JP2018058992A - Intermediate coating composition, multilayer coating film and method for forming multilayer coating film - Google Patents

Abstract

An object of the present invention is to provide an intermediate coating composition capable of forming a multilayer coating film having a high single film hardness of an intermediate coating layer and excellent chipping resistance and appearance without using a chipping primer. The present invention provides an intermediate coating composition for use in forming an intermediate coating layer directly laminated on the surface of an electrodeposition coating film constituting a vehicle outer plate, wherein the content of the entire resin component is 0. 1 to 5% by weight polycaprolactone triol, 20 to 30% by weight pyrazole block isocyanate, 1 to 20% by weight melamine resin, 40 to 70% by weight Polyester, epoxy resin of more than 0% by mass and less than 10% by mass, talc having a pigment mass concentration of 1% by mass to 10% by mass, and more than 0.01 parts by mass with respect to 100 parts by mass of the whole resin component It is characterized by containing a urethane curing catalyst in an amount of not more than 0.01 parts and a sulfonic acid-based catalyst in an amount of more than 0.01 parts by mass and not more than 2 parts by mass. [Selection figure] None

Description

  The present invention relates to an intermediate coating composition, a multilayer coating film, and a method for forming a multilayer coating film.

  For example, when an automobile travels at a high speed, it is inevitable that pebbles and the like collide with the painted surface of the outer panel of the automobile. Such collision of pebbles or the like may cause damage phenomena (so-called chipping) such as cracks or peeling of the coating on the vehicle outer plate. When chipping occurs, water or the like enters from this chipping portion, and rusting may occur on the base of the outer plate.

  Especially in cold foreign countries such as North America, Canada, and Northern Europe, chipping resistance in the coating on the outer panel of automobiles is important because a large amount of rock salt and sand is sprayed on the road surface in the winter to melt snow. Even if the coating film is not damaged or peeled off, a coating film that does not rust the substrate of the vehicle outer plate is desired.

  Generally, in the coating of automobile outer panels of automobiles, electrodeposition paint (undercoat paint), intermediate coat paint, and top coat paint are sequentially applied onto steel sheets that have been subjected to chemical conversion treatment of iron phosphate / zinc. In order to improve the anticorrosive property and the anticorrosive property, anti-chipping primers laminated on the electrodeposition coating film and the intermediate coating layer have been developed (Japanese Patent Laid-Open Nos. 6-41494, 6-93227, and 6). No. 322059, JP-A-6-346024, JP-A-7-228834, JP-A-9-241580, and JP-A-2002-180000). However, the application of these chipping resistant primers leads to an increase in production cost, which is contrary to today's demand for cost reduction.

  On the other hand, techniques for imparting chipping resistance to the intermediate coating layer have also been developed (see Japanese Patent Application Laid-Open Nos. 4-77580 and 2011-50916). However, at present, sufficient chipping resistance is not obtained even with these techniques.

  In addition, the appearance of a vehicle outer plate of an automobile is also regarded as important. This deterioration in appearance may also induce coating film defects.

  Furthermore, in the coating of the vehicle outer plate, the surface of the intermediate coating layer may be polished by a water polish etc. in order to ensure the appearance, but if the hardness of the intermediate coating layer is insufficient, workability decreases, As a result, the manufacturing efficiency of the vehicle outer plate is lowered.

  Therefore, in the coating of the vehicle outer plate of an automobile, it is desired to improve the chipping resistance and appearance by the intermediate coating layer and to increase the hardness of the single intermediate coating layer, and these issues include motorcycles, automobile parts, forklifts, The same applies to external coating such as heavy machinery.

JP-A-6-41494 JP-A-6-93227 JP-A-6-322059 JP-A-6-346024 JP-A-7-228834 JP-A-9-241580 JP 2002-180000 A JP-A-4-77580 JP 2011-50916 A

  The present invention has been made based on the circumstances as described above, and the purpose thereof is a multilayer having high single film hardness of the intermediate coating layer and excellent chipping resistance and appearance without using a chipping primer. An object of the present invention is to provide an intermediate coating composition capable of forming a coating film, and such a coating film and a method for producing the same.

  The present invention made to solve the above problems is an intermediate coating composition used for forming an intermediate coating layer directly laminated on the surface of an electrodeposition coating film constituting a vehicle outer plate, and as a resin component, (A) polycaprolactone triol having a content of 0.1% by mass to 5% by mass in the entire resin component, (b) pyrazole-blocked isocyanate having the content of 20% by mass to 30% by mass, and the above content (C) melamine resin having a content of 1% by mass or more and 20% by mass or less, (d) polyester having a content of 40% by mass or more and 70% by mass or less, and a content of more than 0% by mass and 10% by mass or less ( e) containing an epoxy resin, and containing, as a pigment component, (f) talc having a pigment mass concentration of 1% by mass or more and 10% by mass or less, and exceeding 0.01 parts by mass with respect to 100 parts by mass of the whole resin component. 2 mass And following (g) urethane curing catalyst, characterized in that it contains 0.01 parts by ultra 2 parts by weight of (h) sulfonic acid catalyst with respect to the entire resin components 100 parts by weight.

  Another aspect of the present invention made to solve the above problems is an electrodeposition coating film constituting a vehicle outer plate, an intermediate coating layer directly laminated on the surface of the electrodeposition coating layer, and a lamination on the surface of the intermediate coating layer. A multi-layer coating film comprising a top coating layer, wherein the intermediate coating layer is obtained by curing the intermediate coating composition.

  Yet another aspect of the present invention made to solve the above-described problems includes a step of forming an electrodeposition coating film constituting a vehicle outer plate, a step of directly forming an intermediate coating layer on the surface of the electrodeposition coating film, A method of forming a multi-layer coating film comprising a step of forming an overcoat layer on the surface of the intermediate coating layer, wherein the intermediate coating composition is applied in the intermediate coating layer forming step.

  Here, “melamine resin” refers to an initial condensate of melamine and aldehyde having a mass average molecular weight of 300 to 2,000, and “mass average molecular weight” refers to JIS-K-7252-1 (2008). ), And refers to a value measured using gel permeation chromatography (GPC). “Whole resin component” means the whole resin component in terms of solid content. “Pigment mass concentration” refers to a value (mass%) calculated by the mass of the pigment × 100 / (mass of the entire pigment component + mass of the resin component in terms of solid content).

  According to the intermediate coating composition and the method for forming a multilayer coating film of the present invention, the multilayer coating film has a high single film hardness and excellent chipping resistance and appearance without applying a chipping primer. A film can be formed. In addition, the coated coating film of the present invention has a single film hardness of the intermediate coating layer, and is excellent in chipping resistance and appearance even without application of a chipping resistant primer.

  The present invention includes an intermediate coating composition, a coating film, and a method for forming a multilayer coating film. Hereinafter, these will be described.

<Intermediate coating composition>
The intermediate coating composition of one embodiment of the present invention is used to form an intermediate coating layer that is directly laminated on the surface of an electrodeposition coating film constituting a vehicle outer plate.

  The intermediate coating composition contains (a) polycaprolactone triol, (b) pyrazole block isocyanate, (c) melamine resin, (d) polyester, and (e) epoxy resin as resin components. The pigment component contains (f) talc, and the other components contain (g) a urethane curing catalyst and (h) a sulfonic acid catalyst. Moreover, the said intermediate coating composition may contain another arbitrary component in the range which does not impair the effect of this invention.

  Since the intermediate coating composition contains (a) polycaprolactone triol, (b) pyrazole blocked isocyanate, (c) melamine resin and (d) polyester as the resin component, it is relatively dense with many crosslinking points. A coating film containing polyurethane having a three-dimensional network structure is formed. Specifically, the blocked isocyanate mainly crosslinks between the polyesters by urethane bonds, and further the melamine resin auxiliaryly crosslinks between the polyesters. Therefore, it is presumed that the intermediate coating layer made of the intermediate coating composition has excellent flexibility and elasticity, and as a result, can exhibit high cushioning properties. With such a function, the intermediate coating composition can form an intermediate coating layer having high chipping resistance.

  Here, the melamine resin has not only a crosslinkability with a resin (polyester) as a substrate but also a self-condensation property. For this reason, when a melamine resin is used alone as a curing agent, a self-condensation of the melamine resin partially proceeds preferentially to easily form a coating film in which viscoelasticity and crosslinkability are nonuniform. On the other hand, since the block isocyanate is preferentially cross-linked with the base resin, it is easy to form a relatively uniform coating film. In particular, pyrazole blocked isocyanate dissociates at 110 ° C. or more and 140 ° C. or less and reacts with OH groups, so that it can form many highly flexible crosslinking sites even at low temperature baking. Therefore, the intermediate coating composition contains (a) polycaprolactone triol, (b) pyrazole-blocked isocyanate, and (c) melamine resin as a curing agent, thereby improving the uniformity of strength and the like. A hardened coating film can be formed, and the coating film can be prevented from being peeled off along with the plating of the coating material during chipping, and the coating material (substrate) such as a steel plate can be prevented from being exposed by chipping.

  In addition, the intermediate coating composition should contain a relatively soft (a) polycaprolactone triol content of a certain amount or less and promote crosslinking of the melamine resin (h) a certain amount of a sulfonic acid catalyst. Thus, the hardness of the coating film can be remarkably increased in combination with the increase in the crosslinking density due to the pyrazole-blocked isocyanate described above.

  Further, the intermediate coating composition contains (g) a urethane curing catalyst and (h) a sulfonic acid-based catalyst, whereby the difference in curing speed in the thickness direction of the coating is reduced. As a result, occurrence of appearance defects such as wrinkles in the coating film can be suppressed.

  Moreover, the said intermediate coating composition can improve the toughness of an intermediate coating layer by containing the (f) talc which has a layered structure, As a result, chipping resistance can be accelerated | stimulated.

  Hereinafter, each component of the intermediate coating composition will be described.

<(A) Polycaprolactone triol>
(A) Polycaprolactone triol is a compound having a structure represented by the following formula, for example. (A) Polycaprolactone triol represented by the following formula can be obtained, for example, by adding ε-caprolactone to triol.

In the above formula, R ¹ is a group derived from triol. m and n are each independently an integer of 0 or more. p is an integer of 1 or more. m + n + p is 2 or more.

Examples of the group derived from the triol represented by R ¹ include a 2,2-dimethylbutane-triyl group, a propane-1,2,3-triyl group, and a triethylamine-triyl group.

Examples of the triol that gives R ¹ include trimethylolpropane, glycerin, triethanolamine, and the like. The carbon number of the triol is preferably 2 or more and 8 or less, and more preferably 3 or more and 6 or less.

  (A) As a minimum of the number average molecular weight (Mn) of polycaprolactone triol, 200 is preferable and 400 is more preferable. On the other hand, the upper limit of the number average molecular weight is preferably 4,000, and more preferably 3,000. By setting the number average molecular weight within such a range, chipping resistance can be improved. In addition, "number average molecular weight" refers to the value measured using gel permeation chromatography (GPC) based on JIS-K-7252-1 (2008).

  (A) A commercially available product may be used as the polycaprolactone triol. (A) Examples of commercially available products of polycaprolactone triol include “Placcel 303”, “Placcel 305”, “Placcel 308”, “Placcel 309”, “Placcel 312” and “Placcel 320” manufactured by Daicel Corporation.

  (A) As a minimum of the content rate in the whole resin component of a polycaprolactone triol, it is 0.1 mass%, 0.5 mass% is preferable and 2 mass% is more preferable. On the other hand, the upper limit of the content is 5% by mass, preferably 4% by mass. When the content is less than the lower limit, chipping resistance may be reduced and peeling of the coating film may occur. Conversely, if the content exceeds the upper limit, the hardness of the coating film may be reduced. In addition, (a) the content of polycaprolactone triol within the above range can optimize the value of loss tangent tan δ, elongation and Young's modulus of the coating film at low temperature, and dynamic glass transition temperature (dynamic Tg). Can be optimized. Therefore, it can suppress that a coating film peels with plating of a to-be-coated material at the time of chipping etc., and can suppress to-be-coated material (base material), such as a steel plate, by chipping. Loss tangent tan δ is a value indicating the ratio between viscosity and elasticity. When the target substance receives a certain external force, it undergoes viscous deformation, converts the received mechanical energy into thermal energy, and indicates the rate of absorption. It is. That is, a coating film having a large loss tangent tan δ has a high ratio of absorbing (consuming) external energy as heat energy. Here, “loss tangent tan δ” is a value measured in accordance with the tensile vibration-non-resonance method of JIS-K7244-4: 1999. Specifically, the heating rate is 2 ° C./min and the frequency is 8 Hz. Under conditions, it can be measured using a forced stretching vibration type viscoelasticity measuring device such as “Vibron” manufactured by Orientec.

<(B) Pyrazole blocked isocyanate>
(B) Pyrazole blocked isocyanate is a compound obtained by blocking the isocyanate group of polyisocyanate with a pyrazole-based blocking agent. Polyisocyanate is a compound having two or more isocyanate groups in one molecule. The polyisocyanate may contain a burette structure or a nurate structure. Bullet is a dimer of isocyanate, and nurate is a trimer of isocyanate.

  A blocking agent is a compound that is added to an isocyanate group and is stable at room temperature, but can regenerate a free isocyanate group when heated to a temperature higher than the dissociation temperature.

Examples of the polyisocyanate include:
Aliphatic polyisocyanates such as hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate, lysine diisocyanate;
1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4′-dicyclohexylmethane diisocyanate (hydrogenated MDI), methylcyclohexane diisocyanate, isopropylidene dicyclohexyl-4,4′-diisocyanate, 1,3-diisocyanate (Isocyanatomethyl) cyclohexane (hydrogenated XDI), 1-methylcyclohexane-2,4-diyl diisocyanate (hydrogenated TDI), 2,5- or 2,6-bis (isocyanatomethyl) -bicyclo [2 2.1] Cycloaliphatic polyisocyanates such as heptane (norbornane diisocyanate);
Aromatic polyisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate, naphthalene diisocyanate;
Aromatic-aliphatic polyisocyanates such as xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI);
These modified polyisocyanates (urethanes, carbodiimides, uretdiones, uretonimine modified products), and the like. These polyisocyanates may be used alone or in combination of two or more.

  The pyrazole-based blocking agent is generally used in an equimolar amount with the isocyanate group of the polyisocyanate in the preparation of the pyrazole-blocked isocyanate.

  (B) As a minimum of the content rate in the whole resin component of pyrazole block isocyanate, it is 20 mass%, 22 mass% is preferable, and 25 mass% is more preferable. On the other hand, the upper limit of the content is 30% by mass, preferably 29% by mass, and more preferably 28% by mass. There exists a possibility that the hardness in the case of the chipping resistance of a coating film and low temperature baking may fall that the said content rate is less than the said minimum. Conversely, if the content exceeds the upper limit, the adhesion of the coating film may be reduced.

  (A) The lower limit of the molar ratio of the isocyanate group of the (b) pyrazole-blocked isocyanate to the OH group of polycaprolactone triol (hereinafter also referred to as “NCO / OH ratio”) is preferably 0.4, more preferably 0.5. 0.6 is more preferable. On the other hand, the upper limit of the NCO / OH ratio is preferably 2.0, more preferably 1.5, and even more preferably 1.0. By setting the NCO / OH ratio within the above range, the chipping resistance and hardness of the coating film can be improved.

<(C) Melamine resin>
(C) The melamine resin is a thermosetting resin synthesized from melamine and aldehyde. Examples of (c) melamine resins include methylated melamine resins, butylated melamine resins, and methylated / butylated melamine resins.

(C) As a melamine resin, a commercial item can also be used. (C) Examples of commercially available melamine resins include "Resimene CE" from INEOS Melamines, "Cymel" from Nippon Cytec, "Uban" from Mitsui Chemicals, "Sumimar" from Sumitomo Chemical.

  (C) As a minimum of the content rate in the whole resin component of a melamine resin, it is 1 mass%, 5 mass% is preferable and 10 mass% is more preferable. On the other hand, the upper limit of the content is 20% by mass, preferably 18% by mass, and more preferably 17% by mass. There exists a possibility that the hardness of a coating film may fall that the said content rate is less than the said minimum. On the other hand, when the content exceeds the upper limit, chipping resistance is lowered and the coating film may be peeled off.

<(D) Polyester>
(D) Polyester is a resin having an ester bond in the main chain (except for those corresponding to (a) polycaprolactone triol). Examples of (d) polyester include saturated polyester and unsaturated polyester. Such (d) polyester can be obtained, for example, by heat condensation of a polybasic acid and a polyhydric alcohol. Examples of the polybasic acid include a saturated polybasic acid or an anhydride thereof, an unsaturated polybasic acid or an anhydride thereof, and the like. Examples of the saturated polybasic acid and its anhydride include phthalic anhydride, terephthalic acid, succinic acid and the like. Examples of the unsaturated polybasic acid and its anhydride include maleic acid, maleic anhydride, fumaric acid and the like. Examples of the polyhydric alcohol include dihydric alcohol and trihydric alcohol. Examples of the dihydric alcohol include ethylene glycol and diethylene glycol. Examples of the trihydric alcohol include glycerin and trimethylolpropane.

  (D) As a minimum of the number average molecular weight of polyester, 500 is preferable and 800 is more preferable. The upper limit of the number average molecular weight is preferably 6,000, and more preferably 5,000.

  (D) As a minimum of the content rate in the whole resin component of polyester, it is 40 mass% and 45 mass% is preferable. On the other hand, as an upper limit of the said content rate, it is 70 mass%, and 60 mass% is preferable. If the content is less than the lower limit, the coating suitability of the intermediate coating composition may be reduced. On the other hand, when the content exceeds the upper limit, the contents of (b) pyrazole blocked isocyanate and (c) melamine resin are relatively decreased, and the chipping resistance and appearance of the coating film may be decreased.

<(E) Epoxy resin>
(E) An epoxy resin is a resin containing an epoxy group. By including an epoxy resin in the intermediate coating composition, the chipping resistance and water resistance of the coating film can be further improved. (E) As an epoxy resin, the bisphenol-type epoxy resin obtained by reaction of bisphenol and epichlorohydrin etc. is mentioned, for example. Examples of bisphenol include bisphenol A and bisphenol F. Examples of commercial products of the bisphenol type epoxy resin include “Epototo” manufactured by Nippon Steel & Sumikin Co., “Epicoat” manufactured by Shell Chemical Co., Ltd. Moreover, as (e) epoxy resins, those obtained by chain extension of these epoxy resins using a chain extender can also be used.

  (E) The content rate in the whole resin component of an epoxy resin is more than 0 mass%. Moreover, as a minimum of the said content rate, 5 mass% is more preferable. On the other hand, the upper limit of the content is 20% by mass, preferably 10% by mass. If the content is less than the lower limit, the dynamic Tg (glass transition temperature) of the coating film increases, and chipping resistance may be insufficient. Conversely, if the content exceeds the upper limit, the low temperature curability may be reduced.

<(F) Talc>
(F) It does not specifically limit as talc, For example, well-known things, such as S talc and PS talc, are mentioned.

  (F) The average particle diameter of talc is usually 1 μm or more and 10 μm or less. When the average particle diameter is in the above range, it is possible to suppress a decrease in the appearance of the coating film. If the average particle diameter is less than 1 μm, the effect of improving the chipping resistance by talc may be insufficient. Conversely, when the average particle diameter exceeds 10 μm, the appearance may be deteriorated. The average particle diameter of (f) talc is the median diameter derived from the volume distribution measured by the laser diffraction scattering method.

  (F) The lower limit of the pigment mass concentration of talc is 1% by mass, preferably 1.5% by mass, and more preferably 2% by mass. On the other hand, the upper limit of the pigment mass concentration is 10 mass%, preferably 6 mass%, and more preferably 5 mass%. If the pigment mass concentration is less than the lower limit, the chipping resistance of the coating film is lowered and the coating film may be peeled off. Conversely, if the pigment mass concentration exceeds the upper limit, the adhesion of the coating film may be reduced. Moreover, there exists a possibility that the heating residual amount (NV) of the said intermediate coating composition may fall, and smoothness may deteriorate.

<(G) Urethane curing catalyst>
(G) The urethane curing catalyst is a substance that promotes a urethane bond forming reaction between (a) polycaprolactone triol, (b) pyrazole blocked isocyanate, (c) melamine resin, and (d) polyester. (G) Examples of the urethane curing catalyst include bismuth compounds, aluminum compounds, tin compounds, and zinc compounds.

  Examples of the bismuth compound include bis (acetylacetone) bismuth, bismuth 2-ethylhexanoate, bismuth neodecanoate, and bismuth salicylate.

  Examples of the aluminum compound include aluminum triacetylacetonate and aluminum triacetoacetate.

  Examples of the tin compound include dimethyltin dilaurate, dibutyltin dilaurate, dimethyltin chloride, dibutyltin chloride, di-n-octyltin dilaurate, and the like.

  Examples of the zinc compound include zinc acetylacetonate, zinc propionate, zinc octoate, zinc 2-ethylhexanoate, zinc neodecanoate, zinc laurate, zinc stearate, zinc linoleate, zinc naphthenate, and benzoic acid. Examples include zinc and zinc salicylate.

  (G) Content with respect to 100 mass parts of the said resin component whole of a urethane curing catalyst is more than 0.01 mass part, and 0.1 mass part is preferable as a minimum of content. On the other hand, the upper limit of the content is 2 parts by mass, preferably 1 part by mass. There exists a possibility that the crosslinking density of a coating film may become inadequate that the said content is less than the said minimum. Conversely, if the content exceeds the upper limit, the appearance of the coating film may be deteriorated.

<(H) Sulfonic acid-based catalyst>
(H) The sulfonic acid-based catalyst is a compound having a sulfonic acid group. (H) The sulfonic acid-based catalyst acts on the main chain and / or terminal of the melamine resin and promotes crosslinking of the melamine resin, thereby improving the hardness of the coating film. In addition, due to this action, the difference in the speed of melamine curing with respect to urethane curing promoted by pyrazole-blocked isocyanate is reduced, and generation of wrinkles can be suppressed.

  Examples of the sulfonic acid catalyst include p-toluenesulfonic acid (pTSA), sodium dodecylbenzenesulfonate (DDBSA), dinonylnaphthalenedisulfonic acid (DNNDSA), dinonylnaphthalenesulfonic acid (DNNSA), and the like.

  As the sulfonic acid catalyst, a compound in which a sulfonic acid group is blocked with a blocking agent can be used. For example, an amine block sulfonic acid can be suitably used. Note that (h) when the sulfonic acid group of the sulfonic acid catalyst is blocked, the blocking agent blocking the sulfonic acid group is dissociated by heating or the like to regenerate the free sulfonic acid group.

  (H) The content of the sulfonic acid catalyst with respect to 100 parts by mass of the entire resin component is more than 0.01 parts by mass, and the lower limit of the content is preferably 0.1 parts by mass. On the other hand, the upper limit of the content is 2 parts by mass, preferably 1 part by mass. When the content is smaller than the lower limit, the effect of promoting the crosslinking of the melamine resin is insufficient, and it is difficult to obtain the effect of improving the hardness of the coating film. On the other hand, when the content exceeds the above upper limit, crosslinking proceeds excessively, and it may be difficult to obtain functions such as chipping resistance of the coating film.

  (C) As a minimum of mass ratio of content of (h) sulfonic acid system catalyst to melamine resin, 0.001 is preferred, 0.005 is more preferred, and 0.01 is still more preferred. On the other hand, the upper limit of the mass ratio is preferably 0.2, more preferably 0.1, and even more preferably 0.05. When the mass ratio is less than the lower limit, the crosslinking promotion effect of the melamine resin is insufficient, and it is difficult to obtain the hardness and appearance improving action of the coating film. On the other hand, if the mass ratio exceeds the upper limit, crosslinking may proceed excessively and it may be difficult to obtain functions such as chipping resistance of the coating film.

<Other optional components>
Examples of other optional components include resin components other than the components (a) to (e), pigments other than the component (f), phosphoric acid catalysts, and anti-settling agents.

  Examples of the other resin components include (a) polyols other than polycaprolactone triol, polymers such as acrylic resins, and the like.

  Examples of other pigments include inorganic pigments such as titanium white, carbon black, and iron oxide; various organic pigments; extender pigments such as precipitated barium sulfate. The lower limit of the pigment mass concentration for other pigments is preferably 20% by mass, and more preferably 30% by mass. On the other hand, the upper limit of the pigment mass concentration is preferably 70% by mass, and more preferably 60% by mass. By setting the pigment mass concentration of other pigments in the above range, the strength and weather resistance of the intermediate coating layer can be improved and chipping resistance can be promoted.

  The phosphoric acid catalyst is a compound having a phosphoric acid group. The phosphoric acid catalyst suppresses the generation of wrinkles in the coating film by suppressing the dissociation of the blocking agent of the blocked isocyanate.

  Examples of the phosphoric acid catalyst include 2-ethylhexyl acid phosphate, mono- or di-isodecyl acid phosphate, mono- or di-tridecyl acid phosphate, mono- or di-lauryl acid phosphate, mono- or di-nonylphenyl Examples thereof include alkyl phosphates such as acid phosphate, polymers having a phosphate group, and the like.

  As a minimum of content with respect to 100 mass parts of said resin components whole of a phosphoric acid system catalyst, 0.01 mass part is preferred and 0.1 mass part is more preferred. On the other hand, the upper limit of the content is preferably 2 parts by mass and more preferably 1 part by mass. If the content is less than the lower limit, the effect of inhibiting the dissociation of the blocking agent of the blocked isocyanate may be insufficient, and the appearance improving effect of the coating film may be difficult to obtain. On the other hand, if the content exceeds the upper limit, dissociation of the blocking agent of the blocked isocyanate is excessively suppressed, and it may be difficult to obtain functions such as chipping resistance of the coating film.

  Examples of the anti-settling agent include known anti-settling agents such as polyethylene and polyamide.

  The intermediate coating composition may be used as either a water-based paint or an organic solvent-based paint. When the intermediate coating composition is used as an organic solvent-based coating, the organic solvent includes aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as mineral spirits; esters such as ethyl acetate and butyl acetate; methyl ethyl ketone and the like 1 type, or 2 or more types of organic solvents, such as these ketones, can be contained.

<Multilayer coating film>
The multilayer coating film of one embodiment of the present invention is laminated on a material to be coated constituting a vehicle outer plate. The multilayer coating film includes an electrodeposition coating film laminated on the surface of the material to be coated, an intermediate coating layer directly laminated on the surface of the electrodeposition coating film, and a top coating layer laminated on the surface of the intermediate coating layer. The multilayer coating film can be applied to other vehicle skins such as motorcycles, forklifts, heavy machinery, automobile parts, etc. that require chipping resistance, in addition to vehicle skins of automobiles.

(Electrodeposition coating)
The electrodeposition coating film mainly ensures corrosion resistance. What is necessary is just to select the composition of this electrodeposition coating film etc. according to the characteristic etc. which are requested | required of a vehicle outer plate | board.

(Inner coating layer)
The intermediate coating layer mainly ensures smoothness and chipping resistance, and is obtained by curing the intermediate coating composition. That is, the intermediate coating layer is a polyurethane derived from (a) polycaprolactone triol, (b) pyrazole block isocyanate, (c) melamine resin, (d) polyester, (e) epoxy resin, and (a) to (d) components. , (F) talc, (g) a urethane curing catalyst, and (h) a sulfonic acid-based catalyst. In addition, the intermediate coating layer may contain a color pigment in order to exhibit design properties in combination with the top coating layer.

(Overcoat layer)
The topcoat layer ensures smoothness and corrosion resistance, and if necessary, gives a colorful pattern and gives a visual effect such as an optical effect.

  The overcoat layer may be formed as a single layer or a plurality of layers. What is necessary is just to select the number of layers of a top coat layer according to the use etc. of a coating board. For example, in the case of a vehicle outer plate of an automobile, the number of overcoat layers is generally one or two.

  According to such a multilayer coating film, since the intermediate coating layer is formed using the intermediate coating composition, chipping resistance and appearance can be ensured without applying a chipping resistant primer. The intermediate coating layer has a high single film hardness and is easy to polish.

<Formation method of multilayer coating film>
The method for forming a multi-layer coating film according to an embodiment of the present invention is used to form a vehicle outer plate of an automobile, other vehicle outer plates such as a motorcycle, a forklift, and a heavy machine that require chipping resistance, an automobile part, and the like. Applicable. Hereinafter, a method for forming a multilayer coating film constituting a vehicle outer plate of an automobile will be described as an example. However, the formation method of the said multilayer coating film is not limited to the method demonstrated below.

  The method for forming a multilayer coating film of the present invention includes an electrodeposition coating film forming step, an intermediate coating layer forming step, and a top coating layer forming step.

[Electrodeposition coating process]
In the electrodeposition coating film forming step, the electrodeposition coating film is formed by baking after performing a known electrodeposition coating.

(Electrodeposition coating)
Electrodeposition coating is a method in which a material to be coated is immersed in an electrodeposition coating material and a resin component having a charge is deposited on the material to be coated by energizing the material.

  There is no restriction | limiting in particular as a to-be-coated material, What is necessary is just to select according to the use etc. of a coating board. For example, when the painted plate is a vehicle outer plate of an automobile, the coated material is, for example, a steel plate, a zinc plate or the like subjected to a plating treatment or a chemical conversion treatment. As a coating material for a vehicle outer plate of an automobile, a material subjected to chemical conversion treatment after plating treatment is preferable. Examples of the chemical conversion treatment include a method using an iron phosphate / zinc-based chemical conversion agent. Examples of the plating treatment include galvanization treatment.

  The electrodeposition paint is a water-soluble paint or water-dispersed paint in which a resin component is dissolved or dispersed in water. When the resin component is an acidic resin, this electrodeposition paint can be prepared by neutralizing with a base such as ammonia, amine, inorganic alkali, etc. and dissolving or dispersing it in water. On the other hand, when the resin component is a basic resin, the electrodeposition paint can be prepared by neutralizing with an acid such as acetic acid, lactic acid, boric acid or phosphoric acid and dissolving or dispersing in water.

  As the electrodeposition paint, either an anionic resin-based paint or a cationic resin-based paint can be used, but a cationic resin-based paint is preferable from the viewpoint of corrosion resistance.

  The resin component of the electrodeposition paint includes, for example, drying oil, liquid rubber resin such as polybutadiene, maleated oil resin, maleated polybutadiene, amine epoxidized polybutadiene; fatty acid polyester of resinous polyol, or modified derivatives thereof (for example, epoxidation) Body, esterified body); alkyd resin; acrylic resin and the like.

  Common additives such as melamine resins, blocked isocyanates such as blocked isocyanates, pigments and solvents can be appropriately blended in the electrodeposition paint.

  The conditions for the electrodeposition coating are preferably set so that the film thickness of the electrodeposition coating film after baking, which will be described later, is 10 μm or more and 40 μm or less. Usually, the applied voltage is 200 V or more and 300 V or less, and the application time is 90 seconds or more. 300 seconds or less. Of course, the conditions for electrodeposition coating may be appropriately set according to the type of electrodeposition paint used, the target film thickness of the deposited film, and the like. The “film thickness” is a value measured according to JIS-K5600-1-7: 1999 (“Paint General Test Method—Part 1: General Rules—Section 7: Film Thickness”). The same applies to the case of “film thickness” below.

(Bake)
Baking after electrodeposition coating is sufficient if the resin component of the electrodeposition paint can be fixed to the material to be coated, and may be performed according to a conventional method. For example, the baking temperature is 150 to 200 ° C., and the baking time is 5 to 60 minutes.

[Intercoat layer forming step]
In the intermediate coating layer forming step, the intermediate coating is directly applied to the surface of the electrodeposition coating film and cured by baking as necessary to form an intermediate coating layer.

  The intermediate coating composition described above is used as the intermediate coating. That is, the intermediate coating is composed of (a) polycaprolactone triol, (b) pyrazole block isocyanate, (c) melamine resin, (d) polyester, (e) epoxy resin, (f) talc, (g) urethane curing catalyst, and (H) Contains a sulfonic acid catalyst. This intermediate coating may be used as it is, or may be used after diluting with a solvent.

  The application of the intermediate coating is usually performed such that the thickness of the intermediate coating after drying is 5 μm or more and 60 μm or less. Such an intermediate coating can be applied using a known applicator such as an atomizing coater. Examples of the atomizing coating machine include an air spray coating machine, an airless spray coating machine, an air atomizing electrostatic coating machine, and a rotary electrostatic coating machine.

  Baking after application of the intermediate coating may be performed according to a conventional method. For example, the baking temperature is 130 ° C. to 160 ° C., and the baking time is 10 minutes to 60 minutes. Further, baking in the intermediate coating layer forming step may be omitted, and a top coating described later may be applied onto the intermediate coating by a wet on wet method.

[Overcoat layer forming step]
In the topcoat layer forming step, the topcoat layer is formed by baking after applying the topcoat paint on the intermediate coat layer (or intermediate coat paint).

  In the case of forming the topcoat layer as a single layer consisting of only the base layer in the topcoat layer forming step, baking is performed after the topcoat paint is applied.

  As the top coat in this case, a known top coat solid paint, for example, a paint containing a resin component such as acrylic resin, polyester or fluororesin, a color pigment or the like can be used. The film thickness after baking of the single-layer topcoat layer is usually 2 μm or more and 60 μm or less.

  When the top coat layer is formed in two layers, the clear paint is applied by a wet-on-wet method after the solid paint is applied, and the solid paint and the clear paint are baked at the same time.

  When baking is not performed in the intermediate coating layer forming step, the intermediate coating is also baked simultaneously by baking in the top coating layer forming step. For example, the baking temperature is 130 ° C. to 160 ° C., and the baking time is 10 minutes to 60 minutes.

  According to such a method for forming a multilayer coating film, the intermediate coating layer is formed using the intermediate coating composition, and therefore, it is possible to ensure chipping resistance and appearance without applying a chipping primer. A layer coating can be formed. The intermediate coating layer has a high single film hardness and is easy to polish.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

<Preparation of intermediate coating composition>
Each component used for preparation of the intermediate coating composition of an Example and a comparative example is shown below.

[(A) component]
Polycaprolactone triol: Daicel's “Placcel L320AL”

[Component (b)]
Block Isocyanate A: Sumika Bayer “Sumijour BL3175” (isocyanurate type blocked isocyanate whose blocking agent is methyl ethyl ketone oxime)
Block isocyanate B: “DESMODUR PL350” from Bayer (isocyanurate type blocked isocyanate in which the blocking agent is pyrazole)
Blocked isocyanate C: “Trixene BI7960” (a burette type blocked isocyanate in which the blocking agent is pyrazole) manufactured by Baxenden Chemicals

[Component (c)]
Melamine resin A: "Resimene CE1058" from INEOS Melamines
Melamine resin B: "Uban 20N-60" by Mitsui Chemicals
Melamine resin C: “Cymel 325” from Nippon Cytec Industries
Melamine resin D: “Cymel 370” from Nippon Cytec Industries
Melamine resin E: “Cymel 254” from Nippon Cytec Industries
Melamine resin F: "Cymel 327" from Nippon Cytec Industries

[Component (d)]
Polyester A: Nippon Paint Co., Ltd. “PRS-1015”
Polyester B: Nippon Paint Co., Ltd. “PRS-1040”

[(E) component]
Epoxy resin: Nippon Steel &Sumikin's “Epototo EP-O150”

[Component (f)]
Talc: “LMR-100” by Fuji Talc Industrial Co., Ltd.

[(G) component]
Urethane curing catalyst: “K-KAT348” from KING

[(H) component]
Sulfonic acid-based catalyst A: “NACURE 2500” (Amine Block pTSA) from King Industries
Sulfonic acid catalyst B: “NACURE5543” (amine block DDBSA) by King Industries

[Other pigment content]
Titanium white: “Titanium CR97” by Ishihara Sangyo Co., Ltd.
Carbon black: “Carbon MA-100” from Mitsubishi Chemical Corporation
Precipitated barium sulfate: “PS-07” manufactured by GUANGXI XIANZHOU LIANZHUANG CHEMICAL

[Other ingredients]
Phosphoric acid catalyst: “Bisolvex D2EHPA” by Lanxess Deutschland GmbH

[Examples 1 to 8 and Comparative Examples 1 to 21]
The components of the types and blends listed in Table 1 and Table 2 below were mixed and stirred to prepare intermediate coating compositions for Examples and Comparative Examples. In each table, the numerical value of the item “resin component” indicates the content (mass%) in the entire resin solid content, the numerical value of the item “pigment content” indicates the pigment mass concentration (mass%), The numerical value of the item “others” indicates the content (parts by mass) relative to 100 parts by mass of the entire resin solid content.

<Formation of multilayer coating film>
Using the intermediate coating composition of the above-mentioned Examples and Comparative Examples, a multilayer coating film was formed by the following method.

  A GA steel plate (alloyed hot-dip galvanized steel plate) was electrodeposited with a cationic electrodeposition coating composition (“Power Nix 1010” from Nippon Paint Co., Ltd.) so that the film thickness of the dried coating film was 15 μm. After heating for 20 minutes and cooling, a cured electrodeposition coating film was formed.

  Next, the intermediate coating composition was applied onto the cured electrodeposition coating film at room temperature by air spray coating so that the film thickness became 35 μm, and then cured at 140 ° C. for 30 minutes. A base coating composition (“AQUAREX AR-2000” from Nippon Paint Co., Ltd.) as a top coating composition was applied onto the intermediate coating film by air spray coating so that the film thickness was 15 μm, and then at 80 ° C. Preheating was performed for 3 minutes. In addition, a clear coating composition (“MAC FLOW O-1830” from Nippon Paint Co., Ltd.) as a top coating composition is applied onto the coating film of the base coating composition by air spray coating so that the film thickness becomes 35 μm. Then, a test piece having a multilayer coating film was obtained by performing heat curing at 140 ° C. for 30 minutes.

  The intermediate coating composition, the base coating composition, and the clear coating composition were used for coating by diluting them to have a predetermined viscosity using the following dilution solvent.

(Intermediate coating composition)
Viscosity measured with a Ford Cup viscometer (No. 4 cup) using a mixed solvent having a volume ratio of 1: 1 between isobutyl acetate and aromatic hydrocarbon solvent (“S150” manufactured by Exxon) as a diluent solvent (20 (° C.) was 23 seconds.

(Top coating composition)
The base coating composition was diluted with ion-exchanged water as a diluent solvent so that the viscosity (20 ° C.) measured with a Ford Cup viscometer (No. 4 cup) was 45 seconds. The clear coating composition uses a mixed solvent having a volume ratio of 1: 1 between EEP (ethoxyethyl propionate) and an aromatic hydrocarbon solvent (“S150” manufactured by Exxon) as a diluent solvent. It diluted so that the viscosity (20 degreeC) measured by (No.4 cup) might be set to 28 seconds.

<Evaluation>
The intermediate coating compositions of Examples and Comparative Examples, and test pieces on which intermediate coating films and multilayer coating films were formed using these intermediate coating compositions were evaluated by the following methods. The evaluation results are shown in Table 1 and Table 2.

[Intercoat film hardness]
The hardness (pencil scratch hardness) of the obtained intermediate coating film was measured according to JIS-K-5600-5-4 (1999) and evaluated according to the following criteria.
A: F
B: HB
C: B
D: 2B or less

[Appearance of intermediate coating film]
The appearance of the thick film portion of the obtained intermediate coating film was visually evaluated according to the following criteria.
A: No wrinkles E: Wrinkles

[Chip resistance]
Using a gravel tester tester (Suga Test Instruments Co., Ltd.), 300 g of No. 6 crushed stone was applied to the coating plate of the test piece with a pneumatic pressure of 5 kgf / cm ² from a distance of 35 cm to a coated plate previously cooled to −20 ° C. Collided at an angle of °. After washing with water and drying, the peeled film piece was removed using an industrial gum tape (Nichiban Co., Ltd.), and then the degree of peeling of the paint film was visually observed. The chipping resistance was evaluated according to the following evaluation criteria depending on the peeling state of the coating film and the galvanized layer.
(Coating peeling)
A: Excellent (no peeling of coating film)
B: Good (slight peeling of coating film is observed)
C: Slightly poor (exfoliation of the coating film of 1 mmφ or less is seen occasionally)
D: Defect (the peeling of the paint film is conspicuous)
(Zinc plating layer peeling)
A: No peeling E: There is peeling

[Appearance of multilayer coating]
The appearance of the obtained multilayer coating film was evaluated by visual observation of the coating film surface according to the following criteria.
A: Excellent B: Good C: Yes

  From the results of Table 1 and Table 2, the intermediate coating layer of Examples 1-8 is used for the intermediate coating layer, so that the single coating hardness of the intermediate coating layer is as high as HB or higher and a chipping resistant primer is used. It was shown that a multilayer coating film excellent in chipping resistance and appearance can be formed.

  According to the intermediate coating composition and the method for forming a multilayer coating film of the present invention, the multilayer coating film has a high single film hardness and excellent chipping resistance and appearance without using a chipping primer. A film can be formed. This multilayer coating film can be suitably used for external coating of automobiles, motorcycles, automobile parts, forklifts, heavy machinery and the like.

Claims (3)

An intermediate coating composition used for forming an intermediate coating layer directly laminated on the surface of an electrodeposition coating film constituting a vehicle outer plate,
As the resin component, (a) polycaprolactone triol having a content of 0.1% by mass to 5% by mass in the entire resin component, and (b) pyrazole-blocked isocyanate having the content of 20% by mass to 30% by mass. (C) melamine resin having a content of 1% by mass to 20% by mass, (d) polyester having a content of 40% by mass to 70% by mass, and a content of more than 0% by mass to 10% by mass. % Or less of (e) an epoxy resin,
As a pigment content, (f) talc having a pigment mass concentration of 1% by mass or more and 10% by mass or less,
(G) Urethane curing catalyst of more than 0.01 parts by mass and 2 parts by mass or less with respect to 100 parts by mass of the whole resin component, and more than 0.01 parts by mass of 2 parts by mass or less with respect to 100 parts by mass of the whole resin component. (H) An intermediate coating composition comprising a sulfonic acid catalyst. A multilayer coating film comprising an electrodeposition coating film constituting a vehicle outer plate, an intermediate coating layer directly laminated on the surface of the electrodeposition coating film, and a top coating layer laminated on the surface of the intermediate coating layer,
A multilayer coating film, wherein the intermediate coating layer is obtained by curing the intermediate coating composition according to claim 1. A multilayer comprising a step of forming an electrodeposition coating film constituting a vehicle outer plate, a step of directly forming an intermediate coating layer on the surface of the electrodeposition coating layer, and a step of forming a top coating layer on the surface of the intermediate coating layer A method for forming a coating film, comprising:
A method for forming a multilayer coating film, wherein the intermediate coating composition according to claim 1 is applied in the intermediate coating layer forming step.