JPS62191078A - Coating method - Google Patents

Abstract

PURPOSE:To provide stabilized adhesive properties without special pretreatment by spreading specific polyurethane resin as a primer on the surface of an inactivating metal. CONSTITUTION:Polyurethane resin coating containing specific reactive substance as main component is spread on the surface of a material having an inactivating film on the surface used in a wide scope such as electric, automobile parts and the like as pretreatment. In other words, a reactive substance consisting of polytetramethylene glycol or polycaprolactone ester of 1,500-4,000mol.wt. having hydroxyl radical at the end as A component, hexamethylene di-isocyanate or isophorone diisocyanate as B component, and isophorone diamine as a chain extender is the main constituent. In this case, by an arrangement of B/A=1.5-3.0 (mol ratio) and within a scope of molecular weight 10,000-40,000, top coating can be carried out by means of a wet-on-wet coating without baking a primer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for coating a material having a passive film on its surface.

(Prior art) In recent years, electrical parts, office machines'2:), music instruments, automobiles,
Materials with passive films on their surfaces, such as metallized plastics, aluminum, stainless steel, nickel alloys, chromium alloys, titanium alloys, cobalt alloys, copper alloys, tin alloys, and zinc alloys, are used in a wide range of fields such as toys.

Metallized plastics include copper alloys, nickel and nickel alloys, chromium and chromium alloys, iron-nickel alloys, tin-cobalt alloys on the surface of plastics such as ABS resin, polypropylene resin, polyethylene resin, nylon resin, acrylic resin, and polycarbonate resin. It is a composite material of plastic and metal on which a metal film such as tin, tin alloy, zinc alloy, etc. is formed, and has a passive film on the surface.

Since these materials passivate the metal surface, they do not corrode for a long period of time and retain a beautiful metallic luster.

However, in recent years, for design reasons, part or all of the surface is often painted.

Since these materials having passive films have inert surfaces, they cannot obtain good adhesion when painted, and require special pretreatment and special etching primers.

Special pre-treatments include aluminum anodizing treatment,
Generally, examples of pretreatment include chromate treatment using a mixture of chromic acid and hydrofluoric acid, and phosphate-based chemical conversion treatment.

Special etching primers include wash primers (e.g. Niso San Wash Primer, Nippon Oil & Gas Co., Ltd. Co., Ltd., product name) is used.

Another method is electrodeposition, which utilizes the presence of a conductive metal film on the surface.

(Problem to be solved by the invention) However, even with such special pretreatment and painting method using special etching primer, adhesion is poor.
Problems remained in that the topcoat film was easily peeled off and secondary adhesion was poor, especially after a moisture resistance test or a hot water resistance test. Furthermore, in order to perform special pretreatment, it is necessary to go through a complicated pretreatment process, which increases the amount of capital investment and requires bath management for complicated pretreatment, which results in low work efficiency. However, in terms of quality control, there was a fatal problem of instability.

In addition, when applying an etching primer, it is necessary to strictly control the film thickness; if it is too thin or too thick, sufficient adhesion cannot be obtained, and furthermore, the drying conditions after applying the primer must be within a narrow range. There was a problem in that it was difficult to control the painting work conditions.

On the other hand, a method of applying electrodeposition coating has been used, but although this method can stably obtain sufficient adhesion, it not only requires special equipment for electrodeposition coating, but also causes the paint to bake. Because the temperature is as high as 150°C to 180°C,
In the case of materials based on plastics with low heat resistance, such as metallized plastics, the material itself undergoes thermal deformation, which impairs its commercial value. had.

(Means for Solving the Problems) In order to solve these problems, the inventors of the present invention have conducted extensive research and found that by painting a specific polyurethane resin as a brimer on the passivated metal surface, a special pretreatment method has been developed. It has been discovered that stable adhesion can be obtained without any treatment, and the present invention has been achieved.

That is, the present invention provides a material having a passive film on its surface, (A) a molecule having 11,500 to 4,000 molecules having a hydroxyl group at the terminal.
A reaction product of polytetramethylene glycol or polycaprolactone ester, CB) hexamethylene diisocyanate or isophorone diisocyanate, and (c) isophorone diamine, with B/A = 1.5 to 3.0 (molar ratio),
The present invention also relates to a coating method characterized by coating a polyurethane resin paint whose main component is a reactant having molecular groups in the range of 10,000 to 40,000.

The polyols used in polyurethane resins include dibasic acids such as adipic acid and ethylene glycol (PEA),
Polyester polyols made of diols such as 1,4-butanediol (PBA), and polyether polyols such as polypropylene glycol ether (PPG) and polyethylene glycol ether (PEG) are common. However, the glass transition temperature of polyurethane resins made of these polyols is lower than that of polyurethane resins made of polytetramethylene glycol (PTG) or polycaprolactone ester (PCL).
Since it is generally high, it not only has poor impact resistance at low temperatures, but also poor secondary adhesion after a humidity test or a hot water test.

On the other hand, examples of diisocyanates used in polyurethane resins include tolylene diisocyanate (TDI) and 4.
4'-diphenylmethane diisocyanate (MDI)
is common, but polyurethane resins made of these diisocyanates also include hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI).
), painting workability, topcoat appearance, impact resistance at low temperatures, and secondary adhesion after humidity tests and hot water tests are significantly worse.

However, by further combining a specific chain extender with the above-mentioned combination of polyol and diisocyanate in a specific range in the present invention, it is possible to improve adhesion to metal materials having a passive film on the surface and impact resistance at low temperatures. Not only is the molecular weight of the polyurethane resin easily controllable, but it also does not show significant softening even at temperatures of 180°C, and has a baking temperature of 140°C to 140°C for commonly used top coats for metals. It has sufficient high-temperature properties that it does not soften or melt even at 150℃, allowing wet-on-wet painting of the topcoat without baking the primer, and does not adversely affect the finished appearance of the topcoat. It has been found that this method provides a beautiful painted surface without causing any damage.

Moreover, unlike general polyurethane resins that are difficult to dissolve in solvents, the polyurethane resins in the specific range of the present invention are soluble in organic solvents used for paints, and can be easily spray-painted. be able to.

The specific range of the polyurethane resin in the present invention means that the molecular weight of PTG or PCL used is 1500 to 40.
It must be in the range of 00. If a polyol with a molecular weight of less than 1500 is used, the proportion of urethane groups will be high, resulting in significantly poor impact resistance and secondary adhesion at low temperatures. Furthermore, if the molecular weight of the polyol exceeds 4000, the proportion of the polyol will be high and the properties of the polyol will be noticeable, resulting in not only a decrease in high temperature properties but also a weak resin that exhibits tackiness even at room temperature, making it difficult to use as a top coat. Can't do wet-on-wet painting.

Furthermore, even when using a polyol within this range,
When combined with isocyanates with aromatic rings such as TDI and MDI, secondary adhesion and impact resistance at low temperatures will be significantly impaired, and they will also become difficult to dissolve in common organic solvents for paints, resulting in poor painting workability. And the appearance of the top coat becomes extremely poor.

When HDI or IPDI is combined with a polyol within the above-mentioned range, a product with excellent secondary adhesion, low-temperature impact resistance, coating workability, and topcoat appearance is obtained.

Furthermore, the ratio of A component and B component is set to B/A=1.5 to 3.
0 (molar ratio), i.e. NGOloH = 1,
By setting it in the range of 5 to 3.0 (molar ratio), a balance between high temperature properties and solubility in organic solvents can be achieved, but by using isophoronediamine (IPOA) as a chain extender, it becomes even more excellent. The top coat can be applied wet-on-wet without baking the primer.

In addition, the molecule 1150 having a hydroxyl group at the terminal which is component A
The molar ratio of NC01011 of polytetramethylene glycol or polycaprolactone ester of 0 to 4000 and hexamethylene diisocyanate or isophorone diisocyanate as component B is 1.5 to 3.0, and the molecular weight of the reactant is in the range of 10,000 to 40,000. By specifying that, the amount of isophoronediamine used is automatically specified.

If the molar ratio of NC0101i is less than 1.5 moles, the resin becomes sticky and weak even at room temperature, which not only reduces the secondary adhesion of the coating, but also makes it difficult to apply wet-on-wet topcoat paint. Moreover, the appearance of the top coat becomes very poor.

If the molar ratio of NGOloil exceeds 3.0 moles, the solubility in organic solvents will be extremely reduced, the coating workability and appearance of the top coat will be poor, and the impact resistance at low temperatures will be extremely poor.

Ethylene glycol and 1,4-butanediol are generally used as chain extenders for polyurethane resins, but in the field of application of the present invention, these are difficult to dissolve in organic solvents because the softening point of the resin is too low. Sexuality becomes poor,
Not only is it difficult to manufacture paint, but it also reduces painting workability.
Problems occur in forming a uniform coating film.

However, isophoronediamine (IPDA), which has an alicyclic structure,
) was found to increase the softening point due to the collection of urea groups generated by the reaction with isocyanate groups, and to improve the solubility in solvents due to the effect of the alicyclic structure.

The polyurethane resin obtained by such a combination is used by dissolving it in an organic solvent such as toluene, ethyl acetate, acetone, methyl ethyl ketone, isopropyl alcohol, or cyclohexanone. However, if the molecular weight of the polyurethane resin is less than 10,000, the polyurethane resin The impact resistance and secondary adhesion at low temperatures are significantly reduced, and the wet-on-wet properties with the top coat and the appearance of the top coat are extremely poor. On the other hand, if the molecular weight of the polyurethane resin exceeds 40,000, spray coating becomes impossible, and the appearance of the top coat deteriorates significantly.

Therefore, from the viewpoint of coating workability and coating film performance, the molecular weight of the polyurethane resin is preferably in the range of 10,000 to 40,000.

The polyurethane resin used in the present invention is manufactured in a similar manner.

As the first stage reaction, molecules 11
NGO of 500-4000 polytetramethylene glycol or polycaprolactone ester and hexamethylene diisocyanate or isophorone diisocyanate
Prepare an amount of 10i+ with a molar ratio in the range of 1.5 to 3.0, add and dissolve an organic solvent such as toluene, ethyl acetate, acetone, methyl ethyl ketone, or cyclohexanone, and then heat at 70 to 90°C in a nitrogen gas stream. Allow to react for 2 to 6 hours.

Next, as a second stage reaction, isophoronediamine and the first
Add the organic solvent used in the step reaction and a mixture of lower alcohols such as isopropyl alcohol and n-butyl alcohol, and react at 70 to 90'C for 1 to 6 hours to form molecules.
A polyurethane resin having a molecular weight of 1oooo to 40,000 is obtained.

When painting the polyurethane resin obtained in this way, use a normal polyisocyanate used in polyurethane paints as a curing agent, such as Coronate 1 Coronate HL or Coronate EH (product names: both manufactured by Nippon Polyurethane Industries). etc., their block compounds,
For example, Coronate D C-2974, Coronate 1-2
507 (trade name: both manufactured by Nippon Polyurethane Industries, Ltd.), Duranate 17B-60CX (trade name: manufactured by Asahi Kasei Industries, Ltd.), etc. may be used.

A pigment may be used as the primer, which is a paint containing a polyurethane resin as a main component, used in the present invention.

The primer can be produced by a known method.

When pigments are not included, ester-based, ketone-based, alcohol-based, or aromatic solvents, which are generally used as organic solvents for paints, are used, and a uniform polyurethane resin solution is produced by stirring with a disilver, etc. can do.

In addition, when a pigment is included, the pigment is dispersed in part or all of the polyurethane resin solution. The pigment is dispersed using a known method, ie, a dispersing machine such as an attritor or a sand mill. After dispersing the pigment, a primer can be manufactured by adding the remaining polyurethane resin solution and diluting it to a predetermined viscosity with a commonly used organic solvent.

Pigments used include extender pigments such as talc, precipitated barium sulfate, silica, and calcium carbonate; inorganic coloring pigments such as titanium dioxide, carbon blank, and iron oxide; and organic coloring pigments such as cyanine blue and quinacridone red. can be used.

When containing pigment, pigment/polyurethane resin (
The ratio of (solid content) is preferably 2.5 or less; if it exceeds 2.5, the strength of the coating film will decrease, and the impact resistance and secondary adhesion at low temperatures will be significantly reduced, and After the top coat is applied, fine shrinkage may occur in the finished appearance of the top coat, making it impossible to obtain a beautiful appearance.

Furthermore, as additives, silicone-based and non-silicon-based additives, ultraviolet absorbers, antioxidants, light stabilizers, antistatic agents,
Acrylic surface conditioners, amide waxes, etc. can be used.

The painted primer will last for 1 to 5 minutes at room temperature or 50 to 1
After drying at a temperature of about 20°C for 10 to 30 minutes, a top coat is applied. Although there are no particular limitations on the top coat paint,
Two-component polyurethane resin paints, lacquer paints, acrylic-melamine resin paints, alkyd or polyester paints
There are melamine resin paints, block isocyanate curing type/liquid type polyurethane resin paints, etc., which are baked at the required temperature and for the required time depending on the top coat.

As a method for applying the polyurethane resin paint of the present invention,
Commonly used painting methods such as air spray,
Painting methods such as airless spray, air electrostatic, airless electrostatic, electrostatic atomization type electrostatic, dip coating, and flow coating can be applied.

(Effect of the invention) By applying the coating method of the present invention to a material having a passive film on its surface, the coating conditions and film thickness can be controlled within a narrow range without special pretreatment. Excellent adhesion can be stably obtained, the top coat can be applied wet-on-wet, the coating workability is also excellent, and the coating process can be significantly simplified.

Furthermore, by applying the polyurethane resin paint as a primer according to the method of the present invention, it has excellent impact resistance and secondary adhesion not only at room temperature but also at low temperature.
Since there is little softening when baking at a high temperature of 80℃, you can freely select the top coat and obtain a beautiful finished appearance.Using a high quality top coat will ensure long-term durability. Paint quality can be obtained. Furthermore, it is possible to obtain extremely excellent chipping resistance against damage caused by flying stones such as automobile parts.

(Example) Next, the present invention will be described in detail by giving examples and comparative examples of the present invention.

A. Production of polyurethane resin solution (1) Polyurethane resin solution 1 As the first stage reaction, PCL (PCL-1500) 1500 with a molecular weight of 1500 was prepared based on the formulation shown in Table 1.
g (1 mol), 666 g (3 mol) of IPDI, and 3,540 g of toluene were charged into a four-eye IOR flask and dissolved, and reacted at 80°C in a nitrogen gas stream for 3 hours.

Next, as a second stage reaction, 360 g of IPDA (2
, 12 mol) and 2360 g of isopropyl alcohol were added and reacted at 80° C. for 1 hour. A polyurethane resin having a number average molecular weight of 20,000 was obtained.

(2) Polyurethane resin solution 7 As the first stage reaction, PCL with a molecular weight of 2000 (PCL-2000) 2000 was prepared based on the formulation shown in Table 1.
g (1 mol), ethylene glycol 68 g (1,0
9 mol) and 5860 g of methyl ethyl ketone in 10
After charging and dissolving in the four-eye flask of 1, IPIII
444 g (2 mol) was added thereto, and the mixture was reacted at 80° C. for 5 hours in a nitrogen gas stream.

A polyurethane resin with a number average molecular weight of 30,000 was obtained.

(3) Polyurethane resin solutions 2 to 6 and polyurethane resin solutions 8 to 12 Based on the formulations shown in Table 1, polyurethane resin solutions l
It was manufactured in the same manner.

Table 1 shows the characteristic values of the obtained polyurethane resin solution.

B. Production of primer (1) Primer used in Examples 1 to 3, Examples 7 to 9, and Comparative Examples 1 to 9 The aforementioned polyurethane resin solution was used as it was as a primer.

(2) Primer used in Examples 4 to 6 and Comparative Example 10 Based on the formulations shown in Tables 2 and 3, a polyurethane resin solution or a polyurethane resin solution was diluted with an organic solvent, and titanium dioxide and talc were added thereto. The mixture was kneaded and dispersed in an experimental sand mill for 60 minutes to obtain a primer.

(3) Primer used in Comparative Example 11 As the etching primer, Niso Sanwo Soshu Primer (trade name, manufactured by NOF ■) was used.

In addition, titanium dioxide used in the formulation was JR602 (manufactured by Teikoku Kako Co., Ltd., trade name), and talc was Hifiller (trade name, made by Tsuchiya Kaolin Kogyo ■).

C3 Test Metal Material for Painting In Examples and Comparative Examples, the following test pieces were used as metal materials for painting.

(1) Metallized plastic panel (a) Chrome-plated ABS panel ABS plate with micropore chrome electroplating (b) Nickel-plated ABS panel ABS plate with double-layer Niso gel electroplating (2) Aluminum panel JISH-4000-1980 A -5005P (3) Stainless steel panel JISG-4305-1980 SUS 304 D, preparation of test piece Clean the above test piece with isopropyl alcohol,
After degreasing, it was dried and used for coating in Examples 1 to 9 and Comparative Examples 1 to 11.

(1) Examples 1 to 7 and Comparative Examples 1 to 10 Using a thinner for dilution having the same composition as the ia solvent shown in Table 1 contained in the polyurethane resin solution used in Examples 1 to 7 and Comparative Examples 1 to 10. dilute the primer with Ford Cup No.
Adjust the viscosity to 13 to 14 seconds/20°C with Step 4, air spray on the test piece, and leave it for 3 minutes at room temperature. (manufactured by Yushi Co., Ltd.) was air sprayed.

Next, it was left at room temperature for 10 minutes and baked at 140° C. for 30 minutes to prepare a test piece. The dry film thicknesses of the obtained primer and top coat are shown in Tables 2 and 3.

(2) Example 8 After air spraying the primer and leaving it at room temperature for 5 minutes,
A test piece was prepared in the same manner as in Example 1 except that it was dried at ℃ for 30 minutes.

Table 2 shows the dry film thickness of the obtained primer and top coat.

(3) Example 9 Hyurethane M5000 Red (trade name, manufactured by NOF ■), which is a two-component polyurethane resin top coat, was air-sprayed as a top coat, left at room temperature for 10 minutes, and then heated to 80°C for 40 minutes.
A test piece was prepared in the same manner as in Example 1 except that it was baked separately. Table 2 shows the dry film thickness of the obtained primer and top coat.

(4) Comparative Example 11 As a primer, Nira Sun Wash Primer (trade name, manufactured by Nippon Oil & Fats ■), which is an etching primer, was used as a primer.
Using a special wash primer thinner (product name, manufactured by Nippon Oil & Fats Corporation), 11 seconds at 20°C at Ford Kambu 4.
A test piece was prepared in the same manner as in Example 1, except that the viscosity was adjusted, air sprayed, and then dried at 60° C. for 10 minutes.

Table 3 shows the dry film thickness of the obtained primer and top coat.

E. Test method and evaluation criteria The following performance tests were conducted on the obtained test pieces and evaluated.

(1) Make 11 scratches at right angles with a sharp cutter at intervals of one crane to reach the adhesive substrate, then rub the cellophane tape and peel it off instantly at a 45° angle to ensure that the paint film adheres. Count the number of folds.

100/100 (excellent) - 0/100 (poor) (2)
Secondary adhesion 1) Humidity test After being left in a humidifier at a temperature of 50°C and a relative humidity of 98% for 240 hours, the same adhesion test as in (1) is conducted.

100/100 (, excellent) -0/100 (poor) 2
) Hot water resistance test: Immerse in hot water at 40°C, and after 240 hours, conduct the same adhesion test as in (1).

100/100 (excellent) -m-〇/100 (poor) (
3) Impact resistance tester: Suga Test Instruments Sumishi Gravelometer Test Stone Near No. Crushed Stone (JIS^5001-77) 250g blowing at one time Air pressure: 4kg/cm2 Test piece temperature: -20"c or more The test is conducted under the following conditions, and the state of peeling of the paint film is observed with the naked eye.

○: Few scratches reached the substrate, and the peeled area was also small. (Excellent) Δ: Many scratches reached the substrate, but the f, 11 separation area was relatively small.

×: There were many scratches that reached the substrate, and the peeled area was also large. (Poor) (4) Painting workability: Painted with F-spray (Wider 61, caliber 1.3 Tsuru Iwata Coating Machine 02, trade name) at an air pressure of 4.0 kg/cm2 to check the smoothness of the primer coated surface. Observe with the naked eye.

○: Gives a smooth and uniform coating surface. (Excellent) △: Gives a fairly uneven painted surface.

×: The unevenness is very noticeable and the coating film is not uniform. (Poor) (5) Wet-on-wet property After air spraying the primer, leave it at room temperature for 2 minutes, then air spraying the top coat, and visually observing the degree of reversal between the primer and the top coat.

○: Not reversed at all. <Excellent) × The nib primer and top coat are reversed, and the top coat and primer are mixed. (Poor) (6) Appearance of top coat The primer and top coat were air-sprayed and baked in the same manner as in Example 1, and the smoothness of the top coat was observed with the naked eye.

○: Normal and smooth painted surface. (Excellent) Δ: The painted surface is quite uneven.

×: The unevenness is very noticeable and the coating film is not uniform. (Poor) The test results of Examples 1 to 9 are shown in Tables 4 to 7, and Comparative Example 1
-11 test results are shown in Tables 8-11.

As is clear from the comparative examples in Tables 8 to 11, Comparative Example 1 is a case in which the type of polyol was changed, and the secondary adhesion and impact resistance were very poor.

Comparative Example 2 is a case where the molecular weight of the polyol is less than 1500, and the secondary adhesion and impact resistance are very poor.

In Comparative Example 3 and Comparative Example 7, the type of isocyanate was changed, and both were very poor in secondary adhesion, impact resistance, painting workability, and topcoat appearance.

Comparative Example 4 is a case where the type of chain extender was changed, and the top coat appearance was very poor and the coating workability was poor.

Comparative Example 5 is a case where the molar ratio of NGOloil exceeds 3.0, and the impact resistance is very poor, as well as the painting workability and the appearance of the top coat are poor.

Comparative Example 6 is a case where the molar ratio of NGOloH is less than 1.5, and a soft polyurethane resin that is sticky at room temperature is obtained, and the wet-on-wet properties, topcoat appearance, and secondary adhesion are very poor. At the same time, painting workability is also poor.

Comparative Example 8 is a case where the molecular weight of the polyurethane resin is less than 10,000, and the secondary adhesion, impact resistance, wet-on-wet properties, and topcoat appearance are very poor.

Comparative Example 9 is a case where the molecular weight of the polyurethane resin exceeds 40,000, and the coating workability and top coat appearance are very poor.

Comparative Example 1O uses the same polyurethane resin solution as Example 1, but contains too much pigment and the ratio of pigment/polyurethane resin (solid content) exceeds 2.5, resulting in secondary adhesion. The properties and impact resistance are very poor, and the appearance of the top coat is also poor.

Comparative Example 11 is a case where a conventionally used general etch lag primer is used, and the impact resistance is very poor and the secondary adhesion is poor.

As is clear from the above test results, the present invention not only provides stable and excellent adhesion when coating materials with a passive film on the surface, but also improves secondary adhesion and impact resistance at low temperatures. This is a new and useful product that has excellent topcoat appearance, as well as excellent coating workability and wet-on-wet properties, allowing it to significantly shorten the coating process and obtain a high level of coating film quality. This is a unique painting method.

Claims (1)

[Claims] 1. A material having a passive film on its surface, (A) having a hydroxyl group at the end and having a molecular weight of 1500 to 4000;
A reaction product of polytetramethylene glycol or polycaprolactone ester, (B) hexamethylene diisocyanate or isophorone diisocyanate, and (c) isophorone diamine, with B/A = 1.5 to 3.0 (molar ratio),
A coating method characterized by applying a polyurethane resin paint whose main component is a reactant having a molecular weight in the range of 10,000 to 40,000.