JPH0352968A - Resin composition for powder coating - Google Patents

Abstract

PURPOSE:To obtain the subject composition, containing an epoxy resin having one or more sulfoxyl groups in one molecule and a polyester resin having carboxyl groups, excellent in low-temperature curability and capable of providing films excellent in appearance, water resistance, etc. CONSTITUTION:The objective composition obtained by blending (A) an epoxy resin which is a reaction product of a diglycidyl ether type epoxy resin of 4,4'-dihydroxyphenyl sulfone with 4,4'-dihydroxydiphenyl-2,2-propane having >=0.1 mequiv. content of sulfoxyl groups in one molecule and <=2000g/equiv. epoxy equiv. with (B) a carboxyl group-containing polyester resin having 20-150mg KOH/g acid value and 60-150 deg.C softening point at 2.0-0.5 equiv. ratio of the components (A/B) and, as necessary, further adding a curing accelerator, pigment, etc., thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a novel and useful resin composition for powder coating 1I. More specifically, the present invention relates to a resin composition for an epoxy polyester powder coating that uses a specific epoxy resin containing a sulfoxyl group, has excellent low-temperature curability, and gives a weight of 1 g with excellent appearance.

[Conventional technology]

In recent years, demand for this type of powder coating has steadily increased as a resource-saving and non-polluting coating in various industries such as building materials, home appliances, agricultural machinery, and automobiles. ．． Acrylic resins, epoxy resins, polyester resins, and the like are widely used as materials for powder coatings. Among them, a certain polyester resin combination is mainly made of a saturated polyester resin whose terminal end is a carboxyl group and a diglycidyl ether type epoxy resin of bisphenol A (also called epi-bis type epoxy resin).
During the curing reaction, there is almost no volatile component, which is why the film thickness is 2.
Over a wide range of about 0 to 200 microns,
It is possible to produce a smooth and beautiful coating film without any "boiling", and it is also able to produce a coating film that is physically and chemically excellent. Therefore, it can be said that it is one of the most preferred materials for powder coatings.

On the other hand, the only fatal flaw is that polyester resins 11 mainly composed of saturated polyester resins containing terminal carboxylic groups and shrimp/bis type epoxy resins are In order to ensure desirable performance as a powder coating through a curing reaction, it is necessary to bake at a high temperature of 180°C or higher.For this purpose, tertiary amines or Low-temperature curing using so-called curing accelerators such as ξidazoles has been adopted. [Problems to be Solved by the Invention] However, if a large amount of the above-mentioned curing accelerator is used for such low-temperature curing, the appearance of the coating film may be deteriorated and corrosion resistance and water resistance may be significantly reduced. Therefore, the emergence of an extremely useful powder coating that has excellent low-temperature curing properties, as well as excellent appearance, physical properties, and corrosion resistance is desperately desired. The current situation is that there are. Therefore, based on the recognition of the current situation and the fundamental solution of various unresolved problems in the prior art, the present inventors have developed an epoxy polyester powder coating of this type.
In order to put this into practical use in the truest sense, we began intensive research. Therefore, the problem to be solved by the present invention is to provide an extremely useful resin composite for powder coatings that has excellent low-temperature curability, excellent appearance, corrosion resistance, and water resistance. That's true.

[Means to solve the problem]

As a result of intensive studies aimed at solving the problems to be solved as described above, the present inventors have determined that a specific epoxy resin having at least one sulfoxyl group in one molecule can be used with a specific polyester resin. By combining the two, we have found a resin combination for epoxy polyester powder coatings that has excellent low-temperature curing properties, appearance, corrosion resistance, and water resistance, and have brought the present invention to its full potential. That is, the present invention has as an essential feature an epoxy resin (A) having at least one sulfoxyl group in one molecule.
) and a terminal carboxyl group-containing polyester resin (B)
It is an object of the present invention to provide a resin assembly for powder coating, which includes the following.

Here, first, the above-mentioned carboxyl group-containing polyester resin (B) refers to a polyester resin having a carboxyl group at the end, which is solid at room temperature, and as a raw material for the solid polyester resin, Any method can be used as long as it provides a resin with preferable characteristic values of the condensation product, that is, an acid value in the range of 20 to 150 and a softening point by the ring and ball method in the range of 60 to 150°C. Carboxylic acids (including anhydrides and various derivatives of carboxylic acids) and polyhydric alcohols can also be employed.

Among them, the most representative examples are as follows. (11 Carboxylic phthalic acid, tetra-do-O phthalic acid, hexahyphthalic acid, tetra-dolphthalic acid, succinic acid and their anhydrides or dialkyl esters; isophthalic acid, terephthalic acid, adivic acid, azelaic acid, cepacin) Acids, trimelif] acids, anhydrides or diarykyl esters of biromellitic acid and moles; or benzoic acid, p-
tert-butylbenzoic acid, monomethylbenzoic acid, dimethylbenzoic acid, isooctanoic acid or isononanoic acid, etc. (2) Polyhydric alcohols (2-1) Dihydric alcohols ethylene glyfur, brobylene Glycol, trimethylene glycol, 1.2-,1.3- or l,4-
Butanediol, neobentyl glycol, hexanediol, hebutanediol, octanediol, 2
, 2.3-}lythylbencune-1,3 diol or 2,2'-bis(4-cyclohexanol)proban, ? 2-2) Trihydric or higher polyhydric alcohols such as glycerin, trimethylolethane, trimethylolepropanol, [························································································−

It is also possible to create a polyester resin that satisfies acid absorption and softening points within the above range by appropriately combining and treating materials other than those listed above. For example, known and commonly used raw materials can be used without any restrictions.

In order to prepare the desired polyester resin using these raw materials, conventional anti-core operations such as the melt condensation method and azeotropic condensation method are used, but the softening point of the resin can be adjusted during the assembly of the raw materials. The combination ratio of hard components such as phthalic acid, isophthalic acid, terephthalic acid, ethylene glycol or 2.2'(4-cyclohexanol)propane, and soft components such as adivic acid or -9xanediol ( This is accomplished by changing the ratio.

On the other hand, acid damage on the resin can be controlled by changing the ratio of b-carboxylic acid and polyalcohol in the raw material composition.

If the polyester resin obtained in this way has a softening point of less than 60°C, it is inevitable that the blocking resistance after forming into a powder coating (during storage or transportation, due to outside temperature and pressure) On the other hand, if the temperature exceeds 150°C, the melt viscosity of the powder coating will inevitably increase and the melting process will deteriorate. Both are undesirable because they reduce the flowability of the coating film, cause corrosion, and make it difficult to obtain a flat and smooth coating film. In addition, if the acid value of the polyester resin is less than 20, the physical properties and solvent resistance of the cured coating film will be poor, while if it exceeds 150, the storage stability of the powder coating will deteriorate. The flatness and smoothness of the cured coating will be poor, making it impractical.

Therefore, the acid value of the polyester resin (B) and 1-
f. A suitable temperature range is 20 to 150°C, preferably 20 to 10°C, and more preferably 24 to 80°C. Furthermore, regarding the terminal groups of the polyester resin (B), 60% or more, preferably 80% or more are carboxyl groups, and during the curing reaction, the epoxy group or glycidyl group that the epoxy resin (A) has It is desirable that L's reaction be dominant.

In addition, the number average molecular weight of the polyester resin (B) is 500 to io. Preferably within the range ooo
j,,1. A range of 000 to 5.000 is appropriate.

If C is less than 500, a decrease in physical properties will inevitably be observed, while if it exceeds 10,000,
Since the grindability of the powder coating inevitably deteriorates, both are preferable.

On the other hand, the above-mentioned epoxy resin (A) having a sulfoxyl group in its molecule means that the sulfoxyl group is 0. The sulfoxyl group-containing epoxy resin (A) refers to one having 1 milliequivalent/gram person (seq/g) or more.
To cite only representative examples, sulfoxyl group-containing bisphenols such as 4,4'-dihydroxydiphenyl sulfone, which is called bisphenol S, and, if necessary, 4,4'-, which is called bisphenol A. Glycidyl ether type epoxy resin obtained by reacting other sulfoxyl group-free bisphenols such as dihydroxydiphenyl-2,2-propane with shrimp chlorohydrone; , if necessary, a glycidyl ether type epoxy resin obtained by further reacting other sulfoxyl group-free bisphenols; or a glycidyl ether type epoxy resin obtained by reacting a sulfoxyl group-containing glycidyl ether type epoxy resin with a sulfoxyl group-free bisphenol. Such as epoxy resin. Of course, it is also possible to use a combination of glycidyl ester type epoxy resins.

A particularly desirable epoxy resin (A) has 0.00 sulfoxyl group in one molecule. 1 meq/g or more, preferably 0.2 gleq/g or more, and has an epoxy equivalent of 2,000 or less,
In addition, the resin has a softening point of 50 to 150°C according to the ring and ball method. The content of sulfoxyl groups is 0. If it is less than 1 meq/g, it is undesirable because it becomes difficult to obtain the curing accelerating effect based on the sulfoxyl group.
On the other hand, if the softening point exceeds 150°C, the melt viscosity of the powder coating increases, making it difficult to obtain a coating film with a smooth appearance, which is undesirable. If it exceeds, by all means,
This is not preferable because the curability decreases.

The thus obtained sulfoxyl group-containing epoxy resin (A
) and the carboxyl group-containing polyester resin (B) are (A)/(B)-2. O~0.5
An equivalent ratio of 1.5 to 0.7 is suitable, and only within this range can the object of the present invention be achieved. The resin composition for powder coatings of the present invention may further contain various known and commonly used additives such as curing accelerators, inorganic fillers, pigments, or flame retardants, as necessary. ．． Among them, the most typical curing accelerators include various imidazoles and tertiary amines, and the most typical inorganic fillers include zircon powder, These include quartz glass powder, talc powder, calcium carbonate powder, magnesia powder, calcium silicate powder, or silica powder. In addition, to describe an example of the method for preparing the composite sole of the present invention, various components blended in a predetermined composition ratio are sufficiently mixed in a ξ mixer, then melt-kneaded, and then,
The best method is to crush it using a crusher. [Effects of the Invention] The resin composite for powder coatings of the present invention has excellent low-temperature curing properties, and is extremely effective in providing coating films with excellent appearance, physical properties, corrosion resistance, and water resistance. It is useful.

(Example) Next, the layers will be specifically explained using reference examples, examples, and comparative examples.

In the following, all parts and percentages are based on weight unless otherwise specified.

Reference Examples 1 to 3 [Carboxyl group-containing polyester resin (
Preparation example of B)] 970 parts of dimethyl terephthalate, 316 parts of ethylene glycol, 530 parts of neopentyl glycol, and 0.44 parts of zinc acetate were charged into a reaction vessel, and heated at 140°C.
The transesterification reaction was carried out while raising the temperature from 220° C. to 220° C. over 3 hours. Next, 747 parts of isophthalic acid was added, and an esterification reaction was carried out while raising the temperature from 220°C to 240°C over 12 hours.

Then, 96 parts of trimellitic anhydride was added, and 24 parts of trimellitic anhydride was added.
When the reaction was carried out at 0°C for 30 minutes, 8 pieces of polyester resin were obtained, and as a result of composition analysis by nuclear resonance spectroscopy (NMR), it was found that some of the acids were phinophthalic acid. /Isophthalic acid/Trimellitic acid-4
B74 is 8/4 (mol%), and the polyol alcohol content (glycol content) is ethylene glycol/neobentyl glycol -50/50 (mol%), and the number average molecular weight (hereinafter referred to as molecular weight) is 50/50 (mol%). It was an orange-colored, transparent solid with a melting point of 2,800, a softening point of 98° C., and an acid value of 52.

Hereinafter, this will be abbreviated as polyester resin (B-1).

In step 17, polyester resins (B-2) and (B-3) as shown in Table 1 were prepared on the same frame.

Chapter ---1. ．． --- Pickling reference example 4 [Example of preparation of sulfoxyl group-containing epoxy resin (A)] In a 1e flask equipped with a thermometer, a stirrer and a heating device, "Epique 0-N 850J (Dainippon Ink & Chemicals Co., Ltd.)" was added. Diglycyl ether type epoxy resin of Bisfu Y, Nol A manufactured by Manufacturer;
/eq), 128 g of bisphenol A, 100 g of bisphenol S, and 0.1 g of 10% sodium hydroxide aqueous solution were added and reacted at 170°C for 6 hours, and the epoxy equivalent was 506 g/eq, and the softening point was is 91”C, and the melt viscosity at 150℃ is 24CI
) A target resin named S was obtained. Below, this is made using epoxy resin (
It is abbreviated as A-1), and the sulfoxyl group content of this product is 0.40 meq/g.

Reference Example 5 (same as above) In a reaction vessel similar to Reference Example Liao,
1514J (sulfoxyl group-containing diglycidyl ether type epoxy resin manufactured by the same company; epoxy equivalent: -3 1
0 g/eq. Bisfu Black Nol S content 10%]
117 g, 64 2 g of "R Ebikuron 850",
241 g of bisphpenol and 0.16 of a 10% aqueous sodium hydroxide solution were added and allowed to simmer at 190°C for 4 hours to produce a mixture with an epoxy equivalent of 600 g/eQ, a softening point of 96°C, and 150 g/eQ. Melt viscosity at °C is 40ep
A key lI niboxy resin named s was obtained. Hereinafter, this will be abbreviated as epoxy resin (A-2), and the sulfoxyl group content of this resin was 0.28 q/g.

Examples 1 to 5 and Comparative Examples 1 to 4 The respective epoxy resins and polyester resins L, face #4, and curing accelerator obtained in each reference example were mixed with Mi as shown in Table 2. The resin mixture for powder coating of the present invention was obtained by blending in a mixer, melt-kneading, pulverizing with a pulverizer, and classifying with a 150-mesh wire mesh. .

In addition, for comparison, a control resin composition for powder coating was obtained in the same manner except that a commercially available bis-type epoxy resin was used.

Next, using an electrostatic powder coating machine, the coating was applied separately onto mild steel plates specified in JIS G-3141 to a film thickness of 50 to 70 mm, and then heated at 160°C for 20 minutes. Burnt.

Afterwards, a coating film performance test was conducted on each of the thus obtained coated steel sheets. The results are summarized in the same table. The various performance evaluations were conducted in the following manner. Erichsen value: Based on JIS Z-2247.
Storage stability: Changes in coating workability and smoothness of the resulting painted surface after storing the powder coating in a constant temperature room at 35°C for one month compared to the initial state. We comprehensively evaluated whether there was a change, the degree of change, etc. DuPont impact value: Based on JIS κ-5460, the load was 1 kg and the test was performed with a 1/2 inch notch. Smoothness of painted surface: Based on visual judgment. Painted surface gloss value/
...60@Specular reflectance (%) Corrosion resistance...JIS
Compliant with K-5400. Adhesion after humidity test: temperature is 50℃ and humidity is 98℃
%RH for 120 hours, and 24 hours later, a test for adhesion was conducted. ／ ／

Claims (1)

[Claims] 1. A resin composition for powder coatings comprising an epoxy resin (A) having at least one sulfoxyl group in one molecule and a carboxyl group-containing polyester resin (B). 2. The epoxy resin (A) having at least one sulfoxyl group in one molecule has a sulfoxyl group content of 0.1 meq/g or more, and 2,000
The resin composition for powder coating according to claim 1, which has an epoxy equivalent of 0 g/equivalent or less. 3. The carboxyl group-containing polyester resin (B) is 20-
The resin composition for powder coating according to claim 1, which has an acid value within the range of 150 milligrams KOH/gram and a softening point within the range of 60 to 150C. 4. The epoxy resin (A) having at least one sulfoxyl group in one molecule is a siglycidyl ether type epoxy resin of 4,4'-dihydroxyphenyl sulfone, 4,4'-dihydroxydiphenyl-2, 2-
The resin composition for powder coating according to claim 1, which is a reaction product with propane. 5. The epoxy resin (A) having at least one sulfoxyl group in one molecule is a diglycidyl ether type epoxy resin of 4,4'-dihydroxydiphenyl-2,2-propane, and 4,4'- The resin composition for powder coating according to claim 1, which is a reaction product of dihydroxydiphenyl sulfone and 4,4'-dihydroxydiphenyl-propane.