JPH0576979B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a metal coating paint with improved adhesion and boiling water resistance, and a method for producing the same, and is particularly suitable for hygienically protecting the contents as an inner surface paint for beverage cans. The purpose is to provide paints that are of high quality. (Prior Art and Problems) Conventionally, copolymers mainly composed of vinyl chloride, especially vinyl chloride-vinyl acetate copolymer resins, have excellent physical properties, especially toughness, flexibility, and excellent chemical properties. It is known as a suitable vehicle for metal paints because it has properties such as water resistance, acid resistance, alkali resistance, oil resistance, and alcohol resistance, as well as organic solvent solubility and heat fusion properties. It also has the advantage of not impairing the flavor of the food contained therein as a top coat on the inner surface of a beverage can. However, vinyl chloride-vinyl acetate copolymer
Because it has poor adhesion to metal surfaces such as tinplate, aluminum, and chrome-plated steel sheets, for example, undercoating these metal surfaces with a phenol-epoxy or epoxy-amino resin based on epoxy resin, which has good adhesion, and then A vinyl chloride-vinyl acetate copolymer composition may be applied to the surface, or a phenol resin, epoxy resin,
Efforts have been made to improve adhesion by using amino resins, alkyd resins, etc. A primer coated with epoxy resin or the like provides desirable adhesion, but has the drawback of requiring two steps. In addition, if epoxy resin, phenol resin, etc. are mixed with copolymer resin, the adhesion to metal surfaces can be improved to some extent, but since the compatibility of both resins is poor, copolymers mainly composed of vinyl chloride This method has not yet provided a satisfactory means for improving the adhesion of the composition, its resistance to boiling water, and its elution from the coating film. As a method for improving the above-mentioned drawbacks, a vinyl chloride-vinyl acetate-maleic acid copolymer or a vinyl chloride-vinyl acetate-vinyl alcohol copolymer is used. Although the former can improve adhesion to metals to some extent, it is insufficiently compatible with other resins used in combination, so it is not satisfactory in terms of higher adhesion, chemical resistance, and boiling water resistance, and metal foils, etc. It is unsuitable for applications that require flexibility. Furthermore, although the latter improves the compatibility and pigment dispersibility to some extent, it has poor adhesion and is therefore not fully satisfactory as a vehicle for metal coatings. In view of these circumstances, the inventors of the present invention aimed to provide an improved coating material suitable for painting the interior and exterior surfaces of metal containers, etc., in particular by combining it with vinyl acetate, which is mainly composed of vinyl chloride, which has been conventionally used. As a result of extensive research into coating compositions that provide improved coating films without losing the desirable properties of the copolymer, we have discovered a coating composition for metal coating that is highly desirable in practice, leading to the present invention. (Structure of the Invention) The first invention of the present invention is (a) vinyl chloride 75 to 90% by weight (b) carboxylic acid vinyl ester 7 to 20% by weight (iii) unsaturated carboxylic acid monomer 0.4 to 10% by weight The second invention relates to a metal coating paint characterized by containing a graft polymer having a side chain containing an epoxy group in the backbone of a vinyl chloride copolymer consisting of It is. This will be explained in detail below. There are many documents on vinyl chloride graft copolymers, especially J. Polymer. Sci. Vol. 61, 185.
-194 (1962) describes a graft polymer of an epoxy-vinyl compound, exemplified by glycidyl methacrylate, using a vinyl chloride-vinyl acetate copolymer as a backbone polymer. However, although this method shows excellent adhesion to aluminum plates and tinplate plates, it has the disadvantage that the coating film not only whitens and absorbs water in the boiling water resistance test, but also that the adhesion of the coating film decreases. The grafted polymer according to the invention has improved the above-mentioned drawbacks. As described above, the present invention uses a graft polymer having a side chain containing an epoxy group on a vinyl chloride copolymer as a resin for metal coating paint. It is important that the vinyl chloride-based graft polymer according to the present invention contains 75 to 90% by weight of vinyl chloride, the component (a). If the vinyl chloride content is less than 75% by weight, the boiling water resistance will be poor and the adhesion after the boiling water resistance test will be reduced. On the other hand, if it exceeds 90% by weight, the coating film becomes too hard and the amount of solvent that can be dissolved is severely limited, impractical. (b) As the carboxylic acid vinyl ester component, vinyl esters of lower fatty acids such as vinyl acetate,
Vinyl propionate and vinyl versatate (manufactured by Schiel Chemical Co., Ltd.) are preferred, but it is important to contain 7 to 20% by weight of these carboxylic acid vinyl esters; if it is less than 7% by weight, the solubility will decrease. , the usable solvent is limited, and the viscosity of the solution increases, reducing workability.
Moreover, if it exceeds 20% by weight, the coating film will absorb water and become white in the boiling water resistance test, and the adhesion after the boiling water resistance test will decrease. (c) The component unsaturated carboxylic acid monomer is -COOH
base or

[Formula] It is important to contain the group-containing monomer component in the total copolymer in an amount of 0.4 to 10% by weight. absorbs whitening and at the same time, adhesion strength decreases. Specific examples include unsaturated carboxylic acids such as maleic acid, fumaric acid, itaconic acid, acrylic acid, methacrylic acid, and crotonic acid, their anhydrides, and monoesters of unsaturated dicarboxylic acids. Other monomers that can be copolymerized with vinyl chloride include acrylic esters, methacrylic esters, itaconic diesters, maleic acid diesters, fumaric acid diesters, alkyl vinyl ethers, ethylene, propylene, isobutylene,
Acrylonitrile, acrylamide, etc. can be used as optional components, but should be kept at 10% by weight or less in order not to impair the function of the graft polymer according to the present invention. The vinyl chloride copolymer resin according to the present invention can be easily produced from the above-mentioned monomers by a commonly known polymerization method. The polymerization method may be any method such as solution polymerization, suspension polymerization, emulsion polymerization, or bulk polymerization. For example, when producing by suspension polymerization, the monomers are heated and stirred in water or a monomer-insoluble organic solvent in the presence of an oil-soluble polymerization initiator. Water-soluble polymer suspending agents such as polyvinyl alcohol, methyl cellulose, hydroxyalkyl cellulose, polyvinyl pyrrolidone, polystyrene, and maleic acid, and nonionic surfactants are added to create a stable suspended copolymer slurry. Obtainable. This slurry is also separated, washed with water, and dried by commonly known methods. In any of the above polymerization methods, molecular weight regulators and redox initiators can be used as necessary, and known polymerization techniques such as continuous or intermittent delayed addition of selected monomers can be employed as appropriate. Of course. Using the vinyl chloride copolymer thus obtained as a backbone, a vinyl compound having an epoxy group in the molecule is reacted with it. Examples of vinyl compounds include the following. glycidyl methacrylate

[ka] glycidyl acrylate

[ka] butadiene monoepoxide

[ka] Allyl glycidyl ether

[ka] glycidyl vinyl ether

[Chemical formula] 1-Methyl-4-isopropenylcyclohexane-1,2 oxide

[Chemical] Free radical catalysts include benzoyl peroxide, acetyl peroxide, methyl ethyl ketone peroxide, di-(2-ethylhexyl)
Examples include peroxydicarbonate and azobisisobutyronitrile. These can be selected from those used as oil-soluble polymerization initiators. The synthesis method, grafting method, and performance of the core vinyl chloride copolymer according to the present invention will be specifically described below. Graft polymerization is carried out as follows. An organic solvent for dissolving or dispersing the vinyl chloride copolymer in 100 parts by weight, such as a ketone,
200 to 1000 parts by weight of esters, aromatic hydrocarbons, alcohols, ethers, etc., 0.5 to 5 parts by weight of free radical forming agents such as organic peroxides and azo compounds, such as di-2-ethylhexyl peroxydicarbonate, and epoxy. Add 2 to 30 parts by weight of a vinyl compound and react by heating and stirring at 40 to 80° C. for 2 to 6 hours under a nitrogen atmosphere. If the epoxy-vinyl compound is less than 2 parts by weight, the adhesion and boiling water resistance will not be sufficiently improved, and if it is more than 30 parts by weight, the advantages of the vinyl chloride copolymer will be diminished and the chemical resistance and boiling water resistance will decrease. Not only that, but it is also insoluble in the solvents used during paint manufacturing. The product is cooled and a poor solvent for the polymer, such as 1,500 to 3,000 parts by weight of isopropyl alcohol (IPA) or methanol, is added under stirring to remove the liquid, and if necessary, the unreacted epoxy-vinyl compound is further washed with IPA or methanol. Remove and dry. In general, in such a grafting reaction, the product is actually a three-component mixture of a trunk polymer, a graft polymer, and a branch homopolymer, and although it is desirable to obtain a graft polymer, it is expensive to separate and obtain only the graft polymer from the mixture. It is used in practical mixtures. In the graft polymer according to the present invention, metal adhesion and boiling water resistance are optimal when used alone; if a large amount of the main polymer exists, the boiling water resistance decreases, and if a large amount of homopolymer is also mixed, the graft polymer and epoxy Homopolymers have different solubility in solvents, and in practical use, they produce undesirable results such as the formation of insoluble matter, turbidity, and precipitates in organic solvents used in coatings. Therefore, reaction conditions are selected to suppress as much as possible, but the presence of a small amount of is not a practical problem. As a method for measuring grafting efficiency, epoxy
Since vinyl compound homopolymers have different solubility in organic solvents than graft polymers and backbone polymers, it is possible to separate epoxy-vinyl compound homopolymers. For example, when using glycidyl methacrylate (GMA),
GMA homopolymer is insoluble in methyl isobutyl ketone (MIBK), and the backbone copolymer and graft polymer are soluble, so when the resulting polymer mixture is dissolved in MIBK to a solid content of 10 to 15% by weight, GMA homopolymer can be separated and removed as a cloudy, undissolved substance by centrifugal sedimentation. MIBK was added to the precipitate and the mixture was stirred again to elute a small amount of the stem polymer and graft polymer, which were then centrifuged to remove polyGMA. This precipitate has 10.8% oxirane oxygen (*calculated value
11.3%) The vinyl chloride (VC) content was 0.5% or less, and it was confirmed that it was essentially a GMA homopolymer. The polymer solution after removing the homopolymer in the above operation is reprecipitated with isopropyl alcohol or methanol, and after the liquid is removed, it is dried to obtain a polymer powder. The oxirane oxygen content of this polymer was quantified, and the grafting efficiency f of GMA was determined as follows. f=(Amount of GMA component in the polymer after removing the GMA homopolymer)/(Total amount of GMA before separating the GMA homopolymer) The resin for metal coating paint according to the present invention has an epoxy group due to grafting, but it also has a -COOH group. and

Since the [Formula] group is present in the same molecule, it can be crosslinked advantageously by heating and baking the coating film, resulting in a product that shows a significant difference in performance compared to conventional products. For example, Koka type flow tester (manufactured by Shimadzu Corporation)
When calculating the flow curve according to The graft polymer according to the present invention does not crosslink and flow at ~180°C, and is insoluble in ethyl acetate in a solvent resistance test of a coating film baked at 160-200°C for 20 minutes, but the PVC-vinegar The graft polymer according to the present invention exhibits excellent performance as a resin for metal coating paints, such as the fact that the GMA graft polymer is soluble in the bicarbonate polymer. Examples are given below. Example 1 1 The inside of an autoclave was purged with nitrogen, and the following items were charged into it. Vinyl chloride 168 parts by weight Vinyl acetate 56 Maleic anhydride 8 Deionized water 680 Polyvinyl alcohol 2 Benzoyl peroxide 2 The above components were heated to 65° C. with stirring and reacted. Furthermore, 168 parts by weight of vinyl chloride (VC) was continuously pressurized over a period of 6 hours, and when the internal pressure became 1.0 Kg/cm ² G or less, the remaining VC was removed, and the slurry obtained after cooling was filtered and deionized. The mixture was washed three times with water, deliquified, and dried to obtain 360 parts by weight of copolymer powder.
This is referred to as trunk copolymer A. The results of this analysis are
The VC content was 86.2%, the vinyl acetate (VAc) 12.7%, the maleic acid content 1.1%, and the degree of polymerization was 430. Next, the flask equipped with a stirrer was purged with nitrogen, and the following components were charged, dissolved, and reacted with stirring at 60° C. for 1.5 hours. Stem copolymer A 200 parts by weight Methyl ethyl ketone 600 Glycidyl methacrylate 28.4 Benzoyl peroxide 4.0 After the reaction was cooled, 2500 parts by weight of IPA was added dropwise to precipitate the polymer. After this, unreacted GMA was removed by washing and drying three times with 1250 parts by weight of IPA to obtain 212 parts by weight of graft polymer powder. The oxirane oxygen is 1.18% and the grafting effect is
It was 0.91. This was used as a polymer for practical tests. 2 Production of paint Polymer 100 parts by weight Methyl isobutyl ketone 150 Methyl ethyl ketone 150 Toluene 100 The above components were dissolved by heating at 50°C to obtain a metal coating paint. Table 1 shows data for the trunk copolymer A and the polymer. 3 Grafting efficiency was determined as follows. As mentioned above, polyGMA homopolymer is
Because it does not dissolve in MIBK, 100g of the above polymer powder
Stir and dissolve in 650 g of MIBK, and insoluble matter is separated.
2300 g of IPA was dropped into the separated solution to precipitate it, filtered and dried to obtain 99.0 g of polymer. The oxirane oxygen content of this polymer was 1.09%.
The MIBK-insoluble polymer was further washed with 50 g of MIBK and dried to obtain 1.0 g of a polymer believed to be a polyGMA homopolymer. The oxirane oxygen content was 10.8%.

[Table] Grafting efficiency f=99.0×9.7/100/(99.0g×9.7/100)+(1.0×9
5.9/100) = 0.91 4 Oxirane oxygen determination method Hydrochloric acid-dioxane method 1 0.1 to 0.5 g (Wg) of sample to 25 ml of dioxane
Dissolve in. 2 Add approximately 0.2N-HCl-dioxane reagent (100ml of dioxane + 1.6ml of Conc.HCl) at least twice the epoxy equivalent and leave at room temperature for at least 15 minutes. 3 Titrate phenolphthalein with 0.1N NaOH-methanol as an indicator (titer volume 1
ml) [If the amount of caustic soda is less than the specified amount of 6 ml, use a smaller sample and try again] 4. Perform the same operation as a blank test using pure dioxane. (Appropriate amount Lml) 5. If the resin is acidic in advance, measure the equivalent weight separately by titration to correct this.
(x eq/100) If the specified number of 0.1N NaOH-methanol is N, then epoxy value (eq/100) = (L-l) N/W x 10 + x Oxyrane oxygen amount (%) = 16 x (epoxy value) Example 2 to 4 and Comparative Examples 1 to 7 1 Stem copolymers B, C, D, and E were polymerized in the same manner as in Example 1, except that the monomer composition was changed to have the copolymer composition shown in Table 1. , F, and G were obtained. 2 Graft Reaction In Examples 2 to 4 and Comparative Examples 3 to 5, the graft reaction and purification were carried out in the same manner as in Example 1 except for the graft conditions shown in Table 1 to obtain graft polymers of polymers. 3 In Comparative Examples 1 and 2, the trunk copolymers A and C in Examples 1 and 3 were used as they were for comparison. 4 Comparative Examples 6 and 7 are obtained by mixing, dissolving, and adjusting a polyglycidyl methacrylate homopolymer in the trunk copolymers A and B as shown in Table 1. This dissolved composition was tested according to the measurement method and criteria described below, and the results are shown in Tables 1 and 2. The polymer ~ based on this example has extremely good boiling water resistance and adhesion to aluminum plates, tinplate plates, and chromium-treated steel plates.
Furthermore, it is excellent in water extraction rate and potassium permanganate consumption. (Measurement method and judgment method) 1 Metal plate adhesion test A #24 bar of the graft polymer solution composition was applied to a metal plate such as an aluminum plate, a tin plate, a chrome-plated steel plate, and an epoxy resin-coated steel plate (all manufactured by Nippon Test Panel Kogyo Co., Ltd.). Apply with a coater (dry film thickness approx. 15 μm), dry for 1 hour, then apply at 180℃ x 5
The mixture was dried by heating for 30 minutes to form a coating film. A grid test using cellophane tape was conducted and the results were evaluated in four stages. The numbers are the grid numbers (1 mm intervals) of the remaining amount. Judgment values: ◎: 100-95 〇: 94-80 △: 79-60 After being immersed for 1 hour, the samples were taken out, cooled with water, and the surface water was wiped off. Immediately, the following 4-grade evaluation was performed. Judgment values: ◎: Transparent 〇: Almost transparent △: Cloudy ×: Whitening 3 Metal plate adhesion test after boiling water resistance test The test panel treated in Test 2 was air-dried, and the same test as the grid test in Test 1 was performed. A graded evaluation was conducted. 4 Solvent Resistance Test After immersing the tinplate top coating film prepared in Test 1 in ethanol (99.5% special grade ethanol) and ethyl acetate (special grade) at 2.5℃ for 48 hours,
The following four-level evaluation was performed. Judgment value: ◎: Transparent 〇: Almost transparent △: Cloudy ×: Whitening 5 Water extraction rate test According to "Chapter 2 of PL grade 6th edition, Material test and elution test method" based on Ministry of Health and Welfare Notification No. 98 Water extraction was performed at 100°C for 30 minutes, and the evaporation residue (ppm) was expressed as the water extraction rate. 6 Potassium permanganate consumption The potassium permanganate consumption (ppm) was determined for the leaching solution prepared using water in the same manner as in 5. Abbreviations in Table 1: VeoVa #10: Vinyl versatate (manufactured by Schiel Chemical) MA: Maleic acid ItA: Itaconic acid MOM: Monooctyl maleate DBM: Dibutyl maleate BA: Butyl acrylate AGE: Allyl glycidyl ether GA: Glycidyl Acrylate BPO: Benzoyl peroxide OPP: Di-2-ethylhexyl peroxydicarbonate PGMA: Polyglycidyl methacrylate

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Claims (1)

[Scope of Claims] 1. A vinyl chloride copolymer consisting of (a) 75 to 90% by weight of vinyl chloride, (b) 7 to 20% by weight of vinyl carboxylic acid ester, and (c) 0.4 to 10% by weight of unsaturated carboxylic acid monomer. A coating material for metal coating characterized by containing a vinyl chloride-based graft polymer having a side chain containing an epoxy group in the polymer trunk. 2 (a) Vinyl chloride 75 to 90% by weight (b) Carboxylic acid vinyl ester 7 to 20% by weight (c) Unsaturated carboxylic acid monomer 0.4 to 10% by weight are copolymerized to obtain a vinyl chloride copolymer. A method for producing a paint for metal coating, which comprises reacting a polymer with a vinyl compound having an epoxy group in the molecule in the presence of a free radical catalyst, and mixing the resulting graft polymer with a desired paint component. .