JPS6118586B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a resin composition for powder coatings which uses a reaction product of a polyester resin and a half-block polyisocyanate as a curing agent. Powder coating compositions using conventional OH functional resins have the following properties: (a) surface appearance such as smoothness, wrinkles, and gloss, (b) physical properties, and (c) blocking resistance.
It had the drawback of not being able to satisfy all three conditions (a), (b), and (c). In other words, powder coatings containing low-melting point resins, solid fluidizing agents, or other additives have excellent melt fluidity during baking, giving a smooth and glossy painted surface. but,
On the other hand, the melting point of the paint system is low, and there is a problem in so-called blocking resistance, in which finely pulverized particles coagulate in the high-temperature working atmosphere during baking. On the other hand, in paints that use curing agents with excellent crosslinking properties or resins with a large amount of functional groups, the molecular weight between crosslinks is small, and therefore, although they produce good results in physical property tests such as Erichsen values and bending tests, However, there is a drawback that the surface appearance is extremely poor due to the amount of condensate generated, and the appearance of the painted surface is damaged. In addition, when the curing agent is a blocked isocyanate, there is a problem of smoke generation during baking, and when an amino resin is used, problems such as formalin odor during baking adversely affect the working atmosphere remain. As a result of intensive research aimed at improving these drawbacks, the present invention has been achieved. That is, the present invention uses (A) a half-block polyisocyanate in which 20 to 80% of the moles of isocyanate groups are coated with a blocking agent containing active hydrogen, and a polyisocyanate having a number average molecular weight of 2000 to 20000 and containing active hydrogen. 10 to 45% by weight of a curing agent with a softening point of 40 to 120°C obtained by blending and reacting with a polyester resin, and (B) an OH group with a number average molecular weight of 5000 to 20000 and a softening point of 60 to 130°C. This is a resin composition for powder coating consisting of 55 to 90% by weight of a resin containing. The composition of the present invention has excellent compatibility between the curing agent and the base resin because the difference in molecular weight is small, and as a result, the smoothness and sharpness of the baked coating film are superior to other powder coatings. It also improves the appearance of armpits. Good compatibility also improves the dispersion of the curing agent and has a positive effect on physical properties. In the curing agent of the present invention, 20 to 80% of the number of moles of isocyanate groups is reacted with the polyester resin in advance, so compared to conventional blocking isocyanates, there is less blocking agent, and therefore smoke is generated less during baking. Significantly reduce environmental pollution. In addition, the coating film is free from wrinkles caused by the blocking agent, and an elegant coating film can be obtained due to the mutual effect of the above-mentioned good compatibility. The lower volatiles during baking are more economical than traditional blocked isocyanate cured forms. In addition, the curing agent of the present invention has a high softening point because its main skeleton is a high molecular weight polyester resin.
Therefore, the blocking resistance of the resulting powder coating is extremely excellent. In the present invention, the half-block polyisocyanate (a) used in the synthesis of the curing agent is (a) an aromatic or aliphatic diisocyanate, such as tolylene diisocyanate, xylene diisocyanate, phenyl At least one of isocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, methylxylylene diisocyanate, hydrated tolylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, and (b) addition with an isocyanate group. One or more blocking agents having a reactive group, such as ε-caprolactam, various alcohols, and cellosolves, are used with a molar ratio of active hydrogen to NCO of 0.2 to
Mix at a ratio of 0.8 and heat in a solvent at 40-120℃
It can be obtained by reacting for 0.5 to 8 hours. On the other hand, the active hydrogen-containing polyester resin that forms the skeleton of the curing agent has a molecular weight of 2000 to 20000, preferably forms a solid at temperatures below 50°C and a low-viscosity melt that flows well at 140 to 170°C. 5000～
13000 resin is required. The active hydrogen contained in such a resin is preferably an OH group. In addition, the OH value of such resin is 15.0 to 150.0.
mg/g, preferably 40 to 80 mg/g. The carboxylic acid that can be used as a raw material for the polyester resin that can be used in the present invention is a di- or tricarboxylic acid, an anhydride thereof, or a mixture such as a dialkyl ester (alkyl group having 1 to 4 carbon atoms) of a dicarboxylic acid. Moreover, a monocarboxylic acid can also be used in combination. As the polyhydric alcohol, trihydric or higher alcohols or a mixture of these and dihydric alcohols can be used. Representative examples of raw materials that can be used as raw materials for the polyester resin in the present invention are as follows. (a) Carboxylic acids 1,2,4-benzenetricarboxylic acid, phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, endobicyclo[2-2-1]-5heptene-2,3-dicarboxylic acid, tetrachlorophthalic acid acids, succinic acid and their anhydrides or their dialkyl esters; isophthalic acid, terephthalic acid, azelaic acid, adipic acid, sebacic acid and their dialkyl esters; benzoic acid, p
-t-butylbenzoic acid, monomethylbenzoic acid, dimethylbenzoic acid, isononitsic acid, isooctanoitsucnic acid. (b) Dihydric alcohols ethylene glycol, diethylene glycol,
Propylene glycol, trimethylene glycol, 1,3-, 1,2- and 1,4-butanediol; heptanediol, hexanediol,
octanediol, neopentyl glycol,
2,2-bis(4-cyclohexanol)propane, 2,2,3-trimethylpentane-1,3-
Diol, 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate, 1,4-cyclohexanedimethanol. (c) Trivalent or higher alcohols: glycerin, trimethylolpropane, trimethylolethane, tris(2-hydroxyethyl)isocyanurate, pentaerythritol. Raw materials other than those listed above can be used as long as they can be polyesterified and, when combined appropriately, satisfy all of the predetermined conditions of number average molecular weight softening point and OH value. It is. The polyester resin in the present invention can be produced by a conventional manufacturing method. That is, when only carboxylic acid and/or its anhydride and polyhydric alcohol are used as raw materials, the mixture is heated to 180-300°C in the presence or absence of a small amount of a solvent that can be azeotroped with water. When a dicarboxylic acid dialkyl ester is used as one of the dicarboxylic acid components, the dialkyl ester and polyhydric alcohol are first mixed with lead monoxide, lead fatty acid salt, and naphthenic acid. After esterification by transesterification by heating to 200-300°C in the presence of well-known catalysts for transesterification such as salts, lithium hydroxide, fatty acid salts of lithium, and naphthenates, carboxylic acids and/or their It can be obtained by adding anhydride and further heating to 180 to 300°C for dehydration condensation. The curing agent (A) is prepared from the half-blocked isocyanate obtained as above and the polyester resin.
To produce , the NCO group of the half-blocked isocyanate and the OH group in the polyester resin are blended so that the molar ratio is 0.5 to 2.0, and the mixture is heated at 70 to 150°C for 2 to 8 hours in the presence of an appropriate solvent. Mix. As a reaction catalyst, a tin compound such as dibutyltin oxide or triphenyltin oxide may be used. After that, by removing the solvent under reduced pressure, the non-volatile content is 99.5% or more, the softening point is 40-120℃,
A solid with a number average molecular weight of 6,000 to 25,000 is obtained. The composition of the present invention comprises 10 to 45 parts by weight of the curing agent (A), a resin (B) having a functional group capable of reacting with free isocyanate groups generated by elimination of the blocking agent, e.g. 60~130℃, number average molecular weight 5000~
55 to 90 parts by weight of 20,000 OH group-containing acrylic or OH group-containing polyester resin, as well as curing accelerators such as pigments and organotin compounds such as triphenyltin oxide and dibutyltin oxide, anti-cissing agents, or coating surface. Apply smoothing agent, etc. to 100% using a hot roll or co-kneader.
It can be obtained by melt-kneading at ~150°C and pulverizing this. Next, the present invention will be explained according to Reference Examples and Examples. In addition, parts mean parts by weight. Reference Example 1 Synthesis of half-blocked isocyanate In a reactor equipped with a thermometer, a stirrer, a reflux condenser, and a dropping funnel, isophorone diisocyanate was added.
Charge 683 parts of 65% methyl isobutyl ketone solution and raise the temperature to 70°C while stirring. While maintaining the reaction temperature at 70°C, 362 parts of a 65% solution of ε-caprolactam in methyl ethyl ketone was added dropwise over 2 hours. After the temperature was maintained at the same temperature for 1 hour after the completion of the dropwise addition, the content of free isocyanate groups in the half-blocked isocyanate obtained was examined. As a result of butylamine titration, the free isocyanate groups were 47% of the charged isocyanate groups. Reference Example 2 Synthesis of curing agent skeleton polyester resin 194.0 parts (1.0 mol) of dimethyl terephthalate, 174.6 parts (0.9 mol) of dimethyl isophthalate, and 146.0 parts (1.4 mol) of neopentyl glycol were placed in a reaction vessel equipped with a stirrer, a thermometer, and a separator. ), 1, 3-
126.0 parts (1.4 mol) of butylene glycol and 27.6 parts (0.3 mol) of glycerin were charged and melted by heating.
After melting, stir and heat further until the temperature reaches 160℃.
When the temperature reached 1.0 part of lead oleate, the mixture was further heated to 240°C and kept at this temperature for 1 hour. During this time, by-produced methanol was removed through a separator. Then 116.2 parts of isophthalic acid (0.70
mol) and 43.8 parts (0.3 mol) of adipic acid.
The temperature was reduced to approximately 180°C by this preparation.
Continue heating and when the temperature returns to 240°C, gradually add 30 parts of xylene and keep at this temperature for 2 hours. During this time, water produced as a by-product was separated from xylene using a separator and removed. After maintaining the temperature at 240°C for 2 hours, the reaction vessel was evacuated to remove xylene. The resulting resin has a softening point of 78℃, an OH value of 59.6,
The acid value was 7.1. Next, after cooling this resin to 180°C, 406 parts of methyl isobutyl ketone was added.
A 65% resin solution was obtained by keeping at 120° C. for 1 hour while heating. Reference Example 3 Synthesis of Curing Agent (A) In the same reaction vessel containing 1246 parts of the polyester resin (65% methyl isobutyl ketone solution) produced in Reference Example 2, half-blocked isocyanate (65% methyl isobutyl ketone solution) synthesized in Reference Example 1 was added. Add 314 parts of ketone solution and add 4 parts of ketone solution while continuing to stir at 90℃.
Allow time to react. After the reaction, the solvent is removed under reduced pressure at 90°C for 10 minutes, then the temperature is further raised to 140°C, the solvent is removed under reduced pressure for 15 minutes, and the contents are taken out while still fluid. The nonvolatile components of the light brown transparent solid obtained are
99.3%, its softening point is 75℃, and its number average molecular weight is
It was 10800. The free NCO value contained in the curing agent (A) was determined to be less than 0.3% by butylamine titration. Reference Example 4 Synthesis of base acrylic resin B-1 In the same reactor as Reference Example 1, n-butanol was added.
Pour 1800 parts and raise the temperature to 117℃. Add to this 800 parts of styrene, 200 parts of methyl methacrylate, 500 parts of 2-hydroxyethyl methacrylate, 400 parts of 2-ethylhexyl methacrylate, and 100 parts of methacrylic acid.
1 part, and 70 parts of azobisisobutyronitrile were thoroughly stirred and mixed, and the total amount was added to 3 parts using a dropping funnel.
Drip over time. After aging at the same temperature for 1 hour, 7 parts of additional catalyst azobisisovaleronitrile was dissolved in 200 parts of n-butanol and added dropwise to the above reaction product over 1 hour. After another hour of aging,
When the contents were heated to 150℃ and the pressure was reduced for 10 minutes to remove n-butanol from the contents, the OH value was 103 and the softening point was
108℃, number average molecular weight 8900 acrylic resin B-1
I got it. Reference Example 5 Production Example of Polyester Resin B-2 In a reaction vessel equipped with a stirrer, a thermometer, and a separator, 232.8 parts of dimethyl terephthalate, 135.8 parts of dimethyl isophthalate, and 146.0 parts of neopentyl glycol were added.
126.0 parts of 1,3-butylene glycol and 27.6 parts of glycerin were charged and melted by heating. After melting, heat it further while stirring until the temperature reaches 160℃.
℃, add 1.0 part of lead oleate, further raise the temperature to 240℃, and keep at this temperature for 1 hour. During this time, by-produced methanol was removed through a separator. Next, 116.2 parts of isophthalic acid and 43.8 parts of adipic acid were added. The temperature is approximately 180℃ with this preparation.
The temperature dropped to ℃. Continue heating, and when the temperature returns to 240℃, gradually add 30 parts of xylene to this temperature.
Keep time. During this time, water produced as a by-product was separated from xylene using a separator and removed. After being maintained at 240°C for 2 hours, the reaction vessel was evacuated to remove xylene, cooled, and the contents were taken out while still fluid. The resulting resin had a softening point of 88°C, an OH value of 49.2, and an acid value of 7.1. Example

【table】

[Table] The curing agent and base resin obtained in the reference example were blended as shown in Table 1, and to these blends was added 1 part of triphenyltin chloride as a curing accelerator, and Modaflow (Monsanto Co., Ltd.) as an anti-cissing agent. 5 parts of cyclohexanone-based ketone resin (trade name ``Aron KR'' manufactured by Mitsui Toatsu Co., Ltd.) as a coating surface smoothing agent, and 50 parts of titanium white pigment were added. These components were uniformly melted and mixed at 100° C. for 15 minutes using a hot roll mill for testing with a roll diameter of 8.8 cm. Next, this molten mixture was pulverized using a hammer mill for fine pulverization, and the powder was sieved through a 100-mesh sieve to obtain a white powder coating. In Table 1, Examples 1 and 2 are examples of powder coatings obtained by the present invention, and the column below shows Comparative Example 1 used to clarify the characteristics of the present invention.
~4. The obtained white powder paint was applied to a polished mild steel plate with a thickness of 0.8 mm using an electrostatic coating method to change the film thickness in stages, and the cured film was applied to a thickness of about 70μ. , and hardened by baking at 180℃ for 30 minutes. The film thickness at which wrinkles occur (maximum film thickness at which wrinkles do not occur) was measured for the former coated plate, and the performance test results for the coated plate coated with 70μ are shown in Table 2.

[Table] The test methods and evaluation methods for the test items listed in Table 2 are as follows. Smoothness: Depending on the degree, ◎, 〇, ○△, △, ×
And so. Sharpness: JCRI-GGD-166 type Gd meter (Nihon Shikiken
(manufactured by KK), and the larger the value from 0.1 to 2.0, the better the image clarity. Gloss value: JIS-K-5400, 6/7 (60° gloss) Smoke during baking: Depending on the degree, ◎, 〇, ○△,
It was set as △ and ×. Heating loss: This is the percentage of weight loss when approximately 10mg of each powder coating was measured at a constant temperature of 180℃ for 30 minutes using a thermobalance (manufactured by Rigaku Denki Co., Ltd.). Erichsen test value: Measured according to JIS-2-2247. The larger the value, the better the flexibility. Impact test value: According to JIS-K-5400, 6.13.3.
(1/2 inch, 500g) Blocking resistance: 15g of white enamel powder was placed in a 40mmφ test tube, a load of 20g/ ^cm2 was applied, and the sample was left at 35°C for 240 hours. If it returns to a fine powder state, depending on the degree, ◎, 〇,
It was marked as ○△, and those that did not return were marked as △ and ×.

Claims (1)

[Scope of Claims] 1 (A) A half-block polyisocyanate in which 20 to 80% of the moles of isocyanate groups are coated with a blocking agent containing active hydrogen and a number average molecular weight of 2000.
~20,000 and the softening point obtained by blending and reacting with a polyester resin containing active hydrogen.
10-45% by weight of a curing agent at 40-120°C, and (B) OH with a number average molecular weight of 5000-20000 and a softening point of 60-130°C.
A resin composition for powder coatings comprising 55 to 90% by weight of a group-containing resin. 2. The resin composition for powder coating according to claim 1, wherein the blocking agent containing active hydrogen is ε-caprolactam. 3. The resin composition for powder coatings according to claim 1, wherein the isocyanate component of the half-block polyisocyanate is isophorone diisocyanate. 4. The polyester resin containing active hydrogen is
The resin composition for powder coating according to claim 1, which is a polyester resin having an OH value of 15.0 to 150.0 mg/g. 5. The powder according to claim 1, wherein the (B) resin containing an OH group is an acrylic resin obtained by copolymerizing a vinyl monomer containing 5.0 to 50.0% by weight of an acrylate monomer containing an OH group. Resin composition for body paint. 6. The resin composition for powder coating according to claim 1, wherein the (B) resin containing an OH group is a polyester resin containing an OH group or other active hydrogen.