JPS5949947B2 - Internal coating composition for iron making - Google Patents

Description

[Detailed description of the invention] The present invention relates to an 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.

However, these paints may pose problems in terms of hygiene when used as interior paints for can manufacturing, especially when applied to food cans. For this reason, it is conceivable that the inner surface of the can be coated with a sanitary-safe polyolefin 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. The cans have serious defects that make this powder coating method inapplicable. Additionally, since more resin coating is formed than necessary, it is not a desirable method from the standpoint of resource conservation, and conventional coating equipment cannot be used, and a large-scale equipment manager is required, which is the current situation. It is very 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 very thick coatings, and polyolefins do not adhere to metal surfaces or epoxy base coats, and their high melting points usually make them difficult to combine with ethylene-vinyl acetate. Polymer (
(abbreviated as EVA) is added and used. 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 completed an inner coating composition for can manufacturing in which a polar group-containing polyolefin is dispersed in a solid state in a hydrocarbon solvent having a boiling point higher than the softening point of the polar group-containing polyolefin. (Japanese Patent Application No. 49-148030), this coating composition can form a uniform and smooth coating film on the inner surface of cans, can be used with conventional coating systems, and can be applied using powder coating methods. It has great industrial advantages, such as being able to greatly reduce the amount of resin compared to the case where the method is applied. However, in the above coating composition, depending on the type of polar group-containing polyolefin, the suspended solids may swell too much, resulting in increased particle size.
It was found that there were some systems that clogged the gun during spray painting, making it difficult to paint, and that there were problems that needed further improvement in terms of sagging and leveling.

The present invention was researched and invented in order to solve these problems, and a polar group-containing polyolefin is combined with one or two hydrocarbon bath agents having a boiling point higher than the softening point of the polar group-containing polyolefin. The present invention relates to an inner surface coating composition for making cans, characterized in that it is dispersed in a solid state in a mixed solvent of at least one species and one or more organic solvents other than the above-mentioned hydrocarbon solvents.

The polar group-containing polyolefin in the present invention includes polyethylene or polypropylene with a hydroxyl group, an epoxy group,
or a polymerizable unsaturated monomer containing a carboxyl group,
For example, 2-hydroxyethyl (meth)acrylate,
Polymers of 2-hydroxypropyl (meth)acrylate, glycidyl (meth)acrylate, (meth)acrylic acid, maleic anhydride, etc. are used. The grafting method involves generating radicals by powerful mechanical kneading of the polyolefin backbone polymer 1 in the coexistence of the above-mentioned polymerizable unsaturated monomers using a secondary mixer, Banbury mixer, etc., and grafting polymerization to the active sites of the polyolefin base polymer 1. Examples include a so-called mechanochemical method in which the polymer is irradiated with radiation, a radiation graft polymerization method in which the graft polymerization is performed by irradiation with radiation, and the like. Commercially available products include Zal manufactured by Seitetsu Kagaku Kogyo Co., Ltd.
kthen-F. CMPC-90 of Toa Fuel Industry Co., Ltd.
There are 2X-MA, C-802X-MA, L-900X, etc. These polar group-containing polyolefins also exhibit excellent adhesion to treated or untreated metal surfaces and base coat surfaces. Further, these polar group-containing polyolefins are preferably selected from those having an average molecular weight of about 1,000 or more and a softening point within the range of about 100°C to 180°C.

One of the organic solvents used in the present invention is a hydrocarbon solvent, and the boiling point is selected from those with a boiling point higher than the softening point of the polar group-containing polyolefin used, but the boiling point is not too high than the baking temperature. If a hydrocarbon solvent is used, the solvent may remain in the formed coating film, which is not preferable.

Specifically, aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as isooctane, nonane, and decane, methylcyclohexane, ethylcyclohexane,
Examples include oily hydrocarbons such as decahydronaphthalene, and solvent naphthas or mixtures of two or more thereof. Further, other solvents used in the present invention are not particularly limited, except for hydrocarbon solvents having a boiling point higher than the softening point of the polar group-containing polyolefin, such as benzene, hexane, hephthalate, mineral spirits, etc. , hydrocarbon solvents with a boiling point below the softening point of polar group-containing polyolefins, alcohol solvents such as ethanol, methanol, propanol, isopropanol, butanol, octanol, cetyl alcohol, diacetone alcohol, ethyl acetate, butyl acetate, cellosolve acetate Ester solvents such as methyl ethyl ketone,
Ketone solvents such as methyl isobutyl ketone, cyclohexanone, isoborone, ethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether,
Ether solvents such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, carbon tetrachloride,
Examples include halogenated hydrocarbon solvents such as trichlorethylene, and one or more of these can be used.

In the present invention, using only a hydrocarbon solvent with a boiling point higher than the softening point of the polar group-containing polyolefin has the above-mentioned problems, and using only other organic solvents causes the problem to occur after painting or at the initial stage of baking. A whitening phenomenon due to resin precipitation is observed before the resin particles soften.

If baking is performed with this whitening phenomenon still occurring, a uniform and smooth coating film cannot be formed. The present invention is characterized by the use of a mixture of both bathing methods, and the swelling of the polar polyolefin can be completely prevented, and sagging and leveling are also improved. The ratio of bathing between the two is approximately 5/95 to 95/5 (weight 8, preferably 3
The ratio is appropriately selected from about 0/70 to 70/30 depending on the type of the polar group-containing polyolefin used in each solvent. In the present invention, the method of dispersing the extreme group-containing polyolefin in a solid state in a mixed solvent includes a method of dispersing using a dispersion machine such as a ball mill or a sand mill;
Heat and dissolve the polar group-containing polyolefin in a portion of the solvent,
There are appropriate methods such as dropping this into the remaining cold bath agent and dispersing it.In this case, a suspension is prepared in a hydrocarbon solvent having a softening point higher than the softening point of the polar group-containing polyolefin. It is desirable to stabilize the system by adding an organic solvent. In addition, pigments, fillers, dispersibility improvers, and other various additives may be added to the hard can inner surface coating composition of the present invention as long as they do not contradict the purpose.

The present invention will be specifically explained below using Examples. For example, "middle part" refers to parts by weight. Example 1 Graft polyethylene (L-90 manufactured by Toa Fuel Industries Co., Ltd.)
10 parts of 0X) (softening point: approximately 105°C) and 40 parts of xylene are heated to 85°C while stirring to completely dissolve.

This was added dropwise to 50 parts of cold silica while stirring to obtain a milky white dispersion with an average particle size of 15 μm. A paint was prepared by adding 50 parts of isopropanol to this while stirring. This paint is stable not only immediately after preparation, but also after three months of aging, and does not cause gun clogging during painting. The above paint was applied to the inner surface of the molded aluminum can at a ratio of 70y/M2 using an air spray gun, and baked at 180°C for 5 minutes.

The smoothness of this painted product was visually inspected and the adhesion was good.
The bending resistance and boiling resistance were sufficient for practical use.

Comparative Example 1 In Example 1, when xylene was used instead of isopropanol, there were almost no problems when making the paint, but after a week, the air spray clogged, making it difficult to paint, which caused a practical problem. Ta.

Comparative example 2. Comparative example 1. When cyclohexanone is used instead of xylene, the coating film formed becomes rough and uneven, and when benzene, n-octanol, and butyl acetate are used alone, the coating film becomes uneven and is not suitable for internal coatings for can manufacturing. It was unsuitable for this purpose.

According to visual observation, whitening has occurred in the early stages of baking, and it is thought that this has an adverse effect on the final coating film. Examples 2 to 13 It was confirmed that each solvent shown in Table 1 was used in place of isopropanol in Example 1, and that a coating film and a paint with excellent performance could be obtained.

Example 14 Graft polyethylene (L-900X same as Example 1)
While stirring 10 parts and 110 parts of toluene, heat at 85℃ 4 (
Heat until completely dissolved.

When this was cooled, a milky white dispersion with an average particle size of 15 μm was obtained. 30 parts of ethanol was added to this while stirring to obtain a coating composition with good coating suitability and storage stability, which was uniformly applied onto a tin plate using a spray gun at a ratio of 1001'M2, and baked at 160°C for 5 minutes. Ta. Both the smoothness and durability of this coating film were sufficient for practical use. Example 15 Grafted polypropylene (C-9 manufactured by Kaa Fuel Industry Co., Ltd.)
02 .

To this, 10 parts of diethylene glycol monomethyl ether was added with stirring to obtain a coating composition with good applicability and storage stability.
It was applied uniformly at a ratio of V/M2 and baked at 200°C for 5 minutes. This coated product also had excellent retort resistance when left in steam at 130°C for 90 minutes. Comparative Example 3 In Example 15, when ethylcyclohexane was used instead of diethylene glycol monomethyl ether, the sagging and leveling properties were poor, and the suitability of the coating material was not preferable.

Claims (1)

[Claims] 1 A polar group-containing polyolefin is treated with one or more hydrocarbon solvents having a boiling point at a temperature higher than the softening point of the polar group-containing polyolefin, and one or two organic solvents other than the above hydrocarbon solvents. An inner surface coating composition for can making, characterized in that it is dispersed in a solid state in a mixed solvent with the above.