Patent Description:
Grain oriented electrical steel sheets are soft magnetic materials used as materials for iron cores of transformers, generators and the like. Grain oriented electrical steel sheets have a crystal structure in which the <<NUM>> orientation that is an easy magnetization axis of iron is highly-precisely aligned in the rolling direction of the steel sheet. The texture as above is formed through final annealing of a manufacturing process of a grain oriented electrical steel sheet, which final annealing allows crystal grains with the {<NUM>}<<NUM>> orientation referred to as the so-called Goss orientation to preferentially grow to an enormous size. Grain oriented electrical steel sheets as products are required to have such magnetic properties as high magnetic flux density and low iron loss.

The magnetic properties of a grain oriented electrical steel sheet are improved by applying a tensile stress (tension) to a steel sheet surface. As one conventional technique of applying a tensile stress to a steel sheet, a technique in which a forsterite coating of about <NUM> thickness is formed on a steel sheet surface and another coating of about <NUM> thickness of silicon phosphate is formed on the forsterite coating is typically used. The silicon phosphate coating having a lower thermal expansion coefficient than that of the steel sheet is formed at high temperature and cooled to room temperature, whereby a tensile stress is applied to the steel sheet using a difference in thermal expansion coefficient between the steel sheet and the silicon phosphate coating.

By smoothing the steel sheet surface of the grain oriented electrical steel sheet having undergone final annealing, the iron loss reduction owing to the tensile stress of the coating can be further increased.

Meanwhile, the forsterite coating formed on the steel sheet surface by the final annealing adheres to the steel sheet owing to the anchoring effect. Therefore, the smoothness of the steel sheet surface inevitably deteriorates.

Further, adhesion between silicon phosphate and metal is so low that the silicon phosphate coating cannot be formed directly on the steel sheet surface from which the forsterite coating has been removed and which has been smoothed.

Accordingly, techniques using a CVD method or a PVD method to form a ceramic coating composed of, for example, TiN on the steel sheet surface from which the forsterite coating has been removed and which has been smoothed are known (see Patent Literatures <NUM> to <NUM>). Further relevant prior art is disclosed in Patent Literatures <NUM> to <NUM>.

The present inventors studied an embodiment where a coating is continuously formed by a PVD method on a coating formation-target material such as a steel sheet (grain oriented electrical steel sheet having no forsterite coating and having undergone final annealing) that is conveyed. More specifically, the present inventors studied the embodiment where coatings are simultaneously formed on both surfaces of the coating formation-target material conveyed in a longitudinal direction in a chamber. In the foregoing embodiment, targets for use in the PVD method were disposed on both surface sides of the coating formation-target material conveyed in a longitudinal direction, and a coating forming gas was blown on both surface sides of the coating formation-target material in a longitudinal direction.

As a result of the study, it was found that in the foregoing embodiment, the coating formation-target material may sometimes flap. When the coating formation-target material flaps while being conveyed, the coating formation-target material may possibly touch an interior member or another part of a chamber so as to be broken.

In addition, in the foregoing embodiment, when the coating formation-target material flaps, the coating thickness difference between the formed coatings (given that one surface of the coating formation-target material is "surface A" while the other surface is "surface B," the difference between the coating thickness on the surface A and the coating thickness on the surface B) may become large.

The coating thickness difference is a problem peculiar to a PVD method. That is, in a CVD method, since the reaction (coating formation) proceeds only on a surface of a coating formation-target material heated to high temperature, even if the coating formation-target material flaps, the coatings formed thereon would hardly have a coating thickness difference.

On the other hand, in a PVD method (ion plating method, in particular), metal ions (such as Ti ions) are flown and spread from a target (solid object of metal or another substance to be sputtered) to adhere to a coating formation-target material that is negatively charged, whereby a coating is formed. Hence, when the target is far from the coating formation-target material, the coating would be thin while the coating formation area becomes large. On the contrary, when the target is close to the coating formation-target material, the coating would be thick while the coating formation area becomes narrow. Accordingly, the formed coatings would have a large coating thickness difference.

When the coating formation-target material is a grain oriented electrical steel sheet having no forsterite coating and having undergone final annealing, a large difference in coating thickness between the ceramic coatings formed on its surfaces may lead to deterioration of magnetic properties such as iron loss.

The present invention has been made in view of the above and aims at providing a method of using a surface treatment facility for continuously forming coatings by a PVD method on both surfaces of a coating formation-target material conveyed in a longitudinal direction, wherein the coating formation-target material can be prevented from flapping.

The present inventors have made an intensive study and as a result found that when the method described below is employed, the foregoing object is achieved. The invention has been thus completed.

Specifically, the present invention is defined by the appended independent claim <NUM>. Preferable embodiments are described in the appended dependent claims <NUM> to <NUM>.

According to the present invention, a method of using a surface treatment facility for continuously forming coatings by a PVD method on both surfaces of a coating formation-target material conveyed in a longitudinal direction, wherein the coating formation-target material can be prevented from flapping can be provided. By suppressing the flapping of the coating formation-target material, coatings with an even coating thickness can be formed.

Concisely, a method of using a surface treatment facility of the present invention includes a chamber and continuously forms coatings by a PVD method on both surfaces of a coating formation-target material conveyed in a longitudinal direction in the chamber.

The method of using the surface treatment facility of the present invention further includes a conveyance mechanism for conveying the coating formation-target material and a blowing mechanism for blowing a coating forming gas in a longitudinal direction on both surface sides of the coating formation-target material in the chamber, and, when a blowing speed of the coating forming gas is X in the unit of m/minute while a conveyance speed of the coating formation-target material is Y in the unit of m/minute, a ratio expressed by X/Y falls within the range of <NUM> to <NUM>. With this configuration, the coating formation-target material is prevented from flapping.

Below, an embodiment of the present invention is explained with reference to the drawings. However, the present invention should not be construed as being limited to the following embodiment.

First, with reference to <FIG>, the configuration of a surface treatment facility <NUM> is described. Thereafter, a coating formation facility <NUM> provided to the surface treatment facility <NUM> will be described in detail.

<FIG> is a schematic view schematically showing the surface treatment facility <NUM>. The surface treatment facility <NUM> includes a payoff reel <NUM>. A coil <NUM> before conveyance formed from a coating formation-target material S is hung on the payoff reel <NUM>. The coating formation-target material S pulled out from the payoff reel <NUM> is conveyed through various sections of the surface treatment facility <NUM> and then again wound by a winding reel <NUM> to form a coil <NUM> after conveyance.

The payoff reel <NUM>, the winding reel <NUM> and other components such as rolls provided to the various sections (including rolls <NUM> and rolls <NUM> to be described later) constitute the conveyance mechanism conveying the coating formation-target material S. The conveyance speed of the coating formation-target material S is controlled by the driving of the various sections constituting the conveyance mechanism.

The surface treatment facility <NUM> includes, in order of a conveyance direction of the coating formation-target material S, an entry decompression facility <NUM> having multistage entry decompression chambers <NUM>, a pretreatment facility <NUM> having a pretreatment chamber <NUM>, a coating formation facility <NUM> having a coating formation chamber <NUM> as a chamber, and an exit decompression facility <NUM> having multistage exit decompression chambers <NUM>. The coating formation-target material S is conveyed in an air atmosphere except in the entry decompression chambers <NUM>, the pretreatment chamber <NUM>, the coating formation chamber <NUM> and the exit decompression chambers <NUM>.

The coating formation-target material S is not particularly limited in composition or material, and examples of the coating formation-target material S include a metal strip, a film and a semiconductor. When the coating formation-target material S is a metal strip made from a steel sheet or another metal, the coating formation-target material S is conveyed, for example, in a rolling direction.

Described below is an exemplary case where the coating formation-target material S is a grain oriented electrical steel sheet having undergone final annealing as a type of metal strip. The coil <NUM> before conveyance formed from a grain oriented electrical steel sheet S having undergone final annealing (hereinafter also simply called "steel sheet S") is hung on the payoff reel <NUM>.

Typically, a grain oriented electrical steel sheet having undergone final annealing has a forsterite coating.

When the steel sheet S has a forsterite coating, the steel sheet S is subjected to polishing process in, for instance, a polishing facility (not shown) to have the forsterite coating removed before the steel sheet S is introduced into the entry decompression chambers <NUM> of the entry decompression facility <NUM>. When the steel sheet S has no forsterite coating or another oxide coating, on the other hand, the steel sheet S is introduced into the entry decompression chambers <NUM> of the entry decompression facility <NUM> without polishing process.

The internal pressure in the multistage entry decompression chambers <NUM> is reduced stepwise toward the pretreatment chamber <NUM>. Thus, the pressure applied to the steel sheet S (grain oriented electrical steel sheet having no forsterite coating) that is introduced into the entry decompression chambers <NUM> approaches the internal pressure in the pretreatment chamber <NUM> and the coating formation chamber <NUM> from the atmospheric pressure. The number of the stages of the entry decompression chambers <NUM> is preferably at least three.

As shown in <FIG>, the steel sheet S that has passed through the entry decompression chambers <NUM> is introduced into the pretreatment chamber <NUM>. In the pretreatment chamber <NUM>, the steel sheet S is stretched over a plurality of rolls <NUM> and is conveyed. The steel sheet S being conveyed is subjected to pretreatment under a reduced pressure condition. Impurities such as oxides adhering to a surface of the steel sheet S are removed by the pretreatment. In this manner, adhesion of a coating (e.g., nitride coating) to the steel sheet S is remarkably improved. Therefore, although not essential, it is preferable to provide the pretreatment facility <NUM>.

A favorable method of the pretreatment is ion sputtering. In the case of ion sputtering, as ion species for use, ions of inert gases such as argon and nitrogen and ions of metals such as Ti and Cr are preferably used.

The pressure in the pretreatment chamber <NUM> is reduced, and the internal pressure in the pretreatment chamber <NUM> is preferably <NUM> to <NUM> Pa for the sake of increasing the mean free path of sputtering ions. A bias voltage of -<NUM> to -<NUM> V is preferably applied with the steel sheet S serving as the cathode.

The steel sheet S having undergone the pretreatment is introduced into the coating formation chamber <NUM> of the coating formation facility <NUM>. A coating is formed on a surface of the steel sheet S being conveyed through the coating formation chamber <NUM> under a reduced pressure condition. The coating formation facility <NUM> and the coating formation chamber <NUM> will be described later in detail.

The steel sheet S on which the coating has been formed is introduced into the exit decompression chambers <NUM> of the exit decompression facility <NUM>. The internal pressure in the multistage exit decompression chambers <NUM> is increased stepwise with distance away from the coating formation chamber <NUM>. Thus, the pressure applied to the steel sheet S returns from the internal pressure in the pretreatment chamber <NUM> and the coating formation chamber <NUM> to the atmospheric pressure. The number of the stages of the exit decompression chambers <NUM> is preferably at least three.

The steel sheet S that has exited from the exit decompression facility <NUM> is wound around the winding reel <NUM> to form a coil <NUM> after conveyance. Thereafter, a known tensile insulating coating may be formed on the steel sheet S or stress relief annealing may be performed on the steel sheet S.

Next, the coating formation facility <NUM> is described in further detail with reference to <FIG>.

<FIG> is an enlarged cross-sectional view showing the coating formation chamber <NUM> of the coating formation facility <NUM>. The coating formation chamber <NUM> of the coating formation facility <NUM> has a decompression space therein as a result of exhausting (suctioning) through suction portions <NUM> to be described later. The steel sheet S is conveyed through the decompression space in the coating formation chamber <NUM> in a direction of arrows shown in <FIG> (also called conveyance direction).

In <FIG>, the steel sheet S conveyed in the coating formation chamber <NUM> is stretched over a roll 43a, a roll 43b, a roll 43c and a roll 43d (hereinafter, also collectively called "rolls <NUM>") in order of the conveyance direction. The steel sheet S turns by <NUM> degrees when passing each of the rolls. In this manner, the steel sheet S is conveyed in a longitudinal direction (vertical direction), for example, between the roll 43a and the roll 43b and between the roll 43c and the roll 43d. Here, the vertical direction is a direction perpendicular to a horizontal plane or a level plane.

When the steel sheet S is conveyed in a longitudinal direction, normally, there is a concern that the steel sheet S deforms due to gravity. However, as described later, since the coating formation temperature in a PVD method is about <NUM> at the highest, the Young's modulus of the steel sheet S does not largely decrease, and hence the steel sheet S hardly deforms.

In a case where a height by which the steel sheet S is brought up in a longitudinal direction (e.g., a distance between the roll 43a and the roll 43b in <FIG>) is about <NUM>, the steel sheet S hardly deforms. Accordingly, the height by which the steel sheet S is brought up in a longitudinal direction is preferably not more than <NUM>. Meanwhile, this height is preferably not less than <NUM> taking into account the distance required to form a coating.

In the coating formation chamber <NUM>, there may be a region in which the steel sheet S is conveyed in a lateral direction (horizontal direction) such as a region between the roll 43b and the roll 43c.

As shown in <FIG>, in the coating formation chamber <NUM>, targets T for use in a Physical Vapor Deposition (PVD) method are disposed on each surface side of the steel sheet S conveyed in a longitudinal direction. The targets T are held by holders that are not shown.

In the example shown in <FIG>, two rows of the targets T are arranged on one surface side of the steel sheet S each between the roll 43a and the roll 43b and between the roll 43c and the roll 43d. However, this is not the sole case. Meanwhile, when the number of the rows of the targets T is too large, the coating formation chamber <NUM> becomes too long, or another problem arises. Therefore, the number of the rows is preferably about <NUM> or less.

The number of the targets T in each row (number of the targets T disposed in a width direction of the steel sheet S) will be described. Reference should be made to <FIG>.

<FIG> is a schematic view showing an arrangement of the targets T. The number of the targets T in each row is not particularly limited and is appropriately set according to a length in the width direction of the steel sheet S. For instance, as shown in <FIG>, seven targets T may be disposed in each row. In <FIG>, the targets T are linearly arranged along the conveyance direction of the steel sheet S as with a virtual line L1.

<FIG> is a schematic view showing another arrangement of the targets T. As shown in <FIG>, the targets T may be arranged in a staggered fashion (arranged in a zigzag manner) along the conveyance direction of the steel sheet S as with a virtual line L2. This arrangement is preferable since a coating is formed using the targets T without a disproportion in the width direction of the steel sheet S.

The description of <FIG> is now resumed. As shown in <FIG>, a jetting port <NUM> for jetting a coating forming gas G is provided on each surface side of the steel sheet S conveyed in a longitudinal direction. The coating forming gas G is a gas for use in coating formation such as nitrogen gas or TiCl<NUM> gas.

Jetting ports <NUM> are situated on an upstream side or a downstream side of the targets T. For instance, referring to <FIG>, the jetting ports <NUM> between the roll 43a and the roll 43b are situated on an upstream side of the targets T in the conveyance direction of the steel sheet S. In the meantime, the jetting ports <NUM> between the roll 43c and the roll 43d are situated on a downstream side of the targets T in the conveyance direction of the steel sheet S.

Each of the jetting ports <NUM> is connected to a jetting device that is not shown and jets the coating forming gas G toward a region between the targets T and the steel sheet S opposing to the targets T.

A suction portion <NUM> is disposed on each surface side of the steel sheet S to correspond to the jetting port <NUM>. The suction ports <NUM> are situated on an upstream side or a downstream side of the targets T as with the jetting ports <NUM>. Meanwhile, the suction ports <NUM> are situated on the opposite side to the jetting ports <NUM> across the targets T. For instance, referring to <FIG>, the suction ports <NUM> between the roll 43a and the roll 43b are situated on a downstream side of the targets T. In the meantime, the suction ports <NUM> between the roll 43c and the roll 43d are situated on a downstream side of the targets T.

The suction ports <NUM> are connected to a suction pump that is not shown and exhaust (suction) the interior of the coating formation chamber <NUM> to achieve a decompression space.

In addition, each of the suction ports <NUM> is disposed to face a region between the targets T and the steel sheet S opposing to the targets T and suctions the coating forming gas G jetted from the jetting port <NUM>.

The jetting ports <NUM> and the suction ports <NUM> constitute the blowing mechanism blowing the coating forming gas G in a longitudinal direction on each surface side of the steel sheet S.

By adjusting a jetting amount of the coating forming gas G from the jetting ports <NUM> and/or a suction amount through the suction ports <NUM>, the blowing speed of the coating forming gas G is controlled.

The coating forming gas G jetted from the jetting ports <NUM> (at least partly) passes between the targets T and the steel sheet S and is suctioned by the corresponding suction ports <NUM>. Taking into consideration that the coating forming gas G may not sufficiently reach the steel sheet S when the exhaust (suction) through the suction ports <NUM> is excessively strong, the suction ports <NUM> exhaust in such a manner that a desired internal pressure is achieved.

A space defined by tip ends of the jetting ports <NUM>, tip ends of the suction ports <NUM> and the targets T is called a coating formation space <NUM> for convenience. Basically, a coating is formed on the steel sheet S in the coating formation space <NUM>.

In <FIG>, a blowing direction of the coating forming gas G between the roll 43a and the roll 43b coincides with the conveyance direction of the steel sheet S. Between the roll 43c and the roll 43d, on the other hand, a blowing direction of the coating forming gas G is opposite to the conveyance direction of the steel sheet S.

A blowing direction of the coating forming gas G may coincide with or may be opposite to the conveyance direction of the steel sheet S as above.

In the coating formation chamber <NUM>, partition plates <NUM> are disposed to prevent the coating forming gas G from flowing around the rolls <NUM> and forming a coating on the surfaces of the rolls <NUM>.

For instance, as shown in <FIG>, a partition plate <NUM> is disposed between the roll 43a and the jetting port <NUM>, and another partition plate <NUM> is also disposed between the suction port <NUM> and the roll 43b.

In the foregoing configuration, in the coating formation chamber <NUM>, the steel sheet S is conveyed in a longitudinal direction, the coating forming gas G is blown on each surface side of the steel sheet S, and a coating is continuously formed by a PVD method. During the coating formation, the targets T are subjected to sputtering or arc discharge. The targets T are heated by a heater that is not shown.

To be more specific, arc discharge is generated, for example, between the targets T serving as a cathode and an anode so that the targets T are ionized. The ions (metal ions) are also used for maintaining plasma. The steel sheet S is applied with negative bias voltage and thereby attracts metal ions in plasma. For forming a coating of nitride such as TiN, a nitrogen gas is introduced as the coating forming gas G.

In this process, the blowing speed of the coating forming gas G is defined as X (unit: m/minute), and the conveyance speed of the steel sheet S as Y (unit: m/minute). When the ratio expressed by X/Y (hereinafter, also called "X/Y ratio") falls within the range of <NUM> to <NUM>, the conveyed steel sheet S is prevented from flapping.

This is probably because, with the X/Y ratio falling within the foregoing range, the conveyance speed of the steel sheet S and the blowing speed of the coating forming gas G are nearly synchronized with each other, resulting in suppression of the flapping of the steel sheet S.

Suppression of the flapping of the steel sheet S would prevent, for example, the steel sheet S from touching the partition plates <NUM> or other members to be broken.

By suppressing the flapping of the steel sheet S, the coating thickness difference between the coatings formed by a PVD method (given that one surface of the steel sheet S is "surface A" while the other surface is "surface B," the difference between the coating thickness on the surface A and the coating thickness on the surface B) can be reduced. By reducing the coating thickness difference, deterioration in magnetic properties such as iron loss can be suppressed.

The blowing speed of the coating forming gas G is defined as the blowing speed at an intermediate position <NUM> in a longitudinal direction in the coating formation space <NUM>. A means for measuring the blowing speed of the coating forming gas G is not particularly limited, and a known measurement means may be appropriately adopted.

The blowing speed of the coating forming gas G is set to be same on both surface sides of the steel sheet S.

The range of the foregoing X/Y ratio is preferably <NUM> to <NUM> and more preferably <NUM> to <NUM> because the flapping of the steel sheet S can be further suppressed.

The steel sheet S is preferably heated during the coating formation. For a means for heating the steel sheet S, since the interior of the coating formation chamber <NUM> is a decompression space, a burner or such devices may not be inevitably employed. However, any means may be suitably adopted without particular limitation as long as it is a means that does not require oxygen, such as induction heating (IH), electron beam irradiation, laser light, or infrared light.

A preferred PVD method is an ion plating method. The coating formation temperature is preferably <NUM> to <NUM>, and the pressure (internal pressure) in the coating formation chamber <NUM> is preferably <NUM> to <NUM> Pa. During the coating formation, a bias voltage of -<NUM> to -<NUM> V is preferably applied with the steel sheet S serving as the cathode. When plasma is used for ionization of the raw material, the coating formation rate can be increased.

For the coating formed on the steel sheet S, a nitride coating is preferred, a metal nitride coating is more preferred, and a metal nitride coating including at least one metal selected from the group consisting of Zn, V, Cr, Mn, Fe, Co, Ni, Cu, Ti, Y, Nb, Mo, Hf, Zr, W and Ta is even more preferred. These coatings can easily have a rock salt structure, and since this structure easily matches the body-centered cubic lattice of the base iron of the steel sheet S, the adhesion of the coating can be improved.

The coating formed on the steel sheet S may be a single layer coating or a multilayer coating.

The present invention is specifically described below with reference to examples. However, the present invention should not be construed as being limited to the following examples.

A coil <NUM> before conveyance (total mass of <NUM> t) formed from a grain oriented electrical steel sheet S (sheet thickness: <NUM>) having undergone final annealing was set in the surface treatment facility <NUM> described with reference to <FIG>, and a coating was formed. To be more specific, first, the steel sheet S having a forsterite coating removed by mechanical polishing was introduced into the pretreatment chamber <NUM>, and impurities on the surface were removed by Ar ion sputtering.

Subsequently, in the coating formation chamber <NUM>, TiN coatings (target coating thickness on one surface: <NUM>) were formed on the surfaces of the steel sheet S by a PVD method using the targets T. The PVD method was an ion plating method, and the coating formation temperature was <NUM>. The number of the targets T in each row was three. The target T had a shape with Φ100 mm and a hight of <NUM>.

In this process, in the coating formation chamber <NUM>, the blowing speed X (unit: m/minute) of the coating forming gas G and the conveyance speed Y (unit: m/minute) of the steel sheet S were controlled for each row so as to have the ratio of the blowing speed X/conveyance speed Y (X/Y ratio) as shown in Table <NUM> below.

On the exit side of the coating formation chamber <NUM>, the thus formed TiN coatings on both surfaces (one being "surface A," and the other "surface B") of the steel sheet S were checked for their thicknesses. The coating thickness was checked through measurement of Ti intensity with X-ray fluorescence.

Table <NUM> also shows the coating thickness difference (difference between the coating thickness on the surface A and the coating thickness on the surface B). When the coating thickness difference is smaller, it can be evaluated as the flapping of the steel sheet S being suppressed.

In addition, Table <NUM> also shows the value of "coating thickness difference/target coating thickness on one surface x <NUM>.

Thereafter, a tensile insulation coating (coating thickness: <NUM>) made of silicon phosphate glass was formed on the surface of the steel sheet S on which the TiN coating had been formed. More specifically, a predetermined treatment solution was applied by roll coating, then dried, and subsequently baked in a nitrogen atmosphere at <NUM> for <NUM> seconds. Thereafter, stress relief annealing was carried out in a nitrogen atmosphere at <NUM> for <NUM> hours.

In this manner, a grain oriented electrical sheet sheet formed of steel sheet/TiN coating/tensile insulation coating was obtained. Of the obtained grain oriented electrical steel sheet, the iron loss W<NUM>/<NUM> (unit: W/kg) was measured.

Claim 1:
A method of using a surface treatment facility (<NUM>) comprising a chamber (<NUM>) for continuously forming coatings by a physical vapor deposition method on both surfaces of a coating formation-target material (S) conveyed in the chamber (<NUM>) in a longitudinal direction, the facility (<NUM>) further comprising:
a conveyance mechanism (<NUM>, <NUM>, <NUM>, <NUM>) for conveying the coating formation-target material (S); and
a blowing mechanism (<NUM>, <NUM>) for blowing a coating forming gas (G) in a longitudinal direction on both surface sides of the coating formation-target material (S) in the chamber (<NUM>),
the method characterized in that, when a blowing speed of the coating forming gas is X in a unit of m/minute while a conveyance speed of the coating formation-target material is Y in a unit of m/minute, a ratio expressed by X/Y falls within a range of <NUM> to <NUM>.