JPH07116405B2 - Intermediate paint - Google Patents

Description

TECHNICAL FIELD The present invention relates to a paint having excellent pitting resistance and capable of having a higher coating solid content at the time of coating than that of a conventional middle coat paint, particularly to a middle coat paint suitable for automobile middle coat. It is a thing.

[Conventional technology]

There are two recent requirements for coating films in the field of automobile industry, namely, improvement of coating film durability, especially chipping resistance and finish appearance. The first improvement in chipping resistance means that salt and crushed stones sprinkled on the road to prevent road freezing in winter in the cold regions of Europe and the United States are caught in the wheels when the car is running and are automatically or automatically applied to the car body of the following car. It means the improvement of the resistance of the coating film against the peeling of the coating film due to the collision with the film or the scratches reaching the steel plate as the material.

The second is to improve the appearance of the automobile by improving the smoothness of the coating applied to the car body and enhancing the glossiness of the coating to improve the appearance of the automobile and increase the commercial value of the automobile. It is what

[Problems to be solved by the invention]

Conventionally, a method based on the design of an intermediate coating film is mainly used for improving the chipping resistance. As one of the methods, an inorganic flat pigment, for example, talc, sericite or the like is contained in an intermediate coating film, and a chipping-resistant intermediate coating composition which causes cohesive failure inside the coating film during chipping is disclosed in Japanese Examined Patent Publication No. 52-43657. , Japanese Patent Publication No. 53-45813.

However, the method of mixing these inorganic flat pigments has a cohesive failure function at the time of chipping when the content is large, but the area causing peeling of the coating film tends to be large and tends to impair aesthetics. If the content is too small, the cohesive failure function is inferior, and there is a problem that rusting occurs due to the exposure of the steel sheet as a raw material.

In addition, as another measure, Japanese Patent Publication No. Sho 61-36995 discloses that an undercoating film contains a blocked isocyanate compound having an NCO concentration of 0.1 to 5 mmol / g and a polyhydroxy compound having an OH concentration of 0.05 to 20 mmol / g as main components. A coating film forming method has been proposed, which comprises the steps of coating a soft urethane resin as described above, coating an intermediate coating composition, baking and drying the coating composition, and baking and drying the top coating composition.

However, this method has a problem in that the urethane resin layer is formed in addition to the conventional three-layer coating film forming layer, so that the number of coating steps increases and the productivity of the coating step deteriorates.

As another measure for improving the chipping resistance, there is a method of increasing the molecular weight of the polyester resin used in the intermediate coating material to impart toughness to the coating film and improve the chipping resistance.

However, in the method of using the polyester resin having a high molecular weight for the intermediate coating composition, the viscosity of the polyester resin is high, so that the coating solid content at the time of coating is inevitably lowered.
As a result, there is a problem that the hiding property of the undercoat is lowered and the smoothness of the intermediate coating surface itself is lost.

Further, in order to improve the finished appearance, so-called high solid type paints are used, which have excellent flowability as a paint such as leveling property and flow property and have a high paint solid content during painting. In this high solid type paint,
The molecular weight of resins used for paints is usually reduced. Similarly, for intermediate coatings, it is possible to obtain a high solid type intermediate coating by lowering the molecular weight of the polyester resin used in the coating, but although the finished appearance can be improved, the polyester resin has a lower molecular weight, so the crosslinking density Significantly increased, resulting in loss of toughness of the coating film itself,
There is a problem that chipping resistance is reduced.

The present invention is intended to solve the above problems, and an object of the present invention is to provide an intermediate coating composition capable of simultaneously achieving improved chipping resistance and improved finished appearance.

[Means for solving problems]

The present invention is synthesized from a polyester resin raw material containing 10 to 45% by weight of one or more ring structural polyester resin raw materials selected from the group consisting of a dibasic acid having a ring structure in the chemical structure, an acid anhydride and a diol. , And number average molecular weight 500
-1500, a hydroxyl value of 100-225, an acid value of 5-20, a urethane-modified polyester resin obtained by coupling 0.2-1.4 mol of a diisocyanate compound to 2 mol of the polyester resin is contained as a coating film forming component, An intermediate coating composition containing a melamine resin as a curing agent.

The intermediate coating material of the present invention is a urethane-modified polyester resin obtained by coupling a low molecular weight polyester resin having a ring structure with a diisocyanate compound as a coating film forming component, and thus has excellent finished appearance and is used as a high solid type intermediate coating material. Despite the low viscosity possible, it has excellent chipping resistance.

The ring-structured polyester resin raw material in the present invention is one or more selected from the group consisting of dibasic acids, acid anhydrides and diols having a benzene ring structure and / or an alicyclic structure in the chemical structure. Is. Of these, examples of the ring-structured dibasic acid include orthophthalic acid, isophthalic acid, terephthalic acid, hexahydroorthophthalic acid, hexahydroisophthalic acid, and hexahydroterephthalic acid. Examples of ring-structured acid anhydrides include phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, and hexahydrophthalic anhydride. Examples of ring-structured diols include bishydroxyethyl terephthalate, cyclohexyldimethanol, cyclododecanediol, hydrogenated bisphenol A, bisphenol A, bishydroxyethylhydroquinone, and the like.

The polyester resin in the present invention is prepared by mixing these ring-structured polyester resin raw materials in the polyester resin raw material 10
A resin synthesized from a polyester resin raw material containing 55 to 90% by weight, preferably 60 to 85% by weight of a polyester resin raw material having no ring structure. Average molecular weight 500-1500, preferably 7
It has a hydroxyl value of 50 to 1250, a hydroxyl value of 100 to 225, and an acid value of 5 to 20.

Further, the urethane-modified polyester resin in the present invention is obtained by coupling the above polyester resin with a diisocyanate compound.

Examples of the diisocyanate compound for coupling the polyester resin include hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, and tolylene diisocyanate, which are used in an amount of 0.2 to 1.4 mol per 2 mol of the polyester resin. A diisocyanate compound is used.

The reason why the urethane-modified polyester resin used in the present invention is limited to the above is as follows. First, when the compounding ratio of the ring-structured polyester resin raw material is less than 10% by weight, the hardness of the coating film is remarkably reduced and it cannot be put to practical use.
If it exceeds 5% by weight, the rigidity of the coating film increases and the chipping resistance decreases. The molecular weight of the polyester resin is 500
If it is less than the above range, the film-forming reaction due to crosslinking becomes extremely difficult and it cannot be put to practical use. On the other hand, if it exceeds 1500, the resin viscosity is so high that it cannot be a high-solid type paint excellent in finished appearance. When the hydroxyl value of the polyester resin is less than 100, it becomes difficult to generate a three-dimensional structure by crosslinking and the water resistance is reduced. On the other hand, when it exceeds 225, the crosslink density becomes extremely high, so that the toughness of the coating film is lost and the chipping resistance is lowered. When the acid value of the polyester resin is less than 5, curing failure occurs when the melamine resin is used as a crosslinking agent, and the coating film cannot have sufficient hardness. On the other hand, when the acid value exceeds 20, the hydrophilicity is excessively increased and the water resistance is lowered. When the diisocyanate compound is less than 0.2 mol, the increase in the molecular weight of the polyester resin is insufficient, so improvement in chipping resistance is not observed, while when it exceeds 1.4 mol, the resin viscosity after coupling is significantly increased, depending on the case. Since it gels, it cannot be used for high solid type paints.

In the intermediate coating composition of the present invention, the above urethane-modified polyester resin is used as a coating film forming component. In this case, as a curing agent, a melamine resin such as butoxymethylol melamine resin, isobutoxymelamine resin, methoxymethylol melamine resin is used. This curing agent is blended with the urethane-modified polyester resin as the film-forming component to form a one-pack type intermediate coating material.

It is preferable to use 5 to 100 parts by weight of the above curing agent with respect to 100 parts by weight of the urethane-modified polyester resin.

In the intermediate coating composition of the present invention, conventional polyester resins, epoxy resins, fibrin-based resins and the like can be used together with the urethane-modified polyester resin as a coating film forming component.

In the intermediate coating composition of the present invention, as a pigment in addition to the coating film forming component and the curing agent, for example, talc, titanium dioxide, zinc white, carbon black, barium sulfate, kaolin, calcium carbonate, sericite, aluminum tripolyphosphate,
It may also contain pigments used in conventional paints, such as monobasic lead sulfate. Of these, talc causes cohesive failure inside the coating film, and further improves chipping resistance, so it is preferable to use 1 to 5% by weight in the coating material.
However, when the amount used exceeds 5% by weight, the peeled area during chipping becomes large, and when it is less than 1% by weight, the effect is insufficient.

The intermediate coating composition of the present invention may further include xylene, toluene, Solvesso # 100 (trade name, manufactured by Exxon),
A solvent such as acetic acid butyl ester, methyl isobutyl ketone, and acetic acid ethylene glycol monoethyl ether, and a commonly used additive can be included.

The intermediate coating composition of the present invention is suitable as an intermediate coating composition for automobiles, but can be applied as an intermediate coating composition for other purposes. The painting method is spray painting, electrostatic painting,
General coating methods such as roll coating and brush coating can be applied.

〔The invention's effect〕

The intermediate coating composition of the present invention uses a urethane-modified polyester resin obtained by coupling a low molecular weight polyester resin having a ring structure with a diisocyanate compound as a coating film forming component, and uses a melamine resin as a curing agent. A high solid type and one-pack type intermediate coating paint with low viscosity can be obtained even at high temperature, and the coating work is easy and can be hardened by baking at low temperature, which gives the finished appearance, chipping resistance, water resistance, hardness, etc. An excellent coating film can be obtained.

〔Example〕

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples of the present invention. In the examples, parts are parts by weight and% is% by weight.

Production Example (a) Urethane-modified polyester resin varnish AU-1 Esterification reaction of 350 parts of phthalic anhydride, 171 parts of adipic acid, 335 parts of neopentyl glycol and 144 parts of trimethylolpropane at 230 ° C. for 6 hours, and after cooling, xylene 197 And 197 parts of ethylene glycol monoethyl ether acetate were added to obtain a polyester resin varnish A having a nonvolatile content of 70%. Next, add 700 parts of polyester resin varnish A with 33 parts of hexamethylene diisocyanate, 0.03 parts of dibutyltin dilaurate and 72 parts of xylene, and add 1 part at 80 ° C.
The reaction was carried out for a time to obtain a urethane-modified polyester resin varnish AU-1 having a nonvolatile content of 65%.

(B) Urethane-modified polyester resin varnishes AU-2 to NU Polyester resin varnishes B to N were prepared in the same manner as the polyester resin varnish A based on the composition and reaction conditions shown in Table 1.

Next, based on the composition and reaction conditions in Table 2, in the same manner as the above urethane-modified polyester resin varnish AU-1,
Urethane-modified polyester resin varnishes AU-2 to NU were prepared.

Examples 1 to 10 and Comparative Examples 1 to 15 Each of the formulations of Examples shown in Table 3 and Comparative Example shown in Table 4 was kneaded in a pot mill until the particle size became 10 μm or less, Comparative paints of Comparative Examples 1 to 15 were obtained.

In Tables 3 and 4, the isobutylene melamine resin varnish is manufactured by Nihon Reichhold Co., Ltd., Super Beckamine L-116-70 (trade name, solid content 70%), and the epoxy resin varnish is Yuka Shell (stock). ), Epicoat 1001 (trade name, solid content 60%), titanium dioxide is Teikoku Kako Co., Ltd., JR-602
(Product name), carbon black is Columbia Carbon Co
Raven 1255 (trade name), fine powder talc is Fuji Talc Industry Co., Ltd., LMS-200 (trade name).

The intermediate coatings obtained in Examples and Comparative Examples were mixed with an aromatic solvent (Solvesso # 100, trade name, manufactured by Exxon Co.) and an equal weight mixed solvent of butyl acetate, and the viscosity of each was 23 seconds (Ford Cup # 4. Temperature was adjusted to 20 ° C).
Next, after treating 0.8 mm x 100 mm x 150 mm dull steel plate with zinc phosphate (manufactured by Nippon Parkerizing Co., Ltd., trade name, Bonderite # 3004), cationic electrodeposition paint (manufactured by Nippon Oil & Fat Co., Ltd., product Name, Aqua No.4100) Dry coating thickness 20
It is coated to a thickness of μm and baked at 165 ° C for 30 minutes, then the above-mentioned intermediate coating paint is air-sprayed to a dry coating film thickness of 40 μm, baked at 140 ° C for 30 minutes, and then overcoated with aminoalkyd. Resin paint (Nippon Yushi Co., Ltd.,
The product name, Melami No. 1500 Red) was air-sprayed to a dry coating film thickness of 40 μm and baked at 140 ° C. for 30 minutes.

For the test pieces prepared as described above, the finish appearance, chipping resistance, water resistance, pencil hardness, and coating non-volatile content of the top coating film were measured by the following test methods, and Table 3 (implementation) The results shown in Examples) and Table 4 (Comparative Examples) were obtained.

Test Method 1) Finished Appearance of Top Coated Film The finished appearance of the top coated film was evaluated using a portable image clarity measuring device (HA-ICM) manufactured by Suga Test Instruments Co., Ltd. The higher the value, the better the finished appearance of the top coating film.

2) Chipping resistance tester: Suga Tester Co., Ltd. diamond shot tester Diamond weight: 0.01g Diamond shot speed: 90km / hr, 140km / hr, 17
0km / hr Number of shots: 10 points for each speed Specimen temperature: -20 ° C 10 points of diamond were struck at each of the above-mentioned diamond shot speeds on 1/3 of the area of the obtained specimen. .

Coating film peeling area: Total peeling area of top coating film by diamond test (unit: mm ² ) Number of substrates reached: JI for test pieces that were diamond shot
S K5400 7.8 Based on the salt spray test, the total number of points (unit: pieces) that rusted after being left in the salt spray tester for 72 hours 3) Water resistance The test piece was immersed in warm water at 40 ° C for 240 hours, The adhesion was tested. The adhesion of the coating reaches the substrate by holding the cutting edge of the single-edged razor placed on the vertical surface at about 30 degrees to the effective surface.
Make 100 pieces of 1 mm (10 x 10 pieces), make 12 mm wide cellophane adhesive tape according to JIS Z1522 completely adhere to the eyes, and immediately keep one end of the tape at right angles to the coating surface, Peel off instantaneously and count the number of the eyes where the coating film is attached.

4) Pencil hardness Based on JIS K5400 6.14 Pencil scratch test.

As is clear from the results of Table 3, the intermediate coating composition of the present invention maintains the non-volatile content of the coating composition at high coating viscosity,
Excellent finish appearance, chipping resistance, water resistance and pencil hardness of the top coating film.

On the other hand, Comparative Examples 1 to 3 and 5 to 6 in which the polyester resins A to C and EF are not coupled with the diisocyanate compound are inferior in chipping resistance and water resistance. In Comparative Example 4 in which the polyester resin D is not coupled with the diisocyanate compound, the finish appearance of the top coating film is inferior. Comparative Example 7 in which the diisocyanate compound was coupled in an amount of less than 0.2 mol with respect to 2 mol of the polyester resin was inferior in finish appearance and chipping resistance of the top coating film. Further, Comparative Example 8 in which the raw material having a ring structure is less than 10% of polyester resin is inferior in finished appearance and pencil hardness of the top coating film. A raw material with a ring structure
Comparative Example 9 made of polyester resin exceeding 45% is inferior in chipping resistance. Further, Comparative Example 10 in which the hydroxyl value of the polyester resin is less than 100 is inferior in chipping resistance and water resistance. Comparative Example 11 in which the hydroxyl value of the polyester resin exceeds 225 is inferior in chipping resistance. Comparative Example 12, in which the acid value of the polyester resin is less than 5, is inferior in chipping resistance, water resistance and pencil hardness. The acid value of the polyester resin
Comparative Example 13 exceeding 20 is inferior in chipping resistance and water resistance. Comparative Example 14 in which the number average molecular weight of the polyester resin is less than 500 is inferior in chipping resistance. In Comparative Example 15 in which the number average molecular weight of the polyester resin exceeds 1500, the finish appearance of the top coating film is inferior.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-59-210977 (JP, A) JP-A-60-144368 (JP, A) JP-A-61-211322 (JP, A) JP-B-48- 32568 (JP, B1)

Claims (4)

[Claims] 1. A polyester resin raw material containing 10 to 45% by weight of one or more ring structural polyester resin raw materials selected from the group consisting of a dibasic acid having a ring structure in the chemical structure, an acid anhydride and a diol. And a number average molecular weight of 50
A urethane-modified polyester resin obtained by coupling a polyester resin having a hydroxyl value of 0 to 1500, a hydroxyl value of 100 to 225 and an acid value of 5 to 20 with 0.2 to 1.4 mol of a diisocyanate compound to 2 mol of the polyester resin is contained as a coating film forming component. An intermediate coating composition containing a melamine resin as a curing agent. 2. The intermediate coating composition according to claim 1, wherein the ring structure is a benzene ring structure and / or an alicyclic structure. 3. A ring structure polyester resin raw material is orthophthalic acid, isophthalic acid, terephthalic acid, hexahydroorthophthalic acid, hexahydroisophthalic acid, hexahydroterephthalic acid, phthalic anhydride, trimellitic anhydride,
Patent that is one or more selected from the group consisting of pyromellitic dianhydride, hexahydrophthalic anhydride, bishydroxyethyl terephthalate, cyclohexyldimethanol, cyclododecanediol, hydrogenated bisphenol A, bisphenol A, and bishydroxyethylhydroquinone The intermediate coating material according to claim 1 or 2. 4. The diisocyanate compound is one or more selected from the group consisting of hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, and tolylene diisocyanate. The intermediate coating material according to any one of item 3.