JPS5829820B2 - Polyester materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel polyester resin composition having particularly favorable properties as a material for powder coatings.

Powder coatings have the advantage of being easier to prevent pollution than conventional solvent-based coatings, being able to be coated thickly with one coat of 100 microns or more, and being able to collect and reuse the paint. It has many advantages and has shown remarkable growth in recent years.

Normally, in order to use a resin as a paste resin for a powder coating, it is desirable that the following requirements be satisfied.

(1) Can be ground into micro powder at room temperature.

(2) The pulverized powder does not flora during transportation or storage.

(3) Pigmentation is easy at relatively low temperatures.

(4) Scales that form a strong and beautiful coating by painting and baking.

(5) The coating film has excellent properties such as weather resistance, heat resistance, and corrosion resistance.

Until now, many materials have been provided as base resins for powder coatings, but there is still no ideal material that can satisfy all of the requirements.

For example, resin compositions for powder coatings consisting of polyester resin and amino resin such as hexamethoxymethylmelamine are disclosed in Japanese Patent Publication No. 48-6615 and Japanese Patent Publication No. 48-3.
It is conventionally known in Japanese Patent Application Laid-open No. 5709, Japanese Patent Application Laid-Open No. 1045-1982, Japanese Patent Application Laid-Open No. 31248-1982, and Japanese Patent Application Laid-open No. 94723-1989.

However, in these known examples, aromatic dicarboxylic acids such as isophthalic acid or aliphatic dicarboxylic acids such as adipic acid are copolymerized in order to lower the softening point and melt viscosity of polyester resin in order to improve the workability of forming paints. There are many examples of polyester resin H copolymerized with 5 mol% or more of aliphatic dicarboxylic acid or 20 mol% or more of aromatic dicarboxylic acid with poor symmetry.
Fats are known to have the effect of lowering the softening point and melt viscosity to improve the workability of making paints, but they often have extremely poor blocking resistance, making it difficult to crush by normal mechanical means, and making it difficult to store them. Alternatively, the blocking phenomenon during transportation causes serious disadvantages from an industrial standpoint.

The present inventors have discovered a special effect by copolymerizing a terephthalic acid component with a p-oxybenzoic acid component having good symmetry,
That is, (1) although the softening point is significantly lowered, the secondary transition point is hardly lowered.

Therefore, although the workability of forming the coating material is greatly improved, there is no decrease in blocking resistance at all.

(2) Excellent crushability is provided.

(3) A hard coating film with excellent gloss can be obtained.

In order to develop a polyester resin composition that is ideal as a material for powder coatings by taking advantage of the throat effect, we aim to improve the crushability, blocking resistance, workability of coating, coating film performance, etc. of polyester resin compositions. Balance it (
The present invention was achieved as a result of extensive research into the composition, number average degree of polymerization, secondary transition point, acid value, and amount of hexaalkoxymethylmelamine as a curing agent of the polyester resin.

That is, in the present invention, the terephthalic acid component is 30 to 80 mol%.
, p-oxybenzoic acid component 20-65 mol% and aliphatic dicarboxylic acid 0-5 mol% as main acid components, ethylene glycol 30-90 mol% and neopentyl glycol 10-70 mol% as main alcohol components Trivalent or higher polyhydric alcohol or/in an amount that does not cause gelling as
and a number average polymerization degree of 11 to copolymerized with polyhydric carboxylic acid
50, which is obtained by reacting a polyester resin with a secondary rearrangement point of 40 to 70°C with a dicarboxylic acid or/and a polyhydric carboxylic acid of 3 or more valences, or an anhydride thereof at a temperature of 180°C or higher, and contains carboxyl in the molecule. polyester resin having an acid value adjusted to an arbitrary value within the range of 4 to 12, and hexaalkoxymethylmelamine or its condensate (M is the alkoxy group possessed by hexaalkoxymethylmelamine or its condensate). A polyester resin composition for powder coatings is obtained by mixing amounts that satisfy the following formula: equivalent number (H is the equivalent number of hydroxyl groups in the polyester resin).

The polyester resin composition of the present invention is prepared, for example, by the following method.

That is, dimethyl terephthalate as a terephthalic acid component and p-oxyethoxymethylbenzoate as a p-oxybenzoic acid component are transesterified using ethylene glycol and neopentyl glycol in the presence of a transesterification catalyst such as zinc acetate, and then Intrinsic viscosity obtained by adding a polycondensation reaction catalyst such as antimony trioxide and carrying out a polycondensation reaction under reduced pressure [in a mixed solvent of phenol/tetrachloroethane = 1/1 (weight ratio) at 20 °C]
] A polyester with a high degree of polymerization of 0.4 or more, preferably 0.6 or more is prepared by using a substantially non-volatile polyhydric alcohol or/and an ester having at least one alcoholic hydroxyl group in one molecule. A depolymerization reaction is carried out to prepare a polyester resin having a controlled number average degree of polymerization in the range of 11 to 50, and then the acid value of the polyester resin is adjusted to any value in the range of 4 to 12. After controlling the temperature, the obtained polyester resin and hexaalkoxymethyl melamine are heated to 150°C or lower, preferably 120°C, together with a pigment and a leveling agent, if necessary.
It can be prepared by melt mixing at the following temperatures.

However, the polyester resin composition of the present invention is not limited to the polyester resin composition prepared by the above method.

In addition to this, the polyester resin of the present invention may contain aliphatic dicarboxylic acids such as co-phosphoric acid, adipic acid, azelaic acid, and sebacic acid as is or with aliphatic dicarboxylic acids in an amount of 5 mol% or less. After completion of the transesterification reaction, a product esterified with a dialcohol such as ethylene glycol can be added to the reaction system for copolymerization.

In addition, alcohol components other than ethylene glycol and neopentyl glycol include 1,2-propanediol,
■・3-propanediol 1,3-butanediol,
1,4-butanediol, 1,6-hexanediol,
Diethylene glycol, cyclohexane dimetatool, etc. can be used in an amount of up to 50 mol% of the total alcohol component.

In addition, trivalent or higher polyhydric carboxylic acid components used in the present invention include trimellitic acid, pyromellitic acid, or their anhydrides, and trivalent or higher polyhydric alcohol components include glycerin, trimethylolethane,
Examples include trimethylolpropane, pentaerythritol, cichentaerythritol, mannitol, and the like, and these branching molecules can be used in amounts that do not cause gelation depending on the number average degree of polymerization of the polyester resin.

The number average degree of polymerization of the polyester resin used in the present invention is 11
-50 is suitable; if a polyester resin with a number average degree of polymerization exceeding 50 is used, the melt viscosity when making it into a paint will be high, making it difficult to make it into a paint at low temperatures, and furthermore, the resin itself will be tough. This is not preferable because it makes it difficult to pulverize by ordinary mechanical pulverization.

Further, when a polyester resin having a number average degree of polymerization of less than 11 is used, it is not preferable because the crushability and blocking property deteriorate regardless of the composition.

Substantially nonvolatile alcohols or esters used in the depolymerization reaction to control the number average degree of polymerization include the aforementioned polyhydric alcohols or dicarboxylic acids, trivalent or higher polyhydric carboxylic acids, dicarboxylic acid anhydrides, Bis-β hydroxyethyl terephthalate, bis-β- obtained by reacting a trivalent or higher polyhydric carboxylic acid anhydride, oxyacid or their lower alkyl ester with a dialcohol.
Hydroxyethyl isophthalate, bis-β-hydroxyethylbutarate, p-oxyethoxy(β-hydroxyethyl)benzoate, trisβ-hydroxyethyl trimellitate, tetraβ-hydroxyethylpyromellitate, dineopentyl sebacate or There are copolymerized low polymers thereof, and they can be used alone or in combination of two or more.

The acid value of the polyester resin is adjusted by mixing the polyester resin with a dicarboxylic acid, a trivalent or higher polycarboxylic acid, or an anhydride thereof at a temperature of 180°C or higher, preferably 200°C or higher. It is necessary to react one or more carboxyl groups per molecule so that the polyester resin has carboxyl groups in its molecules, and to control the acid value to any value within the range of 4 to 12.

The acid value of the polyester resin used in the present invention is suitably in the range of 4 to 12. If the acid value is less than 4, the speed of the crosslinking reaction will be slow and curing will be insufficient. On the other hand, if the acid value exceeds 12, the crosslinking reaction will be insufficient. The rate of reaction is too fast, making it difficult to obtain a smooth coating film, which is undesirable.

Hexaalkoxymethylmelamine or its condensate used as a curing agent in the present invention is used in an amount that satisfies the following formula.

If the amount of the curing agent is outside the range shown in the above formula, curing during baking will be insufficient, making it difficult to obtain a tough coating film, which is not preferred.

Next, the present invention will be explained in more detail with reference to Examples and Reference Examples.

Example 1 Dimethyl terephthalate (hereinafter abbreviated as DMT) and methyl p-oxyethoxybenzoate (hereinafter OEB) were added in the amounts shown in Table 1.
(abbreviated as M), ethylene glycol (hereinafter abbreviated as EG),
Neopentyl glycol (hereinafter abbreviated as NPC) was placed in a stainless steel reactor, 0.01 mol of zinc acetate was added as a catalyst, and a transesterification reaction was carried out at 150 to 250°C under normal pressure to remove the theoretical amount of methanol from the reaction system. After removal, 0.02 mol of trimethylphosphny) and 0.02 mol of antimony dioxide were added, and a polycondensation reaction was performed at 270°C under reduced pressure to prepare a highly polymerized polyester with an intrinsic viscosity of 0.65 to 0.68. Then, trimethylolpropane (hereinafter abbreviated as TP)** or/and pentaerythritol (hereinafter abbreviated as PE) in the amount shown in Table 1 was added and heated at 270°C.
A depolymerization reaction was carried out to prepare polyester resins shown in Table 2.

To each polyester resin shown in Table 2, trimellitic anhydride (hereinafter abbreviated as TMAD※) in the amount shown in Table 3 was added and reacted at 200°C for 60 minutes to adjust the acid value shown in Table 3. .

Next, with the formulation shown in Table 4, 10
A polyester resin** composition was prepared by kneading at 0°C for 5 minutes.

After pulverizing each of the obtained polyester resin compositions using a Micron Victory Mill VP-1 type pulverizer, 100×2
00 was evaluated, and the results shown in Table 5 were obtained.

(1) Eriksen test; JIS Z 224
7.

(2) Impact resistance test; DuPont type 1/4- ※※
500g.

(3) Boiling water resistance test: Erichsen test 2 hours after wastewater treatment.

(4) Acetone resistance test; JIS K 6911
In accordance with

(5) 60° specular reflectance; conforms to JIS Z 8741.

(6) Weather resistance test; Sunshine Weather Camera 5
Gloss retention after 00 hours exposure.

In addition, even when the powder of each polyester resin composition was left at 40° C. for one week, no blocking occurred.

Example 2 Polyethylene terephthalate) 10.37 kg (54 moles as a terephthalic acid component), polyethylene oxybenzony) 6.89 kg (42 moles as a p-oxybenzoic acid component), sebacic acid 0.81 kg (4 moles), EG
2.48 kg (40 mol) and NPC 6.24 kg (
60 mol) in a stainless steel reactor and heated to 150-250°C.
A depolymerization reaction and an esterification reaction were carried out, followed by a polycondensation reaction and a depolymerization reaction in the same manner as in AI of Example 1 to obtain a number average degree of polymerization of 25, a secondary dislocation point of 50°C, and a softening point of 80°C.
, carboxyl group 69.4 geq/t, hydroxyl group 5
A polyester resin of 98.6 geq/t was prepared.

The acid value of the obtained polyester resin was adjusted and made into a paint in the same manner as AI in Example 1 to prepare a polyester resin composition with M/H = 1.39, which was then crushed, painted, and baked. The coating film was evaluated and the results shown below were obtained.

Erichsen〉9 pieces, impact resistance〉5oCrIL, boiling water resistance〉9 momme Good acetone resistance, 600 specular reflectance 105, weather resistance 98%.

Example 3 10.75 kg of polyethylene terephthalate (56 mol as a terephthalic acid component), 7.22 ky of polyethylene oxybenzoate (44 mol as a p-oxybenzoic acid component), 3.72 kg (60 mol) of EG and 4.16 kg of NPC (40 mol). Similar to Example 2, a depolymerization reaction, a polycondensation reaction, and a depolymerization reaction were carried out to obtain a number average degree of polymerization of 25, a secondary rearrangement point of 55°C, a softening point of 85°C,
Carboxyl group 66.8geq/t, hydroxyl group 604
．． A 6 geq/t polyester resin was prepared.

Subsequently, the acid value was adjusted and the coating was made to obtain M/H=1.
No. 38 polyester resin compositions were prepared, pulverized, coated, and baked, and the coating films obtained were evaluated, and the results shown below were obtained.

Eriksen〉9 Demons, impact resistance 50 CrrL, boiling water resistance〉
9 pieces, good acetone resistance, 6-part specular reflectance 102%, weather resistance 95%.

Reference Example Polyester resins shown in Table 6 were prepared in the same manner as AI in Example 1, except that in the depolymerization reaction, instead of 4 mol of TP, 5 mol of TP1 or 20 mol of TP was used.

Polyester resin with a number average degree of polymerization of 66.7 is tough, so it is not only difficult to pulverize it by mechanical pulverization.
Due to its high melt viscosity, it could not be made into a paint at temperatures below 150°C.

In addition, polyester resin with a number average degree of polymerization of 5 is difficult to mechanically crush due to blocking properties, and as with AI in Example 1, however, hexamethoxymethylmelamine 5
A polyester resin composition with M/H = 0.89 was prepared using 20 parts instead of 1 part, and the polyester resin composition was freeze-pulverized, painted, and baked, but a beautiful coating film could not be obtained due to significant "boiling". I couldn't.

Reference Example 2 Using the same polyester resin as AI of Example 1, polyester resin compositions having acid values and M/H shown in Table 7 were prepared.

Each polyester resin composition was crushed, painted, and baked in the same manner as in Example 1 to obtain the results shown in Table 8.

In addition, since the polyester resin composition 1-D also exhibited significant blocking properties, it was freeze-pulverized.

Comparing Examples and Reference Examples, it is clear that the polyester resin composition of the present invention is an extremely ideal material for powder coatings.

The present invention has been achieved by ideally balancing the composition, number average degree of polymerization, secondary rearrangement point, acid value, and amount of curing agent of the polyester resin, and it has been achieved by ideally balancing the composition, number average degree of polymerization, secondary rearrangement point, acid value, and amount of curing agent. The object of the present invention is to provide a polyester resin composition that has excellent workability in chemical processing and can form an excellent coating film.

Claims (1)

[Scope of Claims] 1 The main acid components are 30 to 80 mol% of a terephthalic acid component, 20 to 65 mol% of a p-oxybenzoic acid component, and 0 to 5 mol% of an aliphatic dicarboxylic acid, and 30 to 90 mol% of ethylene glycol. and neopentyl glycol 10~
A polyester resin with a number average degree of polymerization of 11 to 50 and a secondary rearrangement point of 40 to 70°C, which is copolymerized with 70 mol% of the main alcohol component and an amount of trivalent or higher polyhydric alcohol or/and polyhydric carboxylic acid that does not cause gelling. A compound having a carboxyl group in the molecule obtained by reacting a dicarboxylic acid or/and a polyhydric carboxylic acid of trivalent or higher valence or anhydride thereof at a temperature of 180°C or higher and having an acid value in the range of 4 to 12. Polyester resin adjusted to an arbitrary value and hexaalkoxymethylmelamine or its condensate (M is the number of equivalents of alkoxy groups in hexaalkoxymethylmelamine or its condensate, H is the number of equivalents of hydroxyl groups in the polyester resin) A polyester resin composition for powder coatings obtained by mixing amounts satisfying the following formula.