JPS6224463B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel inner surface coating agent for can manufacturing. The inner coating agent for can manufacturing is used for the purpose of not damaging the taste and flavor of the contents and preventing corrosion of the can material, and first of all, it is non-toxic and can withstand heat sterilization treatment. It is required to have a small amount of eluted substances, good adhesion, and good processability. Polyvinyl chloride polymers are currently used as inner coating agents for can manufacturing, but they currently have the following serious problems. First, it has been pointed out that vinyl chloride monomers remaining in polyvinyl chloride polymers are carcinogenic and other serious hygiene problems. Next, when discarded cans are incinerated, highly toxic and corrosive chlorine gas and hydrogen chloride gas are generated from polyvinyl chloride polymers, leading to environmental pollution and corrosion of incineration equipment. Furthermore, polyvinyl chloride-based polymers have insufficient contact with the metal that is the material of the can, and the coating process is complicated, such as requiring treatment with an epoxy resin before coating. In order to solve these problems with polyvinyl chloride coating agents, attempts have been made to use various polymers, but no satisfactory results have been obtained. Attempts have been made to use polyester resin, which has excellent contact with metals and does not emit toxic or corrosive gas when incinerated, as an inner coating agent for can manufacturing, but it has excellent blister resistance and whitening resistance during heat sterilization. No polyester resin has been obtained. The inventors of the present invention have continued to conduct extensive research to solve the above-mentioned drawbacks of polyester resin in terms of blister resistance and whitening resistance.As a result, they have found that they not only have excellent blister resistance and whitening resistance, but also have a small amount of eluted substances. The present invention was achieved by successfully discovering an inner coating agent for can making that has excellent processability. That is, the present invention comprises (A) as a polycarboxylic acid component, (1) 90 to 5 mol% of terephthalic acid, (2) 5 to 50 mol% of isophthalic acid and/or orthophthalic acid, and (3) terpene-maleic anhydride 5 -45 mol%, and (B) as a polyol component, is an inner coating agent for can manufacturing mainly consisting of a polyester resin having a reduced viscosity of 0.4 or more and consisting of (4) glycol having 2 to 10 carbon atoms. The can manufacturing inner surface coating agent of the present invention not only has excellent blister resistance and whitening resistance during heat sterilization treatment, but also has excellent adhesion to metals.
Furthermore, surprisingly, the amount of extractable substances is extremely small, and the results of the extraction test according to the method of FDA No. 175300 show that there is only an amount of extractable substances that is far below the FDA regulation value. In the polyester resin of the present invention, if the terephthalic acid component exceeds 90 mol% and the isophthalic acid and/or orthophthalic acid component is less than 5 mol%, the whitening resistance decreases and a coating agent having the desired performance cannot be obtained. I can't. On the other hand, if the terephthalic acid content is less than 5 mol % and the isophthalic acid and/or orthophthalic acid component exceeds 50 mol %, the flexibility decreases and cracks occur during can manufacturing, making it unusable. Furthermore, if the amount of the terpene-maleic anhydride adduct used in the present invention is less than 5 mol %, the solubility in general-purpose organic solvents will not be sufficient.
On the other hand, if it exceeds 45 mol %, flexibility and blister resistance decrease, making it impossible to obtain a coating agent with the desired performance. When an aliphatic dicarboxylic acid component is used as the polycarboxylic acid component, not only the whitening resistance and blister resistance are significantly reduced, but also the amount of eluted substances is significantly increased. In the polyester resin of the present invention, the reduced viscosity is
If it is less than 0.4, not only the blister resistance and flexibility will be significantly reduced, but also the amount of eluate will increase, making it impossible to obtain a coating agent with the desired performance. The terpene-maleic anhydride adduct used in the present invention refers to an adduct of maleic anhydride and an essential oil purified and isolated from natural plants, such as terpene and maleic anhydride. A typical example is an adduct of isolated α-terpinene and maleic anhydride. The glycol component used in the polyester resin of the present invention is a glycol having 2 to 10 carbon atoms,
ethylene glycol, propylene glycol,
1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,4-pentanediol, 1,6
Specific examples include -hexanediol, 1,5-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanedimethanol, p-xylylene glycol, and the like. Although 1,4-cyclohexanedimethanol and p-xylylene glycol can be used alone, they are preferably used in combination with the other glycols mentioned above from the viewpoint of solvent solubility. The polyester resin of the present invention can be assembled by a method for producing high molecular weight polyester according to a conventional transesterification method or direct esterification method,
There is no manufacturing method limited to the present invention.
However, when considering food applications, heavy metals and compounds that pose hygiene problems should be avoided as catalysts or additives. The polyester resin of the present invention has blister resistance,
It has excellent whitening resistance and adhesion, has an extremely small amount of eluted substances, and poses no hygienic problems, making it ideal for use as an inner coating agent not only for tableware, water-based soft drinks, and alcoholic beverages, but also for can manufacturing for non-food applications. EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to the Examples. In the examples, parts simply refer to parts by weight. Mol% of each component in polyester resin is NMR
(solvent: CDCl ₃ ) and gas chromatography. Reduced viscosity was measured using phenol/tetrachloroethane (6/4 weight ratio) as the solvent.
Measurements were made at 30° C. at a concentration of 0.100 g/25 ml. Blistering resistance and whitening resistance tests were conducted as follows. Dissolve 100 parts by weight of polyester in a mixed solvent of 200 parts by weight of methyl ethyl ketone and 200 parts by weight of toluene, and dry this solution to form a film with a thickness of 10 μm.
A 150mm x 70mm x 0.8mm mild steel plate (JIS
G 3141) using a bar coater, air-dried for 30 minutes, and then dried at 150°C for 4 minutes to obtain a test piece. This test piece was immersed in boiling distilled water for 1 hour, and the occurrence of blisters and whitening were visually determined. A case where there was no abnormality in the coating film was judged as good, and a case where blistering or whitening occurred was judged as poor. The adhesion test was conducted as follows, also serving as an evaluation of processability. Dissolve 100 parts by weight of polyester in a mixed solvent of 200 parts by weight of methyl ethyl ketone and 200 parts by weight of toluene.
It was coated on a 150 mm x 70 mm x 0.3 mm tin plate (JIS G 3303) using a bar coater so as to have a thickness of μ, air-dried for 30 minutes, and then dried at 150° C. for 4 minutes to obtain a test piece. Bending test using this test piece (JIS K 5400: Mandrel φ2mm, auxiliary plate thickness 4mm)
The product was evaluated as good if no cracks occurred at the bent portion, and poor if cracks occurred. The amount of extracted substances was measured by the following method in accordance with FDA No. 175300. 100 parts by weight of polyester was dissolved in a mixed solvent of 200 parts by weight of methyl ethyl ketone and 200 parts by weight of toluene, and this solution was coated on an aluminum foil of 200 mm x 300 mm x 0.05 mm using a bar coater so that the film thickness after drying was 10 μm. Apply on both sides,
After air drying for 30 minutes, the sample was dried at 150° C. for 4 minutes to obtain a test piece. This test piece was immersed in water (250 ml), n-heptane (150 ml), and 8% ethanol (150 ml) for 2 hours, and the immersion liquid was concentrated and dried, and the amount of extracted material per square inch was measured. Example 1 In a stainless steel autoclave equipped with a stirrer, a thermometer, and a partial reflux condenser, 77.6 parts of dimethyl terephthanate, 58.2 parts of dimethyl isophthanate, 74 parts of propylene glycol, 1.4 parts
90 parts of -butanediol and 0.13 parts of tetra-n-butyl titanate were added, the temperature was gradually raised, and the reaction was continued for 4 hours until the reaction temperature reached 220°C. Then, α-terpinene-maleic anhydride adduct 70.2
The reaction was continued for 1 hour and 30 minutes while gradually increasing the temperature from 210°C to 260°C. Next, the pressure of the reaction system was gradually reduced at 260°C, and the reaction was carried out for 2 hours under a reduced pressure of 0.2 mmHg or less to obtain a polyester resin (A). The obtained polyester resin (A) was pale yellow and transparent with a reduced viscosity of 0.710, and the measured composition was as follows. Dicarboxylic acid components Terephthalic acid 40 mol%, Isophthalic acid 30 mol%, α-terpinene-maleic anhydride adduct 30 mol% Glycol components Propylene glycol 46 mol%, 1,4-butanediol 54 mol% Various polyester resins (B to F) shown in Table 1 were manufactured. Table 1 shows the reduced viscosity of each polyester resin and the measured composition analysis results. Table 2 shows the test results of coating films obtained using each polyester resin.

【table】

[Table] Comparative Example 1 Various polyester resins (G to M) shown in Table 3 were produced using the same reaction apparatus as in Example 1 and in the same manner as in Example 1. Table 3 shows the reduced viscosity of each polyester and the measured composition analysis results. Table 4 shows the test results of the coating films obtained using each polyester resin (G to M).

【table】

【table】

Claims (1)

[Claims] 1 (A) As a polycarboxylic acid component, (1) 90 to 5 mol% of terephthalic acid, (2) 5 to 50 mol% of isophthalic acid and/or orthophthalic acid, and (3) terpene-maleic anhydride. Addenda 5-45
% by mole, and (B) as a polyol component, (4) an inner coating agent for can manufacturing, which is mainly composed of a polyester resin comprising glycol having 2 to 10 carbon atoms and having a reduced viscosity of 0.4 or more.