JP7666888B2 - Unsaturated polyester resin, putty composition using same, and coating method - Google Patents

Description

The present invention relates to an unsaturated polyester resin and a putty composition using the same.

Unsaturated polyester resins are generally relatively inexpensive compared to other resins, and have excellent workability as they harden in a short time even at room temperature. Furthermore, depending on the selection of the main raw material, they have a variety of excellent physical and chemical properties, so they are used in a variety of applications such as putty, paint, FRP molded products, resin concrete, and cast products.

In conventional putty compositions, styrene monomer has been used as a reactive diluent for unsaturated polyester resins in terms of curing properties and physical properties. However, in recent years, styrene monomer has become subject to regulation under the Regulations for Prevention of Harm from Specified Chemical Substances, and there is a need to develop putty compositions that do not contain styrene, so-called non-styrene type putty compositions.

For example, Patent Document 1 discloses a non-styrene type putty composition (sometimes called a styrene-free putty composition) that uses an unsaturated polyester resin composition in which hydroxyalkyl methacrylate is used as a reactive diluent instead of styrene monomer. This composition has a low odor and is excellent in curing stability and surface drying, but when the substrate is a zinc-plated steel sheet, there are cases in which the adhesion, particularly water-resistant adhesion, is significantly insufficient.

Patent documents 2 and 3 disclose putty compositions containing a specific polymerizable unsaturated compound as a reactive diluent, a specific aromatic amine compound as a curing accelerator, and a rust inhibitor. Such compositions can form a putty layer that has good surface drying properties, a good appearance without yellowing of the finished surface after topcoat painting, excellent internal drying properties when applied thickly, and excellent adhesion to both the substrate and the topcoat coating. However, when the substrate is a zinc-plated steel sheet, there are cases where adhesion is insufficient.

Galvanized steel sheets are steel sheets with a zinc plating applied to the surface thereof, and have excellent rust and corrosion resistance. In recent years, applications requiring durability such as long-term rust resistance, such as substrates for European cars and railway vehicles, may include hot-dip galvanized steel sheets with a large amount of zinc applied (basis weight) as part of the material. Galvanized steel sheets are generally chemically treated with phosphoric acid or the like on the substrate surface in order to improve adhesion to the composition to be painted next and rust resistance, but there are also some that are not phosphate-treated in order to reduce labor hours, and when a putty composition is painted on a substrate including a galvanized steel sheet, the substrate may be subjected to a surface treatment such as polishing, and the chemical treatment layer may be scraped off during the application. In such cases, when a putty layer is formed on a galvanized steel sheet using a putty composition containing a conventional unsaturated polyester resin, there is a problem that poor adhesion such as peeling and blisters occurs frequently from the base point between the galvanized steel sheet and the putty composition layer.

Patent Document 4 discloses an unsaturated polyester resin composition for paint, which is characterized by blending a specific amount of unsaturated carboxylic acid with a composition consisting of air-drying unsaturated polyester resin, filler, and vinyl monomer in specific ratios for the purpose of improving adhesion to zinc plating. When this composition is used, adhesion to zinc-plated steel sheets is slightly improved, but water-resistant adhesion is particularly insufficient.

JP 2005-162830 A JP 2005-206781 A JP 2006-206863 A Special Publication No. 06-102753

The object of the present invention is to provide an unsaturated polyester resin and putty composition that does not contain styrene monomer, has excellent drying properties, and can form a putty layer that has extremely good adhesion even when the substrate is a zinc-plated steel sheet.

As a result of intensive research to solve the above problems, the inventors discovered that a putty layer with excellent adhesion (particularly water-resistant adhesion) can be obtained by adding a specific amount of a specific cyclic acid anhydride to the polybasic acid component of the unsaturated polyester resin, and thus arrived at the present invention.

That is, the present invention encompasses the following aspects:

Item 1. An unsaturated polyester resin having an acid value in the range of 10 to 60 mgKOH/g, which comprises an acid component (a) containing a cyclic acid anhydride (a1) having _{a pKa2} of 5.8 or less and a hydroxyl group-containing component (b) as constituent units, wherein the unsaturated polyester resin is a polyester resin having a radically polymerizable unsaturated group, a carboxyl group, and a hydroxyl group;
The amount of the cyclic acid anhydride (a1) having a _pKa2 of 5.8 or less used is within the range of 1 to 50 mol % based on the total number of moles of the acid component (a).

Item 2. The unsaturated polyester resin (A) according to Item 1, wherein a cyclic acid anhydride (a1) having a _pKa2 of 5.8 or less is used as an acid source for the carboxyl group of the unsaturated polyester resin (A).

Item 3. An unsaturated polyester resin (A) according to item 1, in which the acid component (a) further contains methyltetrahydrophthalic acid and/or its anhydride.

Item 4. An unsaturated polyester resin (A) according to any one of items 1 to 3, in which the acid component (a) contains an unsaturated polybasic acid and a saturated polybasic acid, with the molar ratio of unsaturated polybasic acid/saturated polybasic acid being within the range of 99/1 to 50/50.

Item 5. The unsaturated polyester resin (A) according to any one of Items 1 to 4, wherein the unsaturated polyester resin (A) is a resin obtained by reacting a polyester intermediate (X) having a carboxyl group and a hydroxyl group with a cyclic acid anhydride (a1) having a _pKa2 of 5.8 or less.

Item 6. A putty composition containing the unsaturated polyester resin (A) described in any one of items 1 to 5.

Item 7. A putty composition comprising the unsaturated polyester resin (A) according to any one of items 1 to 6 and a polymerizable unsaturated compound (B), the polymerizable unsaturated compound (B) containing a secondary hydroxyl group-containing polymerizable unsaturated monomer (b1) as part of its components.

Item 8. The putty composition according to item 7, containing 10 to 200 parts by mass of the component (b1) per 100 parts by mass of the resin solid content of the unsaturated polyester resin (A).

Item 9. The putty composition according to any one of items 6 to 8, which contains a dehydrating agent (C).

Item 10. The putty composition according to any one of items 6 to 9, which contains hollow particles (E).

Item 11. A coating method comprising coating a substrate surface with the putty composition according to any one of items 6 to 10 to form a putty layer.
Item 12. The coating method according to item 11, wherein the substrate surface is any one substrate surface selected from the group consisting of bullet train cars, railway cars, and automobile cars.

When the unsaturated polyester resin of the present invention is used as a putty composition, it dramatically improves adhesion to galvanized steel sheets without maintaining or impairing drying properties, paint workability (pot life), and other coating properties, and can provide a stable putty layer with excellent coating durability.

The unsaturated polyester resin (A) of the present invention has a specific acid value and contains a specific amount of a specific cyclic acid anhydride, and is particularly suitable for use in putty compositions. The unsaturated polyester resin (A) of the present invention will be described in detail below.

<<Unsaturated polyester resin (A)>>
The unsaturated polyester resin (A) of the present invention is characterized in that it has as constituent units a specific acid component (a) and a hydroxyl group-containing component (b), and uses, as the acid component (a), 1 to 50 mol % of a cyclic acid anhydride (a1) having a pKa ₂ of 5.8 or less, based on the total number of moles of the acid component (a).

[Cyclic acid anhydride (a1) having a _pKa2 of 5.8 or less]
In the present invention, the cyclic acid anhydride is a compound having one or more cyclic carboxylic acid anhydride structures in the molecule. The cyclic carboxylic acid anhydride structure is a structure in which a compound having two or more carboxyl groups in one molecule is dehydrated and condensed intramolecularly to form a ring. When a cyclic acid anhydride is used as the acid component (a), a carboxyl group can be stably introduced into the side chain or end of the polyester polymer chain of the unsaturated polyester resin (A) by the ring-opening reaction of the acid anhydride (hereinafter sometimes referred to as half-esterification reaction), and the adhesion to the substrate, especially the water-resistant adhesion, is improved, which is preferable.

The cyclic acid anhydride (a1) having a pKa ₂ of 5.8 or less that can be applied to the unsaturated polyester resin (A) of the present invention is a compound that can form a _cyclic carboxylic acid anhydride structure by intramolecularly dehydrating a polybasic acid having a pKa ₂ of 5.8 or _less , the smaller the acid dissociation exponent pKa value, the stronger _the acidity, and generally, the pKa ₂ value of the second dissociation stage is greater than the pKa ₁ value of the first dissociation stage, but in the present invention, it is important that the acid dissociation exponent pKa ₂ of the second stage is 5.8 or less.

In the present invention, by using a cyclic acid anhydride (a1) constituting the unsaturated polyester resin (A) having a _pKa2 value of 5.8 or less, it is possible to exhibit an excellent effect of adhesion to a substrate surface, particularly a galvanized steel sheet. The lower limit of the _pKa2 value is not particularly limited, but it is preferably a value exceeding 0.

The _pKa2 value is given by Brown, HC et al., in Braude, EA and FC Nachod Determination of Organic Structures by Physical Methods, Academic Press, New York, 1955, and if not described therein, it can be determined by potentiometric titration.

Specific examples of the cyclic acid anhydride (a1) having a pKa ₂ of 5.8 or less include succinic anhydride, tetrahydrophthalic anhydride, bromomaleic anhydride, phthalic anhydride, chloromaleic anhydride, malonic anhydride, glutaric anhydride, adipic anhydride, suberic anhydride, and azelaic anhydride. From the viewpoints of storage stability, water-resistant adhesion, cost, and the like, at least one selected from succinic anhydride and phthalic anhydride is preferred.

The content of the cyclic acid anhydride (a1) having _a pKa2 of 5.8 or less is within the range of 1 to 50 mol %, and more preferably 2 to 40 mol %, based on the total number of moles of the acid component (a) from the viewpoint of adhesion to the substrate surface, particularly to a zinc-plated steel sheet.

As the acid source for the carboxyl group of the unsaturated polyester resin (A), it is preferable to use a cyclic acid anhydride (a1) having a _pKa2 of 5.8 or less.

[Acid component (a)]
In the present invention, the acid component (a) constituting the unsaturated polyester resin (A) is a compound having one or more acid groups in the molecule, and examples of such compounds include polybasic acids, fatty acids, and rosin acids.

A polybasic acid is specifically a compound that has two or more acid groups, such as carboxylic acid, in one molecule. In the present invention, acid anhydrides are also included in the polybasic acid.

Polybasic acids are classified into unsaturated polybasic acids and saturated polybasic acids depending on whether they contain radically polymerizable unsaturated groups.

In the present invention, it is suitable that the acid component (a) contains a cyclic acid anhydride (a1) and also contains an unsaturated polybasic acid. By containing an unsaturated polybasic acid as part of the acid component (a), it is possible to introduce a radically polymerizable unsaturated group into the unsaturated polyester resin (A), thereby improving the drying property.

[Unsaturated polybasic acid (containing radically polymerizable unsaturated groups in the molecule)]
The unsaturated polybasic acid is a compound having a functional group having a carbon-carbon double bond exhibiting radical polymerizability in the molecule and two or more acid groups, and examples thereof include maleic acid, fumaric acid, itaconic acid, tetrahydrophthalic acid, tetrabromophthalic acid, tetrachlorophthalic acid, HET acid, himic acid, and methyltetrahydrophthalic acid (methyltetrahydrophthalic acid has isomers depending on the position of the methyl group and the double bond). For example, cis-3-methyl-4-cyclohexene-cis,cis-1,2-dicarboxylic acid (hereinafter sometimes abbreviated as β-PMAA), trans-3-methyl-4-cyclohexene-cis,cis-1,2-dicarboxylic acid, cis-3-methyl-4-cyclohexene-cis,trans-1,2-dicarboxylic acid, trans-3-methyl-4-cyclohexene-cis,trans-1,2-dicarboxylic acid, 4-methyl-Δ4-tetrahydrophthalic anhydride (structural isomer of 3-methyl-Δ4-tetrahydrophthalic anhydride), etc., and anhydrides thereof, etc., are included, and from the viewpoint of surface drying properties, it is preferable to contain methyltetrahydrophthalic acid and/or its anhydride, particularly β-PMMA (cis-3-methyl-4-cyclohexene-cis,cis-1,2-dicarboxylic acid and/or its anhydride). Also, from the viewpoint of curing properties inside the coating film, it is preferable to use fumaric acid or maleic acid, particularly fumaric acid, in combination.

When methyltetrahydrophthalic acid and/or its anhydride are used as the unsaturated polybasic acid component, the amount used is preferably within the range of 1 to 50 mol %, 2 to 45 mol %, and more preferably 3 to 40 mol % based on the total number of moles of the acid component (a).

[Saturated polybasic acid (no radically polymerizable unsaturated groups in the molecule)]
The saturated polybasic acid is a compound having two or more acid groups but not a functional group having a carbon-carbon double bond exhibiting radical polymerizability in the molecule, and examples thereof include phthalic acid, phthalic anhydride, halogenated phthalic anhydride, isophthalic acid, terephthalic acid, hexahydrophthalic acid, hexahydrophthalic anhydride, hexahydroterephthalic acid, hexahydroisophthalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, sebacic acid, 1,12-dodecane diacid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid anhydride, 4,4'-biphenyldicarboxylic acid, and dialkyl esters thereof.

The unsaturated polybasic acids or saturated polybasic acids described above can be used alone or in combination of two or more.

In the present invention, the content ratio of the unsaturated polybasic acid and the saturated polybasic acid constituting the unsaturated polyester resin (A) can be appropriately adjusted within a molar ratio of 99/1 to 50/50 (unsaturated polybasic acid/saturated polybasic acid), preferably within a range of 96/4 to 60/40, from the viewpoints of surface drying property and water resistance.

[Hydroxyl Group-Containing Component (b)]
The hydroxyl-containing component (b) which is the reaction partner of the acid component (a) constituting the unsaturated polyester resin (A) of the present invention is a compound having one or more hydroxyl groups in the molecule, specifically, a polyhydric alcohol having two or more hydroxyl groups in the molecule, a hydroxy compound having an allyl ether group, etc.

[Polyhydric alcohol]
Examples of the polyhydric alcohol include polyols such as alkane polyols, oxyalkylene polyols, polyoxyalkylene polyols, and alicyclic polyols. Specifically, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 2-methyl-1,3-propanediol, 1,3-butanediol, neopentyl glycol, hydrogenated bisphenol A, 1,4-butanediol, 1,6-hexanediol, 1,9-nonanediol, bisphenol compounds, adducts of bisphenol compounds such as bisphenol A with alkylene oxides such as propylene oxide and ethylene oxide, 1,2,3,4-tetrahydroxybutane, glycerin, trimethylolpropane, 1,3-propanediol, 1,2-cyclohexane glycol, 1,3-cyclohexane glycol, 1,4-cyclohexane glycol, 1,4-cyclohexanedimethanol, paraxylene glycol, bicyclohexyl-4,4'-diol, 2,6-decalin glycol, 2,7-decalin glycol, bishydroxyethyl terephthalate, and the like can be mentioned, and these can be used alone or in combination of two or more.

The unsaturated polyester resin (A) may contain the polyhydric alcohol in a range of 40 to 70 mol %, preferably 45 to 60 mol %, based on the total number of moles of the acid component (a) and the hydroxyl group-containing component (b).

[Hydroxy Compound Having Allyl Ether Group]
In the present invention, from the viewpoint of improving surface drying properties, it is preferable to use, as the hydroxyl group-containing component (b), a radically polymerizable hydroxy compound, in particular a hydroxy compound having an allyl ether group.

A hydroxy compound having an allyl ether group is a compound having at least one allyl ether group in one molecule, and examples thereof include ethylene glycol monoallyl ether, diethylene glycol monoallyl ether, triethylene glycol monoallyl ether, polyethylene glycol monoallyl ether, propylene glycol monoallyl ether, dipropylene glycol monoallyl ether, tripropylene glycol monoallyl ether, polypropylene glycol monoallyl ether, 1,2-butylene glycol monoallyl ether, 1,3-butylene glycol monoallyl ether, hexylene glycol monoallyl ether, octylene glycol monoallyl ether, trimethylolpropane diallyl ether, glycerin diallyl ether, and pentaerythritol triallyl ether.

The unsaturated polyester resin (A) can contain a hydroxy compound having an allyl ether group in a range of 1 to 30 mol %, preferably 3 to 20 mol %, based on the total number of moles of the acid component (a) and the hydroxyl group-containing component (b).

When using a hydroxy compound having an allyl ether group as the hydroxyl group-containing component in the production of the unsaturated polyester resin (A), the compound may be mixed with the polyhydric alcohol in advance or may be added later to cause a condensation reaction.

In addition, as the acid component (a) and the hydroxyl group-containing component (b), other acid components and hydroxyl group-containing components other than those mentioned above can be used as necessary. Such other acid components are not particularly limited, and examples thereof include saturated fatty acids, unsaturated fatty acids, rosin, etc., and other hydroxyl group-containing components are not particularly limited, and examples thereof include monoalcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, 2-ethylbutanol, 2-ethylhexanol, stearyl alcohol, and 2-phenoxyethanol; propylene oxide, butylene oxide, and alcohol compounds obtained by reacting a monoepoxy compound such as "Cardura E10P" (trade name, manufactured by Momentive Specialty Chemicals, glycidyl ester of synthetic highly branched saturated fatty acid) with an acid, etc.

It is preferable to adjust the content of hydroxyl group-containing component (b) so that the reaction ratio between acid component (a) and hydroxyl group-containing component (b) is 1.0 to 1.25 moles per mole of acid component (a).

The unsaturated polyester resin (A) of the present invention is a polyester resin having a radically polymerizable unsaturated group, a carboxyl group, and a hydroxyl group, and it is suitable to use a cyclic acid anhydride (a1) having a _pKa2 of 5.8 or less as an acid source for the carboxyl group of the unsaturated polyester resin (A). In particular, it is preferable that the unsaturated polyester resin (A) is a resin obtained by reacting a polyester intermediate (X) having a carboxyl group and a hydroxyl group with a cyclic acid anhydride (a1) having a _pKa2 of 5.8 or less.

<Method for producing unsaturated polyester resin (A)>
The method for producing the unsaturated polyester resin (A) is not particularly limited, but a preferred method is, for example, a production method including a step of reacting an acid component (a) with a hydroxyl group-containing component (b) to obtain a polyester intermediate (X) having a carboxyl group and a hydroxyl group, and then a step of reacting the polyester intermediate (X) with a cyclic acid anhydride (a1) having a _pKa2 of 5.8 or less.

The polyester intermediate (X) can be obtained by a known method for producing polyester resins, specifically, by subjecting the acid component (a) to a condensation reaction with the hydroxyl group-containing component (b).

The condensation reaction for producing the polyester intermediate (X) may be carried out in one stage by charging the acid component (a) and the hydroxyl group-containing component (b) all at once, or may be carried out in multiple stages by dividing the materials into two or more batches. When the reaction for producing the polyester intermediate (X) is carried out in multiple stages, the types and amounts of the acid component (a) and the hydroxyl group-containing component (b) used can be appropriately adjusted.

In the present invention, the cyclic acid anhydride (a1) having a pKa ₂ of 5.8 or less is used as an essential component to obtain the unsaturated polyester resin (A) into which a relatively high acid strength and active carboxyl group is stably introduced. Therefore, when such unsaturated polyester resin (A) is used as a putty composition, it has an effect of providing excellent water-resistant adhesion to a substrate, particularly to a zinc-plated steel sheet, which is a poorly adherent substrate.

In the present invention, the cyclic acid anhydride (a1) having _{a pKa2} of 5.8 or less may be used at any stage of the production of the unsaturated polyester resin (A) as long as the amount used is within the range of the present invention, but it is suitable to use it as a production raw material at the stage of half-esterification reaction with the polyester intermediate (X) from the viewpoint of improving the water-resistant adhesion to the substrate. It is presumed that the unsaturated polyester resin (A) obtained by such a production method can efficiently arrange carboxyl groups having relatively strong acid strength at the terminal and/or side chain of the polymer chain of the polyester intermediate (X). That is, the amount of the cyclic acid anhydride (a1) used in the half-esterification reaction is preferably in the range of 1 to 30 mol %, more preferably in the range of 2 to 20 mol %, based on the total mole number of the acid component (a).

In the present invention, in the production of the unsaturated polyester resin (A) and the polyester intermediate (X), a polycondensation catalyst, a heavy metal oxide, and a polymerization inhibitor may be used as necessary. The temperature conditions during the condensation reaction to produce the polyester intermediate (X) are preferably within the range of 150 to 250°C, and more preferably 160 to 200°C, from the viewpoint of preventing gelation. In addition, the heating temperature conditions during the half-esterification reaction of the polyester intermediate (X) and the acid anhydride (a1) are preferably within the range of 80°C to 150°C, and more preferably 100 to 140°C, from the viewpoint of production stability.

In the present invention, the acid value of the unsaturated polyester resin (A) is within the range of 10 to 60 mgKOH/g, preferably 12 to 50 mgKOH/g, and more preferably 15 to 40 mgKOH/g, from the viewpoint of improving water resistance.

When the unsaturated polyester resin (A) is obtained by a half-esterification reaction, the acid value of the polyester intermediate (X) before half-esterification is preferably within a range of 3 to 50 mgKOH/g, and more preferably 5 to 40 mgKOH/g. Here, the acid value in this specification is the value expressed in mg of the mass of potassium hydroxide required to neutralize the protonic acid contained in 1 g of resin, and can be measured in accordance with JIS K-6901 (2008) liquid unsaturated polyester resin test method.

In addition, the hydroxyl value of the unsaturated polyester resin (A) of the present invention is preferably within the range of 5 to 100 mgKOH/g, more preferably 20 to 80 mgKOH/g, and even more preferably 35 to 80 mgKOH/g, from the viewpoint of water-resistant adhesion.

When the unsaturated polyester resin (A) is obtained by a half-esterification reaction, it is preferable from the viewpoint of production stability that the hydroxyl value of the polyester intermediate (X) before half-esterification is in the range of 20 to 120 mgKOH/g, preferably in the range of 40 to 100 mgKOH/g. Here, the value of the hydroxyl value in this specification is a calculated value based on the blend amount (mgKOH/g resin).

The weight average molecular weight (Mw) of the unsaturated polyester resin (A) described above is preferably in the range of 1,000 to 100,000, more preferably 2,000 to 50,000. In the present invention, the weight average molecular weight is a value measured by gel permeation chromatography and converted into polystyrene. As the gel permeation chromatograph device, "HLC8120GPC" (manufactured by Tosoh Corporation, product name) can be used, and as the columns to be used therewith, four columns, "TSKgelG-4000HxL", "TSKgelG-3000HxL", "TSKgelG-2500HxL", and "TSKgelG-2000HxL" (all manufactured by Tosoh Corporation, product names), can be used. Here, tetrahydrofuran was used as the mobile phase, the measurement temperature was 40°C, the flow rate was 1 cc/min, and an RI refractometer was used as the detector.

<<Putty Composition>>
In the present invention, the unsaturated polyester resin (A) can be used to prepare a putty composition. The putty composition of the present invention contains the specific unsaturated polyester resin (A) and a polymerizable unsaturated compound (B).

<Polymerizable unsaturated compound (B)>
The polymerizable unsaturated compound (B) is a compound other than the unsaturated polyester resin (A) and has one or more polymerizable unsaturated groups in the molecule. The polymerizable unsaturated group means an unsaturated group capable of radical polymerization. Examples of such polymerizable unsaturated groups include vinyl groups, (meth)acryloyl groups, and (meth)allyl groups. Here, "(meth)acryloyl groups" means acryloyl groups or methacryloyl groups, and "(meth)allyl groups" means allyl groups or methallyl groups.

As the polymerizable unsaturated compound (B), it is particularly preferable to contain a secondary hydroxyl group-containing polymerizable unsaturated monomer (b1) from the viewpoint of water-resistant adhesion.

Examples of the secondary hydroxyl group-containing polymerizable unsaturated monomer (b1) include polymerizable unsaturated monomers having a secondary hydroxyl group with 2 to 8 carbon atoms, particularly 3 to 6 carbon atoms, and more particularly 3 or 4 carbon atoms in the alkyl group of the ester moiety, such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-hydroxybutyl (meth)acrylate; and adducts of (meth)acrylic acid and epoxy group-containing compounds (e.g., Cardura E10, product name, manufactured by Hexion Specialty Chemicals, neodecanoic acid glycidyl ester). Among these, 2-hydroxypropyl (meth)acrylate is particularly preferred in terms of water resistance and water-resistant adhesion.

When the unsaturated group-containing polyester resin (A) of the present invention and a secondary hydroxyl group-containing polymerizable unsaturated monomer (b1) as the polymerizable unsaturated compound (B) are mixed to form a putty composition, it is particularly preferable because it can suppress odor after the putty composition is applied to a substrate, while maintaining the coating hardness and surface drying properties and improving water-resistant adhesion.

Examples of hydroxyl-containing polymerizable unsaturated monomers other than component (b1) include monoesters of (meth)acrylic acid and dihydric alcohols having 2 to 10 carbon atoms (excluding those having a secondary hydroxyl group), such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and hydroxyl-containing polymerizable unsaturated monomers modified by ring-opening polymerization of ε-caprolactone (excluding those having a secondary hydroxyl group).

Specific examples of other polymerizable unsaturated compounds include aromatic vinyl compounds such as vinyltoluene, t-butylstyrene, and divinylbenzene; (meth)acrylic acid ester compounds of monohydric alcohols such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, norbornyl (meth)acrylate, and adamantyl (meth)acrylate; trimethylolpropane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,9-nonanediol di(meth)acrylate, (meth)acrylic acid ester compounds of polyhydric alcohols such as 2-butyl-2-ethyl-1,3-propanediol di(meth)acrylate, 2,2-bis(4-(3-methacryloxy-2-hydroxypropoxy)-phenyl)propane, di(methacryloxyethyl)trimethylhexamethylenediurethane, and 2,2-bis(4-methacryloxypolyethoxyphenyl)propane; hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate (excluding the secondary hydroxyl group-containing polymerizable unsaturated monomers listed in the preceding section (b1)); ethylene glycol dimaleate, propylene glycol diitaconate, and the like; 4-(meth)acryloyloxymethoxycarbonylphthalic acid, 4-(meth)acryloyloxyphenyl ... aromatic polycarboxylic acids containing 4-(meth)acryloyloxy groups, such as diaryloxyethoxycarbonylphthalic acid, and their acid anhydrides; allyl compounds, such as diallyl phthalate, diallyl isophthalate, and triallyl phthalate; epoxy (meth)acrylates; polyester (meth)acrylates; polydimethylsilicon di(meth)acrylates; urethane (meth)acrylates; polyfunctional (meth)acrylates having a heterocyclic structure, such as tris(2-(meth)acryloyloxyalkyl)isocyanurate; dicyclopentenyloxyethyl acrylate, dicyclopentenyloxyethyl methacrylate, dicyclopentenyloxypropyl (meth)acrylate, and dicyclopentenyl (meth)acrylate. Examples of the monofunctional and/or polyfunctional (meth)acrylates having a cyclic structure include dicyclopentenyl group-containing polymerizable unsaturated compounds such as cyclohexanedimethanol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, hydrogenated bisphenol A di(meth)acrylate, and the like; difunctional (meth)acrylates having an aromatic ring derived from a diepoxy compound or diol compound having a bisphenol skeleton, naphthalene skeleton, or biphenyl skeleton; and monofunctional and/or polyfunctional (meth)acrylates having a cyclic structure such as modified products of these polyfunctional (meth)acrylates with ethylene oxide, propylene oxide, caprolactone, and the like. These can be used alone or in combination of two or more. Among the monofunctional and/or polyfunctional (meth)acrylates having a cyclic structure, monofunctional and/or polyfunctional (meth)acrylates having a cyclic structure without a hydroxyl group in the molecule are particularly preferred from the viewpoint of water resistance.

Here, "(meth)acrylate" means acrylate or methacrylate, "(meth)acrylic acid" means acrylic acid or methacrylic acid, "(meth)acryloyl" means acryloyl or methacryloyl, and "(meth)acrylamide" means acrylamide or methacrylamide.

The content of the polymerizable unsaturated compound (B) is preferably 10 to 200 parts by mass, and more preferably 40 to 120 parts by mass, based on 100 parts by mass of the resin solid content of the unsaturated polyester resin (A).

When the polymerizable unsaturated compound (B) contains the component (b1), the content is preferably within a range of 10 to 200 parts by mass, more preferably 40 to 80 parts by mass, per 100 parts by mass of the resin solid content of the unsaturated polyester resin (A).

<Dehydrating Agent (C)>
The putty composition of the present invention preferably contains a dehydrating agent (C). By containing the dehydrating agent (C), the deterioration of the surface dryness, water resistance, and adhesion of the putty layer over time is suppressed, and a putty composition of stable quality can be obtained. Although it is not intended to restrict the present invention, it is considered that the dehydrating agent (C) appropriately adjusts the water content in the composition, suppresses the deterioration of the surface dryness, water resistance, and adhesion of the putty layer over time, and obtains a putty composition of stable quality. As the dehydrating agent (C), conventionally known inorganic dehydrating agents and organic dehydrating agents can be used without any restrictions.

Specific examples of inorganic dehydrating agents include calcium compounds such as calcium hydride, calcium oxide (quicklime), calcium chloride, and calcium sulfate (gypsum); barium compounds such as barium oxide; magnesium compounds such as magnesium sulfate; sodium compounds such as sodium sulfate and sodium carbonate; copper compounds such as copper sulfate; inorganic silicon compounds such as silica gel; and aluminum compounds such as aluminum oxide (hydraulic alumina, lithium aluminum hydride, non-crystalline silica alumina, and crystalline aluminosilicates (molecular sieves).

Specific examples of organic dehydrating agents include alkyl orthoformate, alkyl orthoacetate, alkyl orthoborate, vinyl silane, alkoxysilane compounds, monoisocyanate compounds, aliphatic diisocyanate compounds, alicyclic diisocyanate compounds, aromatic diisocyanate compounds, trivalent or higher organic polyisocyanate compounds, dimers or trimers of these polyisocyanate compounds, prepolymers obtained by subjecting these polyisocyanate compounds to a urethane reaction with a polyhydric alcohol, a low molecular weight polyester resin, or water under conditions of excess isocyanate groups, aliphatic acid anhydrides such as acetic anhydride, aromatic acid anhydrides such as benzoic anhydride, carbodiimide compounds such as N,N'-dicyclohexylcarbodiimide and 1-ethyl-3(3-dimethylaminopropyl)carbodiimide hydrochloride, etc. The above-mentioned examples can be used alone or in combination of two or more.

The amount of the dehydrating agent (C) is preferably within the range of 0.1 to 50 parts by mass, and more preferably 2 to 30 parts by mass, based on 100 parts by mass of the total of the unsaturated polyester resin (A) and the polymerizable unsaturated compound (B).

<Polyvalent Metal Compound (D)>
The putty composition of the present invention is suitable for containing a polyvalent metal compound (D). By containing the polyvalent metal compound, it is possible to form a putty layer having excellent water resistance and adhesion. The polyvalent metal compound means a compound containing a polyvalent metal having a valence of 2 or more (other than monovalent).

Specific examples of polyvalent metal compounds (D) include metal oxides such as zinc oxide, calcium oxide, magnesium oxide, aluminum oxide, iron oxide, and copper oxide; metal carbonates such as magnesium carbonate, calcium carbonate, and zinc carbonate; and metal hydroxides such as calcium hydroxide, zinc hydroxide, aluminum hydroxide, and magnesium hydroxide.

In the present invention, a compound containing a Group 2 element of the Periodic Table, particularly magnesium, is preferred as the polyvalent metal compound.

When such a polyvalent metal compound (D) is contained, the content is suitably 0.1 to 50 parts by mass, preferably 5 to 30 parts by mass, based on 100 parts by mass of the total mass of the unsaturated polyester resin (A) and the polymerizable unsaturated compound (B).

The putty composition of the present invention may contain a curing accelerator or a polymerization inhibitor to adjust the curing speed.

<Curing accelerator>
By including a curing accelerator, the curing property can be further improved in some cases. As the curing accelerator, any conventionally known one can be used without any particular limitation, but aromatic amines are particularly preferred from the viewpoints of curing property and drying property. Specifically, N,N-substituted anilines such as aniline, N,N-dimethylaniline, N,N-diethylaniline, p-toluidine, N,N-dimethyl-p-toluidine, N,N-bis(2-hydroxyethyl)-p-toluidine, 4-(N,N-dimethylamino)benzaldehyde, 4-[N,N-bis(2-hydroxyethyl)amino]benzaldehyde, 4-(N-methyl-N-hydroxyethylamino)benzaldehyde, N,N-bis(2-hydroxypropyl)-p-toluidine, N-ethyl-m-toluidine, m-toluidine, pyridine, phenylmorpholine, piperidine, N,N-bis(hydroxyethyl)aniline, and diethanolaniline, N,N-substituted-p-toluidines, 4-(N,N-substituted amino)benzaldehyde, and 4-dimethyl dimethylaminobenzoic acid, ethyl 4-dimethylaminobenzoate, (n-butoxy)ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, 3-dimethylaminobenzoic acid, ethyl 3-dimethylaminobenzoate, (n-butoxy)ethyl 3-dimethylaminobenzoate, isoamyl 3-dimethylaminobenzoate, 2-ethylhexyl 3-dimethylaminobenzoate, 2-dimethylaminobenzoic acid, ethyl 2-dimethylaminobenzoate, (n-butoxy)ethyl 2-dimethylaminobenzoate, isoamyl 2-dimethylaminobenzoate, 2-ethylhexyl 2-dimethylaminobenzoate, and other dimethylamino group-containing benzoic acids, which can be used alone or in combination of two or more.

Furthermore, among such aromatic amines, compounds having a dimethylamino group are preferred because they cause less yellowing of the topcoat film applied on the putty composition. Of these, 4-dimethylaminobenzoic acid and 3-dimethylaminobenzoic acid are particularly suitable.

When an aromatic amine is contained, the content is desirably within the range of 0.01 to 2.0 parts by mass, preferably 0.05 to 1.5 parts by mass, per 100 parts by mass of the unsaturated polyester resin (A) from the viewpoints of pot life (gelation time), air drying properties and sandability of the formed coating film, and heat yellowing resistance of the topcoat coating film.

Examples of curing accelerators other than the above aromatic amines include metal driers such as cobalt naphthenate, copper naphthenate, barium naphthenate, cobalt octoate, manganese octoate, zinc octoate, and vanadium octoate; aliphatic amines such as triethanolamine and diethylenetriamine other than the aromatic amines listed above, tertiary amines, and quaternary ammonium salts, which can be used alone or in combination of two or more. When using a curing accelerator other than the above aromatic amines, the amount is suitably in the range of 0.01 to 5 parts by mass per 100 parts by mass of the unsaturated polyester resin (A).

As the polymerization inhibitor, for example, those mentioned in the section on polymerization inhibitors for unsaturated polyester resin (A) can be suitably used.

<Coloring pigment>
The putty composition of the present invention may contain a coloring pigment. Examples of the coloring pigment include inorganic pigments such as titanium white, red iron oxide, carbon black, iron black, and zinc oxide; and organic pigments such as molybdenum red, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, threne pigments, perylene pigments, dioxazine pigments, and diketopyrrolopyrrole pigments. These coloring pigment components can be used alone or in combination of two or more.

The above color pigments can be used in relatively small amounts, and from the standpoint of ease of polishing and finishing properties when used as a putty, inorganic pigments are preferred, and it is preferable for them to contain titanium white.

When the above color pigments are used, their content is not particularly limited as long as the desired design can be obtained, but it is appropriate to use a content of, for example, 1 to 100 parts by weight, preferably 1 to 50 parts by weight, per 100 parts by weight of the total weight of the unsaturated polyester resin (A) and the polymerizable unsaturated compound (B).

<Extender pigment>
The putty composition of the present invention may contain an extender pigment.

Examples of the extender pigment include talc, mica, barium sulfate, kaolin, calcium carbonate, clay, silica, quartz, and glass. Hollow particles (E) may also be included. These extender pigment components may be used alone or in combination of two or more. From the standpoint of polishing workability, finish, and cost in putty applications, the extender pigment is preferably at least one selected from talc, barium sulfate, kaolin, clay, silica, and calcium carbonate, and particularly preferably contains talc.

When the above-mentioned extender pigment is used, its content is preferably within the range of 1 to 300 parts by weight, more preferably 70 to 250 parts by weight, per 100 parts by weight of the total weight of the unsaturated polyester resin (A) and the polymerizable unsaturated compound (B), in terms of ease of polishing and finish when used as a putty.

<Hollow Particles (E)>
Among the body pigments, it is preferable to contain hollow particles (E) since this has the effect of reducing the weight of the putty layer obtained and improving the sanding workability and water-resistant adhesion.

The hollow particles (E) (hollow particles are sometimes called balloons) are not particularly limited, and examples thereof include resin foam particles such as expanded polystyrene particles, expanded polyethylene particles, expanded polypropylene particles, and expanded polyurethane; inorganic foam particles such as perlite, volcanic gravel, and baked vermiculite; resin-based hollow particles such as acrylic resin, styrene resin, acrylic-styrene copolymer resin, acrylic-acrylonitrile copolymer resin, acrylic-styrene-acrylonitrile copolymer resin, acrylonitrile-methacrylonitrile copolymer resin, acrylic-acrylonitrile-methacrylonitrile copolymer resin, and vinylidene chloride-acrylonitrile copolymer resin; inorganic balloons such as glass balloons such as silica balloons and shirasu balloons, and ceramic balloons such as alumina silica balloons; and organic-inorganic composite balloons in which the surfaces of the resin-based hollow particles are modified with inorganic materials such as silica, alumina, and calcium carbonate. These can be used alone or in combination of two or more.

In particular, from the standpoint of abrasiveness and water-resistant adhesion, shirasu balloons and organic-inorganic composite balloons modified with inorganic materials are preferred.

When the hollow particles (E) are used, their content is preferably within the range of 1 to 20 parts by mass, more preferably 2 to 10 parts by mass, per 100 parts by mass of the total of the unsaturated polyester resin (A) and the polymerizable unsaturated compound (B), from the viewpoints of polishing workability and finishing quality in putty applications.

<Rust inhibitor>
The putty composition of the present invention may contain a rust inhibitor.

Examples of the rust inhibitor include phosphate-based agents such as zinc phosphate, calcium phosphate, zinc phosphite, potassium phosphite, and calcium phosphite; polyphosphate-based agents such as aluminum dihydrogen tripolyphosphate; molybdate-based agents such as zinc molybdate and calcium molybdate; phosphomolybdate-based agents such as aluminum phosphomolybdate; borate-based agents; metaborate-based agents such as barium metaborate; zinc calcium cyanamide-based agents; modified silica in which cations such as calcium, zinc, cobalt, lead, strontium, and barium are bound to porous silica particles; Examples of the organic rust inhibitors include ion-exchanged silica bonded with an aluminum pyrophosphate; rust-preventive pigments such as zinc oxide; and further benzothiazole compounds such as 1-(benzothiazole-2-ylthio)succinic acid and (2-benzothiazole-2-ylthio)succinic acid di-(C12-14 alkyl)ammonium salt; and ketocarboxylic acid compounds such as an addition product of 4-methyl-γ-oxo-benzenebutanoic acid and N-ethylmorpholine, and an addition product of 4-methyl-γ-oxo-benzenebutanoic acid and zirconium. These can be used alone or in combination of two or more.

When a rust inhibitor is included, the content is preferably in the range of 0.1 to 50 parts by mass, and more preferably 5 to 45 parts by mass, per 100 parts by mass of the total of the unsaturated polyester resin (A) and the polymerizable unsaturated compound (B), from the viewpoints of the polishing workability and finish of the putty layer, the curing and drying properties, the ease of application with a spatula, and the heat yellowing resistance.

The putty composition of the present invention may also contain, for example, organic solvents, UV stabilizers, UV absorbers, shrinkage reducing agents, antioxidants, anti-skinning agents, plasticizers, aggregates other than the hollow particles, flame retardants, stabilizers, reinforcing materials, viscosity regulators such as viscosity reducers, pigment dispersants, modifying resins, thixotropic agents, thixotropic assistants, defoamers, leveling agents, silane coupling agents, aldehyde scavengers, etc.

The putty composition of the present invention can provide a putty layer that is easy to apply with a spatula and has excellent physical properties even without substantially blending any organic solvent, but it may contain organic solvents such as ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, methanol, ethanol, propanol, butanol, toluene, and xylene in order to adjust the viscosity.

The composition containing the unsaturated polyester resin (A) and the polymerizable unsaturated compound (B) described above can be used as the base agent of a putty composition, and its viscosity can be adjusted appropriately depending on the intended use of the putty composition, but in terms of thick application, spatula application, and surface finish, it is generally suitable to have a viscosity in the range of 100 to 2,000 Pa·sec, preferably 200 to 1,300 Pa·sec.

In this specification, the viscosity of the putty composition was measured using a Brookfield viscometer "VISCOMETER TV-22" (product name, manufactured by Toki Sangyo Co., Ltd.) with the sample temperature adjusted to 25°C, a No. 7 rotor, and a rotation speed of 2 rpm.

The putty composition of the present invention can be a multi-component system in which the main component is a component containing the unsaturated polyester resin (A) and the polymerizable unsaturated compound (B), and the curing agent component is a component containing an organic peroxide.

Specific examples of the organic peroxides that can be used include conventionally known peroxides such as diacyl peroxides, peroxy esters, hydroperoxides, dialkyl peroxides, ketone peroxides, peroxy ketals, alkyl peresters, and percarbonates, and these may be used alone or in combination of two or more.

The content of the organic peroxide is not particularly limited and can be adjusted as appropriate depending on the coating environment and the physical properties of the coating film, but is preferably within the range of 0.1 to 6 parts by mass per 100 parts by mass of the total of the unsaturated polyester resin (A) and the polymerizable unsaturated compound (B).

The putty composition of the present invention may be a two-component system consisting of a base component and a hardener component. In this case, if the putty composition contains a dehydrating agent (C), a polyvalent metal compound (D), a hardening accelerator, a coloring pigment, an extender pigment, a polymerization inhibitor, etc. as necessary, they can be included in the base component.

The putty composition of the present invention may be a multi-component system consisting of three or more components, including a base component, a hardener component, and a dehydrating agent (C), a polyvalent metal compound (D), a hardening accelerator, a color pigment, an extender pigment, a polymerization inhibitor, etc., as separate components. For example, when a water-reactive dehydrating agent is contained as the dehydrating agent (C), it may be blended with either the base component or the crosslinking agent, but from the viewpoints of storage stability and painting workability, it is preferable to use a three-component system in which the base component, hardener, and dehydrating agent are mixed together immediately before use.

The putty composition obtained as described above provides a putty layer with excellent surface drying and internal curing properties even without containing styrene, and can be used as a non-styrene type putty composition (styrene-free putty composition), but does not exclude the inclusion of styrene.

<Substrate>
The substrate surface to which the putty composition of the present invention is applied is not particularly limited, and examples thereof include metal material surfaces such as iron, zinc, aluminum, brass, copper, tinplate, stainless steel, zinc-plated steel, zinc alloys (Zn-Al, Zn-Ni, Zn-Fe, etc.), plated steel, and aluminum alloys, as well as chemically treated surfaces thereof, various plastic materials, and composite materials thereof.

There are no particular limitations on the applications to which the putty composition of the present invention can be applied, but because of its excellent paint workability and water-resistant adhesion, it is useful for new painting of railway vehicles such as bullet trains and electric trains, or repair painting of painted bodies, and repair painting of painted bodies of vehicles such as automobiles. In particular, it is preferable to use any one of bullet train vehicles, railway vehicles, and automobile vehicles as the substrate surface.

<<Painting method>>
The putty composition can be applied to a substrate surface to form a putty layer.

The putty composition can be applied using, for example, a spatula.

Before applying the putty composition, the surface of the substrate may be subjected to surface preparation such as cleaning or sanding.

Methods for drying the putty composition include, for example, room temperature drying or forced drying, and this drying process allows the coating to harden to the inside. In the case of room temperature drying, specifically, the composition is left to stand at room temperature (approximately 5 to 40°C) for 5 hours or more, or in the case of forced drying, the composition can be heated at 40°C to 120°C for 5 to 60 minutes. In the case of forced drying, the composition can be allowed to set (stand still) at room temperature for 2 to 30 minutes before heat hardening in terms of the finish.

The resulting putty layer may be polished, for example using waterproof paper or sandpaper.

After polishing the putty layer obtained, a paint composition such as a base paint composition may be applied to the polished surface. Examples of paint compositions that may be applied to the putty layer include acrylic lacquer, acrylic melamine resin paint, two-liquid type urethane curing paint containing a hydroxyl group-containing resin and a polyisocyanate compound, acid-epoxy curing paint, fluororesin paint, alkyd resin paint, alkyd melamine resin paint, polyester melamine resin paint, and other commonly used organic solvent-based, water-based, and powder-based undercoat paints, colored base paints, and top clear paints, etc., which can be used without any particular restrictions.

By using a putty composition containing the unsaturated polyester resin (A) of the present invention, it is possible to form a putty layer with extremely excellent adhesion, even when the substrate is a zinc-plated steel sheet, and it also has excellent adhesion and finish to both the substrate and the topcoat coating.

The present invention will be further described below with reference to examples. Here, "parts" and "%" mean "parts by mass" and "% by mass", respectively.

(Example 1) Unsaturated polyester resin No. 1
A 2-liter four-neck flask equipped with a stirrer, nitrogen gas inlet tube, water separator, thermometer and reflux condenser was charged with 1.35 mol of phthalic anhydride (*1), 3.15 mol of fumaric acid (*5), 4.75 mol of diethylene glycol and 0.63 mol of trimethylolpropane diallyl ether, and heating was started while blowing in nitrogen gas. A dehydration condensation reaction was carried out at an internal temperature of 190°C, and when the acid value reached 20 mgKOH/g, 0.25 mol (5 mol% of the total acid components) of phthalic anhydride (*1) for half esterification was added, and a half esterification reaction of the anhydride was carried out at an internal temperature of 130°C, and 0.33 g of methylhydroquinone was added to obtain unsaturated polyester resin No. 1 with an acid value of 30 mgKOH/g. The obtained unsaturated polyester resin No. The acid value, hydroxyl value and weight average molecular weight of unsaturated polyester resin No. 1, as well as the acid value and hydroxyl value before half-esterification are shown in Table 1. Among the acid components blended when producing unsaturated polyester resin No. 1, the proportion of cyclic acid anhydride (a1) having a pKa ₂ of 5.8 or less was 34 mol % based on the total number of moles of all acid components.

(Examples 2 to 6 and Comparative Examples 1 to 6) Unsaturated polyester resins No. 2 to 12
Unsaturated polyester resins No. 2 to 12 were obtained in the same manner as in Example 1, except that the blending was changed to the blending shown in Table 1. For those that did not undergo half-esterification reaction, the (a1) component was not added, and the subsequent steps were carried out in the same manner to obtain unsaturated polyester resins.

The * in Table 1 or the Examples is as follows:

(*1) Phthalic anhydride (abbreviated as PA in the table): cyclic acid anhydride (a1) having a pKa ₂ of 5.8 or less, saturated polybasic acid, molecular weight 148.10, pKa ₂ = 5.41,
(*2) Succinic anhydride (abbreviated as SA in the table): cyclic acid anhydride (a1) having a pKa ₂ of 5.8 or less, saturated polybasic acid, molecular weight 100.07, pKa ₂ = 5.48,
(*3) β-PMMA: cis-3-methyl-4-cyclohexene-cis,cis-1,2-dicarboxylic anhydride, cyclic acid anhydride with pKa ₂ not less than 5.8, unsaturated polybasic acid, molecular weight 166.17,
(*4) Hexahydrophthalic anhydride: a cyclic acid anhydride with a _pKa2 of not less than 5.8 (Hexahydrophthalic Anhydride, abbreviated as HHPA in the table), an unsaturated polybasic acid, molecular weight 154.17,
(*5) Fumaric Acid (abbreviated as FA): Unsaturated polybasic acid, molecular weight 116.07,
(*6) Maleic anhydride (abbreviated as MA in the table): a cyclic acid anhydride having a pKa ₂ of not less than 5.8, an unsaturated polybasic acid, a molecular weight of 98.10, and a pKa ₂ = 6.23.

(Examples 7 to 25 and Comparative Examples 7 to 12)
Each component was mixed and stirred with each unsaturated polyester resin obtained in the above Examples and Comparative Examples so as to obtain the composition shown in Table 2-1, and mixed and dispersed for 20 minutes with a high-speed kneader to obtain each main component. 2% by mass of a hardener component containing 30 parts of cyclohexanone peroxide and 70 parts of an ester-based organic solvent was added to each main component, and mixed uniformly by hand stirring to obtain putty compositions (P-1) to (P-25). The pot life of each putty composition was evaluated, and the results are shown in Table 2-1.

<Creating test panels>
Each of the putty compositions obtained above was applied to one surface of a substrate with a spatula, smoothed out, and coated to a thickness of 2 mm to prepare a test coated plate, and the surface drying property, coating hardness (Martens strength) and abrasion property were evaluated. The results are shown in Table 2-2.

The following materials were used as substrates:

Substrate 1: A hot-dip galvanized steel sheet (thickness 0.8 mm, no chemical conversion treatment) was used, the surface of which was lightly polished with waterproof paper #240 to serve as the substrate surface.

Substrate 2: Mild steel plate, "SPCC-SB" (product name, manufactured by Nippon Testpanel Co., Ltd.), was used. The surface was lightly polished with waterproof paper #240, and this was used as the substrate surface.

Substrate 3: A stainless steel plate, "SUS#304" (product name, manufactured by Paltec Co., Ltd.), was used. The surface was lightly polished with waterproof paper #240, and this was used as the substrate surface.

Substrate 4: Aluminum steel plate, "A5052P" (product name, manufactured by Paltec Co., Ltd.), was used. The surface was lightly polished with waterproof paper #240, and this was used as the substrate surface.

<Creating topcoat painted boards>
The test coated plates coated with each of the putty compositions obtained above were left to dry at room temperature (20°C) for 6 hours to form a putty layer, and then the coating surface was lightly polished with #400 waterproof paper, and "Retan PG80 White Base" (trade name, acrylic polyol and polyisocyanate-based topcoat paint, manufactured by Kansai Paint Co., Ltd.) was spray-coated on the putty layer to a dry film thickness of 50 μm, and dried at 60°C for 30 minutes to prepare coated plates each having a topcoat coating film formed on the putty layer, which were then subjected to a water immersion test [water resistance (blister evaluation) and adhesion]. The results are shown in Table 2-2.

The compounding composition of each putty composition is shown in Table 2-1, and the results of the corresponding evaluation tests are shown in Table 2-2. Note that the amount of unsaturated polyester resin listed in Table 2-1 is expressed as solid content.

The * in Table 2 is as follows:

(*7) Ethoxylated bisphenol A dimethacrylate (EO: 2.3 moles): (product name: NK Ester BPE-80N, average ethoxylated mole number: 2.3 moles), manufactured by Shin-Nakamura Chemical Co., Ltd., a dimethacrylate having a cyclic structure without a hydroxyl group in the molecule. (*8) Ethoxylated bisphenol A dimethacrylate (EO: 10 moles): (product name: NK Ester BPE-500, average ethoxylated mole number: 10 moles), manufactured by Shin-Nakamura Chemical Co., Ltd., a dimethacrylate having a cyclic structure without a hydroxyl group in the molecule.
(*9) Tricyclodecane dimethanol dimethacrylate: (product name: NK Ester DCP), manufactured by Shin-Nakamura Chemical Co., Ltd., a dimethacrylate having a cyclic structure without a hydroxyl group in the molecule.

(*10) Hollow particles: Silafine (registered trademark) MSB-301, product name, manufactured by Axes Chemical Co., Ltd., Shirasu Balloon (inorganic hollow particles), average particle diameter 50 μm.

(*11) Pot life (painting workability):
The putty compositions, in which the hardener was uniformly mixed with each base agent, were left at room temperature (20°C) for a predetermined time, and then were mixed by hand again to mix uniformly. The putty compositions were applied to the substrate surface with a spatula, and the time until the spatula application became difficult (defective), such as spreading, spatula breakage, or spatula handling, was measured and evaluated.
S: If left for 10 minutes or more, the putty composition begins to show an increase in viscosity, but if left for less than 10 minutes, there is no problem with the spatula application work.
A: When left for 5 minutes or more but less than 10 minutes, the putty composition begins to increase in viscosity, but at a level that does not cause any problems when applying with a spatula.
D: In less than 5 minutes, the putty composition began to show an increase in viscosity, making application with a spatula difficult.

The * in Table 2-2 is as follows:

(*12) Surface drying property:
Each coated test plate (substrate 1: hot-dip galvanized steel plate) was left to stand at room temperature (20° C.) for a predetermined time, and then the surface dryness of each coated test plate was checked by touching with a finger.

S: After 20 minutes, the surface was good with no tack.
A: After 25 minutes, the surface was good with no tack.
D: After 30 minutes, there is tack on the surface.

(*13) Paint film hardness:
Each test coated plate (substrate 1: hot-dip galvanized steel plate) was left at room temperature (20° C.) for 12 hours, and then the coating hardness was examined using a FISCHERSCOPE HM2000S manufactured by Helmut Fischer (conditions: maximum test force 1,000 mN/20 seconds and minimum test force 0.100 mN/5 seconds).

S: Martens hardness 80 or more,
A: Martens hardness 60 or more but less than 80;
D: Martens hardness less than 60.

(*14) Abrasiveness:
Each test coated plate (substrate 1: hot-dip galvanized steel plate) was left to stand at room temperature (20° C.) for 12 hours, and then polished with #400 waterproof paper, and the polished state was evaluated.

S: Good, no clogging;
A: There is a very small amount of clogging, but it is not a problem for practical use.
D: Clogged and heavy polishing.

(*15) Water resistance (blistering)
Each topcoated sheet (substrate 1: hot-dip galvanized steel sheet) was immersed in water at 40° C. for 10 days, then removed from the water and the presence or absence of blisters on the coating surface was observed.

S: No blisters on the entire coating surface.
A: Some swelling is observed at the edge of the coating film or in the thin film, but it is not a problem for practical use.
D: Significant blisters are observed over the entire coating film.

(*16) Water-resistant adhesion:
Each of the substrates 1 to 4 (hot-dip galvanized steel plate, mild steel plate, stainless steel plate, aluminum steel plate) was coated with a topcoat paint to form a topcoat coating layer on the putty layer. The coated plates were then immersed in water at 40°C for 10 days, and then removed from the water. Each coated plate was then folded 180 degrees from the center, and the state of the coating at the folded portion was observed.

S: No peeling of the putty coating film was observed.
A: The putty coating film has peeled off very slightly from between the steel plate and the putty, but at a level that does not cause any practical problems. D: The putty coating film has peeled off significantly from between the steel plate and the putty.

Claims (12)

An unsaturated polyester resin having an acid value in the range of 10 to 60 mgKOH/g, the unsaturated polyester resin comprising structural units of an acid component (a) containing a cyclic acid anhydride (a1) having a _pKa2 of 5.8 or less and a hydroxyl group-containing component (b), the unsaturated polyester resin having a radical polymerizable unsaturated group, a carboxyl group, and a hydroxyl group;
the amount of the cyclic acid anhydride (a1) having _a pKa2 of 5.8 or less is within the range of 1 to 50 mol % based on the total number of moles of the acid component (a);
The unsaturated polyester resin (A) is a resin obtained by half-esterification reaction of a polyester intermediate (X) having a carboxyl group and a hydroxyl group with a cyclic acid anhydride (a1) having a _pKa2 of 5.8 or less. The unsaturated polyester resin (A) according to claim 1, wherein a cyclic acid anhydride (a1) having a _pKa2 of 5.8 or less is used as an acid source for the carboxyl group of the unsaturated polyester resin (A). An unsaturated polyester resin (A) according to claim 1 or claim 2, wherein the acid component (a) further contains methyltetrahydrophthalic acid and/or its anhydride. An unsaturated polyester resin (A) according to any one of claims 1 to 3, in which the acid component (a) contains an unsaturated polybasic acid and a saturated polybasic acid, with the molar ratio of unsaturated polybasic acid/saturated polybasic acid being within the range of 99/1 to 50/50. An unsaturated polyester resin (A) according to any one of claims 1 to 4, wherein the hydroxyl group-containing component (b) contains a hydroxy compound having radical polymerizability. A putty composition containing the unsaturated polyester resin (A) according to any one of claims 1 to 5. A putty composition comprising the unsaturated polyester resin (A) according to any one of claims 1 to 5 and a polymerizable unsaturated compound (B), wherein the polymerizable unsaturated compound (B) contains a secondary hydroxyl group-containing polymerizable unsaturated monomer (b1) as a part of its components. The putty composition according to claim 7 contains 10 to 200 parts by mass of the component (b1) per 100 parts by mass of the resin solid content of the unsaturated polyester resin (A). The putty composition according to any one of claims 6 to 8, which contains a dehydrating agent (C). The putty composition according to any one of claims 6 to 9, which contains hollow particles (E). A coating method in which the putty composition according to any one of claims 6 to 10 is applied to a substrate surface to form a putty layer. The coating method according to claim 11, wherein the substrate surface is any one substrate surface selected from the group consisting of Shinkansen trains, railway cars, and automobiles.