JPS6138744B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a coating composition for metal cans that has excellent processability and adhesion. Metal cans are made of materials such as tinplate, stain-free steel, and aluminum, and usually a protective coating is used on the inside and outside of the can to prevent these metals from corroding and metals from leaching into the contents. There is. The protective paint for the inner surface of the can (hereinafter referred to as inner surface paint) includes epoxy resin-phenol resin paint, epoxy resin-amino resin paint,
Epoxy resin-acrylic resin paints are commonly used. These protective coatings have excellent adhesion to metal materials and are effective in preventing corrosion of materials. However, these conventional paints cannot be said to be sufficient in terms of processability;
Processing such as flanging the can body, folding the side seam, drawing the can into a two-piece can, and seaming may result in exposure of the base metal. Therefore, exposed metal parts are often repaired after processing. Such repairs complicate the can making process and are disadvantageous in terms of cost, so there is a demand for paints with excellent workability that do not require repairs. In response to this demand, vinyl chloride resin-based organosol paints have been developed. This organosol paint contains a vinyl chloride resin for dispersion, a solution-type vinyl chloride copolymer, a plasticizer, an epoxy resin, a phenol resin as an adhesive component, and an epoxidized resin as a plasticizer and a stabilizer. It is blended with oil. Examples are also known in which an acrylic resin is further blended. Such organosol paints have excellent adhesion to metal materials and workability, and are useful as paints that do not require repair. However, when these paints are used as interior paints for metal cans, plastic or epoxidized oils are extracted and migrated into the contents, which is not sanitary.
There is also the problem of changing the flavor of the contents. In addition, there are other problems such as thickening of the paint or changes in processability due to changes over time, making it extremely difficult to manage the paint. The present inventors conducted studies to improve the extraction transfer to the above-mentioned contents and the stability of the paint, and found that the cause of the above-mentioned problem was mainly caused by the plasticizer in the organosol paint. That is, conventionally known plasticizers include low viscosity substances such as phthalate esters, phosphate esters, and sebacate esters, medium viscosity substances such as epoxidized oil, and high viscosity substances such as polyester, but in organosol paints, In view of plasticizing performance and compatibility, it has been common to use a low viscosity substance as a main plasticizer and a medium to high viscosity substance as an auxiliary plasticizer. However, because low- and medium-viscosity substances have a strong solubility in vinyl chloride resin, they have a negative effect on the storage stability of paints, and they also tend to migrate to the paint film surface and be extracted into the contents. . Therefore, we investigated conventional organosol paints that do not contain plasticizers, but the adhesion to metal materials and processability deteriorated. The inventors of the present invention have further conducted research, and by blending resins such as carboxyl group-containing resins, phenolic resins, amino resins, and epoxy resins, as well as polyester resins of a specific molecular weight, the present inventors have created a system that does not substantially contain plasticizers. We have developed an organosol paint with excellent adhesion to metal materials and processability. That is, the present invention provides a vinyl chloride resin-based organosol coating composition in which the nonvolatile components of the composition are (A) 30 to 80 parts by weight of a vinyl chloride resin, and (B) 5 to 30 parts by weight of a polyester resin having an average molecular weight of 5,000 to 10,000. (C) A carboxyl group-containing vinyl chloride resin copolymer with an acid value of 0.5 to 15 that does not belong to (A) or (B)
A carboxyl group-containing polyester resin with an average molecular weight of 10,000 to 50,000 and an acid value of 0.5 to 15, which does not belong to This is a characteristic coating composition for metal cans. The vinyl chloride resin (A) in the present invention is a homopolymer of vinyl chloride, and so-called vinyl chloride paste resin having an average degree of polymerization of about 1000 to 1800 can be used. Commercially available resins include Denka Vinyl SE-130 manufactured by Denki Kagaku Co., Ltd. and Mitsui Chemicals.
Vinicron paste resin manufactured by Nippon Zeon Co., Ltd.
Manufactured by Zeon 121, Zeon 103EPF, Kanepaste XP-900, XP-1700, manufactured by Kanebuchi Chemical Co., Ltd., manufactured by Bahelite
QXPA, QYNL, etc. can be used. (B) The polyester resin having an average molecular weight of 5,000 to 10,000 is a substantially linear polyester resin made of dicarboxylic acid and glycol, or a branched polyester resin containing a trifunctional or more functional polybasic acid or a trifunctional or more functional polyhydric alcohol. It may be a resin, or it may use a monocarboxylic acid or monohydric alcohol component to adjust the molecular weight, but
The molecular weight used is 5,000 to 10,000. If the molecular weight is less than 5000, although the metal can has excellent adhesion and processability, the metal can will have insufficient water resistance when subjected to steam sterilization treatment, and the flavor of the contents will deteriorate. Moreover, if it is larger than 10,000, there is a possibility that the adhesion and processability will be insufficient. The acid component of the polyester resin includes aromatic carboxylic acids such as phthalic anhydride, isophthalic acid, terephthalic acid, naphthalene dicarboxylic acid, and oxybenzoic acid, fatty acid carboxylic acids such as adipic acid and sebacic acid, and polyesters such as trimellitic acid. Examples of alcohol components include glycols such as ethylene glycol, propylene glycol, 1,3-butanediol, and neopentyl glycol, and polyhydric alcohols such as glycerin and pentaerythritol. The resin of component (C) in the present invention is described below.
It maintains the physical properties such as water resistance of the coating film formed by curing with component (D) phenolic resin, amino resin or epoxy resin by heating. Such resins do not belong to (A) and have an acid value of 0.5 to 15.
A carboxyl group-containing vinyl chloride resin copolymer or an average molecular weight of 10,000 or less that does not belong to (B)
50,000 and a carboxyl group-containing polyester resin with an acid value of 0.5 to 15. If the acid value of the resin is less than 0.5, the adhesion to metal materials is insufficient, and if it is greater than 15, the water resistance of the coating film is poor. becomes worse. Such vinyl chloride copolymers are generally vinyl chloride-vinyl acetate-maleic acid copolymers, and commercially available resins include Bakelite's Vinyrite VMCH, Nippon Zeon's 400X110A, and Denka Kagaku's Denka. There are vinyl 1000C etc. Further, although the polyester resin having an average molecular weight of 10,000 to 50,000 has a different average molecular weight range from (B) the polyester resin having an average molecular weight of 5,000 to 10,000, the same constituent components can be used. And those using polyester resin with an average molecular weight of 10,000 to 50,000 have an average molecular weight of 5,000 to 50,000.
By combining with 10000 polyester resin, the physical properties of the coating film can be improved. In other words, the average molecular weight mentioned for component (B) is
Adhesion and processability, which may be insufficient when polyester with a molecular weight greater than 10,000 is used, can be improved by combining with (B) a polyester resin with an average molecular weight of 5,000 to 10,000. A coating film can be formed. (D) Phenol resin in the present invention includes carbolic acid,
It is a condensate of P-cresol, O-cresol, m-cresol, P-t-butylphenol, P-amylphenol, bisphenol A, etc., and an aldehyde, and both novolac type and resol type can be used. There is no problem even if the group is alkyl etherified. The amino resin is a condensation product of an amino compound such as urea, melamine, benzoguanamine, or acetoguanamine and an aldehyde, and the methylol group may be alkyl etherified. The epoxy resin is an epoxy resin produced from epihalohydrin and bisphenol A, and has a molecular weight of 5,800 or less, preferably 2,000 or less. The compounding ratio of each component of the coating composition for metal cans of the present invention is
(A) 30 to 80 parts by weight of vinyl chloride resin, (B) 5 to 80 parts by weight of polyester resin with an average molecular weight of 5,000 to 10,000.
30 parts by weight, (C) a carboxyl group-containing vinyl chloride resin copolymer with an acid value of 0.5 to 15 that does not belong to (A) or an average molecular weight of 10,000 to 50,000 that does not belong to (B)
20 to 50 parts by weight of a carboxyl group-containing polyester resin with an acid value of 0.5 to 15; (D) 1 to 15 parts by weight of one or more of phenolic resins, amino resins, and epoxy resins; If it deviates from this, the adhesion and processability with the metal material, which are the objectives of the present invention, will not be maintained. The composition for metal cans of the present invention uses an organic solvent in addition to the above-mentioned nonvolatile components. Such organic solvents include (A) which does not dissolve vinyl chloride resin and other (B) (C) (D)
Any material that dissolves the components can be used, but from the viewpoint of storage stability of the paint, it is necessary to select the resin composition and blending ratio used in the paint.
As the organic solvent, alcohol solvents, ketone solvents, hydrocarbon solvents, ester solvents, ether alcohol solvents, etc. can be used.
Can be used as a mixed solvent of more than one species. In addition to the above composition, the coating composition for metal cans of the present invention may further contain additives such as surfactants and flow control agents, or pigments such as titanium dioxide and aluminum. The coating composition for metal cans of the present invention can be used as a non-correction coating for the inner surface of easy-to-open ends, as well as oval cans,
It is particularly useful as a coating for the inner surface of punched cans such as square cans and DR cans, but is also useful for coating other inner surfaces. Although the above-mentioned composition can be used as it is for use without correction of the inner surface of an easy-opening end, opening property is improved and it becomes even more useful by dispersing and blending the following fine powder having a particle size of 1 to 15 μm into the above composition. Such fine powders include general fillers such as calcium carbonate fine powder silicic acid, calcium silicate, aluminum hydroxide, barium sulfate, and diatomaceous earth, as well as fine powders such as polyolefin resins, fluorine resins, and metal salts of higher fatty acids. can also be used. It should be noted that if the fine powder is less than 1 μm, no improvement in opening property is observed, and if it is more than 15 μm, the surface condition of the coating film is deteriorated. Further, the amount of fine powder added is preferably in the range of 0.2 to 10 parts by weight per 100 parts by weight of non-volatile components. In addition, the paint composition for metal cans of the present invention is useful not only for the inner surface of cans but also as a paint for the outer surface of cans. In particular, when used as a paint for the outer surface of can lids, there is no damage caused by seaming, and there is no rusting during long-term storage. You will get a can without. The coating composition for metal cans of the present invention can be applied onto a metal material by a known method, such as roll coating, spray coating, or brush coating.
The appropriate paint thickness is between 3μ and 20μ.
A cured paint is obtained by baking at 160°C to 230°C for 2 to 20 minutes. The present invention will be specifically explained below with reference to Examples. The middle part of the example shows parts by weight. Example 1 (1) Preparation of polyester resin (A) 146 parts of adipic acid, 34 parts of ethylene glycol
4 parts and 42 parts of propylene glycol were placed in a 4-liter tube equipped with a thermometer, nitrogen inlet pipe, distillation device, and stirring device.
Place in a neck flask and store at 250°C in a nitrogen stream.
The reaction was carried out at 260°C for 1.5 hours while distilling off the produced water to obtain a polyester resin with a number average molecular weight of 8200. (2) Preparation of organosol paint Swazol #1000, (Maruzen Oil Co., Ltd. aromatic solvent) 70 parts, butyl cellosolve 70 parts, methyl isobutyl ketone 80 parts and Vinyrite VMCH (Union Carbide vinyl chloride-vinyl acetate-maleic acid copolymer) , acid value 10), 37 parts of the polyester resin (A) prepared in (1) above, and Yuban 20SE (manufactured by Mitsui Toatsu Chemical Co., Ltd.).
10 parts of amino resin) were added and thoroughly mixed and stirred. Next, 100 parts of Zeon 121 (vinyl chloride base resin manufactured by Nippon Zeon) was added, and after high-speed dispersion, a mixed solvent of 1:1 of butyl cellosolve and Swasol #1000 was added, and the viscosity (25℃ No.4
Viscosity below the food cup is measured under the same conditions) 150
An organosol paint with a solid content of 41.5% was obtained. The various performances of the above organosol paint are shown in the table along with other examples. Example 2 (1) Preparation of polyester resin (B) 29.5 parts of isophthalic acid, 26.1 parts of adipic acid, 36.4 parts of diethylene glycol, and 8.0 parts of trimethylpropane were placed in a four-necked flask in a nitrogen stream.
React for 4 hours while distilling off the water produced at 250°C to 260°C. The obtained polyester resin had an acid value of 7.2 and a number average molecular weight of 24,600. (2) Preparation of organosol paint Swasol #1000 20 parts, butyl cellosolve
20 parts of polyester resin (B) was dissolved in 20 parts of methyl isobutyl ketone, and 37 parts of polyester resin (A) and 10 parts of Yuban 20SE were added thereto and thoroughly mixed and stirred. Next, 100 parts of Zeon 121 was added and dispersed at high speed, and then a mixed solvent of 1:1 of butyl cellosolve and Swasol # was added until the viscosity was 150.
An organosol paint with a solid content of 52.3% was obtained. Example 3 50 parts of low-density polyethylene powder with an average particle size of 10μ was added to Vinyrite VMCH solution (Swazol #1000 25
part, butyl cellosolve 25 parts, methyl isobutyl ketone 25 parts, vinylite VMCH 25 parts) 50 parts and 3
After forming into a paste using this roll, 8 parts of the paste was added to 100 parts of the organosol paint of Example 1 to obtain an organosol paint containing fine powder. The various properties of the obtained paint are shown in the table. Examples 4 to 6, Comparative Examples 1 to 7 (1) Preparation of polyester resins (C) to (G) 180.1 parts of isophthalic acid, 93.1 parts of ethylene glycol, and 135.2 parts of 1,3-butanediol were added to (1) of Example 1. ) into a four-necked flask,
The reaction was carried out at 260°C for 2 hours under reduced pressure using 0.2 part of antimony trioxide as a catalyst. The results are shown in the table by changing the degree of vacuum. Four types of polyester resins (C) to (F) were obtained.

[Table] Performance evaluation (1) Storage stability The paint was stored at 50°C for 1 month and changes in its viscosity were observed. (2) Adhesion of cellophane tape A dry film of 150 mg/cm ² was applied to a tin plate with a thickness of 0.23 mm and a plating amount of 50/50 using a roll coater and baked at 190°C for 10 minutes. The obtained painted board was stood upright, 11 cuts of 1 mm width were made on each side, and a peel test was performed using cellophane adhesive tape, and the number of unpeeled sheets was indicated in the numerator. (2) Bending property The coated plate used in (2) was folded in half, and another coated plate was sandwiched between the samples, and the flat contact surface was folded.
A kg weight was dropped from a height of 20 cm and cracks at the bends were observed. (4) Punching properties of square No. 5 cans A 0.23 mm thick stain-free steel plate was painted and baked in the same manner as in (2) to obtain a coated plate. A No. 5 square can was punched out from the obtained coated plate with the painted surface as the inner surface, and the peeling status of the coating film after punching was observed. (5) Corrosion resistance The No. 5 can obtained in (4) was filled with 1% saline solution, the lid was tightly tied, and the can was stored at 50°C for 1 month. After the cans were opened, the state of rust was observed. (6) Flavor The No. 5 can obtained in (4) was filled with distilled water, sealed with a tight lid, and stored at 50°C for one month. After opening the can, its flavor was evaluated. (7) Pull tab end opening property A painted plate was obtained on an aluminum plate with a thickness of 0.35 mm using the same procedure as in (2). An end shell was punched out from the obtained painted board with the painted surface as the inner surface, and then a pull tab end was made. The metal exposure of the resulting pull tab end was observed. (8) Pull-tab end opening property The pull-tab portion of the pull-tab end obtained in (7) was pulled and the remaining state of the coating film when opened was observed. (9) Sealing properties When a 307φ end was punched out from the painted plate obtained in (4) and wrapped around a No. 2 can, damage to the seamed portion was observed.

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Claims (1)

[Scope of Claims] 1. A vinyl chloride resin-based organosol coating composition in which the nonvolatile components of the composition are (A) 30 to 80 parts by weight of a vinyl chloride resin, and (B) 5 to 30 parts by weight of a polyester resin having an average molecular weight of 5,000 to 10,000. Parts by weight, (C) A carboxyl group-containing vinyl chloride resin copolymer with an acid value of 0.5 to 15 that does not belong to (A) or (B)
A carboxyl group-containing polyester resin with an average molecular weight of 10,000 to 50,000 and an acid value of 0.5 to 15, which does not belong to Characteristic paint composition for metal cans.