Simple and efficient coating agent preparation process

Abstract

The invention relates to a simple and efficient coating agent preparation process. The process is particularly suitable for a preparation process of a wax emulsion type coating agent taking natural wax as a film forming substance. The process adopts a one-step emulsification method and comprises the following steps: heating and mixing fatty acid, natural wax, water and an emulsifier in a closed reaction kettle, adding a neutralizer to adjust the pH value, heating to an emulsification temperature, further heating to 100-120 DEG C to form pressure in a system, effectively reducing or eliminating bubbles generated in the emulsification process, and then cooling and filtering to obtain a stable emulsion product. Compared with a traditional two-step method or a multi-kettle process, the process is simple in equipment, convenient to operate, high in emulsion stability, remarkable in bubble control effect and suitable for large-scale continuous production. The obtained wax emulsion can be widely applied to the fields of fruit and vegetable preservation, seed coating, biological medicine and the like, and has good economic and popularization values.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of high polymer functional materials, food contact materials and emulsion preparation process, and specifically relates to a simple, efficient and low-cost film forming agent preparation process, which is especially suitable for the preparation process of wax emulsion type film forming agent with natural wax as the main film forming material. Based on simplifying the traditional emulsification process, the process introduces a pressure emulsification bubble control technology, effectively solves the problem of difficult elimination of foam in the emulsification process, significantly improves the production efficiency and product quality, and is suitable for the large-scale preparation of surface functional coating materials in food, agricultural, daily chemical, biological and pharmaceutical industries. BACKGROUND

[0002] In recent years, food film forming agent (also known as food wax emulsion) is a kind of functional material that can form a dense protective film on the surface of food, agricultural products or related materials, which can effectively block oxygen and moisture, delay decay and metamorphic, improve product appearance, and prolong shelf life, and is widely used in fruits, vegetables, eggs, baked foods, aquatic products, pharmaceutical raw materials and their packaging materials and other fields.

[0003] The film forming agents currently used in the market can be roughly divided into two categories according to the source and nature of the main component wax: natural waxes such as beeswax, shellac, Brazil palm wax, rice bran wax, etc., which are natural, safe and renewable, and have good film forming properties, biodegradability and application compatibility; petroleum-based waxes such as paraffin wax and microcrystalline wax, which have low raw material cost but poor biodegradability, and long-term use has food contact safety risks. In the actual film forming agent production process, wax materials usually need to be emulsified and dispersed in water phase by means of high shear stirring, high temperature dissolution, high speed homogenization, etc. to form a stable emulsion system. However, such conventional process generally has the following outstanding problems. First, the amount of emulsifier added is large: in order to ensure the stability and film forming properties of the emulsion, a large amount of emulsifier is often added, and the emulsifier is easy to induce a large amount of foam under high-speed stirring, resulting in a decrease in the effective volume utilization rate of the reactor. The second is that the foam is generated seriously and difficult to control: a large amount of air is entrained to form foam or microbubble during stirring or homogenization, which not only affects the appearance and use performance of the product, but also significantly prolongs the production cycle and reduces the production line efficiency. The third is that the process flow is complex: some processes need to use multiple reactors, stepwise feeding and temperature control emulsification, which is complicated to operate, has high equipment investment and high production cost.

[0004] Although some patents have tried to optimize the emulsion system of wax emulsion, the problem of difficult control of foam has not been effectively solved.

[0005] For example, Chinese invention patent CN101633785A discloses a paraffin emulsion for waterproofing artificial board and its preparation method, which uses paraffin, hydrophilic non-ionic surfactant, oil ester and water to form a paraffin emulsion by high-speed (3000 rpm) stirring. Although the waterproof performance of artificial board is improved, this method requires a large amount of surfactant, and a large amount of bubbles is generated during high-speed stirring, which needs to be defoamed for a long time or remains in the product, affecting the quality.

[0006] For example, patent CN105860856A discloses a wax emulsion for leather polishing, which uses Brazil palm wax, polyester wax and paraffin mixed and then melted at high temperature, and the emulsion is prepared by dispersing and emulsifying for 0.5-1.0 hours under stirring condition of 1000-2000 rpm. This process also generates a large amount of foam which is difficult to eliminate during emulsification, further increasing the complexity and cost of operation.

[0007] Based on the above problems, the inventors propose a one-step emulsification process with simplified process, higher efficiency and controllable foam, by introducing a closed pressurized emulsification control strategy, which effectively suppresses the generation and accumulation of foam while improving the emulsification quality, so that the preparation of foam-free, homogeneous and stable wax emulsion can be realized without the aid of additional equipment. This method is particularly suitable for film-forming agent systems using various waxes as the main film-forming material, and is widely applicable to fields such as fruit and vegetable preservation, seed coating, biological medicine and other fields with high requirements for film-forming quality, and has significant technical popularization value and industrialization prospect. SUMMARY

[0008] (I) Technical problems solved The present application aims to provide a simple, efficient and controllable foam wax emulsion preparation process, which introduces a one-step emulsification process and a closed pressurized control technology to significantly reduce the generation and residual problems of foam during emulsification while ensuring emulsification efficiency and system stability, thereby preparing uniform, stable, low-foam and high-quality film-forming agent products suitable for various food contact and functional coatings.

[0009] In view of the problems of complex process, uncontrollable foam and strong dependence on equipment in the prior art, the present application proposes an improved scheme which is technically feasible, simple in process and strong in adaptability, especially suitable for the preparation of wax emulsion type film-forming agent using natural waxes such as beeswax and candelilla wax as the main film-forming material.

[0010] The technical scheme of the present application is as follows: A simple, efficient and low-foam environmentally friendly film-forming agent preparation process, comprising the following specific steps: 1. Raw material pretreatment and premixing: Add fatty acids (such as biobased fatty acids such as myristic acid, lauric acid, etc.), emulsifiers (which can be selected from natural or food-grade surfactants), natural waxes (such as beeswax, candelilla wax), and water into a closed reaction kettle in proportion, stir and mix at a temperature of 70-80°C, so that the wax materials are fully melted and uniformly dispersed in the water phase to form a pre-emulsified system.

[0011] 2. Emulsification reaction stage: Slowly add a basic neutralizing agent (such as ammonia, sodium hydroxide solution, etc.) to the above mixture to neutralize the fatty acids and adjust the pH of the system to the appropriate range. Continue heating and stirring to 90-100°C to promote the role of the emulsifier and form a stable emulsion structure with the wax wrapped and dispersed. During this process, the system will generate some bubbles.

[0012] 3. Pressurized bubble control treatment: Further heat the emulsified system to 100-120°C, and use the pressure generated by the internal heating of the closed container to promote the escape and rupture of the bubbles in the system, significantly reducing the amount of foam residue. This step can effectively avoid the problem of difficult bubble elimination in traditional processes.

[0013] 4. Cooling and final treatment: After emulsification, appropriate hot water can be added to dilute and adjust the emulsion concentration as needed, and then quickly cooled to room temperature (about 30-40°C). After filtration, a stable, low-foam wax emulsion type coating agent product is obtained.

[0014] (Beneficial effects) 1. Simple and efficient process: One-step single-kettle operation is adopted, avoiding the complex process of traditional multi-kettle emulsification and multi-stage feeding, which helps to reduce equipment investment, operation threshold, and energy consumption cost, and is suitable for industrial scale production.

[0015] 2. Strong controllability of foam: The internal automatic bubble control is achieved by heating and pressurizing, which significantly improves the production efficiency and avoids the influence of foam on the quality and storage stability of the emulsion.

[0016] 3. Excellent product quality: The prepared coating agent emulsion has uniform distribution, moderate viscosity, and excellent film-forming performance, and is suitable for fruit and vegetable preservation, agricultural seed coating, biological medicine coating, daily fragrance release, and other fields.

[0017] 4. Environmentally friendly and regulatory compliant: The invention preferably uses natural waxes and biobased emulsifying components, meeting the requirements of food contact and sustainable development, and has good ecological safety and market application prospects.

[0018] In summary, the present invention provides a method for producing a coating agent with simple equipment, stable performance and strong adaptability by optimizing the preparation process of the wax emulsion. It is particularly suitable for use in industries with high requirements for coating performance and environmental protection standards, and has broad application value and technical promotion significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a process flow chart of the present invention; Figure 2 The water absorption rates of Example 1, Example 2 and Comparative Example 1 of the present invention are compared. DETAILED DESCRIPTION

[0020] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0021] The present invention provides a technical solution, such as Figures 1-2 As shown, a simple, efficient, low-foaming and environmentally friendly film preparation process, the specific steps of which include: 1. Raw material pretreatment and premixing: Add fatty acids (such as myristic acid, lauric acid and other bio-based fatty acids), emulsifiers (can be selected from natural or food-grade surfactants), natural waxes (such as beeswax, candelilla wax) and water into a closed reactor in proportion, stir and mix at a temperature of 70-80°C to fully melt the waxes and evenly disperse them in the water phase to form a pre-emulsified system.

[0022] 2. Emulsification Reaction Stage: Slowly add an alkaline neutralizer (such as ammonia or sodium hydroxide solution) to the above mixture to neutralize the fatty acids and adjust the pH of the system to an appropriate range. Continue heating and stirring to 90-100°C to allow the emulsifier to take effect, encapsulating and dispersing the waxes to form a stable emulsion structure. During this process, some bubbles will form.

[0023] 3. Pressurized foam control: The emulsified system is heated to 100-120°C. The pressure generated by the elevated temperature within the closed container promotes the escape and collapse of bubbles, significantly reducing residual foam. This step effectively avoids the difficulty in eliminating bubbles in traditional processes.

[0024] 4. Cooling and final treatment: After emulsification is completed, hot water can be added as needed to dilute and adjust the emulsion concentration, and then quickly cooled to room temperature (about 30-40°C). After filtering, a stable, low-foaming wax emulsion film-forming agent product is obtained.

[0025] Example 1 Preparation of Myristic Acid Emulsified Candelilla Wax Film Forming Agent (One Step, Single Kettle Emulsification) Into a closed reaction vessel, 18 g of myristic acid, 5 g of anionic emulsifier sodium lauryl sulfate, 200 g of water and 120 g of candelilla wax (melting point 67-73°C) were added. The mixture was heated and stirred at 500 rpm until the candelilla wax was completely melted and uniformly dispersed. Then, a mixture of 6 g of 25% ammonia water and 59.6 g of water was slowly added, and the emulsification reaction was continued at 90-100°C to emulsify the candelilla wax into a stable emulsion. The temperature was then further increased to 120°C, and the mixture was kept at this temperature for 20 minutes to promote the escape of bubbles and reduce the foam content. The mixture was then rapidly cooled to 30-40°C and filtered to obtain a uniform and stable light brown candelilla wax emulsion with a solid content of 35.0%.

[0026] Example 2 Preparation of Lauric Acid Emulsified Beeswax Film Forming Agent (One Step, Single Kettle Emulsification): Into a closed reaction kettle, 18 g of lauric acid, 4.8 g of sodium lauryl sulfate, 200 g of water and 120 g of beeswax (melting point 60-65°C) were added. The mixture was heated to 70-80°C and stirred at 500 rpm until the beeswax was completely melted and uniformly mixed with the system. Then, a mixture of 6.3 g of 25% ammonia water and 58.9 g of water was added, and the emulsification reaction was continued at 90-100°C. The temperature was then increased to 120°C for 20 minutes to eliminate foam, and finally cooled to 30-40°C and filtered to obtain a uniform and stable white beeswax emulsion with a solid content of 35.0%.

[0027] Comparative Example 1 Preparation of Myristic Acid Emulsified Candelilla Wax Film Forming Agent (Two Step, Double Kettle Emulsification): Into a first closed reaction kettle, 18 g of myristic acid, 5 g of sodium lauryl sulfate, 50 g of water and 120 g of candelilla wax were added. The mixture was heated to 80-90°C and stirred at 500 rpm until the wax was completely melted. Then, a mixture of 6 g of 25% ammonia water and 50 g of water was added, and the mixture was heated to 90-100°C to obtain a pre-emulsified mixture. At the same time, 159.6 g of water was added to a second closed reaction kettle and heated to 95°C with a stirring speed of 1000 rpm. The pre-emulsified mixture from the first kettle was slowly poured into the second kettle and continued to be stirred and emulsified. This process produced a large amount of foam, so a reserve volume was prepared to prevent overflow. Finally, a stable emulsion was obtained, which was kept at 95°C for 20 minutes and then cooled to 30-40°C. The light brown candelilla wax emulsion was filtered to obtain a solid content of 35.0%.

[0028] Performance Test a. Stability Test The wax emulsion sample was stored at room temperature for 4 weeks, and the instability phenomena such as wax floating, oil-water separation or precipitation were observed regularly.

[0029]

[0030] From the results in the above table, it can be seen that no obvious phase separation was observed for the emulsions prepared in Example 1, Example 2 and Comparative Example 1, showing good storage stability. It should be noted that compared with the two-step method and two-kettle operation process adopted in Comparative Example 1, the one-step emulsification single-kettle process of Example 1 and Example 2 is more simplified, and the operation is more convenient. In addition, the amount of foam generated during emulsification is significantly reduced, and the foam is easier to eliminate, reducing the difficulty of subsequent defoaming treatment.

[0031] b. Water resistance test The emulsions obtained in Example 1, Example 2 and Comparative Example 1 were respectively applied uniformly on the surface of untreated white cardboard at a coating amount of 6 g / m 2 The coating surface was observed for phenomena such as whitening, foaming, blocking, peeling, etc. Then the water absorption rate of the coated paperboard per square meter in 10 minutes was tested according to the method of GB / T 1540-2002, Determination of Water Absorption of Paper and Paperboard (Cobb method).

[0032]

[0033] From the above test results, it can be seen that the three samples all show good hydrophobicity and film integrity, without obvious discoloration or structure damage, and have excellent resistance to water erosion. Figure 2 The water absorption rates of the coatings in the three samples are almost the same, indicating that the wax emulsions prepared by one-step method and two-step method have similar performance.

[0034] From the above examples and performance tests, it can be clearly seen that the "one-step single-kettle emulsification + closed pressurized foam control" process proposed in the present application greatly simplifies the production process while ensuring the stability and performance of the coating agent, significantly reduces the equipment investment and energy consumption burden, and achieves good results in controlling foam generation. Compared with the two-step method and two-kettle operation of Comparative Example 1, Example 1 and Example 2 not only have the same or even better emulsion quality, but also have significant advantages in operation convenience, process stability, cost control, etc., fully verifying the practicality, advancement and promotion potential of the present application.

[0035] The process is particularly suitable for industrialized preparation of natural wax-based emulsion type film forming agent, especially suitable for food preservation, seed coating, biological medicine coating, paper protection coating and other high performance demand fields, and provides an environmentally friendly, efficient and low cost material solution for related industries, and has good economic benefits and social value.

[0036] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely divergences, modifications, replacements and variations of the embodiments, and the scope of the application is defined by the appended claims and their equivalents.

Claims

1. A simple and efficient process for preparing a film-forming agent, characterized in that: The following steps are involved: 1) Raw material pretreatment and premixing: Add fatty acids, natural wax, water and emulsifier into a closed reactor, heat to 70-80°C, stir until the wax is completely melted and fully mixed with water to form a uniform system; 2) Emulsification reaction: Slowly add ammonia or other neutralizing agents to the above mixed system to adjust the pH value, while continuing to heat and stir until the temperature reaches 90-100°C to promote the emulsification reaction and obtain a preliminarily stable wax emulsion; 3) Defoaming by heating and pressurizing: Continue heating the emulsified system to 100-120°C. In a closed environment, the system internal pressure is generated by increasing the temperature, which effectively suppresses and eliminates bubbles generated during the stirring process and enhances the stability of the emulsion. 4) Cooling the finished product: If the solid content needs to be adjusted, add hot water to dilute the system and then quickly cool it to 30-40°C. Filter it to obtain a uniform and stable film-forming product.

2. The preparation process according to claim 1, wherein the fatty acid is a fatty acid derived from animal and plant oils and fats, including one or a combination of myristic acid, lauric acid or stearic acid.

3. The preparation process according to claim 1, wherein the natural wax comprises beeswax, candelilla wax, carnauba wax or a mixture thereof.

4. The preparation process according to claim 1, wherein the emulsifier is an anionic emulsifier, preferably sodium lauryl sulfate.

5. The preparation process according to claim 1, wherein the neutralizing agent is aqueous ammonia with a mass concentration of 5% to 30%.

6. The preparation process according to claim 1, wherein the stirring speed in the reactor is 300 to 800 rpm.

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