JP2003020380A - Aqueous dispersion, coating film formed therefrom, and process for producing aqueous dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous dispersion which contains a polyester resin, is made without using an endocrine disruptor such as bisphenol A for a raw material and is used for coating the inside of a can to form a coating film excellent in retorting resistance. SOLUTION: This aqueous dispersion contains a copolyester resin grafted with a radical-polymerizable monomer having a hydrophilic group or a functional group that can be converted into a hydrophilic group, and a hydrophobic resin. The process for producing the aqueous dispersion is characterized in that the graft polyester resin is neutralized with a basic compound. This coating film is formed from the aqueous dispersion.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an aqueous dispersion containing a graft polyester resin which is excellent as a paint for the inner surface of a can and a method for producing the same. Furthermore, the present invention relates to a coating film formed from the above water dispersion.

[0002]

2. Description of the Related Art Paints mainly composed of epoxy resin are often used for coating the inner surface of cans. Among them, water-dispersed (water-based) epoxy-acrylic paints have been widely used as can inner surface paints in place of solvent-based paints in order to protect the natural environment and improve the working environment. The epoxy-acrylic resin has good stability after being dispersed in water, and also has excellent processability after being coated on the inner surface of the can and retort resistance.

However, since bisphenol A, which is a raw material for epoxy-acrylic paints, is an endocrine disruptor (environmental hormone), polyester resins are attracting attention as an alternative water-based paint that avoids the use of bisphenol A. In particular, since there is a problem in retort resistance, a suitable polyester resin for can inner surface coating has not been obtained yet.

For example, Japanese Patent Laid-Open No. 9-296100,
11-61035, 11-124542, 11-236529, and JP-A-2000-26.
According to Japanese Patent Publication No. 709, it is preferable to depolymerize a polyester resin with a dicarboxylic acid, a glycol, a polycarboxylic acid-anhydride or the like, or to perform a ring-opening addition reaction to give an acid value to the resin end. Furthermore, it is dispersed in water by neutralizing the carboxyl group in the molecule with a basic compound,
A water-based coating resin composition containing an amino resin and a protective colloid has been proposed. Although these paints have excellent curability and processability, amino resins have poor hygienic properties, and melamine-formaldehyde resins have poor retort resistance.
It is also possible to use a hydrophobic amino resin (such as benzoguanamine-formaldehyde resin) in order to improve the retort resistance, but the polyester resin obtained by the method described in these patent publications has a carboxyl group. Is unevenly distributed at the terminal of the molecule, so the dispersion stability is low. Therefore, it is necessary to use a protective colloid in order to stabilize the paint, but there is a problem that this protective colloid deteriorates retort resistance and hygiene. Further, since the dispersion stability is low, there is a problem that when spray coating as a paint for the inner surface of a can, clogging of the spray nozzle and sagging after coating occur.

Japanese Patent Laid-Open No. 11-315251 discloses that a coating material in which a polyester resin and a resol type phenol resin are combined improves curability, processability, retort resistance and hygiene. However, the resol type phenolic resin described in the publication is poor in water dispersibility because a part thereof is alkyl etherified, and it is necessary to use a protective colloid or a surfactant to stabilize the dispersion in water. , Which causes the retort resistance to decrease.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides an aqueous dispersion containing a polyester resin for coating the inner surface of a can which forms a coating film excellent in retort resistance without using an environmental hormone such as bisphenol A as a raw material. The purpose is to do.

[0007]

The water dispersion of the present invention is a grafted polyester resin obtained by grafting a copolymerizable polyester resin with a radically polymerizable monomer having a hydrophilic group or a functional group capable of changing to a hydrophilic group. And a hydrophobic resin.

The hydrophilic group is preferably a carboxyl group, and the hydrophobic resin is preferably a condensate of phenol and formaldehyde.

In this method for producing an aqueous dispersion, the graft polyester resin is neutralized with a basic compound.

The coating film of the present invention is formed by the above water dispersion.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to an aqueous dispersion containing a polyester resin obtained by grafting a radically polymerizable monomer onto a copolyester resin and a hydrophobic resin.

(Copolymerized Polyester Resin) The copolymerized polyester resin means a copolymer having an ester bond which is generally obtained by condensation or transesterification of dicarboxylic acid or dicarboxylic acid ester and glycol.

The dicarboxylic acid used for producing the copolyester resin includes aromatic dicarboxylic acid, aliphatic dicarboxylic acid, alicyclic dicarboxylic acid and dicarboxylic acid having a polymerizable double bond.

Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid and biphenyldicarboxylic acid. Examples of the aliphatic dicarboxylic acid include succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid and dimer acid. Examples of the alicyclic dicarboxylic acid include 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid and its anhydride. The dicarboxylic acid having a polymerizable double bond, fumaric acid, maleic acid, maleic anhydride,
There are α, β-unsaturated dicarboxylic acids such as itaconic acid and citraconic acid, as well as 2,5-norbornene dicarboxylic acid anhydride, tetrahydrophthalic anhydride and the like, and fumaric acid, maleic acid and 2 , 5-Norbornene dicarboxylic acid anhydride is preferred.

As glycols used for producing the copolyester resin, there are aliphatic glycols having 2 to 10 carbon atoms, alicyclic glycols having 6 to 12 carbon atoms, glycols having an ether bond and the like.

As the aliphatic glycol having 2 to 10 carbon atoms, ethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-petanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-
Examples include pentanediol, 1,9-nonanediol, 2-ethyl-2-butylpropanediol and the like. Carbon number 6
Examples of the alicyclic glycol of to 12 include 1,4-cyclohexanedimethanol. As the glycol containing an ether bond, diethylene glycol,
Examples include triethylene glycol and dipropylene glycol, and examples include polyethylene glycol, polypropylene glycol and polytetramethylene glycol.

Polycarboxylic acids and / or polyols having three or more functional groups can be used in the present invention. Examples of the polycarboxylic acid having three or more functional groups include (anhydrous) trimellitic acid, (anhydrous) pyromellitic acid, (anhydrous) benzophenonetetracarboxylic acid, trimesic acid, ethylene glycol bis (anhydrotrimellitate), and glycerol tris. (Anhydro trimellitate) and so on. On the other hand, examples of the polyol having 3 or more functional groups include glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol.

The weight average molecular weight of the copolyester resin used as a raw material in the present invention is 5,000 to 5,000.
0 is preferred. When the weight average molecular weight is less than 5,000, the resin physical properties such as processability of the coating film after drying are deteriorated, and the resin is easily water-solubilized, and it becomes difficult to form a core-shell structure described later. On the other hand, weight average molecular weight 50,000
If it is larger, it becomes difficult to disperse in water.

In the present invention, a copolymerized resin is used as a raw material in order to achieve the performance to be satisfied as a paint for the inner surface of a can such as adhesiveness and workability. The copolyester resin used in the present invention has a polymerizable double bond that can be grafted by radical polymerization. By grafting a monomer having a hydrophilic group to the polymerizable double bond site, the inherently water-insoluble copolyester resin is rendered hydrophilic.

The aromatic dicarboxylic acid is preferably contained in an amount of 70 to 100 mol% with respect to the total acid components in order to maintain the water resistance of the coating film and the stability of the aqueous dispersion. The aliphatic dicarboxylic acid is preferably 0 to 30 mol% based on all acid components. Further, in the case of a dicarboxylic acid having a polymerizable double bond, it is preferably 0.5 to 10 mol% and more preferably 2 to 7 mol% based on the total acid components. When the dicarboxylic acid having a polymerizable double bond is less than 0.5 mol%, it is difficult to effectively graft the radically polymerizable monomer onto the copolyester resin, and the dispersed particles during water dispersion become large. Dispersion stability decreases. On the other hand, when the content of the dicarboxylic acid having a polymerizable double bond is more than 10 mol%, the viscosity increases too much in the latter stage of grafting, which hinders the uniform progress of the reaction.

The polycarboxylic acid and / or polyol having 3 or more functional groups can be used in an amount of 0 to 10 mol% based on the total acid component or the total glycol component, but it is preferably 0 to 5 mol%. preferable. If it is more than 5 mol%, the workability tends to decrease.

The copolymerized polyester resin before grafting is preferably 95% by weight or less with respect to the grafted polyester resin. It is more preferably 90% by weight or less, and even more preferably 85% by weight or less. If it exceeds 95% by weight, the dispersibility in water may decrease. When high processability is required, the copolymerized polyester resin before grafting is preferably 75% by weight or less, more preferably 73% by weight or less, and particularly preferably 70% by weight or less. On the other hand, the lower limit of the copolyester resin before grafting is preferably 40% by weight, more preferably 50% by weight, further preferably 55% by weight,
It is particularly preferably 60% by weight.

(Radical Polymerizable Monomer) In the present invention, the copolymerizable polyester resin is grafted with a radical polymerizable monomer having a hydrophilic group or a functional group capable of changing into a hydrophilic group. The copolyester resin before grafting does not disperse or dissolve in water and is essentially water-insoluble,
The water-insoluble copolyester resin is rendered hydrophilic by grafting a radical-polymerizable monomer having a hydrophilic group or a functional group capable of changing to a hydrophilic group.

As the radical-polymerizable monomer, a radical-polymerizable monomer having a hydrophilic group or a functional group capable of changing into a hydrophilic group is used, and other radical-polymerizable monomer is included. You can The hydrophilic group includes a carboxyl group, a hydroxyl group, a sulfonic acid group, an amide group, and a quaternary ammonium salt, and the functional group that can be converted into a hydrophilic group includes an acid anhydride group and a glycidyl group. Since the functional group that can be converted to a hydrophilic group is changed to a hydrophilic group by the action of an acid or a base, the radical polymerizable monomer having a functional group that can be converted to a hydrophilic group in the present invention has a hydrophilic group. It functions similarly to the radical-polymerizable monomer that it has, and can exhibit the same effect. Among the hydrophilic groups, a carboxyl group is preferable because it is easy to control the water dispersibility by changing the acid value. Therefore, the radically polymerizable monomer is preferably one having a carboxyl group or a functional group capable of being converted into a carboxyl group.

As the radically polymerizable monomer having a carboxyl group, acrylic acid, methacrylic acid, maleic acid,
There are fumaric acid, itaconic acid, citraconic acid and the like, and acrylic acid and methacrylic acid are preferable from the viewpoints of grafting efficiency and stability of the aqueous dispersion. On the other hand, as the radically polymerizable monomer having a functional group capable of changing to a carboxyl group, there are maleic anhydride, itaconic anhydride, methacrylic anhydride and the like, and in terms of grafting efficiency and stability of the aqueous dispersion. Maleic anhydride is preferred. The radically polymerizable monomer may be used alone or in combination of two or more.

In the practice of the present invention, it is preferable from the viewpoint of grafting efficiency to use a radical polymerizable monomer having no carboxyl group and a radical polymerizable monomer having a carboxyl group together. Examples of the radically polymerizable monomer having no carboxyl group include methyl acrylate, ethyl acrylate, isopropyl acrylate, and n-acrylate.
Butyl, 2-ethylhexyl acrylate, acrylic acid 2
-Hydroxyethyl, hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, methacrylic acid Acrylic and methacrylic acid esters such as hydroxylpropyl, acrylonitrile, methacrylonitrile, acrylamide, N-methylol acrylamide, diacetone acrylamide, vinyl acetate, vinyl ethers, N-vinylpyrrolidone, styrene, α
-Methylstyrene, t-butylstyrene, vinyltoluene, etc., and methyl acrylate in terms of grafting efficiency,
Ethyl acrylate, n-butyl acrylate, methyl methacrylate, 2-hydroxyethyl methacrylate and styrene are preferred. One or more of these may be selected and used.

The radical-polymerizable monomers are preferably used as a mixture of 2 or 3 or more. When the component is one type and only the carboxyl group-containing monomer is present, grafting to the polyester chain does not occur smoothly, it is difficult to lead to a good water dispersion, and the second component ester of acrylic acid or methacrylic acid is used. Grafting with high efficiency can be achieved only by using a group of the like and copolymerizing them.

The upper limit of the ratio of the radically polymerizable monomer having a carboxyl group is preferably 95% by weight or less, more preferably 90% by weight or less, based on the total amount of the radically polymerizable monomer. On the other hand, the lower limit is 5% by weight
The above is preferable, and 10 wt% or more is more preferable. The ratio of the monomer having a carboxyl group can be determined in consideration of the acid value of the graft polyester resin.

The total acid value before being neutralized graft polyester resin of the present invention is preferably at least 500eq / 10 ⁶ g, more preferably at least 600eq / 10 ⁶ g. Fifty
If it is less than 0 eq / 10 ⁶ g, it becomes difficult to obtain a dispersion having a small particle size when dispersed in water, and the dispersion stability decreases. On the other hand, the total oxide is preferably from 4000eq / 10 ⁶ g, more preferably at most 3000eq / 10 ⁶ g. Four
If it is more than 000 eq / 10 ⁶ g, the water resistance of the coating film formed from the water dispersion becomes low.

(Grafting) The grafted polyester resin of the present invention can be obtained by grafting a radically polymerizable monomer to the polymerizable double bond in the copolyester resin. Grafting is carried out by reacting a mixture of a radical initiator and a radically polymerizable monomer in a state where the copolyester resin is dissolved in an organic solvent. After grafting, it is considered that unreacted copolymerized polyester resin and unreacted radically polymerizable monomer are also contained in addition to the grafted polyester resin, but the grafting rate is low and unreacted copolymerization When the ratio of the polyester resin and the unreacted radically polymerizable monomer is high, an aqueous dispersion having good stability cannot be obtained.

At the time of grafting, the radically polymerizable monomer and the radical initiator can be added at once to the copolymerized polyester resin dissolved in the solvent. Alternatively, the radical-polymerizable monomer and the radical initiator may be separately added dropwise over a fixed period of time, and then the mixture may be stirred for a fixed period of time to continue heating to allow the reaction to proceed. In addition, a portion of the radical polysynthetic monomer is added at a time, and then the remaining radical monomer and radical initiator are separately added dropwise over a certain period of time, while further stirring for a certain period of time. The reaction can be progressed by continuing heating.

Prior to the reaction, the copolymerized polyester resin and the solvent are charged into the reactor and the temperature is raised with stirring to dissolve the resin. The weight ratio of the copolymerized polyester resin and the solvent is preferably 70:30 to 30:70 from the viewpoint of the reactivity between the copolymerized polyester resin and the radical polymerizable monomer, the solubility in the solvent and the uniformity of the polymerization. .

The proportion of the radical-polymerizable monomer is preferably 60% by weight or less based on the graft polyester resin,
It is more preferably 45% by weight or less, particularly preferably 40% by weight or less. When the amount of the radical-polymerizable monomer is more than 60% by weight, the amount of the copolymerized polyester resin is relatively small, and the excellent performance of the copolymerized polyester resin, that is, high processability, excellent water resistance, and excellent for various base materials In addition, the adhesiveness cannot be sufficiently exerted, and undesired performances such as acrylic resin compounded as a radical-polymerizable monomer, that is, processability, gloss, and water resistance become low. . On the other hand, the ratio of the radically polymerizable monomer is 5% by weight with respect to the graft polyester resin.
The above is preferable, 7 wt% or more is more preferable, and 10 wt% or more is particularly preferable. If the amount of the radical-polymerizable monomer is less than 5% by weight, hydrophilic groups such as carboxyl groups contained in the graft chain become insufficient, and it becomes impossible to obtain a good aqueous dispersion.

In order to proceed the grafting sufficiently, the grafting reaction temperature is preferably 50 to 120 ° C., and the reaction time is preferably 1 to 5 hours.

Well-known organic peroxides and organic azo compounds can be used as the radical initiator (eg, grafting radical initiator). Benzoyl peroxide and t-butylperoxypivalate are used as the organic peroxide, and 2,2′-azobisisobutyronitrile and 2,2′-azobis (2,4-) are used as the organic azo compound.
Dimethyl valeronitrile) etc. The radical initiator is selected in consideration of the radical generation rate at the reaction temperature, that is, the half-life, and the half-life at that temperature is generally 1
Radical initiators that are minutes to 2 hours are preferred.

The amount of the radical initiator used is preferably 02% by weight or more based on the radical-polymerizable monomer from the viewpoint of initiating the radical reaction and performing sufficient grafting.
It is more preferably 0.4% by weight or more.

A chain transfer agent such as octyl mercaptan or mercaptoethanol is preferably used in an amount of 0 to 5% by weight based on the radical-polymerizable monomer from the viewpoint of controlling the degree of polymerization of the graft chain.

(Reaction Solvent) The solvent used in the grafting is preferably an aqueous solvent because it readily dissolves the radically polymerizable monomer having a hydrophilic group, and it is easy to use a water-insoluble copolyester resin originally An organic solvent is preferable in that it dissolves in. As such an aqueous organic solvent, an organic solvent having a solubility in water at 20 ° C. of 10 g / L or more is preferable, and an organic solvent having a solubility of 20 g / L or more is more preferable.
The boiling point of the solvent is preferably 50 to 250 ° C. When the boiling point is higher than 250 ° C, the evaporation rate is slow and the solvent cannot be sufficiently removed even by baking the coating film at a high temperature. On the other hand, if the boiling point is less than 50 ° C, an initiator that generates radicals at less than 50 ° C must be used, which increases the handling risk.

As the first group of aqueous organic solvents having such characteristics, the copolyester resin is well dissolved,
In addition, it is a solvent which dissolves a polymerizable monomer having a hydrophilic group such as a carboxy group relatively well, and also the graft polyester resin after the reaction. Specifically, esters such as ethyl acetate, ketones such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, cyclic ethers such as tetrahydrofuran, dioxane and 1,3-dioxolane, ethylene glycol dimethyl ether, propylene glycol methyl ether, propylene glycol propyl Ether, glycol ethers such as ethylene glycol ethyl ether and ethylene glycol butyl ether, carbitols such as methyl carbitol, ethyl carbitol and butyl carbitol, glycols or glycol ethers such as ethylene glycol diacetate and ethylene glycol ethyl ether acetate. Lower esters, ketone alcohols such as diacetone alcohol, and Le formamide, dimethyl acetamide, and the like N- substituted amides such as N- methylpyrrolidone.

As the second group of aqueous organic solvents, which hardly dissolve the copolyester resin, but relatively well dissolve the radical polymerizable monomer having a hydrophilic group such as a carboxyl group and the graft polyester resin,
There are water, lower alcohols, lower carboxylic acids, lower amines and the like, but in the present invention, alcohols and glycols having 1 to 8 carbon atoms are preferable from the viewpoint of coatability and workability during coating.

When the grafting is carried out with a single solvent, one kind can be selected from the first group of aqueous organic solvents. When a mixed solvent is used, it is possible to select plural kinds only from the first group of aqueous organic solvents, and at least one kind is selected from the first group of aqueous organic solvents, and at least one kind selected from the second group of aqueous organic solvents. Can also be added. However, from the viewpoints of the progress and behavior of grafting, the appearance and properties of the graft polyester resin and the water dispersion derived therefrom, and the like, solvents selected from the first group and the second group of aqueous organic solvents and mixed are preferable. The copolyester resin molecular chain has a large spread in the solvent of the first group and is in a stretched state, but it is small in the mixed solvent from the first group and the second group and entangled like a thread. It has been confirmed by viscous measurement that it is in a closed state. Therefore, it is effective to prevent gelation by adjusting the dissolution state of the copolyester resin to prevent intermolecular cross-linking. Therefore, in terms of efficient grafting and suppressing gelation, the first group and the second group A mixed solvent consisting of one kind of an aqueous organic solvent is preferable.

When the mixed solvent of the first group solvent and the second group solvent is used, the compounding amount of the first group solvent is preferably 95% by weight or less, and 90% by weight or less, based on the total amount of the mixed solvent. The following is more preferable, and 85% by weight or less is particularly preferable. The lower limit is preferably 10% by weight or more, and 20% by weight
The above is more preferable, and 30% by weight or more is particularly preferable.
The mixing ratio of the solvent in each reaction is specifically determined depending on the solubility of the copolyester resin used as the raw material.

(Hydrophobic Resin) The water dispersion of the present invention contains a hydrophobic resin in addition to the fine particles of the graft polyester resin. By blending the hydrophobic resin, the retort resistance of the coating film formed by the water dispersion is improved and it becomes suitable as a paint for the inner surface of a can.

The hydrophobic resin is a resin that has no affinity for water, does not absorb water when dried, and repels water. Generally, there are epoxy resin, olefin resin, phenol resin and the like. Condensates of phenols and formaldehyde are preferable because they satisfy the compatibility with the graft polyester resin and the performance as a paint for cans. As phenols, alkylated (methyl, ethyl, propyl, isopropyl, butyl, etc.) phenol, p-te
rt-amylphenol, 4,4′-sec-butylidenephenol, p-tert-butylphenol, o
-, M-, p-cresol, p-cyclohexylphenol, 4,4'-isopropylidenephenol, p-nonylphenol, p-octylphenol, 3-pentadecylphenol, phenol, phenylcresol,
There are p-phenylphenol, xylenol and the like, and o-cresol, m-cresol and p-cresol are preferable from the viewpoint of compatibility and reactivity with the graft polyester resin.

The blending amount of the hydrophobic resin is preferably 0.1 to 20 parts by weight, more preferably 0.5 to 15 parts by weight, and more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the graft polyester resin.
Part by weight is especially preferred. If the blending amount is less than 0.1 part by weight, the retort resistance of the coating film formed by the aqueous dispersion will not be sufficiently improved. On the other hand, if the blending amount is more than 20 parts by weight, workability becomes poor.

The hydrophobic resin can be blended in a state of being dissolved in an organic solvent or dispersed in water. The hydrophobic resin may be blended in (1) a method of blending with an aqueous dispersion of a graft polyester resin to dissolve or disperse it, and (2) a method of blending after grafting but before water dispersing, It can be selected according to the type and properties of the hydrophobic resin. Further, a catalyst such as dodecylbenzene sulfonic acid may be used together with the hydrophobic resin as an accelerator.

(Water Dispersion) The present invention relates to an aqueous dispersion containing a graft polyester resin.

In this water dispersion, fine particles of the graft polyester resin are dispersed in water. The fine particles of the graft polyester resin preferably have an average particle diameter of 500 nm or less in order to maintain stability as an aqueous dispersion. The graft polyester resin according to the present invention can be easily dispersed in fine particles having an average particle diameter of 500 nm or less by neutralizing with a basic compound.

As the basic compound, ammonia and organic amines are preferable in that they volatilize at the time of forming a coating film by baking and curing. As organic amines, triethylamine, N, N-diethylethanolamine, N, N-dimethylethanolamine, aminoethanolamine, N-
Methyl-N, N-diethanolamine, isopropylamine, iminobispropylamine, ethylamine, diethylamine, 3-ethoxypropylamine, 3-diethylaminopropylamine, sec-butylamine, propylamine, methylaminopropylamine, dimethylaminopropylamine, methyl Examples include iminobispropylamine, 3-methoxypropylamine, monoethanolamine, diethanolamine and triethanolamine. Among these, triethylamine, N, N-diethylethanolamine, N, N-dimethylethanolamine and triethanolamine are preferable from the viewpoint of stability of the aqueous dispersion and volatility at the time of baking and curing.

From the viewpoint of producing a stable aqueous dispersion, the basic compound is added in an amount of at least partial neutralization or complete neutralization depending on the amount of acid groups such as carboxyl groups contained in the graft polyester resin. PH is 5.0 ~
It is preferable to adjust so as to be 9.0.

As a method of water dispersion, a method of adding water containing a basic compound into the reaction product immediately after the completion of grafting and stirring with heating (one-pot method) is stable. It is preferable in terms of obtaining an aqueous dispersion. As another method of water dispersion, after the grafting, the solvent contained in the graft polyester resin is removed in advance under reduced pressure by an extruder or the like to form a melt or a solid (a state of pellets, powder, etc.), and then a base. There is also a method in which the graft polyester resin is poured into water containing a polymerizable compound and stirred while heating. When the boiling point of the solvent used for grafting is 100 ° C. or lower, part or all of the solvent can be easily removed by distillation.

The solid content concentration of the graft polyester resin in the water dispersion is 20 to 20 in order to maintain the stability of the water dispersion.
60% by weight is preferred.

(Characteristics of Aqueous Dispersion) In the present invention, the raw material copolymer polyester resin is grafted with a radical-polymerizable monomer. The degree of polymerization of the radical-polymerizable monomer after grafting is weight. Average molecular weight 500-500
00 is preferable. It is generally difficult to control the weight average molecular weight to less than 500, and if it is less than 500, the grafting efficiency is low and the introduction of hydrophilic groups into the copolyester resin becomes insufficient. Also, the polymer of radical-polymerizable monomer (graft chain) forms a hydrated layer of dispersed particles, but the weight average molecular weight is sufficient to form a hydrated layer of sufficient thickness and obtain a stable dispersion. It is preferably 500 or more. On the other hand, the upper limit of the weight average molecular weight is preferably 50,000 from the viewpoint of polymerizability in solution polymerization. Weight average molecular weight 500-5
The molecular weight in the range of 0000 can be controlled by adjusting the amount of the radical initiator, the dropping time of the radical-polymerizable monomer, the grafting time, the reaction solvent, and the composition of the radical-polymerizable monomer. It can be carried out by appropriately combining and using a transfer agent and a polymerization inhibitor.

The aqueous dispersion of the present invention has a translucent to milky white appearance. The particle size of the aqueous dispersion can be adjusted by the polymerization method, and the average particle size measured by the laser light scattering method is 1
0-500 nm is preferable. If it is larger than 500 nm, the surface gloss of the coating film tends to be lowered.

When the aqueous dispersion of the present invention is measured by 13 C-NMR, the full width at half maximum of the signal of the carbonyl group in the ester portion of the copolyester resin is as large as 300 Hz or more. Further, the full width at half maximum of the signal after neutralization of the carboxyl group of the polymer (graft chain) of the radical-polymerizable monomer is 150 Hz or less, which is small and observed. Generally, in NMR, the signal of the resin dissolved in the measurement solvent has a small full width at half maximum, and the signal of the resin insoluble in the measurement solvent has a large full width at half maximum. From this fact, in the water dispersion of the present invention, the copolyester resin, which is not originally dispersed or dissolved in water, is present in the core portion in an agglomerated state, and the periphery thereof is a polymer of a radical-polymerizable monomer having a hydrophilic group (graft). It is understood that the chain) expresses a structure in which it is wrapped as a shell part, that is, a core-shell structure. The core-shell structure refers to a two-layer structure in which a core part made of a resin insoluble in the dispersion medium and in an aggregated state is wrapped with a shell part made of a resin soluble in the dispersion medium. The core-shell structure is a structure characteristically appearing in a dispersion in which resins having different solubilities in the dispersion medium are chemically bonded, and is a structure that cannot be exhibited simply by mixing resins having different solubilities in the dispersion medium. Also, a mere mixture of resins having different solubilities in the dispersion medium is 5
It cannot exist as an aqueous dispersion with a particle size below 00 nm.

(Use of Water Dispersion) The water dispersion of the present invention can be used as a vehicle for paints, inks, coating materials, adhesives, etc., or as a processing agent for fibers, films and paper products. A coating film having retort resistance is formed. The aqueous dispersion of the present invention can be used as it is, but it is also possible to add a cross-linking agent (curing resin) to carry out bake curing, whereby high water resistance can be exhibited.
Examples of the crosslinking agent include amino resins, isocyanate compounds and various blocked isocyanate compounds thereof, and polyfunctional aziridine compounds.

Examples of amino resins include formaldehyde adducts such as urea, melamine and benzoguanamine, and alkyl ether compounds of these alcohols having 1 to 6 carbon atoms. Specifically, there are methoxylated methylolurea, methoxylated methylol-N, N-ethyleneurea, methoxylated methylol dicyandiamide, methoxylated methylol melamine, methoxylated methylol benzoguanamine, butoxylated methylol melamine, butoxylated methylol benzoguanamine, and the like. Methoxylated methylol melamine, butoxylated methylol melamine and methylolated benzoguanamine are preferable from the viewpoint of reactivity with the resin. These can be used alone or in combination.

As the isocyanate compound, there are aromatic and aliphatic diisocyanates and polyisocyanates having 3 or more valences, and both low molecular weight compounds and high molecular weight compounds can be used. Specific examples thereof include tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, and trimers of these isocyanate compounds. Further, with an excess amount of these isocyanate compounds, for example, ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, low molecular weight active hydrogen compounds such as triethanolamine or various polyester polyols, Examples thereof include compounds containing a terminal isocyanate group obtained by reacting with polyether polyols, high molecular weight active hydrogen compounds such as polyamides, and the like.

Blocked isocyanates can also be used. The blocked isocyanate can be obtained by adding the isocyanate compound and an isocyanate blocking agent by a usual method. As the isocyanate blocking agent, phenols such as phenol, thiophenol, methylthiophenol, cresol, xylenol, resorcinol, nitrophenol and chlorophenol, acetoxime, oximes such as methylethylketoxime and cyclohexanone oxime, methanol, ethanol, propanol and butanol. Alcohols such as ethylene chlorohydrin,
Halogenated alcohols such as 1,3-dichloro-2-propanol, tertiary alcohols such as t-butanol and t-pentanol, ε-caprolactam, δ-valerolactam, γ-butyrolactam, β-propyllactam and the like. Lactams, other aromatic amines, imides,
Examples include active methylene compounds such as acetylacetone, acetoacetate and ethyl malonate, mercaptans, imines, ureas, diaryl compounds and sodium bisulfite.

The method of blending the crosslinking agent is (1) a method of directly dissolving or dispersing in an aqueous dispersion, (2) adding a crosslinking agent after grafting and before water dispersion, and coexisting with a polyester resin in the core portion. There is a method of making it possible, and it can be selected depending on the type and properties of the crosslinking agent. A curing agent or an accelerator may be added to these crosslinking agents.

The curing reaction generally involves the aqueous dispersion 10 of the present invention.
Cross-linking agent (curing resin) 5 to 0 parts by weight (solid content)
It can be performed by blending 40 parts by weight (solid content) and heating at 60 to 250 ° C. for about 0.5 to 60 minutes depending on the type of the curing agent. The aqueous dispersion of the present invention includes a pigment,
Dyes, various additives and the like can be added. The processability of the water dispersion of the present invention can be improved by using it in combination with other aqueous resin and water dispersion.

Since the paints, inks, coating agents, adhesives and various processing agents based on the water dispersion of the present invention have excellent redispersibility, they are subjected to the dip coating method, the brush coating method,
It can be applied to all of the roll coating method, spraying method and various printing methods.

[0063]

[Example] (Production of copolymerized polyester resin) Stirrer,
Dimethyl terephthalate 45 was added to a stainless steel autoclave equipped with a thermometer and a partial reflux condenser.
5 parts by weight, dimethyl isophthalate 455 parts by weight, ethylene glycol 472 parts by weight, diethylene glycol 3
5 parts by weight and tetra-n-butyl titanate 0.37
Part by weight was charged and the transesterification reaction was carried out at 160 to 220 ° C. for 4 hours. Then, 29 parts by weight of fumaric acid was added, and the temperature was raised from 200 ° C to 220 ° C over 1 hour.
An esterification reaction was performed. Then raise the temperature to 255 ° C,
After the pressure of the reaction system was gradually reduced, the pressure was reduced to 26.6 Pa for 1 hour 3
The reaction was carried out for 0 minutes to obtain a copolyester resin (A-1). The copolyester resin (A-1) was light yellow and transparent and had a weight average molecular weight of 12000. As a result of measurement by NMR or the like, it was a copolyester resin having a composition shown in Table 1.

[0064]

[Table 1]

Various copolyester resins (A-2) to (A-5) were produced by the same method. Table 1 shows the results of the composition analysis by NMR of each copolyester resin.

Example 1 90 parts by weight of copolymerized polyester resin (A-1) and 137 parts by weight of methyl ethyl ketone were placed in a reactor equipped with a stirrer, a thermometer, a reflux device and a constant amount dropping device, and stirred at 65 ° C. The polymerized polyester resin was dissolved. After the resin was completely dissolved, 46 parts by weight of isopropyl alcohol was added and mixed. Next, a solution of a mixture of 11 parts by weight of acrylic acid and 19 parts by weight of ethyl acrylate, and 0.74 parts by weight of benzoyl peroxide in 45 parts by weight of methyl ethyl ketone and 15 parts by weight of isopropyl alcohol was copolymerized polyester at 0.2 ml / min. The solution was added dropwise to the resin solution, and stirring was continued for another 2 hours and 30 minutes. After sampling for analysis (5 g) from the reaction solution, 14 parts by weight of N, N-dimethylethanolamine and 244 parts by weight of water were added to the reaction solution and stirred for 1 hour. Then, the temperature of the dispersion was raised to 100 ° C., and methyl ethyl ketone and isopropyl alcohol were distilled off. An aqueous dispersion (B-1) was prepared by adding 5 parts by weight of a phenol resin (PCE1050 manufactured by Showa High Polymer Co., Ltd.) and 0.3 part by weight of dodecylbenzenesulfonic acid to 100 parts by weight of the generated white graft polyester resin dispersion. Got The water dispersion (B-1) was applied on an aluminum plate so that the film thickness after drying was 10 μm, and baked in an atmosphere of 200 ° C. for 0.5 minutes to form a coating film.

Table 2 shows the solid content concentration, particle size and B-type viscosity of the water dispersion (B-1), and the evaluation results of the retort resistance, processability and solvent resistance of the formed coating film.

Each characteristic was evaluated by the following methods. (1) Particle size of water dispersion The solid dispersion concentration of the water dispersion is 0.1 using only ion-exchanged water.
Adjusted to wt%, laser light scattering particle size distribution meter Coulte
2 by r model N4 (manufactured by Coulter)
It was measured at 0 ° C.

(2) Viscosity of water dispersion The viscosity was measured at 25 ° C. using a rotational viscosity viscometer (EM viscometer manufactured by Tokyo Keiki Co., Ltd.).

(3) Retort resistant coated aluminum plate is placed in a stainless steel cup in an upright state,
After adding ion-exchanged water to about half the height of the aluminum plate,
Treatment is carried out at 125 ° C. for 30 minutes in a steam atmosphere. For the liquid phase part, visually observe the roughened state of the coating film for the gas phase part, and for the gas phase part, if there is no whitening for the liquid phase part, evaluate as ○, and if there is, for the gas phase part Was evaluated as ◯ if the coating film was not rough, and was evaluated as x if there was.

(4) Workability A metal plate having the same thickness as the coated aluminum plate is sandwiched and bent in a 180 ° direction with a vise. 1% NaCl in this bent part
A sponge impregnated with the aqueous solution was brought into contact with the sponge, and a current value when a voltage of 5.5 V was applied was measured. The smaller the current value, the better the workability.

(5) Solvent resistant coating The coating film of an aluminum plate was rubbed with gauze impregnated with methyl ethyl ketone, and the number of times until the undercoat appeared was recorded.

[0073]

[Table 2]

Examples 2, 5, 6, 10, 12 and 13 In the same manner as in Example 1, various aqueous dispersions (B-2), (B-5), having the compositions shown in Tables 2 and 3 were prepared. (B-6),
(B-10), (B-12) and (B-13) were produced, a coating film was formed, and various characteristics were evaluated. The results are shown in Tables 2 and 3.

[0075]

[Table 3]

Example 3 90 parts by weight of copolymerized polyester resin (A-1) and 137 parts by weight of methyl ethyl ketone were placed in a reactor equipped with a stirrer, a thermometer, a reflux device and a metering dropping device, and the mixture was stirred at 65 ° C. The polymerized polyester resin was dissolved. After the resin was completely dissolved, 46 parts by weight of isopropyl alcohol was added and mixed. Next, a mixture of 11 parts by weight of acrylic acid and 19 parts by weight of ethyl acrylate and 0.45 parts by weight of benzoyl peroxide dissolved in 45 parts by weight of methyl ethyl ketone and 15 parts by weight of isopropyl alcohol were added to the copolymerized polyester at 0.2 ml / min. The solution was added dropwise to the resin solution, and stirring was continued for another 2 hours and 30 minutes. After sampling for analysis (5 g) from the reaction solution, 14 parts by weight of N, N-dimethylethanolamine, 5 parts by weight of a phenol resin (PCE1015 manufactured by Showa Polymer Co., Ltd.) and 244 parts by weight of water were added to the reaction solution. , Stirred for 0.5 hour.
Then, the temperature of the dispersion is raised to 100 ° C., methyl ethyl ketone and isopropyl alcohol are distilled off,
A milky white aqueous dispersion (B-3) was obtained. Water dispersion (B-
3) was applied on an aluminum plate so that the film thickness after drying was 10 μm, and baked in an atmosphere of 200 ° C. for 0.5 minutes to form a coating film.

Table 2 shows the solid content concentration, particle size and B-type viscosity of the aqueous dispersion (B-3), and the evaluation results of the retort resistance, processability and solvent resistance of the formed coating film.

Examples 4, 7, 8, 9 and 11 In the same manner as in Example 3, various water dispersions (B-4), (B-7) and (B-8) having the compositions shown in Table 2 were prepared. , (B-9) and (B-11) were produced, a coating film was formed, and various characteristics were evaluated. The results are shown in Tables 2 and 3.

Comparative Example 1 90 parts by weight of copolyester resin (A-1) and 137 parts by weight of methyl ethyl ketone were placed in a reactor equipped with a stirrer, a thermometer, a reflux device and a metering dropping device, and the mixture was stirred at 65 ° C. The resin dissolved. After the resin was completely dissolved, 46 parts by weight of isopropyl alcohol was added and mixed. Next, 11 parts by weight of acrylic acid, 19 parts by weight of ethyl acrylate, 0.45 parts by weight of benzoyl peroxide, 45 parts by weight of methyl ethyl ketone and 15 parts of isopropyl alcohol.
The solution dissolved in 1 part by weight was added dropwise to the copolyester resin solution at 0.2 ml / min, and stirring was continued for 2 hours and 30 minutes. After sampling for analysis (5 g) from the reaction solution, 14 parts by weight of N, N-dimethylethanolamine and 244 parts by weight of water were added to the reaction solution and stirred for 1 hour. Then, the temperature of the dispersion was raised to 100 ° C., and methyl ethyl ketone and isopropyl alcohol were distilled off. The produced white water dispersion (B-14) was applied onto an aluminum plate so that the film thickness after drying would be 10 μm,
The coated film was formed by baking in an atmosphere of 200 ° C. for 0.5 minutes.

Table 4 shows the solid content concentration, particle size and B type viscosity of the water dispersion (B-14), and the evaluation results of the retort resistance, processability and solvent resistance of the formed coating film.

[0081]

[Table 4]

Comparative Example 2 and Comparative Example 3 In the same manner as in Comparative Example 1, the water dispersion (B
-15) and (B-16) were produced, a coating film was formed, and various properties were evaluated. The results are shown in Table 4.

From the results shown in Tables 2 to 4, the graft polyester resin and the hydrophobic resin obtained by grafting the copolymerized polyester resin with a radical polymerizable monomer having a hydrophilic group or a functional group capable of changing into a hydrophilic group are shown. It was found that the water dispersion containing water forms a coating film having retort resistance and is excellent as a polyester resin for coating the inner surface of a can.

The embodiments and examples disclosed this time are to be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description but by the scope of the claims, and is intended to include meanings equivalent to the scope of the claims and all modifications within the scope.

[0085]

According to the present invention, there is provided an aqueous dispersion containing a polyester resin for coating the inner surface of a can, which does not use an environmental hormone such as bisphenol A as a raw material and forms a coating film excellent in retort resistance. You can

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI Theme Coat (reference) C09D 161/06 C09D 161/06 201/00 201/00 (72) Inventor Osamu Morimoto Nii Katata, Otsu, Shiga 1-1-1, Toyobo Co., Ltd., Research Institute (72) Inventor Hideki Tanaka 2-1-1, Katata, Otsu City, Shiga Prefecture Toyobo Co., Ltd., Research Institute F-term (reference) 4F070 AA47 AA71 AA72 AB03 AB05 AB06 AB06 AB08 CA01 CB02 4J002 AA01X AA03X BB00X BN17W CC03X CD00X GH01 4J038 CP121 GA06 NA06

Claims (5)

[Claims] 1. An aqueous dispersion containing a grafted polyester resin obtained by grafting a copolymerizable polyester resin with a radically polymerizable monomer having a hydrophilic group or a functional group capable of changing into a hydrophilic group, and a hydrophobic resin. 2. The aqueous dispersion according to claim 1, wherein the hydrophilic group is a carboxyl group. 3. The aqueous dispersion according to claim 1, wherein the hydrophobic resin is a condensate of phenol and formaldehyde. 4. An aqueous dispersion containing a graft polyester resin in which a copolymerizable polyester resin is grafted with a radical polymerizable monomer having a hydrophilic group or a functional group capable of changing into a hydrophilic group, and a hydrophobic resin. Coating film. 5. A method for producing an aqueous dispersion containing a graft polyester resin in which a copolymerizable polyester resin is grafted with a radical polymerizable monomer having a hydrophilic group or a functional group capable of changing to a hydrophilic group, and a hydrophobic resin. In the method for producing an aqueous dispersion, the graft polyester resin is neutralized with a basic compound.