JPH0518643B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a steel plate for painting and a method for producing the same, and in particular to a steel plate for painting and a method for manufacturing the same, and in particular, the invention relates to a steel plate for painting and a method for manufacturing the same. Steel sheets for painting, which are manufactured through press forming and painting processes and are suitable for the outer panels of automobile bodies and household appliances that require high image clarity, and their manufacturing methods, as well as the surfaces of the rolling work rolls used in their manufacturing. It relates to a processing method for roughening the surface.

(Prior Art) Conventionally, cold-rolled thin steel sheets are a typical example of steel sheets for painting used in automobile bodies and household electrical appliances.
Normally, the steel is manufactured by degreasing and cleaning after cold rolling, further annealing, and then temper rolling. One of the purposes of chamber rolling is to give the steel plate an appropriate surface roughness by performing light rolling using work rolls with a dull surface finish, and to improve seizure resistance during press forming. It is about improving.

By the way, as a method for dull finishing the surface of a work roll used in such temper rolling, conventionally a method using shot blasting and a method using electrical discharge machining have been put into practical use. In the case of dull finishing of work rolls for skin pass rolling by these methods, an irregular roughness profile is formed on the roll surface, so the steel plate surface after skin pass rolling is composed of irregular peaks and valleys. It exhibits a rough surface. For example, if a steel plate with such a rough surface is pressed, lubricating oil will be stored in the valleys, reducing the frictional force between the press die and the steel plate, making the press work easier, and at the same time Seizing can be prevented by trapping the metal powder separated by the frictional force in the valley.

In recent years, the quality of the paint finish on the body of not only passenger cars but also light cars, wagons, and even trucks after painting has become a direct visual indicator of the overall high quality of the car to customers. This is an extremely important quality control item because it can be sued. By the way, there are various evaluation items for painted surfaces, but among them, it is especially important that the painted surface has low diffused reflection and has excellent gloss, and that there is little distortion in mapping, that is, that it has excellent image clarity. The combination of gloss and image clarity is generally referred to as image clarity.

The sharpness of the painted surface is affected by the type of paint and the painting method, but it is also strongly influenced by the roughness of the surface of the steel plate that serves as the base for painting. In other words, if the proportion of flat parts on the steel plate surface is small and the rough surface is highly uneven, the painted surface will also have large unevenness.
As a result, diffused reflection of light occurs, impairing gloss, and distortion of the image, resulting in a decrease in image clarity.
This will worsen the image clarity mentioned above. Generally, the roughness of a steel plate surface is often expressed by the center line average roughness Ra, but the larger the center line average roughness, the larger the amplitude of the peaks and valleys, and the more uneven the painted surface becomes. The sharpness of the image deteriorates.

Various methods have been developed to evaluate sharpness, but the most commonly used method is the method used by Hunter Associates Laboratory in the United States.
Measurements using DORIGON meters manufactured by AssociatesLaboratory, or DOI
(Distinctness of Image) value is used.
This DOI value is determined by the specular reflection light intensity R _S and the scattered light intensity R at ±0.3° with respect to the specular reflection angle when light is incident on the surface of material S at an incident angle of 30° as shown in Figure 9. _0.3
It is expressed by the following formula using the value of .

DOI value = 100 x (Ra - R _0.3 ) / Rs By the way, as mentioned above, when a steel plate is subjected to skin pass rolling using a work roll that has been dull finished by shot blasting or electric discharge machining, The steel plate surface exhibits a rough surface consisting of irregular peaks and valleys, and there are very few planes parallel to the plate surface. When a steel plate surface with irregular peaks and valleys is painted in this way, a coating film is formed along the slopes between the peaks and valleys, so for example, as will be explained later, a coating film is formed along the slopes parallel to the plate surface. The proportion of the coating surface decreases, resulting in poor image clarity.

Conventional shot blasting and electric discharge machining methods cannot avoid such problems, and it has been difficult to obtain sufficiently excellent image clarity of the coating surface.

Therefore, in order to improve the sharpness of the coating surface, attempts have recently been made to use temper-rolled work rolls that have been subjected to dull processing using high-density beam energy such as laser beams.

As a method of manufacturing a steel plate for painting using a rolling work roll subjected to dull processing using high-density beam energy such as a laser beam,
The applicant has already disclosed this in, for example, Japanese Patent Application No. 61-278876.

The gist of this Japanese Patent Application No. 61-278876 will be explained with reference to the drawings.

First, as shown in FIG. 11, the steel plate for painting of the present invention has a centerline average roughness Ra of the plate surface of the steel plate 7.
The microscopic form that is within the range of 0.3 to 2.0 μm and that constitutes the surface roughness surrounds a trapezoidal peak 10 having a flat peak 8 and all or part of its surroundings. Between the groove-shaped trough 11 and the crest 10 formed as shown in FIG.
and an intermediate flat part 9 formed at a lower or the same height, and as shown in FIG. The average diameter of the outer edge of
The average diameter of the flat top surface 8 of the mountain portion 10 is d ₀ , and the flat top surface 8 of the mountain portion 10 and the intermediate flat portion 9 are
The ratio of the sum of the areas of the flat surfaces to the total area of the plate surface is defined as η%, 1.7<Sm/D≦3.0 Sm−D≦450μm 30μm≦d ₀ ≦500μm 80%≦η≦95% This method of manufacturing a steel plate for painting is such that, as shown in FIGS. It consists of a set of a crater-shaped recess 1 and a ring-shaped raised part 2 on the surface at the outer edge of the recessed part 1, and the average center distance Sm between adjacent recessed parts 1 and 1 and the ring-shaped raised part 2 , the ratio of the outer edge diameter D of 2
A patterning process is performed using a high-density energy source (not shown) to form a surface pattern (hereinafter referred to as "dart") 12 in which Sm/D is within the range of 1.7 to 3.0 and Sm-D is 450 μm or less. Then, as shown in FIG. 13, the work roll 3 with the dull weight is used on one or both sides of the steel plate 7 to be subjected to temper rolling, and the temper rolling reduction ratio λ is set to 0.3% or more, and the temper rolling is carried out. By doing so, the dowels 12 on the surface of the work roll 3 are transferred to the surface of the steel plate 7.

In other words, the steel plate 7 that has been temper-rolled using the work roll 3 whose surface has been roughened by such laser machining (hereinafter referred to as laser dull steel plate) has a regular and large flat profile that forms the surface roughness. It has a surface area λ and does not contain undulations of 200 μm or more, so it can significantly improve image clarity after painting.

(Problem to be Solved by the Invention) However, when performing the laser rounding on the work roll 3 used to implement the technique described in the specification of Japanese Patent Application No. 61-278876, As shown in Fig. 14, the rotating work roll 3 is irradiated with an intermittent laser beam 13 of short pitch perpendicularly while moving parallel to the rotation axis of the work roll 3, melting the surface of the work roll 3 and giving it a dull weight. However, the laser beam trajectory of the work roll 3 becomes a spiral as shown in the enlarged view in FIG. The phases of the dowels 12 on adjacent spiral circumferences do not match. Therefore, when looking microscopically at the pattern of the dowels 12 on the surface of the work roll 3, as shown in _FIG. In contrast, the line segments L _M in the roll axis direction are arranged irregularly, so if we look at the steel plate 7, we can see that it has anisotropy in the vertical and horizontal directions as a dull pattern on the surface. Become.

When the steel plate 7 having such anisotropy is pressed and painted, sufficient high definition may not be achieved depending on the area where it is used. The reason for this is explained below.

Generally, an object to be painted has a surface that is horizontal to the ground surface and a surface that is not horizontal. On a horizontal surface, after the paint is sprayed, the paint can approach a smooth surface due to microflows to soften unevenness. This process also occurs during the baking process after paint spraying. The more uniform the profile that forms the roughness of the underlying steel plate, the more uniform the microflow of the paint becomes.

However, for example, a steel plate that has been temper-rolled using a work roll whose surface has been roughened by conventional shot blasting or electrical discharge machining (hereinafter referred to as shot dull steel plate and discharge dull steel plate, respectively) has a roughened profile. The flow of such paint is uneven due to the unevenness of the paint, and the flat area ratio is small, and the profile that forms roughness is
Containing large undulations of 200 μm or more causes poor image clarity after painting.

Here, the regularity of the profile that forms the roughness of the steel sheet surface described above will be explained in more detail.

In the case of a laser dull steel plate, as shown in Fig. 17, the dull holes 12 constituting the rough surface in the rolling direction are uniform in size and arranged at regular intervals and are extremely regular. The arrangement of the dowels 12 in the direction (hereinafter referred to as the board width direction) cannot be said to be regular. This is because the surface of the work roll is roughened in such a way that the distance between the dots is constant along the circumference of the work roll in a spiral pattern, and as a result, the roughness of the adjacent helical grooves on the surface of the work roll is The relative position of the upper dowel 12 is not constant and has so-called anisotropy.

The inventors conducted various coating experiments with laser dull steel sheets having such anisotropy (hereinafter referred to as anisotropic laser dull steel sheets), and found that although sufficiently high sharpness can be obtained when painting on horizontal surfaces, for example, when painting on vertical surfaces, It has been found that in non-horizontal areas, such as on horizontal surfaces, it is difficult to significantly improve image clarity as much as on horizontal surfaces, which can provide better image clarity than conventional shot dull steel plates and discharge dull steel plates.

In other words, the test panel of the anisotropic laser dull steel plate shown in Fig. 17 was made, and the sharpness of the paint film was examined when three coats of paint were applied while it was held in a vertical position. The results are shown in Fig. 18. It was shown to. Here, "painting position" is when the test panel is held so that the rolling direction is horizontal (therefore, the board width direction is vertical), and "painting position" is when the rolling direction is vertical (therefore, the board width direction is vertical). This is the case when it is held so that it is horizontal. In addition, the method of painting was to first apply a chemical conversion treatment to the surface of the test panel using zinc phosphate dip treatment, then apply an electrodeposition base coat of 18 to 20 μm in thickness, and an intermediate coat of 30 to 30 μm in thickness.
Three coats of 35 μm and a top coat of 30 to 35 μm are applied.

As is clear from FIG. 18, it can be seen that the DOI value of the test panel in the painting position is higher than that of the test panel in the painting position.

The reason why there is such a difference in DOI values is considered to be due to the following.

(a) On a vertical surface, the sprayed paint once adheres to the surface of the copper plate and then flows downward as if hanging due to gravity.

(b) At the start of painting, as shown in Fig. 19a, irregularities appear regularly in the straight line L _P1 direction along the dot 12, and the paint flows regularly over the area A and the dot 12. , 12, there is a part B where the paint flows on a smooth surface with no unevenness along the straight line L _P2 passing through the flat part 9 between them. However, in Laserdal steel plate, the distance between the straight line L _P1 and the straight line L _P2 is usually less than several 100 μm. Therefore, the downward flow of the paint, that is, the dripping, becomes uniform without the parts A and B influencing each other due to the viscosity of the paint.

(c) On the other hand, in the painting position, as shown in Figure 19b, the paint flows, for example, along straight lines L _M1 , L _M3 , L _M5
Since the unevenness varies and is irregular depending on the area, the flow of the paint is affected by these irregularities, resulting in uneven areas C and D as shown in Figure 19c, which causes the paint film to deteriorate. The skin will become rough.

Therefore, when using such anisotropic laser dull steel sheet to assemble and paint, for example, automobile parts, the sharpness of the painted image after painting depends on whether the steel sheet is rolled vertically or horizontally. If the properties of the parts are different, and if a single component is made up of parts using vertically oriented steel plates and parts using horizontally oriented steel plates, the sharpness of the coating may differ depending on the part of the component. appear.

Furthermore, if a steel plate is used horizontally, the sharpness of the image will deteriorate, but for example, for automobile exterior parts, it is difficult to use for economic reasons such as press work efficiency and its size.
It is required to be able to freely use the rolling direction of the steel plate, either vertically or horizontally, but in order to prevent differences in image clarity, it is necessary to control the steel plate so that it can be rolled only vertically, for example. This becomes a design constraint on the press operation.

The present invention was made against the background of the above-mentioned circumstances, and an object of the present invention is to provide a steel plate with excellent sharpness on vertical surfaces after coating, and a method for manufacturing the same.

Another object of the present invention is to propose a method for appropriately roughening the surface of a work roll used directly in a method of manufacturing a steel plate with excellent image clarity.

(Means for Solving the Problem) This invention provides a plate surface having a center line average roughness Ra within a range of 0.3 to 2.0 μm and a microscopic form constituting the surface roughness being flat. A trapezoidal peak having a simple peak surface and a groove-like valley formed to surround all or part of the periphery of the trapezoid, and the valley between the peak and outside the valley. and an intermediate flat part that is higher than the bottom of the valley and lower than or at the same height as the top surface of the valley, and the average distance between the centers of adjacent peaks is Sm, and the outer edge of the valley is The average diameter is D, the average diameter of the flat top surface of the mountain portion is _d0 , and the sum of the areas of the flat top surface of the mountain portion and the flat surface of the intermediate flat portion accounts for the total area of the plate surface. percentage η%
Defined as, 1.7<Sm/D≦3.0 Sm−D≦450μm 30μm≦d ₀ ≦500μm 80%≦η≦95% When the steel plate is temper-rolled, The deviation angle between a straight line connecting the centers of the two nearest peaks adjacent to each other in a direction perpendicular to the rolling direction and a straight line parallel to the rolling direction is set within 20°. Steel plate for coating (first invention) characterized by a collection of minute crater-shaped recesses and a ring-shaped raised part on the front side at the outer edge of the recess on the surface of a work roll for temper rolling. and the average center distance between adjacent recesses Sm
and the diameter D of the outer edge of the ring-shaped raised part
Sm/D is within the range of 1.7 to 3.0, Sm-D is 450 μm or less, and a straight line connecting the centers of any two recesses closest to each other in the direction of the rotation axis of the work roll is a straight line parallel to the rotation axis. The declination angle is 20℃
Using a high-density energy source, a patterning process is applied to form a surface pattern within the specified range, and the work roll with the surface pattern is then tempered using one or both sides of the steel plate to be temper-rolled. A method for manufacturing a steel plate for painting (second invention), characterized in that a pattern on the surface of a work roll is transferred to the surface of the steel plate by temper rolling with a rough rolling elongation rate λ of 0.3% or more (second invention), and a rotating workpiece. The surface of the roll is irradiated with concentrated high-density beam energy intermittently while moving in the axial direction of the work roll, and the dots are transferred to the surface of the steel plate rolled by the work roll in a checkerboard pattern. When forming dowels on the surface of a work roll, set pitch between adjacent dowels in the circumferential direction of the work roll according to equation (1) below.
A work roll dulling process characterized by determining the number of high-density beam energy irradiations per unit time Q based on SmL ₀ using the following equation (2), and limiting the high-density beam energy irradiation based on this number of irradiations. This is a method (third invention).

πD _R /NSmL ₀ SmL ₁ +1/N (δ−Smctan20°) …(1) However, δ<SmL ₁ where D _R : Diameter of the work roll SmL ₁ : Between adjacent dowels in the circumferential direction of the work roll Setting pitch N: Maximum natural number determined from πD _R /SmL ₁ δ: Phase difference between dull stitches Smc: Setting pitch between adjacent dull stitches in the axial direction of the work roll Q=πD _R /SmL ₀・M …(2) Here M: Number of rotations per unit time of the work roll Note that a laser or an electron beam can be used as the high-density energy source.

(Function) As a result of intensive study to improve the surface roughness profile of the steel sheet that would be more advantageous for improving image clarity, the inventors found that the ridges with flat ridges were formed only in the rolling direction. They discovered that if they are arranged regularly in a straight line in the width direction of the board, it is possible to equalize the downward flow of the paint even when painting in a vertical position, leading to the completion of the first and second inventions. .

That is, even if a steel plate manufactured using a work roll subjected to laser dull processing is used in either the vertical or horizontal direction, it is sufficient to arrange the dowels in the vertical direction close to each other in a straight line. Therefore, when roughening the surface of the work roll 3 using a high-density energy source such as a laser, as shown in FIG. A round eye 1 consisting of a ring-shaped raised part 2 and a ring-shaped raised part 2.
Processing is performed by controlling the laser processing points on the work roll surface so that the steel sheets 2 are regularly arranged in a checkerboard pattern both in the roll rotation axis direction and in the roll circumferential direction, and the steel plate is processed using this work roll. By rolling, it is possible to obtain an isotropic laser dull steel sheet.

The principle of this invention will be explained using FIGS. 2 and 3.

A straight line L _p connecting the centers of any two adjacent dowels 12 in the roll circumferential direction Y of the work roll 3,
Any two dots 1 adjacent to each other in the roll axis direction
Let L _H be the straight line connecting the centers of 2, let α be the declination angle between the straight lines L _P and Y, and let β be the declination angle between the straight lines L _H and X, then the declination angles α and β are α≦20, respectively. If the following conditions are satisfied: °...(1) β≦20°...(2), it is possible to obtain the above-mentioned regularly arranged dowels on the surface of the work roll 3.

As already mentioned, there is no problem with the argument α as long as the technique disclosed in the above-mentioned Japanese Patent Application No. 1983-27886, which is the prior art of the present invention, is applied (with this method, the specific Specifically, α≦0.02°).

On the other hand, regarding the deviation angle β, in order to find the allowable value of the deviation angle β when vertical painting is performed with the width direction of the anisotropic laser dull steel plate in the longitudinal direction as shown in Fig. 19b above, The following experiment was conducted.

As shown in FIG. 4, a conventional anisotropic laser dull steel plate 23 was set on an inclined surface 22 having an inclination of 30° with respect to a plane 21 on a table 20. Inclined surface 22
Let θ be the angle of deviation that the center line C ₂ of the steel plate 23 makes with respect to the center line C ₁ of the steel plate 23 .

Five gauge points on line _A at arbitrary positions on steel plate 22
A ₁ to _{A 5} are provided, and 5 points B ₁ to B ₅ corresponding to the gauges A ₁ to A ₅ are provided on the lower line _B at a fixed distance of 20 mm from these, and the gauges A ₁ ~A 1 each in ₅
Drop 0.005 cc of oil with a viscosity of 4.5 centipoise per gauge point using a syringe to measure the corresponding gauge points B ₁ to _{B 5.}
The time required for the flow to reach this point was measured while changing the declination angle θ. The results are shown in FIG. In addition, the flow form and final length of the oil droplets were measured, and the results are shown in FIGS. 6 and 7.

As is clear from Fig. 5, as the deviation angle θ increases, the falling speed of the oil droplets increases and they become more prone to dripping.
It can also be seen that there is a large variation in the flow velocity.
Furthermore, as can be seen from FIGS. 6 and 7, as the declination angle θ increases, disturbances in the flow become more noticeable, and the dispersion in the final flow length also increases.

From the above, it is thought that the larger the declination angle θ is, the more likely the paint will drip during painting and will flow unevenly, impairing the smoothness of the paint film. The limit for θ is 20°.

Therefore, the upper limit of the deflection angle β, which represents the irregularity of the arrangement of the dulls in the width direction of the isotropic laser dull steel plate, that is, the arrangement of the dulls in the roll axis direction of the work roll, is set to 20°.
All you have to do is

As explained above, the method according to the second invention can impart good image clarity to the steel plate, but micro-craters must be introduced in a so-called checkerboard pattern into the work roll directly used in the second invention. However, the reality is that no method has been proposed for realizing this rounding process on the surface of a work roll.

In other words, regarding a rolling work roll that has been subjected to a dull finish, Japanese Patent Publication No. 11922/1983 discloses that a rotating work roll is irradiated with a continuous laser beam of short pitch perpendicular to the work roll while moving parallel to the rotation axis of the work roll. , discloses that the surface of a work roll is melted and dulled. The laser beam trajectory of this work roll is spiral, and when viewed on this spiral trajectory, the dots are connected on a straight line, but the phases of the dots on adjacent spiral circumferences of the work roll generally do not match.

Therefore, a steel plate subjected to temper rolling with such rolls inevitably has anisotropy in the longitudinal and lateral directions as a dull pattern on the surface.

Therefore, the inventors created a method of imparting a regular checkerboard pattern to the roll surface by arranging microcraters in a straight line both in the axial direction and the circumferential direction on the surface of the rolling roll. As a result of intensive study on methods for efficient surface roughening,
High-density beam energy is used as processing energy for microcraters, and the number of irradiations of high-density beam energy per unit time on the rotating roll surface is determined by the distance SmL between adjacent microcraters in the circumferential direction of the roll and the roll control based on the diameter D of the roll and its rotation speed M per unit time, and if processing on the roll surface is in progress, the circumferential surface of the roll that has already been processed is controlled before irradiation with high-density energy. By controlling the number of irradiations per unit time of high-density beam energy and the irradiation time in relation to the microcraters on the spiral machining trajectory along the cylinder surface, regular microcraters in a checkerboard pattern are created on the cylinder surface. They discovered that they could be arranged, and completed the third invention.

Next, the third invention will be explained in detail with reference to FIG.

Figure 20a shows the trajectory 33 of the laser beam irradiation point when the work roll 31 with diameter D _R is rotated and the laser beam 32 is moved parallel to the rotation axis of the roll 31 and irradiated, and the distance between adjacent trajectories is shown. is set in Smc.

In addition, FIG. 1b shows the i-th and i+1-th trajectories developed on a plane. In order to arrange microcraters in the shape of arbitrary adjacent trajectories on a straight line (hereinafter referred to as reference line) on the roll surface parallel to the rotation axis of roll 1, as shown in Figure c, When the intersection point 35 of the line 34 is the first micro-crater on the i-th spiral, the last micro-crater 36 on the i-th spiral or the next micro-crater 3 after the micro-crater 36
6a so that the intersection of the i+1th spiral and the reference line 34 coincides with each other.

The distance Sm between micro-craters formed on the roll is selected to be less than 450 μm depending on the intended use of the steel plate to be temper rolled with this roll.
For example, if the target steel plate is for automobiles, approximately
300μm, and even if this value fluctuates by about ±10%, the microcrater spacing will change as will be explained later.
As long as Sm and the diameter D of the microcrater satisfy 0.85Sm/D3.0 Sm-d<450μm, high image clarity can be obtained after coating.

Here, first, the microcrater interval SmL in the roll circumferential direction is set to a desired SmL ₁ , and a microcrater is formed on the i-th spiral.

If the number of microcraters formed on the i-th spiral is N, then πD _R = N・SmL ₁ + δ where δ<SmL ₁ where D _R : Roll diameter δ : From the dull phase difference, NπD _R /SmL It becomes ₁ .

Next, the circumferential interval SmL ₀ of the microcraters formed on the i+1th spiral is determined within the range of the following equation (1).

πD _R /NSmL ₀ SmL ₁ +1/N (δ-Smctan20°) ...(1) Furthermore, based on the determined SmL ₀ , the number of laser irradiations per unit time Q is determined by the following formula (2), and the determined laser irradiation Microcraters are formed on the roll surface according to the number of times Q.

Q=πD _R /SmL ₀・M...(2) Here, M: Number of revolutions per unit time of the roll By selecting SmL ₀ as described above, the i-th and i+1 The deflection angle β between the straight line connecting the centers of arbitrary microcraters and the straight line parallel to the axis on the roll surface on the th spiral can always be β20°.

Therefore, if temper rolling is performed using rolls that have been given dullness through the above processing, micro-craters arranged in a grid pattern will be transferred onto the steel plate, causing the steel plate to become non-horizontal. Even when painted and used in a posture, high image clarity can be obtained regardless of the rolling direction of the steel plate.

In addition to a laser, an electron beam or the like can be used as the high-density beam energy source.

(Example) Example 1 Using a laser as a high-density energy source, the deflection angle β was adjusted while controlling the laser processing point in Example 2, which will be described later.
The following four types of surface roughness were obtained using the method of
A work roll of 2.2μmRa was manufactured.

Declination angle: α≦0.02° β=0°, 20°, 30°, 45°, Surface roughness profile: Sm/D=1.5 Sm−D≦225μm Using these work rolls, annealing was performed after cold rolling. A cold-rolled steel plate with a thickness of 0.8 mm was temper-rolled with an elongation rate λ
By applying temper rolling with the surface roughness Ra as 0.8%,
A steel plate of 1.1±0.3μm was obtained.

Subsequently, each steel plate after temper rolling was subjected to chemical conversion treatment under the following conditions.

Treatment agent: Fine-grained phosphate-based chemical for dip treatmentDip conditions: 43℃ x 120 seconds Film weight: 2.2p±0.2g/cm ² Pretreatment: Degreasing, water washing, surface conditioning Post-treatment: Water washing, pure water washing, After drying and chemical treatment, three coats were applied under the following conditions.

Painting position: Vertical position Undercoat: Kachiton ED paint 18-20 μm thick Intermediate coat: Sealer 30-35 μm thick Top coat: Top coat 30-35 μm thick Note that sanding was not performed in each step.

After painting, the DOI value was measured using a Dorigon meter on the surface of the paint film. The measurement results are shown in FIG.

As can be seen from this figure, the DOI value of the coated steel sheet with a declination angle β of 20° is slightly lower than that of the one with a declination angle β of 0°, but it still has the DOI value required as an outer panel for an automobile body. I'm fully satisfied.

Example 2 A rotary chopper shown in Fig. 21 was used as a blocking means for intermittently irradiating laser light, and in imparting dull marks to the surface of a work roll with an axial length of 1600 mm and a diameter of 530 mm, First, the microscale interval SmL ₁ in the circumferential direction of the roll is set to 320 mm to form the first row of dull stitches, and then the interval SmL ₀ of the dull stitches to be provided is determined by the calculators 40 to 42, Furthermore, based on SmL ₀ , the calculation unit 43 calculates the number of laser irradiations per unit time Q, and according to this, operations to add dull marks are sequentially performed to form a checkerboard-shaped microcrater on the work roll surface. did.

Control of the number of laser irradiations is done using Chippad Disc 4.
The number of holes 45 through which the laser beam irradiated on 4 passes is T,
The rotation speed of the motor 46a for driving the tipper is m
[rpm], and the roll rotation speed obtained from the rotation speed detector 48 attached to the roll rotation motor 47 is M [rpm], so that mT=πD _R /SmL ₀・M (=Q). to be done. Note that 46b is a rotational speed controller for the motor 46a.

In addition, a shutter shown in FIG. 22 may be used as a laser beam shielding means. In this case, the number of laser irradiations per unit time Q is determined by the shutter.
It may be controlled in relation to SmL ₀ , roll diameter D _R and roll rotation speed M.

Note that the computing units 40 to 42 are the same as those shown in FIG. 21, and in the figure, 49 is a computing unit, 50 is a shutter opening/closing controller, 51 is a laser oscillator, 52 is a shutter, and 53 is a mirror.

(Effects of the Invention) As explained above, according to the steel plate for painting of the first invention, even if the painting is applied in a vertical position, the press formability is not impaired, and the sharpness of the paint film is improved compared to the conventional one. According to the method for manufacturing a steel plate for painting according to the second aspect of the invention, it is possible to actually manufacture a steel plate with excellent coating film clarity as described above.

Further, according to the third invention, it is possible to provide the surface of the work roll with dull marks arranged in a checkerboard pattern,
By using this work roll for temper rolling, it is possible to transfer microcraters without anisotropy to the steel plate, and therefore it is possible to produce a steel plate with high sharpness regardless of the coating orientation. .

[Brief explanation of the drawing]

FIG. 1 is a developed view schematically showing the arrangement of the dowels on the surface of a work roll for producing an isotropic laser dull steel plate according to the method of the present invention, and FIG. 2 shows the deviation of the dots in the circumferential direction of the work roll. FIG. 3 is a developed view schematically showing the angle of deviation, FIG. 3 is a developed view schematically showing the declination angle of the work roll in the direction of the roll axis, and FIG. 4 is an experimental setup for determining the declination angle β. Fig. 5 is a characteristic diagram showing the relationship between the declination angle and the flow time between gauges, Fig. 6 is a plan view showing the flow form of oil droplets, and Fig. 7 shows the final flow of oil droplets. Figure 8, a characteristic diagram showing the variation in length, shows the declination angle β of the painted steel plate.
A characteristic diagram showing the relationship between DOI values. Figure 9 is an explanatory diagram showing a method for measuring DOI values that indicate image clarity. Figure 10 is a work roll that has been subjected to dulling using a laser as a high-density energy source. A cross-sectional view, b plan view schematically showing the rough surface profile of the surface of
Fig. 11 is a sectional view and b plan view schematically showing the rough surface profile of the steel plate surface temper-rolled by the rolls of Fig. 10, and Fig. 12 is a work roll for temper rolling and a rough surface profile of the steel plate surface. FIG. 13, an explanatory drawing for showing the definition of the dimensions of each part of the profile forming the rough surface, schematically shows a state in which a steel plate is subjected to temper rolling using the work roll of FIG. 10. 14 is a perspective view schematically showing a state in which a work roll is subjected to dull processing using laser pulses; FIG. 15 is a perspective view schematically showing an enlarged laser beam locus; FIG. FIG. 16 is a developed view schematically showing the dull pattern of a work roll subjected to laser dull processing, and FIG. 17 is a plan view showing the dull pattern of an anisotropic laser dull steel plate.
Figure 18 is a characteristic diagram showing the DOI value of the coating film when the surface of the anisotropic laser dull steel plate is coated with different coating positions, and Figure 19 is a characteristic diagram showing the coating film applied with the anisotropic laser dull steel plate in a vertical position. Figure 20a is an explanatory diagram showing the trajectory of the laser beam on the work roll, Figures b and c are developed diagrams of the trajectory, and Figure 21 is an apparatus applied to the present invention. FIG. 22 is an explanatory diagram showing another example of the apparatus. 1... Crater-shaped recess on the work roll surface, 2
... Ring-shaped raised part on the surface of the work roll, 3 ... Work roll, 7 ... Steel plate, 8 ... Flat peak surface of the mountain part on the surface of the steel plate, 9
...Intermediate flat part on the surface of the steel plate, 10... Mountain part on the surface of the steel plate, 11... Valley part on the surface of the steel plate, 12... Dart, 13... Laser beam, 14... Spiral trajectory, 20... Table, 21... Plane, 22... Inclined surface, 23... Steel plate, 31... Work roll, 32
... Laser beam, 33 ... Trajectory, 34 ... Reference line, 35 ... Intersection, 36, 36a ... Micro crater, 40 to 42, 49 ... Arithmetic unit, 44 ...
Chiyotupadisk, 45... Hole, 46, 47...
Motor, 48...Rotational speed detector, 50...Shutter opening/closing controller, 51...Laser oscillator, 52...
...Shatsuta, 53...Mirror.

Claims (1)

[Claims] 1. The centerline average roughness Ra of the plate surface is within the range of 0.3 to 2.0 μm, and the microscopic form constituting the surface roughness is trapezoidal with a flat peak surface. between the ridge and a groove-like trough formed to surround all or part of the periphery of the ridge, and which is higher than the bottom of the trough and located outside the trough. and an intermediate flat part formed at the same height as or lower than the peak surface of the mountain, and the average distance between the centers of adjacent peaks is Sm, the average diameter of the outer edge of the valley is D, and the average diameter of the valley is D. The average diameter of the flat peak surface is d ₀ , and the ratio of the sum of the areas of the flat peak surface of the mountain part and the flat surface of the intermediate flat part to the total area of the plate surface is η%
Defined as, 1.7<Sm/D≦3.0 Sm−D≦450μm 30μm≦d ₀ ≦500μm 80%≦η≦95% When the steel plate is temper-rolled, The deviation angle between a straight line connecting the centers of the two nearest peaks adjacent to each other in a direction perpendicular to the rolling direction and a straight line parallel to the rolling direction is set within 20°. Characteristic steel plate for painting. 2 The surface of the work roll for skin pass rolling is made up of a collection of minute crater-shaped recesses and a ring-shaped raised part on the front side at the outer edge of the recess, and the average center distance between adjacent recesses. The ratio Sm/D between the distance Sm and the diameter D of the outer edge of the ring-shaped raised portion is within the range of 1.7 to 3.0, and Sm-D is within the range of 1.7 to 3.0.
The deviation angle between a straight line connecting the centers of any two recesses closest to each other in the direction of the rotational axis of the work roll and a straight line parallel to the rotational axis, which is 450μm or less.
A patterning process that forms a surface pattern within 20 degrees is applied using a high-density energy source,
The work roll with the surface pattern is used on one or both sides of the steel plate to be temper rolled, and the pattern on the surface of the work roll is applied to the surface of the steel plate by temper rolling with the temper rolling elongation ratio λ of 0.3% or more. 1. A method for manufacturing a steel plate for painting, characterized by transferring the image onto the surface. 3. The method of manufacturing a steel plate for painting according to claim 2, wherein a laser is used as the high-density energy source. 4. The surface of the rotating work roll is irradiated with concentrated high-density beam energy intermittently while moving in the axial direction of the work roll, and the dots transferred to the surface of the steel plate rolled by the work roll are When forming grid-like dots on the surface of a work roll, the high-density beam energy per unit time is calculated based on the set pitch SmL ₀ between adjacent dots in the circumferential direction of the work roll according to the following equation (1). A method for dulling a work roll, characterized in that the number of irradiations Q is determined by the following equation (2), and high-density beam energy irradiation is controlled based on this number of irradiations. πD _R /NSmL ₀ SmL ₁ +1/N (δ−Smctan20°) …(1) where δ<SmL ₁ where D _R : Diameter of the work roll SmL ₁ : Interval between adjacent dowels in the circumferential direction of the work roll Setting pitch N: Maximum natural number determined from πD _R /SmL ₁ δ: Phase difference between dull stitches Smc: Setting pitch between adjacent dull stitches in the axial direction of the work roll Q=πD _R /SmL ₀・M …(2) Here M: Number of revolutions per unit time of work roll