JP4369843B2 - Curtain coating method and multilayer coating product - Google Patents

Description

  The present invention relates to a curtain coating method and a multilayer coating product product in which a curtain composed of a plurality of liquid films is dropped and a plurality of films are coated on the surface of a traveling plate.

  In the curtain coating method, a liquid film can be formed by a curtain discharge device, the liquid film can be freely dropped as a curtain, and the curtain can be collided on a traveling board to coat the film on the surface of the board. The end in the width direction of the free-falling curtain is regulated by the guide device, and the width of the curtain during the free-fall is maintained at a predetermined width. Without using the guide device, both ends of the curtain can be free ends. Patent Document 1 describes a curtain coating method in which a curtain is formed as a liquid film having a plurality of layers, and a plurality of layers are coated on the surface of a traveling plate. Yes.

  In the coating position on the plate, if the curtain width is equal to or smaller than the plate width, the thickness of the film coated on the surface of the plate tends to be thick at the end in the width direction, The film thickness uniformity may not be maintained. On the other hand, if the width of the curtain is made wider than the width of the plate at the coating portion on the plate, the thickness of the film coated on the plate can be made uniform in the width direction.

  When the width of the curtain is made wider than the width of the plate, the curtain portion located outside the both ends of the width of the plate will fall below the plate. About this falling curtain part, if a curtain is a liquid film of a single layer, it can collect | recover and it can reuse as a curtain liquid film raw material. However, when coating a plurality of layers of liquid film as described in Patent Document 1, the curtain is a liquid film of a plurality of layers even in the curtain portion that falls outside the both ends of the width of the plate. Becomes a mixture of two or more different compositions and cannot be reused as a curtain liquid film raw material.

  In the invention described in Patent Document 2, it is mainly used as a photographic film manufacturing technique, and one layer of a plurality of liquid films constituting a curtain is larger than the width of a web (plate). And the other layers have a width that does not overflow the web. Thus, since the liquid film overflowing from the edge of the web is a single layer, the overflowing composition can be collected and recycled into the liquid feed of the same composition layer. Here, a layer having a width larger than the width of the web and having the same width as the curtain width is called a wide layer, and a layer having a width that does not overflow the web is called a narrow layer.

  The application method using the curtain coating method is also considered to be used for coating a metal plate, and Patent Document 3 discloses a liquid film in which the width of each liquid film layer constituting the curtain is the same as the metal plate. Shown to paint on.

Japanese Patent Publication No.49-24133 Japanese Patent Publication No.62-47075 Japanese Patent Laid-Open No. 06-190335

  The invention relating to the curtain coating method described in Patent Documents 1 and 2 has been developed mainly as a photographic film manufacturing technique. Therefore, the liquid film constituting the curtain is mainly an aqueous solution, and is an aqueous solution in which gelatin having a molecular weight of 100,000 or more is dissolved.

  On the other hand, when the curtain coating method is used for surface coating such as steel strip, the liquid film constituting the curtain is mainly a paint, and the paint is mainly composed of a resin-based polymer having a molecular number of 30000 or less. A liquid obtained by dissolving the resin polymer in an organic solvent is used.

  Even in the case of using a curtain coating method for surface coating of a steel strip or the like, as shown in FIG. 1, out of a plurality of layers of liquid films constituting the curtain 10, the curtain width is larger than the width of the plate 11. A wide layer 12 having the same width and a narrow layer 13 having a width that does not overflow the plate 11 can be used. Thereby, since the liquid film overflowing from the edge of the plate is a single layer, this overflowing composition can be collected and recycled into the liquid feed of the same composition layer. Of the entire width of the curtain, the outer portion in the width direction forms a curtain having only a wide layer and is usually a single layer. This portion is referred to as “outer monolayer portion 36”. The central portion in the width direction forms a curtain of at least two layers of a wide layer and a narrow layer. This portion is referred to as “inner multilayer portion 35”.

  When applying multiple layers of paint on the surface of the steel strip, if a curtain coating method is used that forms a liquid film composed of a wide layer and a narrow layer, the curtain will fall free and arrive at the surface of the steel strip. In the interval up to this point, as shown in FIG. 2, the width of the inner multilayer portion 35, that is, the width of the narrow layer 13 may become narrower as it goes downward. At this time, as the width of the inner multilayer portion 35 becomes narrower, the width of the outer single layer portion 36 expands as it goes downward, and at the same time, a part of the outer single layer portion 36 becomes thinner and the thin film becomes thin. There is a case where the phenomenon of forming the crystallization portion 14 occurs. This phenomenon is hereinafter referred to as “thinning phenomenon”. When the thinning phenomenon occurs, the state of the free-falling curtain becomes unstable, the curtain is broken, or an air entrainment phenomenon occurs at the boundary between the inner multilayer portion 35 and the outer single layer portion 36 of the coated steel sheet. . As a result, the quality of the coated steel sheet becomes unstable, and it becomes a cause of hindering productivity, which is not preferable.

  In a curtain coating method in which a multilayer film is coated on a traveling plate, in the curtain coating in which the width of each layer in the free fall curtain is the same width, all the layers at the end of the curtain during free fall are guided by 5 is touching. In such curtain coating, only a limited layer of the multilayer film may be detached from the guide device 5. After the separation, as a result, the free fall curtain is composed of a wide film and a narrow film, and in this case, the thinning phenomenon may occur.

  The present invention is a curtain coating method for dropping a curtain composed of a plurality of layers of liquid film and coating the surface of a traveling plate with a plurality of layers of film, wherein the liquid film layer comprises a wide layer and a narrow layer. The object is to provide a curtain coating method in which the thinning phenomenon does not occur when a polymer material solution having a molecular weight of 30,000 or less is used as the liquid film.

  Another object of the present invention is to provide a multilayer coating product that can be produced without causing a thinning phenomenon even when the liquid film layers all have the same width.

That is, the gist of the curtain coating method of the present invention is as follows .
( 1 ) In a curtain coating method of dropping a curtain 10 composed of a plurality of layers of liquid film and coating the surface of the traveling plate 11 with a plurality of layers of film, at least one layer of the liquid film constituting the falling curtain 10 The width of is a width narrower than the full width of the curtain, and a layer having a width narrower than the full width of the curtain ( hereinafter referred to as “ narrow layer 13 ” ) is a polymer material solution having a molecular weight of 3000 to 30000, and is the same as the full width of the curtain. A layer having a width ( hereinafter referred to as “ wide layer 12 ” ) is a polymer material solution having a molecular weight of 10,000 to 30,000, and a factor Z is obtained by the following formula (3a) and formula (4a). The relationship between the molecular weight of the molecular material (wide film molecular weight) and Z satisfies the following formula (1b), and the relationship between the molecular weight of the polymer material constituting the narrow layer 13 (narrow film molecular weight) and Z is as follows (2b) ) Curtain Nurikutsugae wherein the satisfying.
Z ≦ Y1 = A1 × wide film molecular weight + B1 (1b)
Z ≧ Y2 = A2 × Narrow film molecular weight + B2 (2b)
Here, A1 = 0.005, B1 = −50, A2 = −0.0006, and B2 = 1.8.
Z = Z1 (3a)
Z1 = −10 × (wide film surface tension−narrow film surface tension) +9 (4a)
However, the unit of surface tension is mN / m. same as below.
( 2 ) The curtain coating method according to ( 1 ) above, wherein the formula (3a) is replaced with the following formula (3b), and the factor Z is obtained from formulas (3b), (4a), and (5).
Z = Z1 + Z2 (3b)
Z2 = −0.03 × (wide film viscosity−narrow film viscosity) −1 (5)
The unit of surface tension is mN / m, and the unit of viscosity is seconds. same as below.
( 3 ) The curtain coating method according to the above ( 1 ) or ( 2 ), wherein Z1 is determined by the following formula (4b) instead of the formula (4a).
Z1 = −0.9 × (corrected solvent surface tension of wide film−corrected solvent surface tension of narrow film) +9 (4b)
However, the modified solvent surface tension of a film means the surface tension of the solvent most contained in the film when the film does not contain additives, and when the film contains additives. The value obtained by subtracting 16.7 from the surface tension of the solvent most contained in the film. same as below.
( 4 ) The curtain coating method according to any one of (1) to ( 3 ), wherein the molecular weight of the narrow film is smaller than the molecular weight of the wide film.
( 5 ) The curtain coating method according to any one of (1) to ( 4 ), wherein the traveling plate is a strip steel.

  When the widths of the liquid film layers are all the same and the surface tensions of the lowermost layer film and the uppermost layer film are different, when only a limited layer of the multilayer film is detached from the guide device, the liquid film layer is detached. The film was found to be the film with the higher surface tension. Further, it has been found that in order to prevent the occurrence of a thin film phenomenon after separation, the same idea as in the curtain coating method may be used.

  The present invention is a curtain coating method for dropping a curtain composed of a plurality of layers of liquid film and coating the surface of a traveling plate with a plurality of layers of film, wherein the liquid film layer comprises a wide layer and a narrow layer. When a polymer material solution with a molecular weight of 30000 or less is used as the liquid film, it is possible to prevent the occurrence of thinning by optimizing the shrinkage margin of the narrow layer of the curtain during free fall Thus, it becomes possible to stably perform surface coating of a strip steel or the like.

  In the present invention, as the curtain discharge device 1 for forming a liquid film, for example, the device shown in FIG. 1 can be used. The curtain discharge device 1 has two or more discharge slits 2. When a liquid is discharged from each discharge slit 2, the discharged liquid becomes a liquid film and flows down along the inclined surface of the curtain discharge device 1. The curtain discharge device 1 shown in FIG. 1 has three discharge slits (2a to 2c) from the first layer to the third layer. The liquid film discharged from the third-layer discharge slit 2c flows down to the position of the second-layer discharge slit 2b and forms a two-layer liquid film in contact with the liquid film discharged from the second-layer discharge slit 2b. The two-layer liquid film flows down to the first-layer discharge slit 2a and contacts the liquid film discharged from the first-layer discharge slit 2a to form a three-layer liquid film. The three-layer liquid film flows down along the inclined surface, leaves the inclined surface at the inclined end, and freely falls as the three-layer curtain 10.

  Below the curtain discharge device 1, a plate 11 is running as an object for curtain coating. The multi-layer curtain 10 dropped on the surface of the board adheres to the surface of the board while maintaining the multi-layer state, and a plurality of layers of films are coated on the surface of the board.

  In the present invention, the width of at least one layer of the liquid film constituting the falling curtain 10 is narrower than the full width of the curtain, and the full width 32 of the curtain when the curtain collides with the plate is larger than the width 34 of the traveling plate. Wide width. A layer having a width smaller than the full width of the curtain is called a narrow layer 13, and a layer having the same width as the full width of the curtain is called a wide layer 12. In the example of the curtain discharge device 1 shown in FIG. 1, the first layer forms the wide layer 12 having the same width as the entire curtain width, and the second layer and the third layer form the narrow layer 13. Of the full width of the curtain, the outer portion in the width direction forms a single-layer curtain of only the first layer. This portion is referred to as “outer monolayer portion 36”. The central portion in the width direction forms a three-layer curtain from the first layer to the third layer. This portion is referred to as “inner multilayer portion 35”. The total curtain width 32 (width of the wide layer) when the curtain collides with the board is wider than the width 34 of the traveling board, and as a result, the curtain located at the outer portions at both ends of the board width is applied to the board surface. It will flow down without being covered.

  In the present invention, the liquid constituting the narrow layer 13 is a polymer material solution having a molecular weight of 3000 to 30000. In coatings mainly made of resin-based polymers, the lower limit of molecular weight when increasing the hardness of the coating film is 3000, while the upper limit of molecular weight when forming a soft coating film that requires high workability is 30000. This is because the effects of the present invention can be exhibited in the molecular weight range of 3000 to 30000. The liquid constituting the wide layer 12 is a polymer material solution having a molecular weight of 10,000 to 30,000. If it is 10,000 or less, a film is not stably formed when a narrow layer is present, while the upper limit of the molecular weight in the case of forming a soft coating film that requires high workability is 30000, and the molecular weight is in the range of 10,000 to 30,000. This is because the effects of the invention can be exhibited.

  Examples of the resin used in the paint include polyester resins, acrylic resins, fluorine resins, and epoxy resins, but other resins may be used as long as they satisfy the surface tension and viscosity.

  When the narrow layer 13 is composed of two or more layers having different compositions, the molecular weight of the liquid constituting the narrow layer 13 is determined by the average molecular weight of the upper layer film. Similarly, when the wide layer 12 is composed of two or more layers having different compositions, the molecular weight of the liquid constituting the wide layer 12 is determined by the average molecular weight of the wide film.

  As described above, the width of the inner multilayer portion 35 (the width of the narrow layer 13) may become narrower as it goes downward in the section until the curtain 10 falls freely and reaches the surface of the steel strip. Corresponding to the narrowing of the width of the inner multilayer portion 35, as shown in FIG. 2 (a), the width of the outer single layer portion 36 expands as it goes downward, and at the same time, part of the outer single layer portion expands. There is a case where a thinning phenomenon occurs in which the thinned portion 14 is formed and the thinned portion 14 is formed. Here, a value obtained by subtracting the width 33 of the narrow layer when the curtain collides with the plate from the width 31 of the narrow layer at the start of curtain falling is defined as a shrinkage allowance X (mm). The contraction allowance X can take a positive value and a negative value. When X is a positive value, the thinning phenomenon occurs in the outer single layer portion 36. On the other hand, as shown in FIG. 2B, when X is a negative value, that is, when the width of the narrow layer 13 increases as it goes downward, the thinned portion 14 is formed at the inner multilayer portion. is there.

  In the present invention, when the width of the narrow layer narrows or widens as it goes downward in the free fall curtain, there is an appropriate range of shrinkage allowance X that does not cause a thinning phenomenon, and the appropriate range of X is the wide layer. It was clarified that it is determined by the molecular weight of the polymer constituting each of 12 and the narrow layer 13.

When the shrinkage allowance X is a positive value, that is, when the width of the narrow layer 13 becomes narrower as it goes downward, the appropriate range of the shrinkage allowance X is the molecular weight of the polymer material constituting the wide film 12 (wide film molecular weight). The appropriate range is expressed by the following equation (1a).
X ≦ Y1 = A1 × wide film molecular weight + B1 (1a)
Here, A1 = 0.005 and B1 = -50. The same applies to equation (1b) below.

When the shrinkage allowance X is a negative value, that is, when the width of the narrow layer 13 increases as it goes downward, the appropriate range of the shrinkage allowance X is the molecular weight (width) of the polymer material constituting the narrow film 13. The appropriate range is expressed by the following equation (2a).
X ≧ Y2 = A2 × Narrow film molecular weight + B2 (2a)
Here, A2 = −0.0006 and B2 = 1.8. The same applies to equation (2b) below.

  That is, when the width of the narrow layer becomes narrower as it goes downward, the thinner the film becomes, the more difficult the thinning phenomenon occurs, and when the width of the narrow layer becomes wider as it goes down, The higher the value is, the more difficult the thinning phenomenon occurs.

  In determining the above formulas (1a) and (2a), the total flow rate of the narrow film and the wide film was mainly tested in the range of 5 to 15 ml / mm / min. The experiment was conducted with the viscosity in the range of 50 to 600 seconds and the surface tension in the range of 30 to 40 mN / m. Moreover, the experiment was performed in the range where the curtain falling distance was mainly 150 to 350 mm, the width of the wide film was mainly 300 to 1100 mm, and the width difference between the wide film and the narrow film was mainly 30 mm to 80 mm. The difference in the width of the narrow film can be applied even at about 200 mm. In this experiment, in calculating the limit value of the shrinkage allowance of the wide film or the narrow film, the film is assumed to be stable up to a value of 5 mm at which the wide film or the narrow film is thinned.

  In the present invention, the shrinkage allowance X of the narrow layer is influenced by the difference between the surface tension of the wide layer 12 and the surface tension of the narrow layer 13, and the difference between the viscosity of the wide layer 12 and the viscosity of the narrow layer 13. I found it to be received. And by defining the degree of the effect of the difference between the surface tension of the wide layer and the surface tension of the narrow layer, and the difference between the viscosity of the wide layer and the viscosity of the narrow layer on the shrinkage allowance of the narrow layer as “Factor Z” It has been clarified that there is an appropriate factor Z range in which the thinning phenomenon does not occur, and the appropriate range of Z is determined by the molecular weight of the polymer constituting each of the wide layer 12 and the narrow layer 13.

When factor Z is a positive value, the appropriate range of factor Z is determined by the molecular weight of the polymer material constituting the wide film 12 (wide film molecular weight), and the appropriate range is expressed by the following equation (1b).
Z ≦ Y1 = A1 × wide film molecular weight + B1 (1b)
When the factor Z is a negative value, the appropriate range of the factor Z is determined by the molecular weight of the polymer material constituting the narrow film 13 (the narrow film molecular weight), and the proper range is expressed by the following equation (2b). .
Z ≧ Y2 = A2 × Narrow film molecular weight + B2 (2b)
Here, A1, B1, A2, and B2 are constants, and the same values as the constants A1, B1, A2, and B2 in the above formulas (1a) and (2a) can be used.

  Next, the factor Z will be described.

When the surface tension is adopted as an influencing factor for the factor Z, the following formulas (3a) and (4a) can be used.
Z = Z1 (3a)
Z1 = −10 × (wide film surface tension−narrow film surface tension) +9 (4a)
However, the unit of surface tension is mN / m.

  About the measuring method of surface tension, it measured at 20 degreeC using the dynometer (product made from BYK-ChemieGmbH) using a platinum ring, and measured it as a ring moving speed of 1.5 mm / min.

  Here, when the wide film 12 is composed of a plurality of liquid film layers, the surface tension of the wide layer constituting the outermost layer of the curtain is defined as the wide film surface tension. When the narrow film 13 is composed of a plurality of liquid film layers, the surface tension of the narrow layer constituting the outermost layer of the curtain is defined as the narrow film surface tension.

  When the wide film surface tension is smaller than the narrow film surface tension, the value of Z becomes a positive value and a larger value as the difference between the two becomes larger. Here, when the expression (1b) is satisfied, that is, when the value of Z is smaller than the value of Y1 (positive value) determined as a function of the wide film molecular weight in the expression (1b), the thinning phenomenon does not occur. It is possible to perform good curtain coating.

  On the other hand, when the wide film surface tension is larger than the narrow film surface tension, the value of Z changes in the negative direction as the difference between the two increases. Here, when the expression (2b) is satisfied, that is, when the value of Z is larger than the value of Y1 (negative value) determined as a function of the narrow film molecular weight in the expression (2b), the thinning phenomenon does not occur. Therefore, it is possible to perform good curtain coating.

When both surface tension and viscosity are employed as factors affecting factor Z, the following equation (3b), the above equation (4a), and the following equation (5) can be used.
Z = Z1 + Z2 (3b)
Z2 = −0.03 × (wide film viscosity−narrow film viscosity) −1 (5)
The unit of surface tension is mN / m, and the unit of viscosity is seconds.

  For the measurement of paint viscosity, Iwata Cup No. The viscosity (unit: seconds) measured at 20 ° C. using 4 was used. This cup has a capacity of about 47 cc and can be easily measured. Even when 4 (capacity 100 cc) is used, a result having a good correlation with the Iwata cup can be obtained.

  Here, when the wide film | membrane 12 is comprised from a some liquid film layer, it is set as the wide film | membrane viscosity with the average value of the viscosity of a some liquid film layer. Further, when the narrow film 13 is composed of a plurality of liquid film layers, calculation is performed in the same manner as in the case of the wide film, and this value is used as the narrow film viscosity.

  When the wide film viscosity is smaller than the narrow film viscosity, the value of Z becomes a positive value and a large value as the difference between the two increases. Here, when the expression (1b) is satisfied, that is, when the value of Z is smaller than the value of Y1 (positive value) determined as a function of the wide film molecular weight in the expression (1b), the thinning phenomenon does not occur. It is possible to perform good curtain coating.

  On the other hand, when the wide film viscosity is larger than the narrow film viscosity, the value of Z changes in the negative direction as the difference between the two increases. Here, when the expression (2b) is satisfied, that is, when the value of Z is larger than the value of Y1 (negative value) determined as a function of the narrow film molecular weight in the expression (2b), the thinning phenomenon does not occur. Therefore, it is possible to perform good curtain coating.

  The factor Z calculated using the above equations (3b), (4a), and (5) is more accurate than the Z calculated using the above equations (3a) and (4a). It is possible to set a value close to the shrinkage allowance. As a result, if the curtain coating conditions are determined based on the equations (1b), (2b), and (3b), it is possible to more accurately grasp the coating conditions in which the thinning phenomenon does not occur.

  A characteristic of resin paints, which are paints applied to the surface of steel materials and are based on polymers, is that the amount of solvent is as high as approximately 50% to 70% of the paint. As a result, there is a very good correlation between the surface tension of the solvent and the surface tension of the paint. It was also found that the surface tension of the solvent used in the largest amount is related to the surface tension of the paint in the paint using a plurality of solvents simultaneously. Specifically, the fluctuation of the surface tension of the paint is 0.09 times the fluctuation of the surface tension of the solvent used in the largest amount.

  Since the above correlation exists, it is possible to use the surface tension of the solvent itself contained in the paint in the largest amount in place of the surface tension of the paint in determining the above-described factor Z. all right.

  The influence of the surface tension of the solvent contained in the paint in the largest amount on the surface tension of the paint varies depending on whether or not the paint contains an additive. The additive is added in an amount of at most several% for the purpose of reducing the surface tension as an antifoaming agent or leveling agent. By adding the additive to the paint, the surface tension of the paint is reduced by 1.5 mN / m.

  Here, an index “corrected solvent surface tension” is defined, and the effect of the additive on the surface tension of the paint is included in the corrected solvent surface tension. Specifically, when no additive is contained in the film, the surface tension itself of the solvent most contained in the film is taken as the corrected solvent surface tension. When an additive is contained in the film, the value obtained by subtracting 16.7 (= 1.5 / 0.09) from the surface tension of the solvent most contained in the film is taken as the corrected solvent surface tension. Thereby, the factor Z can be calculated using the same formula regardless of whether or not the additive is contained in the film.

  As a result, it is possible to determine whether or not the thinning phenomenon has occurred by expressing the factor Z as the modified solvent surface tension of the film (a value determined by the surface tension of the solvent most contained in the film and the presence or absence of additives). I found out that

That is, in the above (3a) and (3b), Z1 may be obtained by the following equation (4b) instead of the above equation (4a).
Z1 = −0.9 × (corrected solvent surface tension of wide film−corrected solvent surface tension of narrow film) +9 (4b)
In the above formula (3b), when the calculated Z value is a positive value, when the formula (1b) is satisfied, that is, the value of Z is determined as a function of the wide film molecular weight in the formula (1b). When the value is smaller than the value of Y1 (positive value), the thinning phenomenon does not occur and good curtain coating can be performed. On the other hand, when the calculated Z value is a negative value, when the formula (2b) is satisfied, that is, the Z value is determined as a function of the narrow membrane molecular weight in the formula (2b) ( When it is larger than (negative value), the thinning phenomenon does not occur and good curtain coating can be performed.

  In the present invention, the traveling plate is preferably a strip steel. When the curtain coating method is used for the surface coating of the steel strip, the coating material is mainly composed of a resin-based polymer having a molecular number of 30000 or less. This is because the effect of preventing the thinning phenomenon can be exhibited by using the invention.

  As described above, in the curtain coating method in which the multilayer film is coated on the traveling plate, in the curtain coating in which the width of each layer in the free-falling curtain is the same width, all of the end portions of the curtain during free-falling are used. The layer is in contact with the guide device 5. In such curtain coating, only a limited layer of the multilayer film may be detached from the guide device 5. After the separation, as a result, the free fall curtain is composed of a wide film and a narrow film, and in this case, the thinning phenomenon may occur.

  In curtain coating of multi-layer films of the same width, when a phenomenon occurs in which a limited layer of the multi-layer film is detached from the guide device, the film with the larger surface tension of the uppermost layer and the lowermost film is guided. It was found that it was easy to leave the device. After the film having a large surface tension is detached from the guide device 5, the layer separated from the guide device exhibits the same behavior as the narrow layer in the present invention, and the layer not detached from the guide device is the wide film in the present invention. It was also found that the same behavior was exhibited.

  Therefore, also in this case, when the layer separated from the guide device (layer having a large surface tension) is further contracted, the other layer attached to the guide device is pulled, and as a result, the film attached to the guide device is thinned. Finally the film becomes unstable.

  Here, it has been found that the same conditions as those of the present invention in which the wide layer and the narrow layer exist from the beginning can be applied to the condition that the film attached to the guide device does not become thin.

  In this case, the application of the film formation stability condition can be applied to all multilayer coating products coated by the curtain coating method. Since the layer that is separated from the guide device and becomes a narrow layer is the layer with the larger surface tension, the conditions under which the thinning phenomenon does not occur are as follows for a product having a multilayer coating on the surface of the plate: Can be expressed in

Of the lowermost film and the uppermost film, the film having the higher surface tension is referred to as the P film, and the film having the lower surface tension is referred to as the Q film. The P film is a polymer material having a molecular weight of 3000 to 30,000, and the Q film is a polymer material having a molecular weight of 10,000 to 30,000. Factor Z is obtained by the following formula (7a), and the relation between the molecular weight of the polymer material constituting the Q film (Q film molecular weight) and Z satisfies the following formula (6). .
Z ≦ Y1 = A1 × Q film molecular weight + B1 (6)
Z = −10 × (Q film surface tension−P film surface tension) +9 (7a)

Also, a good product can be defined even when the surface tension of the solvent most contained in the coating film is used instead of the surface tension of the coating film. This is also the same as the present invention. That is, the surface tension of the coating film is obtained on the basis of the surface tension of the corrected solvent of the film. However, as mentioned above, the modified solvent surface tension of the film refers to the surface tension of the solvent most contained in the film when the film contains no additive, and the film contains the additive. Sometimes it is the value obtained by subtracting 16.7 from the surface tension of the solvent most contained in the film. Since 0.09 times the corrected solvent surface tension of the film becomes the surface tension of the coating film, the magnitude of the surface tension of the coating film can be compared by comparing the magnitude of the corrected surface tension. That is, after the film having the higher correction solvent surface tension of the film is a P film and the film having the lower correction solvent surface tension of the film is a Q film, the factor Z is replaced by the above equation (7a), and the following ( It calculates | requires by 7b) type | formula.
Z = −0.9 × (corrected solvent surface tension of Q film−corrected solvent surface tension of P film) +9 (7b)

  In the present invention, both the P film surface tension and the Q film surface tension are preferably 30 mN / m or more. If the surface tension of the coating film is less than this value, there is a high possibility of instability if the manufacturing conditions such as the flow rate of the curtain fluctuate.

  Moreover, it is preferable that both the correction solvent surface tension of the P film and the correction solvent surface tension of the Q film are 30 mN / m or more. If the corrected solvent surface tension is less than this value, the surface tension of the coating film will be too low, and if the production conditions such as the flow rate of the curtain fluctuate, the possibility of instability will increase.

  The present invention can exert its effect in a multilayer coating product in which a multilayer coating film is curtain-coated.

  In the present invention, the polymer material and additives contained in the multilayer coating film can be specified as follows. First, after peeling a film | membrane from the upper layer of the steel plate coated with the multilayer film for every layer and exposing the film | membrane of each layer, what peeled the film | membrane from the steel plate is made into a sample. The components in each film are extracted with a solvent and analyzed using an infrared spectroscopic analyzer or a pyrolysis gas chromatograph to identify the substance and molecular weight of the polymer material. In addition, when a substance having a molecular weight lower than that of the polymer material is detected by the above analysis, the substance is specified and it is determined whether or not it is an additive. If it is an additive, the additive is identified.

  Next, the identification of the solvent contained in the product can be performed as follows. After collecting a plurality of steel sheets coated with a multilayer film, the steel sheets are divided into a plurality of samples having a measurable size.

  First, one of these divided samples is heated as it is to 230 ° C. in a non-open system, and volatile gas is collected and subjected to gas chromatography analysis to identify the type of one or more volatile gases. Check the type. When two or more kinds of solvents are confirmed, one or more kinds of each confirmed solvent are contained and a sample whose amount is known in advance is used to heat the sample from room temperature to 230 ° C. Collect, perform gas chromatographic analysis, create a calibration curve, compare each peak value of gas chromatography of two or more volatile gases detected above with the calibration curve, and quantify the amount of volatile gas collected Turn into.

  Next, using another sample with the uppermost layer mechanically peeled off and exposing the lower layer directly below the uppermost layer, the sample was heated and volatile gas was collected and gas chromatographic analysis was performed as described above. In addition to identifying the type of volatile gas, create a calibration curve to quantify the amount of volatile gas.

  Similarly, another sample exposing each layer is prepared, and these samples are used to identify and quantify the type of gas that has volatilized from the remaining unexfoliated layer.

  Using these results, the amount of gas determined for each type of volatile gas with one layer peeled from the value of the amount of gas determined for each type of volatile gas with each layer remaining By subtracting this value, the amount of gas for each type of volatile gas present in that layer is obtained.

  Among the gas amounts for each type of volatile gas, the type of volatile gas having the largest amount is set as the type of solvent most contained in the layer.

  The surface tension of the paint should be confirmed by measuring the surface tension of the polymer material confirmed by the above method, the most abundant solvent, and if it can be confirmed, create a paint consisting of additives. Can do. Moreover, about the surface tension of a solvent, it can confirm by measuring the surface tension of the solvent contained most by the said method. In the confirmation of the surface tension of the paint, the polymer material, the solvent, and the additive are mixed and adjusted so that the solvent concentration is 50% and 80%. The surface tension can be measured by the above-described method using a dynamometer at 25 ° C.

  As long as the multilayer coating product of the present invention is coated with a curtain on the multilayer coating film, even if the product is manufactured using a multilayer curtain composed of a wide film and a narrow film, the above relation is obtained as a result. Will be satisfied.

  When the resin-based polymer coating is applied to the surface of the steel strip using the curtain coating method as shown in FIG. 1, a polyester-based material having a molecular weight of 11000 as a wide layer coating material and a polyester-based material as a narrow layer coating material are used. The coating was performed by combining those having a molecular weight of 15000. The width of the wide membrane was 350 mm, and the width was kept constant using a guide chain. The narrow layer slit was ejected as 245 mm, but it was 268 mm at the exit from the slide. The narrow layer shrunk to 264 mm 200 mm below the slide exit side, and the shrinkage margin was 2 mm. In this case, a thinned portion did not occur at the boundary between the wide film and the narrow film, but when the flow rate of the narrow film was increased, the narrow film became 260 mm, 200 mm below the slide exit side. A thinned portion of 5.1 mm was generated. In this case, the operation was stopped because there was a risk that the operation would become unstable after long-time painting. In addition, the thin film part coated on the steel plate involved air, and was unsatisfactory in terms of quality.

  Coating was performed by combining a polyester film with a molecular weight of 16000 as a wide film paint and a polyester film with a molecular weight of 16000 as a narrow film paint. When the difference between the surface tension of the narrow membrane and the surface tension of the wide membrane was 1.7 mN / m, the narrow membrane was 249 mm at the exit from the slide, but it became 203 mm at 200 mm below the exit side of the slide and 24 mm at one side. Shrinked. At this stage, a thinned portion was generated at the boundary, and the curtain generation at the boundary became unstable. It should be noted that the film formation was stable at a shrinkage of 23 mm or less.

  Coating was performed using a combination of a polyester film having a molecular weight of 15000 as a wide film paint and a polyester film having a molecular weight of 11,000 as a narrow film paint. In this case, the shrinkage margin of the narrow film of 15 mm on one side was observed, but the film formation was stable.

  From these facts, the higher the width of the wide film, the wider the allowable range of the narrow film shrinkage margin X. Therefore, as the limit value, the maximum stable shrinkage margin when the molecular weight of the wide film is 16000 and 11000. The values of 2 mm and 23 mm are connected to obtain a thinning limit shrinkage allowance Y1 in the case of narrow film shrinkage (FIG. 3A). The range of X ≦ Y1 is a good range.

When these are formulated,
In the case of narrow film shrinkage, the thinning limit shrinkage margin Y1 = 0.005 × wide film molecular weight−50. From this value, in formulas (1a) and (1b), A1 = 0.005 and B1 = −50.

  On the other hand, when the molecular weight of the narrow film is 3000 and the surface tension of the wide film is greater than the surface tension of the narrow film, a thinning phenomenon occurs in the vicinity of the boundary between the narrow film and the wide film. The film formation became unstable.

  Further, when the molecular weight of the narrow film and the molecular weight of the wide film are 16000, when the difference between the surface tension of the wide film and the surface tension of the narrow film is 1.7 mN / m, the width of the narrow film is expanded by 8 mm. The formation of the narrow film became unstable due to the thinning of the film near the boundary between the narrow film and the wide film.

  From these facts, the wider the narrow film, the wider the permissible range of the expansion width of the narrow film (the sign of the contraction width X of the narrow film is minus). The values of 8 mm and 0 mm, which are the maximum expansion allowances for the cases of 16000 and 3000, were combined to obtain the thinning limit shrinkage allowance Y2 for the wide film expansion (FIG. 3B). The range of X ≧ Y2 is a good range.

If you formulate this,
In the case of narrow film expansion, the thinning limit shrinkage margin Y2 = −0.0006 × wide film molecular weight + 1.8. From this value, A2 = −0.0006 and B2 = 1.8 in the equations (2a) and (2b).

  When a resin-based polymer paint is applied to the surface of a steel strip using the curtain coating method as shown in FIG. 1, when two layers of a molecular weight of 11000 and a molecular weight of 15000 are applied, one layer Was covered with a wide layer and the other layer was a narrow layer. The processing conditions are shown in Table 1. In Table 1, the width of the thinned portion and the shrinkage allowance X are actually measured values, the factor Z is a value calculated using the equations (3b), (4a), and (5), and Y1 and Y2 are the equations (1) and (2). This is a value calculated using an equation. The surface tensions of the wide film and the narrow film were both 33 mN / min.

  First, No. 1 in Table 1. As shown in FIG. 1, when the wide layer is a low molecular weight (molecular weight 11000) layer and the narrow layer is a high molecular weight (molecular weight 15000) layer, a boundary thinning phenomenon between the wide film and the narrow film occurs. The wide membrane became unstable. Next, No. in Table 1 As shown in Fig. 2, when the wide layer is a high molecular weight (molecular weight 15000) layer and the narrow layer is a low molecular weight (molecular weight 11000) layer, the thinning phenomenon does not occur and good coating can be performed. It was.

  When this is applied to each equation of the present invention, No. 1 is obtained. 1, the shrinkage allowance X = 13 mm with respect to Y1 = 11 (mm), the factor Z = 11.42 mm calculated by the equations (3b), (4a), and (5), and the equations (1a) and (2a) are It was an area where the thinning phenomenon occurred without satisfaction. In contrast, no. 2, the shrinkage allowance X = 5 mm with respect to Y1 = 31 (mm), the factor Z = 5.87 mm calculated by the equations (3b), (4a) and (5), and the equations (1a) and (2a) It is clear that the present invention is in the region where the thinning phenomenon does not occur.

  When a resin-based polymer paint is applied to the surface of a steel strip using the curtain coating method as shown in FIG. 1, two liquid film layers having a wide film width of 750 mm and a narrow film width of 630 mm are formed. Curtain coating was performed. At this time, the molecular weight of the wide film was changed from 11000 to 15000, the surface tension was changed from 31 to 32.7 mN / m, the viscosity was changed from 196 to 513 seconds, and the flow rate was set to 1219 ml / mm / min. Further, the molecular weight of the narrow membrane was changed in the range of 11000 to 15000, the surface tension was 31.3 to 32.5 mN / m, the viscosity was 196 to 615 seconds, and the flow rate was changed to 305 to 1219 ml / mm / min.

  Perform curtain coating under the above conditions and measure the shrinkage allowance X (mm), which is the value obtained by subtracting the width of the narrow layer when the curtain collides with the plate from the width of the narrow layer at the start of curtain falling. did. The factor Z was calculated based on the equations (3a) (3b) (4a) (5).

  4A shows the factor Z calculated by the equations (3a) and (4a) on the horizontal axis and the contraction allowance X on the vertical axis. FIG. 4B shows the results of (3b), (4a) ( 5) The factor Z calculated by the equation is set on the horizontal axis, and the shrinkage allowance X is set on the vertical axis. In any case, it is clear that there is a correlation between the factor Z and the contraction allowance X. Furthermore, it is clear that the formula for calculating Z is preferably the formula (4b) rather than the formula (4a).

  Using the same method as in Example 3, a resin-based polymer paint was applied to the surface of the steel strip. The molecular weight range and viscosity of the upper wide film and the lower narrow film were the same as in Example 3. Here, the surface tension of the solvent most abundant in the wide film and the surface tension of the solvent abundant in the narrow film are changed, curtain coating is performed, and the curtain is determined from the width of the narrow layer at the start of curtain falling. The shrinkage allowance X (mm), which is a value obtained by subtracting the width of the narrow layer when colliding with the plate, was measured.

  In the example shown in FIG. 5, no additive is added to the coating film.

  FIG. 5A plots the evaluation results with “horizontal axis of the surface tension of the solvent most abundant in the wide film−the surface tension of the solvent most abundant in the narrow film” and the vertical axis the shrinkage allowance X. Is. It is clear that there is a good correlation between the vertical and horizontal indices.

  FIG. 5B shows the factor Z calculated by the equations (3b), (4b) and (5) as the horizontal axis and the contraction allowance X as the vertical axis. It is clear that there is a correlation between the factor Z and the shrinkage allowance X.

  Next, as shown in Table 2, with respect to the upper wide film and the lower narrow film, the molecular weight, the type of solvent, the surface tension of the solvent, and the presence or absence of additives were changed, and the presence or absence of thinning phenomenon was evaluated. It was. Here, the solvent SH is cyclohexanone, the solvent NMP is n-methylpyrrolidone, and the solvent EEP is ethyl-3-ethoxypropionate.

  In addition, Z1 calculated using the formula (4a) based on the surface tension value of the paint, Z1 calculated using the formula (4b) based on the surface tension value of the solvent and the presence or absence of the additive, and the viscosity of the paint Based on the above, Z1 + Z2 was calculated from Z2 calculated using the equation (5) and shown in Table 2. In the value of Z1 + Z2, No. For values 6 and 14, the value calculated from the equation (4b) is used as Z1, and for the other values, the value calculated from the equation (4a) is used as Z1. Table 2 shows the value of Y1 calculated by the equation (1b) and the value of Y2 calculated by the equation (2b).

  Invention Example No. 2 in Table 2 About 3-11, curtain coating was able to be performed favorably, without the thinning phenomenon occurring. Further, both Z1 and Z1 + Z2 are values smaller than Y1 and larger than Y2, and it can be understood from this point that the present invention is in a good range.

  On the other hand, Comparative Example No. 2 in Table 2 was used. As for 12 to 15, in all cases, a thinning phenomenon occurred during curtain coating, and the quality of the coated steel sheet became unstable and the productivity was hindered. Also, Z1 and Z1 + Z2 are larger than Y1 or smaller than Y2, and it is clear that this is also outside the scope of the present invention.

  Using the same method as in Example 3, a resin-based polymer paint was applied to the surface of the steel strip. However, in this embodiment, the widths of the two liquid film layers are both 750 mm, and both films are in contact with the guide device 5 in the two-layer free fall curtain.

  Various changes were made with respect to the molecular weight of the polymer constituting the paint of each layer, the type of solvent, the surface tension of the solvent, and the presence or absence of additives, and curtain coating was performed on the surface of the steel strip. When neither film contains an additive, or when both films contain an additive, the film having the highest surface tension of the solvent contained in the film is the P film, and is contained most in the film. The film having the lower surface tension of the solvent is defined as a Q film. If any film contains an additive, subtract 1.67 from the surface tension for the solvent of the film containing the additive, and then compare the surface tension to determine the P film and the Q film. To do. Table 3 shows the specifications of each film, the value of Z calculated from (7b) to (7d), and the value of Y1 calculated from (1b).

  Invention Example No. 1 in Table 3 As for Nos. 16 to 22, even when the P film was detached from the guide device, the curtain coating could be performed satisfactorily without causing a thinning phenomenon. Also, Z is a positive value and a value smaller than Y1, and from this point, it can be seen that this is a good range of the present invention.

  On the other hand, Comparative Example No. As for Nos. 23 to 24, when the P film was detached from the guide device, a thinning phenomenon occurred in the course of curtain coating, and the quality of the coated steel sheet became unstable and the productivity was hindered. Further, Z is a value larger than Y1, and from this point it is clear that it is out of the scope of the present invention.

  Next, various changes were made to the molecular weight of the polymer constituting each layer of coating and the surface tension of the coating, and curtain coating was performed on the surface of the steel strip. The film with the higher surface tension is the P film, and the film with the lower surface tension is the Q film. Table 4 shows the values of each film, the Z value calculated from (7a), and the Y1 value calculated from (1b).

  Inventive Example No. As for Nos. 25 to 28, even when the P film was detached from the guide device, the curtain coating could be performed satisfactorily without causing a thinning phenomenon. Also, Z is a positive value and a value smaller than Y1, and from this point, it can be seen that this is a good range of the present invention.

  On the other hand, Comparative Example No. As for 29 to 30, when the P film was detached from the guide device, a thinning phenomenon occurred in the course of curtain coating, resulting in unstable quality of the coated steel sheet and hindering productivity. Further, Z is a value larger than Y1, and from this point it is clear that it is out of the scope of the present invention.

It is the schematic which shows the curtain coating method of this invention. It is a figure explaining the thinning phenomenon which generate | occur | produces at the time of curtain coating. It is a figure which shows the relationship between a wide film | membrane molecular weight and a narrow film | membrane molecular weight about the appropriate range of the shrinkage allowance X of a narrow film | membrane. It is a figure which shows the relationship between the factor Z and the shrinkage allowance X. FIG. (A) is a figure which shows the relationship between the surface tension difference of a solvent, and the shrinkage allowance X, (b) is a figure which shows the relationship between the factor Z computed from the surface tension of the solvent and the viscosity of the coating material, and the shrinkage allowance X. is there.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Curtain discharge apparatus 2 Discharge slit 5 Guide apparatus 6 Edge guide 10 Curtain 11 Board 12 Wide layer 13 Narrow layer 14 Thinned part 24 Narrow layer end 25 Curtain end 31 Width of narrow layer (at the start of curtain fall)
32 Full width of curtain (when the curtain collides with the board)
33 Width of narrow layer (when the curtain collides with the board)
34 Board Width 35 Inner Multilayer Part 36 Outer Single Layer Part

Claims (5)

In a curtain coating method in which a curtain composed of a plurality of layers of liquid film is dropped and a plurality of layers of film are coated on the surface of a traveling plate, the width of at least one layer of the liquid film constituting the falling curtain is greater than the total width of the curtain also a narrow width, the layer having a width narrower than the curtain overall width (hereinafter referred to as "narrow layer".) has a molecular weight of the polymer material solution of 3,000 to 30,000, a layer having the same width as the curtain total width (hereinafter " wide layer "hereinafter.) is a polymer material solution having a molecular weight of 10,000 to 30,000, a factor Z below (3a) formula (4a) obtained by the equation molecular weight of the polymer material constituting the wide layer (wide film molecular weight) The relationship between Z and Z satisfies the following formula (1b), and the relationship between the molecular weight (narrow film molecular weight) of the polymer material constituting the narrow layer and Z satisfies the following formula (2b) Painting Method.
Z ≦ Y1 = A1 × wide film molecular weight + B1 (1b)
Z ≧ Y2 = A2 × Narrow film molecular weight + B2 (2b)
Here, A1 = 0.005, B1 = −50, A2 = −0.0006, and B2 = 1.8.
Z = Z1 (3a)
Z1 = −10 × (wide film surface tension−narrow film surface tension) +9 (4a)
However, the unit of surface tension is mN / m. same as below. 2. The curtain coating method according to claim 1 , wherein the expression (3a) is replaced with the following expression (3b), and the factor Z is obtained from the expressions (3b), (4a), and (5).
Z = Z1 + Z2 (3b)
Z2 = −0.03 × (wide film viscosity−narrow film viscosity) −1 (5)
The unit of surface tension is mN / m, and the unit of viscosity is seconds. same as below. The curtain coating method according to claim 1 or 2 , wherein Z1 is obtained by the following equation (4b) instead of the above equation (4a).
Z1 = −0.9 × (corrected solvent surface tension of wide film−corrected solvent surface tension of narrow film) +9 (4b)
However, the modified solvent surface tension of a film means the surface tension of the solvent most contained in the film when the film does not contain additives, and when the film contains additives. The value obtained by subtracting 16.7 from the surface tension of the solvent most contained in the film. same as below. Curtain Nurikutsugae method as claimed in claim 1, characterized in that the narrow film molecular weight <wide film molecular weight. Curtain Nurikutsugae method according to any one of claims 1 to 4, wherein the plate to the traveling is strip steel.

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