JP4662751B2 - Transparent sheet heating element and manufacturing method thereof - Google Patents

Description

  The present invention relates to a transparent sheet heating element and a method for manufacturing the same, and more particularly to a transparent sheet heating element for a liquid crystal element and a method for manufacturing the same.

  In recent years, the demand for liquid crystal display elements has increased, but there are problems such as slow operation of the liquid crystal when used in cold regions, and the liquid crystal display elements are also provided with a transparent surface heater for temperature control. There is a growing need.

  Conventionally, as a liquid crystal display element used under conditions such as cold regions, for example, Patent Document 1 generates heat from a transparent conductive film such as silver, copper, or indium tin oxide (ITO) provided on a transparent substrate. A transparent surface heater having a pair of metal electrodes for use as a surface and for energizing the transparent conductive film has been reported.

  However, with this method, it is not always easy to uniformly heat the entire liquid crystal element, and when a heating resistor made of a transparent conductive film that increases haze and reflection as the thickness increases, the liquid crystal display is viewed. It gets in the way. In addition, at a thin thickness that can ensure transparency, the sheet resistance value is large, so that the amount of current flowing is small and the rise of heat generation may be slow. Furthermore, when a sputtering method, a vapor deposition method, or the like is used, the manufacturing cost is increased.

  Further, in Patent Document 2, a solution of an organic silver compound or the like is spray-coated on a substrate to form a fine network structure film, which is irradiated with radiation to reduce and precipitate silver to form a fine silver network structure. It is described that a transparent conductive film having a slag is obtained, which can be used as a transparent planar heating element. However, this method reduces silver by irradiation with ultraviolet rays or the like, but there is a problem in forming a desired network structure with good stability and reproducibility.

Therefore, there is a demand for a method for more easily manufacturing a high-quality transparent sheet heating element that has high transparency and visibility, has a low resistance value of the conductive portion, and can generate uniform heat.
JP-A-9-306647 Japanese Patent Laid-Open No. 10-312715

  The present invention provides a transparent sheet heating element with high transparency and visibility, low electrical resistance value of a conductive part and high quality surface heating characteristics capable of uniform heat generation, and the transparent sheet heating element. The main object is to provide a method for manufacturing at low cost with good reproducibility.

  As a result of earnest research to solve the above-mentioned problems, the present inventor applied (a) a liquid or dry film-like photosensitive resist to the transparent receiving layer surface of a transparent substrate, and a resin layer. (B) forming a recess corresponding to the shape of the network conductive layer in the resin layer by photolithography, (c) injecting a conductive paste into the recess, and A step of removing excess conductive paste, (d) a step of heat-treating the conductive paste to form a network-like conductive layer, (e) steps (c) and (d) above once more A method for producing a transparent sheet heating element comprising: a step of repeating; (f) a step of removing the resin layer from the transparent receiving layer surface of the transparent substrate; and (g) a step of providing a pair of electrodes on the conductive layer. A transparent sheet heating element manufactured by the manufacturing method, It was found to be able to solve the serial problems. Based on this knowledge, the present inventor has further studied and completed the present invention.

  That is, the present invention provides the following transparent sheet heating element and method for producing the same.

Item 1. A transparent planar heating element having a network-like conductive layer on the transparent receiving layer surface of a transparent substrate provided with a transparent receiving layer on at least one surface, and having a pair of electrodes on the conductive layer. A manufacturing method comprising the following steps (a) to (g):
(A) a step of applying or sticking a liquid or dry film-like photosensitive resist to the transparent receiving layer surface of a transparent substrate to form a resin layer;
(B) forming a recess corresponding to the shape of the network-like conductive layer in the resin layer by a photolithography method;
(C) a step of injecting a conductive paste into the recess and removing excess conductive paste on the resin layer;
(D) a step of heat-treating the conductive paste to form a network-like conductive layer;
(E) a step of repeating the steps (c) and (d) one or more times,
(F) The process of removing a resin layer from the transparent receiving layer surface of a transparent base material, and (g) The process of providing a pair or more electrode in an electroconductive layer.

  Item 2. The transparent receiving layer is composed of an aggregate of fine particles mainly containing at least one selected from titania and alumina, and the average particle diameter of the fine particles is about 10 to 100 nm, and the fine particles are about 10 to 100 nm between the fine particles. Item 2. The production method according to Item 1, wherein the method has pores and the thickness of the transparent receptor is about 0.05 to 20 μm.

  Item 3. The conductive paste is a particulate silver oxide having an average particle size of 2 μm or less, a silver salt of a tertiary fatty acid having a total carbon number of 5 to 30, an aromatic hydrocarbon, an ether ester of ethylene glycol, an ether ester of propylene glycol Item 3. The transparent sheet heating element according to Item 1 or 2, which is a conductive paste containing a solvent mainly comprising at least one selected from the group consisting of terpineol and terpineol.

  Item 4. Item 4. The method for producing a transparent sheet heating element according to any one of Items 1 to 3, wherein the temperature of the heat treatment is about 150 to 200 ° C.

  Item 5. Item 5. The transparent sheet heating element according to any one of Items 1 to 4, wherein the transparent substrate has a hard coat layer on the surface opposite to the surface having the transparent receiving layer.

  Item 6. Item 6. A transparent sheet heating element manufactured by the manufacturing method according to any one of Items 1 to 5.

  Item 7. The liquid crystal display body laminated | stacked in order of a polarizing plate / liquid crystal element / polarizing plate / adhesion layer / transparent planar heating element of claim | item 6, and a transparent insulating layer.

  Item 8. Item 7. A polarizing plate protective film comprising the transparent sheet heating element according to Item 6.

  Item 9. Item 9. A liquid crystal display device, wherein the polarizing plate protective film according to Item 8 is laminated on at least one surface of the polarizing plate.

  Item 10. A retardation film comprising the transparent sheet heating element according to claim 6.

  Item 11. Item 11. A liquid crystal display device comprising the retardation film according to Item 10 laminated on at least one surface of a polarizing plate.

The present invention is described in detail below.
I. Transparent sheet heating element
Transparent base material The transparent base material constituting the transparent sheet heating element of the present invention has transparency enough to allow at least a liquid crystal display (LCD) to be seen through, heat resistance, weather resistance, non-shrinkage, and machine Those having excellent mechanical strength and chemical resistance are preferred.

  The material of the transparent base material is polyester resin such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN); polycarbonate resin; poly (meth) acrylate resin; silicone resin; cyclic polyolefin resin; polyarylate resin; Examples thereof include thermoplastic resins such as ether sulfone resins. Among the above, PET or PEN is preferably employed when comprehensively judged from the viewpoints of transparency, cost, durability, heat resistance, and the like. The thickness is usually about 25 μm to 5 mm.

  Here, the transparency of the transparent base material is not particularly limited as long as it is transparent enough to be used for applications such as a liquid crystal display (LCD). Usually, the total light transmittance measured by JIS K7105 is 80% or more, preferably about 85 to 90%, and the haze value measured by JIS K7105 may be about 0.1 to 3%.

  Examples of the form of the transparent substrate include forms that can be used as a planar heating element, that is, a film form, a sheet form, a flat form, and the like. When the transparent substrate is in the form of a film or a sheet, the thickness is usually about 25 to 200 μm, preferably about 30 to 188 μm. In particular, when used as a heating element of a liquid crystal display (LCD), about 40 to 125 μm is preferable. Moreover, in the case of plate shape, the thickness should just be about 0.5-5 mm normally, Preferably it is about 1-3 mm.

  The transparent substrate used in the present invention is provided with a transparent receiving layer on at least one surface thereof. The transparent receiving layer is composed of an aggregate of fine particles mainly composed of at least one selected from titania and alumina, and the average particle diameter of the fine particles is about 10 to 100 nm, and about 10 to 100 nm between the fine particles. Have pores. The thickness of the transparent receiving layer is about 0.05 to 20 μm.

  By providing the transparent receptive layer on the transparent substrate, the adhesion of the conductive paste to the transparent substrate is greatly improved, and the resulting conductive pattern is firmly bonded on the transparent substrate. Has the advantage. And if it is said transparent receiving layer, it will hardly affect the transparency of a base material.

  The method for forming the transparent receiving layer on the transparent substrate may be either a wet process or a dry process, and is not particularly limited, but a wet process is preferable from the viewpoint of productivity and cost. In the wet process, a predetermined raw material may be coated (applied) on a substrate by a known method. Examples of the raw material include tetraalkoxysilane, tetraalkyl titanate, and hydrolysates thereof. You may add suitably other components, such as resin and surfactant, to the said raw material as needed. Examples of the coating method include gravure coating, offset coating, comma coating, die coating, slit coating, spray coating, plating method, sol-gel method, LB film method and the like. A sol-gel method is particularly preferable. As the dry process, for example, silicon oxide, titanium oxide or the like may be used as a raw material, and the substrate may be coated by CVD, vapor deposition, sputtering, ion plating, or the like.

Hard coat layer In addition, the transparent base material used in the present invention may be provided with a hard coat layer on the surface on which the conductive layer and the resin layer are formed, that is, the surface opposite to the surface having the transparent receiving layer. .

  What is necessary is just to form a hard-coat layer using the hard-coat agent of a general material, and if a transparency is not impaired, there will be no restriction | limiting in particular. Of these, ultraviolet curable acrylate resins are preferred. The main component is not particularly limited as long as it is an ultraviolet curable acrylate having two or more functional groups such as polyester acrylate, urethane acrylate, and epoxy acrylate. 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, tetraethylene glycol acrylate, 1,9-nonanediol diacrylate, tricyclodecane dimethanol diacrylate, neopentyl glycol PO modified diacrylate, EO modified bisphenol A di Bifunctional acrylate such as acrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol hexaacrylate, trimethylolpropane EO modified triacrylate, PO modified glycerin triacrylate, trishydroxyethyl isocyanate Use of polyfunctional acrylates such as nurate triacrylate is preferred.

  In addition, a photopolymerization initiator is usually added to the ultraviolet curable acrylate resin. As a photopolymerization initiator, 1-hydroxycyclohexyl phenyl ketone (Irgacure 184 manufactured by Ciba Specialty Chemicals Co., Ltd.), 2-hydroxy-2-methyl-1-phenyl-propan-1-one, and the like are added. Thus, a sufficient cured film can be obtained. Others, benzoin, benzoin derivative, benzophenone, benzophenone derivative, thioxanthone, thioxanthone derivative, benzyldimethyl ketal, α-aminoalkylphenone, monoacylphosphine oxide, bisacylphosphine oxide, alkylphenylglyoxylate, diethoxyacetophenone, titanocene compound A photopolymerization initiator such as can also be used.

  The blending ratio of these photopolymerization initiators is preferably 1 to 10 parts by weight with respect to 100 parts by weight of the ultraviolet curable acrylate resin. If the amount is less than 1 part by weight, the polymerization does not start sufficiently, and if it exceeds 10 parts by weight, the durability is lowered in some cases.

  In addition, in the said ultraviolet curable acrylate resin, a 3rd component (UV absorber, a filler, etc.) may be included in the grade which does not impair the transparency, and there is no restriction | limiting in particular.

  As a method for forming a hard coat layer on a transparent substrate, a known method can be adopted and there is no particular limitation. For example, the hard coat agent may be applied on a transparent substrate using a Mayer bar or the like, dried, and irradiated with ultraviolet rays. The thickness of the hard coat layer after curing is preferably about 0.1 to 20 μm, particularly preferably about 1 to 10 μm.

  By providing a hard coat layer on a transparent base material, it is possible to suppress whitening and yellowing due to precipitation of oligomers from the base resin during the heat treatment described later. High transparency is ensured. In addition, it is possible to prevent scratches during the manufacturing process of the transparent sheet heating element.

Conductive layer The conductive layer formed on a transparent substrate can be formed using a conductive paste. For example, a metal powder (for example, a composite powder in which nickel powder, silver powder, or silver and copper are mixed in an acrylic resin binder), or a metal powder (for example, gold powder or silver powder) mixed in a solvent can be used. However, the metal powder is not a pure metal, as long as it has a predetermined conductivity obtained through a heating process or the like. In that sense, the metal oxide is a metal oxide, which will be described later, or an organic acid metal salt. Certain tertiary fatty acid silver salts can also be selected. In addition, the resin binder solvent used at the time of pasting can be appropriately selected depending on processability and stability, and is not particularly limited to the above.

  In particular, a conductive paste containing particulate silver oxide, tertiary fatty acid silver and a solvent stably exhibits low resistance, and thus is preferably used. The average particle size of the particulate silver oxide is 2 μm or less, and when silver oxide having a particle size larger than this is used, the average particle size is set in the manufacturing process (kneading step, synthesis step, etc.) of the conductive paste. What is necessary is just to be 2 micrometers or less. The average particle size is more preferably 200 to 500 nm.

  The tertiary fatty acid silver salt is a silver salt of a tertiary fatty acid having a total carbon number of 5 to 30, preferably 10 to 30, and can be dissolved or homogeneously dispersed in a dispersion medium used during paste preparation. This tertiary fatty acid silver salt serves as a lubricant, and when silver oxide and tertiary fatty acid silver salt are kneaded to form a paste, the silver oxide is pulverized to promote micronization and silver oxide. It exists around the grains to suppress reaggregation of silver oxide grains and improve dispersibility. For this reason, it can be made paste without adding a binder. Further, this tertiary fatty acid silver salt has a function of precipitating silver during heating and fusing together silver particles produced by reduction from silver oxide.

  Specific examples of such tertiary fatty acid silver salts include silver pivalate, silver neoheptanoate, silver neononanoate, and silver neodecanoate. The production of the tertiary fatty acid silver salt is carried out, for example, by neutralizing the tertiary fatty acid with an alkali compound in water and reacting this with silver nitrate.

  The blending ratio of the particulate silver oxide and the tertiary fatty acid silver salt in the conductive paste is such that the weight ratio (A / B) is when the weight of the silver oxide is A and the weight of the tertiary fatty acid silver salt is B. It is preferable that it is 1 / 4-3 / 1.

  In the conductive paste, a solvent is contained in addition to silver oxide and tertiary fatty acid silver salt. The solvent is not particularly limited as long as it does not react with silver oxide and the tertiary fatty acid silver salt and can disperse them satisfactorily. For example, aromatic solvents such as toluene, ether esters of ethylene glycol such as triethylene glycol monobutyl ether, ether esters of propylene glycol such as tripropylene glycol normal butyl ether, and organic solvents such as terpineol are used. The usage-amount of a solvent should just be about 1-100 weight part with respect to 100 weight part of particulate silver oxide.

  Further, if necessary, a dispersing agent can be added to disperse the particulate silver oxide well, thereby preventing secondary aggregation of the particulate silver oxide. As the dispersant, a fiber-based polymer such as hydroxypropylcellulose, a water-soluble polymer such as polyvinylpyrrolidone, polyvinyl alcohol, or the like is used. The amount used may be 0 to 20 parts by weight with respect to 100 parts by weight of the particulate silver oxide.

  The conductive paste of the present invention is produced by, for example, a method in which particulate silver oxide, tertiary fatty acid silver salt and a solvent are mixed and then kneaded with a roll mill or the like to form a paste. Since this conductive paste has particulate silver oxide having an average particle diameter of 2 μm or less, metallic silver particles are easily generated even under relatively low-temperature heating conditions (for example, about 150 to 200 ° C.) and melted together. It becomes a continuous coating or lump of metallic silver.

  In addition, the conductive paste is adjusted to have a viscosity and thixotropy suitable for forming a conductive layer, which will be described later, and used for forming the conductive layer. Adjustment of viscosity and thixotropy can be suitably selected according to the particle size of particulate silver oxide, the type of tertiary fatty acid silver salt, the type of solvent, and the like. For example, the viscosity of the conductive paste may be about 10 to 10000 dPa · s, and the thixotropy index may be appropriately selected within the range of about 0.1 to 0.9.

  Examples of such conductive paste include “Doutite XA-9080” and “Doutite XA-9083” manufactured by Fujikura Kasei Co., Ltd.

  Note that these conductive pastes may exhibit volume shrinkage due to heat treatment, and in that case, the resistance value may not be sufficiently low. Therefore, it is preferable not only to perform the conductive paste injection step and the heat treatment step once, but also to repeat at least twice, preferably about 2 to 5 times.

As the resin for forming the resin layer, a photosensitive resist used in a general photolithography method is used.

  The photosensitive resist includes a negative type and a positive type. When the negative type is exposed and receives ultraviolet rays, only the portion is photocured. The positive type has a light characteristic opposite to that of the negative type, and a portion that receives ultraviolet light undergoes photolysis. If both development processes are performed, the unexposed portion is dissolved and removed in the negative type, and the exposed portion is dissolved and removed in the positive type. Accordingly, a positive mask (black mesh pattern is black) is used for the negative (exposure original plate), and a negative mask (black mesh pattern is transparent) is used for the positive mask.

  The resist is not particularly limited, but in general, an acrylic type can be used for a negative type, and a diazo type can be used for a body type. In addition, since the resist is generally in a liquid state, it is applied by a coating method. However, the resist may be in the form of a film in advance like a dry film.

Transparent sheet heating element An embodiment of the transparent sheet heating element of the present invention will be described with reference to the drawings. FIG. 1A is a schematic sectional view of the embodiment, and FIG. 1B is a plan view seen from the A0 side of FIG. FIG.1 (c) is the top view which expanded and showed the A1 area | region which is a part of transparent planar heating element of FIG.1 (b).

  In FIG. 1, 110 is a transparent substrate (base substrate), 130 is a transparent receiving layer, 120 is a conductive layer, 121 is a straight line, 122 is a mesh, 123 is a planar heating region, and 125 is an electrode. .

  One embodiment of a transparent sheet heating element will be described with reference to FIG. The transparent planar heat generating region 123 shown in FIG. 1B includes a transparent substrate 110, a transparent receiving layer 130, and a conductive layer 120, as shown in FIG. In addition, as shown in FIG. 1C, in the transparent sheet-like heat generating region 123, two parallel straight lines made of a conductive material intersect to form a mesh 122, and the mesh serves as a heating element. ing. A network-like conductive layer 120 is provided on a transparent substrate surface.

  The electrode 125 includes the conductive layer 120 and is formed integrally with the mesh 122. However, the electrode 125 and the mesh 122 may be made of different materials.

  The electrode is not particularly limited as long as it has conductivity, and examples thereof include conductive paste, conductive resin, conductive resin and metal foil, metal plating, and metal nanoparticles. From the viewpoint of contact resistance, a lower resistance value is preferred. Any of these electrodes may be employed and may be formed by a known method.

  The group of two parallel straight lines 121 constituting the conductive layer 120 is formed in a mesh shape (or lattice shape) as shown in FIG. The mesh 122 has a lattice shape with the same vertical or horizontal width or different widths, and the opening is not only a right-sided quadrilateral, but is also obliquely intersected at a certain angle, that is, when the opening is a rhombus, The case where the polygonal shape is about a 10-sided, that is, the opening is a 5 to 10-sided shape is also included. Among these, from the viewpoint of uniform surface heat generation characteristics, a conductive layer having a uniform line width and a right-sided quadrangular (particularly square) mesh shape is preferable.

In addition, it is necessary to determine the mesh having an opening degree on the assumption that both the total light transmittance and the surface heat generation characteristic are increased. At least the total light transmittance as the finally obtained transparent sheet heating element is adjusted to 60% or more, preferably 65% or more, more preferably 70% or more.
II. Manufacturing Method of Transparent Planar Heating Element Next, the manufacturing method of the transparent sheet heating element of the present invention will be described with reference to the drawings.

  The method for producing a transparent sheet-shaped heating element of the present invention has a network-like conductive layer on the transparent receiving layer surface of a transparent substrate provided with a transparent receiving layer on at least one surface, and a pair of the conductive layers are provided on the conductive layer. (A) A liquid or dry film photosensitive resist is applied or adhered to a transparent receiving layer surface of a transparent substrate, and a resin layer is formed. A step of forming, (b) a step of forming a recess corresponding to the shape of the network conductive layer in the resin layer by photolithography, and (c) injecting a conductive paste into the recess to cause excess on the resin layer. Removing the conductive paste, (d) heating the conductive paste to form a mesh-like conductive layer, (e) repeating the steps (c) and (d) one or more times. (F) removing the resin layer from the transparent receiving layer surface of the transparent substrate Characterized in that it has steps, and the steps of providing one or more pairs of electrodes (g) conducting layer.

  First, as shown in FIG. 2A, a liquid or dry film photosensitive resist is applied or pasted on the transparent receiving layer 240 of the transparent substrate 210, and a resin layer is formed on the transparent substrate 210. 220 is formed. The film thickness of the resin layer 220 to be formed can be adjusted according to the film thickness of the conductive layer of the target planar heating element.

  Next, the resin layer 220 made of the photosensitive resist of FIG. 2A is removed by photolithography to correspond to the shape of the mesh-like conductive layer shown in FIG. Forming a recess in cross section. The recess is formed between the exposed surface of the transparent receiving layer 4 and the resin layer. The photosensitive resist may be either a negative type or a positive type, and is not particularly limited.

  Next, a conductive paste is applied to the side of the transparent substrate 210 shown in FIG. 2B where the resin layer 220A is formed, and the conductive paste is injected into the recesses in the cross section (FIG. 2C). Thereafter, excess conductive paste present on the resin layer 220A is removed with a rubber or resin squeegee, and then the conductive paste is heated (for example, 150 to 200 ° C.) to form the conductive layer 230A. . Since the conductive paste may exhibit volume shrinkage due to heat treatment, the conductive paste injection step and the heat treatment step are not only performed once, but may be repeated at least twice, preferably about 2 to 5 times. preferable.

  Thereby, the resin layer 220A and the conductive layer 230A are formed on the transparent receiving layer surface of the transparent substrate 210 (FIG. 2D).

  Further, by removing the resin layer 220A from the transparent receiving layer surface of the transparent substrate 210, a mesh-like conductive layer 230A is formed on the surface of the transparent substrate 210 (FIG. 2 (e)). Here, as a method for removing the resin layer 220A from the transparent substrate 210, a known method such as separation in an aqueous sodium hydroxide solution or dissolution in an organic solvent such as acetone can be employed.

  Next, a pair of electrodes are provided on the obtained net-like conductive layer in FIG. The electrodes can be provided at both ends of the transparent planar heating region 123 as shown in FIG. The transparent sheet heating element of the present invention functions as a heating element by energizing this electrode. The electrode used is not particularly limited as long as it has conductivity, and examples thereof include a conductive resin, a conductive resin and metal foil, metal plating, and metal nanoparticles. From the viewpoint of contact resistance, a lower resistance value is preferred. Any of these electrodes may be employed and may be formed by a known method.

Thus, the transparent sheet heating element of the present invention is manufactured. Since this method for producing a transparent sheet heating element can be carried out simply and with good reproducibility, it is suitable for mass production of a transparent sheet heating element.
III. Characteristics of Transparent Planar Heating Element The transparent sheet heating element of the present invention is manufactured as described above. The transparent sheet heating element of the present invention has a high aperture ratio, for example, 75% or more, particularly about 80 to 95%. Therefore, high transparency is achieved. In this specification, the aperture ratio (%) means the ratio of the area of the portion not covered with the conductive layer in the entire area of the transparent sheet-like heat generating region, and specifically, shown in FIG. In one pattern of the mesh-like conductive layer of the transparent sheet heating element to be produced, (area B / area A) × 100 (%) or pattern line width (W), and the pattern line interval (pitch) ( When (P), it means (P−W) ² / P ² × 100.

  Further, the line width (W) of the grid or network pattern of the conductive layer is usually about 10 to 30 μm, preferably about 15 to 20 μm. A pattern having a line width of less than about 10 μm tends to be difficult to produce, and a pattern having a line width of more than 30 μm is not preferable because the pattern tends to be noticeable.

  In addition, the space | interval (pitch) (P) of the line | wire of a grid | lattice-like or mesh-like pattern can be suitably selected in the range with which said aperture ratio and line width are satisfy | filled. Usually, it may be in the range of about 200 to 400 μm.

  The thickness of the conductive layer (the average height of the conductive layer in the vertical direction from the surface of the transparent substrate) changes the thickness of the resin layer (that is, the photosensitive resist layer) used in the photolithography method in the above manufacturing method. Can be adjusted. For example, it is about 1 μm or more, particularly about 1 to 30 μm.

  The transparent sheet heating element of the present invention has a feature that resistance is small and resistance value is less uneven. This is presumably because the resistance is lowered because there is no disconnection of the thin wire of the conductive layer. The surface resistance value of the transparent sheet heating element of the present invention is 5Ω / □ or less, preferably 3Ω / □ or less, more preferably 2Ω / □ or less. When the surface resistance value is too large, a high voltage is required when generating heat, which is not preferable.

Here, from the following equation, the surface resistance value (or volume resistance value) of the transparent sheet heating element can be designed by arbitrarily setting the line width and pitch of the conductive layer.
R = Rs × (P / W)
Rs = ρv / t
R: Surface resistance value of transparent sheet heating element (Ω / □)
Rs: Surface resistance value of conductive layer (Ω · cm)
ρv: Volume resistivity of the conductive layer t: Film thickness of the conductive layer
P: Network conductive layer spacing (pitch)
W: Line width of the network conductive layer The total light transmittance (JIS K7105) of the transparent sheet heating element of the present invention can achieve a high value of about 72 to 91%. The haze value (JIS K7105) is as low as about 0.5 to 6%.

  In the transparent sheet heating element of the present invention, a protective film, a transparent insulating film or the like may be laminated on a conductive layer formed on a transparent substrate. As the protective film, commonly used known resins are used. These resins are laminated by a known method such as dry lamination or wet lamination.

  The transparent sheet heating element of the present invention may be further laminated with a functional film or the like. The functional film includes an antireflection film provided with an antireflection layer for preventing light reflection on the film surface, a colored film colored by coloring or additives, a near infrared shielding film that absorbs or reflects near infrared rays, and a fingerprint. An antifouling film that prevents the contaminants from adhering to the surface.

  The transparent sheet heating element of the present invention is used for the purpose of improving the switching characteristics, simplifying the drive circuit, etc. in a low-temperature environment of the liquid crystal display, and particularly if it is used for such purposes. There is no limitation.

  For example, the transparent sheet heating element of the present invention has an adhesive or the like on the polarizing plate (1) opposite to the display screen of the liquid crystal display composed of polarizing plate (1) / liquid crystal element / polarizing plate (2). To fix the liquid crystal display. Moreover, it is good also as a liquid crystal display body laminated | stacked by polarizing plate (1) / liquid crystal element / transparent planar heating element / liquid crystal element / polarizing plate (2).

  Or the transparent planar heating element of this invention can also be used as a polarizing plate protective film, retardation film, etc. Thereby, it is not necessary to provide a new transparent planar heating element layer on the liquid crystal display.

  The polarizing plate protective film is a liquid crystal display element formed by sandwiching the front and back surfaces of the polarizing plate, but the polarizing plate protective film comprising the transparent sheet heating element of the present invention is at least one of the front and back surfaces of the polarizing plate. And a liquid crystal display element (for example, FIG. 4A). In this case, it is preferable to select an optically isotropic transparent resin substrate.

  Further, the retardation film is a liquid crystal display element formed by sandwiching the front and back surfaces of the polarizing plate, but the polarizing plate protective film comprising the transparent planar heating element of the present invention is at least on the front and back surfaces of the polarizing plate. A liquid crystal display element may be provided on one side (for example, FIG. 4B). In this case, it is preferable to select a transparent resin substrate having an appropriate retardation.

  The transparent sheet heating element of the present invention has high transparency and visibility, low electrical resistance value of the conductive layer, and high quality surface heating characteristics capable of uniform heat generation. The transparent sheet heating element of the present invention can form a uniform conductive layer, so that a low resistance value without variation is achieved, and the rise of heat generation is rapid and has uniform surface heating characteristics. Moreover, high aperture ratio and transparency are ensured.

  Moreover, according to the method for producing a transparent sheet heating element of the present invention, the transparent sheet heating element can be produced easily and inexpensively with good reproducibility, and is excellent in mass productivity.

  Therefore, the transparent sheet heating element of the present invention is particularly useful as a heating element used for heating a liquid crystal display element.

  Next, the present invention will be described in more detail by way of examples together with comparative examples.

The total light transmittance, haze value, sheet resistance, line width, aperture ratio, and line thickness of the transparent sheet heating element of the present invention shown in Examples and Comparative Examples were measured by the following measuring methods.
1. Total light transmittance Measured with a turbidimeter NDH-20D type (manufactured by Nippon Denshoku Industries Co., Ltd.) according to JIS K7105.
2. Haze value According to JIS K7105, it measured with the turbidimeter NDH-20D type (made by Nippon Denshoku Industries Co., Ltd.).
3. Sheet resistance was measured using Loresta EP (Dia Instruments).
4). Line width Measured using an optical microscope.
5. Aperture ratio The aperture ratio is calculated by measuring the line width (P) and line spacing (W) of one mesh pattern of a transparent sheet heating element using an optical microscope, and calculating area A and area B shown in FIG. Then, this was calculated by applying the following equation.

Opening ratio (%) = (area B / area A) × 100 (%) = (P−W) ² / P ² × 100 (%)
6). Layer thickness Measured using a surface roughness meter.

Example 1
As a transparent substrate having a transparent receiving layer on at least one surface, a polyethylene terephthalate film having a transparent receiving layer of alumina film (layer thickness 20 μm) (thickness 120 μm including the transparent receiving layer, manufactured by Pictorico, trade name “ TPX ") was used. On the side of the transparent substrate opposite to the transparent receiving layer, an ultraviolet curable acrylate hard coat agent (manufactured by Dainippon Paint Co., Ltd., trade name “UV clear” solid content concentration 50% by weight) is applied. After coating with a Meyer bar so as to be 2 μm and drying at 80 ° C. for 2 minutes, ultraviolet rays were irradiated at an irradiation amount of 300 mJ / cm ² to form a hard coat layer on the transparent substrate.

Photosensitive resist PMER-N HC600Y (manufactured by Tokyo Ohka Kogyo Co., Ltd.) was coated on the surface opposite to the hard coat layer of the film with a bar coater, dried at 80 ° C. for 10 minutes, and then a glass mask (line width 17 μm, pitch 200 μm). the grid pattern) through and exposed to ultraviolet rays irradiation dose 60 mJ / cm ^2, through development, water washing and drying, the film thickness on the transparent base material to form a transparent resin layer of 13 .mu.m.

  As the conductive paste, conductive paste Doutite XA-9080 (manufactured by Fujikura Kasei Co., Ltd.) was used.

  After injecting the conductive paste and removing the excess, the conductive paste was baked at 170 ° C. together with the film. This was repeated three times (1 to 2 firings for 30 seconds each and 3 firings for 30 minutes) to form a conductive layer depicting a lattice pattern, and finally in a 5% aqueous sodium hydroxide solution at 40 ° C. The photosensitive resist was peeled off to obtain a transparent sheet heating element.

  The grid pattern of the conductive layer of the obtained transparent planar heating element had a line width of 22 μm, a pitch of 200 μm, and an aperture ratio of 79%.

Comparative Example 1
As a transparent base material, a polyethylene terephthalate film (trade name “A4100”, manufactured by Toyobo Co., Ltd.) having a thickness of 175 μm was used, and an ultraviolet curable acrylate hard coat agent (trade name, manufactured by Dainippon Paint Co., Ltd.) was used on the easily adhesive surface. “UV clear” solid content concentration of 50% by weight) was applied with a Meyer bar so that the film thickness after curing was 2 μm. After drying at 80 ° C. for 2 minutes, ultraviolet rays were irradiated at an irradiation amount of 300 mJ / cm ² to form a hard coat layer on the transparent substrate.

A transparent sheet heating element was manufactured by depositing ITO on an approximately base material film by sputtering under conditions of a gas pressure of 5.0 × 10 ⁻² Pa, a sputtering power of 840 kW, and a sputtering time of 53 seconds.

Comparative Example 2
A transparent sheet heating element was prepared in the same manner as in Comparative Example 1 except that the sputtering time was 15 seconds.

  Table 1 shows the evaluation results such as total light transmittance, haze value, sheet resistance, etc. in the transparent sheet heating elements of Example 1 and Comparative Examples 1-2.

  From the results shown in Table 1, the transparent sheet heating elements of Comparative Examples 1 and 2 have a very high sheet resistance value, so that the amount of current is small and it takes time to generate heat. On the other hand, in the transparent planar heating element of Example 1, since the sheet resistance value is small, the amount of current increases and heat can be generated quickly. Therefore, the transparent sheet heating element of the present invention can be suitably used, for example, as a liquid crystal display element excellent in operability in cold regions.

Test example 1 (surface heat generation characteristics)
About the transparent planar heating element of the present invention obtained in Example 1 and the transparent planar heating element sputtered with ITO obtained in Comparative Example 1, surface heating characteristics (applied voltage-terminal current characteristics and voltage-surface temperature characteristics) ) Was evaluated.

  The test method was performed using the sample shown in FIG. Electrodes were prepared using a silver paste of nanoparticles on both ends of a transparent sheet heating element having an electrode width of 10 cm and a distance between electrodes of 10 cm. The electrode was taken out from each of the left and right parts of the transparent sheet heating element, and the sample was placed in the air. The measurement position was the center in the plane. The results are shown in FIGS.

  6 and 7, it can be seen that the transparent sheet heating element of Example 1 has a small resistance value, so that the current between terminals is large even at a low voltage, and it can generate heat quickly. On the other hand, the transparent sheet heating element of Comparative Example 1 has a large resistance value, so the current amount is small and the heat generation is slow, and a larger voltage is required to obtain the same amount of heat generation as in Example 1. End up.

Test example 2 (in-plane temperature distribution)
The in-plane temperature distribution was evaluated for the transparent sheet heating element of the present invention obtained in Example 1 and the transparent sheet heating element sputtered with ITO obtained in Comparative Example 1.

  As a measuring method, using the sample used in Test Example 1, the electrodes and the power source were set as shown in FIG. The measurement conditions were that the heat generation temperature was measured at 16 positions on the surface of each heating element when a predetermined voltage was applied to each transparent sheet heating element and a current was passed for 3 minutes. A schematic diagram of each measurement point (positions A to D and a to d) is shown in FIG. Tables 2 and 3 show the results of in-plane temperature distribution.

  From the above results, it was found that the transparent sheet heating element of Example 1 had uniform surface heating characteristics. This is considered due to the fact that the conductive layer is uniformly formed on the substrate. Moreover, there was little variation in temperature distribution, and Example 1 and Comparative Example 1 were good with almost no difference.

It is the figure which showed one Embodiment in the transparent planar heating element of this invention. It is sectional drawing for demonstrating the process of one Embodiment in the manufacturing method of the transparent planar heating element of this invention. It is the figure which showed typically the measuring method of an aperture ratio. It is a figure which shows the specific example as a liquid crystal display element of the transparent planar heating element of this invention. It is a figure which shows typically the measuring method of the surface exothermic characteristic of Test Example 1. It is a graph which shows the surface heat generation characteristic (applied voltage-current characteristic between terminals) of the transparent planar heating element of Example 1 and Comparative Examples 1 and 2. It is a graph which shows the surface heating characteristic (voltage-surface temperature characteristic) of the transparent planar heating element of Example 1 and Comparative Examples 1 and 2. It is a figure which shows typically the transparent planar heating element heat_generation | fever temperature measurement position (16 places) of the test example 1. FIG.

Explanation of symbols

110 Transparent substrate (base substrate)
120 conductive layer 121 straight line 122 mesh 123 transparent planar heating region 125 electrode 130 transparent receiving layer 210 transparent substrate 220 resin 220A transparent resin layer 230 conductive paste 230A conductive layer 240 transparent receiving layer

Claims (11)

A transparent planar heating element having a network-like conductive layer on the transparent receiving layer surface of a transparent substrate provided with a transparent receiving layer on at least one surface, and having a pair of electrodes on the conductive layer. A manufacturing method comprising the following steps (a) to (g):
(A) a step of applying or sticking a liquid or dry film-like photosensitive resist to the transparent receiving layer surface of a transparent substrate to form a resin layer;
(B) forming a recess corresponding to the shape of the network-like conductive layer in the resin layer by a photolithography method;
(C) a step of injecting a conductive paste into the recess and removing excess conductive paste on the resin layer;
(D) a step of heat-treating the conductive paste to form a network-like conductive layer;
(E) a step of repeating the steps (c) and (d) one or more times,
(F) removing the resin layer from the transparent receiving layer surface of the transparent substrate, and (g) providing a pair of electrodes on the conductive layer ,
Here, the transparent receiving layer is a layer that receives the conductive paste and improves the adhesion of the conductive paste to the transparent substrate. The transparent receiving layer is composed of an aggregate of fine particles mainly containing at least one selected from titania and alumina, and the average particle diameter of the fine particles is about 10 to 100 nm, and the fine particles are about 10 to 100 nm between the fine particles. The method for producing a transparent sheet heating element according to claim 1, wherein the transparent receiving layer has pores and the thickness of the transparent receiving layer is about 0.05 to 20 µm. The conductive paste is a particulate silver oxide having an average particle size of 2 μm or less, a silver salt of a tertiary fatty acid having a total carbon number of 5 to 30, an aromatic hydrocarbon, an ether ester of ethylene glycol, an ether ester of propylene glycol The method for producing a transparent sheet heating element according to claim 1 or 2, wherein the paste is a conductive paste containing a solvent mainly comprising at least one selected from the group consisting of terpineol and terpineol. The method for producing a transparent sheet heating element according to any one of claims 1 to 3, wherein a temperature of the heat treatment is about 150 to 200 ° C. The manufacturing method of the transparent planar heating element in any one of Claims 1-4 in which the said transparent base material has a hard-coat layer in the surface opposite to the surface which has a transparent receiving layer. The transparent planar heating element manufactured by the manufacturing method in any one of Claims 1-5. The liquid crystal display body laminated | stacked in order of a polarizing plate / liquid crystal element / polarizing plate / adhesion layer / the transparent planar heating element / transparent insulating layer according to claim 6. A polarizing plate protective film comprising the transparent sheet heating element according to claim 6. The liquid crystal display element by which the polarizing plate protective film of Claim 8 is laminated | stacked on the at least single side | surface of a polarizing plate. A retardation film comprising the transparent sheet heating element according to claim 6. The liquid crystal display element by which the retardation film of Claim 10 is laminated | stacked on the at least single side | surface of a polarizing plate.

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