Surface-treated copper foil

Abstract

To provide a surface-treated copper foil in which a bonded surface with a base material has appearance with excellent etching resistance and black color tone and without uneven treatment and a bubble mark in order to be used for a display element in particular.SOLUTION: A surface-treated copper foil 10 comprises a copper foil layer 13, which is an electrolytic copper foil, and a blackening treatment layer 14 covering one surface side of the electrolytic copper foil. The blackening treatment layer 14 is a composite metal layer containing copper, nickel, cobalt, and tungsten. An adhesion amount of nickel of the blackening treatment layer is 120 to 400 μg / dm2, an adhesion amount of cobalt is 400 to 700 μg / dm2, and an adhesion amount of tungsten is 70 to 200 μg / dm2. The blackening treatment layer 14 can be formed by subjecting one surface of the copper foil layer 13 to plating treatment by plating bath containing nickel, cobalt, and tungsten.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a surface-treated copper foil, and more particularly to a surface-treated copper foil for use in display elements such as touch panels, and a method for producing the same. [Background technology]

[0002] Conventionally, surface-treated copper foils have been used in the field of display elements for applications such as wiring formation materials for touch panels. Surface-treated copper foils for other applications require that the surface to be bonded to the substrate be etch-resistant enough to withstand the chemicals used in the etching process for wiring formation, and that the surface be treated to have an appearance free of treatment unevenness or air bubble marks. However, surface-treated copper foils used for display elements are also required to have a surface treatment that imparts a black color tone to the foil to prevent reflections when used as a display element.

[0003] As a surface treatment applied to copper foil, for example, Non-Patent Document 1 describes Ni-W alloy plating as an alternative to hard Cr plating, and describes the results of a study on the difference in plating crack behavior of Ni-W alloy films depending on the W content. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Kazuya Ishii et al., "Effect of Internal Stress on Film Cracks in Ni-W Alloy Plating," Surface Technology, Surface Finishing Association of Japan, 2014, Vol. 65, No. 8, pp. 49-53 Summary of the Invention [Problem to be solved by the invention]

[0005] However, although the Ni-W alloy plating described in Non-Patent Document 1 has excellent acid resistance, it does not exhibit a black color tone, and therefore is not suitable as a surface treatment for electrodeposited copper foil for use in display elements. On the other hand, when electrodeposited copper foil is subjected to a surface treatment that exhibits a black color tone, there is a problem that air bubble marks are likely to occur on the surface. The presence of air bubble marks is undesirable in any application, as it may be erroneously detected as a foreign object.

[0006] Therefore, an object of the present invention is to provide a surface-treated copper foil, the surface to be bonded to a substrate of which has excellent etching resistance, a black color tone, and an appearance free of treatment unevenness and air bubble marks, particularly for use in display devices. [Means for solving the problem]

[0007] In order to achieve the above object, one aspect of the present invention is a surface-treated copper foil comprising an electrolytic copper foil and a blackened layer covering one side of the electrolytic copper foil, wherein the blackened layer is a composite metal layer containing copper, nickel, cobalt, and tungsten, and the amount of nickel deposited in the blackened layer is 120 to 400 μg / dm 2 The cobalt deposition amount is 400 to 700 μg / dm 2 The tungsten deposition amount is 70 to 200 μg / dm 2 is.

[0008] The total amount of nickel, cobalt, and tungsten deposited in the blackened layer is 700 to 1200 μg / dm 2 It is preferable that:

[0009] The surface of the surface-treated copper foil on the side of the blackened layer is L * a * b * In the color system, L * The value is 55.0 to 65.0, and a * The value is 0.0 to 10.0, and b * The value is preferably 0.0 to 10.0.

[0010] In another embodiment of the present invention, the surface of the blackened layer side of the surface-treated copper foil is provided with bubbles having a diameter of 50 μm or more and a thickness of 1 m. 2 This is a surface-treated copper foil with no more than 10 particles per surface. [Effects of the Invention]

[0011] According to the present invention, by forming a composite metal layer containing copper, nickel, cobalt, and tungsten as a blackening treatment layer on one surface of the electrolytic copper foil (the surface to be adhered to the transparent substrate of the display element), the surface-treated copper foil has excellent etching resistance, and the surface on the blackening treatment layer side of the surface-treated copper foil can be made black, and an appearance without treatment unevenness or air bubble marks can be achieved. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view schematically showing one embodiment of a surface-treated copper foil according to the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view for explaining an example of use of the surface-treated copper foil shown in FIG. 1 as a wiring-forming material for a touch panel. [Figure 3] FIG. 2 is a schematic cross-sectional view for explaining an example of use of the surface-treated copper foil shown in FIG. 1 as a wiring-forming material for a touch panel. [Figure 4] 1 is a scanning electron microscope (SEM) image showing the adherend surface of a surface-treated copper foil used as a reference for evaluating unevenness in the treatment of the surface-treated copper foil. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the surface-treated copper foil according to the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiment described below.

[0014] [Surface-treated copper foil] The surface-treated copper foil of this embodiment comprises an electrolytic copper foil and a blackening treatment layer covering at least one side of the electrolytic copper foil.

[0015] The thickness of the electrolytic copper foil is preferably, for example, in the range of 1 to 35 μm, more preferably in the range of 2.0 to 6.0 μm, and even more preferably approximately 6 μm. If the copper foil thickness is thinner than 6.0 μm, handling of the electrolytic copper foil may be difficult. Therefore, when using an electrolytic copper foil thinner than 6.0 μm, a copper foil layer 13 is formed on the surface of another copper foil called a carrier foil 11 via a release layer 12, as in the surface-treated copper foil 10 shown in FIG. 1 . In this case, a blackened layer 14 is formed on the surface of the copper foil layer 13 opposite the carrier foil 11. In the copper foil layer 13 with the carrier foil 11, if the thickness of the copper foil layer 13 is less than 1.0 μm, problems such as unstable carrier foil peel strength may occur. On the other hand, if the thickness of the electrolytic copper foil is thicker than 35.0 μm, etching may take a long time and the etching rate may be uneven in the in-plane direction, resulting in partial etching and loss of flatness.

[0016] An electrodeposited copper foil generally has a shiny cathode side, which is the side that was in contact with the electrodeposition drum during its production, and a deposit side formed by plating on the opposite side. The blackening treatment layer may be formed on either the cathode side or the deposit side of the electrodeposited copper foil, but it is preferably formed on the cathode side of the electrodeposited copper foil because it provides a stable shape.

[0017] The blackened layer is a composite metal layer of copper (Cu), nickel (Ni), cobalt (Co), and tungsten (W) that has excellent etching resistance and exhibits a black color tone. The thickness of the blackened layer is, for example, preferably in the range of 1.0 to 100.0 nm, and more preferably in the range of 5.0 to 20.0 nm.

[0018] The amount of nickel deposited is 120 to 400 μg / dm 2 The range is preferably 170 to 350 μg / dm 2 The range of 200 to 300 μg / dm 2 The more preferable range is 120 μg / dm 2If the nickel deposition amount is less than 400 μg / dm, the chemical resistance will decrease, and there is a risk of the copper foil peeling off from areas that should remain during etching. 2 If the temperature exceeds this value, there is a risk that the end portions of the wiring formed during etching will remain unmelted, which may cause a problem of short-circuiting between the wirings.

[0019] The amount of cobalt attached is 400-700μg / dm 2 The range is preferably 400 to 600 μg / dm 2 The range of 400 to 500 μg / dm 2 The range of the cobalt deposition amount is more preferably 400 μg / dm 2 If the amount of cobalt is less than 700 μg / dm, the color tone of the treated surface may become lighter. 2 If the temperature exceeds this value, there is a risk that the end portions of the wiring formed during etching will remain unmelted, which may cause a problem of short-circuiting between the wirings.

[0020] The amount of tungsten attached is 70 to 200 μg / dm 2 The range is preferably 80 to 150 μg / dm 2 The range of 90 to 130 μg / dm 2 The range of 70 μg / dm is more preferable. 2 If the tungsten deposition amount is less than 200 μg / dm, the chemical resistance will decrease, and there is a risk of the copper foil peeling off from the area that should remain during etching. 2 If the temperature exceeds this value, there is a risk that the end portions of the wiring formed during etching will remain unmelted, which may cause a problem of short-circuiting between the wirings.

[0021] The total amount of nickel, cobalt, and tungsten attached (hereinafter simply referred to as "total amount") is 700 to 1200 μg / dm 2 The range is preferably 730 to 1100 μg / dm 2 The range of 760 to 900 μg / dm 2The total amount is more preferably in the range of 700 μg / dm 2 By setting the total amount to 1200 μg / dm or more, excellent chemical resistance can be exhibited, and the problem of peeling off of the copper foil in the area that should be left during etching can be more reliably prevented. 2 By setting the above, it is possible to more reliably prevent the problem that a residue remains at the end of the wiring formed during etching, which may cause a short circuit between the wirings.

[0022] Since such a blackened layer is formed on the electrodeposited copper foil, the color tone of the adherend surface of the surface-treated copper foil is L * a * b * In the color system, L * Value is 65 or less, a * Value is 10 or less, b * The value is 10 or less, and a blackish color tone sufficient for use in a display device can be exhibited.

[0023] L * The value is the brightness, and the lower the value, the darker the color tone. * value and b * The value indicates the color direction, a * The higher the value, the redder the color, and the lower the value, the greener the color. * The higher the value, the more yellow it is, and the lower the value, the more blue it is. * value and b * The color tone that is presented varies depending on the balance between the values, so it is difficult to generalize, but the lower the values ​​of both, the blacker the color will be.

[0024] More preferably, L * Value is 60 or less, a * Value is 5.0 or less, b * The value is preferably 5.0 or less, and more preferably L * Value is 57 or less, a * Value is 2.0 or less, b * The value is 2.0 or less.

[0025] In addition, the surface-treated copper foil provided with the blackened layer of this embodiment has bubbles with a diameter of 50 μm or more on the surface of the blackened layer side. 2 The product has an excellent appearance with no more than 10 bubbles per square meter. 2 It is preferable that there are no more than 5 per 1m 2 It is more preferable that there are no more than three per 1m 2 It is more preferable that there is no more than one per

[0026] The use of such a surface-treated copper foil having a blackening layer in a display element will now be described. To manufacture a display element, as shown in Fig. 2, adhesive layers 22 are formed on both sides of a transparent substrate film 21, such as polyethylene terephthalate (PET), and surface-treated copper foils 10, such as those shown in Fig. 1, are then bonded to both sides of the transparent substrate film 21, with the blackening layers 14 in contact with the adhesive layers 22. After bonding, the carrier foil 11 is peeled off, and the copper foil layer 13 is etched into a predetermined wiring pattern, resulting in the manufacture of a display element in which the copper foil layer 13 is used as a sensor wiring material.

[0027] As shown in Figure 3, blackened layers 14A and 14B, which are also etched into a wiring pattern, are located between copper foil layers 13A and 13B etched into a wiring pattern and a transparent substrate film 21. Therefore, in a display device, the blackened layer 14B prevents the copper foil layer 13B etched into one wiring pattern from being visible between the copper foil layer 13A and the blackened layer 14A etched into the other wiring pattern. This prevents light incident between the copper foils on one side from being reflected, thereby suppressing degradation of the image quality of the display device. The surface-treated copper foil of the present invention is not limited to that with a carrier foil as shown in Figures 1 and 2.

[0028] The surface-treated copper foil 10 of this embodiment may, if necessary, have a silane coupling agent treatment layer (not shown) on the surface of the blackening treatment layer 14. The silane coupling agent treatment layer may be a layer formed by a silane coupling agent treatment that has traditionally been applied to electrolytic copper foils. The silane coupling agent is not particularly limited, and it is preferable to use, for example, an amino-based silane coupling agent or an epoxy-based silane coupling agent.

[0029] Furthermore, the surface-treated copper foil 10 of this embodiment may optionally include a chromate treatment layer (not shown) between the blackening treatment layer 14 and the silane coupling agent treatment layer. The chromate treatment layer may be a layer formed by a chromate treatment that has conventionally been applied to electrolytic copper foils. Chromium trioxide, potassium dichromate, sodium dichromate, or the like is preferably used for the chromate treatment. The chromate treatment layer thus formed contains an oxide or hydroxide of trivalent chromium reduced from hexavalent chromium.

[0030] [Method of manufacturing surface-treated copper foil] An embodiment of a method for producing a surface-treated copper foil will be described below. The method for producing a surface-treated copper foil of this embodiment involves forming a blackening layer on one side of an electrolytic copper foil to obtain the surface-treated copper foil.

[0031] The blackening process involves plating the adherend side of the electrolytic copper foil to form a composite metal layer of copper, nickel, cobalt, and tungsten. To form the blackening process, a plating bath containing the metals contained in the composite metal layer is used. The plating process is preferably performed twice rather than once, as this results in a darker color tone.

[0032] In the first plating treatment, for example, a composite metal layer of copper and cobalt is formed. Specific first plating bath compositions for this purpose are, for example, a copper concentration of 1.3 to 10.2 g / L, a cobalt concentration of 2.1 to 12.6 g / L, a pH of 2.5 to 3.5, and a bath temperature of 25 to 33° C. Conditions for the first plating treatment include a current density of 0.0 to 4.0 A / dm 2 The treatment time is preferably 2.0 to 6.0 seconds. The first plating treatment may be a composite metal layer of copper and nickel, or a composite metal layer of copper and tungsten.

[0033] In this case, the supply source of each metal may be in any form, such as oxide, sulfate, nitrate, carbonate, isopolyacid salt, or metal oxoacid salt. Furthermore, anhydrous sodium sulfate may be added to stabilize the ion concentration in the solution and thereby stabilize the plating results. In this case, the sodium concentration is preferably 5.0 to 30.0 g / L.

[0034] Subsequently, in the second plating process, for example, a composite metal layer of nickel, cobalt, and tungsten is formed. Specific examples of the second plating bath composition for this purpose include a nickel concentration of 1.0 to 4.5 g / L, a cobalt concentration of 1.0 to 3.1 g / L, a tungsten concentration of 0.3 to 2.8 g / L, a pH of 2.5 to 4.0, and a bath temperature of 25 to 33°C. The conditions for the second plating process include a current density of 0.3 to 1.5 A / dm 2 It is preferable to set the current to 0.8 to 1.5 A / dm 2 It is more preferable to set the current to 1.0 to 1.4 A / dm 2 It is more preferable that the treatment time is 2.0 to 4.0 seconds.

[0035] In this case, the supply source of each metal may be in any form, such as oxide, sulfate, nitrate, carbonate, isopolyacid salt, or metal oxoacid salt. Furthermore, anhydrous sodium sulfate may be added to stabilize the ion concentration in the solution and thereby stabilize the plating results. In this case, the sodium concentration is preferably 5.0 to 30.0 g / L.

[0036] In theory, performing the plating process twice in this way should result in the formation of two composite metal layers, but despite various analyses, the interface between the two layers could not be clearly identified, and it is thought that only a single blackened layer was formed.When the amounts of nickel, cobalt, and tungsten in the blackened layer were measured from the surface using a wavelength dispersive X-ray analyzer (WDX), the amounts of each element contained in the two composite metal layers were confirmed.

[0037] In the step of forming the blackened layer, it is preferable to perform water washing or pickling before any plating treatment. After forming the blackened layer, as described above, a silane coupling agent treatment may be performed, or a chromate treatment may be performed before the silane coupling agent treatment. The treatment conditions for the chromate treatment and the silane coupling agent treatment may be the same as those known for electrodeposited copper foils. [Example]

[0038] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0039] [Example 1] First, the surface of a 6 μm thick electrolytic copper foil (manufactured by Nippon Denkai Co., Ltd., product number: SEED foil) was pickled by immersing it in 10 wt % sulfuric acid for 10 seconds. After rinsing the copper foil with water, the cathode side surface of the copper foil was plated with a first plating solution containing copper concentrations of 4.1 to 5.1 g / L, cobalt concentrations of 7.4 to 8.4 g / L, and sodium concentrations of 14.8 to 23.2 g / L, adjusted to a pH of 2.9 and a bath temperature of 30°C, at a current of 2.4 A / dm 2 to form a first composite metal layer containing copper and cobalt.

[0040] Then, after rinsing the copper foil with water, the cathode side surface of the copper foil is further plated with a second plating solution adjusted to a nickel concentration of 2.6 to 2.8 g / L, a cobalt concentration of 1.8 to 2.0 g / L, a tungsten concentration of 0.9 to 1.1 g / L, and a sodium concentration of 14.1 to 23.7 g / L, a pH of 2.9, and a bath temperature of 30°C, at a current of 1.0 A / dm 2 to form a second composite metal layer containing nickel, cobalt, and tungsten.

[0041] Next, the copper foil was washed with water, and the cathode side surface of the copper foil was coated with a chrome solution containing 3.5 g / L of sodium dichromate and adjusted to pH 5.4 and a bath temperature of 28°C on the first and second composite metal layers at a current of 0.9 A / dm 2 A chromate treatment layer was formed by plating at a current density of 1000 ppm.

[0042] The copper foil was then washed with water and immersed for 10 seconds in a silane coupling agent solution containing 0.25 wt % of 3-aminopropyltriethoxysilane to form a silane coupling agent treatment layer on the chromate treatment layer, thereby obtaining the surface-treated copper foil of Example 1.

[0043] [Examples 2 to 4] As shown in Table 1, the current density of the second plating process was 1.1 A / dm 2 , 1.2A / dm 2 , 1.4A / dm 2 The electrolytic copper foils were treated under the same conditions as in Example 1, except for the above change, to obtain surface-treated copper foils of Examples 2 to 4. [Example 5] As shown in Table 1, the electrolytic copper foil was treated under the same conditions as in Example 3, except that the first plating treatment was not carried out, to obtain the surface-treated copper foil of Example 5.

[0044] [Comparative Examples 1 to 4] As shown in Table 1, the current density of the second plating process was 1.6 A / dm 2 , 1.9A / dm 2 , 2.5A / dm 2 , 0.5A / dm 2The electrolytic copper foils were treated under the same conditions as in Example 1, except for changing the temperature to the above, to obtain surface-treated copper foils of Comparative Examples 1 to 4.

[0045] Comparative Example 5 As shown in Table 1, the electrolytic copper foils were treated under the same conditions as in Example 1, except that the second plating treatment was not carried out, to obtain surface-treated copper foils of Comparative Examples 1 to 5.

[0046] The plating time carried out in each of the examples and comparative examples was adjusted within a range of 0.0 to 8.0 seconds while adjusting the deposition amount.

[0047] For the surface-treated copper foils of Examples 1 to 5 and Comparative Examples 1 to 5, the amounts of Ni, Co, and W components attached to the adherend surface of the surface-treated copper foils were measured using the methods described below, and the color tone, etching resistance, and appearance of treatment unevenness and air bubble marks on the adherend surface of the surface-treated copper foils were evaluated.

[0048] (1) Measurement of adhesion amount Adhesion amount of surface-treated copper foil on the adherend surface (μg / dm 2 ) was measured using a scanning X-ray fluorescence analyzer (Rigaku, model number ZSX Primus IVi). Table 1 shows the results for the adhesion amounts of each of the components Ni, Co, and W, as well as the total amount.

[0049] (2) Measurement of color tone The color tone of the adherend surface of the surface-treated copper foil was measured using a color difference meter (Konica Minolta, product number CR-400) in accordance with JIS Z 8781. * a * b * Color space L * value, a * value, b * The values ​​were measured and the results are shown in Table 2.

[0050] (3) Etching resistance The bonded surface of the surface-treated copper foil was laminated to a laminate film (Asuka Corporation, BH907) using a laminator (Fujipla Corporation, LPD3226N) to form a copper-clad laminate, and test specimens were prepared. The test specimens were then immersed in a 40% aqueous solution of ferric chloride for 10 minutes, and etched to form 1 mm-wide traces. If the copper foil trace peeled during this process, it was evaluated as "×" for peeling, and if it did not peel, it was evaluated as "◯." After etching, if there was a residual residue of 1 μm or more at the end of the trace, it was evaluated as "×," and if there was no residual residue of 1 μm or more, it was evaluated as "◯." The results are shown in Table 2.

[0051] (4) Appearance The appearance of the adherend surface of the surface-treated copper foil was evaluated from the perspective of uneven processing and bubble marks. To evaluate uneven processing, the adherend surface of the surface-treated copper foil was observed using a digital camera, and the uneven processing in the image shown in Figure 4 was used as the standard. If the uneven processing was more severe than that shown in Figure 4, it was marked "X", and if it was weaker, it was marked "O". To evaluate bubble marks, a USB camera was used to take a magnified image (field of view 6mm x 8mm). If bubble marks with a diameter of 50μm or more were present, it was marked "X", and if no bubble marks with a diameter of 50μm or more were present, it was marked "O". The results are shown in Table 2.

[0052] [Table 1]

[0053] [Table 2]

[0054] As shown in Tables 1 and 2, the surface-treated copper foils of Examples 1 to 5 all exhibited L * a * b * In the color system, L * Value is 65 or less, a * Value is 10 or less, b * The value of the color tone was 10 or less, and the black color tone usable for display element applications was exhibited. * , a * , b* The results showed that the surface treatment of Examples 1 to 5 had a lower resistance to etching, and thus the possibility of reflection when used as a display element was low. Furthermore, in the evaluation of etching resistance, no residue or peeling occurred in any of the surface-treated copper foils of Examples 1 to 5. Furthermore, in the evaluation of appearance, no air bubble marks or uneven treatment occurred in any of the surface-treated copper foils of Examples 1 to 5. In particular, compared to Example 5, which was not subjected to the first plating treatment, Examples 1 to 4, which were subjected to the first plating treatment, had a * value, b * The lower the value, the better the color tone.

[0055] On the other hand, in the surface-treated copper foils of Comparative Examples 1 to 3, the current density of the second plating treatment was high, so the amount of adhesion of each component increased, and in the evaluation of color tone, L * value, a * value, b * The values ​​were generally lower than those of Examples 1 to 4, and there was no problem with the color tone, but the increase in the amount of adhesion reduced the solubility in the etching solution, and residues were generated after etching. In addition, the increase in current density made it easier for hydrogen gas to be generated on the copper foil side during plating treatment, and therefore, in the evaluation of appearance, air bubble marks and uneven treatment occurred. In particular, in all of the surface-treated copper foils of Comparative Examples 1 to 3, air bubble marks of 1 m or more were observed. 2 There were more than 10 per unit.

[0056] In the surface-treated copper foil of Comparative Example 4, the current density of the second plating treatment was low, so the amount of each component adhered was reduced, and in the evaluation of color tone, L * The value was well above 65, making it impossible to obtain a blackish color tone. Furthermore, the decrease in adhesion amount increased the solubility in the etching solution, causing the copper foil to peel off during etching. On the other hand, the reduction in current density made it difficult for hydrogen gas to be generated on the copper foil side during the plating process, so the appearance evaluation showed no signs of bubbles or uneven processing.

[0057] In the surface-treated copper foil of Comparative Example 5, the second plating treatment was not performed, and therefore, in the evaluation of color tone, L * The value was far above 65, making it impossible to obtain a blackish color tone. Furthermore, in the evaluation of etching resistance, peeling of the copper foil occurred. [Explanation of symbols]

[0058] 10 Surface-treated copper foil 13 Copper foil layer (electrolytic copper foil) 14 Blackening layer 20 Touch Panel 21 Transparent substrate film 22 Adhesive layer

Claims

1. A surface-treated copper foil comprising an electrolytic copper foil and a blackening treatment layer covering one side of the electrolytic copper foil, the blackening treatment layer is a composite metal layer containing copper, nickel, cobalt, and tungsten; The amount of nickel deposited in the blackened layer is 120 to 400 μg / dm ２ The amount of cobalt deposited is 400 to 700 μg / dm ２ and the amount of tungsten deposited is 70 to 200 μg / dm ２ This is a surface-treated copper foil.

2. The total amount of nickel, cobalt, and tungsten deposited in the blackened layer is 700 to 1200 μg / dm ２ The surface-treated copper foil according to claim 1,

3. The surface of the surface-treated copper foil on the side of the blackened layer is L ＊ a ＊ b ＊ In the color system, L ＊ The value is 55.0 to 65.0, and a ＊ The value is 0.0 to 10.0, and b ＊ The surface-treated copper foil according to claim 1 or 2, wherein the value is 0.0 to 10.0.

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