Plant fiber and preparation method thereof and application in preparing powder coating

Abstract

The present invention provides a plant fiber, a preparation method thereof, and an application of the plant fiber in the preparation of powder coatings. The preparation method of the plant fiber of the present invention comprises: A) soaking the fiber raw material in an alkaline soaking liquid; B) steam explosion treatment of the soaked fiber raw material, adding alkaline solution during the steam explosion treatment to obtain the plant fiber; wherein the fiber raw material is sisal fiber. The plant fiber prepared by the present invention has a high aspect ratio and tensile strength, good alkali resistance and good binding properties with organic matter. The use of the plant fiber to prepare powder coatings has significant economic benefits, greatly reduces the production cost of the product, and can well meet the quality requirements of the powder coating. The coating film prepared by the powder coating has high hardness and impact resistance.

Description

Technical Field

[0001] The invention relates to the technical field of powder coatings, in particular to a plant fiber and a preparation method thereof and application thereof in the preparation of powder coatings. Background Art

[0002] Powder coating is a solid powdered synthetic resin coating composed of solid resin, pigment, filler and additives. Unlike ordinary solvent-based coatings and water-based coatings, the dispersion medium of powder coating is air, so it has the characteristics of no solvent pollution, good film-forming property and low energy consumption. At present, powder coatings mainly include two categories: thermoplastic and thermosetting. Thermoplastic powder coatings are less used due to defects such as poor coating appearance and poor adhesion to metal. Thermosetting powder coatings use thermosetting synthetic resin as the film-forming material. During the drying process, the resin first melts and then solidifies into a smooth and hard coating after chemical cross-linking. The coating appearance, various mechanical properties and corrosion resistance can meet the relevant requirements of home appliance coating, automobile coating and other fields.

[0003] Plant fiber is a thick-walled tissue widely distributed in seed plants. It supports, connects, wraps, and fills plants. It is widely found in plant stems, roots, fruits, and fruit shells. The natural content of plant fiber environmentally friendly materials can reach more than 80%. The items made of plant fiber can be naturally degraded after being discarded in the natural environment. It is a new type of green environmentally friendly material. Plant fiber environmentally friendly materials come from crop straw and rapidly regenerating plants. They are inexhaustible renewable resources in nature. At present, products made of plant fiber environmentally friendly materials can replace some plastics, glass, pottery, porcelain and other products; however, there is no relevant research on the use of plant fiber in powder coatings.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The purpose of the present invention is to provide a plant fiber and a preparation method thereof and use in the preparation of powder coatings. The plant fiber has a high aspect ratio and tensile strength, good alkali resistance and good binding properties with organic matter, and the use of the plant fiber to prepare powder coatings has significant economic benefits.

[0006] The present invention provides a method for preparing plant fiber, characterized by comprising:

[0007] A) soaking the fiber raw material with an alkaline soaking liquid;

[0008] B) steam explosion treatment is performed on the soaked fiber raw material, and alkali solution is added during the steam explosion treatment to obtain plant fiber.

[0009] The present invention does not impose strict restrictions on the fiber raw material. The fiber raw material may be, for example, sisal fiber, etc., with an aspect ratio of 40-60 and a tensile strength of 450-500 MPa.

[0010] In step A), the alkaline soaking liquid is a 2-4wt% NaOH solution; the soaking temperature is room temperature, and the soaking time is 20-30 hours. The fiber raw material is soaked in the alkaline soaking liquid, washed with clean water after soaking, and dried at 100°C-120°C for 6-8 hours.

[0011] In step B), the alkali solution used in the steam explosion treatment is a 0.8-1.2wt% NaOH solution; the amount of alkali solution added is 0.8-1.2L of alkali solution per 100g of fiber raw material. Furthermore, the steam explosion treatment includes: first adding the soaked fiber raw material and alkali solution to a steam explosion tank at 180-220°C, then passing high-pressure hot steam into the steam explosion tank, and after the pressure of the steam explosion tank is constant to 2-3MPa, maintaining the pressure for 3-5min, and then instantly releasing the pressure. After the steam explosion treatment, the fiber raw material is washed and dried at 100-120°C for 6-8h. Adding alkali solution during the steam explosion treatment is beneficial to removing small molecules of impurities, increasing the fiber content, and improving the aspect ratio, tensile strength and alkali resistance of sisal fiber; at the same time, the fiber surface after the above treatment has obvious etching, which is particularly beneficial to improving the combination of fiber and organic matter or enhancing the chemical reaction with the coupling agent.

[0012] The present invention also provides a plant fiber, which is prepared according to the above preparation method; in particular, the plant fiber has an aspect ratio of 60-100 and a tensile strength of 560-620 MPa.

[0013] The invention also provides application of the plant fiber in preparing powder coating.

[0014] The present invention also provides a powder coating, comprising the following raw materials in parts by weight: 40-60 parts of carboxyl-terminated polyester resin, 3-5 parts of polyester curing agent, 0.8-10 parts of pigment, 5-20 parts of plant fiber powder, 10-40 parts of filler, 0-1 part of sand grain agent and 0-3 parts of auxiliary agent; wherein the plant fiber powder is obtained by crushing and sieving the plant fiber. Specifically, the crushing can be performed by a high-speed grinder; and the sieving can be performed by passing through a 160-200 mesh sieve.

[0015] Preferably, the powder coating of the present invention comprises the following raw materials in parts by weight: 40-50 parts of terminal carboxyl polyester resin, 3-4 parts of polyester curing agent, 0.5-2 parts of pigment, 10-20 parts of plant fiber powder, 25-35 parts of filler, 0.1-0.5 parts of sand grain agent and 0.1-0.5 parts of auxiliary agent.

[0016] In the present invention, the acid value of the carboxyl-terminated polyester resin is 30-40 mg KOH / g; the polyester curing agent is at least one of TGIC and HAA, specifically triglycidyl isocyanurate, hydroxyalkylamide, etc., such as Japan Nissan TEPIC-G and Shanghai Jinyijing E350; the pigment is various ordinary industrial-grade pigments, which can be selected from at least one of carbon black, titanium dioxide, iron yellow, iron red, flag red, phthalocyanine blue, phthalocyanine green, permanent red and permanent yellow; the filler is selected from at least one of silicon micropowder, mica powder and barium sulfate; the auxiliary agent includes at least one of butyl acrylate leveling agent, polyethylene wax, benzoin and brightener.

[0017] The present invention also provides a method for preparing the above powder coating, comprising: adding each raw material by mass into a mixer for premixing, then mixing and extruding using a twin-screw extruder, cooling, tableting, crushing, grinding and screening after extrusion to obtain the powder coating.

[0018] Specifically, the temperature of zone I of the twin-screw extruder is 95-105°C, the temperature of zone II is 125-135°C, and the screw speed is 750-850rpm; an ACM mill is used for grinding and screening, and the rotary screen mesh is 200 mesh during screening; the median particle size of the powder coating is 30-40μm.

[0019] The present invention also provides a coating film obtained by curing the above powder coating; preferably, the surface hardness of the coating film is ≥2H, and the impact resistance is ≥50kg·cm.

[0020] The present invention improves the aspect ratio, tensile strength and alkali resistance of the fiber by performing specific soaking and steam explosion treatment on the fiber raw material, and improves the bonding force between the fiber and organic matter. The prepared plant fiber can be well used in the preparation of powder coatings, is not only renewable and degradable, but also has significant economy, greatly reducing product costs. The coating film obtained by curing the powder coating has high surface hardness and impact resistance. DETAILED DESCRIPTION

[0021] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0022] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form also includes the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this description, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0023] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] Example 1

[0025] 1. Preparation of plant fiber

[0026] The sisal fibers (ie, fiber raw materials) were soaked in a 3 wt % NaOH solution at room temperature for 24 hours, washed with clean water and dried in a hot oven at 110° C. for 7 hours.

[0027] Put 100g of the sisal fiber treated by the above soaking into a steam explosion tank heated to 200℃, add 1L of 1wt% NaOH solution as cooking liquid, and close the container; pass high-pressure hot steam into the steam explosion tank, and after the pressure of the steam explosion tank is constant to 2.5MPa, maintain the pressure for 4min, and then quickly open the ball valve connected to the receiver to release the pressure instantly. The flash-exploded plant fiber enters the receiver with the help of the pressure difference, is collected, washed with clean water, and dried in a hot oven at 110℃ for 7h to obtain the plant fiber.

[0028] The aspect ratio of the plant fiber was tested by a spiral micrometer, and the tensile strength of the plant fiber was tested by GB 5886-86 Test method for breaking strength of single ramie fiber. The results are shown in Table 1.

[0029] 2. Preparation of powder coating

[0030] The prepared plant fiber is crushed by a high-speed grinder, and then sieved through a 180-mesh sieve to obtain plant fiber powder.

[0031] The powder coating of this embodiment is made of the following raw materials in parts by mass: 46.5 parts of terminal carboxyl polyester resin (acid value 35 mg KOH / g), 3.5 parts of polyester curing agent TGIC, 0.2 parts of sand grain agent, 28.8 parts of barium sulfate (filler), 20 parts of plant fiber powder, 0.8 parts of carbon black (pigment) and 0.2 parts of polyethylene wax powder (additive).

[0032] Add the raw materials into a high-speed mixer according to the above mass ratio, start stirring for 5 minutes, discharge the materials after premixing, use a twin-screw at 130°C and a screw speed of 800rpm; after extrusion, roll cool and tablet crush, use an ACM mill for grinding and screening, and obtain a powder coating with a median particle size (D50) of about 35μm.

[0033] The powder coating was cured at 190°C for 15 minutes. The resulting coating had uniform surface grain and a certain gloss. The surface hardness of the coating was tested using GB / T 6739. The impact strength of the coating was tested using GB / T 1732. The results are shown in Table 2.

[0034] Example 2

[0035] 1. Preparation of plant fiber

[0036] The sisal fibers (ie, fiber raw materials) were soaked in a 2 wt % NaOH solution at room temperature for 30 hours, washed with clean water and dried in a hot oven at 100° C. for 8 hours.

[0037] 100g of the sisal fiber treated by the above soaking treatment was placed in a steam explosion tank heated to 180°C, and 0.8L of 1.2wt% NaOH solution was added as a cooking liquid, and the container was closed; high-pressure hot steam was passed into the steam explosion tank, and after the pressure of the steam explosion tank was constant to 2MPa, the pressure was maintained for 5 minutes, and then the ball valve connected to the receiver was quickly opened to release the pressure instantly. The flash-exploded plant fiber entered the receiver with the help of the pressure difference, and after being collected, it was washed with clean water and dried in a hot oven at 100°C for 8 hours to obtain the plant fiber, and its quality test results are shown in Table 1.

[0038] 2. Preparation of powder coating

[0039] The prepared plant fiber is crushed by a high-speed grinder, and then sieved through a 160-mesh sieve to obtain plant fiber powder.

[0040] The powder coating of this embodiment is made of the following raw materials in parts by mass: 40 parts of terminal carboxyl polyester resin (acid value 35 mg KOH / g), 3 parts of polyester curing agent TGIC, 0.1 parts of sand grain agent, 25 parts of silica powder (filler), 15 parts of plant fiber powder, 0.5 parts of carbon black (pigment) and 0.1 parts of polyethylene wax powder (additive).

[0041] Add the raw materials into a high-speed mixer according to the above mass ratio, start stirring for 5 minutes, discharge the materials after premixing, and use a twin-screw extruder for mixing and extrusion. The working conditions of the twin-screw extruder are: zone I temperature 95°C, zone II temperature 125°C, and screw speed 750rpm; after extrusion, the materials are cooled by rollers and crushed by ACM mill for grinding and screening to obtain a powder coating with a median particle size of about 30μm.

[0042] The powder coating was cured at 190°C for 15 minutes, and the resulting coating had uniform surface grain and a certain gloss. The surface hardness and impact resistance of the coating were tested using the method of Example 1. The results are shown in Table 2.

[0043] Example 3

[0044] 1. Preparation of plant fiber

[0045] Sisal fibers (ie, fiber raw materials) were soaked in a 4 wt % NaOH solution at room temperature for 20 hours, washed with clean water and dried in a hot oven at 120° C. for 6 hours.

[0046] 100g of the sisal fiber treated by the above soaking treatment was placed in a steam explosion tank heated to 220°C, and 1.2L of 0.8wt% NaOH solution was added as a cooking liquid, and the container was closed; high-pressure hot steam was passed into the steam explosion tank, and after the pressure of the steam explosion tank was constant to 3MPa, the pressure was maintained for 4 minutes, and then the ball valve connected to the receiver was quickly opened to release the pressure instantly. The flash-exploded plant fiber entered the receiver with the help of the pressure difference, and after being collected, it was washed with clean water and dried in a hot oven at 120°C for 6 hours to obtain the plant fiber, and its quality test results are shown in Table 1.

[0047] 2. Preparation of powder coating

[0048] The prepared plant fiber is crushed by a high-speed grinder, and then sieved through a 200-mesh sieve to obtain plant fiber powder.

[0049] The powder coating of this embodiment is made of the following raw materials in parts by mass: 50 parts of terminal carboxyl polyester resin (acid value 35 mg KOH / g), 4 parts of polyester curing agent TGIC, 0.5 parts of sand grain agent, 35 parts of mica powder (filler), 10 parts of plant fiber powder, 2 parts of carbon black (pigment) and 0.5 parts of polyethylene wax powder (additive).

[0050] Add the raw materials into a high-speed mixer according to the above mass ratio, start stirring for 5 minutes, discharge the materials after premixing, and use a twin-screw extruder for mixing and extrusion. The working conditions of the twin-screw extruder are: zone I temperature 105°C, zone II temperature 135°C, and screw speed 850rpm; after extrusion, the materials are cooled by rollers and crushed by ACM mill for grinding and screening to obtain a powder coating with a median particle size of about 40μm.

[0051] The powder coating was cured at 190°C for 15 minutes, and the resulting coating had uniform surface grain and a certain gloss. The surface hardness and impact resistance of the coating were tested using the method of Example 1. The results are shown in Table 2.

[0052] Comparative Example 1

[0053] The process is substantially the same as that of Example 1 except that in the step of preparing plant fibers, 1 wt % NaOH solution is not added as cooking liquid during the steam explosion treatment.

[0054] Comparative Example 2

[0055] Except for the different composition of the powder coating in the step of preparing the powder coating, the rest is basically the same as Example 1.

[0056] The powder coating of this control example is made of the following raw materials in parts by mass: 46.5 parts of terminal carboxyl polyester resin (acid value 35 mg KOH / g), 3.5 parts of polyester curing agent TGIC, 0.2 parts of sand grain agent, 48.8 parts of barium sulfate (filler), 0.8 parts of carbon black (pigment) and 0.2 parts of polyethylene wax powder (additive).

[0057] Comparative Example 3

[0058] The process is basically the same as that of Example 1 except that in the step of preparing the powder coating, the sisal fiber raw material of Example 1 is crushed by a high-speed grinder and then sieved through a 200-mesh sieve to obtain the plant fiber powder.

[0059] Table 1 Quality test results of various plant fibers

[0060] fiber Aspect Ratio Tensile strength(MPa) Fiber raw materials 50 480 Example 1 Plant Fiber 90 600 Comparative Example 1 Plant Fiber 65 560

[0061] Table 2 Quality test results of each coating

[0062] Coating Surface hardness Impact strength Example 1 3H 60kg cm Example 2 2H 50kg cm Example 3 2H 55kg cm Comparative Example 1 2H 50kg cm Comparative Example 2 H 60kg cm Comparative Example 3 3H 50kg cm

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An application of plant fiber in the preparation of powder coating, characterized in that: The method for preparing the plant fiber comprises: A) soaking the fiber raw material with alkaline soaking liquid; B) steam explosion treatment is performed on the soaked fiber raw material, and alkali solution is added during the steam explosion treatment process to obtain plant fiber; In step A), the fiber raw material is sisal fiber; the alkaline soaking liquid is 2-4wt% NaOH solution, the soaking temperature is room temperature, the soaking time is 20-30h, and after soaking, it is washed with clean water and dried at 100-120°C for 6-8h; In step B), the steam explosion treatment comprises: firstly adding the soaked fiber raw material and alkali solution into a steam explosion tank at 180-220°C, then passing high-pressure hot steam into the steam explosion tank, and after the pressure of the steam explosion tank is constant to 2-3MPa, maintaining the pressure for 3-5min, and then instantly releasing the pressure; wherein, the alkali solution used in the steam explosion treatment is a 0.8-1.2wt% NaOH solution; the amount of alkali solution added is 0.8-1.2L of alkali solution per 100g of fiber raw material; the aspect ratio of the plant fiber is 60-100, and the tensile strength is 560-620MPa.

2. The use according to claim 1, characterized in that: After the steam explosion treatment, the fiber raw material was washed and dried at 100-120°C for 6-8h.

3. A powder coating, characterized in that: The invention comprises the following raw materials in parts by weight: 40-60 parts of terminal carboxyl polyester resin, 3-5 parts of polyester curing agent, 0.8-10 parts of pigment, 5-20 parts of plant fiber powder, 10-40 parts of filler, 0-1 part of sand grain agent and 0-3 parts of auxiliary agent; wherein the plant fiber powder is obtained by crushing and sieving the plant fiber in the application described in claim 1 or 2.

4. The powder coating according to claim 3, characterized in that The acid value of the carboxyl-terminated polyester resin is 30-40 mgKOH / g; the polyester curing agent is at least one of TGIC and HAA; the pigment is at least one of carbon black, titanium dioxide, iron yellow, iron red, flag red, phthalocyanine blue, phthalocyanine green, permanent red and permanent yellow; the filler is at least one of silicon micropowder, mica powder and barium sulfate; the additive includes at least one of butyl acrylate leveling agent, polyethylene wax, benzoin and brightener.

5. The method for preparing a powder coating according to claim 3 or 4, characterized in that: include: The raw materials are added into a mixer according to the mass proportion for premixing, and then mixed and extruded by a twin-screw extruder. After extrusion, the powder coating is cooled, tableted, crushed, ground and screened to obtain the powder coating.

6. The preparation method according to claim 5, characterized in that The temperature of zone I of the twin-screw extruder is 95-105°C, the temperature of zone II is 125-135°C, and the screw speed is 750-850rpm; ACM mill is used for grinding and screening, and the mesh of the rotary screen is 160-200 mesh during screening; the median particle size of the powder coating is 25-40 μm.

7. A coating film, characterized in that: The powder coating according to claim 3 or 4 is cured to obtain the powder coating.