Research on Application of High Acid Value Polyester Resin in Dry-mixed Matting Coating

Abstract: To study the influence of different types of high acid value resins on the gloss, leveling and fineness of dry-blended matting powder coatings, and to synthesize different types of high acid values ​​by changing the type, quantity and activity of monomers in the synthesis of high acid resins Polyester resin

Keywords: high acid value; dry-mix matting; triglycidyl isocyanurate; powder coating

Study on Application of High Acid Value Polyester Resin in Dry Mixed Matt Coatings

XU Guo-hui, JIA Lin, CHU Hai-tao

 (Zhejiang Guanghua Technology Co.

Abstract: The influence of different kinds of high acid value resins on gloss, leveling and fineness of dry mixed matte powder paint were studied.

Key words: high acid value; dry mixed matt; triglycidyl isocyanurate; powder coatings

0 Preface

Powder coating is a new type of coating that does not contain organic solvents, but is coated in powder form and baked, melted and leveled to solidify into a film.

Polyester resin is the main film-forming substance of powder coatings, which plays a decisive role in the performance of powder coatings.

1 Experimental part

1.

Neopentyl glycol (NPG), ethylene glycol (EG), terephthalic acid (TPA), isophthalic acid (IPA), adipic acid (ADA), monobutyl tin oxide (F4100), trimethylol Propane (TMP), Triphenylethyl Phosphorus Bromide (BETP), Hindered Phenol Antioxidant 1010, Phosphite Antioxidant 168, Triphenyl Phosphite (TPPi), TGIC (Huahui), Precipitated Sulfuric Acid Barium, titanium dioxide, benzoin, etc.

1.

6L Glass Reactor: Self-assembly; Cone and Plate Viscometer: BROOKFIELD 2000+H, American Bollefei; Differential Scanning Calorimeter: DSC1, METTLER TOLEDO; Twin Screw Extruder: SLJ32, Shandong Shengshida Machinery Technology Co.

1.

Put alcohol and F4100 into the reaction kettle according to the amount of formula, wait for it to melt and raise the temperature of the kettle to 120°C, put the polybasic acid into the kettle in turn, vent nitrogen and slowly raise the temperature to 241°C and keep it warm, during which the column top temperature does not exceed 101℃, add antioxidant TPPi, take a sample to measure the acid value of 11~15mg KOH/g, cool to below 220℃, add polybasic acid for acid hydrolysis, continue to heat up to 240℃ and react for 3~4h, when the resin is clarified, sample and test the acid value 62~64mg KOH/g, then vacuum polycondensation, acid value 50~54mg KOH/g can be vented, and finally add a small amount of material, and discharge at 200 ℃
.
Among them, A1, A2, and A3 correspond to resins synthesized with different triphenylethylphosphorus bromide additions (BETP) (0, 0.
05%, 0.
1%); C, F, A1, and B are the same BETP and EG additions, respectively Under the same amount, different amounts of TMP (2%, 2.
5%, 3%, 4%) synthetic resin; E, D, A1, G are respectively the same amount of BETP and TMP, different amounts of EG (0%, 2%) %, 4%, 6%) synthetic resin
.
In addition, the low acid resin used in the slow component is Resin X produced by the company
.

1.
4 Analysis of physical and chemical properties of polyester resin

The acid value of the polyester resin is tested according to GB/T6743-2008; the viscosity is tested according to ASTM D4287, the test temperature is 200℃, the 5# rotor, 200r/min; the glass transition temperature is tested according to GB/T19466.
2-2004, the heating rate is 20℃/ min
.

1.
5 Powder coating and coating preparation

Add the experimental resin, TGIC, pigments, fillers, etc.
into the mixer according to the formula and mix them thoroughly, then melt and extrude → cool and press → crush → sieving → powder, and then electrostatically spray on the cold-rolled steel plate with thickness control It is 70~90μm, and the powdering formula is shown in Table 1
.

1.
6 Powder and coating performance testing

Mixed powder curing conditions: 200℃*15min; powder gelation time: 200℃ test; boiling test: constant temperature water bath 100℃/2h; weather resistance test according to European profile standard, QUVB-313 light intensity 0.
75W/m2, light 4h@50℃, condensation 4h@40℃; dry mixing gel time refers to the gel time of fast component powder and slow component powder at 50:50 dry mixing, measured at 200℃; temperature resistance test: 230 ℃/1h
.
Surface tension test: a) When measuring the contact angle, titrate a drop of pure test liquid onto a solid sample, record the drop with a camera, and evaluate the video image; b) Measure at the tangent point of the cut surface line of the drop profile The contact angle θ, the better the wetting effect, the smaller the angle, when fully wetted, the angle is 0°; c) According to the Young’s equation that has been proven for more than 200 years, the contact angle θ, solid SFE, liquid SFT and liquid Calculate the interfacial tension IFT with the solid
.

2 Results and discussion

2.
1 The influence of the amount of BETP on polyester resin and its dry-blended matting powder coating

As shown in Table 2, the acid value of the synthesized polyester is controlled between 51~53mgKOH/g, from A1 to A3.
With the increase in the amount of curing accelerator BETP in the synthesis of polyester resin, the gelation time of dry blending decreases from 118s.
At 67s, the leveling properties of the coatings obtained by dry mixed powders are getting worse and worse, and the fineness is getting worse.
The storage stability of the mixed powders brought about by this will also become worse.
This is because the increase in BETP improves The activity of the one-component reaction is increased, and the reaction speed during the one-component curing is accelerated, so that the leveling property of the dry-mixed matting coating becomes worse, and the difference in the reaction speed of the fast and slow components is also enlarged, resulting in fineness.
Getting worse
.

Combining Table 2 and Figure 2, we can see that from A1 to A3, the curing accelerator BETP increases, the gel time of the fast component becomes shorter and shorter, and the gloss of the mixed powder coating decreases from 25.
0% to 20.
2%.
This is because the high acid value is fast.
Component and low acid value 34 Xu Guohui and other high acid value polyester resins in dry-blended matting coating application research Discontinuity, so the better the matting effect, the lower the gloss [4]; but it can be seen from Figure 2 that when BETP is added to a certain amount, although the reaction speed continues to increase, the gloss of the matting coating no longer decreases.
This is because the excess BETP causes most of the fast-component paint film to be formed, while the slow-component paint film may only form a small part, making the fast-component paint film act like a "matting filler", and the continuous microscopic roughness does not increase.
Therefore, the gloss of the mixed powder no longer decreases; at the same time, in combination with Table 2, the increase in BETP also leads to the deterioration of leveling and fineness
.
Therefore, the amount of BETP should be well controlled under the conditions of good matting effect, leveling and fineness
.

Figure 3(a) is the non-isothermal curing curve of the one-component powder of synthetic resin and low acid resin X, and Figure 3(b) is the fitting curve of apparent activation energy obtained by fitting the Arrhenius equation
.
It can be seen from Figure 3(a) that from A1 to A3, with the increase of BETP, the peak temperature (Peak) of high acid value fast component powder solidification decreased from 179.
58°C to 168.
93°C, indicating that the addition of the accelerator BETP reduced the system reaction The activation energy increases the speed of the fast component and powder mixing reaction, which is consistent with the result obtained in Figure 3(b)
.

It can be seen from Table 3 that from A1 to A3, with the increase of BETP, the boiled color difference becomes larger and larger.
This may be because the fast component reacts faster and faster, and when the slow component is dry mixed and cured to form a film, the surface The microscopic roughness increases and the discontinuity of the paint film increases.
During the boiling process, water molecules are more likely to enter the coating from the surface fault defects, further destroying the surface and the interior of the coating; in addition, the curing reaction is too fast, which will also cause the coating The weakened adhesion to the substrate will also reduce the boiling resistance of the matting coating
.
As for the temperature resistance, unlike boiling, the surface of the matting coating will not be corroded by small molecules, and the amount of BETP added is very small, so the added amount of BETP has almost no change in the color difference under the baking condition of 230°C
.

Synthesize the changing laws of various properties brought about by BETP, so the amount of BETP should be controlled in resin synthesis
.

2.
2 The effect of TMP addition on polyester resin and its dry-blended matting powder coating

As shown in Table 4, the acid value of the synthesized polyester is controlled between 51~53mgKOH/g, from C to B.
As the amount of TMP in the synthesis of polyester resin increases, the melt viscosity of the polyester resin increases significantly.
The conversion time is reduced from 146s to 78s.
The leveling properties of the coatings obtained by dry-mixed powder are getting worse and the degree of fineness is not much different.
This is because the increase of TMP improves the cross-flow of high acid value polyester resin powder coatings during curing.
The combined density also speeds up the reaction speed during curing; at the same time, the rapid increase of the resin viscosity causes the combined effect to cause the leveling of the matting coating to deteriorate
.
In addition, TMP has three highly reactive hydroxyl structures.
Its addition increases the density of the polyester molecular spatial network structure, hinders the free movement of the chain segments, and significantly increases the glass transition temperature of the polyester resin.
Improve the storage stability of resin and powder [7]
.

Combining Table 4 and Figure 4, we can see that from C to B, when TMP increases from 2% to 4%, the gel time of the fast component becomes shorter and shorter, and the gloss of the dry-mix matte coating decreases from 30.
3% to 20.
3%, indicating that TMP The addition of TMP can also reduce the matting gloss.
There may be two reasons: the addition of TMP improves the reactivity of the fast component and stretches the curing time with the slow component; the slow component uses a low acid value resin generally with a larger molecular weight.
The toughness is good, and the high acid has poor toughness due to the addition of TMP.
The shrinkage degree of the two is inconsistent during dry mixing and curing, which further forms the micro roughness.
Therefore, the addition of TMP can also improve the matting effect
.
However, the increase of TMP will also cause the viscosity of the system to rise sharply, destroying the leveling of the matting coating
.

Figure 5 shows the non-isothermal curing curve of one-component powder.
From C to B, as TMP increases, the peak temperature (Peak) of high acid value and fast component powder curing gradually decreases, which means the curing reaction is activated.
It can be reduced, and the addition of TMP improves the reaction activity of the system, which is consistent with the change law of the gel time of the fast component
.

Table 5 shows the boiling and temperature resistance test results of the matting coating
.
It can be seen from Table 5 that from C to B, with the increase of TMP, the boiled color difference tends to decrease.
This may be because the increase of TMP increases the molecular weight and spatial network structure of the high acid value resin, thereby increasing the matting paint The cross-linking density of the film hinders the erosion of water molecules on the coating surface, improves the boiling resistance, and reduces the color difference; on the other hand, because the dry blending extinction is based on the difference in curing and shrinkage of the fast and slow components, microscopic discontinuities are generated.
Therefore, the faster the reaction rate of the fast component is, the greater the surface roughness of the paint film, and the larger the boiling color difference.
This conclusion can be obtained based on the boiling test results in Table 3.
Therefore, the abnormal situation of A1 color difference becoming larger occurs
.
For the temperature resistance test, the amount of TMP added under the experimental conditions has little effect on the color difference of the temperature resistance of 230 ℃
.

In summary, the addition of TMP is beneficial to matting, boiling, and resin storage stability (Tg), but its addition also sharply increases the viscosity of the system and reduces the leveling of the coating
.

2.
3 The effect of EG addition on polyester resin and its dry-blended matting powder coating

As shown in Table 6, the acid value of the synthesized polyester is controlled between 51~53mgKOH/g, from E to G.
As the amount of EG in the synthesis of the polyester resin increases, the Tg of the polyester resin does not change much, indicating that and Compared with neopentyl glycol, EG with a short carbon chain structure is also rigid, does not reduce the Tg of the resin, and does not affect the storage stability of the resin.
From the perspective of cost, it is cheap and can be used for multiple purposes; dry blending gelation time Distributed between 100~120s, the difference is not big, so the leveling and fineness of the obtained dry-mixed matting powder coating is not much different
.

It can be seen from Figure 6 that from E to G, when the ethylene glycol EG increases from 0% to 6%, the gel time of the high acid value fast component does not change much; while the gloss of the dry-mixed matting coating decreases from 27.
8% to 23.
1% This is mainly because after EG (48.
4mN/m) replaces part of neopentyl glycol (35.
8mN/m), the surface tension of the high acid polyester resin increases, which in turn increases the surface tension of the fast component powder.
When the two components are mixed and cured, the difference in surface tension between the fast component and the slow component is increased by the ethylene glycol of the high acid resin, and the incompatibility of the powder during curing increases, which in turn reduces the gloss of the coating surface and achieves the effect of matting.

.
Figure 7 shows the relationship between the surface tension of high acid value polyester and the amount of EG added: as EG increases, the surface tension of the polyester resin increases
.

Figure 8 shows the non-isothermal curing curve of one-component powder curing
.
It can be seen from Figure 8 that from E to G, with the increase of EG, the peak temperature of high acid value and fast component powder solidification does not change much.
This may be because ethylene glycol and neopentyl glycol have the same glycol structure and cannot Increasing the crosslinking density of the system like TMP does not promote the curing process, which is consistent with the law of fast component gelation time shown in Figure 6
.

Table 7 shows the boiling and temperature resistance test results of the matte coating
.
It can be seen from Table 7 that from E to G, with the increase of EG, the color difference in boiled water gradually becomes larger.
This may be because EG does not have a side dimethyl structure like neopentyl glycol and cannot effectively shield water molecule protection.
The structure of ester bonds and the surface of the coating cause water molecules to easily invade the matte coating at high temperatures, resulting in discoloration of the coating.
On the other hand, in the synthesis of polyester, the ethylene glycol molecule has a single structure and is easier to etherify, resulting in more synthetic resins.
Many ether bonds increase the hydrophilicity, resulting in poor water resistance of the coating
.
As for the temperature resistance, the increase in EG and the larger the color difference are mainly due to the small molecular weight of EG itself, the poor temperature resistance, and the small molecular weight of resins synthesized by EG
.

In summary, the addition of EG is beneficial to matting, but its addition also reduces the resistance of the coating
.

2.
4 The influence of three variable factors on the aging results of paint film

Figure 9 shows the powder coating QUVB 313 aging test results of the synthesized polyester samples.
The test standard is the time it takes for the gloss retention rate to drop to 50% of the initial gloss
.
It can be seen from Figure 9(a) that the addition of BETP has basically no effect on the aging time of the powder coating.
When the gloss retention rate is reduced to 50%, the time consumption is basically maintained at about 310h; in Figure 9(b), the TMP increases and the aging time is maintained.
When the light rate drops to 50%, the time-consuming is slightly increased.
It is possible that the addition of TMP increases the crosslinking density during powder curing and improves the resistance of the coating to light and moisture.
Therefore, the addition of TMP can improve the coating to a certain extent.
In Figure 9(c), when EG increases and the gloss retention rate drops to 50%, the time-consuming gradually decreases, indicating that the addition of EG reduces the weather resistance of the coating.
This may be due to the single molecular structure of ethylene glycol.
It is easier to etherify than neopentyl glycol, resulting in synthetic resins containing more ether bonds, which have poor weather resistance
.

2.
5 The influence of three variable factors on the glass transition temperature of powder

It can be seen from Table 8 that the Tg of the various high-acid resin powders synthesized in the experiment all reached 56℃ or higher, and the physical storage stability reached the requirement; in addition, as analyzed above, the high-activity high-acid resin powder is easy to be activated due to its low activation energy.
The chemical reaction occurs slowly
.
Therefore, the prepared high acid resin powder should not be stored for a long time
.

3 Conclusion

(1) Under the experimental conditions, with the increase of BETP, the gelation time of the fast component is shortened, the dry-mixed matting gloss decreases, the leveling becomes worse, the boiling resistance becomes worse, and the weather resistance is almost unchanged
.

(2) As TMP increases, the gel time is shortened, and the matting gloss decreases, but the leveling performance becomes worse
.

(3) With the increase of EG, the surface tension of the resin increases, and the matting gloss decreases, but the boiling, temperature and weather resistance properties all decrease
.

(4) Therefore, if you want to obtain a fast-component high acid value polyester that takes into account all aspects of performance, the use of polyester resin synthesis monomers and additives needs to be comprehensively evaluated, plus the control of resin indicators, and many factors are considered.
, Continuous cross-experiment can be perfected
.

(5) In addition, the performance of dry-mixed matting coating is the result of the combination of fast components, slow components, pigments, fillers, and additives.
Only when a variety of factors are properly adjusted can a balanced and excellent matting powder coating be obtained.
Layer
.

references

[1] Feng Sulan, Zhang Yufei.
Powder Coatings [M].
Beijing: Chemical Industry Press, 2004: 1-64.

[2] Nan Renzhi.
Powder Coating and Painting Technology [M].
Beijing: Chemical Industry Press, 2014: 43-47.

[3] Ma Zhiping, Xie Jing, Li Yong, et al.
Synthesis and performance study of polyester resin for 93/7 type TGIC cured impact resistant and easy matting powder coatings [J].
Coatings Industry, 2019, 49 (3): 33 -37.

[4] He Tao, Gu Yuxin, Xie Jing, et al.
Preparation and performance study of carboxy-terminated polyester resin for high weather resistance two-component matting powder coatings[J].
Coatings Industry, 2014, 44(3): 1-8.

[5] Ying Mingyou, Yu Zhiqin, Tang Minglin, et al.
Proceedings of the 2018 China Aluminum Processing Industry Annual Conference [C].
Foshan: China Nonferrous Metal Processing Industry Association, 2018: 785-795.

[6] Zhou Weiming, Zhai Chunhai, Wu Deqing.
Synthesis and application of polyester resin for outdoor hydroxyalkylamide-cured dry-mix matting powder coatings[J].
Coatings Industry, 2018, 48(10): 25-29.

[7] Zeng Li, Liu Liang, Peng Haomin, et al.
Synthesis of hybrid polyester resin for indoor thermal transfer powder coatings [J].
Paint Industry, 2020, 50(2): 50-56.