JPS6220909B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a highly workable precoated steel plate. In recent years, in addition to traditional outdoor building materials, home appliances,
In the industry that manufactures products for interior building materials, utensils, and other high-end uses, there is a strong momentum to use prepainted steel sheets in more areas. Coaters are also making efforts to meet these demands, but the required coating film performance is extremely high.For example, the coating maintains the same hardness, stain resistance, chemical resistance, and corrosion resistance as a post coat, and has good processability. There are even examples of such things. From the perspective of pre-coated steel plate manufacturers, this is extremely difficult, and requires consideration of pre-treatment of the steel plate, materials such as paint, and various coating film curing methods such as electron beam curing, heat curing, ultraviolet curing, and other coating film curing methods. However, at present, there is no product that has coating film properties comparable to postcoats and can be processed freely. One possible method to solve this problem is to stop the curing of the coating film at a stage where it can withstand processing, process it into the desired shape, and then heat it again to completely cure it. JP-A-53-85827 is an invention based on this idea, but it is based on a very specific coating material, namely, an epoxy resin and an allyl etherified methylol phenol as main components, with acetalization if necessary. The main point is that polyvinyl alcohol, cellulose derivatives, resol-type phenolic resins, amino resins, etc. can be added, and the amounts used of each component are also limited. Moreover, as stated in the detailed description of the invention in the above-mentioned publication, it is actually quite difficult to stop the thermosetting reaction at the desired stage, and the coating film may become sticky due to insufficient curing, or may be difficult to process due to overcuring. There were many cases where it was inappropriate and unsuitable, and it was not practical. As a result of many years of study, the present inventors intended to develop a pre-coated steel sheet having a semi-cured coating film that solved the drawbacks of the prior invention, and succeeded in this purpose. The present invention has a (meth)acryloyl group per molecular weight of 1000 in the molecule, which reacts and completely cures the coating film by heating after being processed into the desired shape.
A resin system containing 0.1 to 10 unsaturated carbon double bonds that are active to electron beams and 0.05 to 10 functional groups that react with heating per molecular weight of 1000 is added with functional groups that react with heating per molecular weight of 1000. A resin component made by adding a resin having 0.05 to 50 carbon atoms per molecule, or a resin component made by adding a Lutzker type resin system that does not have unsaturated carbon bonds in the molecule, if necessary, is thermally decomposed. The main component is a catalyst added to enable radical polymerization, and the dynamic elastic modulus is semi-cured with an electron beam.
E′ is 1×10 ¹⁰ dyne/cm ² or less, glass transition point is 70℃
This is a highly workable pre-coated steel sheet coated with the following coating film. This steel plate is processed into a desired shape by the user, heated and completely hardened to be used as home appliances, building materials, and other products. While comparing the features of the present invention, the contents of the above-mentioned Japanese Patent Laid-Open No. 53-85827, which is an example of the prior art, will be described and examined in more detail. In other words, the specification of this publication states that (1) it is important to set the conditions at which the coating film should be in a semi-cured state before curing is stopped, and an inappropriate semi-cured state will result in unsatisfactory results. (2) The range of optimal semi-curing conditions for ordinary thermosetting paints is narrow, making it difficult to put it into practical use when considering the fluctuations in drying conditions that can occur in ordinary industrial paint drying equipment. described as difficult. In Japanese Patent Application Laid-Open No. 53-85827, it is thought that the solution to this problem was the use of a paint that uses a very limited resin system and has a specific composition ratio. The greatest feature of the present invention is that in pre-coated steel sheets, which are coated with a paint film in a semi-hardened state after coating the steel sheet, the semi-hardening method utilizes radical polymerization for the curing reaction of the paint polymer. be.
More specifically, if the electron beam curing method is used as the drying and curing method, the conditions for semi-curing the coating film can be freely selected, that is, the range of optimal semi-curing conditions can be improved compared to ordinary thermosetting paints. can be greatly expanded,
Furthermore, it has been experimentally discovered that the fluctuation range of drying conditions that can occur in thermosetting industrial paint drying equipment can be significantly reduced by using an electron beam accelerator even when applied to a practical line. Here, the paint that can be used is one that contains a radically polymerizable unsaturated double bond in its molecule. When semi-curing the coating film, condensation due to heating,
When using curing reactions such as addition and polyaddition reactions, it is difficult to overcome the problems mentioned in JP-A-53-85827. This is considered natural from the perspective of controlling the curing equipment. When semi-curing a paint film, we consider a hot air drying oven, which is the most common industrial method, as an example of a thermal curing method. , time), it would be very difficult to apply it to an industrial experimental line. First, in industrial lines, even if the temperature of the drying oven is set to a certain level, it is unavoidable that the ambient temperature meter will fluctuate by more than ±5°C. Furthermore, the wind speed of hot air,
In addition to unavoidable fluctuations in air volume, etc., the initial temperature of the board during threading, the movement of the board due to the catenary during threading, etc., combined with the synergistic effect with the conditions mentioned above, can lead to drying. It is difficult to set the state upon exiting the furnace, for example, the final plate temperature (=set value of curing conditions) within a very small range. Furthermore, it is impossible to suddenly change the baking conditions in response to a change in line speed due to line trouble before the baking process. Even when the coating film is completely cured, the coated surface is still soft due to the high temperature, and to prevent blocking, it is rapidly cooled and rolled up in the case of coils or laminated in the case of cut plates. In this case, the purpose is only to cool the hardened coated steel sheet, but in the case of semi-hardening, even this cooling condition causes a problem in that the degree of hardening varies. Furthermore, in addition to the factors mentioned above, the influence of plate thickness also plays a large role. As mentioned above, from the equipment point of view, as long as thermosetting equipment is used, stopping the curing reaction at an intermediate stage has many unstable factors. In addition, from the perspective of paint curing reactions, most of the curing reactions by heating belong to sequential reactions among the polymerization reactions shown in Table 1 below.
Taking the polycondensation reaction (crosslinking reaction), which is a typical reaction example of a normal thermosetting coating film, as an example, the relationship between the reaction time (curing time) and the molecular weight of the product (degree of crosslinking or degree of curing) is It is schematically represented as shown in Figure 1 (Kyoritsu Zensho, "Organic Electron Ring", page 281, published in 1960).

[Table] Here, the degree of curing of a normal thermosetting coating film is usually controlled at a reaction time T _A and a molecular weight M _A point, as explained using the example of FIG.
That is, in other words, the coating film is cured in a region where the relationship between curing time and degree of curing is relatively smooth. In this region, the coating film has been completely cured, so it has good hardness, stain resistance, chemical resistance, etc., but as a matter of course, the processability is poor. In the case of semi-curing, the reaction is controlled below the T _A and M _A points in Figure 1, but in conjunction with the equipment factors mentioned above, it is necessary to stably obtain the desired degree of curing. is extremely difficult. The greatest feature of the present invention is that the paint applied to steel plates is made of a resin (component A) that has an unsaturated carbon double bond that is active to electron beams in its molecule and a functional group that reacts with heating. It is a system in which a catalyst that enables radical polymerization by thermal decomposition is added as necessary to a resin composition made by adding a resin having a functional group (component B), and as for the curing method, the first step is A radical polymerization reaction using an electron beam is used as a semi-curing reaction, and after processing into a desired shape, complete curing is carried out by carrying out a condensation reaction and a radical polymerization reaction by heating. Here, in the first stage of semi-curing, using radical polymerization for the curing reaction makes it much easier to control the degree of curing and expands the range of curing conditions compared to sequential reactions, especially for electron beam curing. We have experimentally discovered that the degree of reaction can be controlled extremely easily by using the method, and that from an equipment standpoint, an electron beam irradiator can significantly narrow the range of variation in physical conditions than a heating oven. This is the gist of the present invention. The content of the present invention will be described in more detail. Component A of the resin constituting the paint used in the present invention is a resin that has an unsaturated carbon double bond that is active to electron beams and a functional group that reacts with heating in the molecule, for example, at the molecular end or side chain (metallic acid). ) have a double bond in the molecule, such as those into which acrylic acid has been introduced through an esterification reaction or diene systems, and, for example, carboxyl groups, hydroxyl groups, isocyanate groups,
It has a functional group that enables a thermal reaction, such as a glycidyl group, a methylol group, a methoxymethyl group, an ethoxymethyl group, a butoxymethyl group, an amide group, and an imide group. Component B, a resin having a functional group that reacts with heating, includes, for example, a carboxyl group in the molecule,
It has a functional group that enables a thermal reaction, such as a hydroxyl group, an isocyanate group, a glycidyl group, a methylol group, a methoxymethyl group, an ethoxymethyl group, a butoxymethyl group, an amide group, and an imide group. Incidentally, one or more types of both A and B components can be used here. Any resin such as polyester, acrylic, epoxy, urethane, silicone, melamine, alkyd, etc. may be used as long as both resin systems A and B satisfy the conditions mentioned above. What is important here is the amount of functional groups that enable the thermal reaction of component A and component B, and the amount of unsaturated carbon double bonds in component A. Since the first stage semi-curing reaction is based on electron beam, only the amount of unsaturated carbon double bonds is mainly affected.
However, according to experiments conducted by the present inventors, the appropriate amount is 0.1 to 10 (meth)acryloyl groups, preferably 0.4 to 6, per 1000 molecular weight. That is, if the number of double bonds is more than 10 per molecular weight of 1000, there will be too many crosslinking points and the curability of the coating film will be too high, causing problems such as cracking during processing after semi-curing. In this case, it is possible to loosen the semi-curing conditions, that is, reduce the electron beam irradiation dose, but the degree of curing relative to the dose becomes too steep, and even if electron beam curing is used, it is difficult to control the curing. may not be easy. Furthermore, if the number of double bonds is less than 0.1 per 1000 molecular weight, there will be too few crosslinking points, and the film will be too soft to be used as a semi-cured coating, making it unsuitable for use as a pre-coated steel sheet. and is not industrially practical. Next, we will discuss the number of functional groups that react during the second heating step. This number may be slightly different for the A component and the B component. That is, while it is essential that component A has two bonds, a double bond that is active to electron beams and a functional group that reacts with heating, component B
Since the component has a functional group that reacts with heating, for example, urea (molecular weight 60: difunctional)
It may be. For this reason, component B has a molecular weight of 1000 in terms of the number of functional groups that react when heated.
It may be smaller than the A component when calculated in terms of weight. In other words, regarding component A, the molecular weight
The number of functional groups per 1000 is 0.05 to 10, preferably 0.1 to 8, and for component B it is 0.05 to 10.
50 pieces, preferably 0.1 to 40 pieces. In these cases, if the amount is less than 0.1, the performance of the coating film will not be sufficient even if it is cured by heating, for example, the hardness,
Inferior in stain resistance, chemical resistance, etc. 10 or more ingredients in A, B
If the number of components exceeds 50, the crosslinking density after heating will increase too much, and as a result, cracks may occur in the processed part over time, although it is unclear whether this is due to an increase in internal stress or not. It is inappropriate for this purpose. Furthermore, the molecular weights of component A and component B will be discussed. Regarding component A, the number average molecular weight is 200.
~200000 preferably 300~100000. Regarding component B, the number average molecular weight is 60 to 200,000, preferably 100 to 50,000. In this case, if it is below each lower limit, when a resin system consisting of both components A and B is semi-cured with an electron beam, the coating film generally does not elongate and has insufficient workability. Also,
When the upper limit is exceeded, the viscosity increases, and a large amount of solvent must be added during coating, and it is necessary to heat the coating to a considerably high temperature during the solvent scattering process, making it less economical. Furthermore, in the present invention, a lacquer type resin having no unsaturated carbon bond in its molecule can be added. This lacquer-type resin includes (polymer) acrylic, polyester, urethane, acrylamide, diene, melamine, rubber-based resin, and others, but in this case, the main purpose is to impart flexibility to the coating film. In the first stage of semi-curing and the second stage of complete curing, no curing reaction is expected, so free functional groups such as hydroxyl groups, carboxyl groups, isocyanate groups, amide groups and other stain-resistant and chemical-resistant groups are used. It is better to have zero or as little amount as possible of substances that may adversely affect properties, water resistance, etc., and it is sufficient that the amount is only necessary to increase the affinity with pigments or other resins when making a paint.
Even if it is hot, it is sufficient that it is several mol% or less. still,
The viscosity of this resin is preferably solid or close to solid, and the viscosity of the resin is preferably 10,000 centipoise or more, and the elongation of the resin is preferably 100% or more. The purpose of adding this resin is to compensate for the lack of flexibility and elongation when resins with active unsaturated carbon double bonds in their molecules are semi-cured by electron beam irradiation. Alternatively, this is to relieve internal shrinkage stress during semi-curing. In addition, in the present invention, a catalyst that enables radical polymerization by thermal decomposition may be added as necessary, but this is because the double bonds are not sufficiently bonded when the coating film is semi-cured by the electron beam in the first step. Since it may remain unreacted, it is added in advance to completely cure the coating film by heating after processing into the desired shape in the second stage. Examples of catalysts that enable radical polymerization through thermal decomposition include the following. That is, examples include ketone peroxide, peroxyketanol, hydroperoxide, dialkyl peroxide, diacyl peroxide, peroxydicarbonate, peroxyester type, and the like. However, the decomposition temperature of these catalysts must be at least 50°C or higher, preferably 70°C or higher. This is because after the first stage of semi-curing of the coating film, the pre-coated steel sheet is shipped to users of home appliances, building materials, etc., and by the time it is processed into the desired shape, the radical polymerization hardening reaction due to thermal decomposition of the catalyst has progressed significantly. This is because it should not be. The inventors conducted a follow-up experiment on coating film performance for 12 months after the first stage of semi-curing, and found that the decomposition temperature of the catalyst was 50°C or higher in the resin system mentioned above. It was found that this is good. However, even if the decomposition temperature of the catalyst is too high, it is inappropriate from the viewpoint of energy saving and cost, even if it does not affect the coating film performance, and the temperature is preferably about 200° C. or lower. Further, since both the A component and the B component can be cured by heating, a catalyst may be added in advance as necessary to promote the reaction. In addition, the following additives may be added when the above resin system is made into a paint. That is, polyhydric alcohol (meth)acrylates for adjusting crosslinking density and viscosity, such as ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra or Tri(meth)acrylate or monofunctional oligo(meth)acrylate, such as phenylglycidyl(meth)acrylate,
Phenoxyethyl (meth)acrylate, phenylcarbitol (meth)acrylate, nonylphenoxyethyl (meth)acrylate, nonylphenol ethylene oxide adduct (meth)acrylate, benzoyloxyethyl (meth)acrylate, nonylphenol ethylene oxide Adduct (meth)acrylate, cresol glycidyl ether (meth)acrylate, cresol/propylene oxide adduct (meth)acrylate, styrenated cresol/ethylene glycol (meth)acrylate, butanol/propylene oxide adduct (meth)acrylate,
Examples include dialkyl ethanol (meth)acrylate. Furthermore, a phthalic acid-based or phosphoric acid-based plasticizer such as dibutyl phthalate, dioctyl phthalate, dioctyl terephthalate, and dibutyl terephthalate may be used. Naturally, pigments and, if necessary, conventional thinners may also be added. In addition, when adding thinner, before irradiating with electron beam,
It is necessary to leave it alone or scatter the thinner using jet air, hot air, far (near) infrared electromagnetic wave induction heating, etc., but even if heat is applied, the temperature must be below the decomposition temperature of the radical polymerization catalyst; It is necessary to set conditions carefully so that polymerization reactions such as , radical polymerization, sequential polymerization, etc. do not occur. The above-mentioned paint is applied to a steel plate and semi-cured with an electron beam.The degree of curing in this case requires that the paint film be tack-free, but there are other conditions as well. Glass transition point (peak value of loss tangent tanδ in viscoelasticity measurement) is 70℃
The dynamic elastic modulus E′ is 1×10 ¹⁰ dyne/cm ² at the processing temperature during post-processing by the user.
It has been experimentally found that the object of the present invention is preferably about 9×10 ⁹ dyne/cm ² or less. As a further supplement, the glass transition point of the coating film after semi-curing is preferably 98% or less when expressed in terms of absolute temperature compared to that during heat curing after the second stage of processing (=complete curing). It must be 95% or less. In addition, the glass transition point of the coating film after complete curing is 70℃ or higher, and the dynamic elastic modulus E' is 1×
It has also been experimentally found that it must be at least ^{10 10} dyne/cm ² , preferably at least 2×10 ¹⁰ dyne/cm ² . In the present invention, the painted base plate includes, for example, a steel plate, an electrogalvanized steel plate, a hot-dip galvanized steel plate,
Alternatively, steel plates whose surfaces have already been subjected to chemical conversion treatment with chromic acid, phosphoric acid, etc. in the manufacturing process, stain-free steel, tinplate, aluminum plates, stainless steel plates, etc. can be used. In addition, various known methods can be used to pre-treat the metal plate as necessary. For example, if the metal plate is a steel plate that has already been subjected to chemical conversion treatment in the manufacturing process, , a pretreatment such as simply a cleaning treatment may be applied, or if the material has not been subjected to a chemical conversion treatment, a chemical conversion treatment agent suitable for the material is used.
Pretreatment can be performed. Further, in the present invention, it is preferable to apply a primer to the original plate, and any primer can be used as long as it has good adhesion to the painted original plate and does not cause any trouble with the paint applied thereon. For example, epoxy, epoxy acrylic, epoxy polyester,
Any of heat-curable, ultraviolet-curable, and electron beam-curable coatings such as those based on polyester, acrylic, and vinylphenol may be used, and the coatings are cured by the respective curing means. As a precaution, if the ultraviolet ray or electron beam curable primer contains a solvent, a setting and flash-off process may be included to scatter the solvent. These primers can be applied by conventional methods such as natural roll coating, reverse roll coating, curtain flow coating, and spray coating, and the coating thickness is as follows: It is about 1 to 10μ, preferably about 3μ. The coating system of the present invention may be applied by conventional roll coating, curtain flow coating, spray coating, etc., and heating coating may be used as long as the coating has a very high viscosity. Regarding the electron beam irradiation method, any known equipment can be used, and currently developed and commercially available accelerating voltages
Any voltage from 150kV to several MV can be used. To set the accelerating voltage, film thickness, film specific gravity, and known knowledge (Depth-Dose curve) may be used. For example,
A 300kV, 200mA accelerator is sufficient. In addition, when curing a coating film by irradiating an electron beam, it is known that oxygen or ozone acts as a polymerization inhibitor, so it is desirable to block this, and the oxygen concentration in the electron beam irradiation atmosphere is known to act as a polymerization inhibitor. The content is preferably 5% or less, preferably 0.5% or less. It is also possible to print on the coating film of this product, and furthermore, it is desirable to laminate a protective film to protect the surface of the coating film. This product can also be printed, and the same resin-based inks as mentioned above are suitable for printing. As the protective film, polyvinyl chloride, polypropylene, polyethylene or other materials are used. Example 1 A derivative in which acrylic acid was added to ethyl acrylate, methyl methacrylate, and glycidyl methacrylate, the monomer molar ratio of acrylic acid was 63:30:
5:2, the number average molecular weight is approximately 10,000, the number of acryloyl groups per 1000 molecular weight is approximately 0.48, and the number of carboxyl groups, which are functional groups that react with heating, is approximately 0.19 per 1000 molecular weight (component A). 100 parts (parts by weight, the same applies hereinafter) of hexamethoxymethylolmelamine (molecular weight 390, 15 methoxy groups per 1000 molecular weight) as component B.
10 parts of titanium white and 110 parts of titanium white were added, and 200 parts of xylene was used as a solvent to disperse the paint using three rolls (functional groups of component A that react with heating/B
Number of functional groups of components = 0.19/15 (molar ratio). This paint was applied with a bar coater to a dry film thickness of 25 μm on a hardened electrogalvanized steel sheet, which had been previously coated with a thermosetting epoxy/acrylic primer (film thickness: 3 μm), and xylol was scattered with jet air. This painted board was coated under a nitrogen atmosphere (oxygen concentration
A coated steel sheet with a semi-hardened coating film was obtained by irradiating an electron beam with a dose of 2 Mrad using an accelerator with a voltage of 300 KV and a current of 25 mA. The coating hardness of this coated steel plate was HB, and the workability was good even though it was shockingly bent to 90° (R=0) using a bending machine (at room temperature). This same steel plate was subjected to a stain resistance test. Apply Magic Ink (red, black, blue) and leave at room temperature.
After holding it for 24 hours, I tried wiping it with gauze soaked in ethanol, but it left a strong mark (rating: △). Next, this processed painted steel plate is placed in an atmosphere of 250℃.
After keeping it in the oven for 2 minutes, it was removed from the oven and its hardness was measured to be 3H, and no cracks in the coating were observed in the processed areas. Further, when the same stain resistance test as before was conducted, there were no traces of stain, indicating good stain resistance (rating: ◎). Reference example 1 Instead of electrogalvanized steel sheet, use tin foil (25μ
The same paint as in Example 1 was applied on the foil (thickness) under the same conditions to obtain a tin foil having a semi-cured film, and the tin was dissolved using the amalgam method to obtain a free film.
When this film was examined for viscoelastic behavior using a Vibron DDV--EA tester manufactured by Toyo Baldwin Co., Ltd., the dynamic elastic modulus E' was 8.5×
10 ⁹ dyne/cm ² (20°C), and the temperature at which the loss tangent tanδmax occurred was 45°C. Furthermore, when the viscoelastic behavior of the semi-cured coating film was heated under the same heating conditions as in Example 1, E' was 2.9×10 ¹⁰ dyne/cm ² (20°C), tan δmax
The temperature was 89℃. Comparative Example 1 To 100 parts of an acrylic resin (component A) in which the monomer molar ratio of ethyl acrylate, methyl methacrylate, and acrylic acid was 68:30:2 and the number average molecular weight was exactly the same as in Example 1, component B was added. A paint was made by adding 10 parts of the same melamine and 110 parts of titanium white, and using 200 parts of xylene as a solvent (there are no unsaturated carbon double bonds in the molecule that are active to electron beams). This paint was irradiated with an electron beam under the same conditions and steps as in Example 1 to obtain a coated steel plate. The paint film on this painted steel plate had not hardened (it was very sticky). Comparative Example 2 A paint containing only component A of Example 1 was prepared. This paint was subjected to the same conditions and steps as in Example 1 to obtain a coated steel plate irradiated with an electron beam. The hardness of this coated steel plate was F, and the workability was good, but the stain resistance was △. Next, this steel plate was held in an atmosphere of 250° C. for 2 minutes, and then taken out from the oven, and its hardness was measured, giving it a rating of F and stain resistance. Example 2 To the resin system of Example 1, an additional 100 parts of a Lutzker type resin having a monomer molar ratio of ethyl acrylate and methyl methacrylate of 60:40 and a number average molecular weight of approximately 50,000 (solid) was added. Then, titanium white was added to give the same pigment concentration to make a paint. This paint system was applied under exactly the same conditions as in Example 1, and then irradiated with an electron beam to obtain a coated steel plate having a semi-cured coating film. The hardness of this coated steel plate was B, and when it was shockingly bent to 180° (R=0) using a bending machine, no cracks were observed and the workability was good.
This same board was tested for stain resistance. After applying Magizu ink (red, black, blue) and keeping it at room temperature for 24 hours, I tried wiping it with gauze soaked in ethanol, but it left a strong mark (rating × - △) and the areas where Magizu ink was not applied “Glossiness” occurred. Next, this processed plate was heated in an atmosphere of 220℃ for 10 minutes.
After holding it for a few minutes, it was taken out of the oven and its hardness was measured, and it was 2H, and there were no changes such as cracks in the processed parts. In addition, when we conducted a stain resistance test as before, traces of contamination were easily wiped away (score: ◎).
Moreover, no "shininess" occurred. The dynamic elastic modulus E' and the glass transition point after heating the semi-cured coating using tin foil under the same heating conditions as in Example 2 as in Reference Example 1 were 8.3×, respectively.
10 ⁹ dyne/cm ² , 43℃ and 25×10 ¹⁰ dyne/cm ² , 86
It was warm at ℃.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram illustrating the relationship between the reaction time and the molecular weight of the product in a polymer reaction.

Claims (1)

[Claims] 1 After being processed into the desired shape, it reacts with heating and the coating film is completely cured.
Contains 0.1 to 10 (meth)acryloyl groups per 1,000 molecules of unsaturated carbon double bonds that are active to electron beams and functional groups that react with heating.
The resin system has 0.05 to 10 functional groups per 1000, and 0.05 to 10 functional groups per 1000 molecular weight that react with heating.
If necessary, radical polymerization is performed by thermal decomposition to a resin component obtained by adding a resin having 50 carbon atoms, or a resin component obtained by adding a Lutzker type resin system having no unsaturated carbon bonds in the molecule. The main component is a catalyst added to make it possible,
Dynamic elastic modulus E′ semi-cured by electron beam is 1×
A highly formable pre-coated steel sheet coated with a coating film with a glass transition temperature of 10 ¹⁰ dyne/cm ² or less and a glass transition temperature of 70°C or less.