JP3204394B2 - Resin-coated steel sheet laminate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a resin-coated steel sheet. More specifically, the present invention provides a resin-coated steel sheet having excellent alkali resistance, moisture resistance, and excellent workability.

[0002]

2. Description of the Related Art So-called pre-coated metal (PCM) such as painted steel sheet is used in the field of building materials such as roofing materials and wall materials, outdoor equipment such as shed, radiator unit, etc. by taking advantage of its economical efficiency, productivity and workability. Widely used for home appliances such as VTRs, audios, and washing machines. The first required property of a coated steel sheet is that it be excellent in bending workability. Alkyd resins, acrylic resins, epoxy resins, etc. are currently used as paint resins, but have drawbacks in workability, and high-molecular-weight polyesters are used in fields requiring high workability. is the current situation.

[0003]

[Problems to be Solved by the Invention] At present, not only in the field of building materials, but also in home appliances, the use of PCM is increasing more and more. It is getting more and more attention and is being used. It is essential that high molecular weight polyester as a resin for painted steel sheet tops have properties such as durability suitable for each application in order to replace post-coating with pre-coating for all home appliances.
Among them, high-molecular-weight polyesters with poor alkali-resistance, moisture-resistance, and processability have not been found yet in home appliances such as washing machines and dishwashers, and have not been found to be PCM. Is delayed, and steel plate manufacturers and the home appliance industry are demanding an immediate solution.

[0004]

Means for Solving the Problems In view of the above problems, the present inventors have conducted intensive studies in order to obtain a coating resin composition having excellent workability and moisture resistance, and particularly excellent anti-alkaline resistance. Thus, the present invention has been completed. That is, the present invention relates to a resin-coated steel sheet having a steel sheet coated with a top coat containing a polyester resin.
% Immersion in NaOH aqueous solution at room temperature for 24 hours, the top coat layer after immersion has an area of 0%
A resin-coated steel sheet having a bending workability of 2T or more and a pencil hardness of F or more.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION A resin-coated steel sheet in which a top coat containing a polyester resin is applied on the steel sheet of the present invention,
The area of blistering and gloss abnormality of the top coat layer after immersion in a 5% NaOH aqueous solution at room temperature for 24 hours is 0%. If the top coat layer has blistering or abnormal gloss, when used for home appliances such as washing machines and dishwashers, the detergent used will cause the top coat layer to discolor or peel off, resulting in long-term use. Not tolerable.

[0006] The resin-coated steel sheet of the present invention in which a top coat containing a polyester resin is applied on the steel sheet of the present invention has a bending workability of 2T or more. If the bending workability is lower than 2T, water will enter the inside from cracks in the top coat layer of the bent or folded part of the steel plate when used in household appliances such as washing machines and dishwashers that may be exposed to water. However, there is a possibility that rust or peeling of the top coat layer may occur.

Further, a resin-coated steel sheet in which a top coat containing a polyester resin is applied on the steel sheet of the present invention,
Pencil hardness is F or more. If the pencil hardness is less than F,
It is easily scratched in everyday use and does not play a role as a resin-coated steel plate coated with a top coat.

The resin-coated steel sheet of the present invention in which a top coat containing a polyester resin is applied to the steel sheet according to the JIS
G 3312 8.6 is provided with a prescribed grid,
When a peeling test is performed using cellophane tape after leaving the film for 240 hours in the air of ± 2 ° C. and a humidity of 98% or more, the number of peeled is preferably 10 or less. If the number of peeled layers exceeds 10, the topcoat layer may be peeled when used in home appliances used in places with high humidity such as washing machines and dishwashers.

The resin-coated steel sheet of the present invention is, for example, a polyester resin comprising 100 mol% of an aromatic dicarboxylic acid, 20 to 80 mol% of a long-chain aliphatic diol having 6 to 10 carbon atoms and 70 to 20 mol% of neopentyl glycol. In addition, a resin composition for coatings containing an alkyl etherified formaldehyde resin is applied to a steel sheet and cured. Instead of neopentyl glycol, a glycol component represented by the following general formula (I) may be used. In the case of the glycol component represented by the following general formula (I), the following general formula (I) ) May be set to 100%.

[0010]

Embedded image

(Wherein R1 and R2 each have 2 to 2 carbon atoms)
4)

The polyester resin composition for a paint which can be used for the top coat layer of the resin-coated steel sheet of the present invention comprises 100 mol% of an aromatic dicarboxylic acid as a dicarboxylic acid component, and terephthalic acid or isophthalic acid as an aromatic dicarboxylic acid. Acid, orthophthalic acid, diphenyl-p, p'-
Dicarboxylic acid, diphenyl-m, m'-dicarboxylic acid,
Diphenylmethane-p, p'-dicarboxylic acid, diphenylmethane-m, m'-dicarboxylic acid, 2,2'-bis (4-carboxyphenyl) propane, naphthalene-
1,4-dicarboxylic acid, naphthalene-1,5-dicarboxylic acid, naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid, diphenyl ether-p,
p'-dicarboxylic acid, diphenyl ether-m, m'-
Examples thereof include dicarboxylic acid, diphenylsulfone-p, p'-dicarboxylic acid, diphenylsulfone-m, m'-dicarboxylic acid, and lower alkyl ester derivatives thereof, and these are used alone or in combination of two or more.

The aromatic dicarboxylic acid is appropriately selected from the viewpoints of economy and physical properties, but terephthalic acid, isophthalic acid and orthophthalic acid are preferably used from the viewpoints of moisture resistance and alkali resistance.

When an aliphatic or alicyclic dicarboxylic acid is used in addition to the aromatic dicarboxylic acid, the alkali resistance is significantly reduced.

[0015] The polyester resin composition for a paint which can be used for the top coat layer of the resin-coated steel sheet of the present invention comprises:
For example, the glycol component is composed of 30 to 80 mol% of a long-chain aliphatic diol having 6 to 10 carbon atoms and 70 to 20 mol% of neopentyl glycol. Instead of neopentyl glycol, a glycol component represented by the following general formula (I) may be used. In the case of the glycol component represented by the following general formula (I), the following general formula (I) ) May be set to 100%.

[0016]

Embedded image

(Wherein R1 and R2 each have 2 to 2 carbon atoms)
4)

Examples of the long-chain aliphatic glycol having 6 to 10 carbon atoms include hexanediol, heptanedione, octanediol, nonanediol and dodecanediol, and the glycol component represented by the general formula (I) is 2,2. 2'-diethyl-1,3-propanediol,
2-n-butyl-2-ethyl-1,3-propanediol, 2,2'-di-n-butyl-1,3-propanediol and the like. When the content of neopentyl glycol or the long-chain aliphatic glycol having 6 to 10 carbon atoms in the polyester resin of the present invention exceeds 80 mol%, the hardness of the alkali-resistant cured coating film is undesirably reduced. If the content of neopentyl glycol exceeds 70 mol%, the processability may be reduced.

The polyester resin composition for coating which can be used for the top coat layer of the resin-coated steel sheet of the present invention substantially comprises a dicarboxylic acid and a glycol, but contains a small amount of a trifunctional or higher polycarboxylic acid or / and a polyol. By using it, the alkali resistance and the moisture resistance can be further improved. Examples of trifunctional or higher polycarboxylic acids that can be used for such purposes include aromatic polycarboxylic acids such as trimellitic acid and pyromellitic acid, and aliphatic carboxylic acids such as butanetetracarboxylic acid. Examples of the above polyols include aliphatic polyols such as glycerin, trimethylolpropane, and pentaerythritol, and can be used in an amount of 10 mol% or less, preferably in a range of 1 mol% to 5 mol%.

The polyester resin composition for a paint which can be used for the top coat layer of the resin-coated steel sheet of the present invention has a reduced viscosity of 0.3 to 0.7, a number average molecular weight of 5,000 to 25,
000 is preferred.

Examples of the alkyl etherified formaldehyde resin which can be used in the top coat layer of the resin-coated steel sheet of the present invention include, for example, those having 1 to 4 carbon atoms such as methanol, ethanol, n-propanol, iso-propanol and n-butanol. A condensation product of formaldehyde or paraformaldehyde, etc., alkyletherified with an alcohol of the formula (1) and urea, N, N'-ethylene urea, dicyandiamide, aminotriazine, etc., specifically, methoxylated methylol urea, methoxylated methylol- N, N'-ethylene urea, methoxylated methylol dicyandiamide, methoxylated methylol benzoguanamine, butoxylated methylol melamine, butoxylated metrole benzoguanamine and the like.

The polyester resin composition for a paint which can be used for the top coat layer of the resin-coated steel sheet of the present invention has a ratio of the polyester resin to the alkyl etherified formaldehyde resin of 95 to 60: 5 to 40 (weight ratio). Preferably, there is. The ratio of the polyester resin to the alkyl etherified formaldehyde resin is 95 to 60: 5.
It is preferably from 40 to 40 (weight ratio). If the proportion of the polyester resin exceeds 95% by weight, the intended alkali resistance and hardness are insufficient, which is not preferable. On the other hand, if it is less than 60% by weight, processability is poor, which is not preferable. The resin composition for coating of the present invention may contain a curing catalyst such as p-toluenesulfonic acid, monoalkyl phosphate, or an amine salt of p-toluenesulfonic acid. The amount of the catalyst used is 0 to 5% by weight based on the formaldehyde resin.

The polyester resin composition for a paint which can be used for the top coat layer of the resin-coated steel sheet of the present invention is used in the form dissolved in an organic solvent. As the organic solvent, for example, toluene, xylene, Solvesso # 1
00, Solvesso # 150, ethyl acetate, butyl acetate,
It is appropriately selected from methyl cellosolve, butyl cellosolve, methyl cellosolve acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, ethylene glycol acetate and the like in consideration of solubility and evaporation rate.

The polyester resin composition for paints that can be used in the top coat layer of the resin-coated steel sheet of the present invention has the following objects:
Depending on the application, an extender such as titanium oxide, talc, barium sulfate, or a known coloring agent is added. Further, a surface smoothing agent, an antifoaming agent, a thixotropic agent and the like can be blended. Further, other synthetic resins, for example, an epoxy resin, a vinyl chloride resin and the like can be blended within a range not to impair the object of the present invention.

The resin-coated steel sheet of the present invention can be obtained by optimizing the composition of the polyester resin, the ratio of the curing agent to the polyester resin, the ratio of the pigment and the like to the resin, and the like within the ranges described above. it can.

The above-mentioned polyester resin composition for a coating material is produced by a known dispersing and kneading method such as a roll mill or a medium disperser. The polyester resin composition for coating can be applied by a conventional method such as a roll coater, a curtain coater, a spray coating, and drying and baking temperatures can be appropriately selected, but are usually from 150 to 270 ° C. for 10 seconds to 20 minutes.

[0027]

The present invention will be described in detail below with reference to examples, but the present invention is not limited to the examples. In the examples, "parts" means "parts by weight" and "%" means "% by weight". Each measurement item followed the following method.

(1) Reduced viscosity η sp / c (dl / g) 0.1 g of polyester was dissolved in 25 cc of a mixed solvent of phenol / tetrachloroethane (volume ratio: 6/4), and 30 ° C.
Was measured.

(2) Flexibility (Machinability) When a painted steel plate is bent 180 ° and three cracks having the same thickness are inserted into the bent portion and the 3T, which is determined to be cracked at the bent portion, is bent. Indicates that no cracks occur.

(3) Pencil hardness test Cut the tip of a pencil (JIS standard, Mitsubishi pencil)
It is displayed with the softest hardness that does not hurt by drawing on the painted surface by inclining 5 °.

(4) Moisture resistance The painted board is provided with a checkerboard specified in 8.6 of JIS G 3312, and is placed in a room at 50 ± 2 ° C. and a humidity of 98% or more.
After leaving for 0 hr, a peeling test was performed using a cellophane tape.

(5) Alkali resistance The substrate was immersed in a 5% aqueous NaOH solution at room temperature for 24 hours, and the appearance was judged abnormal.

Production Example 1 916 parts of isophthalic acid, 355 parts of orthophthalic acid, 15.4 parts of trimellitic anhydride, neopentyl glycol 6
66 parts, 1133 parts of hexanediol and 0.82 parts of tetrabutyl titanate were charged into a reaction vessel,
The temperature was raised to 0 ° C over 4 hours to carry out an esterification reaction.
Next, the pressure is reduced to 250 to 270 to 1 mmHg over 30 minutes.
The polycondensation reaction was performed at a temperature of 1 hour. The obtained resin (A) had a reduced viscosity of 0.37. Hereinafter, various polyesters (B) to (H) were synthesized in the same manner. The result is
It is shown in the table.

[0034]

[Table 1]

Examples and Comparative Examples 100 parts of each of the polyester resins (A) to (D) was mixed with a cyclohexanone / solvesso # 150 mixed solvent (weight ratio: 5).
(0/50) dissolved in 100 parts and adjusted to a nonvolatile content of 50%. 200 parts of the above polyester resin solution, methyl etherified methylol melamine (trade name: Sumimar M-40)
S, nonvolatile content 80%, manufactured by Sumitomo Chemical Co., Ltd.) 31.3
Part, titanium oxide (trade name: CR-930 Ishihara Sangyo Co., Ltd.)
100 parts), p-toluenesulfonic acid 0.25 parts, surface smoothing agent (trade name: Polyflow S, Kyoeisha Yushi Co., Ltd.)
0.5 part), and the mixture was shaken and kneaded with a bead disperser for 6 hours to prepare each of the resin compositions (i) to (iv) for a coating material of the present invention. Using polyester resins (E) to (H),
Coating compositions (v) to (viii) were obtained in exactly the same manner. The obtained coating composition was coated on a 0.3 mm thick zinc-iron plate (JISG).
3302) using a # 36 bar coater and applying 230
Bake at 60 ° C for 60 seconds. The coating thickness was about 20 μm.
Table 2 shows the coating film performance of the obtained coated plate.

[0036]

[Table 2]

[0037]

The resin-coated steel sheet of the present invention is excellent in alkali resistance, hardness, workability, and moisture resistance, and is particularly excellent in durability as compared with the case where a conventional high molecular weight polyester resin is used. can get. The high degree of workability, various properties of moisture resistance and alkali resistance achieved by the resin-coated steel sheet of the present invention is of great industrial significance. The resin-coated steel sheet of the present invention can be widely used as a resin-coated steel sheet for home electric appliances such as washing machines and dishwashers, which require the alkali resistance and moisture resistance, taking advantage of the above advantages.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 26/00 C09D 167/02 C09D 201/00

Claims (1)

(57) [Claims] In a resin-coated steel sheet having a steel sheet coated with a top coat containing a polyester resin, when the resin-coated steel sheet is immersed in a 5% NaOH aqueous solution at room temperature for 24 hours, the blister of the top coat layer after immersion is reduced. A resin-coated steel sheet characterized by having an area of abnormal gloss of 0%, bending workability of 2T or more, and pencil hardness of F or more.