JP3171817B2 - Chipping resistant coating method and composition thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anti-chipping coating method for a lower part of a floor of an automobile body, a rocker panel, or a lower structure such as a wheel house (tire house). The present invention relates to a chipping-resistant coating method for forming a film and a composition thereof.

[0002]

2. Description of the Related Art A lower structure portion of an automobile body, that is, a lower portion of a floor, a rocker panel, a wheel house, and the like are provided with:
In order to ensure chipping resistance and rust prevention, chipping-resistant coating, that is, undercoat coating is applied.

[0003] Conventionally, as a chipping-resistant coating composition for this chipping-resistant coating, it is possible to form a thick film having a relatively high elasticity and to have excellent rust prevention properties. A vinyl chloride-based plastisol composition is generally used. This plastisol composition comprises:
The main agent is a vinyl chloride resin consisting of a homopolymer of vinyl chloride or a copolymer with vinyl acetate, etc., and a plasticizer, a filler such as calcium carbonate and the like, and the adhesion (adhesion) of the coating film is improved. For the purpose of the present invention. As the adhesion-imparting agent, since these plastisol compositions are generally applied after undercoating by electrodeposition coating, polyamides exhibiting excellent adhesion to cationic electrodeposition coating films are particularly preferred. Alternatively, blocked isocyanates are commonly used. And regarding this kind of composition, for example, Japanese Patent Publication No. 1-251515
Japanese Patent Application Laid-Open Publication No. Hei 4 (Use of a blocked isocyanate blocked with a special blocking agent as an adhesion-imparting agent)
JP-A-161443 (prevention of cracks during baking of intermediate coat or top coat coated on the coat),
No. 6891 (Improvement of resistance to moisture absorption and foaming by calcium oxide) and the like are disclosed in various modes or modifications.

[0004] The coating composition for chipping resistance is generally applied to the undercarriage of the vehicle body after the undercoating by electrodeposition and prior to the intermediate coating of the outer body of the vehicle body. Generally, curing of the coating composition for chipping is not performed independently. That is, the chipping-resistant coating of the lower body structure portion including the step of applying the chipping-resistant coating composition, after applying the chipping-resistant composition, applying an intermediate coating to the vehicle body outer panel, and applying the intermediate coating. This is performed by heat curing the coating composition for chipping resistance in combination with baking and drying. The baking and drying of the intermediate coating is generally performed at a relatively low temperature of 120 to 140 ° C.

In recent years, such chipping-resistant coating has been applied to wheel houses and the like in order to reduce stone splashing noise caused by pebbles and the like splashed from the road surface hitting the lower structure of the vehicle body. In such a case, it is required that the formed coating film be excellent not only in chipping resistance and adhesion, but also in soundproofing.

[0006] Regarding such a method for enhancing soundproofing properties, for example, Japanese Patent Application Laid-Open Nos. 64-29472 and 2-202560 disclose azodicarbonamide (ADCA) or the like in a chipping-resistant coating composition. Is disclosed.

In the above-mentioned vinyl chloride-based plastisol composition used as the chipping-resistant coating composition, the plasticizer is an average value of all properties such as solubility, paintability and storage stability. The most commonly used is dioctyl phthalate (DOP).

[0008]

As described above, the method for anti-chipping coating of the lower structure portion of an automobile body is to apply a coating composition for chipping resistance to the lower structure portion, and then to apply the chipping-resistant coating composition to the lower body portion. This is generally done by heating and curing together with baking and drying of the intermediate coating. Here, as the coating composition for chipping resistance, a vinyl chloride-based plastisol composition containing a vinyl chloride-based resin and a plasticizer as main components and containing a filler, an adhesion-imparting agent, and the like is generally used.

Then, it has been proposed to mix a foaming agent such as ADCA with the coating composition for chipping resistance comprising such a vinyl chloride-based plastisol composition in order to enhance the soundproofness of the coating film. According to this, the foaming agent foams at the time of heat curing, and the coating film is formed as a foam, so that the soundproofing is effectively improved.

However, the chipping-resistant coating composition containing such a foaming agent is applied to the lower structure of an automobile body, and then heat-cured together with the subsequent baking and drying of the intermediate coating of the body outer panel. As a result, when a foamed chipping-resistant coating film is formed, large open cells are frequently generated, and a plurality of bubbles (cells) are connected to the coating film surface to cause swelling (cell roughening). Occurred.

[0011] Such swelling or the like occurring in the chipping-resistant coating film is not preferable because the appearance of the coating surface is significantly impaired and the coating film is easily broken by stone splashing or the like.

Accordingly, the present invention provides a chipping-resistant coating method and a composition thereof capable of forming a chipping-resistant coating film comprising a foam in which fine bubbles are uniformly dispersed without causing swelling or the like on the coating film surface. The purpose is to provide

[0013]

Means for Solving the Problems The inventors of the present invention have repeatedly studied by paying attention to the viscosity of a coating film during heat curing. As a result, the chipping coating of the lower structure of the automobile body is heated by applying the coating composition for chipping resistance to the lower structure, and then baking and drying the intermediate coating of the outer body of the vehicle body. Although the curing is performed, the temperature at the time of baking and drying of the intermediate coating is generally 120 to 140 ° C., and at such a low temperature, a composition for chipping resistance comprising a conventional general vinyl chloride plastisol composition is used. The material does not reach the molten state, and the curing stops in the gelation process.In this gelation process, the vinyl chloride resin and the plasticizer are not in a completely uniform phase. When the foaming agent foamed, it was found that the generated gas volatilized from the low-viscosity portion of the coating film or was focused on the low-viscosity portion, resulting in large open cells and swelling of the coating film surface. Therefore, the gelation of the plastisol composition is promoted to a molten state, and the viscosity of the coating film at the time of foaming of the foaming agent, that is, the viscosity under heating at the time of heating and curing is set to a certain value or more. We have found and confirmed that the above problems can be effectively solved.

That is, in the chipping-resistant coating method according to the first aspect, a chipping-resistant coating composition comprising a foamable vinyl chloride-based plastisol composition is applied to a lower structure portion of an automobile body, and then is applied. In a method for chipping-resistant coating of a lower structural part of an automobile body, which is formed by forming a foamed chipping-resistant coating film by heating and hardening in combination with baking and drying of a finish coating of a vehicle body outer plate portion, the coating for chipping resistance is provided. The composition contains a vinyl chloride-based resin, a plasticizer, a filler, an adhesiveness-imparting agent, and a foaming agent, and is heated to the temperature of baking and drying of the finish coating with the foaming agent removed. Wherein the viscosity at the time of the application is 0.15 or more in logarithmic decrement λ.

[0015] The chipping-resistant coating composition according to claim 2 comprises a vinyl chloride resin, a plasticizer, a filler, an adhesion-imparting agent, and a foaming agent. The viscosity when heated to the temperature at the time of bake hardening in a state excluding it is 0.15 or more in logarithmic decrement λ.

As described above, in the chipping-resistant coating method according to the first aspect, the chipping-resistant coating composition contains a foaming agent, and is heated to the temperature of baking and drying of the finish coating in a state where the foaming agent is removed. Since the viscosity at the time of application is 0.15 or more in logarithmic decrement λ, it is applied to the lower structure of the vehicle body, and is heat-cured together with baking and drying of finish coating such as intermediate coating of the vehicle body outer panel. In this case, gas generated by foaming of the foaming agent in the coating film is satisfactorily captured without volatilizing from the coating film to form uniform fine bubbles. Therefore, a chipping-resistant coating film made of a foam in which fine bubbles are uniformly dispersed can be formed without causing swelling or the like on the coating film surface.

Further, in the chipping-resistant coating composition according to the second aspect, the foaming agent contains a foaming agent, and the viscosity when heated to the temperature at the time of baking hardening in a state where the foaming agent is removed, has a logarithmic decay rate. Since λ is 0.15 or more, when this is applied to the lower structure of the vehicle body and then heat-cured together with the subsequent baking and drying of the finish coating of the vehicle body outer plate, Similarly, gas generated by foaming of the foaming agent in the coating film is satisfactorily captured without volatilizing from the coating film to form uniform fine bubbles. Therefore, a chipping-resistant coating film made of a foam in which fine bubbles are uniformly dispersed can be formed without causing swelling or the like on the coating film surface.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a chipping-resistant coating method and a composition therefor according to the present invention will be described in more detail.

<Vinyl chloride resin> As the vinyl chloride resin, a homopolymer or copolymer of vinyl chloride, that is, a copolymer of vinyl chloride and another vinyl monomer can be used.

Examples of the vinyl monomer include vinyl esters such as vinyl acetate, vinyl propionate and vinyl stearate; vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; and maleic esters such as diethyl maleate. Fumaric acid esters such as dibutyl fumarate; alkyl or methacrylic acid alkyl esters such as methyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate; 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate Hydroxyalkyl esters of acrylic acid or methacrylic acid, such as N-methylol acrylamide, N-methylol methacrylamide,
Examples thereof include hydroxyalkylamides of acrylic acid or methacrylic acid such as N-hydroxyethylacrylamide and N-dihydroxyethylmethacrylamide, acrylonitrile, vinylidene chloride and the like. Any one or more of these can be used, and they can be copolymerized with vinyl chloride at a ratio of generally 30% by weight or less, preferably 20% by weight or less. However, among these, vinyl acetate is the most common and preferred monomer to be copolymerized with vinyl chloride.

<Plasticizer> As the plasticizer for plasticizing the above-mentioned vinyl chloride resin, basically, any plasticizer generally used for forming this kind of plastisol composition is used. can do. Examples of such a plasticizer include plasticizers such as phthalate esters such as dioctyl phthalate (DOP), aromatic and aliphatic di- and tricarboxylic acid esters, phosphate esters, and epoxy resins. However, the coating composition for chipping resistance comprising the vinyl chloride-based plastisol composition can be obtained at the temperature of baking and drying such as intermediate coating of the outer panel of an automobile body, that is, at a relatively low temperature of 120 to 140 ° C. Since it is heat-cured, in order to obtain a predetermined viscosity necessary for properly capturing gas generated by decomposition of the foaming agent in the coating film at that temperature, a plasticizer that dissolves at such a low temperature ( Low-temperature plasticizers) are preferred.

Here, the solubility of the plasticizer is considered to be substantially proportional to its surface tension, but the low-temperature melting plasticizer used here preferably has a surface tension of 39 dyn / cm 2 or more. As such a plasticizer, for example, butylbenzyl phthalate (BB)
P), alkylbenzyl phthalate such as octylbenzyl phthalate (OBP), diisobutyl phthalate (D
IBP) or dimethylcyclohexyl phthalate (DMCHP). However, since these plasticizers having excellent solubility are inferior in storage stability, from the viewpoint of storage stability, they have good storage stability, and DOP which is the most common general-purpose plasticizer as a plasticizer. And at least one of these low melt plasticizers, with 1.0:
It is preferable to use them together in a ratio (weight ratio) of 3.0 to 1.0: 1.0.

[0023] Such a plasticizer is used to soften the cured coating film in order to reduce the impact due to stone splashing and the like, and to make the coating film sufficiently foam, so that the plasticizer is used in the vinyl chloride resin. Generally, it is preferable to use it in a weight ratio higher than that, preferably in a ratio of 1.5 to 4.0 times (weight ratio), and more preferably in a ratio of 2.0 to 3.0 times. It is most preferable to mix them.

Incidentally, a part of the plasticizer can be replaced with an organic solvent as a viscosity reducing agent, whereby the leveling property of the coated film after coating can be enhanced and the appearance thereof can be further improved. . As such an organic solvent, a solvent having a relatively high boiling point, such as a petroleum solvent such as naphtha, turpentine oil or mineral spirit, or an aromatic solvent, is preferable.

<Filler> A filler is blended to increase the amount of the plastisol composition.

Examples of such a filler include carbonates and sulfates of alkaline earth metals such as calcium carbonate, magnesium carbonate and barium sulfate, mica, silica, talc, diatomaceous earth, kaolin and the like. Is
They can be used alone or in appropriate combinations.
These fillers can be used and compounded generally at a ratio of 70 to 200 parts by weight based on 100 parts by weight of the vinyl chloride resin.

This filler can be partially replaced with a sagging agent consisting of inorganic fine particles, thereby improving the thixotropy of the composition, increasing the viscosity at low shear rates, The sagging resistance of the coating film can be further improved. As the anti-sagging agent also serving as such a filler, fine particle silica, ultrafine particle calcium carbonate (colloidal calcium carbonate) and the like can be suitably used,
It can generally be used in a proportion of from 0.1 to 70% by weight, based on the total composition.

<Adhesiveness-imparting agent> Further, in the coating composition for chipping resistance comprising the vinyl chloride-based plastisol composition, as an adhesiveness-imparting agent for improving the adhesion (adhesion) of the coating film, In particular, it is preferable to use a polyamide in combination with a blocked isocyanate exhibiting excellent adhesion to a cationic electrodeposition coating surface.

Here, the blocked isocyanate is generally used also as a curing agent for paint, and is obtained by blocking a relatively low molecular weight polyisocyanate component with a blocking agent such as methyl ethyl ketone oxime (MEKO). Examples of the polyisocyanate component include aliphatic diisocyanates such as hexamethylene diisocyanate (HDI), aromatic diisocyanates such as tolylene diisocyanate (TDI), alicyclic diisocyanates such as isophorone diisocyanate, hydrogenated TDI, and the like. Biuret of diisocyanate, isocyanurate, ethylene glycol, adduct with polyhydric alcohol such as trimethylolpropane,
Alternatively, a urethane prepolymer or the like may be used. But,
Among these, a block urethane prepolymer obtained by blocking the urethane prepolymer can generally be most suitably used as the adhesion imparting agent.

The polyamide as an adhesion-imparting agent is a polyamide compound containing an active amino group which is generally used also as a curing agent for an epoxy resin or the like, and is generally an aliphatic diamine such as hexamethylenediamine or an aromatic diamine. It is obtained by reacting a polyamine such as an aromatic diamine with a polybasic acid. In addition, as this kind of adhesion imparting agent, any amino compound having active hydrogen may be used, and aliphatic diamines and the like can be used.However, since these are volatile and toxic, the polyamide is used here. used. Typical examples of such a polyamide include a reaction product of a polyamine with a polymerized fatty acid such as dimer acid or trimer acid obtained by thermally polymerizing an unsaturated fatty acid such as linoleic acid.

According to the combination system of these blocked isocyanate and polyamide, the blocking agent of the blocked isocyanate is dissociated at the temperature during heating and baking, and the isocyanate group of the regenerated isocyanate component is coated with the cationic electrodeposition coating. By bonding to the active hydrogen remaining in the film, the adhesion of the coating film of the plastisol composition thereto is improved. In addition, the polyamide promotes the dissociation of the blocked isocyanate to improve the adhesiveness at the time of low-temperature baking, and the active amino group and the amide bond contained therein are polar groups (amino group) of the cationic electrodeposition coating film. , A carboxyl group, a hydroxyl group, etc.) to exhibit excellent adhesiveness. Further, according to the combination system of these blocked isocyanate and polyamide, the viscosity of the coating film of the plastisol composition is increased by the reaction between the isocyanate component regenerated at the time of heat curing and the amine.

Therefore, the adhesion-imparting agent comprising a combination system of these blocked isocyanate and polyamide is
In addition to providing excellent adhesion to the coating film, it also increases the viscosity of the coating film during heating and curing, and allows the gas generated by the decomposition of the foaming agent to be well trapped in the coating film, and has the function of effectively foaming the coating film. are doing.

<Blowing agent> As the blowing agent, a blowing agent which generates a gas by causing a chemical reaction by heat (decomposition type blowing agent)
Use Examples of such a foaming agent include azo compounds such as azodicarbonamide (ADCA), azobisisobutyronitrile (AIBN), and diazoaminobenzene.
N, N-dinitrosopentamethylenetetramine (DP
T), nitroso compounds such as N, N'-dinitrosoterephthalamide, p-toluenesulfonyl hydrazide (TS
H), benzenesulfonyl hydrazide, sulfonyl hydrazide compounds such as p, p'-oxybis (benzenesulfonyl hydrazide), sodium bicarbonate, ammonium carbonate, etc., and a coating for chipping resistance comprising the vinyl chloride-based plastisol composition. Since the composition is heat-cured at the temperature of baking and drying such as intermediate coating of the outer panel of an automobile body, a foaming agent that foams at the temperature of baking and drying such as intermediate coating is appropriately selected and blended. Can be.

These foaming agents can be used in combination with salicylic acid, phthalic acid, stearic acid, uralylic acid, benzoic acid, boric acid, urea, zinc and compounds thereof as a foaming aid, if necessary.

<Others> In addition to the above-mentioned components, a water absorbent, a stabilizer, a leveling agent, a pigment,
Other additives can be appropriately added and blended.

The water absorbing agent is used for capturing moisture adsorbed by calcium carbonate or the like, preventing swelling of the coating film during curing, and improving the moisture absorption and foaming resistance of the coating film. Powders such as magnesium oxide can be suitably used.

Examples of the stabilizer include an epoxy stabilizer, metal soaps, inorganic acid salts, and organometallic compounds. Of these, organotin compounds such as dibutyltin dilaurate, tribasic lead sulfate, and the like are typical, and can be used most commonly. Also,
The leveling agent is appropriately used to further improve the leveling property (smoothing property) of the coating film.
Alternatively, a high-viscosity or low-viscosity dimer acid-modified epoxy resin or the like can be used. However, if too much is added, the sagging resistance deteriorates. Therefore, when this is used, it is preferable that the addition amount be the minimum limit. As the pigment, any pigment can be appropriately used, and a coloring pigment which also functions as an extender such as titanium oxide or carbon black can be particularly preferably used. Further, other additives include a thickener such as organic bentonite and the like, which can be used if necessary.

<Adjustment of Viscosity> By the way, in the coating composition for chipping resistance containing such a foaming agent, the viscosity at the time of heat curing is not only the expansion ratio, but also the internal foaming state of the coating film and the surface condition of the coating film. (Finished appearance).
And since the composition for chipping resistance used in the chipping-resistant coating method of the present invention is heat-cured together with baking and drying of the finish coating such as the intermediate coating of the vehicle body outer panel, the foaming agent is removed. That is, in the state of a composition (plastisol composition base) composed of the above-mentioned components other than the foaming agent, the viscosity when heated to the baking and drying temperature of the finish coating is 0.15 in logarithmic decrement λ. It is made to become above.
When this viscosity is low and the logarithmic decrement λ is lower than 0.15,
The gas generated by the foaming of the foaming agent breaks the coating film without forming bubbles and easily volatilizes to the outside, and the foaming ratio tends to decrease. In addition, multiple bubbles are easily connected, and large open cells frequently occur inside the coating film, and swell on the coating film surface (large air bubbles).
And the appearance tends to decrease.

On the other hand, this viscosity is preferably as high as possible in order to satisfactorily capture the gas generated by the foaming agent foaming in the coating film and to obtain a high expansion ratio with a small amount of the foaming agent. Generally, when the logarithmic decay rate λ is higher than 0.40, the effect of trapping the gas not only reaches a plateau,
Rather, storage stability tends to decrease. Therefore, in general, the logarithmic decrement λ is preferably 0.40 or less, more preferably 0.30 or less. Note that this logarithmic decrement λ is calculated using a pendulum type viscoelasticity
-OPA ”manufactured by Orientic Co., Ltd.
m can be measured on uncured coatings.

The viscosity can be adjusted mainly by adjusting the mixing ratio of the plasticizer, and further by adjusting the mixing ratio of the adhesion-imparting agent.

<Coating method> Then, the coating of the lower structural portion of the automobile body with the coating composition for chipping resistance is performed by first coating the lower structural portion of the vehicle body with the coating composition for chipping resistance, and then thereafter. It is performed by heating and hardening together with baking and drying of the finish coating of the vehicle body outer panel portion. Here, such a coating composition for chipping resistance can be applied in an arbitrary thickness and in an applied form by ordinary coating means such as airless spray coating. In addition, the coating of the coating composition for chipping resistance,
Generally, it can be applied after the undercoating by the electrodeposition coating, and therefore, the subsequent finish coating of the vehicle body outer panel can be an intermediate coating. Therefore, the heat curing is generally performed at a temperature of 120 to 140 ° C. for 20 minutes.
It takes about a minute.

[0042]

The present invention will be more specifically described below with reference to examples and comparative examples.

FIG. 1 is a table showing the composition of the chipping-resistant coating composition used in the chipping-resistant coating methods of Examples and Comparative Examples of the present invention, and the results of evaluation tests thereof. FIG. 2 shows Embodiments 1 and 3 of the present invention.
And the coating composition for chipping resistance used in the chipping-resistant coating method of Comparative Example 1, with the foaming agent removed,
It is a table | surface figure which shows the measurement result of the viscosity (logarithmic decay rate (lambda)) at the time of heating at 130 degreeC.

[Preparation of coating composition for chipping resistance] FIG.
The chipping-resistant coating compositions of Examples 1 to 4 were prepared with the composition (parts by weight) shown below. Further, for comparison with these, coating compositions for chipping resistance used in Comparative Examples 1 to 3 were also prepared.

As shown in FIG. 1, the coating compositions for chipping resistance used in these Examples and Comparative Examples consisted of a vinyl chloride-based plastisol composition mainly composed of a vinyl chloride-based resin and a plasticizer. Vinyl chloride resin, plasticizer,
It is composed of a filler, a sagging agent, an adhesion-imparting agent, a solvent, a moisture absorber, and a foaming agent.

Here, except for the plasticizer and the adhesion-imparting agent,
The types and blending ratios of components such as vinyl chloride resin are the same in each of the examples and comparative examples.

The vinyl chloride resin as a main component is a paste resin having a polymerization degree of 1900 (“PCH-12”), which is made of a vinyl chloride copolymer containing 8% by weight of vinyl acetate.
Z "(manufactured by Kaneka Chemical Industry Co., Ltd.), and 160 parts by weight were blended in each Example and Comparative Example.

As a filler, calcium carbonate (“Shirayuka CCR” manufactured by Shiraishi Kogyo Co., Ltd.) was used, and 300 parts by weight was added in each of Examples and Comparative Examples. Silica ("Aerosil 200" manufactured by Nippon Aerosil Co., Ltd.) was used as a sagging agent also serving as a filler, and its blending amount was 5 parts by weight.

The solvent used was a petroleum-based high-boiling solvent ("Shellsol D-70" manufactured by Shell Japan Co., Ltd./initial boiling point: 204 ° C.) consisting of a paraffin / naphthene mixture. Each part was blended.

As a water absorbent, calcium oxide ("CHL # 41" manufactured by Omi Chemical Co., Ltd.) was used, and the blending amount was 30 parts by weight in each of Examples and Comparative Examples.

Further, an azodicarbonamide (ADCA) type foaming agent having a decomposition temperature of 128 ° C. (“EXCELLA PC # 3” manufactured by Eiwa Chemical Co., Ltd.) was used as a foaming agent. , 30 parts by weight. The amount of gas generated from this blowing agent was 134 mg / g.

In Examples 1 to 4, as a plasticizer for the vinyl chloride resin, dioctyl phthalate (DOP) (MW = 390.000) usually used in this kind of coating composition for chipping resistance is used. 6) and dimethylcyclohexyl phthalate (D
MCHP) were used in different combinations.
However, the total amount of the plasticizer was 400 parts by weight. That is, in the first embodiment, DOP and DMCHP
Was used in a ratio of 3: 1 (weight ratio), 300 parts by weight of DOP and 100 parts by weight of DMCHP were blended. In Example 2, the combined ratio (weight ratio) of DOP and DMCHP was 1: 1.
And 200 parts by weight of each. In Example 3, the combined ratio (weight ratio) of DOP and DMCHP was 1: 3, DOP was 100 parts by weight, and DMCHP was 30.
0 parts by weight were blended. Further, in Example 4, DOP was not blended, and 400 parts by weight of DMCHP was blended.

In each of these examples, the adhesiveness-imparting agent was a combination system of polyamide and a blocked isocyanate. On the other hand, the polyamide as an adhesiveness-imparting agent component had an amine value of 150 mgKOH / g and a molecular weight of about 2,000. Polyamide amine is used, and as the blocked isocyanate as the other adhesiveness-imparting component, a blocked isocyanate having a urethane prepolymer as an isocyanate component and an effective isocyanate group content (effective NCO content) of about 10% by weight is used. And 20 parts by weight of each.

On the other hand, in Comparative Example 1, 400 parts by weight of DOP, which is commonly used in this kind of coating composition for chipping resistance, was used as a plasticizer. Also,
In Comparative Example 2, only polyamide was blended (30 parts by weight) as an adhesion-imparting agent, and in Comparative Example 3, only blocked isocyanate was blended (30 parts by weight). In Comparative Examples 2 and 3, 200 parts by weight of DOP and DMCHP were mixed as plasticizers in the same manner as in Example 2.

The preparation of each of the coating compositions for chipping resistance of Examples and Comparative Examples comprising these blended compositions was carried out by uniformly mixing the materials using a planetary mixer, and then mixing them.
Performed by vacuum degassing and stirring for 0 minutes.

[Chip-Resistant Coating Test] A chipping-resistant coating test was carried out using each of the above-described coating compositions for chipping resistance, and the foaming ratio and the like of the coating film at that time were evaluated.

In the test, a dull steel plate having an appropriate size was previously subjected to an epoxy-based cationic electrodeposition coating and then baked to prepare a test plate. Then, each of the coating compositions for chipping resistance of Examples and Comparative Examples was applied to the test plate in a film thickness of 2.00 mm, and then heated in the same manner as in the baking of a middle coat of a general vehicle body outer panel. By condition,
That is, heat curing was performed at 130 ° C. for 20 minutes.

<Expansion Ratio> The thickness of the cured coating film of the chipping resistant coating thus formed was measured and divided by the thickness before curing (2.00 mm) to calculate the expansion ratio.

<Appearance (Surface Condition)> The appearance test (surface condition) of the coating film of the chipping resistant coating was also evaluated separately.

That is, in the same manner as in the measurement of the expansion ratio, a test plate subjected to cationic electrodeposition was prepared, and the chipping-resistant coating compositions of Examples and Comparative Examples were added thereto with a thickness of 0 to 2 mm.
, And then cured at 130 ° C. for 20 minutes.

The surface condition of the thus formed anti-chipping coating film was visually observed, and the appearance of the film was evaluated by examining the presence or absence of blisters (irregularities) due to abnormal foaming.

<Internal Foaming State> Further, an evaluation test of the internal foaming state of the coating film of the chipping-resistant coating was separately performed. That is, in the same manner as in the evaluation test for appearance, a test plate subjected to cationic electrodeposition coating was prepared, and the coating compositions for chipping resistance of Examples and Comparative Examples were coated thereon with a coating film thickness of 0 to 2 mm. Then, each was tilt-coated, and then cured at 130 ° C. for 20 minutes.

The coating film of the chipping resistant coating thus formed was partially cut off using a cutter, and its cross section was visually observed to evaluate the internal foaming state.

The results of these evaluation tests are shown in FIG.

[Viscosity Test] Separately, each of the chipping-resistant coating compositions of the above Examples and Comparative Examples was heated to a temperature at the time of heat curing in the chipping-resistant coating in a state where the foaming agent was removed. The viscosity (logarithmic decrement λ) upon heating was measured.

First, in the composition of each of the above-described coating compositions for chipping resistance, components other than the foaming agent were uniformly mixed using a planetary mixer, followed by vacuum degassing and stirring for 60 minutes to obtain a non-foamable plastisol. A composition (plastisol composition base) was prepared. Then, using a pendulum-type viscoelasticity measuring device (“DDV-OPA” manufactured by Orientec), each plastisol composition base of the example and the comparative example applied to a film thickness of 200 μm was heated to 130 ° C. in 10 minutes. For an additional 20 minutes. The viscosity was evaluated by measuring the logarithmic decay rate λ 15 minutes after the start of the temperature rise. The logarithmic decrement λ is shown in FIG. FIG. 2 shows the time-dependent changes in the logarithmic decrement λ during the heat curing of the plastisol composition bases of Example 1, Example 3, and Comparative Example 1.

In this pendulum type viscoelasticity measuring apparatus, an uncured coating film of the composition is set on a sample stage equipped with a heating device.
A pendulum having a knife blade is placed on the uncured coating film, and the logarithmic decay rate λ is obtained from a change in vibration of the pendulum accompanying the curing during the baking process.

[Test Results] As shown in FIG. 1, in Examples 1 to 4, the coating composition for chipping resistance comprising a vinyl chloride-based plastisol composition was obtained by baking hardening with the foaming agent removed. The viscosity when heated to a temperature is 0.15 or more in logarithmic decrement λ. The formed coating film has a smooth surface and no abnormal open cells are observed inside. (Surface state) and internal foaming state show good results. Good values were also obtained for the expansion ratio. And D which is a plasticizer
Comparing these examples in which only the combined ratio of MCHP and DOP is different and the other compositional conditions are the same,
As the proportion of DMCHP increases, the logarithmic decay rate λ increases, and a higher expansion ratio is obtained. Therefore,
From the viewpoint of the expansion ratio, it can be seen that it is preferable to use DMCHP having excellent solubility. However, DMCHP
, A large amount tends to lower the storage stability. Therefore, from the viewpoint of the storage stability, in the composition of this example, DO
Example 2 in which P and DMCHP are used together in a ratio of 1: 1 (weight ratio) is the most preferable.

On the other hand, in Comparative Example 1 using only DOP as the plasticizer, the logarithmic decay rate λ was low and the viscosity was low. In addition to the low foaming ratio of the formed coating film, large open cells are frequently generated inside the coating film, and the surface of the coating film swells, and concavities and convexities are conspicuous, and appearance is obtained. Not been. Further, in Comparative Example 2 using only polyamide as an adhesion promoter and Comparative Example 3 using only blocked isocyanate,
In both cases, the logarithmic decay rate λ is low and the viscosity is low. Abnormal open cells were observed inside the formed coating film, and remarkable blisters were scattered on the surface.

From the results of these tests, it can be seen from the results of these tests that the lower structural portion of the vehicle body is coated with a chipping-resistant coating composition comprising a foamable vinyl chloride-based plastisol composition, and then the outer body portion of the vehicle body is formed. In the method of anti-chipping coating of the lower structure portion of an automobile body, which is formed by forming a foamed anti-chipping coating by heating and curing together with baking and drying of the finish coating, the vinyl chloride-based plastisol composition contains Vinyl resin,
The viscosity when heated to the temperature of baking and drying of the final coating in a state containing a plasticizer, a filler, an adhesion-imparting agent, and a foaming agent, and excluding the foaming agent, is a logarithmic decay rate. It can be seen that by using one having a λ of 0.15 or more, a chipping-resistant coating film composed of a foam in which fine bubbles are uniformly dispersed can be formed without causing swelling or the like on the coating film surface. . In addition, it turns out that the combined use system of a polyamide and a blocked isocyanate is preferable as the adhesiveness imparting agent.

Although the chipping-resistant coating method and the chipping-resistant coating composition according to the present invention have been specifically described with reference to examples, in order to achieve the object of the present invention, as in the examples, Without being limited to the composition of the vinyl chloride resin or the like, the viscosity when heated to the temperature at the time of bake hardening in a state where the foaming agent is removed from the coating composition for chipping resistance is 0.1 logarithmic decrement λ. If it is 15 or more, the type of the compounded resin component, the type of the additive, and the mixing ratio of each can be variously changed.

[0072]

As described above, in the chipping-resistant coating method according to the first aspect, a chipping-resistant coating composition comprising a foamable vinyl chloride-based plastisol composition is applied to the lower structure of an automobile body, By heat-setting together with baking and drying of the finish coating of the car body outer panel to be performed thereafter, a chipping-resistant coating method for a lower structural portion of an automobile body, which comprises forming a foamed chipping-resistant coating film, The chipping-resistant coating composition contains a vinyl chloride-based resin, a plasticizer, a filler, an adhesiveness-imparting agent, and a foaming agent, and in a state where the foaming agent is removed, the finish coating is performed. The viscosity when heated to the temperature of baking and drying is 0.15 or more in logarithmic decrement λ.

Therefore, according to this chipping-resistant coating method, the coating composition for chipping resistance contains a foaming agent, and the viscosity when heated to the temperature of baking and drying of the finish coating in a state where the foaming agent is removed. Is 0.15 in logarithmic decrement λ
Because it is above, it is painted on the lower structure part of the car body,
The gas generated by foaming of the foaming agent in the coating film when heated and cured together with baking and drying of the finish coating of the car body outer panel,
It is well captured without volatilizing from the coating film and forms uniform fine bubbles. Therefore, there is an effect that a chipping-resistant coating film made of a foam in which fine bubbles are uniformly dispersed can be formed without causing swelling or the like on the coating film surface.

The coating composition for chipping resistant coating according to claim 2 is a foamable vinyl chloride-based plastisol composition coated on an automobile body, wherein the foamable vinyl chloride-based plastisol composition comprises a vinyl chloride-based resin, a plasticizer, a filler, and an adhesive. A viscous agent having a logarithmic decay rate λ of 0.15 or more when heated to a temperature at the time of baking hardening in a state containing a imparting agent and a foaming agent, and excluding the foaming agent. It is.

Therefore, according to the chipping-resistant coating composition, the viscosity when heated to the temperature at the time of baking hardening in a state where the foaming agent is contained and the foaming agent is removed is 0 at logarithmic decrement λ. .15 or more, this is applied to the lower structure of the vehicle body, and then heat-cured together with the subsequent baking and drying of the finish coating of the vehicle body outer panel, as in claim 1, Gas generated by foaming of the foaming agent in the coating film is satisfactorily captured without volatilizing from the coating film to form uniform fine bubbles. Therefore, a chipping-resistant coating film made of a foam in which fine bubbles are uniformly dispersed can be formed without causing swelling or the like on the coating film surface.

[Brief description of the drawings]

FIG. 1 is a table showing the composition of a chipping-resistant coating composition used in chipping-resistant coating methods of Examples and Comparative Examples of the present invention, and the results of evaluation tests thereof.

FIG. 2 is a diagram showing a chipping-resistant coating composition used in the chipping-resistant coating methods of Example 1, Example 3 and Comparative Example 1 of the present invention, which is obtained by removing 130% of the foaming agent.
It is a table | surface figure which shows the measurement result of the viscosity (logarithmic decay rate (lambda)) at the time of heating at ° C.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yutaka Ohashi 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (56) References JP-A-2-202560 (JP, A) JP-A-62-190267 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B05D 7/24 301 C08J 9/04 CEV C09D 5/00 C09D 127/06

Claims (2)

(57) [Claims] 1. An anti-chipping coating composition comprising a foamable vinyl chloride-based plastisol composition is applied to a lower structure portion of an automobile body, and then baking and drying of a finish coating of an outer body portion of the automobile body is performed. A chipping-resistant coating method for an undercarriage of an automobile body comprising forming a foamed chipping-resistant coating film by heat-setting together, wherein the coating composition for chipping-resistant is a vinyl chloride resin, , A filler, an adhesiveness-imparting agent, and a foaming agent, and in a state where the foaming agent is removed, the viscosity when heated to the baking and drying temperature of the finish coating has a logarithmic decrement λ. And 0.15 or more. 2. A chipping-resistant coating composition comprising a foamable vinyl chloride-based plastisol composition applied to an automobile body, comprising: a vinyl chloride-based resin; a plasticizer; a filler; A coating composition for chipping resistance, comprising a foaming agent, and having a viscosity of 0.15 or more in logarithmic decrement λ when heated to a temperature at the time of bake hardening in a state excluding the foaming agent. object.