WIPO Lex

The translation does not have any legal effect and the Judiciary of the Republic of Korea does not guarantee the accuracy of the translated text. Please refer to the original decision in Korean for an accurate statement of law.

PATENT COURT OF KOREA
THIRD DIVISION
DECISION

Case No. 2017Heo3720 Rejection (Patent)
Plaintiff BlueScope Steel Limited
Australia
Defendant: Commissioner of Korean Intellectual Property Office
Intervenor Dongkuk Steel Mill Co., Ltd.
joining the Defendant¹

Date of Closing Argument Nov. 23, 2018
Decision Date Jan. 25, 2019

ORDER
1. The plaintiff’s claim is dismissed.

2. The litigation costs relating to the intervention is assessed against the intervenor joining the defendant. The rest is assessed against the plaintiff.

PLAINTIFF’S DEMAND
The IPTAB Decision 2015Won2751 dated March 29, 2017 shall be revoked.

OPINION
1. Basic Facts
A. Plaintiff’s Subject Invention at Issue (Plaintiff’s Exhibit 5)

1) Title of Invention: Metal-coated Steel Strip

2) International Application Date/ Date of Claimed Priority/ Translation Filing Date/ Application Number: Mar. 13, 2009/ Mar. 13, 2008/ Jun. 30, 2010/ No. 10-2010-7014576

3) Claims (as amended on June 18, 2015)
Claim 1. A hot-dip coating method to form a corrosion-resistant Al-Zn-Si-Mg alloy coating on a steel strip, wherein said method comprises: the process of passing the steel strip through a hot-dip coating bath that contains Al, Zn, Si, and Mg (“Element 1”); the process of forming an alloy coating on the strip so that the coating thickness is no more than 30μm and the coating thickness variation is no more than 40% in any given 5mm diameter section (“Element 2”); and the distribution of Mg₂Si particles in the coating microstructure is no more than 10% by weight on the surface of the coating (“Element 3”).

Claims 2–8, 10: (Omitted)
Claims 9, 11–26: (Deleted)

4) Summary of Invention

(1) Technical Field and Background Art
The subject invention describes a strip, particularly a steel strip having corrosion-resistant² metal alloy coating. More particularly, it relates to a corrosion-resistant metal alloy coating containing Aluminium (Al) - Zinc (Zn) - Silicon (Si) - Magnesium (Mg) (hereinafter “Al-Zn-Si-Mg alloy”) as the main elements of the coating.

Typically, corrosion-resistant metal alloy coating is formed on a steel strip by the method of hot-dip coating. Fifty-five percent Al-Zn alloy coating is a known metal alloy coating on a steel strip. It usually includes α-Al dendrites and β-Zn phase in the inter-dendritic region of the coating after solidification. In relation to hot-dip metal coating method, it is known to add silicon to the coating alloy composition to prevent excessive alloying between the steel substrate and the molten coating.

(2) Solution to Problem
The applicant of the subject invention discovered that, when Mg is added to 55% Al-Zn-Si alloy coating composition, Mg changes the properties of the formed corrosion product, which in turn brings useful effect on the product performance, such as enhanced cut-edge protection.³ However, the applicant also discovered that Mg reacts to Si to form a Mg₂Si phase, which offsets the above useful effect of Mg.

The subject invention focuses on a surface defect called “mottling.” Mottling is a defect where multiple coarse (i.e. with large- and rough-sized crystals) Mg₂Si particle clusters on the coating surface result in a blotchy surface that is aesthetically unacceptable. More particularly, the clustered Mg₂Si particles form darker areas of approximately 1mm-5mm in size, causing non-uniformity of the surface appearance.

The subject invention is about Al-Zn-Si-Mg alloy coated steel strip having Mg₂Si particles in the coating microstructure but the coating surface has an insignificant proportion of Mg₂Si particles or is substantially free of Mg₂Si particles.

The applicant of the subject invention discovered that the Mg₂Si particle distribution within the coating microstructure as the above provides substantial benefits and that such distribution may be achieved by any of the following methods:

(a) adding strontium on the coating alloy;
(b) selecting the cooling rate while the coated strip exiting a coating bath solidifies in relation to a given coating mass (i.e. coating thickness); and
(c) minimizing coating thickness variation.

The applicant of the subject invention discovered that, by minimizing coating thickness variation, Mg₂Si phase’s distribution properties may be controlled so that the coating surface would have Mg₂Si only insignificantly or not have it at all. This is found to greatly reduce the mottling risk of Mg₂Si. The insignificant proportion of Mg₂Si on the coating surface region is 10wt% or less of Mg₂Si particles. The coating thickness of Al-Zn-Si-Mg alloy is typically 30μm or less.

The subject invention provides a hot-dip coating method for forming a corrosion-resistant Al-Zn-Si-Mg alloy coating on a steel strip and includes the process of passing the steel strip through a hot-dip coating bath that contains Al, Zn, Si, and Mn, and optionally other elements, and the process of forming an alloy coating having minimum coating thickness variation, so that the distribution of Mg₂Si particles in the coating microstructure is such that there is only a small proportion of Mg₂Si particles or substantially no Mg₂Si particles on the coating surface. Preferably, the coating thickness variation is 40% or less in any given 5mm diameter section of coating.

(3) Details to Exploit Invention
The applicant of the subject invention discovered two factors that affect the coating microstructure, especially the Mg₂Si particle distribution within the coating.

The first factor is the impact of the cooling rate of the steel strip that exits the coating bath before solidification is complete. Mottlings can be prevented by controlling the cooling rate.

The second is the uniformity of the coating thickness across the coating surface. The coating thickness variation on the coating surface is measured in (a) long range (by weight-strip-weight method of a 50mm diameter disk across the entire width of the strip) and (b) short range (on the cross-section of the coating by 500x microscope in every 25mm across the width of the strip). In a manufacturing environment, the long-range thickness variation is typically controlled to meet the minimum coating requirements as defined in the relevant standards. However, experiments commonly show that a product perfectly meeting the minimum coating requirements as defined in the relevant standards still shows coating thickness variation, caused by two or more factors, in a short range of 5mm. Such a short-range coating thickness variation is certain to affect Mg₂Si on the coating surface.

For example, the applicant of the subject invention discovered that, if the short-range coating thickness variation is greater than 40% above the nominal coating thickness within a distance of 5mm across the strip surface, Mg₂Si particles are formed on the coating surface for AZ150 Class coatings even within a preferable range of cooling rate and this increases the risk of having mottlings. Therefore, to prevent mottlings, short-range coating thickness must be controlled to have 40% or less variation than nominal coating thickness within 5mm range across the strip surface.

(4) Effect of Invention
The subject invention removes the mottling defects and improves first-time-prime production rate. It at least substantially removes the risk of mottling defects and thus gives a coating surface a beautiful, silverly metallic appearance. As a result, first-time-prime production rate is improved, and profitability is boosted.

B. Prior Arts
1) Prior Art 1 (Plaintiff’s Exhibit 8)
Prior Art 1 relates to “Al-Zn-Mg Alloy Coated Steel Products,” published on November 8, 2002 as JP Laid-open No. 2002-322527. The main content and drawings are as below.

Prior Art 1 relates to primary and secondary steel products that are hot-dip coated with Al-Zn-Mg alloy, principally consisting of Al and Zn and containing Mg. The technical task is to provide Al-Zn-Mg alloy coated steel products having excellent corrosion-resistance.

To solve this task, Prior Art 1 consists of the following: (1) Al-Zn phase takes 50% or more by volume on a coating film when surface analysis is performed using an X-ray microanalyzer on a cross section of the coating film; (2) at least some Mg-Si phase is precipitated on the surface of the coating film; and (3) the Mg-Si phase takes 70% or less by area on the surface of the coating film.

Fig. 1 below is a result of 1,000x magnification of cross-section of specimens of coatings with an X-ray microanalyzer. Roughly, three types of layer are shown. Al and Zn are found in the region corresponding to phase (a). Nearly no other elements are found from the phase. A small amount of Mg is shown in the region corresponding to phase (b), but the phase mostly consists of Zn. The region corresponding to phase (c) is a Mg-Si phase, as both Mg and Si are found in the region.

Prior Art 1 is characterized by some of Mg-Si phase being present exposed on the surface of the coating, which has the effect of enhancing corrosion-resistance. However, corrosion-resistance diminishes if the area rate of the Mg-Si phase to the total surface exceeds 70%. Therefore, it is preferred that the area rate of the Mg-Si phase to the total coating surface is 70% or less. In addition, while there is no particular lower limit value, it is desirable to have at least 2%–3% Mg-Si phase, and typically 5%–10% is present.

The coating uses a coating bath with molten quaternary alloy consisting of Al, Zn, Mg, and Si. The ratios of these elements are not specified, but preferably Al is 25wt% or more, Mg is 10wt% or less, Si is 0.5wt% or more in proportion to Al, and the remaining part is Zn. Particularly, if the amount of Mg exceeds 10wt%, the coating becomes brittle and the surface readily develops cracks. The coating bath is set to high temperature, to at least melting point and preferably 40°C–50°C higher than the melting point, and steel materials are dipped into the bath for coating. The duration of immersion should be appropriately determined based on the shape or size of the steel material. After the steel material is withdrawn from the bath, it is cooled as rapidly as possible, at in excess of 40°C/sec.

[Fig. 1]

Fig. 1

2) Prior Art 2 (Plaintiff’s Exhibit 9)
Prior Art 2 relates to “High Corrosion-resistant Steel Plate with Hot-dip Zn-Al Alloy Coating Containing Mg Exhibiting Good Surface Appearance,” published on November 28, 2000 as JP Laid-open No. 2000-328214. The main content and drawings are as below.

Prior Art 2 relates to steel plates coated with hot-dip Zn-Al alloy containing Mg. Its technical task is to provide steel plates, coated with hot-dip Zn-Al alloy containing Mg, that can be mass-produced on an industrial scale, exhibiting good appearance and high corrosion-resistance.

Fig. 1-1 below is a steel plate coated with hot-dip Zn-Al alloy not containing Mg. It shows a smooth and good surface appearance. Fig. 1-2 is a steel plate coated with hot-dip Zn-Al alloy with approximately 1% Mg. White stripes from both edges of the strip extending obliquely downward are observed. The surface of the stripes has wrinkle-like embossings. Fig. 1-3 is a steel plate coated with hot-dip Zn-Al alloy containing 6% Mg. Wrinkle-like defects are found not only on the edges but also in the middle of the steel plate. Accordingly the surface appearance is significantly inferior.

Addition of a small amount of Sr can significantly prevent such wrinkle-like defects. Thus, highly corrosion-resistant steel plates coated with hot-dip Zn-Al alloy containing Mg, having good surface appearance, can be obtained by forming a coating layer on the surface of the plate that contains Al: 25wt%–70wt%, Mg: 1.5wt%–6.0wt%, Sr: 0.01wt%–1.0wt% and preferably 0.07wt%–1.0wt%, Si within the range specified by formula (1), and preferably by formula (1)’, and the remaining part of Zn and unavoidable impurities.

Al(wt%) × 0.005 ≤ Si(wt%) ≤ 10 ··· (1)
Al(wt%) × 0.03 ≤ Si(wt%) ≤ 10 ··· (1)’

Mg is combined with Zn and Si in the coating layer to form inter-metallic compounds of MgZn₂ and Mg₂Si. These inter-metallic compounds are stable products that work as a protective film by rapidly and uniformly covering the coating surface, thereby enhancing corrosion-resistance of the coating layer.

When Mg is less than 1.5wt% in the Zn-Al alloy, corrosion-resistance is not sufficiently enhanced. At the same time, if it exceeds 6wt%, wrinkle-like defects are not sufficiently suppressed on the coating surface even when Sr is added. For these reasons, Mg in the coating layer ranges between 1.5wt%–6.0wt% in the subject invention. The problem of wrinkle-like defect can be solved when an appropriate amount of Sr is added to the coating layer. It is believed that this is because Sr is oxidized prior to Mg in an unsolidified surface layer exiting the coating bath, thereby suppressing oxidization of Mg.

Si is added to make the iron-containing alloy layer, formed on the interface between the coating layer and the steel plate, thin and regular. If Si in the coating layer exceeds 10wt%, clusters are precipitated, which diminishes processability and simultaneously increases melting point and, as such, is undesirable. Therefore, the amount of Si in the coating layer should be within the range set out in the above formula (1), and particularly, the range in the formula (1)’ is preferable.

[Fig. 1-1]

[Fig. 1-2]

[Fig. 1-3]

3) Prior Art 3 (Plaintiff’s Exhibit 10)
Prior Art 3 relates to a “Method for Manufacturing Hot-dip Zn-Mg-Al Coated Steel Plate with Excellent Coating Appearance,” published on February 10, 2005 as JP Laid-open No. 2005-36304. The main content and drawings are as below.

Prior Art 3 relates to a method for manufacturing hot-dip Zn-Mg-Al coated steel plates having excellent coating appearance. Zn-Mg-Al coated steel plate is an excellent coated steel plate commonly used as a highly corrosion-resistant coated steel plate. However, its complex solidification structure of the coating layer makes it necessary to control the cooling rate, for otherwise it may develop visible spots, crepe-like⁴ microscopic embossings on the surface, white and rough surface, or microscopic feather-like⁵ defects, thus calling for improvement.

The technical task of Prior Art 3 is to solve these defects on Zn-Mg-Al coated steel plates and provide uniform and excellent coating appearance.

Prior Art 3 relates to a generally known method of manufacturing hot-dip Zn-Mg-Al coated steel plates, which is to dip a steel plate into a Zn coating bath having Al: 0.1wt%–60wt% and Mg: 0.1wt%–10wt%, withdraw the coated steel plate, control the coating mass by gas wiping,⁶ and then cool it to solidify the coating layer. However, amid this typical process, Prior Art 3 contacts a solid surface with the unsolidified surface of the coating layer before cooling, thereby forming solidification nuclei in the coating layer. This process enables manufacturing of a hot-dip Zn-Mg-Al coated steel plate having excellent appearance.

The solid surface contacted to the unsolidified surface of the coating has embossings, which may have average depth of 0.01μm–500μm and average in-between distance of 1μm–3,000μm. The numerical range is selected because the surface appearance of the coating was the most excellent within the range.

The above Zn coating bath may include 10% or less of Si, Sn, Cr, Ti, B, Ni, Fe, Co, Sb, Pb, and Cu, alone or combined. After solidification nuclei are formed in the unsolidified coating layer, the steel plate may be water-cooled or naturally cooled at a rate of 5°C/sec or above.

While its mechanism is not clear, it is believed that the number of initial solidification nuclei in the Zn-Mg-Al coating layer and the distance between the nuclei is affected by the embossing of the solid surface. Then, in case of the primary Al or Zn crystal⁷ and the ternary Zn-Mg-Al alloy phase and further, Zn-Mg-Al coating having Si or Sn, the formation state of the inter-metallic compounds such as Mg₂Si and Mg₂Sn is changed. This solves the above-mentioned problems of spots, crepe-like microscopic embossings on the surface, white and rough surface, or microscopic feather-like shapes, leading to improved appearance.

4) Prior Art 4 (Plaintiff’s Exhibit 11)
Prior Art 4 relates to “Surface-treated Steel Plate with Excellent Corrosion Resistance and Processability and Its Manufacturing Method,” published on May 9, 2002 as JP Laid-open No. 2002-129300. The main content and drawings are as below.

Prior Art 4 relates to hot-dip Al-Zn-Mg-Si coated steel plate with excellent corrosion-resistance and processability. It is invented to overcome the problem of diminished corrosion-resistance of the conventional Al-Zn-Mg-Si coated steel plate due to its Mg-based inter-metallic compound (Mg₂Si) in the coating layer that has a high rate of dissolution in the corrosive environment.

The essence of Prior Art 4 is a method of manufacturing coated steel plates characterized by: (1) the coating layer having Mg: 0.5wt%–2wt%, Si: 0.2wt%–5wt%, Al: 40wt%–65wt%, Zn: 30wt%–60wt%, and 99% or more of total Mg is solid solution in the coating layer; (2) the coating includes Mg: 0.5wt%–2wt%, Si: 0.2wt%–5wt%, Al: 40wt%–65wt%, Zn: 30wt%–60wt%, and the maximum cooling rate of the coated steel strip after it exits the coating bath is controlled to 30°C/sec or above, (3) the steel strip to be dipped into the coating bath is preliminarily coated with Ni, Fe, Cu, and Cr and then hot-dip coated, and (4) one, two, or more among Ca, Be, Bi, Cr, and Co are included 0.01%–1.0% in the coating layer.

The long-term high corrosion-resistance comes from having 99% or more of total Mg in solid solution in the coating layer. For this purpose, it is desirable to set the maximum cooling rate to 30°C/sec or above after the steel strip is dipped, coated, and exited from the coating bath. Once the cooling rate is decreased, it becomes easier to extrude inter-metallic compounds such as Mg₂Si, leading to diminished long-term corrosion resistance.

C. Procedural History
1) On June 20, 2014, the patent examiner of Korean Intellectual Property Office (the “KIPO”) sent a Notice of Grounds for Rejection (Plaintiff’s Exhibit 6) to the plaintiff regarding the subject invention, stating that “The entire claims of the subject invention, claims 1–26, lack clarity and thus fail to meet the written description requirement. In addition, a person having ordinary skill in the art (a “skilled person”) can easily invent (i) claims 1–3, 6–20, 22, and 26 from Cited Arts 1–6,⁸ (ii) claims 4, 5, and 21 from Cited Arts 1–6, and (iii) claims 23–25 from Cited Arts 1–5 and 7, and thus the entire claims of the subject invention lack an inventive step. Therefore, the subject invention may not be granted patent for the above grounds.”

2) In response, on December 18, 2014, the plaintiff filed a written amendment (Defendant’s Exhibit 1) and a written argument (Defendant’s Exhibit 2), deleting the original claims 1-9 and rewriting original claims 10–26 as claims 1–10, and adding a new claim 11 that refers to claim 1 among others. However, on February 16, 2015, the KIPO patent examiner decided to reject the subject invention (Plaintiff’s Exhibit 2), concluding that the ground for rejection with regards to claims 1–10 as amended on December 18, 2014, i.e. lack of inventive step, remained unresolved.

3) The plaintiff filed an appeal against the above rejection with the Intellectual Property Trial and Appeal Board (“IPTAB”) on May 19, 2015. Further, on June 18, 2015, it filed an amendment seeking reexamination, moving the feature of limiting coating thickness to 30μm or less that was recited in claim 9 to claim 1 and deleting previous claims 9 and 11 (Plaintiff’s Exhibits 4 and 5). However, on July 9, 2015, the KIPO patent examiner sent a notice to the plaintiff of the reexamination result that the original decision would stand because claims 1–8 and 10, as amended on June 18, 2015, still lacked an inventive step and thus the ground for rejection remained (Defendant’s Exhibit 3).

4) The IPTAB heard the above appeal under Case No. 2015Won2751 and dismissed the appeal on March 29, 2017 (Plaintiff’s Exhibit 1), ruling that “Element 1 of claim 1 of the subject invention is substantially identical to the corresponding elements of Prior Arts 1 or 2. Element 2 can be easily derived by a skilled person from the disclosures of Prior Arts 3 and 4. Element 3 can be easily derived by a skilled person from the disclosures of Prior Arts 1–4. Therefore, claim 1 lacks an inventive step as it may be easily invented by a skilled person by combining Prior Arts 1–4, and a patent application must be rejected in its entirety when any one of the claims has a ground for rejection.”

2. Summary of Parties’ Argument and Issues
A. Plaintiff
Claim 1 of the subject invention does not lack an inventive step with regards to Prior Arts for the following reasons, and thus the IPTAB decision concluding otherwise is erroneous.

1) The technical task of claim 1 is to improve the appearance of a coated surface by reducing mottlings, which are surface defects caused by Mg₂Si. However, Prior Arts show no recognition of such a task.

2) In addition, claim 1 provides a method to prevent mottlings based on the technical idea that controlling the concentration gradient of Mg and Si to the thickness direction of the coating would cause the Mg and Si on the coating surface to diffuse into the coating, thereby preventing nucleation of Mg₂Si particles on the surface. The concrete solution is short-range thickness variation control. In this regard, the plaintiff itself has come up with the parameter of “thickness variation of 40% or less in any given 5mm diameter section of the coating” in claim 1. However, Prior Arts do not provide any technical means of controlling short-range coating thickness variation to block the formation of Mg₂Si on the coating surface.

3) Therefore, a skilled person would not have easily invented claim 1 from Prior Arts that have no description or suggestion about the technical task or its solution in claim 1.

4) Meanwhile, a new ground for rejection may not be raised in a judicial action to revoke an administrative decision on rejection. The arguments in the below section B on claim 1’s lack of inventive step, particularly based on the combination of Prior Art 4 with Prior Art 3 or based on Prior Art 3 alone, constitute new grounds for rejection that have never been raised during examination and administrative trial processes. Thus, the inventive step of claim 1 may not be denied based on such arguments.

B. Defendant and Intervenor Joining the Defendant
Claim 1 of the subject invention lacks an inventive step because a skilled person can easily invent it (i) by combining Prior Art 1 with Prior Art 3, (ii) by combining Prior Art 2 with Prior Art 3, (iii) by combining Prior Art 4 with Prior Art 3, or (iv) from Prior Art 3.

Since a patent application having two or more claims must be rejected in its entirety when any one of the claims has a ground for rejection, the subject invention must be rejected as a whole, and the IPTAB decision concluding accordingly was lawful.

C. Issues
In sum, the issues of the present case come down to: (i) whether claim 1 of the subject invention is denied of an inventive step by the combination of Prior Art 1 with Prior Art 3 or the combination of Prior Art 2 with Prior Art 3; (ii) whether the grounds for rejection for claim 1, lack of an inventive step based on the combination of Prior Art 4 with Prior Art 3 or based on Prior Art 3 alone, constitute new grounds for rejection that no opportunity to submit opinion in response was given during the examination or administrative trial, and if not, whether claim 1 lacks an inventive step based on Prior Arts 4 and 3, or on Prior Art 3 alone. The issues are reviewed below respectively.

3. Whether Claim 1 Lacks an Inventive Step
A. Technical Level of a Person Having Ordinary Skill in the Art
The technical level of a skilled person under this case is based on a person who has a bachelor’s degree in metallurgy (mechanical) engineering and has about five years of experience in plating.⁹

B. Comparison with Prior Art 1
1) Element-by-element Comparison

Element	Claim 1 (Plaintiff’s Exhibit 5)	Prior Art 1 (Plaintiff’s Exhibit 8)
1	[A hot-dip coating method to form a corrosion-resistant Al-Zn-Si-Mg alloy coating on a steel strip, wherein said method comprises:] the process of passing the steel strip through a hot-dip coating bath that contains Al, Zn, Si, and Mg;	The technical task of Prior Art 1 is to provide Al-Zn-Mg alloy coated steel product having excellent corrosion-resistance (See Paragraph [0004]). Producing coated steel products by using a hot-dip coating bath that contains 53wt% Al, wt% Mg, 0.8wt% Si, and the remaining part of Zn and unavoidable impurities (See Paragraphs [0001] and [0027])
2	the process of forming an alloy coating on the strip so that the coating thickness is no more than 30μm and the coating thickness variation is no more than 40% in any given 5mm diameter section;	No corresponding element
3	the distribution of Mg₂Si particles in the coating microstructure is no more than 10% by weight on the surface of the coating	If the area rate of the Mg-Si phase to the total surface exceeds 70%, a bad influence is dominant and corrosion-resistance diminishes. Therefore, it is preferred that the area rate of the Mg-Si phase to the total coating surface is 70% or less. In addition, while there is no particular lower limit value, it is desirable to have at least 2%–3% Mg-Si phase, and typically 5%–10% is present (See Paragraph [0013]).

2) Commonalities and Differences
A) Element 1
Element 1 of claim 1 and the corresponding element of Prior Art 1 are common in that a hot-dip coating method to form a corrosion-resistant Al-Zn-Si-Mg alloy coating on a steel strip comprises the process of passing the steel strip through a hot-dip treatment pot (coating bath)¹⁰ that contains Al, Zn, Si, and Mg, thereby showing no difference.

B) Element 2
While Element 2 of claim 1 relates to the process of forming an alloy coating on the strip so that the coating thickness is no more than 30μm and the coating thickness variation is no more than 40% in any given 5mm diameter section, Prior Art 1 has no corresponding element, thereby showing a difference.

C) Element 3
Element 3 of claim 1 and the corresponding element of Prior Art 1 are essentially identical in that the distribution of Mg₂Si particles in the coating microstructure is no more than 10% by weight (typically 5%–10%) on the surface of the coating.

C. Analysis of Difference
For the following reasons, the difference between Element 2 of claim 1 and Prior Art 1 can be easily overcome by a skilled person by combining Prior Art 1 with Prior Art 3 so that the inventive step of claim 1 is denied.

1) Legal Principle
Parameter invention is an invention in which elements of the invention are specified by using the physical, chemical, and biological characteristic values (parameters) newly created by the inventor or by using the correlation between multiple variables.

Considering that the inventive step of a parameter invention which includes the description that specifies an object by means of properties or characteristics should be determined based on the understanding of the technical significance of the parameters, if the parameters are expressed by changing only the expression of the properties of characteristics of a publicly known product by a prior invention, the parameter invention must be regarded as being essentially the same or similar to the prior invention with only difference in terms of technical expression, thereby lacking the novelty and inventive step.

On the other hand, in the case where the parameter has significance as a technical means for solving a problem different from publicly known inventions, and thus has a peculiar effect such as a heterogeneous effect, the inventive step may not be denied. For this, it should be described in the specification in detail that the parameter as a technical means for solving a different problem from publicly known inventions has significance and that there is a causal relationship between the parameter and the peculiar effect such as heterogeneous effect, or it should be possible for a skilled person to infer above significance as a technical means and the causal relationship from the description of the specification.

Meanwhile, even if the above technical significance cannot be recognized with the introduction of the parameter itself, most of parameter inventions take the form of limiting the newly introduced parameters by numerical values. In this case, the parameter invention can also be a numerical limitation invention, and thus the legal principle for numerical limitation invention can be applied to the determination of the invention step. In other words, if significant difference occurs between in and out of a limited numerical range, it should be considered that the inventive step is not denied.

2) Analysis
A) First, “coating thickness variation of no more than 40% in any given 5mm diameter” of Element 2 limits the elements of the invention based on the correlation between the variables such as “distance” of 5mm diameter and “coating thickness variation” of no more than 40%, thereby becoming a new parameter not shown in Prior Art 1.

B) Also, interpretation of claim 1 as a whole yields that having a coating thickness variation of no more than 40% in any given 5mm diameter of Element 2 is designed to have no more than 10% by weight of Mg₂Si particles on the surface of the coating as in Element 3. Together with the description of the specification of the subject invention (Plaintiff’s Exhibit 5) described below, the above parameters shown in Element 2 can be understood as a means to solve the problem by inhibiting the formation of Mg₂Si particles on the surface of the coating, thereby reducing the risk of mottlings, i.e. blotchy surfaces.

[0020] More particularly, mottling is a defect where multiple coarse Mg₂Si particle clusters on the coating surface result in a blotchy surface that is aesthetically not acceptable. (The rest is omitted.)

[0100] The applicant of the subject invention discovered that, if the short-range coating thickness variation is greater than 40%, the nominal coating thickness within a distance of 5mm across the strip surface, Mg₂Si particles are formed on the surface for AZ150 Class coatings ... (omitted) ... and this increases the risk of having mottlings.

[0101] Therefore, ... (omitted) ... to prevent mottling, short-range coating thickness must be controlled to have 40% or less variation than the nominal coating thickness within 5mm range across the strip surface.

C) The technical task of Prior Art 3 is to solve the surface defects such as those caused by inter-metallic compounds including Mg₂Si according to the below description of Prior Art 3 (Plaintiff’s Exhibit 8), of which technical field corresponds to the subject invention and Prior Art 1 as a method for manufacturing hot-dip Al-Zn-Si-Mg coated steel plate. That is, Prior Art 3 directly recognizes surface defects caused by Mg₂Si and includes the improvement thereof as problem to be solved. Also, improving surface defects such as spots and embossings is a basic task to be solved in the relevant technical field for enhanced quality of alloy coated products.

[0003] Zn-Mg-Al coated steel plate ... (omitted) ... is an excellent coated steel plate commonly used as a highly corrosion-resistant coated steel plate. However, its complex solidification structure of the coating layer makes it necessary to control the cooling rate, for otherwise it may develop spots, crepe-like microscopic embossings on the surface, white and rough surface, or microscopic feather-like defects, thus calling for improvement.

[0005] The subject invention ... (omitted) ... relates to a method of manufacturing hot-dip Zn-Mg-Al coated steel plate having excellent coating appearance by controlling the coating mass and contacting a solid surface with the unsolidified surface of the coating layer before cooling, thereby forming solidification nuclei in the coating layer.

[0016] While its mechanism is not clear, ... (omitted) ... when Zn-Mg-Al coating contains Si or Sn, the formation of inter-metallic compounds such as Mg₂Si and Mg₂Sn are affected. This is considered to contribute to solving the problem of aforementioned defects such as spots, crepe-like microscopic embossings on the surface (caused by primary Al crystallization), white and rough surface, and microscopic feather-like shapes, leading to improved appearance.

D) In addition, even though claim 1 relates to a hot-dip coating method and is a process invention relating to a method for manufacturing a product, the method described in Element 2 merely concerns a process of making a final product (coated product) with a characteristic of thickness variation within a certain range at a certain distance, and is silent about specifically how to produce products with such characteristic. In other words, it does not provide any practical means distinguishable from known technologies by its technical significance of providing final products with the coating thickness within the certain range.

E) In addition, the specification of the subject invention (Plaintiff’s Exhibit 8) as described below merely repeats the description that the coating thickness variation is controlled to be no more than 40% within a 5mm diameter across the strip surface so that the Mg₂Si particles on the coating surface is 10wt% or less, thereby reducing the risk of mottling. Thus, it is not specifically stated that there is a causal relationship between the above parameter and the effect of achieving the distribution of Mg₂Si and ultimately the reduction of mottling and it cannot be said that a skilled person can infer this from the description in the specification.

[0030] The applicant of the subject invention discovered that, by minimizing coating thickness variations, Mg₂Si phase’s distribution properties may be controlled so that the coating surface would have Mg₂Si only insignificantly or not have it at all. This is found to greatly reduce the mottling risk.

[0032] The small proportion of Mg₂Si particles on the surface of the coating is no more than 10 weight % of the Mg₂Si particles.

[100] For example, the applicant of the subject invention discovered that, if the short-range coating thickness variation was greater than 40% above the nominal coating thickness within a distance of 5mm across the strip surface, Mg₂Si particles are formed on the coating surface and this increases the risk of having mottlings.

[0101] Therefore, to prevent mottlings under the experimental conditions tested, short-range thickness variation must be controlled to have 40% or less variation than nominal coating thickness within 5mm range across the strip surface.

[0111] The short-range coating thickness variation has to be controlled to be no greater than 40% above the nominal coating thickness within a distance of 5mm across the strip surface to achieve the distribution of Mg₂Si particles of the subject invention.

F) In consideration of all the above circumstances, the parameter in Element 2 does not appear to hold significance as technical means to solve problems different from those of publicly known inventions and have different and unique effects. Therefore, as the introduction of the parameter itself cannot be said technically significant, inventive step of claim 1 cannot be acknowledged based on the introduction of the parameter alone.

G) However, since Element 2 provides numerical limitations such as having the coating thickness of no more than 30μm and the coating thickness variation of no more than 40% in any given 5mm diameter section and thus claim 1 can also be regarded as a numerical limitation invention, the significance of these numerical limitations will be discussed.

(1) First, the part where the coating thickness of no more than 30μm in Element 2 is merely a numerical limitation that can be appropriately selected by a skilled person through ordinary and repeated experiments for the following reasons.

(A) Coating thickness of no more than 30μm is a value including the thickness of coatings shown in embodiments 1 and 2 (See Plaintiff’s Exhibit 10, Paragraphs [0023] and [0026]) in Prior Art 3. That is, in Prior Art 3, an alloy coating that is formed by being dipped into a bath having Zn-3% Mg-11% Al-0.2% Si has a coating mass of 135mg/m³ under embodiment 1 and is converted into a thickness¹¹ of 24.1μm while having a coating mass of 90mg/m³ under embodiment 2 and is converted into a thickness of 16.1μm, and such values are included in Element 2 where the coating thickness is no more than 30μm.

(B) In addition, according to the Korean Industrial Standards (See Defendant’s Exhibit 4, Chart D.1 on Page 42) which was amended on August 23, 2007, prior to the priority date of the subject invention and published at that time by the Korean Agency for Technology and Standards of the Ministry of Trade, Industry and Energy, the thickness of AZ090 of hot-dip 55% aluminium-zinc alloy-coated steel sheets and coils is 0.02mm while that of AZ100 is 0.023mm, which are converted into a thickness of 20μm and 23μm respectively, thereby also being included in Element 2 where the coating thickness is no more than 30μm.

(C) Meanwhile, the specification of the subject invention provides no description relating to significant difference in effects between in and out of such numerically limited range with respect to coating thickness.

(D) As a result, the fact that the coating thickness is no more than 30μm in Element 2 corresponds not only to the values including the thickness of the alloy coating shown in Prior Art 3 but also merely to what can be appropriately selected depending on the purpose or environment of use as a range of coating thickness ordinarily used in the relevant field.

(2) Second, the part where the coating thickness variation of no more than 40% in any given 5mm diameter section of the coating in Element 2 is merely a simple numerical limitation that can be appropriately selected by a skilled person through ordinary and repeated experiments for the following reasons.

(A) Hot-dip coating method was mainly used as a method for forming an alloy coating layer on the surface of a steel strip at the time of the priority date of the subject invention. Specifically, a steel strip passes through heat treatment furnaces and thereafter into and through a bath of molten metal alloy while the metal alloy is maintained molten in the coating pot by the use of heating inductors. Within the bath, the strip passes around one or more sink rolls and is taken upwardly out of the bath and is coated with the metal alloy as it passes through the bath. After leaving the coating bath, the metal alloy coated strip passes through coating thickness control devices, such as air knives, where the coated surface is subjected to jets of wiping gas to control the thickness of the coating. By regulating the air pressure and the nozzle’s distance from the strip, the coating thickness is controlled (Plaintiff’s Exhibit 5, Paragraphs [0010] to [0012], and the witness testimony of A).

(B) However, if the thickness of the alloy coating layer formed through the hot-dip coating method is not uniform, there is a high possibility of occurrence of defects such as crack, and the surface of the coating layer is not smooth and hinders the appearance of the coating layer. Thus, a uniform thickness of the coating layers is a common task to be solved in the relevant technical field (From witness testimony of A).

(C) Also, the description of the specification of Prior Art 3 (See Plaintiff’s Exhibit 10, Paragraph [0018]) that provides uniform and excellent coating appearance yields that Prior Art 3 also includes the technical task of forming an evenly coated layer on the surface.

(D) Meanwhile, the reason for not using the method for controlling the coating thickness variation within a short distance of 5mm in the process of manufacturing the conventional alloy coating is that the product standard at the time did not specify it and there was no difference in the quality of final products without such standard (From witness testimony of A).

(E) In addition, the coating thickness of no more than 30μm and the coating thickness variation of no more than 40% in any given 5mm diameter section in Element 2 means that the coating thickness can range from 18μm to 30μm. Such range is not only quite wide but also is merely in the range conventionally practiced by air knife which is a device that adjusts the coating thickness in the abovementioned hot-dip coating method (Witness testimony of B).

(F) Furthermore, the specification of the subject invention does not specifically describe that significant difference in effects occurs between in and out of such numerically limited range with respect to the coating thickness variation.

(3) As a result, since the numerical limitation in Element 2 is merely a simple numerical limitation that no significant difference occurs between in and out of the limited numerical range, claim 1 including such numerical limitations should be considered what can be easily invented by combining Prior Art 1 with Prior Art 3.

D. Discussion on Plaintiff’s Argument
1) Regarding this, the plaintiff argues that claim 1 is to reduce the occurrence of mottling, a surface defect caused by Mg₂Si, whereas Prior Arts do not even recognize the above technical task and thus the inventive step of claim 1 should not be denied.

However, although the technical task of Prior Art 1 is to provide alloy coated steel products having excellent corrosion-resistance and does not explicitly describe surface defects, the technical task of Prior Art 3 is to solve surface defects on coated steel plates such as those caused by inter-metallic compounds including Mg₂Si as described above. That is, Prior Art 3 directly recognizes defects on the coating surface caused by Mg₂Si and includes improvement thereof as its technical task.

While alloy coating on steel strip is basically aimed at improving corrosion resistance of steel strip products, improving corrosion resistance and controlling defects on the coating surface should be viewed as basic tasks to be considered and pursued together, rather than being incompatible.

Therefore, a skilled person has a sufficient motivation to combine Prior Art 1 relating to improving corrosion resistance of alloy coating with Prior Art 3 which concerns the same technical field as Prior Art 1 and regards suppressing defects on the coating surface as technical task, and there will be no technical difficulties in trying such combination.

Therefore, this part of the plaintiff’s argument fails.

2) In addition, the plaintiff argues that since Prior Arts do not disclose technical concept of suppressing the occurrence of mottling by allowing magnesium and silicon to diffuse into the coating layer by using the concentration gradient of magnesium and silicon in coating thickness direction as in claim 1, the inventive step of claim 1 should not be denied.

However, the specification of the subject invention does not describe specifically how the coating thickness of no more than 30μm and the coating thickness variation of no more than 40% in any given 5mm diameter section of the coating affect the concentration gradient of magnesium and silicon in coating thickness direction, and as long as such relationship is not considered a general technical knowledge that can be deduced by a skilled person without a specific description of the specification, it cannot be concluded that claim 1 uses the concentration gradient of magnesium and silicon in coating thickness direction. Then, the plaintiff’s above argument premised on the foregoing fails without further discussion.

E. Summary of Analysis
According to the above findings, claim 1 of the subject invention can be easily invented by a skilled person by combining Prior Art 1 with Prior Art 3, thereby lacking inventive step.

4. Conclusion
As long as claim 1 of the subject invention lacks an inventive step, according to the legal principle that a patent application having two or more claims must be rejected in its entirety when any one of the claims has a ground for rejection, the IPTAB decision that affirms the original decision that the subject invention may not be granted a patent has no erroneous grounds as asserted by the plaintiff, and the claim to revoke the administrative decision by the plaintiff has no merit.

Presiding Judge Kyu hong LEE

Judge Sung yop WOO

Judge Jin hee LEE

¹ This court rejected the intervenor’s request to join the proceeding on October 29, 2018. However, the intervenor filed an immediate appeal from the order, which is still pending. As such, pursuant to Article 75(1) of the Civil Procedure Act, the Intervenor may continue to act in the litigation until the above order is confirmed.

² “Corrosion-resistance” refers to a property of being resistant to corrosion or erosion. See Iron & Steel Dictionary of Korea Iron & Steel Association at www.kosa.or.kr.

³ “Cut-edge protection” means protection of a cut edge from corrosion like “

.” See eLibrary of Australian Steel Institute at www.steel.org.au.

⁴ The original text in Prior Art 3 is “梨地狀.” The “crepe-like” shape, as provided in the party’s translation, refers to the shapes like spots on the pear (梨) skin or textile in gingham pattern.

⁵ The dictionary meaning of the original text in Prior Art 3, “羽根,” is “a golden rain tree drilled to make holes to put bird feathers into the holes,” or “a badminton shuttlecock.”

⁶ “Gas wiping” is a technology controlling the coating amount by using air knives (devices that jet compressed air or compressed nitrogen gas from nozzles) so that the compressed air or nitrogen gas would collide with the coating layer attached to the coated steel plate. See Engineering Dictionary, ENGNET (Engineering Network) at www.engnetglobal.com.

⁷ Primary crystal refers to the crystal that is firstly gained from molten metal.

⁸ Cited Arts 1 to 7 were submitted at the examination process of the subject invention. Prior Arts 1 to 4 were submitted at the administrative trial and this lawsuit. The corresponding relations between Cited Arts and Prior Arts are as per the chart on the right.

Prior Art	1	2	3	4
Cited Art	1	2	6	5

⁹ There is no dispute between the parties on this matter (See the first Court Record for Trial dated November 23, 2018).

¹⁰ The item enclosed in parentheses refers to the element of Prior Art 1 corresponding to the elements of claim 1 of the subject invention. Hereinafter, all are expressed in the same manner in the case of comparing claim 1 with Prior Art 1.

¹¹ The density of the alloy having the composition of Zn-3% Mg-11% Al-0.2% Si is about 5.59g/cm3, and the conversion is carried out based on this.

Republic of Korea

KR002-j

Patent Court Decision, 2017Heo3720, dated January 25, 2019