JP2002348362A - Polyester resin and coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester resin suitable for a coating for coating a steel plate used for home electric appliances, office supplies, food containers and the like, in particular, a polyester resin for coating a metallic can for foods, drink and the like to give a coating film excellent in processability, retort resistance and adhesion to metal. SOLUTION: The polyester resin comprises a dicarboxylic acid component comprising 40-100 mole % of an aromatic dicarboxylic acid component and a glycol component comprising 20-70 mole % of propylene glycol, 20-70 mole % of 1,4-butanediol and 10-50 mole % of an alicyclic glycol, and has an intrinsic viscosity of at least 0.3 and a glass transition temperature of at least 35 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester resin suitable for coating metal steel sheets used for home electric appliances, office supplies, food containers, etc., and particularly to a metal can for food and beverages. The present invention relates to a polyester resin which becomes a coating film having excellent workability, retort resistance, and metal adhesion.

[0002]

2. Description of the Related Art Conventionally, when coating a metal steel sheet, polyester resin, epoxy resin, acrylic resin, vinyl resin, and the like have been used as paints. It is used in various applications such as office supplies, food containers and the like. Above all, paints used for food and beverage cans are used for the purpose of preventing the corrosion of the can material caused by various kinds of foods without impairing the flavor and flavor of the contents, and are therefore non-toxic. , Heat resistance, heat resistance, excellent adhesiveness and workability.

Conventionally, polyvinyl chloride resins, epoxy-phenol resins and the like have been widely used as coating resins used for this purpose, but these have the following problems. It is.

[0004] That is, polyvinyl chloride resin has excellent retort resistance, content resistance, and processability, but the vinyl chloride monomer remaining in the resin has serious hygiene problems such as carcinogenicity. It is pointed out that it is a substance.
In addition, when incinerating discarded cans, toxic and corrosive chlorine gas, hydrogen chloride gas, and highly toxic dioxin are generated from the polyvinyl chloride resin, leading to corrosion of incinerators and environmental pollution. There is. Further, the polyvinyl chloride-based resin has an inadequate adhesiveness to metal as a can material and requires a coating after being treated with an epoxy resin, so that the coating process is complicated.

[0005] Epoxy-phenol resins are mainly spray-coated because of their high baking temperature, which tends to cause poor appearance such as foaming during baking, and also have poor workability.

In order to solve such a problem, Japanese Patent Publication No. 60-42829 and Japanese Patent Publication No. 61-36548 disclose easy coating and baking, excellent metal adhesion, toxic and corrosive gas during incineration. As a resin that does not generate, polyester resins have been proposed, but in recent years, the shape of food cans and beverage cans has become complicated, and for such complicated processing, the processing step after lamination, especially drawing. There is a disadvantage that whitening and cracking of the coating film easily occur in the processing step.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above problems and provides a polyester resin suitable for a coating composition having good workability, retort resistance and metal adhesion, and a coating composition containing the polyester resin. The purpose is to provide things.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to solve the above-mentioned drawbacks of the polyester resin, and as a result, it has butanediol and an alicyclic structure as glycol components constituting the polyester resin. By introducing a glycol component, it shows high metal adhesion,
The inventors have found a polyester resin having excellent workability and retort resistance, and have reached the present invention. That is, the present invention has the following configuration. (1) A polyester resin composed of a dicarboxylic acid component and a glycol component, wherein the aromatic dicarboxylic acid component is 40 to 100 mol% of the dicarboxylic acid components, and propylene glycol is 2 of the glycol components.
0-70 mol%, 1,4-butanediol is 20-7
A polyester resin having 0 mol%, 10 to 50 mol% of alicyclic glycol, an intrinsic viscosity of 0.3 or more, and a glass transition temperature of 35 ° C. or more. (2) Among the dicarboxylic acid components, the alicyclic dicarboxylic acid is 6
The polyester resin according to (1), which is 0 mol% or less. (3) A coating composition comprising the polyester resin according to (1) or (2).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
It is necessary that the aromatic dicarboxylic acid in the dicarboxylic acid component constituting the polyester resin of the present invention is 40 to 100 mol%. 40 mol of aromatic dicarboxylic acid
% Is not preferable because retort resistance and whitening resistance are inferior. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid and the like, and preferably terephthalic acid and isophthalic acid.

[0010] Of the dicarboxylic acid components, an alicyclic dicarboxylic acid is preferably copolymerized, and the copolymerization amount is preferably 60 mol% or less. A polyester resin obtained by copolymerizing an alicyclic dicarboxylic acid has improved metal adhesion and extensibility, and is suitable for a paint having excellent workability. 6 alicyclic dicarboxylic acids
If it exceeds 0 mol%, the glass transition temperature of the obtained polyester resin is low, the resin after the production tends to be easily blocked, and the retort resistance tends to be inferior. Examples of the alicyclic dicarboxylic acid include 1,4-cyclohexanedicarboxylic acid, 1,3
-Cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, tetrahydrophthalic acid and the like.

[0011] Of the glycol components constituting the polyester resin of the present invention, propylene glycol is 20 to 70 m
ol%, 20-70 mol of 1,4-butanediol
% And the alicyclic glycol must be 10 to 50 mol%, preferably 30 to 50 mol%.
６０60 mol%, 1,4-butanediol is 30６０60
mol%, alicyclic glycol is 20 to 50 mol%.

When the copolymerization amount of propylene glycol is 20 m
%, the glass transition temperature is low, and the solubility in a solvent is extremely poor.
If the content exceeds ol%, the processability becomes poor, which is not preferable. If 1,4-butanediol is less than 20 mol%, processability is poor, and if it exceeds 70 mol%, the glass transition temperature is low, which is not preferable. Further, if the alicyclic glycol is less than 10 mol%, the processability is poor, and if it exceeds 50 mol%, the solubility in a solvent and the stability of the dissolved product are poor, which is not preferable.

The alicyclic glycols include 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,2-cyclohexanedimethanol,
Examples thereof include 4-cyclohexanediethanol, 1,3-cyclohexanediethanol, 1,2-cyclohexanediethanol, 1,4-cyclohexanediol, 1,3-cyclohexanediol, and 1,2-cyclohexanediol.

The polyester resin of the present invention may contain the following copolymer components as long as its properties are not impaired. As the dicarboxylic acid component to be copolymerized, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecandionic acid, saturated aliphatic dicarboxylic acids such as hydrogenated dimer acid, fumaric acid, maleic acid, maleic anhydride, Itaconic acid, mesaconic acid, citraconic acid, unhydrogenated dimer acid, cyclohexenedicarboxylic acid,
And unsaturated dicarboxylic acids such as terpene-maleic acid adducts.

The glycol components to be copolymerized include ethylene glycol, 1,3-propanediol,
Neopentyl glycol, 1,5-pentanediol,
1,6-hexanediol, diethylene glycol, dipropylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, dimethylol heptane, dimethylol pentane, 2-ethyl-2-butylpropanediol, 2-methyl- 1,3-propanediol, 3
-Methyl-1,5-pentanediol, 3-ethyl-
1,5-pentanediol, 3-propyl-1,5-pentanediol, 3-methyl-1,6-hexanediol, 4-methyl-1,7-heptanediol, 4-methyl-1,8-octanediol , 4-propyl-1,8
-Octanediol, tricyclodecane glycols,
Bisphenols include ethylene oxide or propylene oxide derivatives and hydrogenated bisphenols.

The intrinsic viscosity of the polyester resin of the present invention must be 0.3 or more. Intrinsic viscosity is 0.3
If it is less than 10%, the coating film becomes brittle, resulting in poor workability and retort resistance, which is not preferable.

The polyester resin of the present invention needs to have a glass transition temperature of 35 ° C. or higher, preferably 50 ° C. or higher. When the glass transition temperature is lower than 35 ° C., the resin after the production is liable to be blocked, and further, the retort resistance becomes poor, which is not preferable.

The polyester resin of the present invention preferably contains a trifunctional or higher functional ester-forming polyfunctional compound in an amount of 0.1 to 5 mol%.
By copolymerizing an ester-forming polyfunctional compound having three or more functional groups, the number of hydroxyl groups in the polyester resin increases, and the adhesion to the metal surface is further improved by the hydroxyl groups. Examples of trifunctional or higher functional ester-forming polyfunctional compounds include trimellitic acid, trimellitic anhydride, pyromellitic acid, benzophenonetetracarboxylic acid, trimethylolpropane, trimethylolethane, glycerin, mannitol, sorbitol, pentaerythritol, α- Methyl glucoside, dimethylolbutanoic acid and the like can be mentioned.

The method for producing the polyester resin of the present invention is not particularly limited, and it can be produced by a conventionally known polyester production method. For example, a dicarboxylic acid component, a glycol component as described above,
And, if necessary, using an ester-forming polyfunctional compound as a raw material, performing an esterification or transesterification reaction at a temperature of 200 to 260 ° C. by a conventional method, adding a polycondensation catalyst, and reducing the pressure to 220 under a reduced pressure of 5 hPa or less. It can be prepared by performing a polycondensation reaction at a temperature of from 260 to 260C, preferably from 230 to 250C. As the polycondensation catalyst, conventionally used metal compounds such as tin, titanium, antimony, germanium, and cobalt are suitable.

The terminal of the polyester resin of the present invention may be further provided with a carboxyl group or a hydroxyl group, if necessary. When a carboxyl group is imparted, it can be obtained by performing a polycondensation reaction by a conventional method, and then performing a depolymerization reaction with an acid component such as trimellitic anhydride, trimellitic acid, pyromellitic acid, and benzophenonetetracarboxylic acid. it can. When a hydroxyl group is imparted, a method of similarly performing a depolymerization reaction with a glycol component such as trimethylolpropane, trimethylolethane, glycerin, mannitol, sorbitol, pentaerythritol, α-methylglucoside, an esterification reaction or a polymerization reaction It can be obtained by a method in which the above-mentioned trifunctional or higher functional ester-forming polyfunctional compound is added during the condensation reaction, and the polycondensation reaction is carried out until a predetermined degree of polymerization is reached.

The polyester resin of the present invention may contain, if necessary, a heat stabilizer such as phosphoric acid, an antioxidant such as a hindered phenol compound, a pigment such as titanium oxide, a filler, an antibacterial agent and a deodorant. And other thermoplastic resins and the like.

The polyester resin of the present invention can provide excellent coating properties even when used alone as a coating material, but it can accelerate the curing of phenol resins, amino resins, epoxy resins, isocyanate compounds, and other curing agents, and imidazole compounds. It is preferable to use the composition as a coating composition by adding an agent.

The phenolic resin used as the curing agent is not particularly limited, but is a resol type resin obtained by reacting an aldehyde with a phenol in the presence of an alkali catalyst, and a novolak obtained by reacting an aldehyde with a phenol in the presence of an acidic catalyst. And a resol type resin suitable as a crosslinking agent. Phenols used for these phenolic resins are phenol, o-cresol, p-
Cresol, m-cresol, m-methoxyphenol, 2,3-xylenol, 2,5-xylenol, p
Examples thereof include -tert-butylphenol, p-ethylphenol, bisphenol A, and bisphenol F, and alkylphenols are preferable from the viewpoint of compatibility with the polyester resin. Mono- to trimethylol compounds of these phenols and condensates thereof, or alkyl ether compounds thereof, preferably butyl ether compounds, or those obtained by subjecting them to various modifications such as epoxy modification, oil modification, melamine modification, and amide modification can be used. .

Examples of the amino resin include formaldehyde adducts such as urea, melamine and benzoguanamine, and alkyl ether compounds of these alcohols having 1 to 6 carbon atoms. Specific examples include methoxymethylolated urea, methoxylated methylol-N, N-ethylene urea, methoxymethylol dicyandiamide, methoxylated methylol melamine, methoxylated methylol benzoguanamine, butoxylated methylol melamine, butoxylated methylol benzoguanamine, and the like. Are methoxylated methylolmelamine, butoxylated methylolmelamine, and methylolated benzoguanamine, each of which can be used alone or in combination.

Examples of the epoxy compound include diglycidyl ether of bisphenol A and its oligomer, diglycidyl ether of hydrogenated bisphenol A and its oligomer, diglycidyl orthophthalate, diglycidyl isophthalate, diglycidyl terephthalate, and p-glycidyl ester. Diglycidyl oxybenzoate, diglycidyl tetrahydrophthalate,
Diglycidyl hexahydrophthalate, diglycidyl succinate, diglycidyl adipate, diglycidyl sebacate, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1, 6-hexanediol diglycidyl ether and polyalkylene glycol diglycidyl ethers, trimellitic acid triglycidyl ester,
Triglycidyl isocyanurate, 1,4-diglycidyloxybenzene, diglycidyl propylene urea, glycerol triglycidyl ether, trimethylol ethane triglycidyl ether, trimethylol propane triglycidyl ether, pentaerythritol tetraglycidyl ether, glycerol alkylene oxide adduct Triglycidyl ether and the like.

Further, as the isocyanate compound, there are aromatic and aliphatic diisocyanates, and polyisocyanates having a valency of 3 or more, and either low molecular weight compounds or high molecular weight compounds may be used. For example, tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate or trimers of these isocyanate compounds, and excess amounts of these isocyanate compounds And low molecular active hydrogen compounds such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, triethanolamine or various polyester polyols, polyether polyols, and polymers of polyamides Obtained by reacting with active hydrogen compounds It includes an end isocyanate group-containing compound.

The isocyanate compound is preferably a blocked isocyanate. Examples of the isocyanate blocking agent include phenols such as phenol, thiophenol, methylthiophenol, ethylthiophenol, cresol, xylenol, resorcinol, nitrophenol, chlorophenol, oximes such as acetoxime, methylethylketoxime, and cyclohexanone oxime, methanol, ethanol, Alcohols such as propanol and butanol, halogen-substituted alcohols such as ethylene chlorohydrin and 1,3-dichloro-2-propanol, tertiary alcohols such as t-butanol and t-pentanol, ε-caprolactam, Lactams such as δ-valerolactam, γ-butyrolactam, β-propyrolactam and the like, and other aromatic amines, imides, acetylacetone, acetoacetate ester , Active methylene compounds such as malonic acid ethyl ester, mercaptans, imines, ureas also include diaryl compounds sodium bisulfite and the like. The blocked isocyanate can be obtained by subjecting the above isocyanate compound to an isocyanate blocking agent to undergo an addition reaction by a conventionally known appropriate method.

When a curing agent is used in the coating composition of the present invention, the above-mentioned phenol resin, amino resin, epoxy resin, isocyanate compound and the like may be used in combination for the purpose of improving the curability, and depending on the type. A selected known curing agent or accelerator may be used in combination.

Examples of the organic solvent used for coating include, for example, toluene, xylene, solvesso, ethyl acetate, butyl acetate, methyl ethyl ketone, cyclohexanone, isophorone, methyl cellosolve, butyl cellosolve, ethylene glycol monoacetate, and the like. It is selected in consideration of.

[0030]

The present invention will be specifically described below with reference to examples. Each measurement and evaluation item followed the following method. (1) Measurement of resin composition 1H-NMR spectrometer JNM manufactured by JEOL Ltd.
-Measured on LA400 instrument. (2) Measurement of intrinsic viscosity The viscosity was measured at a temperature of 20 ° C. using an equal mass mixture of phenol and ethane tetrachloride as a solvent. (3) Measurement of glass transition temperature (Tg) It was measured at a heating rate of 10 ° C./min using a differential scanning calorimeter SSC5200 manufactured by Seiko Instruments Inc. (4) Solubility The obtained polyester resin was dissolved in cyclohexanone to form a 30% by mass solution, and the dissolution stability after standing at 25 ° C. was evaluated as solubility. ：: good ×: cloudy, solidified or insoluble (5) Preparation of test piece The obtained polyester resin was dissolved in cyclohexanone to form a 40% by mass solution, and then the polyester resin / blocked isocyanate = 80/20 (mass ratio). A quantity of blocked isocyanate and 0.3 parts by weight of dibutyltin dilaurate were added. After that, TFS (Tin Free Steel, 70mm × 150mm × 0.3mm)
Was coated with a bar coater # 38 so that the film thickness became 10 to 15 μm, and heat treatment was performed at 180 ° C. for 30 minutes to obtain a test piece. (6) Workability The test piece was sandwiched by 18 pieces so as to sandwich the same two TFS substrates as the test piece.
After bending in the 0-degree direction, the bent portion was observed with a loupe, and the presence or absence of cracks, peeling, and cracks in the coating film was visually determined. ：: good ×: crack, peeling or cracking (7) Metal adhesion According to JIS K 5400, the test piece was scratched in a grid pattern with a cutter knife, the grid section was peeled off with cellophane tape, and the grid pattern was cut. The metal adhesion was evaluated based on the number of crosses remaining in 100 pieces. ：: The number of remaining grids is 90 or more ×: The number of remaining grids is less than 90 (8) Retort resistance After treating the test piece under steam at 130 ° C. for 30 minutes, the state of cloudiness and whitening of the coating film is visually observed. Was determined. ：: good ×: cloudy, whitened

Example 1 116 parts by mass of terephthalic acid, 52 parts by mass of cyclohexanedicarboxylic acid, 49 parts by mass of propylene glycol, 36 parts by mass of butanediol, 4 parts of cyclohexanedimethanol
3 parts by mass and 0.7 parts by mass of trimethylolpropane were charged into an esterification reactor, and the pressure was 0.5 MPa and the temperature was 240.
The esterification reaction was performed at 4 ° C. for 4 hours. The obtained polyester oligomer was transferred to a polymerization reactor, and 0.3 parts by mass of tetrabutyl titanate was charged.
The pressure was gradually reduced to 0.4 hPa over minutes, and then a polycondensation reaction was performed at a temperature of 230 ° C. for 3 hours to obtain a polyester resin of the present invention. Using this polyester resin, a test piece was obtained by the method described above. Table 1 shows the obtained evaluation results.

Examples 2 to 9 and Comparative Examples 1 to 6 A polyester resin and a test piece were prepared in the same manner as in Example 1 except that the raw material charging conditions were changed and the composition of the polyester resin was changed as shown in Table 1. I got Table 1 shows the obtained evaluation results.

Example 10, Comparative Example 7 A polyester resin and a test piece were obtained in the same manner as in Example 1 except that the polycondensation reaction time was changed. Table 1 shows the obtained evaluation results.

[0034]

[Table 1]

As is clear from Table 1, the polyester resin of the present invention has excellent solubility, and the coating film obtained from the coating composition containing the polyester resin of the present invention has good processability, metal adhesion and retort resistance. It was excellent. on the other hand,
In Comparative Example 1, since the amount of the aromatic dicarboxylic acid was small, the retort resistance was poor. In Comparative Example 2, since propylene glycol was not copolymerized, the solubility was poor, and the paint was not evaluated. In Comparative Example 3, the processability was inferior because the copolymerization amount of butanediol was small. In Comparative Example 4, since the copolymerization amount of butanediol was large, the resin became crystalline and had poor solubility. Comparative Example 5 was inferior in processability because no alicyclic glycol was copolymerized. In Comparative Example 6, since the copolymerization amount of the alicyclic glycol was large,
The solubility was poor. In Comparative Example 7, since the intrinsic viscosity was low, the workability and the retort resistance were poor.

[0036]

The polyester resin of the present invention is suitable for a paint for coating a metal steel sheet used for home electric appliances, office supplies, food containers and the like. Above all, it is non-toxic and is excellent in workability, metal adhesion, retort resistance and the like, and thus is particularly useful as an inner paint for food cans.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J029 AB01 AC02 AD01 AD07 AE11 BA01 BA02 BA03 BA04 BA05 BA07 BA08 BA10 BD04A BD06A BD07A BF08 BF09 BF10 BF25 BF26 CA02 CA04 CA05 CA06 CA09 CB04A CB05A CB064 DD061 MA13 MA15 NA11 NA14 PB04 PC02

Claims (3)

[Claims] 1. A polyester resin comprising a dicarboxylic acid component and a glycol component, wherein an aromatic dicarboxylic acid component of the dicarboxylic acid component is 40 to 100 mol.
1%, 20 to 70 mol% of propylene glycol and 2 of 1,4-butanediol in the glycol component.
0 to 70 mol%, alicyclic glycol is 10 to 50 mo
1%, an intrinsic viscosity of 0.3 or more, and a glass transition temperature of 35 ° C. or more. 2. The polyester resin according to claim 1, wherein the alicyclic dicarboxylic acid in the dicarboxylic acid component is 60 mol% or less. 3. A coating composition comprising the polyester resin according to claim 1 or 2.