Low-odor, low-VOC waterborne tactile barrier varnish composition containing PHA, its preparation method and application

Abstract

This invention discloses a low-odor, low-VOC water-based tactile barrier varnish composition containing PHA, its preparation method, and its applications, belonging to the field of papermaking chemicals and surface coating technology. This composition innovatively introduces polyhydroxyalkanoate microspheres with a bimodal particle size distribution. By precisely controlling the ratio of fine to microparticle phases, a dense micro-nano composite oil-resistant layer is constructed in conjunction with an acrylic emulsion. Compared with existing technologies, this invention utilizes the synergistic stacking effect of large and small microspheres to effectively solve the industry problem of traditional water-based coatings struggling to achieve both a low-gloss matte finish and a high oil-resistant rating. This composition achieves excellent matting effects without relying on matting powders that could disrupt coating continuity, and significantly improves barrier efficiency, achieving excellent oil and abrasion resistance with a low coating weight. The product contains no fluorinated compounds and is low in odor and VOCs, combining environmental safety and high performance advantages, making it particularly suitable for high-end food packaging.

Description

Technical Field

[0001] This invention belongs to the field of papermaking chemicals and surface coating technology, specifically relating to a low-odor, low-VOC water-based tactile barrier varnish composition containing PHA, its preparation method, and its application. Background Technology

[0002] With increasing global environmental awareness and the implementation of plastic bans, paper packaging materials are being used more and more widely in the food packaging industry due to their biodegradable and recyclable properties. However, paper fibers have a porous structure that is both hydrophilic and oleophilic. When used directly to package fried or high-fat foods, grease can easily penetrate, affecting not only the packaging's appearance but also potentially reducing its structural strength. Therefore, oil-resistant treatment of the paper surface is essential.

[0003] Traditional paper oil-resistant treatments primarily employ fluorinated chemicals, such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), or polyethylene (PE) coating. While fluorinated compounds offer excellent oil-resistant properties, they are difficult to degrade in the environment and exhibit bioaccumulation, posing potential hazards to human health and the ecological environment, and their use has been restricted in many countries and regions. Although PE coating is inexpensive, it makes paper difficult to recycle and degrades slowly in the natural environment, causing "white pollution."

[0004] In recent years, waterborne acrylic coatings have gained attention as an environmentally friendly alternative. However, conventional acrylic emulsions form dense films, which, while offering good barrier properties, often have high gloss and a noticeable "plastic feel," failing to meet the demands of high-end packaging for a natural matte texture and premium tactile feel. To reduce gloss, existing technologies typically add inorganic matting agents such as silica, but this significantly disrupts the film-forming continuity of the coating, creating microscopic defects that allow the coating to penetrate when exposed to hot oil or prolonged contact with grease, thus drastically reducing its oil resistance. In other words, under current technological systems, "high oil resistance" and "low-gloss matte effect" are often an irreconcilable contradiction. Meanwhile, polyhydroxyalkanoates (PHAs), as a type of bio-based polyester synthesized by microorganisms, possess excellent biodegradability, biocompatibility, and hydrophobicity, and are considered ideal environmentally friendly coating materials. However, current research on the application of PHA in waterborne oil-resistant coatings mainly focuses on emulsions with a single particle size or the direct addition of powder. PHA emulsions with a single small particle size form a film with an overly smooth surface and high gloss; while PHA particles with a single main large particle size or irregular shape can matte the gloss, they are very easy to damage the density of the coating, resulting in reduced mechanical strength, poor wear resistance and easy pinholes.

[0005] In summary, the industry urgently needs a water-based coating composition that is free of fluorine and plastic coatings, can simultaneously achieve a low-gloss natural matte feel and high oil barrier properties, and has excellent film-forming properties and wear resistance. This is precisely the technical problem that this invention aims to solve. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a low-odor, low-VOC water-based tactile barrier varnish composition containing PHA, its preparation method, and its application.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a varnish composition, comprising, by weight, the following components relative to 100 parts of the composition: 40 to 70 parts of PHA microsphere aqueous dispersion, 20 to 40 parts of acrylic emulsion, 1 to 5 parts of aqueous wax emulsion, 0.1 to 1.0 parts of wetting and leveling agent, 0.05 to 0.5 parts of defoamer, and 0 to 20 parts of water; the solid content of the PHA microsphere aqueous dispersion is 35 wt% to 45 wt%, and the PHA microspheres in the PHA microsphere aqueous dispersion are spherical particles with a bimodal particle size distribution, including a particle size D. 50 The fine-grained phase is 0.2 μm to 0.5 μm and the particle size D is... 50 The phase consists of fine particles ranging from 1.0 μm to 2.0 μm, with a mass ratio of the fine particles to the fine particles ranging from 1:9 to 4:6.

[0009] The amount of the PHA microsphere aqueous dispersion can be 40 parts, 45 parts, 50 parts, 55 parts, 60 parts, 65 parts, or 70 parts; the amount of the acrylic emulsion can be 20 parts, 25 parts, 30 parts, 35 parts, or 40 parts; the amount of the water-based wax emulsion can be 1 part, 2 parts, 3 parts, 4 parts, or 5 parts; the amount of the wetting and leveling agent can be 0.1 parts, 0.3 parts, 0.5 parts, 0.6 parts, 0.8 parts, or 1.0 parts; the amount of the defoamer can be 0.05 parts, 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, or 0.5 parts; and the amount of water can be 0 parts, 5 parts, 6.3 parts, 8.4 parts, 10 parts, 13.5 parts, 15 parts, 16.1 parts, or 20 parts. The solid content of the PHA microsphere aqueous dispersion can be 35wt%, 38wt%, 40wt%, 42wt%, or 45wt%. The particle size D of the fine-grained phase... 50 The particle size can be 0.2 μm, 0.25 μm, 0.3 μm, 0.4 μm, or 0.5 μm; the particle size D of the microparticle phase 50The particle size can be 1.0 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.8 μm, or 2.0 μm. The mass ratio of the fine-grained phase to the microparticle phase can be 1:9, 2:8, 2.5:7.5, 3:7, or 4:6.

[0010] The PHA microspheres have a crystallinity of 40% to 70%, for example, 40%, 45%, 50%, 55%, 60%, 65%, or 70%; a melting point of 120°C to 175°C, for example, 120°C, 130°C, 145°C, 150°C, 160°C, 172°C, or 175°C; the PHA used in the PHA microspheres is selected from short-chain PHA, medium- and long-chain PHA, or copolymers between monomers forming short-chain and medium- and long-chain PHA; the short-chain PHA is selected from poly(3-hydroxybutyrate) (PHB). The poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) are selected from one or more of poly(3-hydroxyhexanoate) (PHHx), poly(3-hydroxyoctanoate) (PHO), and poly(3-hydroxydecanoate) (PHD); the copolymer between the monomers forming the short-chain and medium-chain PHAs is selected from poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH).

[0011] The acrylic emulsion is an acrylic copolymer emulsion with a glass transition temperature (Tg) of -10°C to 20°C, for example -10°C, -5°C, 0°C, 7°C, 10°C or 20°C; and a minimum film-forming temperature (MFFT) <5°C, for example 4°C, 2°C, 0°C or lower.

[0012] The aqueous wax emulsion is selected from one or more of polyethylene wax emulsion, oxidized polyethylene wax emulsion, paraffin wax emulsion, and carnauba wax emulsion, and its average particle size is 0.05 μm to 0.20 μm, for example, 0.05 μm, 0.08 μm, 0.10 μm, 0.12 μm, 0.15 μm or 0.20 μm; the wetting and leveling agent is selected from one or more of polyether modified polysiloxane, acetylation glycol polyoxyethylene ether, alkyl polysaccharide glycoside, and phosphate ester surfactant, and the wetting and leveling agent does not contain organic fluorine structural units.

[0013] The composition has a pH of 7.5 to 9.0, for example 7.5, 8.0, 8.2, 8.3, 8.5 or 9.0; a viscosity of 50 to 300 mPa·s, for example 50 mPa·s, 85 mPa·s, 100 mPa·s, 120 mPa·s, 150 mPa·s, 180 mPa·s, 200 mPa·s or 300 mPa·s, determined at 25°C; and a solid content of 30% to 45%, for example 30%, 35.2%, 37.5%, 38.8%, 40%, 42.1% or 45%.

[0014] The total fluorine content of the composition is <20 ppm, for example 10 ppm, 12 ppm, 15 ppm or lower, and the thermal weight loss at 200°C is <4%, for example 2.5%, 2.8%, 3.0%, 3.2% or 3.5%; perfluorooctanoic acid and its salts (PFOA) and perfluorooctane sulfonic acid and its salts (PFOS) are not used in the preparation of the PHA microsphere aqueous dispersion.

[0015] The coating sample formed after the composition is applied, dried, and cured has a 60-degree gloss ≤ 5 GU, for example 2.5 GU, 3.0 GU, 3.5 GU, 4.5 GU, or 5.0 GU; a surface roughness Ra of 0.4 to 2.0 μm, for example 0.4 μm, 1.2 μm, 1.3 μm, 1.5 μm, 1.6 μm, 1.8 μm, or 2.0 μm; a Kit oil resistance grade ≥ 9, for example 9, 10, 11, or 12; and an abrasion resistance score ≥ 4 points, for example 4 points or 5 points.

[0016] The present invention also provides a method for preparing the PHA-containing low-odor, low-VOC water-based tactile barrier varnish composition, comprising the following steps:

[0017] Step 1: Preparation of PHA microsphere aqueous dispersion: The emulsifier is dissolved in water to form an aqueous phase. PHA resin is added to the aqueous phase and sheared to form a coarse PHA dispersion. The particle size D is prepared by adjusting the shear rate and surfactant concentration. 50 PHA emulsions with fine particles ranging from 0.2 μm to 0.5 μm and particle size D 50 PHA emulsions with a fine-particle phase of 1.0 μm to 2.0 μm were physically blended with the fine-particle phase at a mass ratio of 1:9 to 4:6 to obtain a PHA microsphere aqueous dispersion with a bimodal particle size distribution.

[0018] Step 2: Paint Mixing: Under stirring, add water, wetting and leveling agent, acrylic emulsion, PHA microsphere aqueous dispersion with bimodal particle size distribution, aqueous wax emulsion, and defoamer sequentially to the paint mixing tank. After dispersion at 300 r / min to 1000 r / min (e.g., 300 r / min, 500 r / min, 800 r / min, or 1000 r / min) for 10 min to 30 min (e.g., 10 min, 15 min, 20 min, or 30 min), adjust the pH value to 7.5 to 9.0, filter, and obtain a low-odor, low-VOC aqueous tactile barrier varnish composition containing PHA.

[0019] The present invention also provides the application of the aforementioned low-odor, low-VOC water-based tactile barrier varnish composition containing PHA in paper food packaging materials.

[0020] The substrate of the paper food packaging material is cardboard, kraft paper, corrugated paper, or molded pulp; the coating amount of the composition is 4g / m² to 8g / m² dry weight, for example 4g / m², 5g / m², 6g / m², 7g / m² or 8g / m², used to replace the polyethylene coating layer in the coated paper.

[0021] Compared with the prior art, the following significant advantages can be obtained by using the present invention:

[0022] This invention introduces PHA microspheres with a specific bimodal particle size distribution, combined with acrylic emulsion, water-based wax emulsion, and other components, to construct a micro-nano composite oil-resistant coating. This composition achieves excellent oil-resistant performance without using fluorinated compounds, reaching a Kit rating of 9 or higher, and is resistant to hot oil penetration. Simultaneously, the composition exhibits a low-gloss matte finish and a suitable surface feel, solving the problems of high gloss and poor feel associated with traditional water-based varnishes. Furthermore, this composition has low odor, low volatile organic compound (VOC) content, good film-forming properties, and heat resistance, meeting environmental and food safety requirements, and is suitable as a replacement for traditional polyethylene coatings and fluorinated oil-resistant coatings. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the coating structure after the low-odor, low-VOC water-based tactile barrier varnish composition containing PHA of the present invention is applied to a paper substrate.

[0024] In the figure, 1-paper substrate; 2-acrylic emulsion (the continuous phase formed); 3-coating surface; 4-aqueous wax emulsion (particles); 5-fine phase (polyhydroxyalkanoate microspheres); 6-particulate phase (polyhydroxyalkanoate microspheres). Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention. Unless otherwise stated, the raw materials used in this embodiment are commercially available industrial products or can be prepared by conventional methods. Unless otherwise specified, performance testing methods are performed according to the standards described in the invention summary section.

[0026] As shown in the figure, this structural diagram illustrates the cross-sectional microstructure of the composite coating formed after the fluorine-free oil-resistant water-based varnish of the present invention is applied to a paper substrate 1. The acrylic emulsion (the continuous phase formed) 2 provides adhesion and sealing, while the core "bimodal particle size distribution" strategy constructs a rough structure on the coating surface 3 through the larger particle size micro-phase (polyhydroxyalkanoate microspheres) 6 to achieve a matte effect, and fills the gaps with the smaller particle size micro-phase (polyhydroxyalkanoate microspheres) 5 to improve density and oil resistance. At the same time, the uniform dispersion of the water-based wax emulsion (particles) 4 further assists in improving the smoothness and wear resistance of the coating, together forming this multi-scale micro-nano composite structure that balances low gloss and high oil resistance.

[0027] Main reagents and raw materials:

[0028] Table 1. Names, Brands, and Manufacturers of Main Reagents and Raw Materials:

[0029]

[0030] Main analytical and testing instruments:

[0031] Table 2 mainly analyzes the names, models, and manufacturers of the testing instruments:

[0032]

[0033] Main testing standards:

[0034] Conditioning and testing environment: ISO 187:2022 "Standard atmosphere for the treatment and testing of paper, paperboard and pulp specimens and procedures for its monitoring and treatment";

[0035] Gloss: ISO 2813:2014 "Determination of gloss values ​​at 20, 60 and 85 degrees for paints and varnishes";

[0036] Surface roughness: ISO 21920-2:2021 "Geometric Specifications for Products (GPS) - Surface Texture: Profile Method - Part 2: Terms, Definitions and Surface Texture Parameters" and ISO 21920-3:2021 "Geometric Specifications for Products (GPS) - Surface Texture: Profile Method - Part 3: Specification Operators";

[0037] Solid content: ISO 3251:2019 "Determination of nonvolatile substances in paints, varnishes and plastics for use with paints and varnishes";

[0038] Particle size distribution and D 50 ISO 13320:2020 Particle size analysis – Laser diffraction method;

[0039] pH value: GB / T 9724-2007 "General Rules for the Determination of pH Value of Chemical Reagents";

[0040] Minimum film-forming temperature (MFFT): ISO 2115:1996 "Determination of white point temperature and minimum film-forming temperature for aqueous dispersions of plastic polymers";

[0041] Kit oil resistance rating: TAPPI T 559cm-22 "Oil Resistance Test for Paper and Paperboard";

[0042] Cobb absorbency value: ISO 535:2023 "Determination of absorbency of paper and paperboard (Cobb method)";

[0043] Abrasion resistance: ASTM D4060-25, "Standard Test Method for Determining the Abrasion Resistance of Organic Coatings by Rotary Abrasion Tester"; the test uses a rotary abrasion tester, rubber-bonded grinding wheels (e.g., Taber CS-10 or CS-10F or equivalent), a load of 500g / wheel, and 50 cycles (speed at the instrument's default standard speed); the grinding wheels are pre-ground according to the instrument's operating procedures before abrasion; after abrasion, the abraded area is photographed and binary image analysis is performed, calculating the exposed substrate area percentage = exposed substrate area / total abrasion area × 100%, and a score of 1 to 5 is assigned accordingly; where an abrasion resistance score of 5 indicates an exposed substrate area percentage of 0%, a score of 4 indicates an exposed substrate area percentage of <5%, a score of 3 indicates an exposed substrate area percentage of 5% to 15%, a score of 2 indicates an exposed substrate area percentage of 15% to 25%, and a score of 1 indicates an exposed substrate area percentage of ≥25%;

[0044] Odor rating: DIN 10955:2024-01 "Sensory analysis of the effects of food contact materials and packaging materials on the sensory properties of food";

[0045] VOC content: ISO 17895:2024 "Determination of volatile organic compounds (VOCs) in paints and varnishes by headspace gas chromatography";

[0046] PHA melting point and crystallinity: ISO 11357-1:2023 "Plastics - Differential scanning calorimetry (DSC) - Part 1: General" and ISO 11357-3:2025 "Plastics - Differential scanning calorimetry (DSC) - Part 3: Determination of melting and crystallization temperature and enthalpy";

[0047] Thermogravimetric analysis at 200℃: ISO 11358-1:2022 "Thermogravimetric analysis of plastics and polymers (TG) - Part 1: General".

[0048] Total fluorine content: determined by oxygen bomb combustion-ion chromatography, results are expressed as F, unit ppm.

[0049] PHA microsphere crystallinity and melting point testing: PHA microsphere powder was obtained by freeze-drying the PHA microsphere emulsion. Differential scanning calorimetry (DSC) was used for testing according to ISO 11357-1:2023 and ISO 11357-3:2025. A typical test procedure was as follows: Under a nitrogen atmosphere, the temperature was increased to 200℃ at a rate of 10℃ / min, held at that temperature for 3 minutes to eliminate thermal history, then cooled to -20℃ and heated again. The melting peak temperature of the second heating curve was recorded as the melting point Tm. The crystallinity was calculated using the enthalpy of fusion ΔHm combined with the theoretical enthalpy of fusion of PHA (the crystallinity was controlled between 40% and 70%, and the melting point was controlled between 120℃ and 175℃).

[0050] Total fluorine content test: Take the finished varnish or cured coating sample, use oxygen bomb combustion to convert the fluorine-containing components in the sample into fluoride ions and absorb them in the absorption liquid, use ion chromatography to determine the fluoride ion concentration and convert it into total fluorine content (in F, ppm); the total fluorine content of the sample in the example is controlled to be <20ppm.

[0051] 200℃ Thermogravimetric analysis: Take the cured coating sample (or the solid after the varnish is dried) and use a thermogravimetric analyzer (TGA) according to ISO 11358-1:2022 general rules to heat to 250℃ at 10℃ / min under nitrogen atmosphere; record the cumulative weight loss at 200℃. The thermogravimetric analysis of the example sample at 200℃ is controlled to be <4%.

[0052] Preparation of PHA microsphere aqueous dispersion:

[0053] Step 1. PHA Resin Pretreatment: PHB resin, PHBV resin, PHBH resin, or P34HB resin is pulverized at low temperature and sieved to obtain PHA powder; the particle size D of the PHA powder is... 90 ≤500μm.

[0054] Step 2. Preparation of the aqueous phase: Dissolve the emulsifier sodium dodecyl sulfate in deionized water at a mass fraction of 0.5 wt% to 2.0 wt%; then add an aqueous solution of sodium carbonate or sodium bicarbonate (mass fraction of 5 wt% to 10 wt%) to adjust the pH to 8.0 to 9.0; the temperature of the aqueous phase is controlled at 10°C to 25°C; perfluorooctanoic acid and its salts PFOA, perfluorooctane sulfonic acid and its salts PFOS are not used in the aqueous phase or in the subsequent preparation process.

[0055] Step 3. Preparation of PHA coarse dispersion: Add the PHA powder obtained in step 1 to the aqueous phase in step 2, and stir at 200 r / min to 600 r / min for 20 min to 60 min to form a pre-dispersion; wherein the mass fraction of PHA in the pre-dispersion is 5 wt% to 20 wt%, and a PHA pre-dispersion is obtained.

[0056] Step 4. Shear dispersion: The PHA pre-dispersed liquid obtained in Step 3 is shear dispersed using a rotor-stator high-speed disperser. The shear rate corresponds to a rotation speed of 8000 r / min to 12000 r / min, and the dispersion time is 5 min to 15 min to obtain a coarse PHA dispersion. During the dispersion process, the system temperature is maintained at 10℃ to 25℃ by cooling.

[0057] Step 5. Homogenize and refine the particle size distribution to prepare the target particle size distribution.

[0058] Fine-particle phase emulsion: Homogenized under conditions of 1.0 wt% to 2.0 wt% emulsifier, 80 MPa to 100 MPa homogenization pressure, and 6 to 10 cycles to obtain D 50 It is a fine-particle emulsion with a particle size of 0.2 μm to 0.5 μm;

[0059] Particulate emulsion: Homogenized under conditions of 0.5 wt% to 1.0 wt% emulsifier, 50 MPa to 70 MPa homogenization pressure, and 3 to 5 cycles to obtain D 50 The emulsion consists of a particulate phase of 1.0 μm to 2.0 μm; the comparative preparation conditions in step 5 are as follows: when the emulsifier mass fraction is 0.2 wt% to 0.5 wt%, the homogenization pressure is 20 MPa to 40 MPa, and the number of cycles is 1 to 2, a unimodal particle size distribution and D can be obtained. 50 The emulsion has an ultra-large particle size of 2.5 μm to 3.5 μm. Alternatively, under the same homogenization conditions, the PHA emulsion can be fractionated by centrifugation, and the fine-particle phase emulsion and the microparticle phase emulsion can be collected separately.

[0060] Step 6. Concentration: The fine-particle phase emulsion and / or micro-particle phase emulsion are vacuum concentrated at 30°C to 40°C and a vacuum degree of -0.08MPa to -0.095MPa for 30 min to 90 min to remove some water and concentrate to a solid content of 35% to 45%.

[0061] Step 7. Blending and Verification of Bimodal Particle Size Distribution: The fine-particle phase emulsion and the microparticle phase emulsion are physically blended at a fine-particle phase:microparticle phase mass ratio of 1:9 to 4:6. After stirring at 300 r / min to 500 r / min for 10 min to 30 min, a PHA microsphere aqueous dispersion is obtained. The obtained PHA microsphere aqueous dispersion is taken and the particle size distribution (volume distribution) is measured using a laser particle size analyzer. When the particle size distribution curve shows one main peak in the 0.2 μm to 0.5 μm range and one in the 1.0 μm to 2.0 μm range, it is determined to be a bimodal particle size distribution, and a PHA microsphere aqueous dispersion with a bimodal particle size distribution is obtained. In addition, the PHA microsphere aqueous dispersion is freeze-dried to obtain a powder sample. After gold sputtering, the particle morphology is observed using a scanning electron microscope. When most particles are approximately spherical and there are no obvious plate-like / needle-like irregular morphologies, they are determined to be spherical microspheres.

[0062] Preparation of varnish composition:

[0063] Step 1: Preparation of PHA microsphere aqueous dispersion: Following the steps in "Preparation of PHA microsphere aqueous dispersion" above, sodium dodecyl sulfate is dissolved in water to form an aqueous phase. PHA resin is added to the aqueous phase. By adjusting the emulsification speed, homogenization pressure, and emulsifier concentration, fine-particle emulsion and microparticle emulsion are prepared respectively. After concentrating to a solid content of 35% to 45%, the two are physically blended at a fine-particle:microparticle mass ratio of 1:9 to 4:6 to obtain a PHA microsphere aqueous dispersion with a bimodal particle size distribution.

[0064] Step 2: Paint Mixing: In a paint mixing tank equipped with a stirrer and thermometer, add deionized water and wetting / leveling agent in sequence according to the formula amount, and stir at 300 rpm to 500 rpm for 2 to 5 minutes; then add acrylic emulsion and stir at 300 rpm to 500 rpm for 2 to 5 minutes; add the PHA microsphere aqueous dispersion prepared in Step 1 to the paint mixing tank within 5 to 10 minutes, increase the stirring speed to 800 rpm to 1000 rpm and disperse for 8 to 15 minutes; finally add water-based wax emulsion and defoamer, and continue stirring for 3 to 5 minutes; the total stirring and dispersion time should be controlled to 10 to 30 minutes; adjust the pH value to 7.5 to 9.0 using sodium hydroxide aqueous solution (mass fraction of 5 wt% to 10 wt%), filter using a 200-mesh filter, and obtain the finished varnish.

[0065] Examples 1-7:

[0066] Examples 1 to 7 were prepared according to the general preparation process described above. The specific formulations and PHA particle size parameters are shown in Table 3. The solid content of the PHA microsphere aqueous dispersions in Examples 1-7 was 40%.

[0067] Example 1: 60 parts of PHA microsphere aqueous dispersion (PHBV, fine phase D) 50 The particle size is 0.2 μm, and the D particle phase is... 50 The particle size was 1.5 μm, and the particle size distribution was bimodal as measured by a laser particle size analyzer. The mass ratio of fine phase to microphase was 2:8. The PHA type was PHBV (melting point Tm was 160℃, crystallinity was 55%). The composition consisted of 30 parts acrylic emulsion, 3 parts water-based wax emulsion, 0.5 parts wetting and leveling agent, 0.2 parts defoamer, and 6.3 parts water. The remaining preparation steps were the same as those in "Preparation of Varnish Composition".

[0068] Example 2: 40 parts of PHA microsphere aqueous dispersion (PHBV, fine phase D) 50 The particle size is 0.2 μm, and the D particle phase is... 50The particle size was 1.0 μm, and the particle size distribution was bimodal as measured by a laser particle size analyzer. The mass ratio of fine phase to microphase was 1:9. The PHA type was PHBV (melting point Tm was 160℃, crystallinity was 55%). The mixture consisted of 40 parts acrylic emulsion, 5 parts water-based wax emulsion, 1.0 part wetting and leveling agent, 0.5 parts defoamer, and 13.5 parts water. The remaining preparation steps were the same as in Example 1.

[0069] Example 3: 70 parts of PHA microsphere aqueous dispersion (PHBH, fine phase D) 50 The particle size is 0.5 μm, and the D particle phase is... 50 The particle size was 2.0 μm, and the particle size distribution was bimodal as measured by a laser particle size analyzer. The mass ratio of fine phase to microphase was 4:6. The PHA type was PHBH, with a melting point Tm of 145℃ and a crystallinity of 45%. The mixture consisted of 20 parts acrylic emulsion, 1 part water-based wax emulsion, 0.5 parts wetting and leveling agent, 0.1 parts defoamer, and 8.4 parts water. The remaining preparation steps were the same as in Example 1.

[0070] Example 4: 55 parts of PHA microsphere aqueous dispersion (P34HB, fine phase D) 50 The particle size is 0.3 μm, and the D particle phase is... 50 The particle size was 1.8 μm, and the particle size distribution was bimodal as measured by a laser particle size analyzer. The mass ratio of fine phase to microphase was 3:7. The PHA type was P34HB (melting point Tm was 150℃, crystallinity was 50%). The composition included 25 parts acrylic emulsion, 3 parts water-based wax emulsion, 0.6 parts wetting and leveling agent, 0.3 parts defoamer, and 16.1 parts water. The remaining preparation steps were the same as in Example 1.

[0071] Example 5: 60 parts of PHA microsphere aqueous dispersion (PHB, fine phase D) 50 The particle size is 0.25 μm, and the particulate phase D 50 The particle size was 1.2 μm, and the particle size distribution was bimodal as measured by a laser particle size analyzer. The mass ratio of fine phase to microphase was 2.5:7.5. The PHA type was PHB, with a melting point Tm of 172℃ and a crystallinity of 65%. The composition included 30 parts acrylic emulsion, 3 parts water-based wax emulsion, 0.5 parts wetting and leveling agent, 0.2 parts defoamer, and 6.3 parts water. The remaining preparation steps were the same as in Example 1.

[0072] Example 6: 60 parts of PHA microsphere aqueous dispersion (PHBV, fine phase D) 50 The particle size is 0.2 μm, and the D particle phase is... 50 The particle size was 2.0 μm, and the particle size distribution was bimodal as measured by a laser particle size analyzer. The mass ratio of fine phase to microphase was 4:6. The PHA type was PHBV (melting point Tm was 160℃, crystallinity was 55%). The mixture consisted of 30 parts acrylic emulsion, 3 parts water-based wax emulsion, 0.5 parts wetting and leveling agent, 0.2 parts defoamer, and 6.3 parts water. The remaining preparation steps were the same as in Example 1.

[0073] Example 7: 60 parts of PHA microsphere aqueous dispersion (PHBV, fine phase D) 50 The particle size is 0.5 μm, and the D particle phase is... 50 The particle size was 1.0 μm, and the particle size distribution was bimodal as measured by a laser particle size analyzer. The mass ratio of fine phase to microphase was 1:9. The PHA type was PHBV (melting point Tm was 160℃, crystallinity was 55%). The mixture consisted of 30 parts acrylic emulsion, 3 parts water-based wax emulsion, 0.5 parts wetting and leveling agent, 0.2 parts defoamer, and 6.3 parts water. The remaining preparation steps were the same as in Example 1.

[0074] Table 3 Formulation table for Examples 1-7 (Unit: parts by weight):

[0075]

[0076] Comparative Examples 1-7:

[0077] Comparative Example 1: No PHA dispersion added; 90 parts acrylic emulsion, 3 parts water-based wax emulsion, 0.5 parts wetting and leveling agent, 0.2 parts defoamer, and 6.3 parts water; the remaining preparation steps are the same as in Example 1.

[0078] Comparative Example 2: 90 parts of PHA microsphere aqueous dispersion (PHBV, fine phase D) 50 The particle size is 0.2 μm, and the D particle phase is... 50 The particle size is 1.5 μm, exhibiting a bimodal distribution, with a fine-particle phase:microparticle phase mass ratio of 2:8; the melting point Tm of PHA is 160℃, and the crystallinity is 55%), without the addition of acrylic emulsion; 3 parts of water-based wax emulsion, 0.5 parts of wetting and leveling agent, 0.2 parts of defoamer, and 6.3 parts of water; the remaining preparation steps are the same as in Example 1.

[0079] Comparative Example 3: 60 parts of PHA microsphere aqueous dispersion (PHBV, fine phase D) 50 The particle size is 0.2 μm, and the D particle phase is... 50 The particle size is 1.5 μm, exhibiting a bimodal distribution, with a fine-particle phase:microparticle phase mass ratio of 8:2, indicating an excess of fine-particle phase; the melting point Tm of PHA is 160℃, and the crystallinity is 55%); 30 parts of acrylic emulsion, 3 parts of water-based wax emulsion, 0.5 parts of wetting and leveling agent, 0.2 parts of defoamer, and 6.3 parts of water; the remaining preparation steps are consistent with those in Example 1.

[0080] Comparative Example 4: 60 parts of PHA microsphere aqueous dispersion (PHBV, fine phase D) 50 The particle size is 0.2 μm, and the D particle phase is... 50The particle size is 1.5 μm, exhibiting a bimodal distribution, with a fine-particle phase:microparticle phase mass ratio of 0.5:9.5, indicating an excessive amount of microparticle phase; the melting point Tm of PHA is 160℃, and the crystallinity is 55%); 30 parts of acrylic emulsion, 3 parts of water-based wax emulsion, 0.5 parts of wetting and leveling agent, 0.2 parts of defoamer, and 6.3 parts of water; the remaining preparation steps are consistent with those in Example 1.

[0081] Comparative Example 5: PHBV resin was pulverized at low temperature and sieved to obtain PHBV powder (irregular particle morphology, melting point Tm of 160℃, crystallinity of 55%). The PHBV powder was directly sheared and dispersed in deionized water and used for paint mixing. A stable PHA microsphere aqueous dispersion was not formed. The resulting dispersion system had a disordered particle size distribution and did not exhibit a bimodal main peak D in the range of 0.2μm to 2.0μm. 50 The remaining components are the same as those in Table 4, and the remaining preparation steps are the same as those in Example 1.

[0082] Comparative Example 6: 60 parts of PHA microsphere aqueous dispersion (PHBV, single particle size D) 50 The particle size is 1.5 μm, exhibiting a single-peak distribution; the melting point Tm of PHA is 160℃, and the crystallinity is 55%); 30 parts of acrylic emulsion, 3 parts of water-based wax emulsion, 0.5 parts of wetting and leveling agent, 0.2 parts of defoamer, and 6.3 parts of water; the remaining preparation steps are the same as in Example 1.

[0083] Comparative Example 7: 60 parts of PHA microsphere aqueous dispersion (PHBV, single particle size D) 50 The particle size is 3.0 μm, exceeding 2.0 μm, exhibiting a single-peak distribution; the melting point (Tm) of PHA is 160℃, and the crystallinity is 55%; the composition includes 30 parts acrylic emulsion, 3 parts water-based wax emulsion, 0.5 parts wetting and leveling agent, 0.2 parts defoamer, and 6.3 parts water; the remaining preparation steps are consistent with Example 1. The single particle size D... 50 When preparing a 3.0 μm PHA dispersion according to the "Preparation of PHA Microsphere Aqueous Dispersion" procedure, the homogenization pressure was controlled at 20 MPa to 40 MPa, the number of cycles was controlled at 1 to 2, and the emulsifier mass fraction was controlled at 0.2 wt% to 0.5 wt%, resulting in a unimodal particle size distribution and D... 50 It is a dispersion with a diameter of 3.0 μm.

[0084] Table 4 Comparative Examples 1-7 Formulation Table (Unit: Parts by Weight):

[0085]

[0086] *Note: Direct dispersion of PHA powder in Comparative Example 5 cannot form a stable microsphere dispersion and is prone to sedimentation.

[0087] Application Example 1: Basic Coating Performance Test.

[0088] This application example primarily evaluates the basic physical properties of the varnish composition after film formation. Application was performed using a coating sampler in conjunction with a wire rod. The substrate was 250g / m² white cardboard, and the dry coating amount was controlled between 4g / m² and 8g / m². For basic performance testing, 5g / m² to 6g / m² was selected as the representative coating amount. The dry coating amount was adjusted by selecting different wire rod specifications and controlling the wet coating amount by combining the varnish solids content conversion. The dry coating amount was determined using a weighing method: a 10cm × 10cm substrate was taken as the effective area A. The substrate before and after coating were conditioned to equilibration under ISO 187:2022 standard conditions and weighed. The mass difference Δm was calculated and divided by the effective area A. The drying process used a hot air circulating oven, with the effective temperature of the paper surface monitored in real time using an infrared thermometer and maintained between 75℃ and 85℃. The drying time was 30 seconds, followed by post-curing at 23℃ and 50% relative humidity for 24 hours.

[0089] The test items include 60-degree gloss (ISO 2813:2014), surface roughness Ra (ISO 21920-2:2021), tactile score (average of 5 blind tests, 1-5 points, 5 points indicating the finest / closest to matte paper feel), Cobb water absorption value (ISO535:2023), abrasion resistance score (ASTM D4060-25, score 1-5 points), odor level (DIN 10955:2024-01), and VOC content (ISO 17895:2024, results are expressed as mass fraction; when it is less than 0.01%, it is recorded as "<0.01%").

[0090] Crease whitening test: After 24 hours of post-curing, the sample is folded 180° once along both the machine direction (MD) and the transverse direction (CD) (coated side out). A 2kg roller is applied to the crease and moved back and forth once (at a speed of approximately 50mm / s). The degree of whitening at the crease is observed and scored under a standard light source: 0 points = no whitening; 1 point = slight whitening; 2 points = significant whitening; 3 points = severe whitening or accompanied by coating cracking / peeling. Table 5 shows the maximum scores in both the MD and CD directions.

[0091] Table 5. Test results of basic coating performance:

[0092]

[0093] Note: The abrasion resistance rating is based on the appearance wear of the rubber-bonded grinding wheel after a load of 500g and a rotation speed of 50r as specified in ASTM D4060-25; some items were not tested in Comparative Example 2 because film formation was not possible.

[0094] Analysis: Table 5 shows that Examples 1-7, through a specific bimodal particle size distribution strategy, successfully achieved a balance between low gloss (2.5-4.8 GU) and suitable roughness (1.2-1.8 μm), giving the coating excellent matte feel (score ≥4) and good abrasion resistance (score ≥4). In contrast, Comparative Example 1, lacking a microsphere structure, resulted in excessive gloss (35 GU); Comparative Example 3, with excessive fine particles filling the surface, had insufficient matting effect (15 GU); while Comparative Examples 4 and 7, due to excessive microparticles or excessive particle size, although having extremely low gloss, had excessively rough surfaces (Ra ≥ 2.5 μm) and significantly reduced abrasion resistance. Furthermore, Comparative Example 5, using irregular powder, resulted in a loose coating structure, with a Cobb value as high as 45 g / m² and severe flaking. This indicates that precisely controlled fine particle size distribution is key to achieving a balance between optical, tactile, and mechanical properties.

[0095] Application Example 2: Liquid physical property testing.

[0096] This application example aims to verify the physicochemical properties and storage stability of the varnish composition in the liquid state. Test samples were taken from the varnish mother liquor after preparation and standing for 24 hours. Solid content was tested according to ISO 3251:2019, dried to constant weight at 105°C. pH was measured using a precision pH meter at 25°C. Viscosity was tested using a rotational viscometer, measured after holding at 25°C for 5 minutes; a No. 2 rotor (or a rotor with equivalent shear conditions to No. 2 rotor) was used, with a fixed rotation speed of 60 r / min. Data was taken after the reading stabilized for 30 seconds, and the result was repeated three times and the average value was taken. The minimum film-forming temperature (MFFT) was measured using a gradient temperature stage. The lowest temperature point corresponding to the appearance of continuous cracks (single crack length ≥ 1 mm) or chalking area ≥ 10% on the coating surface was defined as the MFFT. In addition, the sedimentation and stratification of the samples after being placed at room temperature for 7 days were observed.

[0097] Table 6. Results of Liquid Physical Properties Tests:

[0098]

[0099] Note: The sample of Comparative Example 5 showed stratification and sedimentation within 24 hours of standing at room temperature. Since no representative single measurement values ​​could be obtained for viscosity, density and MFFT, it is marked with "—" to indicate that it cannot be determined.

[0100] Analysis: Table 6 verifies the excellent colloidal stability and application adaptability of the formulation system of this invention. The viscosity of Examples 1-7 is controlled between 85-180 mPa·s, which is very suitable for anilox roller or bar coating, and the MFFT is below 0°C, achieving good film formation at room temperature. This is due to the good compatibility between the fine-particle PHA microspheres and the acrylic emulsion. In contrast, Comparative Example 2 lacks a continuous film-forming phase, resulting in a surge in MFFT to above 25°C; Comparative Example 5 uses direct powder dispersion, lacking an emulsification stabilization mechanism, leading to system delamination and instability; Comparative Example 7 has an MFFT of 5°C due to the excessively large PHA particles (3 μm) interfering with the fusion of polymer particles. The data show that the preparation process of the bimodal microsphere dispersion is crucial for obtaining a stable water-based varnish system.

[0101] Application Example 3: Oil resistance test.

[0102] This application example focuses on examining the coating's ability to block oils, a key indicator for food packaging materials. The oil resistance test was conducted strictly according to the TAPPI T 559cm:2012 (R2022) standard. A mixture of 12 reagent solutions with different surface tensions was dropped onto the coating surface, and the presence of wetting, discoloration, or penetration was observed after 15 seconds. The highest pass rating was recorded. In addition, to simulate real-world applications, a hot oil barrier test was performed: the coated paper was folded into a 5cm×5cm×2cm box, and the seams were sealed to prevent structural leakage. Edible soybean oil (e.g., 20mL to 30mL) preheated to 60℃ and maintained at (60±2)℃ during the test was injected into the box. The box was placed on white paper, and after 30 minutes, the oil stain area A (cm²) on the white paper and the oil stain area B (cm²) on the back of the coated paper were recorded. The judgment rules are as follows: No oil spots indicate A=0 and B=0; slight oil spots indicate 0<A≤1 or 0<B≤1; oil spots indicate 1<A≤4 or 1<B≤4; severe penetration indicates A>4 or B>4.

[0103] Table 7. Oil resistance test results:

[0104]

[0105] Analysis: As shown in Table 7, Examples 1-7 all exhibited excellent oil-repellent properties, achieving Kit ratings of 9-11, and effectively blocking hot oil at 60°C. This is the result of the combined effect of the dense "lotus leaf effect" surface constructed by the bimodal structure and the continuous acrylic phase. While relying solely on physical packing (Comparative Example 2) showed extremely high instantaneous repulsion (Kit rating 12), severe penetration occurred under prolonged hot oil immersion; and the pure acrylic coating lacking microstructure (Comparative Example 1) only achieved an oil-repellent rating of 5. Comparative Example 3 also suffered from suppressed oil-repellent ability due to its overly smooth surface. This confirms that the hydrophobicity of the material itself is insufficient; a specific micro / nano rough structure combined with a dense film-forming matrix is ​​necessary to achieve effective blocking of highly permeable oils.

[0106] Application Example 4: Temperature Boundary Verification Test.

[0107] In actual industrial production, drying temperatures may fluctuate. This application example aims to verify the film integrity of the varnish composition at different drying temperatures. Varnishes from each example and comparative example were dried at standard coating weights under conditions where the effective paper surface temperature was 50°C (low temperature condition) and 95°C (high temperature condition), respectively. After drying and post-curing for 24 hours, the film quality was evaluated using a pinhole counting method: using a graduated 10x handheld magnifying glass, five 1cm² areas were randomly selected on the coating surface, and the number of visible pinholes was counted and the average value calculated; a pinhole was defined as a clearly identifiable through-hole or obvious film defect with a diameter of not less than approximately 0.1mm under 10x magnification. The acceptance criterion was set at ≤2 pinholes / cm². This test reflects the tolerance of the formulation to the application process window.

[0108] Table 8. Temperature boundary verification test results:

[0109]

[0110] Analysis: Table 8 reveals the crucial role of the bimodal particle size distribution in broadening the application window. Examples 1-7 maintained extremely low pinhole rates (0-1 pinholes / cm²) at both 50°C and 95°C, indicating that the fine-particle PHA effectively filled the gaps between the microparticles, alleviating film-forming stress. In contrast, Comparative Example 6, with its unimodal distribution, showed insufficient fusion at low temperatures and was prone to microcracks due to rapid solvent evaporation at high temperatures, resulting in a significant increase in pinholes. Comparative Examples 4 and 7, due to excessively high proportions of large particles or exceeding particle size limits, severely hindered the formation of continuous films, leading to excessive pinholes. The results demonstrate that the bimodal gradation design of this invention significantly improves the film integrity of the formulation under extreme drying conditions, ensuring the stability of industrial production.

[0111] Application Example 5: Environmental safety and thermal stability testing.

[0112] Experimental Description: This application example aims to verify the environmental characteristics and processing heat resistance of the varnish composition.

[0113] Total fluorine content test: Take a sample of the cured coating of the finished varnish (e.g., 0.10g to 0.30g) and pretreat it using an oxygen bomb combustion system; place the sample in an oxygen bomb and fill it with oxygen to a specified pressure (e.g., 2.5MPa to 3.0MPa), ignite and burn it to convert the fluorine-containing components in the sample into fluoride ions; absorb the combustion products with an absorbent (e.g., a certain volume of sodium hydroxide aqueous solution as the absorbent), and then bring the volume to a fixed volume; subsequently, use an ion chromatograph to determine the fluoride ion concentration in the absorbent and calculate the total fluorine content (in ppm, expressed as F).

[0114] 200℃ Thermogravimetric Analysis (TGA) Test: A solid sample of the varnish dried at 105℃ is weighed and placed in a TGA crucible. The test is conducted under a nitrogen atmosphere. The heating rate is 10℃ / min. The mass change of the sample is recorded as it rises from room temperature to 250℃, and the cumulative mass loss percentage (%) at 200℃ is read. This indicator is used to evaluate the thermal stability of the coating during paper product processing (such as heat sealing and hot pressing).

[0115] Table 9. Environmental safety and thermal stability test results:

[0116]

[0117] Analysis: Table 9 confirms the high environmental standards and excellent thermal stability of the product of this invention. The total fluorine content of all examples is less than 15 ppm, meeting the requirements for fluorine-free food contact materials. Regarding thermal stability, the weight loss at 200℃ in Examples 1-7 is controlled within 3.2%, significantly better than Comparative Example 1 (pure acrylic system, weight loss 5.5%). This indicates that the introduction of high-melting-point, high-crystallinity PHA microspheres significantly improves the overall heat resistance of the coating, enabling it to withstand subsequent high-temperature processing. Although the comparative examples are similar in chemical composition, and therefore the differences in environmental protection and thermal performance data are not significant, combined with the aforementioned physical performance tests, only the formulation system of the examples achieves comprehensive optimization of physical properties while ensuring environmental safety.

[0118] Experimental Results and Analysis:

[0119] Based on the test results of Application Examples 1 to 5 above, this invention successfully prepared a water-based varnish composition that combines low odor, low VOC, matte finish, and high barrier properties. Through in-depth analysis of the experimental data, the following trend conclusions can be drawn regarding the influence of component content and particle size distribution on performance:

[0120] The regulatory effect of bimodal particle size distribution on surface properties:

[0121] The bimodal distribution of PHA microspheres is a core factor determining the coating's gloss and roughness. From Example 2 (fine-grained phase: micro-particle phase = 1:9), Example 1 (fine-grained phase: micro-particle phase = 2:8) to Example 3 (fine-grained phase: micro-particle phase = 4:6), with the fine-grained phase (D... 50 With an increase in the proportion of microparticles (0.2-0.5 μm), the surface roughness Ra of the coating increased from 1.2 μm to 1.8 μm, but remained within the range of 2.0 μm; simultaneously, the 60-degree gloss showed a trend of first decreasing and then stabilizing (from 4.8 GU to 2.5 GU), indicating that an appropriate amount of microparticle phase (D) 50 The fine-grained phase (1.0-2.0 μm) is the main component contributing to surface roughness, while the filling effect of the fine-grained phase further refines the surface structure and enhances the matte effect. If the proportion of the fine-grained phase is too high (e.g., Comparative Example 3, 8:2), the gloss level surges to 15 GU, resulting in a loss of matte finish; if the proportion of the microparticle phase is too high (e.g., Comparative Example 4, 0.5:9.5), the surface becomes excessively rough (Ra = 2.5 μm) and abrasion resistance decreases. Therefore, controlling the mass ratio of the fine-grained phase to the microparticle phase between 1:9 and 4:6 is key to achieving a smooth matte finish.

[0122] The effect of particle size on film integrity and oil resistance:

[0123] The data from the examples show that the presence of a fine-grained phase is crucial for improving film density. Comparative Example 6 (fine-grained phase D) 50 =0.2μm) and Example 7 (fine-grained phase D) 50 Both (particle size = 0.5 μm) achieve good film-forming properties and oil repellency. However, when the PHA particle size exceeds the optimal range (e.g., Comparative Example 7, D), the film-forming properties and oil repellency deteriorate. 50 =3.0μm), film-forming interference is significantly enhanced, leading to an increase in MFFT, and the number of pinholes is significantly increased in the temperature boundary test. This indicates that only when the microsphere particle size is controlled within a certain range (particulate phase ≤2.0μm, fine phase ≤0.5μm) can good stacking and fusion be achieved during the drying process of acrylic emulsion, thereby forming a defect-free barrier layer (Kit grade ≥9) while ensuring microscopic roughness.

[0124] Component synergistic effect:

[0125] Acrylic emulsion, as the continuous phase, provides the necessary adhesion and sealing properties. Comparative Example 2 (without acrylic acid), despite its high PHA content and excellent Kit grade, failed the hot oil test and exhibited extremely poor abrasion resistance (1 point), demonstrating the indispensability of the continuous phase. Conversely, Comparative Example 1 (without PHA), while showing good film formation and high abrasion resistance, suffered from excessively high gloss and poor oil resistance. This invention, by dispersing highly crystalline PHA microspheres in an acrylic emulsion, utilizes the synergistic effect of PHA's "lotus effect" and acrylic acid's "film-forming and sealing" properties to successfully resolve the contradiction between "high gloss - high oil resistance" and "low gloss - low oil resistance" in traditional water-based coatings.

[0126] PHA types and their environmental characteristics:

[0127] Compared with other examples using PHBV, the performance differences in Examples 4 (P34HB) and 5 (PHB) are mainly reflected in thermal properties, but have little impact on the oil resistance and tactile feel of the final coating, indicating that the technical solution of the present invention is universally applicable to different types of PHA. Meanwhile, all examples achieved extremely low VOC (<0.01%), without adding fluorinated compounds and controlling the total fluorine content (<20ppm), and remained stable under high-temperature processing conditions, meeting the requirements of green food packaging.

[0128] In summary, by precisely controlling the bimodal particle size distribution of PHA microspheres and their ratio with acrylic emulsion, this invention obtains a water-based varnish composition with comprehensive performance and strong processing adaptability without using fluorinated compounds.

[0129] Those skilled in the art should understand that the above embodiments are merely exemplary and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the technical solutions of the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A glazing composition, characterized by, The composition comprises the following components in parts by weight relative to 100 parts by weight of the composition: Polyhydroxyaliphatic ester microspheres water dispersion 40 to 70 parts; Acrylic emulsion 20 to 40 parts; Water-based wax emulsion 1 to 5 parts; Wetting and leveling agent 0.1 to 1.0 parts; Defoaming agent 0.05 to 0.5 parts; water 0 to 20 parts; the solid content of the polyhydroxyalkanoate microsphere aqueous dispersion is 35 wt% to 45 wt%, and the polyhydroxyalkanoate microspheres in the polyhydroxyalkanoate microsphere aqueous dispersion are spherical particles with a bimodal particle size distribution, including a fine particle phase with a particle size D 50 of 0.2 μm to 0.5 μm and a microparticle phase with a particle size D 50 of 1.0 μm to 2.0 μm, the mass ratio of the fine particle phase to the microparticle phase being 1:9 to 4:6; The polyhydroxyaliphatic ester microspheres have a crystallinity of 40% to 70% and a melting point of 120°C to 175°C; The acrylic emulsion is an acrylate copolymer emulsion having a glass transition temperature of -10°C to 20°C and a minimum film formation temperature of less than 5°C.

2. The glazing composition according to claim 1, characterized in that, The polyhydroxyaliphatic ester used in the polyhydroxyaliphatic ester microspheres is selected from short-chain polyhydroxyaliphatic esters, medium-chain polyhydroxyaliphatic esters, or copolymers formed between monomers of short-chain and medium-chain polyhydroxyaliphatic esters; The short-chain polyhydroxyaliphatic ester is selected from one or more of poly-3-hydroxybutyrate, poly-3-hydroxybutyrate-co-3-hydroxyvalerate, and poly-3-hydroxybutyrate-co-4-hydroxybutyrate; The medium-chain polyhydroxyaliphatic ester is selected from one or more of poly-3-hydroxyhexanoate, poly-3-hydroxyoctanoate, and poly-3-hydroxydecanoate.

3. The glazing composition according to claim 1, characterized in that, The water-based wax emulsion is selected from one or more of polyethylene wax emulsion, oxidized polyethylene wax emulsion, paraffin wax emulsion, and carnauba wax emulsion, and has an average particle size of 0.05um to 0.20um; the wetting and leveling agent is selected from one or more of polyether-modified polysiloxane, acetylenic diol polyoxyethylene ether, alkyl polyglycoside, and phosphate surfactant, and the wetting and leveling agent does not contain an organic fluorine structural unit.

4. The glazing composition according to claim 1, characterized in that, The composition has a pH value of 7.5 to 9.0 and a viscosity of 50 to 300mPa·s measured at 25°C; the composition has a solid content of 30% to 45%.

5. The glazing composition according to claim 1, wherein The total fluorine content of the composition is <20ppm, and the thermal weight loss at 200°C is <4%; no perfluorooctanoic acid and its salts, or perfluorooctane sulfonic acid and its salts are used in the preparation process of the polyhydroxyaliphatic ester microspheres water dispersion.

6. The glazing composition according to claim 1, wherein The coating sample formed after the composition is coated, dried, and post-cured has a 60-degree gloss of ≤5GU, a surface roughness of 0.4 to 2.0um, a Kit oil resistance level of ≥9 levels, and a wear resistance score of ≥4 points.

7. A method for preparing the glazing composition according to any one of claims 1 to 6, characterized in that, The method comprises the following steps: Step 1: Preparation of polyhydroxyalkanoate microspheres water dispersion: Dissolve emulsifier in water to form water phase, add polyhydroxyalkanoate PHA resin into the water phase and disperse by shearing to form polyhydroxyalkanoate coarse dispersion, by adjusting shearing rate and surfactant concentration respectively to prepare fine particle phase polyhydroxyalkanoate emulsion with particle size D 50 0.2 μm to 0.5 μm and micro-particle phase polyhydroxyalkanoate emulsion with particle size D 50 1.0 μm to 2.0 μm, physically blend the two in a mass ratio of fine particle phase to micro-particle phase of 1:9 to 4:6 to obtain polyhydroxyalkanoate microspheres water dispersion with bimodal particle size distribution; Step 2: In a mixing kettle, water, wetting and leveling agent, acrylic emulsion, the polyhydroxyaliphatic ester microspheres water dispersion with a bimodal particle size distribution, water-based wax emulsion, and defoaming agent are sequentially added under stirring, and after dispersion at 300r / min to 1000r / min for 10min to 30min, the pH value is adjusted to 7.5 to 9.0, and filtration is performed to obtain the glazing oil composition.

8. Use of the glazing oil composition of claim 1 in paper food packaging materials.

9. Use according to claim 8, characterized in that, The base material of the paper food packaging material is cardboard, kraft paper, corrugated paper, or molded paper pulp; the coating amount of the composition is 4g / m² to 8g / m² dry weight, and the composition is used to replace the polyethylene coating layer in the laminated paper.

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