JPH0717770B2 - Coating agent - Google Patents

Description

TECHNICAL FIELD The present invention relates to an aqueous coating agent composed of a polymer containing an acrylic resin as a main component, and more specifically, when applying a vinylidene chloride resin to a plastic surface. The present invention relates to a coating agent for anchor coat of.

(Prior Art) Conventionally, cellophane coated with vinylidene chloride resin has been widely used as a film for heat sealing. Recently, however, due to the rise in cellophane price and the decrease in PP film price, vinylidene chloride coated PP film has been used. It is changing.

In the case of PP film, direct coating of vinylidene chloride resin is very difficult in terms of adhesion, and an anchor coating agent is required.

Aqueous anchor coating agents include U.S. Patent No. 3,753,769
In the publication, an α, β-unsaturated carboxylic acid such as acrylic acid is copolymerized with an acrylic acid ester copolymer, and the free acid is neutralized with a base such as ammonium hydroxide to give a water-soluble copolymer. Attempts to improve adhesion to substrate films have been disclosed.

However, the obtained coating film generally has drawbacks such as low mechanical strength or easy stickiness.

Therefore, the above method lacks the basic and essential requirements as a blocking resistant and abrasion resistant coated film.

Further, since this coating composition is a water-soluble copolymer, it has a drawback that the concentration of the copolymer cannot be increased.

Furthermore, when the above water-soluble copolymer is used as an anchor coating agent on a PP film and a vinylidene chloride resin is applied to the upper layer thereof, the vinylidene chloride layer is significantly discolored due to the large amount of ammonia contained in the anchor coating agent. There are some drawbacks.

Further, as an example, in a water-soluble anchor coating agent as disclosed in JP-B-51-11649, neutralization is performed with an alkaline aqueous solution such as low boiling point amines. The film obtained by applying the vinylidene chloride resin as an agent on the upper layer also discolors.

Further, low-boiling amines have an extremely bad odor, are toxic to the human body, and deteriorate the working environment.

Further, the water-soluble anchor coating agent does not use only water as a solvent but uses a hydrophilic organic solvent of 50% or more, and is substantially the same as the organic solvent-based anchor coating agent. , Fire hazard, hazard to humans,
There are problems such as air pollution and residual solvent on the coated plastic film.

On the other hand, the plastic coating composition disclosed in JP-B-58-55170 is an aqueous dispersion, and when used as an anchor coating agent for vinylidene chloride resin coating,
This is a solution to the problem relating to the organic solvent that occurs in the anchor coating agent containing the organic solvent, but the anchor effect between the plastic film of the base material and the vinylidene chloride resin is insufficient.

Further, a vinylidene chloride coated film using the anchor coating agent disclosed in Japanese Examined Patent Publication No. 49-11267 tends to be colored over time when exposed to sunlight.

(Object of the Invention) An object of the present invention is to have excellent adhesion to a plastic film as a base material, and also to a vinylidene chloride resin layer on the surface, and vinylidene chloride. An object of the present invention is to provide an aqueous coating agent that does not discolor the resin layer.

(Structure of Invention) That is, the present invention relates to “(I) (a) one or more kinds of α, β-unsaturated carboxylic acids having at least one carboxyl group,
1 to 10% by weight and one or more of (b) an alkyl acrylate ester (wherein the alkyl group has 1 to 12 carbon atoms),
And / or one or more kinds of methacrylic acid alkyl ester (wherein the alkyl group has 1 to 12 carbon atoms) 90 to 99.1% by weight and, if necessary, (c) a copolymerizable vinyl monomer. The copolymer obtained by adding one kind or two or more kinds of
(II) (d) at least one α, β-unsaturated carboxylic acid, and (e) (meth) acrylic acid alkyl ester (wherein the alkyl group has 1 to 4 carbon atoms) At least one of
And (f) a copolymer of (d) and (e) and a vinyl-based monomer capable of radical copolymerization, wherein the acid value of the polymer is from 10 to 200, and The composition in which at least 30% of the carboxyl groups contained in the polymer form a salt and the copolymer is dissolved in an aqueous medium or dispersed with a particle size of 0.1 micron or less at a solid content ratio ( I) / (II) = 15-
A coating agent that is mixed so as to be 95 / 85-5. ].

Α having at least one carboxyl group of (a) used in the aqueous dispersion of (I) having the constitution of the present invention,
β-unsaturated carboxylic acid (hereinafter abbreviated as monomer (a))
And, for example, acrylic acid, methacrylic acid, maleic acid,
Itaconic acid, citraconic acid, crotonic acid, fumaric acid, maleic anhydride and the like. When an α, β-unsaturated carboxylic acid having two or more carboxyl groups is used as the monomer (a), its half ester may be used. These carboxylic acids are considered to be mainly involved in the adhesion to the plastic substrate, and the amount used is
It is about 0.1 to 10% by weight (% by weight in the copolymer).

When it is 10% by weight or more, the produced copolymer has a high sensitivity to water and a base, and is generally soluble in a basic aqueous solution.

The coating layer using it tends to have reduced blocking resistance and abrasion resistance.

On the other hand, if it is less than 0.1% by weight, sufficient adhesion to a plastic substrate is generally not exhibited.

These carboxylic acids may be used as a mixture of two or more kinds.

The alkyl acrylate (b) used in the aqueous dispersion (I) (hereinafter abbreviated as monomer (b)) is, for example, methyl acrylate, ethyl acrylate, isopropyl acrylate, or acrylic acid n-. Butyl, isobutyl acrylate, amyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, methacrylic acid Amyl, n-hexyl methacrylate, 2-ethylhexyl methacrylate,
It means an alkyl ester having 1 to 12 carbon atoms of acrylic acid and methacrylic acid such as lauryl methacrylate.

These acrylic acid alkyl esters or methacrylic acid alkyl esters are the main constituents of the film formation, and there are the following combinations of copolymers.

(1) One or more kinds of alkyl acrylate, (2) One or two kinds of methacrylic acid alkyl ester, (3) One or more kinds of acrylate alkyl ester and methacrylic acid alkyl ester 1 or 2 or more.

It is desirable that the use ratio of these alkyl acrylate and / or methacrylic acid alkyl ester is adjusted so that a copolymerizable vinyl monomer is added as necessary so that a desired second-order transition point can be obtained.

Next, examples of the copolymerizable vinyl monomer (c) in the aqueous dispersion (I) (hereinafter abbreviated as monomer (c)) include, but are not limited to, the following.

i) vinyl-substituted aromatic hydrocarbons such as styrene and α-methylstyrene; ii) α, such as acrylonitrile and methacrylonitrile
β-unsaturated aliphatic nitrile, iii) vinyl ester of organic acid such as vinyl acetate and vinyl propionate, iv) vinyl halide such as vinyl chloride and vinylidene chloride, v) acrylamide, methacrylamide, N-methoxyacrylamide and the like Α, β-unsaturated carboxylic acid amide, vi) 2-hydroxyethyl (meth) acrylate, 2
-Α, β such as hydroxypropyl (meth) acrylate
-Hydroxyalkyl esters of unsaturated carboxylic acids, vii) α, β unsaturated carboxylic acid esters having an epoxy group such as glycidyl (meth) acrylate.

viii) Others dicyclopentynyl (meth) acrylate, ester of (meth) acrylic acid with ε-caprolactone, ester of (meth) acrylic acid hydroxyalkyl ester with ε-caprolactone, and the like.

Among these copolymerizable vinyl monomers, more preferable results are obtained by using, as the component (c), one or more of the monomers i) vi) vii).

The amount of these copolymerizable vinyl monomers is preferably 0 to 80% by weight in the above copolymer.

When a hydroxyalkyl ester of α, β-unsaturated carboxylic acid is used, one or more of them may be used in an amount of 0.1-3
It is preferable to use 0% by weight, and use of 5 to 20% by weight gives more preferable results.

These copolymerizable vinyl monomers may be used alone or in combination of two or more, if necessary, and it is considered that they are mainly involved in the hardness of the coating layer formed by the aqueous dispersion, but vi) vii). The monomers listed in 1 above may also contribute to the improvement of adhesion. However, the adhesion of the monomers of vi) and vii) alone is not improved, and it can be achieved by the combined use with the α, β-unsaturated carboxylic acid having at least one carboxyl group.

The polymerization reaction of these copolymers is carried out in an aqueous medium, and the method is known per se (for example, JP-B-49-
36942).

The target copolymer has an average molecular weight of about 5,000 to about 150,0.
At 00, the second-order transition point is about 20-100 ° C.

When the average molecular weight of the copolymer is 150,000 or more, the adhesion to the plastics base material is reduced.

It was also found that the copolymer having an average molecular weight of 5,000 or less loses its properties as an anchor coating agent.

The preferred range of average molecular weight is about 10,000-80,000.

The average molecular weight here is a weight average molecular weight.

The second-order transition point (= glass transition temperature, hereinafter referred to as Tg) is about
The temperature is 20 to 100 ° C, preferably 30 to 70 ° C.

Copolymers with a temperature of 20 ° C or lower will exhibit blocking and cause blocking.

On the other hand, when the temperature is 100 ° C. or higher, the obtained coating is hard and flexibility is low.

These polymers are substantially an aqueous dispersion containing particles.

The "substantially particles" are particles that can be confirmed under an electron microscope, and the particle size of the copolymer is about 0.01 to 0.5.
Micron is preferred, most preferably 0.01-0.3 micron.

And it is sufficient that at least 90% of the number of particles has such a particle size.

Here, the aqueous medium may substantially include water, and an aqueous organic solvent such as alcohol may be mixed therein.

However, the higher the water content, the better.

The concentration of the copolymer of the present invention in the aqueous dispersion is not particularly limited, but is preferably 10 to 60% by weight, more preferably 15 to 45% by weight.

These aqueous dispersions may contain a lubricant, an antiblocking agent, an antistatic agent, a plasticizer, an antioxidant, a stabilizer and the like, if necessary.

The α, β-ethylenically unsaturated carboxylic acid (d) used in the composition (II) constituting the present invention is, for example, (meth) acrylic acid or maleic acid. There are acids, itaconic acid, citraconic acid, crotonic acid, fumaric acid, maleic anhydride, etc., and the same as the monomer (a) can be used.

Next, the (meth) acrylic acid alkyl ester of (e) (wherein the alkyl group has 1 to 4 carbon atoms) (hereinafter abbreviated as monomer (e)) means methyl (meth) acrylate,
Examples thereof include ethyl (meth) acrylate, propyl (meth) acrylate, and butyl (meth) acrylate.

Examples of the radical copolymerizable monomer (f) with the monomer (d), the monomer (e) include, for example, the monomer (b),
Examples of the monomer (c) include monomers excluding the monomer (e).

The amount of the monomer (d) used is such that the acid value of the composition (II) constituting the present invention is 10 to 200, preferably 25 to 100.

When the acid value is less than 10, even if 30% or more of the carboxyl groups are salted, it is extremely difficult to obtain a dispersed state of particles of 0.1 micron or less, and the adhesion required as an anchor coating agent is not achieved. It is difficult to fully express it.

Further, the coating film is easily damaged by the aliphatic organic solvent.

On the other hand, when the acid value exceeds 200, the water resistance of the coating film becomes poor, and when the composition (II) constituting the present invention is obtained via emulsion polymerization, the stability of the emulsion becomes poor. .

The polymer of the composition (II) constituting the present invention has a Tg of about 20-.
It is about 120 ° C, preferably 40 ° C to 100 ° C.

When Tg is 20 ° C or lower, the coating film becomes tacky and causes blocking.

On the other hand, at 120 ° C or higher, the coating film is hard and flexibility decreases,
The adhesion as an undercoat agent is impaired. The composition of (II) may be obtained by polymerizing the above-mentioned monomer (d), monomer (e), and monomer (f) by radical polymerization,
Preferably, it can be obtained by generally known emulsion polymerization using an anionic emulsifier and / or a nonionic emulsifier and a water-soluble radical polymerization initiator.

The composition (II) constituting the present invention can be obtained by neutralizing 30% or more, preferably 30 to 100%, of the carboxyl group of the polymer thus obtained with a base.

In addition, it is preferable to add a hydrophilic organic solvent such as ethyl cellosolve or alcohol at the time of neutralization because the composition of (II) is more finely dispersed, and as the base to be used, ammonia, sodium hydroxide, hydroxide is used. Examples thereof include potassium and the like, or organic amine compounds, but if the carboxyl group in the polymer remains a salt even after the formation of the coating film, the water resistance of the coating film is poor, so a volatile base is preferable, and Ammonia is particularly preferable in terms of odor. The method for obtaining the composition (II) is also described in JP-B-49-36942.

A coating composition is obtained by mixing the aqueous dispersion of (I) and the composition of (II) constituting the present invention so that the solid content ratio is 15 to 95/85 to 5. Upon mixing, a lubricant, an antiblocking agent, an antistatic agent, a plasticizer, an antioxidant, a stabilizer and the like may be added as required.

Next, the plastic film, which is the base material used for the composition of the present invention, will be described.

The plastic film that is the subject of the present invention is, for example, a polyolefin film such as a polyethylene film, a polypropylene film, a polybutene film, or a polyester film.

These may be biaxially stretched, uniaxially stretched or unstretched.

However, the coating composition of the present invention is particularly effective for those which are biaxially stretched.

The surface of the substrate film preferably has a contact angle with water of 85 ° or less.

The polyester film can be used as it is, but it is desirable to use the polyolefin film after activating the surface by corona discharge treatment, oxidant treatment or the like.

The plastic film as the base material of the present invention is not particularly limited to the above, and the thickness of the film may be a thickness called a sheet shape.

When coating the surface of the polyolefin film with the coating composition of the present invention, a gravure coater method,
It can be coated to a desired thickness by a usual coating method such as a reverse roll coater method, a rod coater method, a dip coater method, an air knife coater method.

At this time, the coating amount of the undercoat film is at least 0.1 g / m ² or more,
Particularly, 0.2 to 2.0 g / m ² is preferable.

When the coating amount of the undercoat film is less than 0.1 g / m ² , the adhesive force with the base film when the film is treated with hot water is small, and the coating film is easily peeled off.

Further, when the coating amount exceeds 1.5 g / m ² , the adhesive force to the base film hardly changes, and when it exceeds ² g / m ² , the drying time of the coating film tends to be long.

The above-mentioned coating method can be applied when topcoating.

It is preferable to use a vinylidene chloride copolymer emulsion as the top coat agent not only from the viewpoint of explosion proof, poison proof and cost, but also from the viewpoint of operation.

The thickness of the overcoat film is preferably 2 to 6 μ.

In addition, these top coat film and under coat film may contain additives such as a lubricant, an anti-blocking agent and an anti-fog agent.

(Effects of the Invention) The effects of the coating agent of the present invention can be summarized as described above.

Since it is a water-based coating agent, there is no problem of fire, explosion, harm to human body, and air pollution.

Since the aqueous dispersion and the composition which is dissolved in water or dispersed in particles of 0.1 micron or less are mixed, the adhesion to the plastic film, which cannot be expected by each alone, occurs, and therefore, the base material and the top coat. The adhesion between the layer, especially the vinylidene chloride copolymer layer, that is, the anchoring property is extremely excellent.

Also, a coating film of only a composition that is dissolved in water or dispersed with particles of 0.1 micron or less is likely to cause a problem in water resistance, but since an aqueous dispersion having good water resistance is mixed, an aqueous top coat. A coated plastic film that exhibits sufficient water resistance even when applying a layer, and that the anchor coat layer of the coating agent of the present invention is difficult to dissolve or dissolve in water so that it can fully exert its anchor coat function and is beautiful and highly practical. Is obtained.

Since the coating agent of the present invention contains less ammonia or amine than an anchor coating material of a water-soluble polymer, particularly one containing amine or ammonia, or a polymer dispersed with particles of 0.1 micron or less, the present invention The vinylidene chloride layer is less discolored even when the plastic film in which the coating material is used as the anchor coat layer and the vinylidene chloride copolymer is applied to the top coat layer is exposed to sunlight.

In the coating agent of the present invention, a functional group having a large polarity, particularly a carboxyl group, has a large compatibility with an organic solvent, particularly an aliphatic organic solvent, because it contains a large amount as compared with a normal emulsion, and therefore, In the film coated with the coating agent of the present invention, the organic film is not absorbed into the plastic film as a base material during printing, and the film is not wrinkled or moistened.

The coating agent of the present invention has excellent film-forming properties and is less likely to be blocked, as compared with a coating agent composed of a normal emulsion.

This means that at the time of film formation, the composition of (II), which is a more finely dispersed or dissolved polymer, enters between the particles of the aqueous dispersion liquid of (I) and connects the particles of the aqueous dispersion liquid of (I). It is thought that it is for forming a film in, because even an aqueous dispersion of a polymer having a relatively high Tg forms a dense film,
It's hard to block.

Next, the present invention will be described by way of examples, and the test method used therein is as follows.

1. Preparation of sample film (performed by the method described in Japanese Patent Publication No. 58-55170) The surface of a biaxially stretched polypropylene film (thickness 20 μm) subjected to corona discharge treatment was coated with a bar coater using a coating agent. Is applied so that the solid content application amount is 1 g / m ² ,
A coated film was obtained by drying at a temperature of 110 ° C. for 30 seconds.

This film was used as a sample for cellophane tape test and blocking test.

Then, the film coated with the coating agent was further diluted so that the solid content of the vinylidene chloride copolymer emulsion was 20%, and 4 parts of an aqueous dispersion of carnauba wax (solid content of 20%) (100 parts of polymer resin) ) And fine powder silica: 0.3 part of product name Syloid (based on 100 parts of polymer resin)
And apply so that the solid coating amount becomes 2.0 g / m ² ,
It was dried at a temperature of 110 ° C. for 1 minute.

This film was used as a sample for an anchor property test, a discoloration test and a solvent resistance test.

2. Test method In addition, among the test methods, a), b), and c) were performed by the method described in JP-B-58-55170. B) Cellophane tape test A pressure sensitive adhesive cellophane tape with a size of 24 mm × 200 mm is repeatedly pressure-bonded to the resin-coated surface from end to end to firmly adhere, then the adhesive tape is rapidly peeled off at an angle of 90 °. The state of peeling of the coating film was observed and grading was performed as follows.

◎ No resin peeling at all ………… Excellent ◎ Resin peeling area 10% or less ………… Good ◎ Same as above 10 to 20% ……… Yes ◎ Same as above 20% ……… No b) Blocking test 50mm × 50mm The above film was sandwiched between two glass plates, left at 40 ° C. under a load of 0.5 kg / cm ² for 48 hours, and then allowed to cool to room temperature.

The degree of blocking of the film was ranked as follows.

◎ The film can be divided into one sheet and one sheet without applying force ………… Excellent ◎ It can be divided into sheets by applying a little force ………… Good ◎ It can be separated into sheets by applying force ◎ Cloth resin Is partially peeled off ........ Yes ◎ It is a hard block and cannot be divided into sheets without breaking the film .... No C) Anchor test A film-coated surface and a coated surface should be joined together to form a bar. With a type heat sealer, the heater temperature is 120 ° C and the pressure is 0.5 kg / cm ² ,
Heat sealing is performed under the condition of crimping time 0.5 seconds 15mm × 100
Tensile speed using a Tensilon tensile tester from mm sample
The peel strength of the heat-sealed portion was measured under the condition of 100 mm / min.

If this strength is 50 g / 15 mm or more, the anchoring property is practically sufficient.

D) Discoloration test After irradiating the coated surface of the sample film with UV light for 12 hours with a light resistance tester (Standard UV long life fade meter FAL-5B manufactured by Suga Test Instruments Co., Ltd.), observe the color tone of the sample film before and after irradiation. Then, the one with no change was accepted.

E) Solvent resistance Drop 0.5 g of lubricating oil (machine oil) on a 10 cm x 10 cm corrugated cardboard and immediately cover it with a sample sample.

One day later, the condition of the film was observed, and a film free from wrinkles and tarmi was passed.

The monomers used are indicated by the following abbreviations.

MMA: Methyl Methacrylate EA: Ethyl Acrylate MAA: Methacrylic Acid St: Styrene BA: Butyl Acrylate HEMA: 2-Hydroxyethyl Methacrylate AA: Acrylic Acid Synthesis Examples 1 to 3 Polymerization with Stirrer, Cooler, and Thermometer Into a container was placed 530 cc of water containing 17.1 g of sodium lauryl sulfate as an emulsifier and 1.4 g of potassium persulfate as a polymerization initiator.

The reaction vessel was then heated to about 80 ° C. with stirring.

Then, a mixed solution of 285 g of the monomers (total) shown in Table 1 and mercaptan as a molecular weight modifier was added dropwise little by little over 3 hours.

After dropping the monomer mixture, the reaction vessel is kept at 80 ° C for 30 minutes.
Kept at.

This aqueous dispersion liquid was neutralized with aqueous ammonia, kept at 60 ° C. for 1 hour, and then cooled.

Synthesis Example 4 A polymerization vessel equipped with a stirrer, a cooler and a thermometer was charged with 540 cc of water containing 3.2 g of sodium lauryl sulfate as an emulsifier and 1 g of potassium persulfate as a polymerization initiator.

The reaction vessel was then heated to about 90 ° C. with stirring.

Then, a mixed solution of 97.8 g of EA, 226.0 g of MMA and 16.2 g of MAA and 2.6 g of mercaptan as a molecular weight modifier was added dropwise over 2 hours.

After the dropping was completed, the reaction vessel was kept at 80 ° C for 2 hours, 60 g of isopropyl alcohol and 30 g of carbitol were added, and then
22 g of 10% ammonia water was added to obtain a composition dispersed in 0.04 micron polymer particles.

Synthesis Example 5 A polymerization vessel equipped with a stirrer, a cooler and a thermometer was charged with 12.2 g of sodium nonylphenyl ether polyethylene glycol sulfonate as an emulsifier and 510 g of water and heated to 80 ° C. with stirring.

Then, mixed solution of EA70g, MMA290g, MAA40g and mercaptan 6g, 5% ammonium persulfate aqueous solution 36g, 5%
36 g of sodium bisulfite aqueous solution is added dropwise over 3 hours.

After the dropping is completed, the reaction vessel is kept at 20 ° C for 1 hour and then cooled,
An aqueous dispersion was obtained.

Synthesis Example 6 10% ammonia water 34.8 based on 600 g of the aqueous dispersion of Synthesis Example 5
g was slowly added at a temperature of 80 ° C. and stirred.

Eventually, an aqueous solution of acrylic polymer was obtained.

Examples 1 to 2 The aqueous dispersion obtained in Synthesis Example 1 and the aqueous acrylic polymer solution obtained in Synthesis Example 6 were sufficiently mixed at the ratio (solid content ratio) shown in Table 2 to prepare a coating liquid, and its performance was obtained. Was evaluated.

The evaluation results are shown in Table 3.

Examples 3 to 4 The aqueous dispersion obtained in Synthesis Example 2 and the composition obtained in Synthesis Example 4 were sufficiently mixed in the proportions (solid content ratio) shown in Table 2 to prepare coating solutions.

The performance was evaluated, and the evaluation results are shown in Table 3.

Example 5 The aqueous dispersion obtained in Synthetic Example 3 and the composition obtained in Synthetic Example 4 were thoroughly mixed at the ratio (solid content ratio) shown in Table 2 to prepare a coating liquid, and its performance was evaluated. .

The evaluation results are shown in Table 3.

Comparative Example 1 The performance was evaluated by using the aqueous dispersion obtained in Synthesis Example 1 as a coating liquid.

The evaluation results are shown in Table 3.

Comparative Example 2 The composition containing a large amount of ammonia obtained in Synthesis Example 4 was used as a coating liquid, and its performance was evaluated.

The evaluation results are shown in Table 3.

Comparative Example 3 A coating solution was prepared by thoroughly mixing the aqueous dispersion obtained in Synthesis Example 1 and the aqueous dispersion of Synthesis Example 5 at a solid content ratio of 50:50, and the performance was evaluated. .

The evaluation results are shown in Table 3.

Claims (1)

[Claims] 1. (I) (a) One or two of α, β-unsaturated carboxylic acids having at least one carboxyl group.
1 or more, 0.1 to 10% by weight, and one or more of (b) an alkyl acrylate (wherein the alkyl group has 1 to 12 carbon atoms),
And / or one or more kinds of methacrylic acid alkyl ester (wherein the alkyl group has 1 to 12 carbon atoms) 90 to 99.1% by weight and, if necessary, (c) a copolymerizable vinyl monomer. The copolymer obtained by adding one kind or two or more kinds of
(II) (d) at least one α, β unsaturated carboxylic acid and (e) (meth) acrylic acid alkyl ester (wherein the alkyl group has 1 to 4 carbon atoms) At least one of
A copolymer comprising a seed and optionally (f) the above (d) and (e) and a radically copolymerizable vinyl-based monomer, wherein the acid value of the polymer is from 10 to 20.
0 and a composition in which at least 30% of carboxyl groups contained in the polymer form a salt are dissolved in an aqueous medium or dispersed in a particle size of 0.1 micron or less, A coating agent prepared by mixing so that the ratio (I) / (II) = 15-95 / 85-5.