of the calcium oxide particles incorporated in the moisture absorption layer was 35 μm.

[0060] <Example 18> In Example 1, a hygroscopic sheet was formed in the same manner as in Example 1, except that the binder resin was a cyclic olefin copolymer (COC) with a Tg of 80°C, and the moisture absorption layer was formed using calcium oxide masterbatch (d).

[0061] <Example 19> In Example 1, a hygroscopic sheet was formed in the same manner as in Example 1, except that the binder resin was polyethylene terephthalate (PET) with a Tg of 70°C, and the moisture absorption layer was formed using calcium oxide masterbatch (e).

[0062] <Experimental Example 20> In Experimental Example 1, a hygroscopic sheet was molded in the same manner as in Experimental Example 1, except that a zeolite-containing masterbatch was used to form the hygroscopic layer.

[0063] For the samples prepared in Experimental Examples 1 to 20, each evaluation was performed according to the procedure shown above, and the results are shown in Table 1.

[0064]

Table 1

Explanation of Symbols

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

Claims

1. A hygroscopic sheet used for a substrate having a water content of 2500 ppm or less, wherein the hygroscopic sheet is laminated in the order of a resin layer (A), a hygroscopic layer, and a resin layer (B), the hygroscopic layer is formed of a binder resin having a Tg of 0°C or lower, the binder resin is an olefin resin and contains 5 to 20% by weight of calcium oxide having a median diameter (D50) of 20 μm or less in the binder resin, 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 hygroscopic sheet for absolute drying is characterized in that the thickness of the hygroscopic layer is 20 to 30 μm.

2. The hygroscopic sheet for absolute drying according to Claim 1, wherein the water content of the substrate is 2000 ppm or less.

3. The hygroscopic sheet for absolute drying according to Claim 1 or 2, which is held as a roll body in a state of being laminated adjacent to the substrate or via an adhesive layer having a thickness of 4 μm or less.

4. An absolute drying method for reducing the water content of the substrate to 100 ppm or less by laminating the hygroscopic sheet for absolute drying according to Claim 1 or 2 adjacent to the substrate or via an adhesive layer having a thickness of 4 μm or less and allowing it to stand at 23°C for 7 days.

Images