Base material for mounting electronic device

Abstract

A base material for mounting an electronic device has a metal foil and a protective resin layer. The base material for mounting an electronic device is characterized in that: the protective resin layer is provided on the surface of one side of the metal foil; the surface on the other side of the metal foil is a surface on the electronic device mounting side; and a hygroscopic resin layer is provided on the surface on the other side of the metal foil.

Description

Substrate for mounting electronic devices

[0001] The present invention relates to a substrate for mounting an electronic device, and more particularly to a substrate for mounting an electronic device that is used to block and absorb moisture and keep the electronic device dry.

[0002] Conventionally, moisture-absorbing sheets having a moisture-absorbing resin 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 comprising 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, and describes that a cellophane sheet, an acetate sheet, a nylon sheet, or the like can be used as the moisture-permeable sheet.

[0003] Recently developed organic electronic devices such as organic electroluminescence (organic EL), solar cells, touch panels, and electronic paper are sensitive to charge leakage, and therefore require high moisture barrier properties for plastic substrates forming circuit boards or films sealing circuit boards.

[0004] However, the known moisture-absorbing sheets disclosed in Patent Document 1 and elsewhere do not exhibit satisfactory performance as encapsulants for maintaining the interior of such organic electronic devices in a dry state. That is, they absorb large amounts of moisture that penetrate from the outside of the device, causing the desiccant present in the moisture-absorbing sheet to reach saturation in a short period of time. Further improvement is needed because the moisture absorption properties are impaired or the absorbed moisture is released into the device.

[0005] Furthermore, as the structures of organic electronic devices become increasingly complex, plastic substrates such as sealing films may be subjected to bending stress during installation, attachment, etc., and there is a demand for flexibility that does not impair moisture barrier properties even when subjected to such stress.

[0006] Japanese Patent Application Laid-Open No. 2006-326838

[0007] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a substrate for mounting an electronic device that is capable of preventing moisture penetration and keeping the electronic device dry, and that has excellent flexibility.

[0008] According to the present invention, there is provided a substrate for mounting an electronic device, which has a metal foil and a protective resin layer, wherein the protective resin layer is provided on one surface of the metal foil, the other surface of the metal foil is the electronic device mounting surface, and a moisture-absorbing resin layer is provided on the other surface of the metal foil.

[0009] In the substrate for mounting an electronic device of the present invention, (1) the thickness of the metal foil is 5 to 20 μm, (2) the metal foil is made of aluminum, (3) the protective resin layer is made of polycarbonate resin, silicone resin, polyester resin, fluorine-based resin or acrylic resin, (4) the moisture-absorbing resin layer is made of an olefin-based resin having a desiccant dispersed therein, (5) the desiccant is an agent that chemically captures moisture by reacting with water, (6) an inner resin layer is provided on at least one surface of the moisture-absorbing resin layer, (7) the inner resin layer is made of polyester resin, polyamide resin, olefin-based resin or cyclic olefin-based resin, (8) the metal foil, the protective resin layer, the moisture-absorbing resin layer and the inner resin layer are bonded together with a dry lamination adhesive, (9) the dry lamination adhesive is made of a urethane-based resin or an epoxy-based resin, (10) An ultraviolet blocking layer is provided on the surface of the protective resin layer opposite to the surface on which the electronic device is attached; (11) The overall thickness is 75 to 300 μm; (12) The moisture-absorbing resin layer or the inner surface resin layer is disposed to face the inside of the device; (13) An adhesive layer formed from a hot-melt adhesive is provided on the surface of the moisture-absorbing resin layer on the side on which the electronic device is attached; and (14) The hot-melt adhesive is formed from an olefin-based resin or a cyclic olefin-based resin.

[0010] The substrate for mounting an electronic device of the present invention blocks most moisture penetration by the metal foil, and even trace amounts of moisture that penetrate through pinholes in the metal foil are absorbed by the hygroscopic resin layer. As a result, moisture penetration into the device is prevented, making it possible to keep the device dry for a long period of time. Furthermore, the substrate for mounting an electronic device of the present invention is flexible and has excellent bending resistance. That is, the substrate for mounting an electronic device of the present invention is easy to handle, and the moisture barrier properties of the substrate are not impaired even when stress such as bending is applied.

[0011] In the present invention, since the substrate for mounting an electronic device comprises a metal foil, it is basically used in a portion of the device where light transmittance is not required (for example, a back sheet of a solar cell, other non-light-receiving surfaces of a solar cell or non-light-emitting surfaces of an organic electroluminescence element, or the side surfaces of these devices).

[0012] Fig. 1 is a schematic cross-sectional view showing an example of the layer structure of the substrate for mounting an electronic device of the present invention. Fig. 2 is a schematic cross-sectional view showing another example of the layer structure of the substrate for mounting an electronic device of the present invention. Fig. 3 is a schematic cross-sectional view showing another example of the layer structure of the substrate for mounting an electronic device of the present invention. Fig. 4 is a schematic cross-sectional view showing an example of the layer structure when an adhesive layer is provided on the substrate for mounting an electronic device of the present invention. Fig. 5 is a schematic cross-sectional view showing another example of the layer structure when an adhesive layer is provided on the substrate for mounting an electronic device of the present invention.

[0013] 1 to 6, the substrate for mounting an electronic device of the present invention, generally designated by 1, comprises a metal foil 3 and a protective resin layer 5, the protective resin layer 5 being provided on the outer surface of the metal foil 3, and a moisture-absorbing resin layer 7 being provided on the surface of the metal foil 3 on the side on which the electronic device is mounted.

[0014] <Metal Foil 3> The metal foil 3 serves to block most of the moisture (water vapor) that attempts to enter the device.

[0015] The material of the metal foil 3 is preferably aluminum from the viewpoints of flexibility, ease of thin film formation, and cost reduction.

[0016] The thickness of the metal foil 3 is 5 to 20 μm, more preferably 6 to 20 μm, and particularly preferably 6 to 15 μm. A metal foil 3 with a thickness of less than 5 μm is difficult to manufacture. On the other hand, a metal foil 3 with a thickness of more than 20 μm has insufficient flexibility and is difficult to handle.

[0017] Here, flexibility (bending resistance) refers to the property of having flexibility while being durable against tensile stress and compressive stress. The thinner the metal foil 3, the more flexible it is. Furthermore, the thinner the metal foil 3, the less the amount of metal foil 3 used, which also reduces the overall manufacturing cost of the substrate 1.

[0018] However, it is generally known that the thinner the metal foil 3, the more pinholes there are. Therefore, when the metal foil 3 is thin, the amount of moisture that permeates increases compared to when the metal foil 3 is thick, and there is a risk that sufficient moisture barrier properties will not be exhibited. Therefore, in the present invention, a moisture-absorbing resin layer 7 (described later) is provided on the electronic device side of the metal foil 3. This allows the metal foil 3 to absorb the small amount of moisture that has permeated through the pinholes in the metal foil 3, thereby preventing moisture from permeating into the electronic device and maintaining the electronic device in a dry state. In other words, most moisture attempting to penetrate the device from the outside is blocked by the metal foil 3, but the small amount of moisture that has permeated through the pinholes in the metal foil 3 is also absorbed by the moisture-absorbing resin layer 7. Therefore, the moisture-absorbing resin layer 7 compensates for the reduced moisture barrier properties caused by the thin thickness of the metal foil 3.

[0019] <Protective resin layer 5> The protective resin layer 5 is a layer provided on the side of the metal foil 3 opposite to the side where the electronic device is mounted (i.e., the outer surface side of the metal foil 3) to prevent scratches, holes, and oxidative deterioration of the metal foil 3.

[0020] The protective resin layer 5 is formed using various resins that are known per se, but is generally preferably formed from an olefin resin, a cyclic olefin resin, a silicone resin, a polyimide resin, a polyester resin, a polyamide resin, a polycarbonate resin, a polyacrylonitrile resin, a fluorine-based resin, an acrylic resin, or the like, and is more preferably formed from a polycarbonate resin, a silicone resin, a polyester resin, a fluorine-based resin, or an acrylic resin.

[0021] The thickness of such a protective resin layer 5 is 12 to 200 μm, preferably 12 to 150 μm, and more preferably 12 to 100 μm. If the thickness of the protective resin layer 5 is less than 12 μm, scratches, holes, and oxidative degradation of the metal foil 3 may occur. If the thickness of the protective resin layer 5 exceeds 200 μm, it is too thick to protect the metal foil 3, and the manufacturing cost increases unnecessarily.

[0022] The protective resin layer 5 as described above is obtained by extrusion molding or the like.

[0023] The protective resin layer 5 can be colored. When the protective resin layer 5 is colored, it can provide design features and also provide light blocking properties to the inside of the substrate and the device. When molding the protective resin layer 5, a colored protective resin layer 5 can be obtained by mixing a pigment into the resin or by placing an ink layer adjacent to the resin.

[0024] <Moisture-absorbing resin layer 7> The moisture-absorbing resin layer 7 is a layer in which a desiccant is dispersed in resin, and absorbs trace amounts of moisture that have passed through pinholes in the metal foil 3. The moisture-absorbing resin layer 7 is provided on the surface of the metal foil 3 on which the electronic device is mounted.

[0025] In the moisture-absorbing resin layer 7, known inorganic or organic desiccants are used as the desiccants. Examples of inorganic desiccants include clay minerals such as zeolite, alumina, activated carbon, and montmorillonite, silica gel, calcium oxide, barium oxide, calcium chloride, and magnesium sulfate. Examples of organic desiccants include anionic polymers or crosslinked products of partially neutralized anionic polymers. Examples of such anionic polymers include those obtained by polymerizing or copolymerizing with other monomers at least one anionic monomer, such as a carboxylic acid monomer (e.g., (meth)acrylic acid or maleic anhydride), a sulfonic acid monomer (e.g., halogenated vinyl sulfonic acid, styrene sulfonic acid, or vinyl sulfonic acid), a phosphonic acid monomer (e.g., vinyl phosphoric acid), or a salt of one of these monomers.

[0026] In the present invention, from the viewpoint of being able to capture absorbed moisture without releasing it, an agent that chemically captures moisture by reacting with water is preferred over desiccants that capture moisture by physical adsorption, such as zeolite and silica gel. As such desiccants that exhibit chemical adsorption by reacting with water, for example, calcium oxide and calcium chloride are preferably used.

[0027] In addition, the above-mentioned desiccant preferably has a small particle size so that it can be uniformly dispersed in the resin and has a large specific surface area. For example, it is preferable that the average primary particle size (D50) in terms of volume as measured by a laser diffraction scattering method is 20 μm or less. It is usually preferable that the desiccant be dispersed in the moisture-absorbing resin layer 7 in an amount of 5 to 80 parts by mass per 100 parts by mass of the matrix resin.

[0028] Furthermore, the resin in which the desiccant is dispersed (i.e., the resin matrix) is not particularly limited and any known thermoplastic resin can be used, but generally, from the viewpoints of cost and ease of adhesion to other layers, olefin-based resins such as low-density polyethylene, high-density polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, or random or block copolymers of α-olefins such as ethylene, propylene, 1-butene, and 4-methyl-1-pentene, or cyclic olefin copolymers are preferably used. Among the above-mentioned olefin-based resins, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polypropylene (PP), and blends thereof are preferred in the present invention, as they have relatively low hygroscopicity and prevent deactivation of the desiccant before use. Of these, low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) are particularly preferred.

[0029] The thickness of the moisture-absorbing resin layer 7 is not particularly limited, and may be an appropriate thickness depending on the size of the device to which the substrate is applied.

[0030] The moisture-absorbing resin layer 7 can be colored. When the moisture-absorbing resin layer 7 is colored, it can provide design and light blocking properties to the inside of the substrate. When molding the inner surface resin layer 9, a colored inner surface resin layer 9 can be obtained by mixing a pigment into the resin.

[0031] The moisture-absorbing resin layer 7 as described above can be obtained by extrusion molding or the like.

[0032] <Inner surface resin layer 9> The inner surface resin layer 9 is provided between the metal foil 3 and the electronic device to provide insulation between the metal foil 3 and the electronic device. The inner surface resin layer 9 is provided on at least one surface of the moisture-absorbing resin layer 7.

[0033] Fig. 1 shows a layer structure in which the inner surface resin layer 9 is provided on the electronic device side of the moisture-absorbing resin layer 7. In the case of Fig. 1, the inner surface resin layer 9 is used so as to face the inside of the electronic device. Fig. 2 shows a layer structure in which the inner surface resin layer 9 is provided on the outer surface side of the moisture-absorbing resin layer 7 (i.e., between the metal foil 3 and the moisture-absorbing resin layer 7). In the case of Fig. 2, the moisture-absorbing resin layer 7 is used so as to face the inside of the electronic device. Fig. 3 shows a layer structure in which the inner surface resin layer 9 is provided on both sides of the moisture-absorbing resin layer 7. In the case of Fig. 3, the inner surface resin layer 9 is used so as to face the inside of the electronic device.

[0034] Such an inner surface resin layer 9 is generally formed from a polyester resin, a polyamide resin, a polyimide resin, a polycarbonate resin, a polyacrylonitrile resin, an olefin resin, a cyclic olefin resin, or the like, and is preferably formed from a polyester resin, a polyamide resin, an olefin resin, or a cyclic olefin resin. Polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) are particularly preferred polyester resins. When the inner surface resin layer 9 is provided on the electronic device side of the hygroscopic resin layer 7 and is formed from an olefin resin or a cyclic olefin resin, improved adhesion with adhesives or pressure-sensitive adhesives used to attach the electronic device can be expected.

[0035] The thickness of such an inner surface resin layer 9 is 12 to 250 μm, preferably 12 to 200 μm, and more preferably 12 to 150 μm. If the thickness of the inner surface resin layer 9 is less than 12 μm, the insulation between the metal foil 3 and the electronic device will be insufficient, and there is a risk of electrical conduction. If the thickness of the inner surface resin layer 9 exceeds 250 μm, it will be too thick to insulate the metal foil 3 from the electronic device, and manufacturing costs will increase unnecessarily.

[0036] The inner surface resin layer 9 can be colored. When colored, it is possible to impart design features and also to impart light blocking properties to the inside of the substrate. When molding the inner surface resin layer 9, a colored inner surface resin layer 9 can be obtained by mixing a pigment into the resin or by placing an ink layer adjacent to the resin.

[0037] The inner surface resin layer 9 as described above is obtained by extrusion molding or the like.

[0038] <Adhesive Layer 11 > The metal foil 3, the protective resin layer 5, the hygroscopic resin layer 7, and the inner surface resin layer 9 are bonded together by the adhesive layer 11.

[0039] The adhesive used to form the adhesive layer 11 is preferably an epoxy adhesive or a urethane adhesive known as a dry laminating adhesive.

[0040] Epoxy adhesives: The above-mentioned epoxy adhesives are adhesives that bond by curing a liquid epoxy resin with an epoxy curing agent. Such epoxy resins are liquid resins that have epoxy groups in their molecules, and typical examples include those obtained by reacting epichlorohydrin with a phenol compound, an amine compound, or a carboxylic acid, and those obtained by oxidizing an unsaturated compound such as butadiene with an organic peroxide, and either type can be used.

[0041] Specific examples of epoxy adhesives include, but are not limited to, bisphenol A or bisphenol F epoxy resins, novolac epoxy resins, cyclic aliphatic epoxy resins, long-chain aliphatic epoxy resins, glycidyl ester epoxy resins, glycidyl amine epoxy resins, etc. In the present invention, glycidyl amine epoxy resins are particularly suitable because they can form an adhesive layer 11 with a high elastic modulus.

[0042] Furthermore, known epoxy curing agents such as amine-based, acid anhydride, and polyamide curing agents can be used. However, from the viewpoint of being able to form a coating film (adhesive layer 11) that has a particularly high elastic modulus and is easily adapted to thermal shrinkage, amine-based curing agents, and in particular aromatic polyamines such as metaphenylenediamine, are preferably used.

[0043] The ratio of the amount of epoxy resin to the amount of curing agent may be set in accordance with the epoxy equivalent of the epoxy resin so that a sufficient cured film is formed.

[0044] Urethane adhesives: Urethane adhesives are formed from the reaction product of polyisocyanate and polyol. These adhesives usually contain a known curing catalyst such as an amine catalyst, a metal catalyst, or a phosphate-modified compound. The amount of curing catalyst is determined depending on the type of curing catalyst so that a dense cured film (adhesive layer) can be formed at a temperature and for a time that does not cause thermal deformation of the underlying resin.

[0045] The polyol used to form the polyurethane adhesive is a compound having two or more OH groups per molecule, and representative examples include the following compounds: di-, tri-, tetra-, penta-, and hexa-hydroxy compounds; polyester polyols containing two or more OH groups per molecule; polyether polyols containing two or more OH groups per molecule; polycarbonate polyols containing two or more OH groups per molecule; polycaprolactone polyols containing two or more OH groups per molecule; and polyacrylic polyols containing two or more OH groups per molecule. The most suitable polyols in the present invention are polyester polyols.

[0046] The polyisocyanate to be reacted with the polyol is a compound having two or more NCO groups in one molecule. Specific examples of the polyisocyanate include, but are not limited to, the following compounds: Aliphatic isocyanates such as ethylene diisocyanate, trimethylene diisocyanate, and tetramethylene diisocyanate; alicyclic isocyanates such as isophorone diisocyanate, norbornane diisocyanate, bis(isocyanatomethyl)cyclohexane, and 2-isocyanatomethyl-3-(3-isocyanatopropyl)-5-isocyanatomethyl-bicyclo[2,2,1]-heptane; aromatic isocyanates such as xylylene diisocyanate, bis(isocyanatoethyl)benzene, bis(isocyanatomethyl)naphthalene, and bis(isocyanatomethyl)diphenyl ether; sulfur-containing aliphatic isocyanates such as thiodiethyl diisocyanate; aliphatic sulfide isocyanates such as bis[2-(isocyanatomethylthio)ethyl]sulfide; aromatic sulfide isocyanates such as diphenyl sulfide-2,4'-diisocyanate; Aromatic disulfide-based isocyanates such as diphenyl disulfide-4,4'-diisocyanate; Aromatic sulfone-based isocyanates such as diphenyl sulfone-4,4'-diisocyanate; Sulfonic acid ester-based isocyanates such as 4-methyl-3-isocyanate benzenesulfonyl-4'-isocyanate phenol ester; Aromatic sulfonic acid amide-based isocyanates such as 4-methyl-3-isocyanate benzenesulfonyl anilide-3'-methyl-4'-isocyanate; Sulfur-containing heterocyclic isocyanates such as thiophene-2,5-diisocyanate;

[0047] The polyisocyanate is usually used in an amount such that the amount of isocyanate groups (NCO groups) is about 0.8 to 1.2 moles per mole of hydroxyl groups contained in the polyol.

[0048] The above-mentioned epoxy adhesive and urethane adhesive are applied to a predetermined location using a volatile organic solvent such as a hydrocarbon, alcohol, ketone, ester, or ether solvent, and then dried to form the adhesive layer 11. The adhesive layer 11 thus formed is typically cured by being held at a temperature of about 30 to 50°C for 24 hours or more.

[0049] The thickness of the adhesive layer 11 is 0.1 to 10 μm, preferably 2 to 6 μm. If the thickness of the adhesive layer 11 is less than 0.1 μm, the adhesion between the layers may be insufficient. If the thickness of the adhesive layer 11 exceeds 10 μm, the adhesion between the layers can be ensured, but the manufacturing cost increases unnecessarily.

[0050] <Ultraviolet Blocking Layer 13> An ultraviolet blocking layer 13 can be provided on the surface of the protective resin layer 5 opposite to the surface on which the electronic device is mounted (i.e., the surface on the outer surface side of the protective resin layer 5). This ultraviolet blocking layer 13 has the role of reflecting or absorbing ultraviolet rays, thereby preventing ultraviolet rays from penetrating into the substrate and the device.

[0051] The range of ultraviolet wavelengths reflected or absorbed by the ultraviolet blocking layer 13 is 200 nm to 400 nm, preferably 250 nm to 400 nm, and particularly preferably 280 nm to 400 nm. The ultraviolet transmittance of the ultraviolet blocking layer 13 is 0.1% to 20%, preferably 0.1% to 15%, and more preferably 0.1% to 10%. If the ultraviolet transmittance is less than 0.1%, the quality will be excessive and costs will increase. On the other hand, if the ultraviolet transmittance exceeds 20%, deterioration of the substrate or electronic device will progress.

[0052] This UV-blocking layer 13 can be formed from a general thermoplastic resin, but from the standpoints of weather resistance and cost, it is preferable to form it from a resin such as polycarbonate resin, silicone resin, polyester resin, fluorine-based resin, or acrylic resin. The resin forming the UV-blocking layer 13 can be dispersed with an inorganic pigment such as carbon black, which absorbs UV rays, or titanium oxide, which scatters UV rays, as a UV-blocking agent. Furthermore, when UV rays are to be absorbed, an organic UV-absorbing additive such as a benzotriazole, benzophenone, or triazine additive can be dispersed in the resin. When the UV-blocking layer 13 is formed from a resin, it is preferable that the layer be bonded to the protective resin layer 5 with an adhesive layer 11, particularly a dry lamination adhesive.

[0053] Alternatively, the ultraviolet blocking layer 13 can be formed by applying a paint directly to the surface of the protective resin layer 5. In this case, the ultraviolet rays can be blocked from penetrating into the device by reflecting or absorbing all or part of the ultraviolet rays. Suitable paints for such purposes include fluorine-based, silicone-based, urethane-based, and acrylic-based paints.

[0054] <Production and Application of Substrate> A substrate having the layer structure described above is produced by bonding a metal foil 3 to a pre-prepared protective resin layer 5, a hygroscopic resin layer 7, an inner surface resin layer 9, and, if necessary, an ultraviolet blocking layer 13, using an adhesive layer 11. The bonding operation can be performed by any suitable means depending on the type of adhesive layer 11. For example, when using a dry laminating adhesive as the adhesive, a resin that forms the dry laminating adhesive is applied to one or both surfaces of each layer, and the layers are then heated and pressed to obtain the substrate of the present invention. Furthermore, each layer may be pressed sequentially, or all layers may be pressed at once.

[0055] The substrate 1 obtained in this manner has an overall thickness of 75 to 300 μm, preferably 80 to 280 μm, and more preferably 85 to 270 μm. If the overall thickness of the substrate 1 is less than 75 μm, the strength of the entire substrate is insufficient, which may result in tearing, holes, etc. On the other hand, if the overall thickness of the substrate 1 exceeds 300 μm, sufficient flexibility is not obtained, making handling difficult. Note that the overall thickness of the substrate 1 described here does not include the thickness of the adhesive layer 15, which will be described later.

[0056] The substrate of the present invention is used by being disposed so that the moisture-absorbing resin layer 7 or the inner surface resin layer 9 faces the inside of the device. This prevents electrical conduction between the metal foil 3 and the electronic device, while the metal foil 3 and the moisture-absorbing resin layer 7 can exert a barrier property against moisture penetrating from the outside.

[0057] The organic electronic device is not particularly limited, and the substrate of the present invention can be applied to all electronic devices that are susceptible to charge leakage due to the presence of moisture, such as organic EL elements, solar cells, touch panels, etc. The method for installing the substrate 1 is not particularly limited, and the substrate is installed by a method appropriate for the application. For example, when the substrate of the present invention is used as a back sheet for a solar cell, it is fixed integrally with the cell or the like by a frame.

[0058] Furthermore, when the substrate 1 is used in an organic EL device or the like, an adhesive or the like can be applied to the surface of the hygroscopic resin layer 7 or the inner surface resin layer 9 on the side where the electronic device is mounted, to provide an adhesive layer 15 and attach it to the device surface. In this form, the moisture absorption capacity of the hygroscopic resin layer 7 can absorb and dry moisture inside the device via the adhesive layer 15. Furthermore, providing the substrate in a form provided with the adhesive layer 15 can also reduce the number of processing steps at the recipient.

[0059] Examples of materials constituting the adhesive layer 15 include known pressure-sensitive adhesives such as acrylic, silicone, and butadiene-based adhesives; hot-melt adhesives such as ethylene-vinyl acetate copolymer resins, polyvinyl butyral, olefin, and cyclic olefin-based adhesives; UV-curable adhesives such as epoxy and acrylic adhesives; and heat-curable adhesives such as silicone adhesives. Among these, hot-melt adhesives are preferred because they do not require a drying process, and hot-melt adhesives made from olefin or cyclic olefin-based adhesives are more preferred in terms of cost and ease of handling. The thickness of the adhesive layer 15 may be determined appropriately depending on the application.

[0060] The adhesive layer 15 is disposed on the innermost surface of the substrate 1 of the present invention, i.e., at a position facing the electronic device during use. FIGS. 4 to 6 show examples of layer configurations when the adhesive layer 15 is provided on the substrate 1 of the present invention. As shown in FIG. 4 , when the inner resin layer 9 is provided only on the electronic device mounting side of the moisture-absorbing resin layer 7, the adhesive layer 15 is provided on the electronic device mounting side of the inner resin layer 9. Also, as shown in FIG. 5 , when the inner resin layer 9 is provided only on the metal foil 3 side of the moisture-absorbing resin layer 7, the adhesive layer is provided on the electronic device mounting side of the moisture-absorbing resin layer 7. Furthermore, as shown in FIG. 6 , when the inner resin layer 9 is provided on both sides of the moisture-absorbing resin layer 7, the adhesive layer 15 is provided on the electronic device mounting side of the inner resin layer 9 provided on the electronic device mounting side of the moisture-absorbing resin layer 7 via the adhesive layer 11. Although not shown, when the inner resin layer 9 is not provided, the adhesive layer 15 is provided on the electronic device mounting side of the moisture-absorbing resin layer 7.

[0061] Furthermore, since the substrate 1 of the present invention has the metal foil 3, it can be used on the side of the above-mentioned device where light transparency is not required, such as the non-light-receiving surface of a back sheet of a solar cell, the non-light-emitting surface of an organic electroluminescence element, or the side surface of various devices.

[0062] In the substrate 1 of the present invention, most of the moisture that attempts to penetrate into the device is blocked by the metal foil 3, thereby maintaining the moisture absorption capacity of the hygroscopic resin layer 7. As a result, moisture penetration into the device is prevented, and the device can be kept dry for a long period of time. Furthermore, the substrate 1 of the present invention is flexible, and therefore easy to handle.

[0063] <Preparation of Substrates> A coating solution containing a urethane adhesive resin dissolved or dispersed as a dry lamination adhesive was prepared on aluminum foil having the thickness shown in Table 1 as the metal foil, and the coating solution was then applied and dried. A 25 μm-thick PET resin film obtained by extrusion molding was then heat-pressed onto the metal foil as a protective resin layer. Next, the coating solution was applied to the surface of the metal foil opposite the surface to which the protective resin layer was applied and dried. An olefin resin having 25 parts by mass of desiccant dispersed in a resin matrix was then extruded and heat-pressed onto the dried coating solution as a moisture-absorbing resin layer. If necessary, the coating solution was further applied to the surface of the moisture-absorbing resin layer and dried. A 25 μm-thick PET resin film obtained by extrusion molding was then heat-pressed onto the surface as an inner resin layer. Substrates A to R shown in Table 1 were prepared by varying the thickness and type of the metal foil, protective resin layer, and inner resin layer. In addition, a substrate S shown in Table 2 was also prepared using a similar method, which has a layer structure in which an inner surface resin layer is provided on the outer surface side of the moisture-absorbing resin layer (i.e., between the aluminum foil and the moisture-absorbing resin layer). A substrate T shown in Table 3 was also prepared using a similar method, which has a layer structure in which an inner surface resin layer is provided on both sides of the moisture-absorbing resin layer. In a similar method, substrates U to Y shown in Table 4 were prepared, which have a layer structure in which an adhesive layer made of a hot-melt adhesive is provided on the device-mounting side of the moisture-absorbing resin layer or the inner surface resin layer.

[0064]

[0065]

[0066]

[0067]

[0068] Experimental Example 1 Calcium Corrosion Method (No Bending Test) The effect of moisture permeation on the substrate A prepared above was measured using the calcium corrosion method (JIS K7129-7). Under an inert gas atmosphere, a calcium film was formed on the surface of a glass substrate to a thickness of 100 nm, and then a pressure-sensitive adhesive was attached. Substrate A was then attached so that the surface of the moisture-absorbing resin layer was in contact with the adhesive, to prepare an evaluation cell. The evaluation cell was stored in a constant temperature and humidity chamber at 40°C and 90% RH for 1000 hours, and the state of the calcium thin film was observed from the glass substrate side using a microscope. The evaluation criteria were as follows. The results are shown in Table 5. Evaluation Criteria ◯: No corrosion of the calcium film was observed. ×: Corrosion of the calcium film was confirmed.

[0069] <Calcium corrosion method (with bending test)> A bending test was performed on substrate A using a tabletop durability tester (manufactured by Yuasa System Co., Ltd.) in an environment of 23°C and 50% RH, with a diameter of 5 mm, in both bending directions, 10,000 times each. Substrate A after the bending test was used to prepare an evaluation cell in the same manner as above. The evaluation cell was stored in a constant temperature and humidity chamber in an environment of 40°C and 90% RH for 1,000 hours, and the state of the calcium thin film was then observed using a microscope from the glass substrate side. The evaluation criteria were the same as above. The results are shown in Table 5.

[0070] Experimental Example 2 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1, except that the substrate A was changed to the substrate B.

[0071] Experimental Example 3 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1, except that the substrate A was changed to the substrate C.

[0072] Experimental Example 4 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1, except that the substrate A was changed to the substrate D.

[0073] Experimental Example 5 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1, except that the substrate A was changed to the substrate E.

[0074] Experimental Example 6 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1, except that the substrate A was changed to the substrate F.

[0075] Experimental Example 7 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1, except that the substrate A was changed to the substrate G.

[0076] Experimental Example 8 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1, except that the substrate A was changed to the substrate H.

[0077] Experimental Example 9 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1, except that the substrate A was changed to the substrate I.

[0078] Experimental Example 10 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1, except that substrate A was changed to substrate J.

[0079] Experimental Example 11 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1, except that the substrate A was changed to the substrate K.

[0080] Experimental Example 12 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1, except that the substrate A was changed to the substrate L.

[0081] Experimental Example 13 A coating solution containing a urethane adhesive resin dissolved or dispersed therein as a dry lamination adhesive was prepared on the surface of the protective resin layer of the substrate A, and the coating solution was then applied and dried. An acrylic resin UV-cut film (55 μm) was then heat-pressed onto the coating to form a UV-blocking layer, thereby producing a substrate M. Measurement was carried out using the calcium corrosion method in the same manner as in Experimental Example 1.

[0082] Experimental Example 14 A fluorine-based UV-cut coating layer (10 μm thick) was formed as an ultraviolet blocking layer on the surface of the protective resin layer of the substrate A to prepare a substrate N. Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1.

[0083] Experimental Example 15 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1, except that the substrate A was changed to the substrate O.

[0084] Experimental Example 16 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1, except that the substrate A was changed to the substrate P.

[0085] Experimental Example 17 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1, except that the substrate A was changed to the substrate Q.

[0086] Experimental Example 18 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1, except that the substrate A was changed to the substrate R.

[0087] Experimental Example 19 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1, except that the substrate A was changed to the substrate S.

[0088] Experimental Example 20 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 1, except that the substrate A was changed to the substrate T.

[0089] Experimental Example 21 Calcium corrosion method (no bending test) The effect of moisture permeation on the substrate U prepared above was measured using the calcium corrosion method (JIS K7129-7). Under an inert gas atmosphere, a calcium film was formed on the surface of a glass substrate to a thickness of 100 nm. Next, the substrate U was attached to the glass substrate using the hot melt adhesive attached to the substrate U to prepare an evaluation cell. The evaluation cell was stored in a constant temperature and humidity chamber at 40°C and 90% RH for 1000 hours, after which the state of the calcium thin film was observed from the glass substrate side using a microscope. The evaluation criteria were as follows. The results are shown in Table 5. Evaluation criteria: ◯: No corrosion of the calcium film was observed. ×: Corrosion of the calcium film was confirmed.

[0090] <Calcium Corrosion Method (with Bending Test)> Substrate U, without a hot-melt adhesive, was subjected to a bending test in both bending directions at a diameter of 5 mm using a tabletop durability tester (manufactured by Yuasa System Co., Ltd.) in an environment of 23°C and 50% RH, with 10,000 cycles in each direction. After the bending test, a hot-melt adhesive was attached to the substrate, and an evaluation cell was prepared in the same manner as above. The evaluation cell was stored in a constant temperature and humidity chamber at 40°C and 90% RH for 1,000 hours, after which the state of the calcium thin film was observed with a microscope from the glass substrate side. The evaluation criteria were the same as above. The results are shown in Table 5.

[0091] Experimental Example 22 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 21, except that the substrate U was changed to the substrate V.

[0092] Experimental Example 23 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 21, except that the substrate U was changed to the substrate W.

[0093] Experimental Example 24 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 21, except that the substrate U was changed to the substrate X.

[0094] Experimental Example 25 Measurement was carried out by the calcium corrosion method in the same manner as in Experimental Example 21, except that the substrate U was changed to the substrate Y.

[0095]

[0096] In the calcium corrosion method (with bending test), no calcium corrosion was observed for substrates A to P and S to Y, and the substrate appearance after the bending test was also good. In other words, it can be said that substrates A to P and S to Y are substrates that combine moisture barrier properties and flexibility. On the other hand, for substrate Q, no calcium film corrosion was observed, but creases appeared on the surface. It is believed that substrate Q had a large total substrate thickness and insufficient flexibility, which caused the creases to appear during the bending test. Furthermore, for substrate R, calcium film corrosion was observed. Because substrate R had a large metal foil thickness and insufficient flexibility, numerous pinholes appeared in the metal foil during the bending test, which allowed a large amount of moisture to penetrate, causing the hygroscopic resin layer to swell in a short period of time, and the moisture that was not completely absorbed reached the calcium film.

[0097] 1: Substrate for mounting electronic device 3: Metal foil 5: Protective resin layer 7: Moisture-absorbing resin layer 9: Inner surface resin layer 11: Adhesive layer 13: UV-blocking layer 15: Sticky layer

Claims

1. A substrate for mounting an electronic device, comprising a metal foil and a protective resin layer, the protective resin layer being provided on one surface of the metal foil, the other surface of the metal foil being the electronic device mounting surface, and a moisture absorbing resin layer being provided on the other surface of the metal foil.

2. The electronic device mounting substrate according to claim 1, wherein the metal foil has a thickness of 5 to 20 μm.

3. The electronic device mounting substrate according to claim 1, wherein the metal foil is made of aluminum.

4. The substrate for mounting an electronic device according to claim 1, wherein the protective resin layer is made of a polycarbonate resin, a silicone resin, a polyester resin, a fluorine-based resin or an acrylic resin.

5. The electronic device mounting substrate according to claim 1, wherein the moisture-absorbing resin layer is formed from an olefin resin having a desiccant dispersed therein.

6. The electronic device mounting substrate according to claim 5, wherein the desiccant is an agent that chemically captures moisture by reacting with water.

7. The substrate for mounting an electronic device according to claim 1, wherein an inner surface resin layer is provided on at least one surface of the moisture-absorbing resin layer.

8. The electronic device mounting substrate according to claim 7, wherein the inner resin layer is formed from a polyester resin, a polyamide resin, an olefin resin or a cyclic olefin resin.

9. The electronic device mounting substrate according to claim 8, wherein the metal foil, the protective resin layer, the hygroscopic resin layer and the inner surface resin layer are bonded together with a dry lamination adhesive.

10. The electronic device mounting substrate according to claim 9, wherein the dry lamination adhesive is formed from a urethane resin or an epoxy resin.

11. The substrate for mounting an electronic device according to claim 1, wherein an ultraviolet blocking layer is provided on the surface of said protective resin layer opposite to the surface on which said electronic device is mounted.

12. The electronic device mounting substrate according to claim 1, which has an overall thickness of 75 to 300 μm.

13. The substrate for mounting an electronic device according to claim 7, wherein the hygroscopic resin layer or the inner surface resin layer is disposed so as to face the inside of the device.

14. The substrate for mounting an electronic device according to claim 1, wherein an adhesive layer made of a hot melt adhesive is provided on the surface of the moisture absorbing resin layer on the side on which the electronic device is mounted.

15. The electronic device mounting substrate according to claim 14, wherein the hot melt adhesive is formed from an olefin resin or a cyclic olefin resin.

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