CN101161701A - A kind of polyester aqueous dispersion as paint in automobile and preparation method thereof - Google Patents

Abstract

The invention provides a low acid value, high molecular weight polyester aqueous dispersion that can be used as paint in automobiles, the dispersion comprises (A) water dispersible polyester resin, (B) neutralizing agent and (C ) water invention also discloses the preparation method of the polyester dispersion; the polyester aqueous dispersion has excellent storage stability, and the coating composition formed by cooperating with other components such as curing agent can be used for multi-layer coatings, especially It is suitable to be used as a paint for automobiles, and the coating film obtained after curing has excellent water resistance and stone chip resistance.

Description

A kind of polyester aqueous dispersion as paint in automobile and preparation method thereof

technical field

The invention relates to a low acid value, high molecular weight polyester aqueous dispersion used as a paint for automobiles. The coating film formed by the polyester aqueous dispersion has excellent comprehensive properties and can be widely used in the coating of various automobile bodies. Packing, the present invention also relates to the preparation method of this aqueous polyester dispersion.

Background technique

In recent years, as the concept of environmental protection has become more and more popular, restrictions on volatile emissions (VOC) have become laws and regulations in various countries. The existing solvent-based coating products and supporting coating processes on the market have violated the requirements of sustainable development.

Polyester resin has good performance as a film-forming substance. For the coating of various substrates, its paint film has the characteristics of weather resistance, solvent resistance, and strong adhesion. Therefore, from the perspective of environmental protection and limiting VOC emissions, water-dispersed polyester resin coatings have good development prospects.

Automobile body coating is a multi-layer system, usually including electrophoretic deposition primer layer, middle coat, top coat, etc., among which the middle coat can increase the adhesion between the primer and the top coat, and has a certain hardness and flexibility, providing Anti-stone chip performance of coating film. Usually, in order to improve the anti-stone chip performance, a simple and effective method is to increase the molecular weight of the resin. However, an increase in molecular weight means an increase in resin viscosity, which requires the use of more solvent.

The existing general coating process is to use solvent-based coating resin and melamine formaldehyde resin or other curing agents as film-forming substances, and obtain a coating film with suitable properties after baking and curing. However, the use of organic solvents in large quantities does not meet the requirements for limiting VOC emissions, and there are fire hazards, endangering the health of workers, and especially causing irreversible damage to the ecological environment.

European patent EP 1285937A2 discloses a water-dispersed polyester resin, which uses blocked polyisocyanate as a curing agent to obtain a coating film with excellent stone chip resistance after curing. However, the polyester dispersion has an excessively high acid value and residual carboxyl groups It will adversely affect the water resistance and salt spray resistance of the coating film.

Chinese patent CN 1549849A discloses a low-viscosity anti-gravel impact water-dispersed polyester resin coating, the organic solvent content is less than 5%, but the acid value is as high as 40-50, which also affects the water resistance of the coating film.

Contents of the invention

An object of the present invention is to provide a polyester aqueous dispersion with low acid value, high molecular weight and excellent storage stability, which can be combined with other compositions, and has good water resistance and solvent resistance after curing into a film , strong adhesion and anti-stone impact ability.

The second object of the present invention is to provide a method for preparing the aqueous polyester dispersion.

The technical solution adopted by the present invention to solve its technical problems is:

A kind of polyester aqueous dispersion as paint in automobile, it is characterized in that this dispersion contains (A) water dispersible polyester resin, (B) neutralizing agent and (C) water, described polyester resin It is to mix one or more polybasic acids and one or more polyols evenly, and carry out melt polycondensation reaction. In the late stage of the reaction, hydrophilic groups are introduced into the polyester molecular chain. After the reaction, one or more organic polyols are added. The polymer obtained by solvent dissolution has a molecular weight of 4000-8000, a hydroxyl value of less than 60mg KOH/g, an acid value of 15-35mg KOH/g, and an average particle size of less than 500nm.

The viscosity of the dispersion is lower than 20mPa·S at 40°C, and the content of organic solvent is less than 5%.

The polycarboxylic acid of the present invention can be one or more in terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, trimellitic acid, trimellitic anhydride, or 1,4- One or more of cyclohexanedicarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, and fumaric acid; polyol polyol is ethylene glycol, propylene glycol, 1,3-butane One or more of diol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanedimethanol, 1,3-propanediol, 1,6-hexanediol, and neopentyl glycol.

The polybasic acid component contains at least 50% of aromatic polycarboxylic acid by mole, and the polyol component contains at least 60% of ethylene glycol and/or neopentyl glycol by mole.

The water-dispersible polyester resins employed in the present invention have sufficient -COOH groups to be neutralized to form water-dispersible salts.

The neutralizing agent is NaOH, KOH, ammonia water, diethylamine, triethylamine, diethanolamine or dimethylethanolamine.

The dispersion also contains a curing agent, which is blocked isocyanate or amino resin.

The above-mentioned preparation method of the polyester aqueous dispersion used as the paint in the automobile includes the following steps: adopting the method of step-by-step polymerization to prepare a high molecular weight polyester resin with sufficient -COOH groups, the polyester molecular weight is between 4000 ~ 8000, the acid value is between 15～35mgKOH/g, and the hydroxyl value is lower than 60mgKOH/g; the polyester (A) is dissolved in an organic solvent, and neutralized by adding a neutralizing agent to the necessary degree of neutralization; the resulting poly The ester solution is mixed with water to form a polyester/solvent/water ternary blend, undergoes a phase inversion self-emulsification process, and pumps out the organic solvent at a temperature below 60°C.

During the polymerization reaction, a polycondensation reaction catalyst may be used if necessary, and the catalyst is an organotin type, titanate type or antimony oxide type compound.

Below is the optimum technical scheme that the present invention adopts:

The polyester resin (A) can be dispersed in the water (C) medium without using a surfactant. The acid value of the polyester resin of the present invention is greater than or equal to 15mgKOH/g and less than 35mgKOH/g, if the acid value is greater than 35mgKOH/g, the water resistance of the coating film will decrease. When the acid value is lower than 15mg KOH/g, it is difficult to form a uniform aqueous dispersion. The polyester resin contains a certain amount of hydroxyl functional groups. In order not to affect the water resistance of the coating film, the hydroxyl value should be lower than 60mg KOH/g, preferably 30-50mg KOH/g.

The number average molecular weight of the polyester resin is between 4000 and 8000, preferably 5000 to 7000. When the molecular weight is lower than 4000, it is difficult to obtain better comprehensive performance. When the molecular weight is greater than 8000 or greater, it is not easy to obtain excellent storage stability. water dispersion. There is no particular limitation on the glass transition temperature, but it is preferably between -20°C and 80°C in view of the application requirements of automotive coatings.

The polyester resin (A) of the present invention is synthesized from the following essential components: polyacid (a ₁ ), polyol (a ₂ ), other polybasic acid and polyol (a ₃ ).

The polybasic acid (a ₁ ) can be one or more of aromatic polybasic carboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, tetrahydrophthalic anhydride, and hexahydrophthalic anhydride; it can be aliphatic Carboxylic acid One or more of 1,4-cyclohexanedicarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, and fumaric acid.

Polyol (a ₂ ) can be ethylene glycol, propylene glycol, 1,3-butanediol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanedimethanol, 1,3-propanediol, 1,6-hexane One or more of diol and neopentyl glycol.

Other polyacids and polyols (a ₃ ) include trimellitic anhydride, dimethylolpropionic acid, dimethylolbutyric acid, trimethylolpropane, ε-caprolactone, and the like.

In particular, the molar percentage of the aromatic polybasic acid in the polybasic acid (a ₁ ) is at least 50%, and less than 50% will reduce the hardness and scratch resistance. The mole percentage of ethylene glycol and neopentyl glycol in the polyol (a ₂ ) is at least 60%, and less than 60% will reduce the water resistance and chemical resistance. According to the cost performance, terephthalic acid and isophthalic acid are preferably used in the aromatic polybasic acid, and the mole percentage of the aromatic polybasic acid is more than 60%.

It is also possible to include a trifunctional or higher functional polyol such as glycerol, trimethylolpropane, pentaerythritol, etc. in a molar content not to exceed 5%.

Polyester resin can be prepared by polycondensation reaction of one or more polybasic acids and one or more polyols under well-known process conditions. The chemical reaction lasted for 3-7 hours, and then the polycondensation reaction catalyst was put into it, and small molecular substances such as air and water in the system were removed by vacuum equipment, and the polycondensation reaction was carried out until the polymer reached the required molecular weight.

Depending on the situation, it may be necessary to use a polycondensation reaction catalyst, and commonly used catalysts include organotin, titanic acid, antimony compounds, etc.

In the later stage of the polycondensation reaction, a polyacid or polyol component is added to carry out depolymerization reaction under the protection of nitrogen to obtain the required acid value or hydroxyl value.

The polybasic acid used in the depolymerization reaction is preferably an aromatic polybasic acid, such as an aromatic dibasic acid (terephthalic acid, isophthalic acid, phthalic anhydride) and an aromatic polybasic acid trimellitic acid (anhydride).

The polyhydric alcohol used for the depolymerization reaction is preferably neopentyl glycol, ethylene glycol, or the like.

When removing small molecular substances such as air and water in the system, the pressure in the system is controlled at 1000Pa or lower.

The "depolymerization" method is a polymerization method to effectively control the molecular weight of polyester resin and adjust the polyester functional group. For example, if you want to synthesize polyester resin with higher molecular weight, the molecular weight is not easy to be effectively controlled under the condition of high degree of polymerization. , Therefore, adding an appropriate amount of terephthalic acid in the late stage of polymerization can initiate synchronous depolymerization and polycondensation reactions, thereby providing a suitable acid value and molecular weight for the final polyester resin.

The reaction principle is as follows:

(1) Acidolysis reaction occurs at high temperature, and -COOH group is introduced, resulting in a decrease in the degree of polymerization.

(2) A polycondensation reaction occurs to maintain the relative molecular weight of the polyester.

Neutralizer (B)

The polyester aqueous dispersion of the present invention needs to use a kind of neutralizing agent, and the neutralizing agent can neutralize the carboxyl functional group of polyester resin to produce carboxyl anion, and the mutual repulsion between these ions makes polyester resin can keep certain dispersed particles. diameter, resulting in a stable aqueous dispersion.

Substances that can be used as neutralizers include, but are not limited to, NaOH, KOH, ammonia water, diethylamine, triethylamine, diethanolamine, dimethylethanolamine, and the like.

As long as it can ensure that the aqueous dispersion of the present invention can have satisfactory dispersion stability and storage stability, the amount of neutralizing agent is not particularly limited, and the ratio of the amount of substance added to neutralizing agent to the carboxyl group contained in polyester 60% to 100%.

The water (C) contained in the dispersion is also not particularly limited, and distilled water, ion-exchanged water, tap water, industrial water, etc. can be used, and the amount of water used is 40% or more of the dispersion, and below 40%, it may be difficult to form water dispersion.

An important aspect of the present invention is that the system has undergone a phase inversion process, from W/O type to O/W type, forming a stable low-viscosity emulsion without adding surfactants.

"Phase inversion" of the present invention refers to a process of adding more water than the amount of organic solvent in the system in the organic solution system of polyester resin, so that the system can be changed from organic solution phase to O/W emulsion dispersed phase .

This process is divided into three steps. In the first step, the polyester resin is dissolved in one or more organic solvents. In this step, the percentage of the polyester resin in the solution is 30-50%. In the second step, add a certain amount of neutralizer and water, and at a certain stirring rate, control the temperature not to exceed 40°C, and carry out the phase inversion self-emulsification process. The mass ratio of the added water to the organic solvent is 2:1-5 : 1. In the third step, the temperature is controlled not to exceed 60° C., and the organic solvent is removed under reduced pressure until the mass content of the solvent in the system is lower than 5%.

The organic solvent used for dissolving the polyester can be various well-known and widely used organic solvents, including ketone solvents, aromatic hydrocarbon solvents, ether solvents, alcohol solvents, ester solvents, and the like. Typical ketone solvents include acetone, methyl ethyl ketone, 3-pentanone, 2-pentanone, 4-methyl-2-pentanone, cyclohexanone, cyclopentanone, and the like. Typical aromatic hydrocarbon solvents include benzene, toluene, xylene, and the like. Typical ether solvents include dioxane, tetrahydrofuran, and the like. Typical alcoholic solvents include methanol, ethanol, isopropanol, n-butanol, isobutanol, hexanol, cyclohexanol, and the like. Typical ester solvents include ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, methyl propionate, ethyl propionate, and the like.

The equipment used to extract the organic solvent is not particularly limited. While pumping out the organic solvent after the phase inversion self-emulsification process, it may cause a part of the water and the neutralizing agent not participating in the action to be pumped out at the same time.

Curing agent (D)

When the curing agent is amino resin, at high temperature, its methoxy group reacts with the hydroxyl group on the polyester resin molecular chain to crosslink and cure; when the curing agent is blocked isocyanate, the -NCO group reacts with the hydroxyl group on the polyester molecular chain It reacts with carboxyl groups to cause crosslinking and curing. The curing agent can be melamine resin such as cmyel 303, cmyel350 (please specify the chemical name) and so on. Blocked isocyanates such as isophorone diisocyanate (IPDI), trimerized diisocyanate (HDI) and the like may also be used.

The curing temperature is generally 100°C or higher, and it is particularly preferable to cure at a temperature of 130 to 150°C. The mass percentage of the curing agent in the total coating resin components is not more than 50%, preferably 10-30%.

The curing agent should be added before adding the pigment and other additives, and disperse with a high-speed disperser for 5-10 minutes, and adjust the speed to 600-1000r/min.

The application method of polyester aqueous dispersion is as follows:

The polyester aqueous dispersion of the present invention has excellent film-forming properties, and can form uniform and continuous resin coating films on various substrates, and various well-known methods can be used for film formation.

The polyester aqueous dispersion of the present invention may need to contain some auxiliary agents, colloidal protective agents, pigments, etc., and cooperate with an appropriate amount of curing agent to prepare a water-based automotive interlayer coating composition.

The required additives include anti-settling agents, leveling agents, defoamers, anti-knocking agents, rheology control agents, pigment dispersants, UV absorbers, wetting agents, etc.

Colloidal protective agents required include polyvinyl alcohol, carboxylated cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, modified starch, polyvinylpyrrolidone, polyacrylic acid, some vinyl polymers, and the like.

The aqueous polyester dispersion is combined with various additives, curing agents, and pigments, and the well-known paint mixing method is used to obtain a water-based automotive mid-coat coating composition that can be formed with primers and topcoats in various ways. Excellent performance composite coating.

Traditional automotive multi-layer composite film is generally carried out by three-spray and three-bake process (3C3B). The specific steps are:

Coat a layer of electrophoretic primer on the polished, pickled and phosphated metal substrate, and bake and cure;

Coating one deck of water-based polyester intermediate paint of the present invention on the primer, bake and solidify;

Then apply a layer of topcoat and bake to cure.

The water-based automobile interlayer paint composition of the present invention can adopt three sprays and two bake (3C2B) technology, and concrete steps are:

Coat a layer of electrophoretic primer on the polished, pickled and phosphated metal substrate, and bake and cure;

Coat one layer of water-based polyester intermediate paint according to the present invention on the primer, flash at 80°C for 3min;

Then apply a layer of topcoat and bake to cure.

The beneficial effects of the present invention are: a feature of the coating composition of the intermediate paint of the present invention is that the polyester resin wherein has a higher molecular weight and a lower hydroxyl value, compared with common lower molecular weight polyester resins, it can be used in Use a relatively small amount of curing agent without affecting the performance of the coating film, which also reduces the discharge of VOC in the crosslinking reaction; another feature of the intermediate paint coating component of the present invention is that the polyester resin therein has Higher glass transition temperature, when spraying, after a short flashing step, can quickly form a tougher film, and it is not easy to "bite the bottom" between the topcoat layer coated later, which is very important for realizing "wet The "wet" spray process is advantageous especially when water-based and solvent-based coatings are used. The term "biting" means that the solvent in the topcoat can easily soften the paint film of the primer, and even affect the adhesion of the primer to the bottom layer or substrate. After the topcoat is applied, the primer will be bitten. The phenomenon is called "bottom biting"

Below in conjunction with embodiment the present invention is further described.

Detailed ways

The present invention will be further described in detail below in conjunction with the examples, but not limited to the given examples. If not specified, the quantities in the examples are parts by mass.

Specific examples:

Total amount of monomer 100phr

Solvent 100～200phr

Neutralizer 3～8phr

Water 150～250phr

Curing agent 10～30phr

(1) Number average molecular weight

GPC is used to determine the number average molecular weight, and the molecular weight distribution can also be obtained through GPC analysis.

(2) acid value

Tested according to national standard GB 6743-86.

(3) Hydroxyl value

Tested according to national standard HG/T 2709-95.

(4) Glass transition temperature

Use DSC to draw glass transition temperature (Tg), sample weight: 10mg,

Program control temperature 10°C/min.

(5) Solid content

Tested according to national standard GB 1725-79

(6) Storage stability of aqueous dispersion

Take 30ml of polyester aqueous dispersion and put it into a 50ml glass container, and place it at 25°C for 60 days, and observe whether the appearance of the dispersion has any visible changes.

(7) Viscosity of water dispersion

The domestic NDJ-79 rotational viscometer was used for determination.

(8) Coating adhesion

Tested according to national standard GB 1720-1979.

(9) Water resistance of coating film

Put the standard plate coated with the coating film in a constant temperature water tank, place it at 40°C for 120h, observe the changes in the appearance of the coating film and grade it.

(10) Solvent resistance of coating film

The standard plate coated with the coating film was wiped with acetone, and the number of times of wiping until the coating film was damaged was counted.

(11) Coating film salt spray resistance

Use the salt spray test machine to simulate various environments for testing.

(12) Coating film impact resistance

Tested according to the national standard GB/T 4893.9-1992.

1. The synthesis of self-emulsifying polyester resin (A), the implementation formula is as shown in table 1.

Example 1 synthetic polyester resin (A1)

In the four-necked flask equipped with stirrer, thermometer, condenser, water separator and nitrogen protection device, add 84.1g terephthalic acid according to the formula in Table 1, 21.0g adipic acid, 14.0g ethylene glycol, 54.9g Neopentyl glycol, stir and mix evenly, heat in an oil bath, slowly raise the temperature to 160°C, then raise the temperature by 10°C every half hour until 240°C, carry out the esterification process, and keep the temperature for 5 hours. Add 0.18g of antimony trioxide, use vacuum equipment to gradually reduce the system pressure until it is lower than 1000Pa, keep the pressure, react for 4h, remove the vacuum equipment, add 6g of neopentyl glycol, react at this temperature for 2h, lower the temperature to At 100° C., the polymer was dissolved with 180 g of butanone to obtain a polyester solution.

Add 300g of the polyester solution and 3.2g of N,N-dimethylethanolamine into a flask equipped with a condenser tube and a receiver, raise the temperature to 30°C under stirring, add 250g of deionized water, and use a vacuum device to The organic solvent was removed to obtain a polyester aqueous dispersion.

Example 2 synthetic polyester resin (A2)

In the four-necked flask equipped with stirrer, thermometer, condenser, water separator and nitrogen protection device, add 80.9g terephthalic acid according to the formula in Table 1, 35.2g isophthalic acid, 17.3g ethylene glycol, 39.3 g of neopentyl glycol, stir and mix evenly, heat in an oil bath, slowly raise the temperature to 160°C, and then raise the temperature by 10°C every half hour until 240°C, carry out the esterification process, and keep the temperature for 5 hours. Add 0.38g tetrabutyl titanate, use vacuum equipment to gradually reduce the system pressure until it is lower than 1000Pa, keep the pressure, react for 4h, remove the vacuum equipment, add 7.3g trimellitic anhydride, react at this temperature for 2h, reduce the temperature to 100 °C, the polymer was dissolved with 180 g of butanone to obtain a polyester solution.

Add 300g of the polyester solution and 4.2g of N,N-dimethylethanolamine into a flask equipped with a condenser tube and a receiver, raise the temperature to 30°C under stirring, add 250g of deionized water, and use a vacuum device to The organic solvent was removed to obtain a polyester aqueous dispersion.

Example 3 synthetic polyester resin (A3)

In the four-necked flask equipped with stirrer, thermometer, condenser, water separator and nitrogen protection device, add 82.4g terephthalic acid, 34.9g isophthalic acid, 18.6g ethylene glycol, 40.1 g of neopentyl glycol, stir and mix evenly, heat in an oil bath, slowly raise the temperature to 160°C, and then raise the temperature by 10°C every half hour until 240°C, carry out the esterification process, and keep the temperature for 5 hours. Add 0.18g of antimony trioxide, use vacuum equipment to gradually reduce the system pressure until it is lower than 1000Pa, maintain the pressure, react for 4 hours, remove the vacuum equipment, add 4.0g of trimellitic anhydride, react at this temperature for 2 hours, and lower the temperature to 100°C , Dissolve the polymer with 180 g of xylene to obtain a polyester solution.

Add 300g of the polyester solution and 4.7g of N,N-dimethylethanolamine into a flask equipped with a condenser tube and a receiver, raise the temperature to 30°C under stirring, add 250g of deionized water, and use a vacuum device to The organic solvent was removed to obtain a polyester aqueous dispersion.

Example 4 synthetic polyester resin (A4)

In the four-necked flask equipped with stirrer, thermometer, condenser, water separator and nitrogen protection device, add 98.6g terephthalic acid, 17.3g isophthalic acid, 16.3g ethylene glycol, 41.2 g of neopentyl glycol, stir and mix evenly, heat in an oil bath, slowly raise the temperature to 160°C, then raise the temperature by 10°C every half hour until 240°C, carry out the esterification process, and keep the temperature for 3h. Add 0.18g of antimony trioxide, use vacuum equipment to gradually reduce the system pressure until it is lower than 1000Pa, keep the pressure, react for 4 hours, remove the vacuum equipment, add 6.6g of isophthalic acid, react at this temperature for 2h, lower the temperature The polymer was dissolved with 180 g of xylene at 100° C. to obtain a polyester solution.

Add 300g of the polyester solution and 5.9g of N,N-dimethylethanolamine into a flask equipped with a condenser tube and a receiver, raise the temperature to 30°C under stirring, add 250g of deionized water, and use a vacuum device to The organic solvent was removed to obtain a polyester aqueous dispersion.

Example 5 synthetic polyester resin (A5)

Synthetic steps and formula are the same as example 3, but add 9.6g trimellitic anhydride to carry out depolymerization.

Synthetic formula example and analysis result of table 1 polyester resin

2. Preparation of paint in water-based automotive polyester

Example 1

Pour 200g of the obtained dispersion of resin A1 into a 1L stainless steel container, add 30g of deionized water, 157.5g of TiO2, 52.5g of talcum powder, and 200g of grinding beads, and disperse at high speed for 1h until the fineness is less than 10μm. Reduce the speed of the disperser, gradually add 60g Cymel 350, and adjust the total solid content to about 55%.

Example 2

Pour 200g of the obtained dispersion of resin A2 into a 1L stainless steel container, add 30g of deionized water, 157.5g of TiO2, 52.5g of talcum powder, and 200g of grinding beads, and disperse at high speed for 1h until the fineness is less than 10μm. Reduce the speed of the disperser, gradually add 50g Cymel 350, and adjust the total solid content to about 55%.

Example 3

Pour 200g of the obtained dispersion of resin A3 into a 1L stainless steel container, add 30g of deionized water, 157.5g of TiO2, 52.5g of talcum powder, and 200g of grinding beads, and disperse at high speed for 1h until the fineness is less than 10μm. Reduce the speed of the disperser, gradually add 37.5g Cymel 350, and adjust the total solid content to about 55%.

Example 4

Pour 200g of the obtained dispersion of resin A4 into a 1L stainless steel container, add 30g of deionized water, 157.5g of TiO2, 52.5g of talcum powder, and 200g of grinding beads, and disperse at high speed for 1h until the fineness is less than 10μm. Reduce the speed of the disperser, gradually add 37.5g Cymel 350, and adjust the total solid content to about 55%.

Example 5

Pour 200g of the obtained dispersion of resin A5 into a 1L stainless steel container, add 30g of deionized water, 157.5g of TiO2, 52.5g of talcum powder, and 200g of grinding beads, and disperse at high speed for 1h until the fineness is less than 10μm. Reduce the speed of the disperser, gradually add 37.5g Cymel 350, and adjust the total solid content to about 55%.

(Note: TiO ₂ : titanium dioxide, trade name R706, produced by DuPont. Talcum powder: 3000 mesh, domestic)

3. Properties of paint cured film in waterborne automobiles

Add deionized water to the water-based automotive mid-paint obtained in the above example to adjust the spray viscosity (4 cups: 20S-25S), and let it stand for 12 hours. Use the standard board that has been coated with electrophoretic primer, spray 2 to 3 coats, level it for 10 minutes, put it in an oven to bake and solidify. Baking conditions: 140℃×25min.

TPA: Terephthalic acid IPA: Isophthalic acid ADA: Adipic acid EG: Ethylene glycol

NPG: Neopentyl glycol

PG: 1,3 Propylene Glycol TMA: Trimellitic Anhydride DA ^* : Depolymerizer

Table 2 Polyester aqueous dispersion properties

Table 3 Performance of cured paint film of water-based automotive polyester mid-coat

In summary, the paint films of Example 1, Example 2 and Example 3 have excellent comprehensive properties and meet the requirements for the use of paint in automobiles.

In Example 4, the water resistance of the paint film is slightly poor due to the large acid value of the synthesized polyester resin. And example 5 side because the consumption of trimellitic anhydride is too large when synthesizing polyester resin, cause the viscosity of the water dispersion of polyester resin is big, the water resistance of paint film is poor.

Claims (11)

1. one kind as painted polyester water dispersion in the automobile, it is characterized in that vibrin that this dispersion includes (A) and have automatic emulsifying performance, (B) neutralizing agent and (C) water, described vibrin is that one or more polyprotonic acids and one or more polyvalent alcohols are mixed, carry out melt polycondensation reaction, introduce in the reaction later stage that hydrophilic radical prepares to the polyester molecule chain, the number-average molecular weight of vibrin is higher than 4000, hydroxyl value is lower than 60mgKOH/g, acid number is between 10～30mgKOH/g, with in the neutralizing agent and after add water-dispersion, its median size is less than 500nm.

2. according to claim 1 a kind of as painted polyester water dispersion in the automobile, the content that it is characterized in that described organic solvent is less than 5%.

3. according to claim 1 a kind of as painted polyester water dispersion in the automobile, it is characterized in that described polycarboxylic acid is one or more in terephthalic acid, m-phthalic acid, phthalic acid, phthalic anhydride, trimellitic acid, the trimellitic acid 1,2-anhydride, or 1 in the aliphatic carboxylic acid, one or more in 4-cyclohexane dicarboxylic acid, Succinic Acid, hexanodioic acid, nonane diacid, sebacic acid, the fumaric acid; Described polyvalent alcohol is an ethylene glycol, 1,2-propylene glycol, 1, ammediol, 1,3 butylene glycol, glycol ether, dipropylene glycol, 1,4 cyclohexane dimethanol, 1, one or more in 6-hexylene glycol, the neopentyl glycol.

4. according to claim 3 a kind of as painted polyester water dispersion in the automobile, it is characterized in that in the described polyprotonic acid component containing at least 50% aromatic series polycarboxylic acid in mole, contain at least 60% ethylene glycol and/or neopentyl glycol in the polyol component in mole.

5. according to claim 1 a kind of as painted polyester water dispersion in the automobile, it is characterized in that described vibrin have enough be neutralized formation water-soluble salts-the COOH group, make vibrin have automatic emulsifying performance.

6. according to claim 1 a kind of as painted polyester water dispersion in the automobile, it is characterized in that 40 ℃ of following viscosity of this dispersion are lower than 20mPaS.

7. according to claim 1 a kind of as painted polyester water dispersion in the automobile, it is characterized in that described neutralizing agent is NaOH, KOH, ammoniacal liquor, diethylamine, triethylamine, diethanolamine or dimethylethanolamine.

8. according to claim 1 a kind of as painted polyester water dispersion in the automobile, it is characterized in that also including in this dispersion solidifying agent, described solidifying agent is blocked isocyanate or aminoresin.

9. the preparation method as painted polyester water dispersion in the automobile as claimed in claim 1 is characterized in that the method that it comprises the steps: to adopt melt phase polycondensation, and the preparation high-molecular weight has enough-vibrin of COOH group; Vibrin is dissolved in the organic solvent, adds neutralizing agent and be neutralized to necessary degree of neutralization; The polyester resin solution that obtains is mixed with water, and the polyester of formation/solvent/water ternary blends issues looks counter-rotating self-emulsifying action in high-speed stirring, and extracts organic solvent being lower than under 60 ℃ the temperature, makes polyester water dispersion.

10. the preparation method as painted polyester water dispersion in the automobile according to claim 9 is characterized in that having used polycondensation catalyst when polymerization, described catalyzer is organic tin, titanate ester or weisspiessglanz compounds.

11. the preparation method as painted polyester water dispersion in the automobile according to claim 9 is characterized in that adding a kind of polyprotonic acid or polyol component carries out depolymerization reaction in polymerization reaction late stage, to obtain needed acid number or hydroxyl value.