Study on the Stability of Color Particle of Texture W/W Multicolor Coatings

Peng Hong1,Mao Weijie2 (1. Chongqing Jianzhu CollegeChongqing 400070,China; 2. Gacmotor Co., Ltd. Yichang BranchYichangHubei 443007,China

Abstract:A water-in-water(w / w)multicolor coatings with excellent comprehensive properties was prepared based on the hydrophilic isocyanateas curing agent,lithium magnesium silicate as protective glue,combination of dispersed hydroxyl acrylic resin and elastic polyacrylic latex as dispersed phase,and by using the gelation reaction between interlayer exchangeable cations in lithium magnesium silicate and hydroxyl groups in hydroxyethyl cellulose and the cross-linking of hydroxyl resin and hydrophilic curing agent.The experimental results showed that when the blending ratio of dispersion and latex was 1∶4, —NCO curing agent and —OH component was 1∶2(by molar ratio),and the bleeding was 4% with high concentration protective glue,the obtained color particles was characterized by its moderate stiffness,high color strength,and better color bleeding resistance,as well as good applicability without sagging and good storage stability.Some problems of the w/w multicolor coatings during production and application,such as bleeding,easy breakage of color particles and unevensurface after spraying were solved.

Texture Type water-in-water multicolor coating is a kind of paint that is environmentally friendly and can meet the requirements of high-grade wall decoration. Its dispersed phase and dispersion medium are water-based substances. During construction, a special high-pressure spray gun is used to spray once to obtain imitation matte stone. Texture effect. Compared with natural stone and traditional stone-like coatings, textured water-in-water multicolor coatings have the advantages of excellent decorative effect, strong designability, light weight and safety, environmental protection and energy saving, and simple construction. Therefore, they are popular with many architectural designers and consumers. Favor. However, there are still many problems at this stage, mainly in the aspects of fragile colored particles, bleeding, sedimentation, spraying during construction, and poor storage stability in the later stages.

The texture type water-in-water multicolor coating is mainly composed of a dispersed phase, a dispersion medium and a varnish. As one of the main film-forming substances in coatings, the dispersed phase is a water-based latex coating containing large-size aggregates after tinting. Its composition has a great influence on the performance of the coating film, which must meet the durability, weather resistance and water resistance of the coating film Basic requirements such as chemical properties, as well as the basic conditions of granulation such as high viscosity, high cohesion and high hydrophobicity. In this paper, the disperse phase is taken as the research object, and the effects of film-forming substances, curing agents, protective glue solutions and other components on the granulation effect and color-bleeding properties of sand-containing colored particles are analyzed.

1 Experimental section
1. 1 Main raw materials
Acrylic elastic emulsion (referred to as 4369): industrial grade, Jiangsu Sunrise Chemical Co., Ltd .; dispersion type hydroxy acrylic resin (LR8330): industrial grade, Changshu Linrun Fluorine Silicone Material Co., Ltd .; emulsion type hydroxy acrylic resin (F8590): industrial grade , Shanghai Zhuoyu Technology Co., Ltd .; Emulsion type hydroxy acrylic resin (PA4802), water-based isocyanate curing agent (OS-905): industrial grade, Guangzhou Guanzhi Chemical Co., Ltd .; lithium magnesium silicate: industrial grade, Sihong County Huizhi Fine Chemicals Co., Ltd .; Dispersant F1, Multifunctional Auxiliary Agent AMP 95: Industrial Grade, Sinopec (Shanghai) Co., Ltd .; Defoamer P1: Industrial Grade, Clariant Chemicals (China) Co., Ltd .; Fungicide J1: Industrial grade, Shanghai Rohm and Haas Chemical Co., Ltd .; propylene glycol, wetting agent, viscosity reducing agent, thickener, titanium dioxide, kaolin, quartz sand, color paste: commercially available.

1.2 Main instrument
SDF400 test dispersing sand mill: Changzhou Longxin Chemical Machinery Co., Ltd .; JJ-1 booster electric mixer: Jintan Shengwei Experimental Instrument Factory; UV-visible spectrophotometer: Beijing General Analysis General Instrument Co., Ltd .; STM-IV Stormer Viscometer: Shanghai Pushen Chemical Machinery Co., Ltd .; NDJ-1 Rotary Viscometer: Shanghai Yutong Instrumentation Factory; Spray Gun: Hangzhou Chengyu Industry and Trade Co., Ltd .; HX-T Electronics Balance: Cixi Tiandong Weighing Apparatus Factory.

1.3 Preparation method
1.3.1 Preparation of disperse phase
According to the experimental design, add water to the dispersion container, stir at low speed (about 500 r / min), add dispersant, wetting agent, and defoam in order. Agent, hydroxyethyl cellulose (HEC), etc., stir and mix well at low speed; then add pigments and fillers, and stir at 1 200 r / min for 30 minutes until the pigments and fillers are dispersed uniformly; lower the speed, add emulsion, hydroxy acrylic resin, and cure Agents, bactericides, film-forming aids, etc., add an appropriate amount of high-concentration protective gum solution after stirring well, and stir at high speed (about 1 800 r / min) for 30 minutes.

1. 3. 2 Preparation of high-concentration protective gum solution
Water and viscosity reducing agent are added in sequence. The viscosity reducing agent is completely dissolved in water under high speed stirring, and then a high concentration lithium magnesium silicate protective glue is added and dispersed at high speed (about 1 800 r / min) for 1 h until it is completely swelled in water. For the preparation of dispersed phases. Protective glue should be added several times and added slowly to avoid agglomeration in water and affect dispersion.

1. 3. 3 Preparation of dispersing medium
Add water and viscosity reducing agent in sequence, stir at high speed (about 1 800 r / min) until completely dissolved, and then add a certain amount of lithium lithium silicate protective gum solution to disperse for 1 h to complete. Swell after use.

1. 3. 4 Granulation
Mix the dispersed phase and dispersion medium adjusted to different colors into the container with a mass ratio of 1: 1. According to the specific situation of the desired colored particles, select an appropriate stirring tool and complete it at an appropriate speed. Experimental granulation to obtain multi-colored granules containing sand.

1. 4 Related performance test methods
1. 4. 1 Bleeding performance test of sand-containing colored particles
Add the dispersed phase to the dispersion medium in proportion, and then agitate and granulate. After the granulation was completed, the colored sand-containing suspension was left to stand, and the absorbance of the suspension in the wavelength range of 400 to 700 nm was measured using a UV-visible spectrophotometer (using distilled water as a reference) to characterize the degree of coloring in the system. . The lower the absorbance, the higher the light transmittance, indicating the lighter the degree of bleeding, the higher the intensity of the sand-containing colored particles, and the more stable the system; the higher the absorbance, the lower the light transmittance, indicating that the degree of bleeding is more serious and the The lower the strength of the pellets, the worse the stability of the system.

1. 4. 2 Granulation effect test of sand-containing colored granules
(1)
After the strength of colored granules is finished, take part of colored granules on a glass plate and squeeze the cut granules with a paint knife to observe the colored granules being squeezed and cut. Difficulty, to determine the intensity of color particles. Divided into 3 levels of strong, medium and weak.
(2) Appearance of colored grains
Visually inspect the shape, size, thickness, etc. of colored grains and record them by taking pictures.

1. 4. 3 construction performance test
The construction performance is judged by observing the size, shape, and color bleeding of colored particles formed under different spray gun pressures, whether the spray gun is blocked or whether the color point sags.

1. 4. 4 Viscosity test

The STM-IV Stormer viscometer was used to test the dispersion viscosity. The KU value was used to characterize the viscosity of the sample being measured. The measurement range was 40.2 to 141.0 KU. An NDJ-1 rotary viscometer was used to test the viscosity of the hydroxy resin curing agent. The viscosity of the measured sample was characterized by mPa · s, and the measurement range was 1 ~ 1 × 105 mPa · s.

1. 4. 5 Storage stability test
The prepared water-in-water multicolor coating was sealed in a closed container, placed in an oven at (50 ± 2) ° C, stored for 7 days and then taken out, and then stored at room temperature for 24 h. Observe whether there is bleeding or swelling of the colored particles. Use glass rods to take a few colored particles and place them in clear water. Observe that the colored particles are independent or adhered. Spray to test the workability and observe the spray effect.

1. 4. 6 Corrosion test
Seal the prepared water-in-water multicolor coating in a closed container, put it in an oven at (50 ± 2) ℃, store it for 7 days, then take it out, and then store it at room temperature for 24 hours. Open the container By judging whether the odor emitted by the paint is foul, determine whether the paint is mildew.

2 Results and discussion
2.1 The effect of compound emulsion on the stability of colored particles
By adding a hydroxyl-containing acrylic resin to the dispersed phase, a compound emulsion was formed with the original film-forming material acrylic elastic emulsion (4369) to make the hydroxyl group-containing The acrylic resin and the curing agent undergo a cross-linking reaction to form a high-intensity three-dimensional cross-linking network, and high-intensity wrapping of large-size aggregates can ensure that the sand-containing colored particles are not easily broken and adhered, thereby having strong anti-bleeding performance.


2. 1. 1 Selection of hydroxyacrylic resin types
Three hydroxyacrylic resins with different hydroxyl content, solid content and viscosity (the performance indicators are shown in Table 1) were prepared by mixing with acrylic elastic emulsion at a mass ratio of 1: 1. The dispersed phase is then added to the dispersion medium to granulate to obtain a colored particle suspension. After standing, the upper liquid of the suspension is taken and the degree of turbidity is observed, as shown in FIG. 1.

Table 1 The main performance parameters of dif? Ferent hydroxyl acrylic resins of colour suspension

It can be seen from Figure 1 that when the emulsion-type hydroxy acrylic resins F8590 and PA4802 are used in combination with the acrylic elastic emulsion, the color particle suspension is a pink or dark pink turbid liquid, indicating that the color slurry inside the color particles penetrated into the dispersion medium and penetrated. The degree of color is heavier. This is because the compound emulsion has poor compatibility with the “insoluble system” consisting of hydroxyethyl cellulose (HEC) and lithium lithium silicate selected in the experiment. The lithium magnesium silicate in the system adsorbs or interacts with the functional groups of the emulsion. 2. Emulsifier reacts and causes color particles to bleed. When the dispersion type hydroxy acrylic resin LR8330 is selected, the colored particle suspension is slightly turbid and the color is lighter than the dispersion medium that does not participate in granulation, indicating that the color paste in the particles has not penetrated and the colored particle stability is good. It also shows that the compatibility of the compound emulsion with the “insoluble system” is better. This is because compared with the emulsion-type hydroxyacrylic resin, the dispersion-type hydroxyacrylic resin has higher hydroxyl functionality and a smaller particle size (less than 0.08 μm), has good dispersibility to the curing agent, and the formed coating film is cross-linked. High coupling density and excellent overall performance.
Therefore, in the subsequent experiments, a dispersion-type hydroxyacrylic resin will be selected to participate in the preparation of the dispersed phase of the coating.

2. 1.2 The effect of the compounding ratio on the granulation effect and color bleeding performance of colored granules

In a water-based water-in-water colorful coating, a suitable emulsion compounding ratio is beneficial to the full reaction of the film-forming substance and the curing agent to ensure that The aggregate is effectively wrapped; on the other hand, the colored particles still have a certain elasticity, which is easy to overlap and fuse with each other during the drying process. The effect of the emulsion compounding ratio on the granulation effect of the colored particles is shown in Table 2.

Table 2 The granulation effect of color particles with different emulsion ratios

It can be seen from Table 2 that the emulsion mixing ratio has little effect on the viscosity of the dispersed phase. Due to the addition of quartz sand to the dispersed phase, the viscosity is higher than that of the flat-type water-based multicolor coating, so the dispersion speed selected when dispersing the constituent materials is also higher. However, the compounding ratio of the emulsion has a greater influence on the appearance and shape of the colored particles and the storage stability of the dispersed phase. When the compounding ratio is 1: 0. 25, the appearance of the colored particles is filamentous, the thickness is thin, and the inter-particle adhesion phenomenon is serious; as the amount of the elastic emulsion in the compounded emulsion gradually increases, the elastic emulsion itself gives the colored particles The flexibility of the particles gradually increases, and the appearance of the colored particles develops from flakes and filaments to thick pieces and strips. The adhesion between the particles is weakened and the boundaries are gradually clear. Fig. 2 shows the effect of the compounding ratio of the emulsion on the bleeding performance of the colored particles.

Fig. 2 Effect of compounding ratio on bleeding performance of the colorful granules

It can be seen from FIG. 2 that the emulsion compounding ratio has a significant effect on the bleeding performance of the sand-containing colored particles. As the proportion of the elastic emulsion gradually increases, the absorbance gradually decreases, the bleeding of the colored particles improves, and the stability gradually increases. However, when the compounding ratio was 1: 8, the absorbance slightly increased, indicating that the bleeding situation began to increase, which may be caused by the low content of hydroxyacrylic resin in the compounding emulsion. Insufficient content of hydroxy acrylic resin causes it to fail to fully react with the curing agent, resulting in too low cross-linking density, which is not enough to wrap large particle size aggregates. Therefore, in the process of stirring and granulating, the aggregates are easy to penetrate and bleed. Gel layer, which causes bleeding of colored particles.
Considering the effects of different emulsion mixing ratios on the granulation effect and color bleeding performance of colored particles in the dispersed phase, the relative ratio of the hydroxy acrylic resin to the elastic emulsion in the dispersed phase should be 1: 4.

2. 1. 3 Effect of the content of compound emulsion on the granulation effect and color bleeding performance of colored granules
Under the condition that the relative proportion of compound emulsion is determined, the amount of compound emulsion in the entire dispersed phase system is changed to explore its effect on The effect of the stability of the colored particles is shown in Table 3.

Table 3 Granulation effect of different formulated emulsions

As can be seen from Table 3, as the amount of the compounded emulsion increases, the viscosity of the dispersed phase generally increases. This is because on the premise that the content of the other components of the entire dispersed phase system is unchanged, the content of the mixed emulsion is increased, and the content of the solvent water is reduced, which results in an increase in the viscosity of the dispersed phase. In addition, the compounded emulsions with different amounts have a greater impact on the appearance and strength of the colored particles. When the content is 20%, the overall strength of the color particles is weak and the flexibility is poor. With a little stirring, the color particles will be broken due to collision with each other; with the increase of the compound emulsion content, the strength of the color particles will gradually increase. The size gradually increases. At the same time, the amount of compound emulsion has an effect on the workability. When the blending amount exceeds 40%, the gun blocking phenomenon begins to appear in the spray test, indicating that the colored particles begin to harden at this time. The actual granulation and spraying effects are shown in Figure 3.

Fig. 3 The granulation and the spraying effect of 25% and 40% emulsion dosage

Fig. 4 shows the influence of the blending amount of the compound emulsion on the bleeding performance of the colored particles.

Fig. 4 Effect of different formulation emulsions on color penetra? Tion performance

It can be seen from FIG. 4 that as the blending amount of the compound emulsion increases, the absorbance decreases first and then increases. When the amount of the emulsion is 30% to 35%, the absorbance is generally small, and at this time, the system has the lightest bleeding.
Taking into account the effects of different blending amounts of the compounded emulsion on the granulation effect, spraying effect, and bleeding performance of the colored granules, and combining cost factors, the appropriate blending amount of the compounded emulsion is about 30%.

2. 2 The effect of curing agent on the stability of colored granules
2. 2. 1 The effect of curing agent on the granulation of coatings

The experiment uses polyisocyanate as the curing agent, which is mainly based on the dispersion type hydroxyacrylic resin in the compound emulsion. Isocyanate undergoes cross-linking reaction, and the two react to form a film to obtain a higher cross-linking density. After drying, the coating film has excellent mechanical properties, good chemical resistance and weather resistance. Polyisocyanate curing agents are generally divided into two categories: unmodified low-viscosity polyisocyanates and hydrophilically modified polyisocyanates. The former is generally a low-viscosity aliphatic diisocyanate, and the latter has greatly improved the dispersibility of polyisocyanates in water due to the introduction of hydrophilic groups during the preparation process. By comparison in the literature, hydrophilic modified polyisocyanates are more suitable for the preparation of the dispersed phase of this system. The reason is that the experimental research object is water-based coatings. The hydrophilically modified polyisocyanate curing agent can be better dispersed in the granulated base paint and fully and effectively react with the hydroxyl resin to ensure that the large-size aggregates are effectively treated. Wrap, laying a solid foundation for stable granulation. The main performance parameters of the curing agent are shown in Table 4.

Table 4 The main performance parameters of cur? Ing agents

Table 5 shows the effect of different wrapping methods on the granulation effect of colored granules, and also reflects the effect of the addition of curing agent on granulation.

Table 5 Effect of different package methods on color granulation

It can be seen from Table 5 that the bleeding gel layer of the conventional flat multicolor coating cannot effectively wrap the aggregate (see wrapping method A), thus causing the colored particles to be easily broken and bleeding. However, in the case of wrapping method B, without adding a protective gum solution to the dispersed phase, the dispersed phase cannot be hydrophobized, and the thixotropic ability cannot be improved, resulting in granulation failure. Therefore, it is necessary to adopt the wrapping method C, and use hydroxy acrylic resin, curing agent and protective glue to synergistically wrap the colored granules, so as to reduce problems such as bleeding of the colored granules and broken particles during the granulation process.

2. 2. 2 The effect of the ratio of the amount of —NCO and —OH on the granulation effect and bleeding performance of colored granules
In two-component coatings, the ratio of the amount of -NCO of the curing agent to -OH of the hydroxy resin is usually used to characterize the crosslinking density of the coating film. Because the experiment uses a network structure formed by the cross-linking reaction between the hydroxy acrylic resin and the curing agent to cover the aggregate, and the cost of the curing agent is relatively high, it is necessary to study the degree of reaction between the two to find a suitable cost. The crosslinking density of the coating system optimizes the amount of curing agent. The influence of the ratio of the —NCO and —OH substances on the granulation effect of colored particles is shown in Table 6.

Table 6 Effects of molar ratio of —NCO to —OH on color granulation

It can be seen from Table 6 that as the ratio of the -NCO and -OH substances increases, the amount of the curing agent increases, and the viscosity of the dispersed phase also increases. When the ratio is greater than 1.4: 1, the viscosity of the dispersed phase is too large and exceeds the measurement range of the Stormer viscometer. In terms of particle morphology, when the ratio of the amount of the substance is 0.6: 1, the amount of the curing agent in the dispersed phase is small at this time, and the crosslinking reaction can only be performed with a part of the hydroxyl resin, so that the aggregate in the colored particles cannot be It is completely wrapped. After the granulation, the thickness of the particles is thinner and there are more broken particles, which cannot be used for construction. As the ratio of the amount of the substance increases, the amount of the curing agent also increases, and the previously excess hydroxy acrylic resin also participates in the crosslinking reaction. The aggregate in the colored particles is gradually wrapped, which is reflected in the granulation effect. The strength of the colored particles gradually increases, the thickness becomes thicker, and the number of broken particles decreases. When the ratio is greater than 1.2: 1, the difference in appearance appearance of the colored particles tends to be stable without much change. It is worth noting that, within the scope of the experimental study, the ratio of the amount of -NCO to -OH has little effect on the workability of the coating, and the spraying process is smooth. Figure 5 is the effect of the ratio of the amount of -NCO and -OH substances on the color bleeding performance of the colored particles.

Fig. 5 Effect of molar ratio of —NCO to —OH on bleeding per? Formance of the coating

It can be known from FIG. 5 that as the ratio of the amount of -NCO and -OH substances gradually increases, the absorbance of the colored particle suspension gradually decreases, and the degree of bleeding of the system gradually decreases. When the ratio of the amounts of substances is greater than 1: 1, the absorbances are all low and close to each other. This shows that the amount of curing agent at this time can ensure that it fully cross-links with the hydroxyacrylic resin, can effectively wrap large particle size aggregates, and the bleeding of the system begins to stabilize. When the ratio reaches 1.6: 1, the absorbance of the supernatant in the visible light region is the lowest, and the anti-bleeding performance of the colored particles is the best at this time. Taking into account the higher cost of curing agent, the ratio of the amount of -NCO and -OH substances in the system should be controlled around 1.2: 1.

2.3 Effect of high-concentration protective gum solution on the stability of colored particles
Adding a certain amount of high-concentration protective gum solution to the dispersed phase can not only form a flexible film on the surface of the colored particles, reflect the performance of the protective glue, but also affect the original The “hydrophilic” dispersed phase is “hydrophobic” treated to improve the stability of the colored particles. In the experiment, lithium magnesium silicate was used as the protective glue, and a high-concentration protective glue solution was prepared at a concentration of 10%. The effects of different amounts of the protective glue solution on the granulation effect of the colored particles and the absorbance of the system were investigated. The results are shown in the table. 7.

Table 7 Effect of different hectorite dosage on color granulation

It can be seen from Table 7 that the content of the high-concentration protective gum solution has a greater effect on the viscosity of the dispersed phase. As the content of the high-concentration protective gum solution increases, the viscosity of the dispersed phase increases. The degree of cross-linking of ethyl cellulose (HEC) to form flocculation is related. As the amount of high-concentration protective gum solution is increased, the degree of gel is strengthened, and the viscosity will increase. When the content of the high-concentration protective gum solution is 2.5%, the colored granules cannot stand alone due to poor suspension properties and are too soft, and the adhesion is serious, and there is a corruption phenomenon after storage. The reason is the presence of hydroxyethyl cellulose (HEC) in the dispersed phase which is not fully reacted. When the content of the high-concentration protective gum solution is 3% to 4%, the colored particles are flakes or strips, the hardness is moderate, the spraying is smooth, the edges of the colored particles are clear, and the storage corruption phenomenon gradually improves in the later stage. When the blending amount is more than 4%, the hardness of the colored particles increases obviously, and the gun blocking phenomenon begins to occur during the spraying process.

Therefore, the dosage of the high-concentration protective gum solution should be adjusted between 3% and 4% to prepare the colored particles in a desired form.
Fig. 6 shows the effect of different concentrations of high-concentration protective gum solution on the bleeding performance of colored particles.

The effect of different contents of high concentration pro? Tective gum solution on color permeation properties of color particle

It can be seen from FIG. 6 that when the content of the protective gum solution is small, the absorbance of the colored particle suspension is large, which is caused by insufficient reaction of the protective gum with the HEC gel and insufficient gel strength. With the increase of the amount of the protective gel, the gel reaction began to increase. When the amount of the protective gel solution was 4%, the absorbance was smaller than that under other dosage conditions, indicating that the color particles were bleeding less at this time. When the content of the protective gum solution is higher than 4%, the bleeding of the colored particles is increased. This is due to the excessively high content of the protective gum solution and the increase of the cation concentration, which causes the destruction of the lithium-lithium silicate card palace structure.
Considering the effects of different dosages of high-concentration protective gum solution on the granulation effect and bleeding performance of colored particles, the dosage of high-concentration protective gum solution in the dispersed phase should be controlled at 4%. At this time, colored particles of the desired form can be prepared. And the color granules have better anti-bleeding performance and the system is more stable.

3 Concluding remarks
On the basis of flat water-in-water colorful coatings, the “gelation” reaction between the exchangeable cations between the protective layers of magnesium lithium silicate and the hydroxyl groups in hydroxyethyl cellulose is supplemented with hydroxyl groups. The cross-linking effect of acrylic resin and hydrophilic curing agent to prepare textured water-in-water coatings, which solves the color particle bleeding, color particles easy to break, and spray uniformity that often occur during the production and construction of colorful water-in-water coatings. Poor and other issues. The effects of compound emulsion, curing agent and protective gum solution on the stability of colored particles were discussed in the experiment. A hydrophilic polyisocyanate was used as the curing agent. A dispersion type hydroxyacrylic resin and a polyacrylic elastomer emulsion were used to prepare the dispersed phase. The emulsion system is compatible with the “insoluble system” selected in the experiment. When the emulsion compounding ratio is 1: 4 and the blending amount is 30%, the ratio of the -NCO and -OH substances is 1: 2, and the blending amount of the high-concentration protective gum solution is 4%, the size of the prepared colored particles can be controlled , With good strength, flexibility and stability. After standing, the absorbance of the colored particle suspension in the visible light region is small, that is, the colored particle has a strong anti-bleeding ability and the coating system is stable.

Leave a Reply

Your email address will not be published. Required fields are marked *