JPS5829818B2 - Polyester material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a polyester resin composition for powder coatings which is particularly excellent as a base resin for powder coatings.

Conventionally, polyester resin compositions for powder coatings consisting of polyester resin and hexaalkoxymethyl melamine or its condensate (amino resin) have been disclosed in Japanese Patent Publication No. 48, for example.
It is publicly known from Publication No.-6615 and the like.

However, polyester resin compositions that use hexaalkoxymethylmelamine or its condensate as a curing agent for polyester resins suffer from degassing marks of volatile components called "boiling" during baking, which impairs the aesthetic appearance of the painted surface. There are many cases.

Therefore, the following disadvantages were unavoidable.

○ Thick coating with a film thickness of 100 microns or less is not possible.

○ Requires baking at a relatively high temperature or for a long time while keeping the acid value low.

Furthermore, since such a resin composition for powder coating has a large proportion of polyester resin to curing agent, it is necessary to strictly control the properties of the polyester resin.

In particular, the average degree of polymerization of the polyester resin is related to delicate performances such as the fluidity smoothness of the powder coating and the gloss of the coated surface, so it needs to be controlled within a very narrow targeted range.

Methods for controlling the average degree of polymerization of polyester resin to an arbitrary degree of polymerization from 5 to 50 include: ○Method of detecting the melt viscosity of polyester from stirring power ○Method of collecting and analyzing polyester ○Method of estimating from the amount of distilled glycol Although methods for synthesizing under certain reaction conditions have been proposed, none of these methods are suitable for industrially reproducible production of polyester resins.

The present inventors have found that baking is possible even at relatively low temperatures, and 10
The result of intensive research aimed at preparing a polyester resin composition for powder coatings with good reproducibility, which can provide an excellent coated surface for aesthetic and heavy-duty anticorrosion applications without "boiling" even when applied thickly with a thickness of 0 microns or more. , has effectively achieved these objectives as follows.

That is, the present inventors have determined that the average degree of polymerization is 5 to 50, preferably 20 to 30, and the softening point is 50 to 150°C, preferably 60.
When preparing a polyester resin composition for powder coatings by mixing a polyester resin with an acid value of 4 to 10 and hexaalkoxymethyl melamine or its condensate at ~100°C, the intrinsic viscosity (phenol/tetrachloroethane-1/
An average degree of polymerization of 5 to 50, preferably 2, obtained by depolymerizing a polyester with a high degree of polymerization of 0.4 or more (measured at 20 ° C. using a mixed solvent of 1 weight ratio) with a polyhydric alcohol of 3 or more valences.
0-30, softening point 50-150℃, preferably 60-1
00°C1 A polyester resin having an acid value of 0 to 6 and having a carboxyl group in the molecule obtained by reacting the polyester resin with a divalent or trivalent or higher polyvalent carboxylic acid or an acid anhydride thereof. By mixing a polyester resin with an acid value of 6 to 30 to prepare a polyester resin for powder coatings whose acid value is controlled to an arbitrary value within the range of 4 to 10, it is possible to apply a thick coating of 100 microns or more. Even if
We have discovered scales that can be prepared with good reproducibility of polyester resin compositions that can be advantageously used in the production of powder coatings that can provide excellent coating surfaces for aesthetic and heavy-duty anticorrosion applications without boiling.
The present invention has been accomplished.

In carrying out the present invention, the polyester resin used is aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and phthalic acid, or lower alkyl esters thereof,
Lower alkyl esters of aromatic oxycarboxylic acids such as methyl P-oxybenzoate and methyl P-oxyethoxybenzoate; selected from the group of aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid and dodecanoic acid one or more acid components, ethylene glycol,
Diethylene glycol, 1,2-propanediol, ■
・3-propanediol, ■・3-butanediol, ■
・One or more types of dihydric alcohols such as 4-butanediol, neopentyl glycol, bisphenol A, and hydrogenated hisphenol A, and in some cases, three types of dihydric alcohols such as trimethylolethane, trimethylolpropane, glycerin, pentaerythritol, and mannitol. It is prepared using as a raw material one or more branched components such as polyhydric alcohols with higher valences or higher valences or polycarboxylic acids with higher valences such as trimellitic acid and pyromellitic acid, but it controls the average degree of polymerization of the polyester resin. For this purpose, an aromatic dicarboxylic acid or a lower alkyl ester thereof or/and a lower alkyl ester of an aromatic oxycarboxylic acid, or an aliphatic dicarboxylic acid and a dihydric alcohol are subjected to an esterification reaction or/and transesterification reaction, and then Intrinsic viscosity obtained by performing a polycondensation reaction (measured at 20°C using a mixed solvent of 1/1 weight ratio of phenol/tetrachlorethane) 0
．． It is prepared by depolymerizing a polyester with a high polymerization degree of 4 or more using a polyhydric alcohol of 3 or more valences.

The acid value of the polyester resin prepared by such a method is usually as low as 6 or less, and often as low as about 1 to 4.

However, powder coatings using polyester resin compositions made of polyester resins with relatively low acid values and hexaalkoxymethylmelamine or condensates thereof have a slow curing speed during baking, and cannot be used at relatively high temperatures or for long periods of time. Requires time burn-in.

In addition, the acid value of the polyester resin is derived from carboxyl groups generated by side reactions during the process of preparing the polyester resin, and in particular when controlling the average degree of polymerization, it is not possible to control the acid value to an arbitrary constant value. It is extremely difficult.

For the above reasons, the acid value of polyester resin can be controlled to an arbitrary value by mixing a calculated amount of divalent or trivalent or higher polyvalent carboxylic acid or their acid anhydride with the base polyester resin. being done.

However, in order to control the acid value to an arbitrary value of 4 to 10, the amount of divalent or trivalent or higher polyvalent carboxylic acids or their acid anhydrides to be mixed into the polyester resin with an acid value of O to 6 is The amount is extremely small, and even if various methods are tried, it is difficult to uniformly distribute the carboxyl groups on a microscopic scale, and it is difficult to produce a powder coating that can provide a beautiful coating film using such a polyester resin. It is extremely difficult.

In order to solve these problems and prepare a polyester resin composition for powder coatings that can provide a beautiful coating film, various methods are used to control the acid value of the polyester resin to an arbitrary value within the range of 4 to 10. As a result of studying methods, we have arrived at the present invention.

According to the method of the present invention, it is possible to bake at a relatively low temperature even with the same acid value, and "boiling" during baking is significantly suppressed, allowing for thick coating, making it ideal for cosmetic use or heavy-duty anti-corrosion use. It is possible to prepare a polyester resin composition with good reproducibility, from which powder coatings can be produced.

In carrying out the present invention, hexaalkoxymethylmelamine or its condensate is added to the polyester resin whose acid value has been controlled in advance or when preparing the acid value of the polyester resin, 2 parts by weight per 100 parts by weight of the polyester resin.
~20 parts by weight, preferably 4 to 8 parts by weight, are melt-mixed at 150°C or lower, preferably 120°C or lower.

Further, mixing with pigments such as titanium oxide and carbon black may be carried out at the same time as adjusting the acid value or mixing the curing agent.

In carrying out the present invention, the average degree of polymerization of the polyester resin that can be used is limited to 5 to 50 because if the average degree of polymerization is less than 5, it becomes difficult to pulverize the powder coating due to a coagulation phenomenon called blocking, and the storage stability becomes stable. On the other hand, polyester resins with an average degree of polymerization exceeding 50 are tough and cannot be pulverized by normal mechanical methods, and furthermore, their melt viscosity increases, which significantly reduces the workability of forming paints. Moreover, the flow of the coated surface during baking also deteriorates, making it impossible to obtain a beautiful coat.

In addition, the reason why the softening point of polyester resin is limited to 50 to 150°C is that blocking can be avoided with polyester resins whose softening point is less than 50°C;
The baking temperature of the paint is 160~ for polyester resins exceeding
This is because the flow of the coating film at 200° C. deteriorates, making it impossible to obtain a beautiful coating film.

Next, the present invention will be specifically explained by showing examples and reference examples.

Example 1 Dimethyl terephthalate (hereinafter abbreviated as DMT).

) Methyl P-oxyethoxybenzoate (hereinafter abbreviated as OEBM).

) Sebacic acid (hereinafter abbreviated as SEA), ethylene glycol (hereinafter abbreviated as EG).

), neopentyl glycol (hereinafter abbreviated as NPC).

), were placed in a stainless steel reactor in the amount shown in Table 1, and 1 x 10-2 mol of zinc acetate was added as a catalyst.
After performing the transesterification reaction at 50°C to 230°C and distilling off a theoretical amount of methanol, the esterification reaction was completed at 230°C to prepare a low polymer composition.

Subsequently, 2 x 1-0-2 mol of antimony trioxide and 2 x 10 mol of trimethylphosphine were added as polycondensation reaction catalysts, and the degree of vacuum was 0.5 mmHg and the reaction temperature was 27.
After preparing a high degree of polymerization polyester having an intrinsic viscosity of 0.65 by carrying out a polycondensation reaction at 0°C, the amount of trinotylolpropane (hereinafter abbreviated as TP) shown in Table 1 was prepared.

) or/and pentaerythritol (hereinafter abbreviated as PE).

) was added to conduct a depolymerization reaction to prepare polyester resins shown in Table 2.

Subsequently, succinic anhydride (hereinafter abbreviated as 5UAD) was applied to 10 kg of each polyester resin shown in Table 2.

) or trimellitic anhydride (hereinafter abbreviated as TMAD).

) in the amounts shown in Table 3, mixed and added at 150°C,
The acid value was adjusted as shown in Table 3.

Subsequently, A1 stell resin, A1 1, 2, ①, 3 2, 1 each polyester resin to which the acid anhydride of polyester 2 * * was added, hexamethoxymethylmelamine (hereinafter abbreviated as HMM).

) and acid value titanium in the amounts shown in Table 4, triblended, and then melt-mixed at 100°C to obtain an acid value of 4.6.
A polyester resin composition of No. 8 was prepared.

After finely pulverizing each of the polyester resin compositions AA to ■ shown in Table 4 using a mill, the portion passing through a 150 mesh sieve was coated with an electrostatic powder coater to give a 100X200X0.8%
The film was coated on a zinc-medium steel plate to a film thickness of 110 microns and baked at temperatures of 170°, 180, and 190°C for 30 minutes to obtain a film, and the following items were tested:
The results shown in Table 5 were obtained.

(1) Eriksen test according to JISZ2247 (2) Impact strength test DuPont type +-1kg (3) 6
00 Specular reflectance Compliant with JIS Z8741 (4) Weather resistance test Gloss retention after 100 hours treatment with Ducycle Weather Meter Example 2 Example 10 The same amount of raw material as Resin A2 in Table 1 was taken, Example 1 The reaction was carried out 10 times under the same conditions as **, and the polyester resins shown in Table 2-2 were obtained.

Subsequently, TMAD (2889C1.5 mol) was uniformly added to 10 kg of each polyester resin in Table 2-2, and 1
Mixing and addition were carried out at 50°C.

The acid value of each polyester resin obtained was 18.5 to 19.
It was within the range of 3.

Reference Example 1 □ Polyester resins Al-1, Al-2-1, and Al-31 were prepared in the same manner as in Example 1, and the results shown in Table 6 were obtained.

Next, for polyester resin 2 to 9 of A2-1,
A polyester resin A2-2 having an acid value of 81.15 was prepared by mixing and adding 6 moles (307 g) of TMADl at 150°C.

Each polyester resin in Table 6, polyester resin A2-2, succinic acid, trimellitic acid, HMM, and titanium oxide were taken in the amounts shown in Table 7, and after dry** blending,
A polyester resin composition having an acid value of 4.6.8 was prepared by melt-mixing at 100°C.

Each polyester resin composition of AJ=R shown in Table 7 was finely pulverized using a mill, and then painted, baked, and evaluated in the same manner as in Examples, and the results shown in Table 8 were obtained.

Reference example 2 DMT 56 mol, OEBM 44 mol, EG 70 mol, N
30 mol and 724 mol of PC were placed in a stainless steel reaction vessel, and 10-2 mol of zinc acetate was added as a catalyst to react with 15
Transesterification was carried out at 0 to 230°C, and after the temperature was raised to 270**°C for 2 hours from when the system became transparent, 2 x 10 to 4 mol of antimony trioxide, trimethylphosphny) 2 x 1
0” mole, vacuum degree 30 mm, Hg,
When the reaction was carried out 10 times at a reaction temperature of 270° C. for 4 hours, each polyester resin shown in Table 32 was obtained.

As is clear from a comparison of Examples and Reference Examples, the polyester resin prepared by the method of the present invention is stably synthesized with good reproducibility and at any degree of polymerization, and this polyester resin Polyester resins prepared by mixing and reacting polyhydric carboxylic acids or their acid anhydrides have little variation in acid value, and the mixedly prepared polyester resin composition for powder coatings has a relatively high temperature of 170 to 190°C. It is possible to bake at a low temperature, and even with a thick coating of 100 microns or more, it has a high 60° specular reflectance.
It provides a beautiful coating film with less boiling.

Claims (1)

[Claims] 1. In preparing a polyester resin composition for powder coating by mixing a polyester resin having an average degree of polymerization of 5 to 50, a softening point of 50 to 150°C, and an acid value of 4 to 10 and hexaalkoxymethylmelamine or a condensate thereof, Intrinsic viscosity (measured at 20°C using a mixed solvent with a weight ratio of phenol/tetrachloroethane-1-1) Average obtained by depolymerizing a polyester with a high degree of polymerization of 0.4 or more with a polyhydric alcohol of trihydric or higher valence A polyester resin with a degree of polymerization of 5 to 50, a softening point of 50 to 150'C1, an acid value of 0 to 6, and a
A polyester resin is produced by mixing a polyester resin having a carboxyl group in the molecule and having an acid value of 6 to 3°, which is obtained by mixing and reacting polyhydric or trihydric or higher valent carboxylic acids or their acid anhydrides. A method for producing a polyester resin composition for powder coatings, which comprises controlling the acid value of the polyester resin composition to an arbitrary value in the range of 4 to 10.