CN100528999C - Coating composition for precoated metal sheet and precoated metal sheet with reduced occurrence of trouble due to static electricity - Google Patents

Abstract

Provided is a PCM that can reliably suppress charging due to coating static electricity without significantly increasing cost. The occurrence of troubles due to static electricity at respective temperatures is suppressed by applying a predetermined 2 methods to a PCM having a coating layer formed on at least one surface of a metal plate, wherein the values of charging voltages generated when the PCM is subjected to peeling charging at room temperature or 70 ℃ are less than 0.15kV or 0.25kV, respectively. In the coating material, the charging voltage after peeling charging can be reduced by containing an isocyanate derivative, particularly an isophorone diisocyanate (IPDI) derivative, in a proportion of 5 mass% or more relative to the total solid content, or containing an alkoxyamine salt in a proportion of 1 mass% or more relative to the total solid content together with the isocyanate derivative.

Description

Coating composition for precoated metal sheet and precoated metal sheet which are less prone to failure due to static electricity

technical field

The present invention relates to a precoated metal sheet which is less likely to cause trouble due to static electricity generated by friction of a coating film when used in home appliances or building materials.

Background technique

In the fields of building materials, home appliances, daily necessities, automobiles, etc., the conventional post-coating method of assembling and painting metal sheets after forming has changed, and now pre-coated metal sheets (pre-coated metal Plate: referred to as PCM) for forming, bonding, and forming a pre-coating method for products. Through its use, since the painting process that needs to be at home can be omitted, the pollution and environmental problems caused by painting waste can be solved, and there are also advantages such as the site used for painting can be transferred to other purposes, so its Demand is steadily developing. However, on the PCM processing line, due to the static electricity generated by the friction between the coating and any other raw materials, dust adheres to the surface of the PCM, or the problem of electric shock due to frequent contact with the charged PCM occurs. JP5-278170A and JP5-279641A disclose a method of attaching a protective sheet containing an antistatic agent to the surface of the PCM in order to prevent charging of the PCM. However, in such a method, there is a problem that the production cost of the PCM increases, in addition to the laborious work required for attaching and detaching the protective sheet. It is disclosed in JP9-254296A and JP10-16134A, or by adding fluorine or other additives in the PCM coating, the position on the triboelectric sequence position of the PCM coating is lowered (becomes easily negatively charged), Or by controlling the triboelectric sequence potential relationship inside and outside the PCM surface, to suppress the generation of static electricity. In addition, in JP2-18708B, it is described that the dust adhesion resistance of a coated metal plate coated with an electron beam curing paint and cured when it is irradiated with an electron beam is compared with that measured by a static honest meter. If the half-life is shorter than 100 seconds (preferably 80 seconds), there is a tendency for dust to be difficult to adhere to.

However, there are problems in these inventions. In the invention related to the above-mentioned triboelectric sequence, the position of the coating on the triboelectric sequence depends only on the relative positional relationship of which one is high and which one is low, and is not an invention based on quantitative considerations. Next to this, it is difficult to reliably suppress the generation of static electricity. For example, even with two types of coatings at the same position on the triboelectric sequence, there are cases where the actual degree of dust adhesion caused by static electricity is different. The current situation is an invention. The reliability of the effect is not high. The reason is that there are other factors that affect the electrification besides the shape, hardness, adhesiveness, etc. of the coating, and the triboelectric sequence. These factors combine to determine the electrification of the coating, and further determine the dust adhesion. . In order to reliably obtain a PCM having a good electrostatic suppression effect, an invention based on a quantitative index comprehensively including these factors is required. In addition, although the details will be described later, the half-life measured by the above-mentioned static general meter can probably be used as an indicator of the chargeability of a certain surface of the PCM, but it cannot be obtained for electrostatic barriers that are a problem on the PCM processing line. A clear correlation cannot be called a proper indicator. The present invention intends to provide a PCM capable of reliably suppressing electrification due to static electricity of a coating layer without greatly increasing the cost.

disclosure of invention

In order to achieve the above-mentioned purpose, it is useful to find a quantitative index that comprehensively includes various factors that affect the chargeability, and to find a means to control the value. The inventors of the present invention have found that by applying the charging voltage of the coating layer when the PCM is charged under appropriate conditions as this quantitative index, the degree of obstacles caused by charging (dust attachment to the PCM and electric shock) can be distinguished. Then, the charging voltage was measured for various PCMs, and the boundary value at which various troubles did not occur was determined. Furthermore, the inventors have completed the present invention by conducting various searches for additive resins and additives useful for lowering the charged voltage. The gist of the present invention is as follows.

(1) A coating composition for a precoated metal sheet which is less likely to cause disturbances caused by static electricity, which is a coating composition for coating and curing a precoated metal sheet as the top coat on a metal sheet, It is characterized in that the charged voltage value obtained when the above-mentioned precoated metal sheet is measured by the "method 1" described below is less than 0.15 kV.

(method 1)

In a standard state (temperature 23°C, relative humidity 50%) indoors, in the center of the target coating surface of a smooth pre-coated metal plate cut into 7×15cm, superimposed cut into 5×10cm, hardness 50, carbon black A chloroprene rubber sheet with a content of 31% by mass and a thickness of 5 mm is placed on a horizontal ceramic table with the precoated metal plate on the lower side, and a 1 kg weight is placed on the chloroprene rubber sheet. After crimping for 10 seconds, the weight was removed, the chloroprene rubber sheet was peeled off in the vertical direction, and the charged voltage at the center of the coated surface of the precoated metal plate was quickly measured with a non-contact field meter.

(2) A coating composition for a precoated metal sheet that is less susceptible to disturbances caused by static electricity, which is a coating composition for coating and curing a precoated metal sheet as an outermost coating on a metal sheet, It is characterized in that the charged voltage value obtained when the above-mentioned precoated metal sheet is measured by the "method 2" described below is less than 0.25 kV.

(method 2)

Heat the pre-coated metal plate, chloroprene rubber sheet, ceramic table and weight in the oven at 70°C for 10 minutes in the method (1) above, and within 30 seconds after taking it out, make method 1 The recorded process is all completed.

(3) The coating composition for precoated metal sheets according to (1) or (2) above, wherein an isocyanate derivative is contained in the coating composition.

(4) The coating composition for precoated metal sheets according to (1) or (2) above, wherein the coating composition contains both an isocyanate derivative and an alkoxyamine salt.

(5) The coating composition for precoated metal sheets according to (3) or (4) above, which contains an isophorone diisocyanate (IPDI) derivative as the isocyanate derivative.

(6) The coating composition for precoated metal sheets according to (5) above, wherein the ratio of the isophorone diisocyanate (IPDI) derivative to the total solid content is 5% by mass or more.

(7) The coating composition for precoated metal sheets according to any one of (4) to (6) above, wherein the ratio of the alkoxyamine salt to the total solid content is 1% by mass or more .

(8) A precoated metal sheet obtained by applying and curing the coating composition described in (1) to (7) above on at least one side of the metal sheet as an outermost coating layer.

The best way to practice the invention

The present invention will be described in detail below. As an obstacle caused by static electricity of PCM, firstly, dust adhesion is cited. Although electric shock also often becomes a problem, this occurs when a large amount of static electricity is accumulated by considerable friction, and the problem of dust adhesion generated by a relatively small amount of static electricity is profound. Some examples where dust adhesion is actually a problem are shown below. When the frame made of PCM is processed on the refrigerator assembly line of a home appliance manufacturer, when it is transported by suction with a suction tool made of neoprene rubber, the suction tool adheres to the PCM coating, and due to the static electricity generated during peeling, There is a problem that dust such as metal powder in the assembly line adheres to the part where the suction tool has been in contact with the coating surface. Since the value of the product is lowered if the adhered dust remains intact, the wiping operation becomes necessary, which significantly increases the cost. In order to solve such a problem, it is necessary to suppress the static electricity generated by contacting the PCM coating with other substances.

Several physical quantities have been introduced so far as indicators of the chargeability of the coating.

One is the surface resistance value (JIS K 6911). Regarding plastics, generally when the surface resistance value is 12 to 13 square ohms or less of 10, the electrical conductivity of the material is sufficiently high that dust adhesion does not occur due to the dispersion and discharge of generated static electricity. However, if the surface resistance value of PCM used in home appliances is low, other properties such as corrosion resistance cannot be ensured, so it is necessary to use PCM with a surface resistance value higher than this value. Therefore, in PCM for home appliances, it is meaningless to use the surface resistance value as the chargeability index of the coating.

The second is the initial charging voltage and half-life (JIS L 1094) measured with the above-mentioned static general meter. This is to measure the initial charging voltage when a voltage is forcibly applied to the coating to charge it, and the time (half-life) to decrease to 1/2 of the initial charging voltage after the application of the voltage is released. It is considered that the higher the initial charging voltage, the more It is easy to charge, and the longer the half-life, the harder it is to discharge. Therefore, it is considered that the PCM having a low initial charge voltage and a short half-life is less prone to electrostatic disturbances such as dust adhesion. However, when the initial charging voltage and half-life of various PCMs were measured and compared with the actual effect of dust adhesion on the actual refrigerator assembly line, the initial charging voltage of the PCM coating with no dust adhesion was relatively high and the half-life was long. That is, the actual dust adhesion phenomenon cannot be explained by the theory of the initial charging voltage and the half-life so far, and these values cannot be used as an index of the chargeability of the coating.

Therefore, the inventors of the present invention applied the charging voltage when the coating is charged by contacting and peeling off an appropriate object (hereinafter referred to simply as the charging voltage after peeling charging). The difference between the electrification voltage after peeling off and the initial electrification voltage measured with a static ordinary meter is that the initial electrification voltage is non-contact and charged by applying a certain voltage, so it is based only on the inherent physical properties of the coating. On the other hand, the electrification voltage after the peeling electrification includes not only the inherent physical properties of the coating, but also the shape and adhesion to the coating, etc. The voltage of the factor related to the affinity of the object. As a result, the electrification voltage after peeling electrification was good when the electrification of the coating layer was taken as an overall evaluation index. The charged voltage can be easily measured using a commercially available non-contact field meter.

In addition, the charging voltage corresponds almost uniformly to the degree of dust adhesion. This was confirmed by the inventors of the present invention by the following method. In practical effect, PCM that is easy to adhere to dust, PCM that is difficult to adhere, PCM with thick coating thickness, thin PCM, PCM using solvent coating, PCM using powder coating, PCM with inner coating, Various types of PCM, such as PCM without inner coating, are cut into A4 size, placed vertically on a non-chargeable table, rubbed against chloroprene rubber in this state, and the coating is forcibly charged to make it electrified. The voltage becomes 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 kV. In order to match the charging voltage with the specified voltage, use friction charging in advance until it reaches a slightly higher voltage, and then observe the field measuring instrument while gently touching the PCM with a conductive rod, and discharge until it reaches the specified voltage. When the specified charging voltage is reached, as a substitute for dust, cut the film for OHP into 1cm squares, attach it to the surface of the charged PCM coating, and check whether it falls by its own weight. In this test, regardless of the type of PCM mentioned above, the OHP film dropped when the charged voltage was less than 0.4 kV, but adsorbed without falling when it was 0.5 kV or more. Of course, the charging voltage rise method when rubbing chloroprene rubber differs depending on the type of PCM, but even if the charging voltage is difficult to rise, if it is charged to 0.5kV forcibly, the OHP film will also adhere. From this fact, it can be said that the degree of dust adhesion is almost uniformly determined as long as the electrification voltage of the coating is determined regardless of the type of coating. In other words, the PCM coating, which is less likely to adhere to dust, has a low electrification voltage after peeling electrification (under the same conditions), and even if the electrification voltage is high, it is by no means that dust does not adhere. In addition, once the OHP film is attached, even if it is discharged later and the charging voltage reaches 0, it will still be attached. This is because all the electric charges of the bonded part of the OHP film and the coating film are neutralized to 0, and the charge balance of the bonded part does not change even if it is discharged from this state. Therefore, the instantaneous charging voltage of the dust-attached coating determines the degree of dust adhesion. Conversely, using a material with good discharge properties, even if the charge quickly becomes 0 after dust adhesion, has nothing to do with reducing dust adhesion. From the above discussion, it can be seen that the so-called low electrification voltage after peeling electrification and less dust adhesion caused by static electricity can be treated as equivalent.

Both method 1 and method 2 in the present invention are conditions for measuring the above-mentioned charging voltage after peeling and charging. Method 1 is a so-called room at 23°C and a relative humidity of 50%, superimposing a smooth pre-coated metal sheet cut into 7×15 cm in the center of the target coating surface, cut into 5×10 cm, hardness 50, carbon black 31 %, a chloroprene rubber sheet with a thickness of 5 mm, place the pre-coated metal plate on the lower side on a horizontal ceramic table, place a 1 kg weight on the upper part for 10 seconds, and press it gently. After the weight is removed, the chloroprene rubber sheet is peeled off in the vertical direction, and then the charged voltage of the central part of the painted surface of the pre-coated metal plate is quickly measured with a non-contact field measuring instrument. If it is a PCM with a charging voltage of less than 0.15 kV obtained by method 1, dust adhesion due to static electricity does not occur at room temperature. On the other hand, method 2 is to heat the pre-coated metal plate, chloroprene rubber sheet, ceramic table and weight in an oven at 70°C for 10 minutes, and within 30 seconds after taking it out, make the method 1 The method in which all the processes are completed. If it is a PCM with a charging voltage of less than 0.25 kV obtained by method 2, dust adhesion due to static electricity does not occur even at a high temperature of about 50 to 100°C. For example, dust adhesion resistance at high temperature is required in the refrigerator processing process. After being processed into a refrigerator, foamed polyurethane is injected as a heat insulating material, but the temperature rises to about 80°C due to the heat of reaction of polyurethane. Even in this state, it is required that dust adhesion due to static electricity does not occur. Generally speaking, as the temperature of the coating increases, the static electricity generated by contact and peeling increases. This is considered to be because the coating softens at a high temperature, and adhesion occurs when it comes into contact with an object, thereby increasing the effective contact area.

If the isocyanate derivative is contained in the paint for PCM, it is very effective in suppressing the electrification voltage after peeling electrification. Although the reason is not clear, it is understood that by containing isocyanate derivatives, the position on the triboelectric sequence of the coating is lowered, and it becomes closer to the relative position of chloroprene rubber, so the amount of static electricity generated suppressed.

The so-called isocyanate derivatives refer to IPDI (isophorone diisocyanate), TDI (toluene diisocyanate), MDI (4,4'-diphenylmethane diisocyanate), HMDI (hexamethylene diisocyanate), Monomers, dimers, trimers of various isocyanates represented by hydrogenated MDI, hydrogenated XDI (xylene diisocyanate), hydrogenated TDI, etc., and prepolymers with these isocyanates on the skeleton, methanol, ethanol, butanol , propanol, phenol, cresol, chlorophenol, nitrophenol, hydrogenated phenol, acetylacetone, ethyl acetoacetate, ethyl malonate, caprolactam, phosgene, 1-chloro-2-propanol, MEK oxime Classes etc. represent capping agents capping substances. However, the kind of isocyanate or the kind of blocking agent is not limited to those mentioned above.

As the isocyanate derivative, use of an isophorone diisocyanate (IPDI) derivative is preferable since yellowing during baking of the PCM coating or yellowing over a long period of time can be suppressed. In addition, when the ratio of the IPDI derivative to the total solid content is 5% by mass or more, the static electricity suppression effect becomes remarkable. Regarding the electrostatic suppression effect, although there is no upper limit on the amount of IPDI derivatives added, if the amount added is too large, the effect will be saturated, which is not only uneconomical, but also tends to reduce other properties such as workability, so Hope to add appropriately as needed.

Containing both an isocyanate derivative and an alkoxyamine salt in the paint for PCM is effective in synergistically suppressing the charge voltage after peeling off charge. Although the reason is not clear, it is considered that the dielectric constant of the coating increases and the electrostatic capacity (electricity storage effect) of the coating increases by containing the alkoxyamine salt, so the potential of the coating surface layer decreases, and the charged voltage decreases. possibility. When the ratio of the alkoxyamine salt to the total solid content is 1% by mass or more, the static electricity suppressing effect becomes particularly remarkable. Examples of alkoxyamine salts include Floren AE-2 manufactured by Kyoeisha Chemical Co., Ltd., SNstat 824 manufactured by Sanopco Co., Ltd., and Disperon 1121 manufactured by Kusumoto Chemical Co., Ltd., but are not limited to these.

Regarding the electrostatic suppression effect, although there is no upper limit on the amount of alkoxyamine salt added, if the amount added is too large, the effect will be saturated, which is not only uneconomical, but also tends to reduce other properties such as workability , so expect to add appropriately as needed.

As the resin used in the coating material of the present invention, polymer polyester resins, polyester resins, epoxy resins, acrylic resins, polyurethane resins, fluororesins, vinyl chloride resins, olefin resins, ketone resins, Organic resins such as resins, inorganic resins such as siloxane, boron, and borosiloxane, or organic-inorganic composite resins such as organic resins with inorganic skeletons such as siloxane, borosiloxane, etc. It can be used, and as a curing agent, any of melamine resin-based, phenol-based, isocyanate-based, or a combination of these can be used.

As the metal sheet of the base material of the present invention, cold-rolled steel sheets, hot-rolled steel sheets, various plated steel sheets (such as galvanized, galvanized, tin-plated, lead-plated, aluminum-plated, chrome-plated steel sheets, etc.), stainless steel sheets can be used. , titanium plate, aluminum plate, and other arbitrary metal plates, these metal plates can be used as they are or subjected to general chemical conversion treatment. In addition, in order to improve the adhesion between the metal plate and the coating, as a primer for the metal plate, for example, nylon, polyacrylic acid, polyethylene, polypropylene, polyester, polyurethane, epoxy, polyamide, phenol, etc. can be used. , polyolefin and other primer coatings.

As a method of producing the PCM of the present invention, it can be produced by the same method as usual on a normal PCM production line. As a method of applying paint to the metal plate surface, dipping method, curtain coating method, roll coating method, wire rod coating method, electrostatic method, brush coating method, T-die coating method, lamination method can be used Wait for any method.

Examples of the baking method include hot air, room temperature, near-infrared rays, far-infrared rays, high-frequency induction heating, or a combined heating method of these.

Example

Hereinafter, the present invention will be described using examples and comparative examples.

As the original plate of PCM, use 0.6mm thick hot-dip galvanized steel sheet (YP (yield point): 19kg/mm ² , TS (tensile strength): 34kg/mm ² , EL (elongation): 45 %) (hereinafter referred to as GI), 0.6mm thick electrogalvanized steel sheet (mechanical properties equal to GI, referred to as EG) and 0.6mm thick cold-rolled steel sheet (mechanical properties equal to GI, referred to as cold-rolled). As pretreatments, coating-type chromate treatment and zinc phosphate treatment (phosphate treatment) were carried out under standard conditions in the same manner outside and inside.

Coating composition, the surface is 2 times baking of 2 layers of undercoat and topcoat. The top coat is equivalent to the top coat. As a primer, polyester-based paint A and epoxy-based paint B were applied by roll coating to a dry film thickness of 5 μm, and baked in a hot-air oven at a PMT (maximum plate temperature) of 215°C. Various paints shown in Table 1 were applied thereon as the top coat layer by roll coating to a dry film thickness of 15 μm, and baked at a PMT of 230° C. in a hot air oven. On the inside, the melamine alkyd-based back paint was applied entirely by roller coating to a dry film thickness of 5 μm, and then baked twice in a hot air oven at PMT 215°C and 230°C.

Each of the paints for the top coat layer shown in Table 1 is manufactured by Nippon Paint Co., Ltd., and is a white paint colored with a titanium pigment. The resins used are C (polymer polyester/melamine curing system), D (polymer polyester/phenol curing system) and E (acrylic/melamine curing system). The added isocyanate derivatives are caprolactam blocks of the respective monomers of IPDI (isophorone diisocyanate), MDI (4,4'-diphenylmethane diisocyanate) and HMDI (hexamethylene diisocyanate) isocyanate derivatives. In addition, as an alkoxyamine salt, F (tertiary ammonium salt: (Disperon 1121 manufactured by Kusumoto Chemicals Co., Ltd.) was used. As another additive, 10% by mass of G (the above-mentioned chloroprene di Freezing crushed and classified product of vinyl rubber: maximum particle size 200μm) and H (PTFE (polytetrafluoroethylene) resin powder) additives.

The charging voltage was measured according to Method 1 and Method 2, and was measured as follows.

Method 1, in a room at 23°C and 50% RH, place a smooth PCM cut into 7×15mm in a ceramic cup as an insulator, make the painted surface of the measurement object face up, and ground it at once. Make the charge of PCM 0. Then, place a chloroprene rubber sheet (model: black 350, manufactured by Kawakichira Manufacturing Co., Ltd.) cut into 5×10 cm, hardness 50, carbon black 31%, and thickness 5 mm in the center of the PCM. Place a weight of 1kg with a flat bottom that is evenly loaded on the entire surface of the chloroprene rubber sheet for 10 seconds to crimp, remove the weight lightly, and peel off in the vertical direction within 3 seconds. The chloroprene rubber sheet was placed, and within 3 seconds, the charged voltage at the center of the coated surface of the precoated metal plate was measured using a field measuring instrument FMX-002 manufactured by Shimco Co., Ltd. The same addition was carried out 5 times and the average value was taken.

Method 2, prepare five sets of PCM, neoprene rubber sheets, ceramic cups and weights, heat these in an oven at 70°C for 10 minutes, take out each set, and complete method 1 within 30 seconds after taking out In the charging voltage measurement operation, the values of n=5 thus obtained were averaged.

Each PCM was brought into an actual production line for assembling refrigerators, and dust adhesion resistance and electric shock resistance were investigated. Regarding the dust adhesion resistance, the transport frame using a suction tool made of chloroprene is used in the process before foaming polyurethane injection (normal temperature) and in the process after foaming polyurethane injection (PCM coating surface temperature rises to about 70°C). The degree of dust adhesion behind the body is evaluated. Remarkable dust adhesion was evaluated as x, some dust adhesion was evaluated as Δ, and dust adhesion was not observed as ◯, respectively. With regard to electric shock resistance, it was evaluated whether arc discharge occurs when a metal rod touches the end face of PCM after the PCM coating and the leather material of the conveyor belt undergo intense friction, which is the most frequent electric shock. The occurrence of arc discharge was regarded as Δ, and the occurrence of arc discharge was regarded as ○. Regarding the yellowing during baking, based on Comparative Example 1 in which the isocyanate derivative was not added in advance and no yellowing was observed, the yellowing of the coating after baking was significantly evaluated by visual observation as ×, The evaluation that some yellowing was seen was Δ, and the evaluation that no yellowing was seen at all like Comparative Example 1 was evaluated as ◯.

As can be seen from Examples 1 to 42 and Comparative Examples 1 to 10, there is a high correlation between the electrification voltage after peeling electrification and the dust adhesion resistance. If the charging voltage measured by method 1 exceeds 0.15 kV, and if the charging voltage measured by method 2 exceeds 0.25 kV, the dust adhesion resistance at normal temperature and 70° C. respectively decreases. In Examples 1 to 42, the charging voltage in Method 1 was less than 0.15 kV, so the dust adhesion resistance at room temperature was good. It was found that the charged voltage after peeling charging tended to decrease due to the increase in the addition amount of the isocyanate derivative and the increase in the addition amount of the alkoxyamine salt. In addition, when an isocyanate derivative and an alkoxyamine salt are used in combination, especially in Method 2, the charge voltage after peeling and charging decreases synergistically. If these effects are sufficient, like Examples 9-12, 15-17, 20-22, 27, 32, 33, 35, 36, 38, 39, 41, and 42, the dust adhesion resistance at 70 degreeC is also favorable. In Examples 23 and 24, the pulverized chloroprene rubber and PTFE were added to Comparative Example 1, respectively, and the electrification voltage after peeling electrification decreased. This is considered to be due to the fact that the addition of chloroprene rubber or PTFE relatively brings the positional relationship between the chloroprene rubber sheet and the coating layer in terms of triboelectric sequence potentials relatively close. As in this example, as long as the electrification voltage after peeling electrification is within a predetermined range, the dust adhesion resistance can be improved, and it is not limited to the method of adding an isocyanate derivative or an alkoxyamine salt. Even if the type of original plate is changed from GI to EG or cold rolling (Examples 37-42, Comparative Examples 9 and 10), even if the pretreatment is changed from chromate to zinc phosphate (Examples 34-36, Comparative Example 8), and Changing the undercoat layer from polyester to epoxy (Examples 31 to 33, Comparative Example 7) did not change intentionally in the charging voltage after peeling charging as PCM, nor did it change in dust adhesion resistance. From this point of view, it can be understood that the properties of the outermost coating have a dominant influence on the electrification voltage after peeling electrification. If the resin system of the outermost coating is changed from high molecular polyester/melamine curing system to high molecular polyester/phenol curing system or acrylic acid/melamine curing system (embodiments 25～30, comparative examples 5,6), just see The charging voltage after peeling charging tends to rise as a whole, but the correlation between charging voltage and dust adhesion resistance is on the same line.

The electric shock resistance is also roughly correlated with the electrification voltage after peeling and electrification of PCM. A sign of good electric shock resistance can be said that the charged voltage in method 1 is less than 0.1kV.

When IPDI, MDI and HMDI are used as the type of isocyanate, the effect of reducing the charged voltage after peeling and charging can be seen in the same way, but the yellowing resistance during baking is best for IPDI, and HMDI (Examples 18-22) is resistant to yellowing. The yellowing property is slightly lowered, and the yellowing resistance of MDI (Examples 13 to 17) is greatly reduced. Therefore, when yellowing resistance is required, IPDI is preferably used.

In Comparative Examples 1 to 10, since the electrification voltage after peeling electrification exceeded the range of the present invention, the dust adhesion resistance was not good.

In addition, as a reference, the half-life of the conventional static general meter used as an index of dust adhesion resistance, and the measured value of the surface resistance value are shown in the table|surface. Regarding the half-life, only a part of Examples and Comparative Examples are shown. When measuring each value, S-4104 manufactured by the Dento Shokai was used as a static general meter, and the applied voltage was 8 kV. As a surface resistance meter, Model ST-3 manufactured by Shimko Co., Ltd. was used.

When the half-life is observed, the addition of IDPI tends to increase the half-life, and the addition of an alkoxyamine salt tends to shorten the half-life. Although all the prescriptions showed an effect on the dust adhesion resistance, the opposite tendency was shown about the half-life. In addition, the half-lives of Comparative Examples 1 to 4, which were poor in dust adhesion resistance, were also relatively short. Therefore, the conventional consideration that the shorter the half-life is, the better the dust adhesion resistance is, does not hold here, and no correlation between the half-life and dust adhesion resistance is found. From this, it can be seen that the half-life cannot be used as an indicator of dust adhesion resistance. On the other hand, if the surface resistance value is observed, all PCMs show a value greater than or equal to 10 ¹⁴ ohms, and it cannot be used as an index of dust adhesion resistance.

Industrial Utilization Possibility

As described above, according to the present invention, it is possible to provide a PCM capable of reliably suppressing electrification due to static electricity of a coating layer without greatly increasing the cost.

Claims (9)

1. the prefinished metal plate coating composition of an obstacle that be difficult for to take place to cause by static, it is on metal sheet, as face coat coating and solidify and be used to make the coating composition of prefinished metal plate, it is characterized in that, be selected from the combination of (1) macromolecule polyester resin and melamine cured dose except containing, (2) combination of macromolecule polyester resin and phenol solidifying agent, (3) outside the base resin and solidifying agent in the combination of acrylic resin and melamine cured dose, also contain simultaneously all solids components of coating composition more than or equal to the isocyanate derivates of 5 quality % and the alkoxyamine salt more than or equal to 1 quality % of all solids components of coating composition.

2. prefinished metal plate coating composition according to claim 1 is characterized in that, as isocyanate derivates, contains isoflurane chalcone diisocyanate (IPDI) derivative.

3. prefinished metal plate, this prefinished metal plate on the one side at least of metal sheet as face coat coating and solidify claim 1 or 2 described coating compositions are made.

4. the prefinished metal plate manufacture method of an obstacle that be difficult for to take place to cause by static, thereby be to be coated with prefinished metal plate with coating composition and make it to solidify and be used as top layer and film and make the method for the prefinished metal plate that is difficult for taking place the obstacle that causes by static by one side at least at metal sheet, it is characterized in that, be coated on coating composition on the metal sheet contain simultaneously all solids components more than or equal to the isocyanate derivates of 5 quality % with more than or equal to the alkoxyamine salt of 1 quality %.

5. the precoated metal sheet manufacture method of the obstacle that caused by static of difficult generation according to claim 4; It is characterized in that; As coating composition; Use (a) to adopt electrified voltage value that " method 1 " of following record obtain when measuring for having formed the electrified voltage value that the precoated metal sheet of filming on top layer adopts " method 2 " of following record obtain when measuring and be the composition less than 0.25kV above-mentioned less than the composition of 0.15kV or (b) to the above-mentioned precoated metal sheet of filming on top layer that formed

Method 1

23 ℃ of temperature, the standard state of relative humidity 50% indoor, central authorities at the object application face of the level and smooth prefinished metal plate that is cut into 7 * 15cm, superimposed 5 * the 10cm that is cut into, hardness 50, amounts of carbon black is 31 quality %, the neoprene sheet of thick 5mm, prefinished metal plate is placed it on the platform of pottery system of level with becoming downside, with the counterweight of 1kg place on the neoprene sheet carry out crimping 10 seconds after, remove counterweight, vertically peel the neoprene sheet, promptly measure the electrified voltage of the application face central part of prefinished metal plate then with contactless field measurement instrument;

Method 2

The platform and the counterweight of the prefinished metal plate that will put down in writing in aforesaid method 1, neoprene sheet, pottery system heated 10 minutes in 70 ℃ baking oven, took out the back in 30 seconds, all the operation of Method Of Accomplishment 1 record.

6. the prefinished metal plate manufacture method of the obstacle that is caused by static according to claim 4 or 5 described difficult generations is characterized in that, as isocyanate derivates, contains isophorone diisocyanate (IPDI) derivative.

7. the prefinished metal plate manufacture method of the obstacle that causes by static according to claim 4 or 5 described difficult generations, it is characterized in that, as the prefinished metal plate coating composition, use the base resin among the combination of the combination contain the combination, (2) macromolecule polyester resin and the phenol cured agent that are selected from (1) macromolecule polyester resin and melamine cured dose and (3) acrylic resin and melamine cured dose and the composition of solidifying agent.

8. the prefinished metal plate manufacture method of the obstacle that difficult generation according to claim 6 is caused by static, it is characterized in that, as the prefinished metal plate coating composition, use the base resin among the combination of the combination contain the combination, (2) macromolecule polyester resin and the phenol cured agent that are selected from (1) macromolecule polyester resin and melamine cured dose and (3) acrylic resin and melamine cured dose and the composition of solidifying agent.

9. the prefinished metal plate of the obstacle that causes by static of the difficult generation of wantonly 1 described method manufacturing of adopting claim 4～8.