Conductive sheet and method for manufacturing resin molded article

Abstract

[Problem] To provide a conductive sheet with an attractive exterior design. [Solution] A conductive sheet (1) comprising a base sheet (2) and a conductive wire (3) embedded in the upper surface of the base sheet. The base sheet includes wire retaining section (4) formed so as to rise from an upper surface along edges (31, 32) of the conductive wire, and the ratio of the width W1 of the conductive wire to the width W2 of the wire retaining section is 1:(1.5-4.0).

Description

Conductive sheet and method for manufacturing resin molded product

[0001] The present invention relates to a conductive sheet, and more particularly to a conductive sheet used in a vehicle heater, and a method for manufacturing a resin molded product using the same.

[0002] Japanese Patent Application Laid-Open No. 2019-169417 (Patent Document 1) discloses a conductive sheet in which wires are embedded in the upper surface of a base sheet.

[0003] Japanese Patent Application Laid-Open No. 2019-169417

[0004] The conductive sheet in Patent Document 1 is formed by embedding wires in the area where a base sheet is ultrasonically welded. However, no consideration is given to the appearance design in this process, and there are problems such as the base sheet twisting or turning white due to excessive embedding of the wires.

[0005] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a conductive sheet that can improve the appearance design.

[0006] A conductive sheet according to one aspect of the present invention includes a base sheet and a conductive wire embedded in the upper surface of the base sheet. The base sheet includes a wire holding portion formed to protrude from the upper surface along the edge of the conductive wire. The width dimension W1 of the conductive wire: the width dimension W2 of the wire holding portion is 1:(1.5 to 4.0).

[0007] Preferably, a height position Y2 of the wire holding portion is lower than a height position Y1 of the conductive wire.

[0008] Preferably, 40 to 75% of the height H1 of the conductive wire is embedded in the base sheet, with the upper surface of the base sheet as the reference.

[0009] Preferably, the tensile strength of the conductive wire is 200 to 600 N / mm ２ is.

[0010] A method for manufacturing a resin molded product according to one embodiment of the present invention includes the steps of: preparing a conductive sheet in which a wire holding portion is formed that protrudes from the upper surface of a base sheet along the edge of the conductive wire, and in which the conductive wire is embedded so that the width dimension W1 of the conductive wire: the width dimension W2 of the wire holding portion = 1: (1.5 to 4.0); preparing an injection molding die having a fixed die and a movable die that forms a cavity between the fixed die and the movable die; placing the conductive sheet on one of the cavity surfaces of the die; clamping the injection molding die; injecting molten resin into the cavity to form a resin molded body, while simultaneously adhering the conductive sheet to the surface of the resin molded body; and opening the injection molding die and removing the resin molded body with the adhering conductive sheet.

[0011] A method for manufacturing a resin molded product according to another aspect of the present invention includes the steps of: preparing a conductive sheet in which a wire holding portion is formed that protrudes from the upper surface of a base sheet along the edge of the conductive wire, and in which the conductive wire is embedded so that the width dimension W1 of the conductive wire: the width dimension W2 of the wire holding portion = 1: (1.5 to 4.0); preparing a resin molded body having a shape corresponding to the shape of the conductive sheet; and fixing the resin molded body to the upper and / or lower surfaces of the conductive sheet.

[0012] According to the conductive sheet of the present invention, by properly embedding the wires on the upper surface of the base sheet, twisting of the upper surface of the base sheet and falling off of the wires can be prevented, thereby improving the appearance design.

[0013] 1 is a front view explanatory diagram of a conductive sheet according to the present embodiment; FIG. 2 is a plan view of a conductive sheet according to the present embodiment; FIG. 3 is an explanatory diagram of examples of a conductive sheet according to the present embodiment; FIG. 4 is a table showing various evaluations of the conductive sheets according to Examples 1 to 9; FIG. 5 is a table showing various evaluations of the conductive sheets according to Comparative Examples 1 to 3; and FIG. 6 is a table showing the relationship between the wire embedding ratio and the width dimension of the wire holding portion of the conductive sheet according to Example 10. (a) to (c) are photographs showing the wire embedding portion of the conductive sheet according to Example 10 in plan view.

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, in which like reference numerals denote like or corresponding parts and will not be described repeatedly.

[0015] (Configuration) A conductive sheet 1 according to one embodiment of the present invention will be described with reference to Fig. 1. The conductive sheet 1 includes a base sheet 2 having a rectangular shape in a plan view, conductive wires 3 embedded in the upper surface of the base sheet 2, and wire holding portions 4 formed so as to protrude along the edges of the conductive wires 3. Fig. 1 is an explanatory diagram showing a cut surface of the conductive sheet 1 including the conductive wires 3 as viewed from the front. The direction of arrow A1 shown in Figs. 1 and 2 is referred to as the width direction of the wires.

[0016] The base sheet 2 is formed of a thermoplastic resin, such as polycarbonate, polyethylene terephthalate, polyethylene naphthalate, polypropylene, PC-ABS, polyvinyl chloride, or acrylic resin. The base sheet 2 preferably has a heat shrinkage rate of 2.5% or less and has suitable stretchability for a conductive film used in injection molding. This not only improves moldability during injection molding, but also prevents warpage during molding of the conductive sheet 1.

[0017] The base sheet 2 includes an upper surface 2a and a lower surface 2b, and the upper surface 2a has conductive wires 3 embedded therein. An optional functional layer, such as an adhesive layer or a decorative layer, may be laminated on the lower surface 2b.

[0018] From the viewpoint of good formability, the thickness dimension H3 of the base sheet 2 is preferably 0.2 mm to 0.8 mm. If it is thinner than 0.2 mm, when the conductive pattern 3 is embedded in the base sheet 2, the shape of the conductive pattern 3 will stand out as a white spot on the back surface 2b of the sheet, which may impair the appearance design during molding. If it is thicker than 0.8 mm, molding may become difficult.

[0019] The conductive wire 3 forms an arbitrary pattern on the upper surface 2a of the base sheet. The pattern may be, for example, a meander shape, a spiral shape, or a diagonal line shape. In this embodiment, the pattern is formed by one wire, but two or more wires may be provided. Both ends of the conductive wire 3 are connected to terminal portions (not shown).

[0020] The conductive wire 3 can be appropriately selected from conductive materials such as copper, silver, lead, aluminum, nickel, beryllium, and zirconium depending on the intended use and purpose of the molded product. That is, the conductive material may be one type only, or an alloy containing two or more metals. For the conductive wire 3 of this embodiment, it is preferable to use a material with hardness and resistance that takes into consideration prevention of deformation during embedding and ease of exerting the heater function, and for example, a silver-containing copper alloy is used.

[0021] The diameter of the conductive wire 3 is preferably 0.05 mm to 0.3 mm, and more preferably 0.1 mm to 0.2 mm. If the diameter is thinner than 0.05 mm, the wire is prone to breakage and the resistance becomes too high, resulting in a decrease in heater function. If the diameter is thicker than 0.3 mm, the formed conductive sheet is prone to warping, making handling during the forming process cumbersome.

[0022] The conductive wire 3 is embedded by ultrasonic welding while applying pressure and tension to the base sheet 2. Specifically, a wire embedding device (not shown) uses ultrasonic waves to melt the upper surface 2 a of the base sheet while feeding out the conductive wire 3, and then applies pressure to the upper surface 2 a of the base sheet 2 to embed the wire. In a plan view, both sides in the extension direction of the conductive wire 3 embedded in the base sheet 2 are referred to as wire edges 31, 32.

[0023] The cross-sectional shape of the conductive wire 3 is slightly deformed by the pressure and heat applied during embedding. Specifically, as shown in the photographs of Figures 4 and 5, the top surface of the wire is deformed to be flat. Therefore, the above-mentioned "diameter of the conductive wire" refers to the diameter before embedding, and after embedding, the maximum dimensions in the height and width directions in the cross-sectional view are expressed as "height dimension H1 of the conductive wire" and "width dimension W1 of the conductive wire."

[0024] In order to prevent deformation during embedding, the tensile strength of the conductive wire 3 is set to 200 to 600 N / mm ２ From the viewpoint of preventing the wire from deforming and the stability of the wire embedding process, it is preferable that the wire strength is 300 to 500 N / mm ２ It is more preferable that the tensile strength is 600 N / mm ２In the above cases, the conductive wire 3 tends to return to its original shape like a return spring (elastic force), which makes the conductive wire 3 prone to peeling off from the base sheet 2. By using a conductive wire 3 with a predetermined tensile strength, the conductive sheet 1 of this embodiment can prevent the wire from breaking when embedded and the base sheet 2 from twisting due to excessive deformation of the wire.

[0025] It is preferable that the conductive wire 3 is coated with a coating film (not shown) from the viewpoints of preventing corrosion of the wire and strengthening adhesion to the base sheet 2. The coating film is made of a resin such as polyurethane, and serves to maintain insulation in areas of the conductive wire 3 where no current is required. In this case, the "diameter of the wire" refers to the diameter of the conductive wire only, while the "height dimension of the conductive wire" and the "width dimension of the conductive wire" refer to the height dimension and width dimension of the conductive wire including the coating film.

[0026] The wire holding portion 4 includes a first wire holding portion 41 along one side of the conductive wire 3 in the extending direction and a second wire holding portion 42 along the other side of the conductive wire 3 in the extending direction. The wire holding portion 4 is formed by forming the base sheet 2 to rise upward from the wire edges 31, 32 when the wire is embedded, stretching in the height direction, and then bending in an arc. Here, as can be seen in the photographs of Figures 4 and 5, the wire holding portion is bent to form an air layer 43 inside. Because the base sheet 2 turns white when it absorbs air, this significantly impairs the appearance when used in combination with a molded product with a black design. Therefore, it is preferable to confine the wire holding portion 4 within as small an area as possible.

[0027] The height dimension H2 of the wire holding portion is the height dimension H2 from the edge of the wire to the top end of the wire holding portion in the height direction. Furthermore, the width dimension W2 of the wire holding portion is the width dimension including the width from the width end of the first wire holding portion 41 to the width end of the second wire holding portion 42. It should be noted that the wire holding portion 4 extends outward or inward relative to the wire, drawing an upward arc, and therefore the height dimension H2 and width dimension W2 of the wire holding portion do not necessarily correspond to the end faces of the wire holding portion.

[0028] The height position Y1 of the conductive wire is the height position Y1 of the top end in the height direction of the conductive wire 3. The height position Y2 of the wire holding part is the height position Y2 of the top end in the height direction of the wire holding part. In this embodiment, the height position Y1 of the wire is the upper limit value of the height position Y2 of the wire holding part 4 due to the relationship with a wire embedding device (not shown) provided above the conductive wire 3, and the relationship becomes (height position Y1 of the wire) ≧ (height position Y2 of the wire holding part).

[0029] (Regarding Dimensional Ratios) The conductive sheet 1 of this embodiment is formed so that the width dimension W1 of the conductive wire and the width dimension W2 of the wire holding portion are 1:(1.5 to 4.0). If W2 / W1 exceeds 4.0, the wire holding portion will be too wide in the width direction, significantly impairing the appearance of the conductive sheet. If W2 / W1 is less than 1.5, the wire will not be held securely and will be prone to peeling off. From the viewpoint of design, W1:W2 = 1:(1.5 to 3.5) is more preferable, and from the viewpoint of combining design and prevention of wire peeling off, W1:W2 = 1:(1.7 to 3.0) is even more preferable.

[0030] The height Y2 of the wire holding portion is preferably lower than the height Y1 of the conductive wire and occupies 50% or more of the height Y1 of the conductive wire (0.5Y1≦Y2<Y1). This ensures good wire holding performance while preventing the wire holding portion 4 from spreading along the wire embedding device, ensuring good design.

[0031] In the conductive sheet 1 of this embodiment, the height dimension H1 of the conductive wires and the thickness dimension H3 of the base sheet are 1: (1.7 to 3.5). In the conductive sheet 1 of this embodiment, the base sheet 2 has an appropriate thickness, so that the conductive sheet 1 is resistant to warping and does not form irregularities due to the wires embedded in the back surface 2b of the base sheet. This allows for improved design of the conductive sheet 1.

[0032] In this embodiment, the conductive wires 3 are embedded in the base sheet 2 by 40 to 75% of their height H1, based on the upper surface 2a of the base sheet 2. From the viewpoint of the design of the conductive sheet, a wire embedding rate of 40 to 65% is more preferable, and from the viewpoint of reliably preventing the wires from peeling off, a wire embedding rate of 50 to 65% is even more preferable.

[0033] The wire holding portion 4 of this embodiment is formed by protruding from the wire edge, pushing aside the upper surface 2a of the base sheet when the conductive wire 3 is embedded. Here, if the wire is less than 40%, the wire may peel off from the upper surface 2a of the base sheet, potentially impairing the design. If the wire is more than 75%, the wire holding portion 4 may be turned up and the conductive wire 3 may be buried when the conductive sheet is processed by injection molding, potentially impairing the design. In contrast, the conductive sheet of this embodiment allows the volume of the wire holding portion 4 formed when the wire is embedded to escape outward from the wire edge. This allows for a conductive sheet 1 with excellent conductivity and design.

[0034] (Regarding Examples) Next, examples 1 to 9 of the conductive sheet 1 according to the present embodiment and comparative examples 1 to 3 will be described with reference to Figures 3 to 5. Figure 3 is an explanatory diagram of the conductive sheet according to the present embodiment. Figure 4 is a table showing various evaluation cross sections of the conductive sheets according to examples 1 to 9. Figure 5 is a table showing various evaluation results of the conductive sheets according to comparative examples 1 to 3.

[0035] The substrate sheet was a polycarbonate sheet Makrofol® DE1-4 manufactured by Covestro, and the conductive wire was a silver-impregnated copper wire (wire diameter 0.11 mm; coating layer 0.01 mm; total diameter 0.12 mm) that was embedded using a wire embedding machine WCE150 manufactured by Ruhlamat.

[0036] 3 shows positions when meandering shapes are patterned using wires according to Examples 1 to 9 and Comparative Examples 1 to 3. Positions i and iv indicate the center of the straight line region, positions ii and iii indicate the ends of the straight line region, and positions v and vi indicate the ends of the curved line region.

[0037] Figures 4 and 5 show various evaluation results based on cross-sectional photographs of the conductive wire patterned under the above conditions. Details of each evaluation item are as follows: Position: Indicates the position corresponding to Figure 3. W2 / W1: Indicates the value of the width dimension W2 of the wire holding portion / width dimension W1 of the conductive wire. Size relationship between Y1 and Y2: Indicates the size relationship between the height position Y2 of the wire holding portion and the height position Y1 of the conductive wire. Embedding rate: Indicates the embedding rate of the conductive wire based on the top surface of the base sheet. Evaluation: The external shape of the conductive sheet of each example is represented by ◎, 〇, or ×. Photograph: An SEM image of a cross section corresponding to each example and comparative example.

[0038] The width dimension W2 of the wire holding portion, the width dimension W1 of the conductive wire, the height position Y1 of the wire holding portion, and the height position Y2 of the conductive wire were measured by observing a cross-sectional sample made of mitochrome.

[0039] Referring to Figure 4, the conductive sheets of Examples 1 to 9 had embedment rates of 52.3 to 73.2% and W2 / W1 ratios of 2.4 to 3.2. These results demonstrate that the conductive wires of Examples 1 to 9 have good external design while maintaining good wire retention. Furthermore, the conductive sheets of Examples 7 to 9 had a W2 / W1 ratio of 3.2, indicating that the wire retention portion was wider than in Examples 1 to 6. Therefore, the conductive sheets of Examples 7 to 9 were rated as having an external design within the acceptable range, and the conductive sheets of Examples 1 to 6, which are the most preferable, were rated as excellent.

[0040] 5, Comparative Examples 1 to 3 had embedment rates of 78.3 to 90.9%, and W2 / W1 was 4 or greater. These results indicate that the conductive wires of Comparative Examples 1 to 3 were embedded deeper than those of the Examples, causing the wire holding portions to extend beyond the specified width, impairing the aesthetic design. Therefore, the external shapes of the conductive sheets of Comparative Examples 1 to 3 were deemed undesirable and were rated as x.

[0041] In the examples and comparative examples, conductive wires patterned under specified conditions were evaluated by extracting portions corresponding to the positions shown in Figure 3. Typically, a wire embedding device moves quickly in the central portions i and iv of the straight regions and slowly at the ends ii, iii, v, and vi of the curved regions. However, this example allows for uniform embedding of wires regardless of the patterning position, providing a conductive sheet with a good appearance design.

[0042] Example 10 Next, Example 10 of the conductive sheet of the present embodiment will be described with reference to Figures 6 and 7. Figure 6 is a table showing the relationship between the ratio of W2 / W1 and the wire embedding rate.

[0043] The substrate sheet was a polycarbonate sheet Makrofol DE1-4 manufactured by Covestro, and the conductive wire was a silver-containing copper wire (total diameter 0.19 mm) manufactured by Electrisola, Inc. The conductive wire was embedded using a wire embedding machine WCE150 manufactured by Ruhlamat.

[0044] The table in Figure 6 is a summary of data obtained by operating the wire embedding device under various conditions when embedding conductive wires in the base sheet described above, based on data from cases where no wire peeling was observed. The wire embedding ratio is defined as a region below 50% as a "shallow" region, a region between 50% and 65% as a "medium" region, and a region above 65% as a "deep" region.

[0045] 6, the area indicated by arrow A is the "deep" area of ​​wire embedment ratio, where W2 / W1 = (3.0 to 4.0). The area indicated by arrow B is the "intermediate" area of ​​wire embedment ratio, where W2 / W1 = (1.7 to 3.5). The area indicated by arrow C is the "shallow" area of ​​wire embedment ratio, where W2 / W1 = (1.5 to 2.0).

[0046] Figure 7 shows photographs of one of the conductive wires in each wire embedment ratio range, taken in plan view. (a) is the deep region, where the wire holding portion was observed to have expanded significantly in the width direction. (b) is the intermediate region, and (c) is the shallow region. Compared to the deep region, the expansion of the wire holding portion in the width direction was able to be kept within the acceptable range. In particular, when a black base sheet was used, the wire holding portion turned white, and it was found that a large width dimension of the wire holding portion significantly impaired the appearance design.

[0047] The conductive sheet 1 of this embodiment allows linear wires to be embedded without twisting the conductive sheet. This allows the wires to remain in the desired position, maintaining good radio wave transparency. Furthermore, the wires can be prevented from being buried in the wire holding portion, improving conductivity and appearance design.

[0048] (Manufacturing Method) Next, a method for manufacturing the resin molded product according to this embodiment will be described. The resin molded product according to this embodiment is manufactured by setting a conductive sheet with embedded wires in a mold and performing injection molding.

[0049] First, a conductive sheet is prepared in which a wire holding portion is formed on the upper surface of a base sheet, protruding along the edge of the conductive wire, and the conductive wire is embedded so that the width dimension W1 of the conductive wire: the width dimension W2 of the wire holding portion = 1: (1.5 to 4.0) (conductive sheet preparation process). Next, an injection molding die is prepared, which has a fixed die and a movable die that forms a cavity between the fixed die and the movable die (mold preparation process). Next, a conductive sheet is placed on one of the cavity surfaces of the die (placement process). Next, the injection molding die is clamped (mold clamping process). Next, molten resin is injected into the cavity to form a resin molded product, and at the same time, the conductive sheet is fixed to the surface of the resin molded product (fixing process). Next, the injection molding die is opened, and the resin molded product with the fixed conductive sheet is removed (removal process). This allows the production of a resin molded product.

[0050] The conductive sheet can have a resin molded body fixed to its upper and / or lower surfaces. The conductive wire 3 of this embodiment may be further embedded in the fixing step. At this time, since the entire conductive sheet 1 is heated during injection molding and the interior of the mold is under high pressure, no additional wire holding portion is formed.

[0051] Next, a method for manufacturing a resin molded product according to another embodiment will be described. The resin molded product according to this embodiment is manufactured by bonding a conductive sheet in which wires are embedded and a resin molded body molded by, for example, injection molding.

[0052] First, a conductive sheet is prepared in which a wire holding portion is formed on the upper surface of a base sheet, protruding along the edge of the conductive wire, and the conductive wire is embedded so that the width dimension W1 of the conductive wire: the width dimension W2 of the wire holding portion = 1: (1.5 to 4.0) (conductive sheet preparation step). Next, a resin molded body having a shape corresponding to the shape of the conductive sheet is prepared (resin molded body preparation step). The resin molded body is fixed to the upper and / or lower surfaces of the conductive sheet (fixing step). This allows the resin molded product to be manufactured.

[0053] In addition, in this embodiment, the wire holding portion 4 is injection molded onto the upper surface 2a of the conductive sheet, and the air layer 43 formed inside the wire holding portion 4 is filled with resin, which may make it invisible.

[0054] 1 Conductive sheet, 2 Base sheet, 3 Conductive wire, 4 Wire holding portion, 31, 32 Wire edge portion, 41, 42 Wire holding portion, 43 Air layer, W1 Width dimension of conductive wire, W2 Width dimension of wire holding portion, H1 Height dimension of conductive wire, H2 Height dimension of wire holding portion, H3 Thickness dimension of base sheet, Y1 Height position of conductive wire, Y2 Height position of wire holding portion.

Claims

1. A conductive sheet comprising: a base sheet; and a conductive wire embedded in an upper surface of the base sheet, the base sheet including a wire holding portion formed to rise from the upper surface along an edge of the conductive wire, wherein the conductive wire width dimension W1: the wire holding portion width dimension W2 = 1: (1.5 to 4.0).

2. The conductive sheet according to claim 1, wherein a height position Y2 of the wire holding portion is lower than a height position Y1 of the conductive wire.

3. The conductive sheet according to claim 1, wherein 40 to 75% of the height dimension H1 of the conductive wire is embedded in the base sheet, based on the upper surface of the base sheet.

4. The tensile strength of the conductive wire is 200 to 600 N / mm ２ The conductive sheet according to claim 1 , 5. A method for manufacturing a resin molded product, comprising the steps of: preparing a conductive sheet in which a wire holding portion is formed that rises from the upper surface of a base sheet along the edge of the conductive wire, and the conductive wire is embedded so that the width dimension W1 of the conductive wire: the width dimension W2 of the wire holding portion = 1: (1.5 to 4.0); preparing an injection molding die having a fixed die and a movable die that forms a cavity between the fixed die; placing the conductive sheet on any of the cavity surfaces of the die; clamping the injection molding die; injecting molten resin into the cavity to form a resin molded product, and at the same time, fixing the conductive sheet to a surface of the resin molded product; and opening the injection molding die and removing the resin molded product with the conductive sheet fixed thereto.

6. A method for manufacturing a resin molded product, comprising the steps of: preparing a conductive sheet in which a wire holding portion is formed that rises from the upper surface of a base sheet along an edge of a conductive wire, and the conductive wire is embedded such that the width dimension W1 of the conductive wire: the width dimension W2 of the wire holding portion = 1: (1.5 to 4.0); preparing a resin molded body having a shape corresponding to the shape of the conductive sheet; and adhering the resin molded body to the upper and / or lower surface of the conductive sheet.

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