JP3107869B2 - Resin composition for can coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin composition for can coating which is applied to the outer surface of food cans, beverage cans and the like.

[0002]

2. Description of the Related Art The consumption of canned beverages such as coffee, juice, oolong tea and the like has been remarkably increasing in recent years along with changes in consumer life. Of these cans, the method of manufacturing a can called a three-piece can is to prepare a metal plate that has been cut to the required size in advance, and then apply a coating plate to the interior coating, exterior primer coating, printing, and exterior finishing paint. After that, a can is obtained through a can-making process. Such a painting process for three-piece cans
The number of steps is large and very complicated. Therefore, with the rapid expansion of the canned beverage market, there is a strong demand for streamlining the production process and improving the production speed.

[0003] Conventionally, acrylic, epoxy and polyester paints have been used for these exterior coatings. However, in the case of such a conventional paint, if a more streamlined coating system is assumed, the demand cannot be met, and the development of a new paint system is desired.

[0004]

In recent years, in order to rationalize the coating of cans, a coil coating has been studied instead of a cut plate coating, and this is used for can-end coating. When a can body is coated with a coil coat, simultaneous baking inside and outside is possible and the speed can be increased, so the rationalization effect is enormous. Further, in order to save labor in the printing process, it is possible to save labor and increase the speed by laminating a printed film on a plate to which an external undercoat has been previously coated with a coil coat. The function of the outer surface undercoat plays an important role in enabling the coil coating of the inner and outer surface undercoats and the lamination of the subsequent printing process. The reason is that coil-coated boards can be printed with high-speed lamination for single-mass varieties of cans.However, for small-volume varieties, it is difficult to change the mold. After cutting into cut sheets, printing and painting. In this case, cracks and scratches during the cutting process, peeling of the coating film at the cut end surface, so-called enamel hair, are not allowed. In addition, since a mass-produced product is inevitably laminated with a print film, there is a problem of adhesion during lamination as an outer surface undercoat.

Furthermore, such an outer surface undercoat is usually used as a white coat in which titanium oxide is dispersed for decorativeness as a can, so that it is necessary to have good pigment dispersibility and hiding power. In addition, when applying a coil coat, high-speed, short-time baking is possible,
In addition to preventing blocking during winding and transport of heavy coils, it also has sufficient functions such as retort resistance, adhesion, workability, and scratch resistance required as an undercoat paint for paint for general cans. It is necessary to do.

[0006] As described above, by changing the coating method and the printing method of the three-piece can, there is a strong demand for the development of a paint having a new function in place of the conventional paint for the undercoat for the outer surface of the can.

An object of the present invention is to provide an excellent retort resistance, blocking resistance, moldability, adhesion, and whiteness of a coating film, to enable easy coil coating, to obtain enamel hair upon cutting, and to improve lamination. An object of the present invention is to provide a resin composition for an undercoat paint for an outer surface of a can which is excellent in adhesiveness at the time.

[0008]

In view of the above problems, coil coating can be easily applied and baked, and can be used as an undercoat for the outer surface of cans, which can withstand severe canning and filling processes, and has enamel hair properties and cuts when cut. Excellent adhesion, good pigment dispersibility,
Concealing properties, having both excellent adhesiveness with the laminate film, as a result of intensive studies on the resin composition for the outer surface undercoat paint for cans, the above-mentioned problems were caused by using a specific saturated copolymerized polyester described later. Were found to be solved at once, and the present invention was completed.

That is, the present invention provides a can comprising a saturated polycarboxylic acid and a polyhydric alcohol, and a saturated copolymerized polyester having the following conditions, and an amino resin or / and a blocked isocyanate compound. It is a resin composition for paint. The proportion of the aromatic dicarboxylic acid in the saturated dicarboxylic acid component is 80 to 100 mol%. 0.5 to the total acid component or the total glycol component
5.0 mol% of a tri- or higher functional polycarboxylic acid and / or polyhydric alcohol is a copolymer component. The reduced viscosity (dl / g) is 0.35 to 0.65. Glass transition temperature 20-70 ° C, acid value 5-120eq / 1
0 ⁶ g a specific gravity of 1.24 (30 ° C.) or less.

The saturated copolyester used in the resin composition for can coating of the present invention mainly comprises a saturated polycarboxylic acid and a polyhydric alcohol.

Among saturated polycarboxylic acids, aromatic dicarboxylic acids include, for example, terephthalic acid, isophthalic acid,
Orthophthalic acid, 2,6-naphthalenedicarboxylic acid, 5
-Sodium sulfoisophthalic acid and the like. As the saturated polycarboxylic acid other than the aromatic dicarboxylic acid, an aliphatic dicarboxylic acid is used.As the aliphatic dicarboxylic acid, for example, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecandioic acid, dimer acid, tetrahydroacid Examples thereof include phthalic acid, hexahydrophthalic acid, hexahydroisophthalic acid, and hexahydroterephthalic acid. Further, examples of the trivalent or higher functional polycarboxylic acid include trimellitic acid and pyromellitic acid.

The polyhydric alcohol component includes ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 12-dodecanediol, 2-methyl-1,
8-octanediol, 2,2-dimethylolbutane,
2,2-dimethylolpentane, 3,3-dimethylolpentane, 2,2-dimethylolheptane, 3,3-dimethylolheptane, 4,4-dimethylolheptane,
Aliphatic glycols such as 3,3-dimethyloloctane and 3-methylpentanediol, cyclohexanedimethanol, tricyclodecanedimethanol, ethylene oxide or / and propylene oxide adducts of bisphenol A, ethylene oxide of hydrogenated bisphenol A and / or Representative examples include propylene oxide adducts.

In the saturated copolyester used in the present invention, the ratio of the aromatic dicarboxylic acid to the saturated dicarboxylic acid as a reaction component is 80 to 10 as described above.
It is essential that the content be 0 mol%, preferably 85 to 100 mol%, and more preferably 89 to 100 mol%. When the proportion of the aromatic dicarboxylic acid is less than 80 mol%, the cohesive strength of the resin is reduced, the coating strength is reduced, and the requirements are satisfied in terms of metal adhesion, retort resistance, blocking resistance, and the like. I can't let that happen.

The saturated copolyester used in the present invention has a content of 0.1% based on the total acid component or the total glycol component.
5 to 5.0 mol%, preferably 0.5 to 3.0 mol%,
More preferably, it is essential to copolymerize 1 to 3 mol% of a polyfunctional carboxylic acid and / or polyhydric alcohol having a functionality of 3 or more. As a trifunctional or higher polycarboxylic acid,
For example, trimellitic acid, pyromellitic acid, benzophenonetetracarboxylic acid and the like, and as trihydric or higher polyhydric alcohol, glycerin, trimethylolethane,
Trimethylolpropane. If the content of these trifunctional or higher functional components is less than 0.5 mol%, the adhesiveness at the time of lamination is extremely poor, the workability at the time of cutting is poor, enamel hair is generated, and the coating film is easily peeled off by impact.

The saturated copolymer polyester used in the present invention has a reduced viscosity (dl / g) of 0.35 to 0.6 as a characteristic of the resin.
5, preferably 0.40 to 0.65, more preferably 0.50 to 0.65, and a glass transition temperature of 20 to 7
0 ° C, preferably 35-55 ° C, more preferably 40 ° C.
It is essential that the temperature is ５５55 ° C. If the reduced viscosity (dl / g) is less than 0.35, the cross-linking density of the coating film becomes high and enamel hair is easily generated, and if it exceeds 0.65, the coating viscosity becomes high and the coating property decreases, and It is not economical because the non-volatile content concentration of the compound cannot be increased. Glass transition temperature is 20
If the temperature is lower than ℃, the coating film easily causes blocking,
If the glass transition temperature exceeds 70 ° C, the paint film becomes too hard, and the paint film peels and cracks in the drawing and cutting processes. Become.

The acid value is 5 to 1 for satisfying metal adhesion.
20eq / 10 ⁶ g, preferably 20~100eq / 10 ⁶ g, more preferably from 40~100eq / 10 ⁶ g mandatory. No desired effect an acid value of less than ^{5eq / 10 6 g, 120eq /} 10 6
If it exceeds g, the desired effect in terms of retort resistance cannot be obtained.

It is essential that the specific gravity of the resin at 30 ° C. is 1.24 or less, preferably 1.22 or less.
The specific gravity of the resin is important in satisfying the dispersibility of the pigment, the concealing property of the coating film, and the whiteness, and when the specific gravity exceeds 1.24,
It is difficult to obtain a coating film having excellent whiteness and excellent hiding power.

The following are examples of the composition of the saturated copolymerized polyester desired to satisfy the above conditions. That is, 80 to 100 mol% of terephthalic acid or isophthalic acid as an aromatic dicarboxylic acid, and 0 to 2 mol of adipic acid or sebacic acid as an aliphatic dicarboxylic acid.
0 mol%, as a polyhydric alcohol component, ethylene glycol, neopentyl glycol, 1,6-hexanediol, 1,9-nonanediol, 3,3-dimethylolheptane, cyclohexanedimethanol, ethylene oxide of bisphenol A or / and A compound selected from 2 to 4 mol% adduct of propylene oxide, and 3
Tri-mellitic acid and / or trimethylolpropane copolymerized as a polyfunctional carboxylic acid or / and / or polyhydric alcohol having a functionality of 0.5 to 5.0 mol% with respect to all acid components or all glycol components. is there.

The method for producing the saturated copolymerized polyester used in the present invention is not particularly limited, but is usually prepared from a saturated polycarboxylic acid and a polyhydric alcohol using a known polymerization catalyst.
It is produced by polycondensation through transesterification.

In the present invention, the acid value of the saturated copolymerized polyester is important, but it is preferable to adjust the acid value by a method of adding a polycarboxylic anhydride at the latter stage of the polycondensation. Examples of polycarboxylic anhydrides used for such acid addition include phthalic anhydride, tetrahydrophthalic anhydride, succinic anhydride, trimellitic anhydride, pyromellitic anhydride, hexahydrophthalic anhydride, and the like. Preferred are phthalic anhydride, succinic anhydride, trimellitic anhydride, and hexahydrophthalic anhydride.

The amino resin used in the present invention includes, for example, methanol, ethanol, n-propanol and n-propanol.
Formaldehyde or paraformaldehyde alkylated with an alcohol having 1 to 4 carbon atoms such as butanol, urea, N, N-ethylene urea,
Condensation products with dicyandiamide, aminotriazine, etc., specifically, methoxylated methylol urea, methoxylated methylol N, N-ethylene urea, methoxylated methylol dicyandiamide, methoxylated methylol melamine, methoxylated methylol benzoguanamine, butoxylated methylol Melamine, butoxylated methylol benzoguanamine and the like.

In the resin composition for can coating composition of the present invention, the amount of the amino resin is 100
2 to 50 parts by weight, preferably 10 to 30 parts by weight based on parts by weight
Parts by weight. If the amount is less than 2 parts by weight, the strength of the coating film may decrease, and if it exceeds 50 parts by weight, the coating film may be too hard.

Examples of the blocked isocyanate compound used in the present invention include aliphatic diisocyanates such as tetramethylene diisocyanate and hexamethylene diisocyanate, alicyclic rings such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated toluene diisocyanate, hydrogenated diphenylmethane diisocyanate and the like. Block isocyanates in which the isocyanate groups of known diisocyanates are blocked, such as aromatic diisocyanates such as aromatic diisocyanates and xylylene diisocyanate, aromatic diisocyanates such as tolylene diisocyanate and 4,4'-diphenylmethane diisocyanate, are required. Can be arbitrarily selected from these.

The compounding amount of the blocked isocyanate compound is 2 to 50 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the saturated copolymerized polyester resin. It is also possible to use a combination of an amino resin and a blocked isocyanate compound.

The resin composition for can coating of the present invention is formed into a coating in a state of being dissolved in a known organic solvent. As the organic solvent used for coating, for example, toluene, xylene, solvesso, ethyl acetate, butyl acetate, methyl ethyl ketone, cyclohexanone, isophorone, methyl cellosolve, butyl cellosolve, ethylene glycol monoacetate, etc. It is appropriately selected.

The resin composition for a can coating composition of the present invention comprises a known inorganic or organic pigment such as titanium oxide, calcium carbonate, red iron oxide, carbon, phthalocyanine pigment, p-toluenesulfonic acid, p-dodecylbenzenesulfonic acid, phosphorus Catalysts for curing amino resins such as acids and their ester compounds, reaction catalysts for blocked isocyanate compounds such as dibutyltin dilaurate and tertiary amines, and other known additives such as surface smoothing agents, defoamers, thixotropic agents, and dispersants Can be blended.

A method for coating the resin composition for can coating of the present invention,
The curing conditions are not particularly limited, and are usually applied by roll coating, and dried and cured at a temperature of 150 to 300 ° C.

[0028]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

The method for measuring the characteristic values of the saturated copolymerized polyester will be described below. Measurement items were resin composition and reduced viscosity (dl /
g), glass transition temperature, acid value, specific gravity.

Resin Composition The molar ratio of the acid component to the alcohol component was determined by nuclear magnetic resonance spectroscopy and gas chromatography analysis using alcoholysis.

Reduced viscosity (dl / g) 0.1 g of polyester was dissolved in 25 cc of a phenol / tetrachloroethane (volume ratio: 6/4) mixed solvent and measured at 30 ° C. using an Ubbelohde viscometer.

Glass transition temperature Measured at a heating rate of 20 ° C./min using a differential scanning calorimeter (DSC).

Acid value 0.2 g of polyester was dissolved in 20 ml of chloroform, and titrated with a 0.1N KOH ethanol solution.
0 was determined equivalents per ^{6 g (eq / 10 6 g} ).

Specific Gravity The specific gravity of the polyester was determined at 30 ° C. by a flotation method using a density gradient tube.

Synthesis Example 1 272 parts by weight of dimethyl terephthalate, 272 parts by weight of dimethyl isophthalate, and ethylene glycol 19 were placed in a reaction vessel equipped with a stirrer, a thermometer and a partial reflux condenser.
5 parts by weight, 253 parts by weight of neopentyl glycol, 3,
After 158 parts by weight of 3-dimethylol heptane and 0.2 parts by weight of tetrabutyl titanate as a catalyst were reacted at 210 ° C. for 3 hours while stirring and heating, 30.1 parts by weight of sebacic acid and trimellitic anhydride were used. 5.7 parts by weight were charged and reacted at 210 ° C. for 60 minutes, and then reacted at 250 ° C. for 60 minutes under a reduced pressure of 0.1 mmHg while gradually reducing the pressure. Next, after the pressure was reduced to normal pressure, 1.75 parts by weight of phthalic anhydride was charged and reacted for 30 minutes to obtain a saturated copolymerized polyester A of the present invention. Table 1 shows the characteristic values of the obtained resin.

Synthesis Examples 2 to 10 As in Synthesis Example 1, the saturated copolymerized polyesters B to
J was obtained. Table 1 shows the characteristic values of the obtained resin.

[0037]

[Table 1]

The names of the abbreviations used in Table 1 are shown below. TPA: terephthalic acid IPA: isophthalic acid AA: adipic acid SA: sebacic acid TMA: trimellitic acid EG: ethylene glycol NPG: neopentyl glycol DMH: dimethylol heptane 1,6HD: 1,6-hexanediol 1,9ND: 1 , 9-nonanediol BPE-20: ethylene oxide 2 of bisphenol A
Molar adduct BPE-40: ethylene oxide 4 of bisphenol A
Molar adduct CHDM: cyclohexanedimethanol TMP: trimethylolpropane OPA: phthalic anhydride ScA: succinic anhydride

Comparative Synthesis Examples 1 to 9 In the same manner as in Synthesis Example 1, saturated copolymerized polyesters K to S
I got Table 2 shows the characteristic values of the obtained resin.

[0040]

[Table 2]

Examples 1 to 8 Saturated copolymerized polyesters A obtained in Synthesis Examples 1 to 10
H is 30 parts by weight of cyclohexanone, Solvesso # 1
50 (manufactured by Esso Corporation) was dissolved at a ratio of 30 parts by weight and saturated copolymerized polyester at a ratio of 40 parts by weight to obtain a polyester resin solution. An amino resin or blocked isocyanate was added to the obtained resin solution, a predetermined amount of titanium oxide was added as a pigment, and beads were dispersed.
Was adjusted so as to obtain a composition for can coating composition of the present invention. The obtained composition for can coating was applied to a rotating steel material for can with a bar coater so that the dry film thickness became 120 mg / 100 cm ^2, and baked at 250 ° C. for 20 seconds. Table 3 shows the coating composition and the properties of the cured coating film.

Comparative Examples 1 to 6 Saturated copolymerized polyesters K to P
Was used to evaluate coating film performance. Table 3 shows the results. As can be seen from Table 3, the resin composition for can coating of the present invention has impact resistance, retort resistance, enamel hair resistance,
It is clear that a coating film having excellent blocking properties and high concealing properties is provided.

[0043]

[Table 3]

The method for evaluating the physical properties of the coating film is described below. Evaluation items are adhesion to the substrate, impact resistance, retort resistance, enamel hairness, blocking properties, hiding properties, and whiteness.

Adhesion to substrate The cross-cut cellophane tape peel test was performed in accordance with JIS D0202.

Impact resistance Using a DuPont impact tester, the diameter of the coating film was measured from the back surface to 8.
A drop impact test of 1 kg × 30 cm to 50 cm was performed using a 5 mm shooting mold, and a five-stage evaluation such as a crack state and a tape peeling test was performed. (The higher the score, the better the evaluation.)

Retort Resistance After the coated plate was treated at 130 ° C. for 30 minutes under steam, the coating was evaluated for blistering and substrate adhesion on a 5-point scale.

Enamel hairness The coated plate is cut from the coating surface side, and the coating film on the cut end surface is cracked.
Peeling was observed and evaluated on a 5-point scale.

Blocking property Tissue paper was sandwiched between the painted surfaces of two identical painted plates, left at 40 ° C. and 90% RH under a load of 1 kg for 24 hours to adhere and push the tissue paper onto the coated surface. The state of the trace was observed and evaluated on a 5-point scale.

Hiding power and whiteness Hiding power was evaluated based on the appearance of the coating film surface. (◎
○, △, ×. ) Also, the whiteness (L value) was measured using a color difference meter (NEC Corporation Z-1001DP).

Examples 9 to 13 and Comparative Examples 7 to 11 In the same manner as in Example 1, saturated copolymerized polyester 100
Methoxylated methylol melamine [Sumimar M] as a melamine resin in a resin solution in which 75 parts by weight of Solvesso # 150 and 75 parts by weight of cyclohexanone were dissolved.
-40S (manufactured by Sumitomo Chemical Co., Ltd.), 25 parts by weight, 125 parts by weight of titanium oxide, 0.25 parts by weight of p-toluenesulfonic acid and 1 part by weight of a surface smoothing agent are mixed and dispersed using a medium dispersing machine. Then, the coating composition was adjusted to a coating viscosity of 120 sec with a Ford cup # 4 to obtain a resin composition for can coating suitable for the coil coating of the present invention. Coil material on a steel material) using a reverse roll coater at a coating speed of 100 m / min, and cured and baked at 250 ° C. for 20 seconds, then printed on a 12 μm polyester film in advance, and epoxy-melamine-based on the printed surface side the coated printed film of adhesive and the coated surface, 180 ° C., under temperature and pressure of 4 kg / cm ^2, subjected to hot roll lamination, printed film lamination can Dokin Created the plate. The resulting printed film lamination can barrel metal plate, as the evaluation of workability,
5 m each from the front and back using an Erichsen bending tester
After extrusion of m, the adhesion to the film and the adhesion after retort were evaluated. Table 4 shows the results.

[0052]

[Table 4]

Comparative Examples 12 and 13 The coating film was evaluated in the same manner as in Examples 1 and 2, using an oil-free alkyd paint and an acrylic paint which are currently used as an outer primer for cans. Table 5 shows the results.

[0054]

[Table 5]

[0055]

The resin composition for a can coating composition of the present invention has the following features (1) to (6) because it is constituted as described above. Ideal for undercoating. In addition, taking advantage of such features, the composition of the present invention is not limited to can paint applications,
It can be used as a paint or coating agent for metals, glasses, plastics, and the like. (1) Blocking of the coating film does not occur, and the productivity is high. (2) In drawing and cutting in the can making process,
Does not cause cracks or enamel hair. (3) Adhesion during printing film lamination is excellent. (4) No blistering or peeling of the coating film occurs during retort sterilization. (5) It is excellent in metal adhesion of a coating film, withstands a shock in a severe beverage can production process and a distribution stage, and does not cause peeling of the coating film. (6) It is excellent in the concealing property and whiteness of the coating film, and also in the appearance and the design.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Hiroshi Fujimoto 2-1-1 Katata, Otsu City, Shiga Prefecture Inside Toyo Spinning Co., Ltd. (72) Inventor Shigeru Akamatsu 3-1-21-2 Nakanocho, Miyakojima-ku, Osaka-shi No. Sakuranomiya Chemical Co., Ltd. (72) Inventor Sadaki Tadafuka 3-1-2 Nakanocho, Miyakojima-ku, Osaka-shi Sakuranomiya Chemical Co., Ltd. (72) Inventor Hiroshi Hasegawa 3-chome, Nakanocho, Miyakojima-ku, Osaka-shi No. 22 Sakuranomiya Chemical Co., Ltd. (56) References JP-A-50-130820 (JP, A) JP-A-57-57746 (JP, A) JP-A-3-35019 (JP, A) 3-71835 (JP, A) JP-A-53-98336 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C09D 1/00-201/10

Claims (1)

(57) [Claims] 1. A saturated copolyester comprising a saturated polycarboxylic acid containing an aromatic dicarboxylic acid component and a polyhydric alcohol and having the following conditions, and an amino resin or /
And a blocked isocyanate compound. Saturated polyvalent carb
The proportion of the aromatic dicarboxylic acid in the saturated dicarboxylic acid component of the acid is 80 to 100 mol%. Saturation
Polyhydric 0.5 to 5.0 mole percent of trifunctional or more valence carboxylic acids or polyhydric alcohols carboxylic acids and / or trifunctional
It is a more polyvalent alcohol function. Reduced viscosity (dl /
g) is from 0.35 to 0.65. Glass transition temperature 20 ~
70 ° C, acid value 5-120 eq / 10 ⁶ g . Specific gravity is 1.
24 (30 ° C) or less.