JPS6017231B2 - Internal coating composition for can manufacturing - Google Patents

Description

[Detailed description of the invention] The present invention relates to a novel internal coating composition for can manufacturing.

Conventionally, epoxy phenol-based, epoxy urea-based, or vinyl chloride-based paints have been used as internal paints for can manufacturing.

It is conceivable to apply polyolefin to the inner surface of the can using a powder coating method.

However, with this method, it is difficult for powder to adhere to the corners of the can, and the coating film in those areas becomes thinner and cannot adequately protect the contents. has a serious drawback that this powder coating method cannot be applied. In addition, it is not a desirable method from the standpoint of resource conservation as more resin coating is formed than necessary, and conventional painting equipment cannot be used, requiring large-scale capital investment. At present, this is extremely disadvantageous industrially. There is also a so-called hot-melt method in which polyolefin is melted and applied, and the coating is solidified by cooling.

However, this method does not solve the problem of creating a very thick coating film, and because polyolefins do not adhere to metal surfaces or epoxy base coats and have a high melting point, they are usually made using ethylene-vinyl acetate copolymer. It is used by adding a compound (abbreviated as EVA). If the amount of EVA increases, the adhesion improves, but the taste of the contents deteriorates, so it is not put to practical use. The present inventors have developed an inner coating composition for can manufacturing (Tokuka Sho 49 - 148030
(No. 55-4411)), one or more hydrocarbon solvents having a boiling point at a temperature higher than the softening point of the polar group-containing poly-IJ olefin, and an organic solvent other than the above hydrocarbon solvents. An internal coating composition for can manufacturing, characterized in that it is dispersed in a solid state in a mixed solvent with one or more solvents (Special Publication No. 50-74306 (Japanese Patent Publication No. 59-49947)) Although a series of inventions such as these have been completed, a large amount of solvent is used, and when dissolving a polar group-containing polyolefin in a solvent, heating of 80 qo or more is required, making it difficult to remove waste solvent and pose a risk of fire. This sometimes caused problems. In addition, dispersing the polar group-containing polyolefin in water was considered to reduce the use of solvent, but the dispersion stability was poor and the spray gun clogged when spray painting was performed.

Therefore, it is possible to use a surfactant for dispersion, but since it is used as a paint for the inside of a can, the surfactant must be safe from a food hygiene perspective. Many of them are poorly soluble in water, and for this reason, it has been difficult to improve dispersion stability. The present invention was developed to solve the above problems, and consists of dissolving a food additive surfactant in an organic solvent and then dispersing a polyolefin containing a caraboxyl group in a solid state in a solution in which water is added. This is an inner surface coating composition for can manufacturing, characterized by:

As the food additive surfactant used in the present invention, those that are sparingly soluble in water can be used, and those that are soluble in organic solvents. Specific examples include sorbitan fatty acid esters such as sorbitan monostearate, sorbitan tristearate, and sorbitan monopalmitate, glycerin fatty acid esters such as stearic acid monoglyceride, and propylene glycol fatty acid esters such as propylene glycol monostearate. Furthermore, the food additive surfactant has a weight ratio of 0.1/99.9 to 8 to 92, preferably 1/9 to the carboxyl group-containing polyolefin.
It can be used in the range of 9 to 5/95, and can be appropriately selected within this range depending on the type of food additive surfactant and the type of carboxyl group-containing polyolefin, but if the amount of food additive surfactant added is 0 If it is less than .1/99.9, the dispersion stability of the paint will be poor, and if it is more than 8/92, the adhesion between the coating film and the base will decrease, which is not preferable.

As the organic solvent used in the present invention, high boiling point solvents are not preferred in order to reduce residual solvent and its odor after coating.

Hydrocarbon solvents such as benzene, hexane/hebutane, toluene, and xylene, ketone solvents such as methyl ethyl ketone and methyl yliptyl ketone, esters such as ethyl acetate and butyl acetate, and alcohol solvents such as ethanol are used. The solvent is 60o surfactant for food additives.
It can be easily dissolved at about 0. The amount of water added after dissolving the food additive surfactant is 5/95 to 30/70, preferably 10/90 in weight ratio of organic solvent to water.
It can be appropriately selected within the range of ~20/80. The carpoxyl group-containing polyolefin used in the present invention is a polyolefin obtained by graft-polymerizing polyethylene or polypropylene with a polymerizable unsaturated monomer such as acrylic acid, methacrylic acid, maleic acid, maleic anhydride, or fumaric acid. Good body stability.

Commercially available products include Zai from Tetsu Seikagaku Kogyo ■.
kthen-F, CMPC-90 of Toa Fuel Industry■
Examples include M-C-80-MA and L-900X.

These carboxyl group-containing polyesters also exhibit excellent adhesion to treated or untreated metal surfaces and base coat surfaces. Further, these magnetic group-containing polyolefins are preferably selected from those having an average molecular weight of about 1000 or more and a softening point within the range of about 100 qo to 180 oo.

In addition, it is preferable to select the size of the grain from the range of about 10 to 7, preferably 10 to 4. Further, in the present invention, a part of the carboxyl group-containing polyolefin is replaced with a polyolefin resin such as waxes such as polyethylene and polypropylene paraffin, ethylene/Q-olefin copolymer, polyptadiene, and ethylene/vinyl acetate copolymer. You can also do that.

These polyolefin resins have a softening point of 50 to 140°C
, preferably in the range of 70 to 110 qo, and the weight ratio of this polyolefin resin to the carpoxyl group-containing polyolefin is 50 to 50 or less, preferably 5
Used in the range of /95 to 40/60, it forms a uniform and smooth coating film and is highly effective in eliminating pinholes and eyeholes. It is not preferable to use a large amount of a polyolefin resin having a softening point too lower than the boiling point of water because it may cause whitening and blistering when the coating film is boiled in water. In the present invention, pigments, fillers, and other additives may be added as long as they do not contradict the purpose. In the present invention, the method for dispersing carboxyl group-containing polyolefins, polar group-containing polyolefins, and polyolefins in a solid state is to dissolve a surfactant for food additives in a solvent, then add water, and sprinkle the mixture with a sprinkler. A method of adding a powdered carboxyl group-containing polyolefin or a carboxyl group-containing polyolefin and a polyolefin, a food additive surfactant is dissolved in a solvent, water is added thereto, and a carboxyl group-containing polyolefin or a polyolefin is added.
Methods such as adding carpoxyl group-containing polyolefins and polyolefins and then dispersing them using a ball mill etc.
Various methods are possible.

In the present invention, it is also effective to disperse the carboxyl group-containing polyolefin in a solid state and then dissolve the polyolefin resin in a solvent and add it.

The coating composition for the inner surface of a can according to the present invention can be applied by a conventional method, and in particular, an air spray gun can be used.

As a method for forming a film, coating may be carried out after applying the inner coating composition for can making according to the present invention before the solvent and water of the composition are completely evaporated. The competition may be conducted after the evaporation.

Baking can be carried out in a conventional manner, for example, by heating in a hot air oven or the like.

Examples will be described below.

In the examples, parts indicate parts by weight. Example 1 One part of food additive surfactant Span 60 (manufactured by Kao Atlas Co., Ltd., Sorbitanmo/Stearate) was mixed with one part of xylene.
Heat and dissolve Ikari Oriko and add 60 parts of water.

While stirring, add carboxyl group-containing polyethylene (manufactured by Seitetsu Kagaku Kogyo ■, Flodex E-4, MI-4, density 0.930, melting point 106 qo, particle size range 150〆, pass grade 99% or more, medium particle size 20-5 Cape). In addition, a paint was created. This paint is stable and can be sprayed with an air spray gun to a tin plate that can be air-sprayed without clogging if used for 3 months.
It was applied at a ratio of 1/100 mm and baked for 5 minutes at 160 mm.

This painted surface was smooth, and when the electrical conductivity was measured using the method described below, no current was detected and there were no eyeholes or pinholes. In addition, even in a boiling test (3 minutes in boiling water), there was no whitening or blistering, and the product could withstand practical use. Moreover, the baked coating film had no odor. In addition, the adhesion was 100/100 when carried out by a normal cross-cut test, and the bending resistance was determined by applying an impact to the painted board with the paint film on the outside and bending it twice. was observed, but no cracks were observed. In addition, tin plate Sakagami coated with an epoxy phenol base coat and an epoxy urea base coat by a conventional method,
Good results were also obtained for chemically treated steel plates coated with the above paint in the same manner.

Comparative Example 1 In Example 1, when the food additive surfactant Span 60 was not used, the gun clogged during painting.

Example 2 1 part of food additive surfactant Span 65 (manufactured by Kao Atlas Co., Ltd., sorbitan tristearate) is heated and dissolved in 10 parts of xylene, and 60 parts of water is added.

This and 2 parts of carboxyl group-containing polyethylene (Flodex E-4) were placed in a ball mill and milled at room temperature for 6 hours to obtain a coating material with an average particle size of 4 mm and excellent stability over time. The dispersion stability of this paint is good, and even after 3 months, it can be air sprayed without clogging the gun. Example 3 Surfactant Atmos 15 for food additives
0 (manufactured by Kao Atlas Co., Ltd., medium purity stearic acid monoglyceride) was heated and dissolved in 1 part of methyl lysoptyl ketone, and 6 parts of water was added.

This and carboxyl group-containing polypropylene (Flodex P-2 manufactured by Steel Chemical Industry Co., Ltd., M120, density 0.92
0, melting point 166° C.) were placed in a ball mill and kneaded at room temperature for 6 hours to obtain a coating material with an average particle size of 4 tsubo and excellent rolling stability. The dispersion stability of this paint is good;
Even after 3 months have passed, you can spray the air without clogging the gun. Apply the above paint to the tin plate using an air spray gun at a ratio of 70 o/100.
qo, scaled for 5 minutes.

This coated product was smooth, and when its conductivity was measured using the apparatus shown in FIG. 1, no current was detected and there were no eyeholes or pinholes. In addition, regarding the boiling resistance of the painted object by immersing it in boiling water for 30 minutes, and the retort resistance of leaving it in 120q0 steam for 9 minutes, we also examine the observation of whitening of the painted object, the presence or absence of blistering, and the adhesion of the painted object. I did the Goban eyes test mentioned above, but no problems were found. Also,
Good results were also obtained for epoxy phenol and epoxy urea base coated plates coated with the above paints in the same manner. Examples 4 to 8 In Example 1, dispersions were obtained using surfactants for food additives as shown in Table 1 in place of Span 60.

Paints consisting of the dispersions obtained in Examples 4 to 8 were applied to the tin plate at a ratio of 70:2/100 using an air spray gun, and baked at 160°C for 5 minutes. After 3 months of aging, a test was performed, and Table 1 shows the results of the clogging of the gun during painting and the condition of the resulting paint film.

Table 1 Examples 9 to 11 In Example 1, carboxyl group-containing polyethylene (
A dispersion was obtained using carboxyl group-containing polyethylene as shown in Table 2 in place of Flowdex E-4).

Paints made of the dispersions obtained in Examples 9 to 11 were uniformly applied onto a tin plate at a ratio of 70 to 9/100 using an air spray gun, and baked for 5 minutes at 160 cm. The conditions obtained are shown in Table 2. The carboxyl group-containing polyethylene used was pulverized. Table 2 Example 12
~14 In Example 3, a dispersion was obtained using a carboxyl group-containing polypropylene as shown in Table 3 instead of the carboxyl group-containing polypropylene (Flodex P-2).

The paints consisting of the dispersions obtained in Examples 12 to 14 were applied onto a tin plate using an air spray gun in a ratio of 70 to 9/100 cm, and 180 cm to 0.5 minutes was applied for 5 minutes.

The obtained conditions are shown in Table 3. Pulverized carboxyl group-containing polypropylene was used. Table 3 Example 15 1.1 parts of a food additive surfactant (Span 60) was dissolved under heat in 1 bottle of xylene, and 60 parts of water was added.

While stirring, add 2 parts of carpoxyl group-containing polyethylene flodex B-4 to prepare a paint. Xylene 1 Mariko Tafmer 0280 (manufactured by Mitsui Petrochemicals, ethylene/Q-olefin copolymer, M16.0 (2300
0), specific gravity 0. Prepare a solution by adding 2 parts of Iso and heating to dissolve. A paint is prepared by adding a tafmer solution to the paint while stirring it with a disperser.

This paint is stable, and even after three months of use, it was possible to air-spray without clogging the gun during painting. The above paint is applied to the tin plate using an air spray gun at a ratio of 70:9/100 and left until the solvent and water have evaporated.

After that, they competed for 16,000 for 5 minutes. This coated product was smooth, and when its conductivity was measured using the method described below, no current was detected, proving that there were no eye holes or pin horns. In addition, there was no whitening or blistering in the boiling resistance test, and the product was found to be suitable for practical use. In addition, there was no odor in the adhesive coating. Further, the adhesion was 100/100 by the cross-cut test, and the bending resistance was also good. Example 16 Heat and dissolve 15 parts of ATOMOS 150, a surfactant for food additives, in 1 part of dichlorobutyl ketone, add 6 parts of water, and stir with a taster to dissolve carboxyl group-containing polypropylene (Flodex P- 2) 18 parts and 2 parts of microcrystalline wax (manufactured by Bareco, Peace Quar-19 I, crushed with a medium particle size of 20 to 5) were added to prepare a paint.

This paint is stable, and after being aged for 3 months, it is
I was able to air spray without the gun clogging when painting. Apply the above paint to the tin plate using an air spray gun at 70 o/1.
Apply at a ratio of 0.00% and leave until the solvent and water evaporate.

Thereafter, it was baked at 180°C for 5 minutes. This coated product was smooth, and when the conductivity was measured, no current was detected and there were no eyeholes or pinholes. In addition, no whitening or blistering was observed in the boiling resistance test in which the coated products were immersed in boiling water for 30 minutes, and no problems were observed in the cross-cut test for adhesion. Good results were also obtained for epoxy phenol and epoxy urea base coated plates coated with the above paints in the same manner.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a device used for the current test, in which a container 4 containing a saline solution 3 is placed on a coating 2 applied to a metal plate 1, and an ammeter 5 detects the current. It is.

Claims (1)

[Claims] 1. An inner surface coating composition for can manufacturing, characterized in that a carboxyl group-containing polyolefin is dispersed in a solid state in a solution obtained by dissolving a food additive surfactant in an organic solvent and then adding water.