JPS625193B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel resin composition for powder coatings,
More specifically, it is a thermosetting polyester-grafted vinyl resin composition for powder coatings that combines the adhesion, mechanical, and chemical properties that are the advantages of polyester with the smoothness of the coating surface that is the advantage of vinyl resins. Regarding. The use of certain polyester-grafted vinyl resins as resins for powder coatings has been described, for example, in JP-A-49-120987 and JP-A-51-125108, and is based on conventionally known methods. That's true. However, the powder coating resins disclosed in these publications are extremely complicated to manufacture, and a phenomenon in which ungrafted polyester homopolymer stands out on the coating surface during coating film formation (hereinafter referred to as
This phenomenon is abbreviated as "floating"), and as a result, the anti-blocking performance of powder coatings is deteriorated, the sharpness of the coating film is reduced, and the hardness, flexibility, and solvent resistance are deteriorated. Baking at high temperatures is required to obtain a coating film with practical properties such as
There were drawbacks such as the need to bake at temperatures above ℃. In particular, baking at a high temperature of 200° C. or higher is not preferable because problems such as melting of the solder joints of the object to be coated and thermal distortion of the material of the object to be coated occur. In view of the above-mentioned current situation, there is currently a strong desire in the market for the development of a resin composition for powder coatings that can be baked at low temperatures and does not cause flaking. In order to meet the above-mentioned needs, the present inventors have conducted extensive research with the aim of providing a vehicle resin composition for powder coatings that can be baked at low temperatures and does not cause flaking. An acid value obtained by reacting a specific prepolyester with an acid value of 5 or less, in which at least 50 mol% of the basic acid units are isophthalic acid units and/or hexahydrophthalic acid units, with a polybasic acid containing a polymerizable unsaturated group. The inventors have discovered that the above object can be easily achieved by using a grafted vinyl resin based on polyester having a polyester of 20 or less as a vehicle resin, and have completed the present invention. Therefore, according to the present invention, [A](i) 100 parts by weight of a prepolyester having an acid value of 5 or less, in which at least 50 mol% of dibasic acid units are isophthalic acid units and/or hexahydrophthalic acid units; , in the presence of 5-80% by weight of a polyester having an acid value of 20 or less obtained by reacting 0.1-5 parts by weight of a polymerizable unsaturated group-containing basic acid, (ii) 10-80% by weight of a polyester containing a glycidyl group-containing vinyl monomer; 40% by weight, (iii) 10 to 70% by weight of a styrene monomer, and (iv) 0 to 60% by weight of other vinyl monomers (hereinafter referred to as this resinous product). A resin composition for a powder coating is provided, which is characterized in that it contains a polyester graft vinyl resin (referred to as a "polyester graft vinyl resin" or a "graft resin"), and [B] a polycarboxyl compound. The resin composition for powder coatings of the present invention has a baking temperature (usually 200°C or higher) when using conventional powder coatings.
It can be cured at a much lower baking temperature (approximately 170°C or lower) than that of the 170°C, and it is smooth, smooth, and has excellent sharpness, and has excellent adhesion after immersion in boiling water. "Boiling water resistant"
) has the remarkable effect of providing a coating film with excellent other physical properties. The exact reason why the resin composition for powder coatings of the present invention exhibits such excellent performance is not clear, but it is believed to be due to the composition of the polyester grafted vinyl resin and its structural method. That is, the present invention provides a polyester used for forming a graft resin in which dibasic acid units are mainly composed of isophthalic acid and/or hexahydrophthalic acid units, and ordinary terephthalic acid units are not present or even if present. In the vinyl monomer mixture to be polymerized with polyester containing a small proportion of polyester, styrene, α
- One feature is that a styrene monomer such as methylstyrene is used as an essential component. As a result, the benzene nucleus concentrations of both the polyester and the vinyl monomer mixture become close to each other, and as a result, the compatibility between the polyester and the vinyl monomer mixture improves significantly, which results in good grafting efficiency between the two. It has been discovered that the resulting graft resin forms a coating film with excellent performance as described above, particularly excellent boiling water resistance and other physical properties. In addition, in the present invention, a specific polyester having an acid value of 20 or less obtained by forming a specific prepolyester in advance and then reacting it with a polybasic acid containing a polymerizable unsaturated group is used. There are two characteristics. It has been found that the use of polyester produced by such a specific method increases the polymerization rate with the vinyl monomer and provides a vehicle resin for powder coatings that does not cause flaking. Hereinafter, the resin composition for powder coating of the present invention will be explained in more detail. (1) Polyester The polyester used to form the graft resin of the present invention has at least 50 dibasic acid units.
An acid value of 20 or less obtained by reacting a prepolyester with an acid value of 5 or less consisting of isophthalic acid units and/or hexahydrophthalic acid units in mol% with a polybasic acid containing a polymerizable unsaturated group. It is polyester. The prepolyester used according to the invention has the following formula as dibasic acid units: as well as The total amount of one or both of the isophthalic acid units and hexahydrophthalic acid units represented by is at least 50 mol% of the total dibasic acid units, preferably
Contains 60 to 90 mol%, and the rest of the dibasic acid units are of the following formula It can be a terephthalic acid unit represented by On the other hand, the alcohol component unit of the prepolyester is not particularly limited, and can be comprised of those conventionally used in the formation of polyesters, such as ethylene glycol, propylene glycol, 1,3-butylene glycol, etc. , 1,4-butylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, 1,6-hexanediol, glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, etc. Included. The prepolyester is prepared using isophthalic acid and/or hexahydrophthalic acid or ester-forming derivatives thereof (for example, acid anhydrides, acid halides, dimethyl esters, etc.), preferably dimethyl isophthalate and/or hexahydrophthalic anhydride, according to a conventional method. An acid, if necessary, together with terephthalic acid or its ester-forming derivative (e.g., acid halide, dimethyl ester, etc.), preferably dimethyl terephthalate, together with at least one of the above-mentioned alcohols, and optionally zinc acetate, litharge, lead oleate, etc. can be produced by condensation polymerization at temperatures of about 200 to about 240° C. in the presence of a catalyst such as benzoic acid,
Molecular weight may be adjusted using pt-butylbenzoic acid, benzoic acid methyl ester, and the like. The reaction ratio between the dibasic acid component and the alcohol component should be adjusted so that the acid value of the resulting prepolymer is 5 or less, preferably 3 or less. Advantageously, it is used in a proportion of 1.05 to 1.2 equivalents per equivalent of component. When using terephthalic acid or its ester-forming derivative as one component in the dibasic acid component,
The amount used is 50 mol% of the total amount of dibasic acid components used.
Below, it should preferably be kept at 40 mol% or less, and when using isophthalic acid or its ester-forming derivative and hexahydrophthalic acid or its ester-forming derivative, the proportion of both is not critical. Although the molar ratio can be varied widely, it is generally preferable to use a molar ratio within the range of 1:4 to 4:1. The molecular weight of the prepolyester is also not particularly limited and can be varied over a wide range, but generally a number average molecular weight in the range of about 500 to about 8,000, preferably about 1,000 to about 4,000 is suitable. The prepolyester produced as described above has an acid value of 5 or less, preferably 3 or less, and the prepolyester is then treated with a polymerizable unsaturated polybasic acid or a reactive derivative thereof such as an acid anhydride,
A polyester with an acid value of 20 or less is produced by reacting with acid halide, dimethyl ester, etc. As the polymerizable unsaturated polyhydrochloric acid, those having at least one ethylenically unsaturated bond and at least two carboxyl groups that can undergo addition polymerization with the vinyl monomer described below are used, such as maleic acid, itaconic acid, etc. , fumaric acid, hymic acid, etc., and examples of these reactive derivatives include:
Maleic anhydride, itaconic anhydride, hymic anhydride (3,6-endomethylenetetrahydrophthalic anhydride), and the like can be used alone or in combination of two or more. These polymerizable unsaturated polybasic acids or their reactive derivatives produce polyesters with an acid value of 20 or less,
Preferably, it can be used in a proportion of 15 or less, and more specifically, it is generally used in an amount of 0.1 to 5 parts by weight, preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the prepolyester. use. The reaction of the prepolyester with the polymerizable unsaturated polybasic acid or reactive derivative thereof is generally carried out in the absence of a solvent or in a suitable inert organic solvent at a temperature of from about 140 to about 230°C, usually for about 1~
This can be done by heating for about 6 hours. This reaction generally does not require a catalyst. The polyester thus obtained has an acid number of less than 20, preferably less than 15, and generally from about 1000 to about
8000, preferably within the range of about 1500 to about 5000. (2) Vinyl monomer In the present invention, a glycidyl group-containing vinyl monomer, a styrene monomer and, if necessary, other vinyl monomers are added to the polyester described in the previous item (1). A vinyl monomer consisting of the following is polymerized. A more specific description of each of these vinyl monomers is as follows. Glycidyl group-containing vinyl monomer: The glycidyl group-containing vinyl monomer has the following formula in the molecule: at least one, preferably only one, glycidyl group represented by and an ethylenically unsaturated bond

Monomers containing at least one, preferably only one of the formula are used, such as glycidyl acrylate, glycidyl methacrylate, glycidyl methacrylate,
Allyl glycidyl ether and the like are included. Styrenic monomer; Styrenic monomers include styrene and its substituted derivatives, such as α
-Methylstyrene, vinyltoluene, chlorostyrene, dichlorostyrene, etc. These styrenic monomers can be used alone or in combination of two or more, with styrene being preferred. Other vinyl monomers: As other vinyl monomers, those that can be copolymerized with the glycidyl group-containing vinyl monomer and/or styrene monomer are used, such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate,
Acrylic acid esters such as 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 3-hydroxypropyl acrylate; methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, 2-ethylhexyl methacrylate, 2 -Methacrylic acid esters such as hydroxyethyl methacrylate; acrylamide, N-methylacrylamide, N.
Acrylic acid amides such as N-diethylacrylamide, methacrylic acid amides such as methacrylamide, N・N-dimethyl methacrylamide, N-ethyl methacrylamide; acrylonitrile,
Examples include methacrylonitrile and vinyl acetate. These vinyl monomers can be used alone, or in combination of two or more. Among them, n-butyl acrylate, methyl methacrylate, and n-butyl methacrylate are preferred. (3) Polymerization According to the present invention, the glycidyl group-containing vinyl monomer and styrene monomer described above are polymerized in the presence of the polyester together with the other vinyl monomers described above, if necessary. It will be done. As a result, as well as the mutual polymerization of the vinyl monomers, the reaction between the vinyl monomer and/or the polymer of the vinyl monomer and the polyester finally produces a polyester-grafted vinyl resin. generate. The above polymerization involves polymerizing the above components, for example according to their own solution polymerization method, in an inert organic solvent in the presence of a suitable polymerization catalyst at a temperature of about 60 to about 150°C, followed by desorption. This can be done by using a solvent. The polymerization can also be carried out using a bulk polymerization method or a suspension polymerization method that is known per se. The proportion of the polyester and vinyl monomer used can be changed depending on the physical properties desired for the coating film formed using the powder coating of the final product, but in general, the proportion of the total resin forming component is Based on the weight of the polyester, 5 to 80% by weight, preferably 10 to 60% by weight; 10 to 40% by weight, preferably 15 to 30% by weight of the glycidyl group-containing vinyl monomer;
Styrenic monomer 10-70% by weight, preferably 20-70% by weight
60% by weight; other vinyl monomers can be used in a proportion of 0 to 60% by weight, preferably 0 to 40% by weight. Suitable inert organic solvents used in the above polymerization include, for example, ethyl acetate, buter acetate, toluene, methyl ethyl ketone, methyl isobutyl ketone, cellosolve, cellosolve acetate, and the like. As the polymerization catalyst that can be used, those used in ordinary acrylic polymerization are suitable, such as peroxides such as benzoyl peroxide and lauroyl peroxide; azobisisobutyronitrile, azobisisowalleronitrile, etc. These can be used in an amount of 1 to 10 parts by weight per 100 parts by weight of the above vinyl monomers, and mercaptans, halides, etc. The chain transfer agent is added in an amount of 0.1 to 100 parts by weight of the vinyl monomer.
It may be used in a proportion of 5 parts by weight. The resinous products obtained by the above polymerizations (graft resins) generally have a number average molecular weight in the range of about 2000 to about 20000, especially about 4000 to about 15000, and about
It is desirable to have a ring and ball softening point (measured by the method described in JIS-K-2513, hereinafter the same) in the range of 70 to about 140°C, preferably about 90 to about 120°C. In addition, the resinous product may be present in a range of about 300 to
It is desirable to have an epoxy equivalent weight within the range of about 1500, preferably about 400 to about 1400. (4) Polycarboxyl compound According to the present invention, the polycarboxyl compound used to form a resin composition for powder coating by blending with the resinous product (graft resin) obtained in the previous item (3) is Advantageously, aliphatic or aromatic compounds having at least two carboxyl groups are used, which serve as crosslinking agents for the graft resin.
Examples include maleic acid, fumaric acid, succinic acid, adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid; phthalic acid, trimellitic acid, pyromellitic acid; or acid anhydrides thereof.
Furthermore, polyester resins having two or more carboxyl groups can also be used as polycarboxyl compounds. These polycarboxyl compounds can be used alone or in combination of two or more. Among these polycarboxyl compounds, particularly preferred are sebacic acid, decanedicarboxylic acid, phthalic anhydride, and the like. (5) Preparation of resin composition for powder coating The resin composition for powder coating of the present invention can be prepared by blending the above-mentioned graft resin with a polycarboxyl compound. The amount of the polycarboxyl compound blended at that time is not critical,
Although it can be varied widely depending on the type of graft resin and/or polycarboxyl compound used, in general, the amount of the polycarboxyl compound is 0.5 to 2 per equivalent of glycidyl group in the graft resin.
It is advantageous to incorporate in equivalents, preferably from 0.6 to 1.3 equivalents. The powder coating composition of the present invention further contains additives commonly used in the preparation of powder coatings, such as curing accelerators (e.g., tin compounds such as dibutyltin oxide and triphenyltin chloride), and Preparations such as Epon 1004 (manufactured by Ciel Chemical Co., Ltd.), Modaflow (manufactured by Monsanto), etc., can also be included in conventionally used amounts. (6) Powder Coating The resin composition provided by the present invention can be baked at a lower temperature than conventional powder coatings, usually about 170°C or lower, as a vehicle resin for powder coatings. It can be advantageously used in the production of powder coatings that provide coatings that are smooth, free from flaking, have excellent sharpness, and have excellent boiling water resistance and other physical properties. A powder coating having such characteristics can be produced by adding, as appropriate, the resin composition of the present invention comprising a graft resin, a polycarboxyl compound, and, if necessary, the above-mentioned additives, according to a method known per se. Add coloring pigments (e.g. titanium oxide, carbon black, cyanine blue, red iron oxide, etc.), extender pigments (e.g. barium sulfate, calcium carbonate, etc.), coating surface conditioner and curing accelerator, etc., and heat using a three-roll mill and extruder. This can be carried out by thoroughly mixing and dispersing the mixture at a temperature of about 90 to about 140°C, and then pulverizing the resulting kneaded product. The obtained powder coating is applied to the surface of an object such as an automobile body or home appliance using an electrostatic spraying method according to a conventional method, and is applied at a temperature of about 160 to about 180℃ for about 10 to about 40℃.
By baking for a few minutes, a cured coating with excellent performance can be formed. Next, the present invention will be explained in more detail using reference examples, working examples, and comparative examples. In addition, in the following, all "parts" are "parts by weight." Reference Example 1 Production of Prepolyester A In a reaction vessel equipped with a stirrer, a thermometer, and a separator, 194 parts (1 mol) of dimethyl isophthalic acid, 194 parts (1 mol) of dimethyl terephthalic acid, and 154 parts of hexahydrophthalic anhydride ( 1 mol), neopentyl glycol 208 parts (2 mol), ethylene diglycol
124 parts (2 moles) and 0.7 parts of zinc acetate were charged.
While stirring in a nitrogen stream, the temperature was raised from 180°C to 230°C over 4 hours, and methanol and water to be distilled out were removed from the system. Thereafter, 178 parts (1 mole) of pt-butylbenzoic acid was added and the temperature was maintained at 230°C for about 5 hours to obtain prepolyester A having an acid value of 0.8 and a number average molecular weight of about 2750. Reference Example 2 Production of Prepolyester B The above Reference Example 1 is for reference except that 2 moles of dimethyl terephthalic acid is used instead of 1 mole of dimethyl isophthalic acid and 1 mole of hexahydrophthalic anhydride, that is, 3 moles of dimethyl terephthalic acid is used in total. Operated in exactly the same manner as Example 1 until the acid value was 1.0.
Prepolyester B having a number average molecular weight of 3500 was obtained. Reference Example 8 Production of Polyester A 1000 parts of the prepolyester A obtained in Reference Example 1 and 15 parts of maleic anhydride are reacted at 150°C for 2 hours. The acid value of the obtained polyester A was 9.5
The number average molecular weight was approximately 2,800. Reference Example 4 Production of Polyester B 1000 parts of the prepolyester A obtained in Reference Example 1 and 30 parts of fumaric acid are reacted at 220°C for 4 hours. The acid value of the obtained polyester B was 12 and the number average molecular weight was 3,000. Reference Example 5 Production of Polyester C 1000 parts of the prepolyester A obtained in Reference Example 1 and 80 parts of maleic anhydride are reacted at 150°C for 2 hours. The acid value of the obtained polyester C was 43 hours, and the number average molecular weight was 3500. Reference Example 6 Production of Graft Resin A 500 parts of the polyester A obtained in Reference Example 3 and 500 parts of toluene are placed in a reaction vessel equipped with a stirrer, a thermometer, and a dropping funnel, and maintained at 100°C. Into it 270 parts of styrene, 180 parts of glycidyl methacrylate
A mixture of 50 parts of n-butyl acrylate, and 20 parts of azobisisobutyronitrile was added dropwise over 3 hours. After that, the temperature was kept at 100°C for 2 hours, and then the pressure was reduced to remove the solvent. The resulting graft resin A had a softening point of 95°C, a number average molecular weight of 6,000, and an epoxy equivalent of 780. Reference Example 7 Production of Graft Resin B Using the same equipment as Reference Example 6 and performing the same operations, 400 parts of styrene, 250 parts of glycidyl methacrylate, 80 parts of methyl methacrylate, 2 −
A liquid mixture consisting of 70 parts of ethylhexyl methacrylate and 35 parts of benzoyl peroxide was added dropwise to carry out polymerization. The resulting graft resin B had a softening point of 90°C, a number average molecular weight of 7,500, and an epoxy equivalent of 590. Reference Example 8 Production of Graft Resin C 1000 parts of prepolyester B obtained in Reference Example 2 and 150 parts of maleic anhydride are reacted at 150°C for 2 hours. The acid value of the obtained polyester was 9.0 and the number average molecular weight was 3,700. Next, in Reference Example 6 above, polyester A
Except using the polyester obtained above instead of
The operation was performed in exactly the same manner as in Reference Example 6. The softening point of the obtained graft resin C was 101°C, and the number average molecular weight was
6200, and the epoxy equivalent was 800. Reference Example 9 Manufacture of Graft Resin D In Reference Example 6, polyester C obtained in Reference Example 5 was used in place of polyester A, and gelation occurred 30 minutes after completion of dropping. This gelled resin is referred to as graft resin D. Reference Example 10 Production of Graft Resin E 5 parts of maleic anhydride was further added to the prepolyester forming components of Reference Example 1, and the same procedure as in Reference Example 1 was carried out. However, the addition of pt-butylbenzoic acid was omitted and the polyester was immediately produced. The acid value of the obtained polyester was 0.5 and the number average molecular weight was 3000. Next, a graft resin E was obtained in exactly the same manner as in Reference Example 6, except that the polyester obtained above was used instead of polyester A. The softening point of this resin is 96℃, and the number average molecular weight is
7000, and the epoxy equivalent was 780. Reference example 11 Production example of resin F Styrene 270 parts, glycidyl methacrylate 180 parts
A mixture of 50 parts of n-butyl acrylate and 20 parts of azobisisobutyronitrile was added dropwise over 3 hours to 500 parts of toluene kept at 100°C, then kept at 100°C for 2 hours, and then depressurized. The solvent was removed. Resin obtained [acid value 0.5; number average molecular weight
8000; epoxy equivalent 410] A mixture of 50% by weight and 50% by weight of the polyester A obtained in Reference Example 3 was
Resin F was manufactured by kneading in a roll mill at ℃. The softening point of this resin F was 86°C. Examples 1 to 2 and Comparative Examples 1 to 8 Resins A to F obtained in Reference Examples 6 to 11 [However, because the graft resin D obtained in Reference Example 9 gelled, it was not possible to prepare a powder coating], Decanedicarboxylic acid, sebacic acid, triphenyltin chloride, dibutyltin oxide, titanium oxide, and Modaflow were blended in the proportions shown in Table 1 below, kneaded at 100°C using an extruder, and then ground with a pin disk mill. The powder coating obtained was applied to the surface of a mild steel plate to a thickness of approximately 60μ using the electrostatic coating method according to a conventional method, and then heated at 170℃.
Bake for 20 minutes.

【table】

[Table] The performance of the coating film of the powder coating obtained in each of the above examples was measured according to the following test method. The results are shown in the second section below.
Shown in the table. Boiling water resistance: Conforms to JISK5400-1970 7, 3.
After immersion in boiling water for 1 hour, a second test is performed, and the permissible limit is ○△, and depending on the degree, ◎, 〇, ○△,
Evaluate on a 5-level scale of △ and ×. Eriksen: According to JIS Z-2247. Impact resistance: JIS K54000−1970 6, 13B method [1/
2", 500g]. Salt spray resistance: reach the substrate with a razor on the painted surface 2
Draw a diagonal line on the book, spray with salt water according to JIS Z2371, and check the width (mm) of the paint film rising from the scratch. Smoothness: Wave height H was measured using Kosaka Seisakusho's SE-3 type universal surface profile measuring instrument, and H1μ, 1μ<
H1.5μ, 1.5μ<H2μ, 2μ<H3
μ and 3μ<H were evaluated as ◎, 〇, ○△, △, and ×, respectively. Sharpness: The sharpness of the image reflected on the painted surface was observed with the naked eye, and when even fairly thin lines could be distinguished, it was rated ◎; when the outline was almost invisible, it was rated △. Blocking resistance: Put 15g of powder paint into a 40mmφ test tube, leave it at 40℃ for 240 hours, then take out the sample. ◎ is the best)
Items that did not return were marked as △ or × depending on the degree of failure.

【table】

【table】

Claims (1)

[Scope of Claims] 1 [A] (i) 100 parts by weight of a prepolyester having an acid value of 5 or less, in which at least 50 mol% of dibasic acid units are isophthalic acid units and/or hexahydrophthalic acid units, is polymerized. (ii) 10 to 40 parts by weight of a polyester having an acid value of 20 or less obtained by reacting 0.1 to 5 parts by weight of a polybasic acid containing a polyunsaturated group; (iii) 10 to 70% by weight of a styrene monomer, and (iv) 0 to 60% by weight of other vinyl monomers; and [B] polycarboxyl. A resin composition for powder coating, characterized by containing a compound.