JP2000345108A - Curtain coater paint having excellent curtain stability and method for producing coated product by curtain coater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paint excellent in curtain stability in application and a method for producing a coated product using the same. The present invention relates to a synthetic resin-based coating material, which comprises the following:
A method for producing a paint for a curtain coater that satisfies condition d) and a coated product using the same. Preferably, the resin is a polyester resin. a) The number average molecular weight of the resin contained in the paint is 10,000
B) The viscosity measured at 25 rpm at 50 rpm with an E-type viscometer is 2
C) The viscosity measured at 25 ° C. and 5 rpm with an E-type viscometer at 23 ° C. is 23
0-690 mPa · s d) The ratio of the measured viscosity at 5 rpm to the measured viscosity at 50 rpm is 1.
15 or more

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a coated product used for home appliances, building materials, and automobiles by using a curtain coater, and a paint used for manufacturing the same.

[0002]

2. Description of the Related Art Curtain coaters are used for coating metal plates, wood, plywood, and plastic products as industrial coating means because of the feature that a smooth coating film can be obtained. As a curtain coating method, a method of forming a paint curtain by dropping paint by gravity or pressure from an orifice provided at a lower portion of the paint reservoir, a method of forming a paint curtain by flowing paint from the upper portion of the paint reservoir, There are several methods, such as a method of forming a paint curtain by applying pressure from a die and extruding paint, and a method of forming a paint curtain by scraping a paint from a roll with a blade from a roll that measures the paint. . Industrially, the coating thickness is within the range that satisfies the required performance,
It is important in terms of cost to be as thin as possible.

However, in any of the methods, there is a minimum paint flow rate at which a paint curtain can be formed, and the flow rate and the line speed determine the minimum paintable film thickness. Since the line speed is restricted by the drying of the paint and the mechanical ability of the line, the paint curtain is formed stably even when the flow rate of the paint is small in order to form a thinner coating film. It is necessary. Although the stability of the paint curtain can be improved by devising a coating machine, there are many parts determined by the paint itself. Therefore, it is important to select a paint that can form a paint curtain more stably.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a paint in which a paint curtain is formed stably when coating with a curtain coater and has few defects that hinder the curtain application. Another object of the present invention is to provide a method for efficiently producing the same.

[0005]

Means for Solving the Problems The present inventors have investigated the relationship between the stability of a paint curtain and the paint composition and paint physical properties of a synthetic resin paint, and have completed the present invention. That is, the paint that can form the paint curtain stably is a synthetic resin paint. By satisfying the following conditions a) to d), the stability of the paint curtain is improved. a) The number average molecular weight of the resin contained in the paint is 10,000
B) The viscosity measured at 50 rpm with an E-type viscometer at 25 ° C. is 2
C) The viscosity measured at 25 ° C. and 5 rpm with an E-type viscometer at 23 ° C. is 23
0-690 mPa · s d) The ratio of the measured viscosity at 5 rpm to the measured viscosity at 50 rpm is 1.
15 or more By coating the above coating material with a curtain coater, a product having a thinner film thickness can be stably manufactured.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a synthetic resin paint is used as a binder component such as polyester resin, amino resin, urethane resin, isocyanate resin, phenol resin, epoxy resin, fluororesin, acrylic resin, olefin resin, butyral resin and the like. This is a coating material containing as a main component a resin in which one or more synthetic resins are used, or a resin in which two or more of these resins are mixed or copolymerized. When the number average molecular weight of the main resin is 10,000 or more, the stability of the paint curtain is improved. The number average molecular weight of the resin is a number molecular weight measured by gel permeation chromatography using a calibration curve obtained from a standard sample of a styrene resin. It has been found that when the molecular weight is 10,000 or more, a paint curtain can be formed stably. Further, the number average molecular weight is desirably 13,000 or more. There is no particular upper limit, but if the molecular weight of the resin is high, it is difficult to synthesize and the solubility in a solvent becomes poor. Therefore, depending on the type of the resin, a resin having a molecular weight that does not cause these inconveniences may be used. There is no particular upper limit to the number average molecular weight of the resin. However, when the number average molecular weight exceeds 30,000, the solubility in a solvent becomes poor, and an inconvenience such as an extreme increase in viscosity and deterioration in color stability due to a decrease in pigment dispersibility occurs. May be undesirable.

In the present invention, the polyester resin paint is a paint containing a polyester resin as a binder component. As the binder component, in addition to the polyester resin, one or more other resins such as an amino resin, a urethane resin, an isocyanate resin, a phenol resin, an epoxy resin, a fluororesin, an acrylic resin, and a butyral resin may be used in combination. These resins are added as a crosslinking agent for the polyester resin or for imparting some performance. Polyester resin paints have good processability and are suitable for products to be processed later, especially for metal coating products.

[0008] The viscosity of the paint is measured with an E-type viscometer and is measured in mPa · s.
Calculate in units of In the present invention, Tokimec Corporation
E type viscometer, “TV-20 type H” rotor No. “1”
A value measured at 25 ° C. using a “R34 ° × R24” type was used. Under the above conditions, the viscosity was measured at 50 rpm and 5 rpm. The viscosity measured at 50 rpm is 200-600
The viscosity measured at 5 rpm at mPa · s is 230-690
mPa · s and the ratio of the measured viscosity at 5 rpm to the measured viscosity at 50 rpm (5 rpm measured viscosity / 50 rpm measured viscosity) is 1.15.
In the above case, the paint curtain is stable, and air entrainment hardly occurs, so that the curtain can be stably applied.

If the viscosities measured at 50 rpm and 5 rpm are less than 200 and 230 mPa · s, respectively, the stability of the curtain is deteriorated. And defects in the coating. If the viscosity ratio is less than 1.15, the curtain will have poor stability. There is no particular upper limit of the viscosity ratio, but if the viscosity ratio exceeds 2.0, the leveling property after application is reduced,
The appearance deteriorates. On the other hand, when the viscosity ratio exceeds 3.0, almost no leveling occurs, and the appearance is significantly reduced. Therefore, the upper limit of the viscosity ratio is preferably 3.0 or less, and more preferably 2.0 or less.

[0010] The viscosity of a paint is mainly determined by the amounts and types of solvents, resins and pigments. These may be appropriately adjusted so as to be in the above viscosity range. In order to make the ratio of the viscosity at 5 rpm to 50 rpm at least 1.15, it is preferable to add silica, various microgels, ethylene amide, other resins having strong hydrogen bonding, inorganic thixotropic agents, and the like to the paint. Thereby, the property of decreasing the viscosity when the paint receives a high shear can be imparted.

[0011] The coating composition comprises a binder component, a pigment component,
It consists of a solvent and other components. As described above, the binder component includes a silane coupling agent, a titanium coupling agent, and the like, which can react with each other, in addition to a resin and a cross-linking agent which are main components of the coating film. Further, a synthetic resin component added for improving the dispersibility of the resin in the pigment can also be added. Examples of the pigment component include inorganic color pigments such as titanium white, iron oxide, carbon black, and zinc white, organic color pigments such as cyanine-based and azo-based such as cyanine blue, extender pigments such as barium sulfate, silica, and kaolin, as well as resins. Known materials such as beads, resin particles, metal foils, metal particles, and aggregates are used. Solvents are added to dissolve the resin or adjust the viscosity of the paint, cyclohexanone, isophorone,
Methyl isobutyl ketone, butyl cellosolve, ethyl cellosolve, xylene, Solvesso 100, Solvesso 1
Known materials such as 50 and butyl acetate are used.

The other components are the remaining components excluding the binder component, the pigment component, and the solvent from the paint, and are, for example, waxes such as polyethylene, polypropylene, microcrystalline, paraffin, fluorine, and synthetic resin. Ingredients include silicon-based, fluorine-based, and synthetic resin-based leveling agents, acrylic-based and silicone-based antifoaming agents, other color separation preventing agents, dispersion stabilizers, and the like.

When the above-mentioned paint is applied by a curtain coater, since the stability of the paint curtain is good, there is no trouble such as occurrence of unpainted portions due to breakage of the curtain and stop of the painting line, and stable operation is possible. is there. In addition, at the time of coating, the generation of bubble defects due to entrainment of air between the object to be coated and the coating material is reduced. As a curtain coating method, a method of forming a paint curtain by dropping paint by gravity or pressure from an orifice provided at a lower portion of the paint reservoir, a method of forming a paint curtain by flowing paint from the upper portion of the paint reservoir, Use a known method, such as a method of forming a paint curtain by extruding paint by applying pressure from a die, a method of forming a paint curtain by scraping a paint from a roll with a blade from a roll that weighs the paint, and the like. Can be. In particular, when a method of forming a paint curtain by scraping the paint passed between the rolls for measuring the paint with a blade as a curtain coater (hereinafter referred to as a roller curtain coater) is used, it is easy to control the film thickness. In particular, it is suitable for coating with a thin film thickness by effectively utilizing the curtain stability of the coating according to the present invention.

The coating speed can be arbitrarily selected. Even if the flow rate of the paint curtain is the same, the moving speed of the work (painting speed)
If the speed is made faster, the film thickness becomes thinner. On the other hand, if it is too early, air is entrained between the paint curtain and the object to be coated at the time of painting, and defects such as bubbles and the like, and the occurrence of unpainted portions are likely to occur. The coating speed may be determined in consideration of these. As an object to be coated, a continuous flat plate unwound from a coil,
A cut flat plate or a plate having a shape close to a flat plate, for example, a plate that is slightly curved or has a hole is used. The types are, for example, metal plate, metal foil, wood plate, plywood, plastic plate, plastic film,
Cloth, paper, etc.

After the object to be coated is curtain-coated by the method described above, the coating film is dried. Known methods can be applied to the method of drying, for example, natural drying, hot air heating, induction heating, a method of applying heat to the coating such as heating with infrared rays to dry and cure, or applying radiation such as ultraviolet rays or electron beams to the coating. There is a method of drying and curing by irradiation, a method of drying and curing the coating film by passing it through a booth filled with catalyst, or a method of combining these, and it can be selected according to the type of painted paint it can.

The object to be coated may be subjected to a pre-coating treatment in advance. For example, treatment to clean the surface of the object to be coated, such as washing with water or a solvent, degreasing, corona discharge treatment, flame treatment, etc., to improve adhesion by generating polar groups on the surface, zinc phosphate treatment, chromate treatment , Treatments mainly applied to metals such as complex oxide film treatment, brushing, grinding, etc., treatments to remove irregularities or components that inhibit surface adhesion, chemical treatments such as pickling and alkali cleaning, or these Can be performed.

Further, the film can be formed by the same means or before or after the application by the curtain coater. For example, apply a coating for undercoating,
Formation, application and formation of an overcoat layer for protection, and the like. These may be performed by a curtain coater or other known methods such as a roll coater, brush coating, electrostatic coating, dipping, and the like.

[0018]

EXAMPLES The present invention will be described specifically with reference to examples and comparative examples. Note that the present invention is not limited by these examples. As the paint, a polyester resin paint shown in Table 1 was used. All of the paints are white, and the density of the coating after drying is 1800 kg / m ³ . The molecular weight of the polyester resin was measured by gel permeation chromatography using a calibration curve obtained from a standard sample of a styrene resin. The paint viscosity is measured using a Tokimec E-type viscometer, "TV-20 H" rotor.
The value measured at 25 ° C. using a No. “1 degree 34 minutes × R24” type was used. Under the above conditions, the viscosity was measured at a rotation speed of 50 rpm and 5 rpm, and the viscosity was obtained in units of mPa · s.

As the curtain coater, a slit type curtain coater (FIG. 1) and a roller curtain coater having two rolls for controlling the amount of coating (FIG. 2) were used.
The slit type curtain coater shown in FIG.
A suitable amount of paint is supplied to the paint reservoir 5 through the
The paint is caused to flow down from the lower slit (orifice) 6 to form a paint curtain 7. For example, the steel plate 8 is a conveyor 9
And the paint curtain 7 is coated on the steel plate 8. Reference numeral 10 denotes a paint receiver.

In the roller curtain coater of FIG. 2, paint is fed from the paint tank to the paint pan 21 in the same manner as in FIG. 1, and a slit (orifice) at the bottom of the paint pan 21 is provided.
The coating material 23 flows down through the coating 22, and the coating material 23 is passed between the two rolls of the applicator roll 24 and the doctor roll 25, thereby controlling the application amount and forming the coating curtain 26. 27 is an object to be coated such as a steel plate.

The height of the paint curtain (vertical height from the falling point of the paint curtain to the object to be coated) was 15 cm. The stability of the paint curtain was measured by measuring the limit flow rate at which the paint curtain could not be cut when the paint flow was reduced. As an object to be coated, a cut sheet of a hot-dip galvanized steel sheet which had been subjected to a chromate treatment to form an undercoat film having a dry film thickness of 5 μm was used. The size of the cutting board is thickness 0.6mm, width 4
At 0 cm and 1 m in length, this plate was curtain-coated while running at a speed of 70 m / min. This plate was coated 10 times, and the flow rate at which the curtain was not cut even once was taken as the minimum flow rate for curtain formation. Those with a small flow rate evaluated that the curtain was stable. Tests were conducted to produce a standard precoated metal sheet product having a dry film thickness of 18-20 μm. Curtain stability was evaluated as follows: 5 points for completely satisfactory stability, 4 points for operable stability, 3 points for concern about operation, 2 points for unmanufacturable product, 1 point
It was judged that the operation of curtain painting was impossible at all.

After the coated plate was baked at a maximum temperature of 230 ° C. in an induction heating furnace, the appearance of the coating film was visually observed to evaluate the presence or absence of defects such as bubbles. If air entrainment occurs at the point where the paint curtain falls onto the object to be coated, bubbles and unpainted defects occur, resulting in poor appearance. 5 points with no problem as a product, 4 points with some defects (level not acceptable for shipment), 3 points with defects, 2 points with remarkable defects, A certain score was given as one point. Only five items can be sold as products.

Table 1 shows the stability test results of the paint curtain (the minimum flow rate at which the curtain is stable and the score of the curtain stability),
The appearance of the coating film after baking, especially the evaluation results of the presence or absence of air entrainment reduction, are shown. Since the stability of the curtain and the appearance after coating did not change regardless of the type of the curtain coater, the results obtained by testing with a roller curtain coater were shown. The ratio of the viscosity measured at 5 rpm to the viscosity measured at 50 rpm is shown as a viscosity ratio in the table. NV in the table is% by weight of nonvolatile components in the paint.

In each of the examples, the stability of the paint curtain was good, and defects such as air entrainment did not occur, and a clean product could be efficiently produced. In Comparative Example No. 8, the viscosity was within the range of the invention, but the viscosity ratio was low. When the viscosity of the coating material is low and the viscosity ratio is low, the stability of the curtain deteriorates. On the other hand, when the viscosity is high and the viscosity ratio is low as in Comparative Example No. 9, air entrainment is likely to occur, which is disadvantageous because bubbles and unpainted defects are generated on the painted surface. Comparative Example N
In the case of o.10, the viscosity ratio is within the range of the present invention, but the curtain stability is poor because the viscosity is low. In Comparative Example No. 11, the viscosity ratio was within the range of the present invention, but due to the high viscosity, air entrainment defects occurred, which was a problem. In Comparative Example No. 12, the molecular weight of the resin was low, and the curtain stability was poor.

[0025]

[Table 1]

[0026]

As described above, the paint according to the present invention is excellent in curtain stability, hardly causes defects such as air entrainment, and is suitable for coating with a curtain coater. Also, by combining this paint with a curtain coater, a coated product can be manufactured stably and efficiently.

[Brief description of the drawings]

FIG. 1 shows a slit-type curtain coater.

FIG. 2 shows a roller curtain coater.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Paint tank 2 ... Pump 5 ... Paint reservoir 6 ... Slit (orifice) 7 ... Paint curtain 8 ... Steel plate 21 ... Paint pan 22 ... Slit (orifice) 23 ... Paint 24 ... Applicator roll 25 ... Doctor roll 26 ... Paint curtain 27 …steel sheet

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D075 AC14 BB26Z CA48 DA03 DB05 DC01 DC11 DC18 EA07 EB32 EB33 EB35 EB38 EB39 EB52 EB57 EC03 EC11 EC13 4F041 AA08 AB02 CA04 CA07 4J038 DD001 EA011 MA14 MA15 PA01 P09 B09

Claims (4)

[Claims] 1. A synthetic resin-based coating composition comprising:
A paint suitable for a curtain coater that satisfies the condition d) and has excellent curtain stability. a) The number average molecular weight of the resin contained in the paint is 10,000
B) The viscosity measured at 50 rpm with an E-type viscometer at 25 ° C. is 2
C) The viscosity measured at 25 ° C. and 5 rpm with an E-type viscometer at 23 ° C. is 23
0-690 mPa · s d) The ratio of the measured viscosity at 5 rpm to the measured viscosity at 50 rpm is 1.
15 or more 2. A paint suitable for a curtain coater having excellent curtain stability according to claim 1, wherein the synthetic resin contains a polyester resin as a main component. 3. A synthetic resin-based coating composition comprising:
A method for producing a coated product using a curtain coater, which comprises applying a paint suitable for a curtain coater excellent in curtain stability that satisfies the condition d) with a curtain coater. a) The number average molecular weight of the resin contained in the paint is 10,000
B) The viscosity measured at 50 rpm with an E-type viscometer at 25 ° C. is 2
C) The viscosity measured at 25 ° C. and 5 rpm with an E-type viscometer at 23 ° C. is 23
0-690 mPa · s d) The ratio of the measured viscosity at 5 rpm to the measured viscosity at 50 rpm is 1.
15 or more 4. The method according to claim 3, wherein the synthetic resin is mainly composed of a polyester resin.