JP3225982B2 - Copolyester resin for steel plate paint - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

This invention relates to a dibasic acid component comprising terephthalic acid, isophthalic acid and an aliphatic dibasic acid having 4 to 12 carbon atoms and a dihydric alcohol component comprising 1,4-cyclohexanedimethanol and neopentyl. The present invention relates to a copolymerized polyester resin for a steel sheet paint which is a glycol, and in particular, the copolymerized polyester resin is used in combination with an amino resin to be applied to a steel sheet as a baking paint for a steel sheet, thereby enabling production of an excellent coated steel sheet. is there. Paints are applied to thin metal sheets such as cold-rolled steel sheets, electro-galvanized steel sheets, hot-dip galvanized steel sheets, and stainless steel sheets, and the coated coiled steel sheets are used in electrical products, office equipment products, industrial machinery products, furniture, etc. The baking paint for a steel sheet is used as a paint suitable for a coated steel sheet called a so-called pre-coated steel sheet, which is supplied for forming processing of the steel sheet, and has excellent balance between high hardness and workability, high weather resistance,
Because it enables the production of coated steel sheets with excellent durability such as chemical resistance, the present invention, including the steel sheet industry,
It can be widely used in various industries such as electric devices, automobiles, transport machines, industrial machines, and building materials that use precoated steel sheets.

[0002]

2. Description of the Related Art Conventionally, a coated steel sheet provided as a coil, a so-called pre-coated steel sheet, has advantages in terms of labor saving, resource saving, environmental protection, coating management, etc., as compared with a post-coated steel sheet coated after forming. Excellent and widely awarded. In general, pre-coated steel sheets have two coats on the outer (front) surface and one coat on the inner (rear) surface. In general, an undercoat is applied to improve the surface roughness, and a paint for the purpose of preventing rust of the steel sheet is applied to the inner (back) surface. The characteristics required for the paint used for such pre-coated steel sheets are that high-speed coating is possible, that high-temperature short-time baking is possible, and that after coating, bending and drawing are performed. High workability, such as excellent resistance to water, is required. Furthermore, the top coat for the outer surface is required to have the same gloss, hardness, stain resistance, chemical resistance, and weather resistance as the post coat.

[0003]

However, none of the paints proposed to date as paints for pre-coated steel sheets which require such properties satisfy the above-mentioned conflicting coating properties. There is no one that satisfies the demand for high workability for processing, and the coating film with improved workability has problems such as insufficient hardness and stain resistance, poor chemical resistance and poor weather resistance. Things. Furthermore, when forming such a pre-coated steel sheet into a predetermined product, the joining is as follows:
Since welding cannot be used, caulking, rivets, screwing, etc. are used, but their joining is not aesthetically pleasing and has the problem that stress is concentrated because the joints are point-like . The present invention solves these conventional problems, and manufactures a coated steel sheet excellent in balance between high workability and hardness, stain resistance, chemical resistance, and weather resistance, and having good assembly adhesion after forming. To make it possible.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies on such problems, and as a result, have found excellent resins as raw materials for steel sheet paints, and have found that they can be solved by using the resins. Was completed. That is, the present invention is for a steel plate paint characterized in that terephthalic acid, isophthalic acid and an aliphatic dibasic acid having 4 to 12 carbon atoms, and 1,4-cyclohexanedimethanol and neopentyl glycol are constituent monomers. It relates to a copolymerized polyester resin.

Hereinafter, the present invention will be described in detail. ○ Copolyester resin Copolyester resin used in the present invention, terephthalic acid as a dibasic acid component, isophthalic acid and C4 to C12 aliphatic dibasic acid and neopentyl glycol as a dihydric alcohol component, 1,4-cyclohexane dimethanol is an essential constituent monomer component, and specific examples of the aliphatic dibasic acid having 4 to 12 carbon atoms include succinic acid, glutaric acid, adipic acid, pimelic acid, Examples include aliphatic dibasic acids such as suberic acid, azelaic acid, sebacic acid, undecylenic acid, and dodecane diacid, and ester derivatives thereof.

The combination ratio of the dibasic acid component is as follows:
20 to 60 mol% of terephthalic acid, 5 to 45 mol% of isophthalic acid, and 10 to 60 mol% of aliphatic dibasic acid having 4 to 12 carbon atoms based on the total amount of the dibasic acid components used
When the terephthalic acid content is less than 20 mol%, the cohesive strength of the resin becomes insufficient and the coating film hardness becomes poor. When it exceeds 60 mol%, the resin becomes hard, The workability of the film is reduced. When the amount of isophthalic acid is less than 5 mol%, the gloss of the coating film is reduced, and when it exceeds 40 mol%, the resin becomes brittle, the workability of the coating film is reduced, and the weather resistance is poor. become. When the amount of the aliphatic dibasic acid component is less than 10 mol%, the resin becomes hard and the workability of the coating film decreases, and when it exceeds 60 mol%, the resin becomes soft and the hardness decreases, Chemical resistance is reduced. As the acid component of the copolymerized polyester resin, in addition to the above acids, aromatic dibasic acids such as orthophthalic acid, α-naphthalenedicarboxylic acid, and β-naphthalenedicarboxylic acid; 1,4-cyclohexanedicarboxylic acid, tetrahydrophthalic anhydride, and hexahydroanhydride An alicyclic dibasic acid such as phthalic acid can be used in combination as long as the properties of the composition of the present invention are not impaired. Also, polyvalent carboxylic acids such as trimellitic acid and pyromellitic acid can be used in combination as long as they do not impair gelation or coating performance during the reaction. When a polycarboxylic acid is used in combination, the amount is 5 to the total acid component.
Desirably, it is in the range of not more than mol%.

As the dihydric alcohol component constituting the copolymerized polyester resin of the present invention, 1,4-cyclohexane dimethanol and neopentyl glycol are essential components. 1, based on the total amount of dihydric alcohol components
5 to 40 mol% of 4-cyclohexanedimethanol and 20 to 70 mol% of neopentyl glycol. When the amount of 1,4-cyclohexanedimethanol is less than 5 mol%, the weather resistance and chemical resistance of the coating film become insufficient, and when it exceeds 40 mol%, the resin becomes hard and the workability of the coating film becomes poor. It will be chipped. When the content of neopentyl glycol is less than 20 mol%, the hardness of the coating film becomes insufficient, and
If it exceeds 0 mol%, the coating film becomes hard and the workability decreases. As the alcohol component of the copolymerized polyester resin, other dihydric alcohol components can be used in combination. Specific examples thereof include ethylene glycol, 1,2-propylene glycol, 1,4-butanediol, , 3-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methylpentanediol, 2,2,3-trimethylpentanediol, diethylene glycol, triethylene glycol,
Examples include aliphatic dihydric alcohols such as dipropylene glycol. As in the case of the acid component, polyhydric alcohols such as glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol can be used in combination. When these polyhydric alcohols are used in combination, it is preferable to use 5 mol% or less based on all alcohol components. A preferable dihydric alcohol other than 1,4-cyclohexanedimethanol and neopentyl glycol is ethylene glycol, which is used to increase the cohesive strength of the resin and impart appropriate hardness to the coating film. ,
Durability can be increased.

The molecular weight of the copolymerized polyester resin of the present invention has a number average molecular weight (GPC, converted to PSt).
It is preferably from 10,000 to 30,000, and more preferably from 12,000 to 25,000. If the ratio is smaller than this range, the processability of the coating film is inferior, and if the ratio is larger, the viscosity when dissolved in a solvent is too high to cause a problem when coating.

[0009] Such a copolyester resin is produced by a usual method. For example, each raw material, that is, a melt polymerization method in which the same molar equivalent of an acid component and an alcohol component are heated at a temperature higher than the melting point of the product, a solid-phase polymerization method in which the polymerization is performed at a temperature lower than the melting point of the product, and a solution weight using a solvent There are legal, etc.
Either method may be adopted, but in order to efficiently obtain a polyester having an appropriate degree of polymerization in accordance with the object of the present invention, and from the viewpoint of economy, a melt polymerization method is preferable, and a transesterification method or a direct esterification method is used. It is manufactured by the method.

Amino Resin The copolyester resin of the present invention is used as a baking coating for steel sheets in combination with an amino resin, as in the case of other coating resins. The amino resin used in combination is melamine, benzoguanamine, A thermosetting resin obtained by reacting formaldehyde with urea or the like, or a resin obtained by subjecting part or all of the methylol groups of the thermosetting resin obtained by such a reaction to alkyl etherification such as methyl and butyl. No. Among the amino resins, melamine resin obtained by converting melamine to methylol is preferable because of excellent balance between hardness and processability after coating film formation, and methylated melamine, i-butylated melamine, and n-butylated melamine are preferable. Specific examples are given below. Such amino resins may be used alone or in combination of two or more. The combined ratio of the copolymerized polyester resin and the amino resin is preferably 90/10 to 60/40 by weight, more preferably 85/15 to 65/45. When the amount of the amino resin is small, the crosslinking density is low, the hardness and durability are low, and the adhesive strength is low. On the other hand, when the amount is large, the amino resin becomes unreacted, which is disadvantageous in terms of durability.

A method for preparing a paint The baking paint for a steel sheet using the copolymerized polyester resin of the present invention is obtained by adjusting the liquid properties of the above-mentioned amino resin and a pigment according to the intended use, and further a paint commonly used in the production of the paint. It is produced by blending a suitable additive used for the purpose of preventing problems at the time of coating and improving the durability of the coating film, and dissolving it in a solvent. As the pigment, for example, titanium dioxide, lead white, graphite, lead red, strontium chromate, zinc chromate, titanium yellow, cadmium yellow,
Inorganic pigments such as titanium black, iron black, molybdenum red, molybdenum white, navy blue, ultramarine, talc, mica, barium sulfate, calcium carbonate, silica, etc .; organic pigments such as carbon black, insoluble azo dyes, soluble azo dyes and phthalocyanine-based pigments No. As additives, for example, a viscosity imparting agent, a pigment dispersant, an antifoaming agent, an anti-skinning agent,
Those widely used in the field, such as a leveling agent, a slick agent, a lubricant, a curing accelerator, an antioxidant, an ultraviolet absorber, and a hydrolysis inhibitor, may be mentioned. The solvent is selected in consideration of the viscosity of the product paint,
Specific examples of the solvent used include aromatic solvents such as toluene, xylene, tetralin, and a mixed petroleum solvent of C9-11, and ketones such as methyl ethyl ketone, methyl isobutyl ketone, diisopropyl ketone, dibutyl ketone, cyclohexanone, and isophorone. Solvent: butanol, ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol butyl ether, 3-methoxybutanol, 3-methyl-
Alcohol solvents such as 3-methoxybutanol; ethyl acetate, propyl acetate, butyl acetate, ethylene glycol methyl ether acetate, ethylene glycol ethyl ether acetate, ethylene glycol butyl ether acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, propylene glycol Examples thereof include ester solvents such as butyl ether acetate, dimethyl adipate, dimethyl glutarate, dimethyl succinate, 3-methoxybutyl acetate, and 3-ethoxypropionate. One or more mixed solvents selected from such solvents are used.

The steel sheet to which the paint obtained as described above is applied is a cold-rolled steel sheet, an electro-galvanized steel sheet, a galvanized steel sheet, an alloyed hot-dip galvanized steel sheet, an electro-galvanized nickel alloy-plated steel sheet And electrotin-plated steel sheets, aluminum-plated steel sheets, stainless steel sheets, and the like, and those obtained by subjecting them to a chemical conversion treatment such as a chromate treatment or a phosphate treatment. Further, the present invention is also applicable to a steel sheet which has been subjected to a chemical conversion treatment and then to an organic thin film treatment.

Coating method A method for coating a steel sheet with a coating material is well known in the art. After adjusting the coating material to an appropriate coating viscosity, a coating method such as a roll coating, a flow coating, or a spray coating is selected. be able to. The coating speed is 30 to 120 m / min, and the film is heated and dried through a furnace such as hot air heating, far infrared heating, and high frequency induction heating. The coating thickness is 3 to 50 μm, preferably 15 to 25 μm.
The temperature is preferably adjusted to 20 to 300 ° C, more preferably 150 to 270 ° C, and the baking time is 1
This is performed within a range of 5 to 80 seconds. Before applying paint,
It is desirable to apply a base paint to the steel sheet to be used in advance in terms of steel sheet adhesion, corrosion resistance, and coating film durability. As such a base coating material, a polyester type, an epoxy type, a modified epoxy type or the like is usually used, and is applied with a dry film thickness of 1 to 10 μm, preferably 3 to 7 μm. In addition, the paint may be applied not only on one side but also on both sides, but usually, on the back side, an epoxy-based or modified epoxy-based paint is applied on a rustproof surface, and the Painted to take advantage of adhesion.

The bonding method The precoated steel sheet obtained by applying the baking paint for steel sheet using the copolymerized polyester resin of the present invention is particularly suitable for bonding with various kinds of adhesives. Urethane, epoxy, polyester,
The adhesive is selected from polyamide-based, acrylic-based, and cyanoacrylate-based adhesives. In addition, an acrylic or rubber-based pressure-sensitive adhesive or pressure-sensitive adhesive tape may be used according to the purpose. The T-peel adhesive strength between the coated steel sheets bonded as described above can exhibit a strength of 15 kg / 25 mm or more, which is appropriate in view of actual applications, and the adhesive is selected in consideration of this point. Among the above-mentioned adhesives, polyester-based and urethane-based adhesives are preferable from the viewpoint of workability at the time of bonding, short-time adhesiveness, adhesive strength, and adhesive durability. It is preferable to use a hot-melt adhesive as a component, using a copolymerized polyester containing terephthalic acid in an acid raw material component in an amount of 20 mol% or more. Adhesives in which various additives for imparting adhesion and fluidity to the copolyester resin are added can also be used. If you actually apply the adhesive,
It can be used in the form of a melt coating using an applicator or the like, a film form, a web form, a powder form, a solution form, or the like. As the urethane-based adhesive, a two-component adhesive composed of a polyol component and an isocyanate component that can be applied in a liquid state is preferable in terms of curability and adhesive strength. The paint is applied to both sides of the steel sheet or to one side of the steel sheet. In the bonding process using a pre-coated steel sheet coated with the paint, the surfaces on which the predetermined coating film is formed are overlapped or the predetermined coating film is not formed. If the surface is compatible with the adhesive to be used, the surface is adhered to the predetermined coating forming surface by using the adhesive. As a means for bonding, a method in which the coated steel sheet and the adhesive are heated and pressed at the same time, and a method in which the bonded portion of the coated steel sheet is heated by high-frequency induction and cooled immediately with a cooled hammer can be used.

Use The pre-coated steel sheet prepared by applying the baking paint for steel sheet using the copolymerized polyester resin of the present invention has excellent coating film performance, excellent coating film durability and excellent adhesiveness. , Refrigerator, washing machine, microwave oven, air conditioner, fluorescent light,
It can be used for electric appliances such as stoves, audio equipment, freezer showcases and vending machines, and office products such as office desks, archives and partitions.

[0016]

The reason why the steel sheet coated with the baking paint for steel sheet using the copolymerized polyester resin of the present invention exhibits excellent performance is presumed as follows. Due to the blocking effect of the bulky cyclohexane ring in which the ester bond portion of 1,4-cyclohexanedimethanol is bulky, deterioration of the coating film due to hydrolysis unique to polyester is reduced, and chemical resistance, water resistance, moisture resistance,
It exhibits an effect excellent in weather resistance and imparts appropriate flexibility to the coating film itself, so that a balance between hardness and workability is exhibited.

Hereinafter, a specific example will be described.

【Example】

Example 1 A four-necked flask equipped with a stirrer, a nitrogen inlet tube, a distillation tube, and a thermometer was charged with 77.6 parts by weight of dimethyl terephthalate, 74.4 parts by weight of ethylene glycol, and 62.5 parts by weight of neopentyl glycol. , 1,4-cyclohexanedimethanol 28.8
Parts by weight, and 0.05 parts by weight of zinc acetate were charged, the temperature was increased while introducing nitrogen, and methanol was distilled at 150 to 200 ° C., followed by 33.2 parts of isophthalic acid, 58.4 parts of adipic acid,
Additional charge of 0.05 parts by weight of antimony trioxide, 200-2
At 40 ° C., water was distilled off. While gradually reducing the pressure, 24
The polyester resin (A) was obtained by continuing the reaction at 0 ° C. under a reduced pressure of 1 mmHg for 3 hours. The obtained polyester resin (A) is a pale yellow transparent solid, the number average molecular weight is 12,000, and the composition of the polyester by NMR analysis is such that the molar ratio of the acid component is terephthalic acid / isophthalic acid / adipic acid = 40. / 20/40, the dihydric alcohol component is ethylene glycol / neopentyl glycol /
1,4-cyclohexanedimethanol = 39/41/20.

Examples 2 to 7, Comparative Examples 1 to 5 Copolymerized polyesters (B) to (L) were synthesized with the polyester compositions shown in Table 1 in the same manner as in Example 1.
(F) to (J) are comparative examples.

[0019]

[Table 1]

Evaluation Test Example 1 70 parts of a polyester resin A was dissolved in 100 parts of a mixed solvent of xylene / cyclohexanone = 1/1 (weight ratio), and titanium oxide TYPAKE CR-50 (manufactured by Ishihara Sangyo Co., Ltd.)
100 parts were blended, and after high-speed stirring, glass beads were added,
Shake on a paint shaker for 5 hours. After mixing 30 parts of amino resin Uban 122 (60% nonvolatile content) (manufactured by Mitsui Toatsu Chemicals Co., Ltd.) and 0.05 part of paratoluenesulfonic acid, the mixture is adjusted with the above-mentioned mixed solvent so that the nonvolatile content becomes 50%. As a result, a baked paint for a steel sheet was obtained. Electro-galvanized steel plate chromate treated plate (0.5mm thick) degreasing this paint
Was coated with a bar coater so as to have a dry film thickness of 20 μm, and was heated in a hot-air heating furnace so as to reach a plate temperature of 240 ° C. in 60 seconds after being charged. After cooling, it was subjected to the following test.
(1) Glossiness A 60-degree glossiness was measured according to JIS K5400 7.6. (2) Pencil hardness A scratch of the pencil hardness was evaluated according to JIS K5400 8.4.2. (3) Bending workability According to JIS K5400 8.1, after bending a cylinder, tightening it with a vise, cracking and peeling of the coating film were determined. (4) Stain resistance Magic ink (blue, black, red) was applied to the surface of the coating film in a length of 20 mm, left in a constant temperature room at 23 ° C. and 60% RH for 24 hours, and wiped off with an ethanol impregnated cloth to remain. Traces were observed. (5) Acid resistance It was immersed in a 5% sulfuric acid aqueous solution at 20 ° C. for 24 hours, and expressed as a gloss retention (%) before immersion. (6) Alkali resistance It was immersed in a 5% aqueous solution of caustic soda at 20 ° C. for 24 hours, and expressed as a gloss retention (%) before immersion. (7) Weather resistance According to ASTM-G53, the test conditions were UV irradiation at 60 ° C and 4 ° C.
The test was carried out for 4 hours at 40 ° C. + moisture exposure, and expressed as a gloss retention ratio after exposure for 480 hours with respect to the glossiness (60 degrees) before the test. (8) Adhesiveness The coated steel sheet is cut into a 25 mm width × 100 mm length, and a polyester adhesive film 100 μm is sandwiched between the coated surfaces of the coated steel sheet as an adhesive, and pressed with a hot press at 150 ° C. for 2 minutes ( 5 kg / cm ² ) and bonded. The T peel adhesion strength (kg / 25 mm) of the adhesive was measured at a crosshead speed of 200 mm / min.

Evaluation Test Examples 2 to 8 The polyester resin B was prepared in the same manner as in Evaluation Test Example 1.
Using E, K, and L, a paint was prepared with the composition shown in Table 2 to prepare a coated steel sheet, and an evaluation test was performed. Table 2 shows the results. Comparative Evaluation Test Examples 1 to 5 In the same manner as in Evaluation Test Example 1, polyester resin F
To J, coating materials were prepared with the formulations shown in Table 2 to prepare coated steel sheets, and evaluation tests were performed. Table 2 shows the results.

[0022]

[Table 2]

[0023]

The steel sheet coated with the stoving paint for steel sheet using the copolymerized polyester resin of the present invention has a film performance which is inconsistent with hardness, stain resistance and workability, and has chemical resistance,
It is a steel plate with excellent weather resistance. Furthermore, after forming processing such as drawing, bending, etc., it is bonded using various adhesives, so that mechanical other than conventional welding such as screwing, winding, caulking etc. It is an alternative to joining and can lead to innovative advances in molding, post-joint aesthetics and design. Such a coated steel sheet is widely used in the fields of electric equipment, office equipment, building materials, transport vehicles, and the like.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C08G 63/00-63/91 C09D 167/00-167/02

Claims (1)

(57) [Claims] 1. A steel sheet paint comprising terephthalic acid, isophthalic acid, an aliphatic dibasic acid having 4 to 12 carbon atoms, 1,4-cyclohexanedimethanol and neopentyl glycol as constituent monomers. Polymerized polyester resin.