JP2865401B2 - Resin composition for baking type can inner coating - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a resin composition for baking-type can inner coatings. More specifically, the present invention relates to a resin composition for a baking-type can inner coating which can be suitably used for the inner surface of a can such as a can for preserving food or the like and a beverage can.

[Prior Art] Conventionally, a metal paint is applied to the inner surface of a metal can, such as a can for storing foods and the like and a can for beverages, in order to protect the surface from corrosion and the like. Epoxy resin paints, polyester resin paints, and the like are mainly used as such metal paints.

However, although the epoxy resin paint is excellent in corrosion resistance and chemical resistance, it is inferior in impact resistance and flexibility, so that when the metal can is deformed, the coating is cracked. When the film thickness is 10 μm or more, unevenness is generated on the surface of the coating liquid due to air blowing during drying, which causes foaming and varnishing. Further, the polyester-based resin can be coated with a thick film and has excellent impact resistance and flexibility, but has a disadvantage that it is inferior in corrosion resistance and chemical resistance.

[Problems to be Solved by the Invention] In view of the above-mentioned conventional technology, the present inventors have simultaneously excellent corrosion resistance, chemical resistance, impact resistance and flexibility,
As a result of intensive studies to develop a baking type can inner coating resin composition that can form a thick and smooth coating film in a short time, finally found such an excellent can inner coating resin composition, The present invention has been completed.

[Means for Solving the Problems] That is, the present invention comprises, as a main component, a block copolymer comprising 5 to 95% by weight of a polyester having carboxyl groups at both ends and 5 to 95% by weight of an epoxy resin, and an organic solvent is compounded. 20 to 100 μm in 1 to 4 minutes
The present invention relates to a resin composition for a baking-type can inner coating material capable of forming a smooth coating film having a thickness of m.

[Functions and Examples] As described above, the resin composition for baking can inner surface coating of the present invention is mainly composed of a block copolymer composed of a polyester and an epoxy resin. Thus, impact resistance and flexibility are simultaneously provided, and chemical resistance and corrosion resistance are simultaneously provided due to the epoxy resin segment.

The polyester having a carboxyl group at both terminals used in the present invention can be obtained by subjecting a dibasic acid and a polyhydric alcohol to a condensation reaction.

Examples of the dibasic acid include aromatic dibasic acids such as phthalic acid, isophthalic acid and terephthalic acid, diphenolic acid, acid anhydrides and hydrogenated products of these aromatic dibasic acids, succinic acid, adipic acid and azelaic acid. Acid, sebacic acid, saturated aliphatic dibasic acids such as dodecanedioic acid and the like, acid anhydrides thereof, dimer acids derived from unsaturated fatty acids, and the like. These dibasic acids are usually used alone or in combination of two or more. Are used as a mixture. Among these dibasic acids, phthalic acid, isophthalic acid, terephthalic acid, adipic acid, sebacic acid, dimer acids, diphenolic acid, etc. are particularly suitable for use because they have excellent safety for the human body. It is a good thing.

Examples of the polyhydric alcohol include ethylene glycol, polyethylene glycol, diethylene glycol, triethylene glycol, propylene glycol,
Polypropylene glycol, 1,3-butanediol, 2,3
-Butanediol, 1,4-butanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2,2-dialkyl-1,3-propanediol, butylene glycol, 1,6-hexanediol Linear diols such as cyclohexanediol, cyclohexane dimethanol, hydrogenated bisphenol A and other alicyclic diols; divalent compounds such as bisphenol A ethylene oxide adducts and bisphenol A propylene oxide adducts Alcohol and the like. Among these polyhydric alcohols, ethylene glycol,
Diethylene glycol, triethylene glycol, neopentyl glycol, butylene glycol, and the like have excellent safety for the human body and can be particularly preferably used.

The mixing ratio of the dibasic acid and the polyhydric alcohol is usually adjusted such that the equivalent ratio of the carboxyl group of the dibasic acid to the hydroxyl group of the polyhydric alcohol is 1.01 / 1 to 2/1. When the equivalent ratio is smaller than 1.01 / 1, the molecular weight of the obtained polyester becomes too large and the viscosity becomes too large, so that the reactivity with the epoxy resin becomes poor. In this case, unreacted dibasic acid remains, resulting in smearing of the coating liquid and deterioration of the physical properties of the coating film.

The number average molecular weight (hereinafter, referred to as n) of the polyester used in the present invention is determined by the mixing ratio of the dibasic acid and the polyhydric alcohol, and is generally 300 to 1000.
0, preferably 500-6000. When n is smaller than the above range, the effect of the block is not exhibited, and effects such as improvement of the processability of the epoxy resin are hardly exhibited, and when it exceeds the above range, the viscosity increases. , Poor reactivity with the epoxy resin.

Examples of the epoxy resin include aliphatic diepoxide, bisphenol A and bisphenol F.
And the like. These epoxy resins are usually used alone or in combination of two or more. Among these epoxy resins, polyglycidyl ether of bisphenol A, so-called epibis-type epoxy resin, is particularly preferred from the viewpoint of safety for the human body.

The number of epoxy groups contained in one molecule of the epoxy resin is 1.1 to 2 on average, particularly preferably two.
When the number of the epoxy groups is less than 1.1,
If the reactivity with the polyester is poor, and if it exceeds two, the reaction system will have a high viscosity during the synthesis of the block copolymer with the polyester, and if it is remarkable, it will gel.

Further, n of the epoxy resin is preferably 340 to 20,000, particularly preferably 340 to 4,000. If the value of n is smaller than the above range, the unreacted epoxy resin is extracted into the contents of the can when it is present, which is not preferable as a paint for the inner surface of the can. , The viscosity becomes too high and the reactivity with the polyester becomes poor.

The mixing ratio (weight ratio) of the epoxy resin and the polyester is adjusted to be usually 5/95 to 95/5, preferably 10/90 to 90/10. When the compounding ratio is smaller than 5/95, it shows properties similar to the polyester resin,
On the other hand, if the ratio exceeds 95/5, the physical properties are the same as those of the epoxy resin, and the effect of the block is less likely to be sufficiently exhibited.

In the present invention, in mixing the epoxy resin and the polyester, an equivalent ratio of a carboxyl group of the polyester to an epoxy group of the epoxy resin is used so that unreacted polyester or epoxy resin does not remain. Is preferably adjusted to be 1/2 to 2/1.

The reaction between the polyester and the epoxy resin can be performed by a usual solution polymerization method. As an example of such a solution polymerization method, for example, a desired amount of a polyester and an epoxy resin are prepared and dissolved in a solvent.
And a method of heating for minutes to 6 hours. As the solvent, a solvent that does not cause a side reaction is selected, and examples thereof include cyclohexanone and xylene. At the time of the reaction, for example, a basic catalyst such as a tertiary amine may be appropriately blended to promote the reaction.

The n of the block copolymer comprising the polyester and the epoxy resin thus obtained is from 1,000 to 30,000, preferably from 3,000 to 20,000. When the value of n is smaller than the above range, the amount of organic substances to be extracted becomes large and becomes unsuitable as a paint for the inner surface of the can. Workability is reduced.

As described above, the resin composition of the present invention contains the block copolymer as a main component. When used, the resin solid content of the block copolymer in the resin composition is 5 to 70% by weight, Preferably 10 to 50% by weight
It is prepared by adding a solvent such that When the resin content of the block copolymer is less than 5% by weight, it is difficult to form a uniform film by a known coating method. It tends to be difficult to paint without losing the required fluidity.

When the resin composition of the present invention is used as an inner coating for cans, it is conceivable to use the resin composition as it is, but in many cases, a melamine resin or a phenol resin is appropriately blended and heat-cured. It is common to use it as a mold paint.

The resin composition of the present invention may further contain, for example, a plasticizer, a colorant, and the like, if necessary.

As a material of a can to which the resin composition of the present invention can be applied,
For example, iron, tin, stainless steel, titanium, copper, aluminum and the like can be mentioned.

The means for applying the resin composition of the present invention is not particularly limited and is optional. Examples of such means include brush coating, spatula coating, spray coating, roll coating and the like.

The thickness of the dried coating film on which the resin composition of the present invention has been formed varies depending on the intended use, but is adjusted to fall within the range of 20 to 100 μm.

Thus, the coating film obtained by forming the resin composition of the present invention on a substrate is thick and smooth, and has excellent corrosion resistance, chemical resistance, impact resistance and flexibility.

Next, the resin composition of the present invention will be described in more detail based on examples, but the present invention is not limited to only these examples.

Example 1 2.0 mol of isophthalic acid was placed in a four-necked flask having a capacity of 3 having a fractionator capable of separating water and a polyhydric alcohol.
2.2 mol of adipic acid, 1.4 mol of neopentyl glycol,
1.4 mol of 1,6-hexanediol and 1.2 mol of ethylene glycol were charged, and heating was started.

When the liquid temperature reached about 160 ° C., water began to evaporate by esterification, and the liquid temperature reached 250 ° C. Next, nitrogen gas was passed into the flask at this temperature to drive off water to complete the reaction.

The obtained polyester has n of 5000 and acid value of 22 mg K
It was OH's.

Next, 500 g of the obtained polyester was placed in a four-necked flask having a content of 3 and then 135.5 as an epoxy resin, Epicoat 1001 (trade name, manufactured by Yuka Shell Epoxy Co., Ltd., epoxy equivalent: 460, n: 1000). After adding g, the mixture was heated to 150 ° C. with stirring, 6.4 g of dimethylbenzylamine was added as a basic catalyst, and the reaction was carried out for 3 hours. As a result, the acid value in the reaction system became 1.0 mg KOH or less. So the reaction was finished.

The n of the obtained block copolymer was 13,000, the weight average molecular weight (hereinafter, referred to as w) was 29,000, and the glass transition temperature was 40 ° C. The epoxy resin segment has 2
1.3% by weight.

The molecular weight of the formed block copolymer from the start of polymerization was examined using high performance liquid chromatography (manufactured by Shimadzu Corporation, product number: LC-2, column: HSG-40 + HSG-20) and an ultraviolet absorption spectrophotometer. The result is shown in FIG.

In FIG. 1, the horizontal axis represents the retention capacity (ml), the vertical axis represents the peak intensity (-), (1) is the chromatogram of the polyester, and (2), (3) and (4) are the reaction start 1 respectively. 1 shows chromatograms of block copolymers after 2 and 3 hours.

From the results shown in FIG. 1, it can be seen that the polyester reacted with the epoxy resin, and the block copolymer grew over time.

After the completion of the reaction, a mixed solvent of xylene and butyl cellosolve (mixing ratio (weight ratio) = 1: 1) was added to the flask so that the resin solid content of the block copolymer became 40% by weight to obtain a block copolymer solution.

Next, 80 parts by weight of the block copolymer solution (resin solid content) and 20 parts by weight of a melamine resin (trade name: Cymel 303, manufactured by Mitsui Cynamid Co., Ltd.) were mixed to prepare a baking type paint.

The obtained baking-type paint is applied to a tin plate (# 25) of 10 cm in length and 20 cm in width so that the thickness of the coating film after drying becomes 20 μm, and then heated at 200 ° C. for 120 seconds to heat the sample. Produced.

The properties of the obtained sample include adhesion, bending,
The retort resistance and corrosion resistance were examined according to the following methods. Table 1 shows the results.

(B) Adhesion Use a cutter knife to cut a 2 mm x 2 mm grid
After 100 pieces were inserted, a cellophane adhesive tape was affixed, and then the number of cross-cut coating films remaining after peeling was counted.

(B) Folding property IT was used for bending, and the amount of current (mA) at the bent portion was measured with an enamellator.

(C) Retort resistance A sample was placed in a stainless steel vat 2 and water 1
Was added, and this was put into a pressure cooker, heated at 130 ° C. for 30 minutes, visually inspected for the presence or absence of stain on the coating film, and evaluated based on the following evaluation criteria.

(Evaluation criteria) ○: No whitening was observed.

 X: Whitening is observed.

(D) Corrosion resistance A sample plate was formed into a can lid. Separately, add 1% saline to a well-painted can body, tighten it, and then
After the time retort, the mixture was left at 55 ° C. for 7 days.

Next, the sample was opened and visually inspected for any abnormality in the coating film, and evaluated based on the following evaluation criteria.

(Evaluation criteria) ：: No abnormality was observed.

 Δ: Small blisters are observed.

 X: Floating is observed on the entire surface of the coating film.

Comparative Examples 1-2 In Example 1, instead of 80 parts by weight of the block copolymer solution (resin solid content), 80 parts by weight of the phenoxy resin (PKHH resin manufactured by UCC) solution (resin solid content) (Comparative Example 1) or high A coating was prepared in the same manner as in Example 1 except that 80 parts by weight (resin solid content) of a molecular polyester (manufactured by Toyobo Co., Ltd., Byron 290) solution (Comparative Example 2) was used. The physical properties were examined. Table 1 shows the results.

As is clear from the results shown in Table 1, when the phenoxy resin was used (Comparative Example 1), the adhesion to the substrate was poor, so that when the corrosion resistance was examined, Floating was observed on the entire surface of the steel sheet, resulting in poor corrosion resistance.
When polyester was used (Comparative Example 2), the retort resistance and the corrosion resistance were poor because the barrier properties were inferior, although the adhesion to the substrate was excellent.

On the other hand, when the resin composition of the present invention was used (Example 1), a coating film having excellent adhesiveness, bending property, retort resistance and corrosion resistance was formed.

Example 2 In the same manner as in Example 1 except that 1.1 mol of adipic acid and 1.0 mol of ethylene glycol were charged into a four-necked flask having a capacity of 3 having a separator capable of separating water and a polyhydric alcohol. A polyester was prepared.

The polyester obtained has an n of 2300 and an acid value of 50 mg K
It was OH's.

Next, 500 g of the obtained polyester was placed in a four-necked flask having a content of 3 and R-366 was used as an epoxy resin.
(Mitsui Petrochemical Co., Ltd., trade name, epoxy equivalent: 101
(0, n: 2050) A block copolymer was prepared in the same manner as in Example 1 except that 600 g was added.

N of the obtained block copolymer is 13000, w is 3
5000, the acid value was 1 mg KOH or less, and the glass transition temperature was 62 ° C.

Next, a mixed solvent of xylene and butyl cellosolve (mixing ratio (weight ratio) = 1: 1) was added to the flask so that the resin solid content of the block copolymer became 40% by weight to obtain a block copolymer solution.

Next, 70 parts by weight of a block copolymer solution (resin solid content), 30 parts by weight of a phenolic resin such as HITANOL 4020 (trade name, manufactured by Hitachi Chemical Co., Ltd.) and 1 part of phosphoric acid as a catalyst
By weight, a phenol-modified paint was prepared.

The obtained paint is a representative aluminum material for cans 50
The thickness of the coating film after drying on 52 materials (length 10 cm, width 20 cm) is 20
After coating to a thickness of μm, the coating was heated at 200 ° C. for 4 minutes to form a coating film, and then processed into a can lid and molded.

Next, in recent years, in food cans such as tuna cans, an easy open end of aluminum is often provided on a tin can body, and corrosion of the aluminum lid due to contact of dissimilar metals has become a problem, so the can lid is unpainted. After being wound around a tin can, the adhesion and bending properties were examined in the same manner as in Example 1, and the corrosion resistance was examined by the following method. Table 2 shows the results.

(E) Corrosion resistance Soy sauce is added to an unpainted tin can so that the volume becomes 90% of the total volume. After the can lid is tightened, the mixture is heated in a pressure cooker at 130 ° C for 1 hour, and then in an atmosphere of 55 ° C. For 3 days. Next, the can lid was taken out, and the presence or absence of abnormality was visually observed, and evaluated based on the following evaluation criteria.

(Evaluation criteria) ：: No abnormality.

 Δ: Blister is observed.

 X: It becomes a perforated can.

Comparative Examples 3 and 4 In Example 2, 70 parts by weight (resin solids content) of the same phenoxy resin solution used in Comparative Example 1 instead of 70 parts by weight (solids content of resin) of the block copolymer solution (Comparative Example 3) or A paint was prepared and applied in the same manner as in Example 2 except that 70 parts by weight of the same high molecular polyester solution (resin solid content) (Comparative Example 4) as used in Comparative Example 2 was used, and a can lid was prepared. did. Next, the physical properties of the can lid were examined in the same manner as in Example 2. Table 2 shows the results.

As is clear from the results shown in Table 2, when the phenoxy resin was used (Comparative Example 3), the flat portion exhibited corrosion resistance, but the processed pressure ridge portion and the ring portion had perforations. Admitted. When polyester was used (Comparative Example 4), blisters were observed on the entire surface of the coating film, and the most prominent ones were perforated.

On the other hand, when the resin composition of the present invention was used, blisters were slightly observed in the processed portion, but did not reach the perforation, and no abnormality was recognized in the flat portion.

Example 3 Adipic acid 4 as dibasic acid and polyhydric alcohol
Moles and 3 moles of ethylene glycol,
A polyester was prepared in the same manner as in Example 1.

The obtained polyester has n of 700 and acid value of 150 mg K
It was OH's.

Next, 140 g of the obtained polyester was placed in a four-necked flask having a content of 3, and R-367 was used as an epoxy resin.
(Mitsui Petrochemical Co., Ltd., trade name, epoxy equivalent: 125
(0, n: 2580) A block copolymer was prepared in the same manner as in Example 1 except that 1000 g was added.

N of the obtained block copolymer is 5500 and w is 17
000, the acid value was 1 mg KOH or less, and the glass transition temperature was 92 ° C.

Next, a mixed solvent of xylene and butyl cellosolve (mixing ratio (weight ratio) = 1: 1) was added to the flask so that the resin solid content of the block copolymer became 40% by weight to obtain a block copolymer solution.

Next, 80 parts by weight of the block copolymer solution (resin solid content) and 20 parts by weight of phenol as a phenol resin were mixed to prepare a coating material.

After applying the obtained paint to a tin plate of 10 cm in length and 20 cm in width so that the thickness of the coating film after drying becomes 20 μm, 21
The coating was formed by heating at 0 ° C. for 2 minutes to obtain a sample.

Next, the adhesion, the bending property and the corrosion resistance were examined in the same manner as in Example 1.

In addition, the inner paint for cans is generally coated with an epoxy-phenol-based paint in a thickness of 5 to 10 μm.
Dry with hot air of / sec. 10μ with conventional epoxy resin
When the film thickness is more than m, the surface of the coating liquid becomes uneven due to the air blow during drying, which causes foaming and varnishing. Therefore,
The surface state of the block copolymer obtained in Example 3 and the conventional epoxy resin at the time of blowing were compared by the following method. Table 3 shows the results.

(F) Surface state at the time of blowing A painted plate was prepared by painting a tin plate of 10 cm × 20 cm so that the film thickness became 20 μm. Immediately after painting, 200 ° C hot air 3
The coated plate was placed in an oven blown at m / sec so that the coated plate was parallel to the blowing direction, and baked for 10 minutes. The surface condition of the baked plate was visually evaluated according to the following evaluation criteria.

(Evaluation criteria) ：: The coating film is smooth, and no foaming or varnish is observed.

X: The coating film has irregularities, and foaming and varnishing are observed.

Comparative Example 5 In Example 3, VD-02 was used as an epoxy resin instead of 80 parts by weight (resin solid content) of the block copolymer solution.
0H (manufactured by Toto Kasei Co., Ltd., trade name, n = about 5000) solution 80
A coating material was prepared and a sample was prepared in the same manner as in Example 3 except that the weight part (resin solid content) was used. Next, the physical properties of the sample were examined in the same manner as in Example 3. Table 3 shows the results.

As is clear from the results shown in Table 3, the resin composition obtained in Example 3 of the present invention had excellent corrosion resistance almost equivalent to the resin composition using the epoxy resin obtained in Comparative Example 5. , But excellent in all of adhesiveness, bendability and surface condition at the time of sending.

From the above results, the resin composition containing a block copolymer composed of the polyester and the epoxy resin of the present invention as a main component has excellent workability and adhesion, and at the same time, has a thick coating film excellent in smoothness during baking. It can be seen that it can be formed.

[Effect of the Invention] The resin composition for baking-type can inner surface coating of the present invention has corrosion resistance,
It is excellent in chemical resistance, impact resistance and flexibility at the same time, and can form a thick and smooth coating film in a short time. For example, metal such as cans for storing foods and cans for beverages It can be suitably used as a paint for the inner surface of a can.

[Brief description of the drawings]

FIG. 1 is a chromatogram of the block copolymer obtained in Example 1 of the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-180521 (JP, A) JP-A-54-21498 (JP, A) JP-A-54-102399 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) C09D 163/00-163/10 C09D 167/00-167/03 C08G 59/14

Claims (2)

(57) [Claims] 1. A block copolymer comprising 5 to 95% by weight of a polyester having carboxyl groups at both terminals and 5 to 95% by weight of an epoxy resin, containing an organic solvent, and for 1 to 4 minutes. A resin composition for a baking-type can inner coating capable of forming a smooth coating film having a thickness of 20 to 100 μm. 2. The resin composition according to claim 1, wherein the equivalent ratio of the carboxyl group of the polyester to the epoxy group of the epoxy resin is adjusted to 1/2 to 2/1.