Waterproofing varnish, preparation method thereof and waterproofing heat-shrinkable label

Abstract

This invention discloses a waterproof varnish, its preparation method, and a waterproof heat-shrink label, relating to the field of beverage packaging technology. The raw materials of this waterproof varnish, by mass percentage, include 50-70% organic solvent, 20-30% acrylic resin, 1-10% chloroprene resin or cellulose resin, 0.1-3% rigid transparent microspheres, and 0.1-3% slip wax; the rigid transparent microspheres have a diameter of 5-6 μm and a particle size distribution variation coefficient ≤10%. This invention can fundamentally eliminate the micro-gap light interference effect between the label and the bottle, avoiding the formation of false water stains; it constructs a stable micron-level fluid channel, enabling rapid escape of retained moisture and preventing the formation of true water stains; it also ensures that the distance between the two light-reflecting surfaces of the label inner wall and the beverage bottle is much greater than the interference distance, avoiding the formation of interference phenomena; simultaneously, it guarantees the high transparency and adhesion of the varnish, reduces friction noise between the label and the bottle, and improves product quality.

Description

Technical Field

[0001] This invention relates to the field of beverage packaging technology, and more specifically, to a waterproof varnish, its preparation method, and a waterproof heat-shrink label. Background Technology

[0002] The beverage industry is becoming increasingly competitive, and the appearance and quality of products, along with consumers' first sensory experience, have become key factors influencing brand image and purchasing decisions. Transparent labels, which perfectly showcase the bottle's shape and the color of its contents, giving products a high-end and pure visual impression, are widely used in the packaging of premium products such as mineral water, tea drinks, juices, and functional beverages. However, the "water stains" phenomenon under transparent labels has long been a technical problem plaguing the industry, severely undermining the advantages of transparent label dew-removal design. These mottled watermark-like imperfections under the label can easily be mistaken by consumers as product leakage, packaging contamination, or recycled bottles, raising questions about product freshness, hygiene, and brand reputation.

[0003] Traditionally, the industry has attributed water stains to excessively high humidity in the production environment or inadequate bottle cleaning. However, even under strictly controlled production conditions, this problem still occurs frequently, especially in high-temperature and high-humidity environments, indicating that there is a more complex physicochemical mechanism behind the water stain phenomenon. In-depth analysis and eradication of this problem are of urgent practical significance for improving packaging reliability, maintaining product quality, enhancing the brand's premium image, and strengthening consumer trust. This paper first systematically explains the three core mechanisms underlying the "water stain" phenomenon on transparent labels from the perspectives of fluid mechanics, mass and heat transfer, and optical principles. Building upon this foundation, it focuses on an innovative solution based on microstructure control: introducing a rigid, transparent microsphere support layer on the inner surface of the label. This study details the principles, material selection, structural design, and performance advantages of this solution, and highlights its successful application in well-known beverage brands, aiming to provide the beverage packaging industry with a proven and effective technical reference.

[0004] In-depth analysis of the generation mechanism of the "water stain" phenomenon. "Water stains" are not caused by a single factor, but rather are a collective term for visual appearance problems caused by multiple conditions. Their formation mechanisms can be mainly summarized into the following three categories: Mechanism 1: Residual water droplets from the filling / spraying process remain, forming true water stains. On high-speed filling production lines, although the bottles undergo multiple high-pressure air purging processes, trace amounts of water droplets may still remain in complex geometric structures such as the threaded neck, bottle body, and bottom recesses. When waterproof heat-shrink labels shrink, the label adheres tightly to the bottle body, sealing the remaining water droplets within the extremely narrow gap between the bottle and label. Due to the barrier between the label and bottle, the moisture cannot quickly diffuse into the atmosphere. During subsequent storage and transportation, fluctuations in ambient temperature cause the sealed water droplets to slowly evaporate. However, the evaporated water vapor cannot escape in time and can only condense and evaporate within the narrow gap, or eventually precipitate at the interface. Trace minerals dissolved in the water or soluble substances on the label / bottle surface migrate, concentrate, and crystallize with the moisture, forming irreversible white or cloudy marks—typical "true water stains." This process is similar to evaporative deposition in capillary tubes; the smaller the gap, the slower the evaporation rate, and the more pronounced the solute deposition. Figure 1 As shown. Mechanism 2: Condensation during the shrinkage process exacerbates water stain problems during sealing. During the hot and humid summer or rainy season, the ambient temperature and humidity in storage or production workshops are high. When beverage bottles (generally <30℃ when passing through the label shrinking station) enter the station, their surface temperature may be lower than the dew point temperature of the surrounding air. At this time, water vapor in the air condenses into fine dewdrops on the cold bottle surface. If the label is shrunk under these conditions, the label will directly encapsulate these condensed water droplets between the bottle and the label. After label shrinking, the condensed water is sealed, and its subsequent behavior is similar to mechanism one, but because the amount of water may be larger, the resulting patches are larger and the visual impact is more severe. Mechanism 3: "Pseudo-water stains" generated by micro-gap optical interference (Newton's rings effect) This is the most easily overlooked and deceptive mechanism. When a transparent label is bonded to a smooth bottle (especially a PET bottle) with extremely high adhesion, the air layer between them can be compressed to the micrometer or even submicrometer level. According to the principle of thin-film interference, when a beam of white light shines on this air film, it will be reflected from the inner surface of the label and the outer surface of the bottle at the upper and lower interfaces. The two reflected beams interfere due to the optical path difference. For an air film with uneven thickness, the optical path difference varies at different locations, causing some wavelengths of light to be enhanced and others to be weakened, thus visually forming irregular, colored, or alternating light and dark ring or cloud-like patterns. This pattern is highly similar to the traces left by residual water evaporation, hence it is called "pseudo-water stains" or "interference patterns." This interference phenomenon is extremely sensitive to the thickness of the air layer; the critical thickness for visible light interference is usually between several hundred nanometers and several micrometers. Once the label undergoes microscopic deformation due to temperature and pressure changes, resulting in uneven air layer thickness, the interference pattern changes accordingly, giving the impression of... Figure 2 The illusion shown is that "water stains are flowing".

[0005] The three mechanisms mentioned above often occur in an intertwined manner and influence each other. However, existing varnishes for beverage labels only meet basic printing and bonding performance requirements and are not formulated to address the core mechanism of water stain formation. They suffer from defects such as uneven particle size, inability to build stable moisture escape channels, and easy formation of micro-gap light interference. Furthermore, they lack a technical approach to actively build stable gaps to simultaneously address multiple water stain mechanisms, thus failing to fundamentally solve the label water stain problem. Therefore, there is an urgent need to develop a waterproof varnish specifically for waterproof heat-shrinkable labels that can completely eliminate various water stain phenomena while maintaining transparency and adhesion.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a waterproof varnish, its preparation method, and a waterproof heat-shrink label.

[0008] This invention is implemented as follows: In a first aspect, the present invention provides a waterproof varnish, the raw materials of which, by mass percentage, include 50-70% organic solvent, 20-30% acrylic resin, 1-10% chloroether resin or cellulose resin, 0.1-3% rigid transparent microspheres and 0.1-3% slip wax; wherein the rigid transparent microspheres have a diameter of 5-6 μm and a particle size distribution variation coefficient ≤10%.

[0009] In an optional embodiment, the rigid transparent microsphere is one or more of solid glass microspheres, hollow glass microspheres, and cross-linked PMMA microspheres.

[0010] In an optional embodiment, the mass ratio of the rigid transparent microspheres to the slippery wax is 5-6:1; And / or, the slippery wax is polyethylene wax powder.

[0011] In an optional embodiment, the organic solvent is one or a mixture of two of ethyl acetate and n-propyl acetate; And / or, the acrylic resin is one of the following: a copolymer of methyl methacrylate and butyl methacrylate, a copolymer of methacrylate resin and butyl acrylate, or a copolymer of methyl methacrylate, butyl methacrylate, and butyl acrylate. And / or, the chloroether resin is a copolymer resin of vinyl chloride and ethylene isobutyl ether; And / or, the cellulose resin is one or more of cellulose acetate butyrate, cellulose acetate propionate, and cellulose nitrate.

[0012] Secondly, the present invention provides a method for preparing a waterproof varnish as described in the above embodiments, comprising: mixing the raw materials evenly.

[0013] In an optional embodiment, mixing the raw materials uniformly includes: The rigid transparent microspheres and the slippery wax are dispersed in a portion of the organic solvent to obtain a first slurry; The acrylic resin, the chloroether resin, or the cellulose resin are dissolved in the remaining organic solvent to obtain a second slurry; The first slurry and the second slurry are mixed to obtain the final product.

[0014] In an optional embodiment, the rigid transparent microspheres and the slippery wax are stirred and dispersed at a speed of 1500-2000 r / min for 30-60 min.

[0015] In an optional embodiment, based on the total organic solvent content of the raw materials being 100%, the mass percentage of a portion of the organic solvent and the remaining organic solvent is 10%-90%: 60%-40%.

[0016] Thirdly, the present invention provides a waterproof heat shrink label, which is made by applying the waterproof varnish described in any of the foregoing embodiments to the adhesive surface of a transparent heat shrink film, with a wet film thickness of 10-15 μm, and drying it in an oven at 40-60°C.

[0017] Preferably, the coating includes gravure coating or differential coating; Preferably, the transparent heat-shrinkable film is one of PETG, PVC, and BOPP.

[0018] Fourthly, the present invention provides the application of waterproof heat-shrinkable labels as described in the foregoing embodiments in the field of beverage packaging.

[0019] The present invention has the following beneficial effects: The waterproof varnish provided by this invention uses an organic solvent, acrylic resin, and chloroether resin (or cellulose resin) to form a solvent system, effectively ensuring the varnish's adhesion strength and film-forming properties, and matching the refractive index of the microspheres and bottle materials. The varnish has a light transmittance >90% and a haze <2%, maintaining the label's high transparency while ensuring coating adhesion. By adding hard, transparent microspheres with a diameter of 5-6 μm and a particle size distribution variation coefficient ≤10% to the raw materials of the waterproof varnish, the microspheres can act as "micro-pillars" to support the label and bottle body, creating a uniform air gap. This facilitates the formation of a stable gap of about 4 μm between the label and bottle body, disrupting light interference conditions, and providing a channel for water vapor to escape, completely solving the three types of water stain mechanisms. Simultaneously, this invention also incorporates a slippery wax, which helps reduce the coefficient of friction between the label and bottle body. Combined with the microspheres to reduce the contact area, it significantly reduces frictional noise (≤35dB) when squeezing the bottle body, improving tactile smoothness and reducing the "plastic feel." By selecting the aforementioned raw materials, the micro-gap light interference effect between the label and the bottle can be fundamentally eliminated, avoiding the formation of false water stains. A stable micron-level fluid channel is constructed, enabling the rapid escape of moisture trapped between the label and the bottle, preventing the formation of true water stains. While solving the water stain problem, the high transparency and adhesion of the varnish are ensured, and friction noise between the label and the bottle is reduced, improving product quality. The varnish formula is highly compatible with existing label production lines, requiring no major equipment modifications and enabling industrial application. Its preparation method is simple and easy to operate, and the resulting waterproof varnish can be widely used on heat-shrink labels in the beverage packaging industry. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a diagram illustrating the phenomenon of water stains caused by the inability of moisture to drain from a regular label. Figure 2 A schematic diagram of the "pseudo-water stains" produced by optical interference in the micro-gap of a conventional label; Figure 3 This is a schematic diagram of a liquid sample of waterproof varnish provided in an embodiment of the present invention; Figure 4 A photograph of a product formed after printing with the waterproof varnish provided in an embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] Please see Figure 3 The present invention provides a waterproof varnish, the raw materials of which, by mass percentage, include 50-70% organic solvent, 20-30% acrylic resin, 1-10% chloroether resin or cellulose resin, 0.1-3% rigid transparent microspheres and 0.1-3% slip wax; the rigid transparent microspheres have a diameter of 5-6 μm and a particle size distribution variation coefficient ≤10%.

[0024] In this invention, an organic solvent, acrylic resin, and chloroether resin (or cellulose resin) are compounded to form a solvent system, effectively ensuring the adhesion strength and film-forming properties of the varnish, and matching the refractive index of the microspheres and bottle materials. The varnish has a light transmittance >90% and a haze <2%, maintaining the high transparency of the label while ensuring the coating's adhesion. By adding hard, transparent microspheres with a diameter of 5-6 μm and a particle size distribution variation coefficient ≤10% to the raw materials of the waterproof varnish, the microspheres can act as "micro-pillars" to support the label and bottle body, creating a uniform air gap. This facilitates the formation of a stable gap of about 4 μm between the label and the bottle body, disrupting light interference conditions, and providing a channel for water vapor to escape, completely solving the three types of water stain mechanisms. Simultaneously, this invention also incorporates a slippery wax, which helps reduce the coefficient of friction between the label and the bottle body. Combined with the microspheres to reduce the contact area, it significantly reduces frictional noise (≤35dB) when squeezing the bottle body, improves the smoothness of the touch, and reduces the "plastic feel." By selecting the aforementioned raw materials, the micro-gap light interference effect between the label and the bottle can be fundamentally eliminated, avoiding the formation of false water stains; a stable micron-level fluid channel can be constructed to enable the rapid escape of water trapped between the label and the bottle, preventing the formation of real water stains; while solving the water stain problem, the high transparency and adhesion of the varnish are ensured, and the friction noise between the label and the bottle is reduced, improving product quality; the varnish formula is highly compatible with existing label production lines, requiring no major equipment modifications, and can be applied industrially.

[0025] The rigid transparent microspheres refer to micron-sized particles with high rigidity, high transparency, and a near-spherical structure. In this invention, solid glass microspheres, hollow glass microspheres, and cross-linked PMMA microspheres, or one or more mixtures thereof, are preferred. These microspheres effectively support the label and bottle body, facilitating the formation of a stable gap of approximately 4 μm between them. If the diameter of the rigid transparent microspheres is too small, they will not effectively support the label and bottle body, leading to an unstable gap structure, uneven air layer thickness, and altered interference patterns, thus failing to eliminate the problem of false water stains. If the diameter of the rigid transparent microspheres is too large, it will affect the surface smoothness, causing a visually rough appearance, and will also affect the implementation of gravure printing.

[0026] In this invention, rigid transparent microspheres and slippery wax work together to achieve a synergistic effect. The mass ratio of rigid transparent microspheres to slippery wax is 5-6:1. By making the mass of the rigid transparent microspheres higher than that of the slippery wax, the effects of spatial support and reduced transparency can be achieved.

[0027] Preferably, the slippery wax is polyethylene wax powder. Polyethylene wax powder (also known as PE wax powder) is a functional additive made from polyethylene as a base material through micronization. It has multiple functions such as wear resistance, scratch resistance, lubrication, dispersion, matting, and slipperiness. It can form a microcrystalline protective layer on the varnish surface, significantly improving scratch resistance and friction resistance. It helps reduce the coefficient of friction between the label and the bottle body, and, combined with microspheres, reduces the contact area, significantly reducing frictional noise when squeezing the bottle (≤35dB), improving the smoothness of the touch, and reducing the "plastic feel."

[0028] Water-resistant varnishes form a dense, smooth, water-resistant, and stain-resistant transparent protective film on the substrate surface through the synergistic effect of organic solvents, acrylic resins, and chloroprene resins (or cellulose resins).

[0029] Organic solvents primarily function to disperse and dissolve the varnish, adjusting its consistency for easier application. These organic solvents include, but are not limited to, one or a mixture of two of ethyl acetate and n-propyl acetate.

[0030] Acrylic resins are used to cure and form a continuous, dense film that physically blocks water, stains, and moisture, and also possesses certain weather resistance and yellowing resistance. Acrylic resins include, but are not limited to, copolymers of methyl methacrylate and butyl methacrylate, copolymers of methacrylic resin and butyl acrylate, and copolymers of methyl methacrylate, butyl methacrylate, and butyl acrylate.

[0031] Chlorinated ether resins and cellulose resins are both functional modified resins. Chlorinated ether resins are used to improve water and chemical resistance, and they have good miscibility and strong system compatibility with acrylic resins and cellulose resins. Chlorinated ether resins include, but are not limited to, vinyl chloride and vinyl isobutyl ether copolymer resins; while cellulose resins are used to improve application and appearance, and they have properties such as high gloss, high transparency, and reduced orange peel effect. They can also improve the film hardness, abrasion resistance, and scratch resistance of waterproof varnishes. Cellulose resins include, but are not limited to, one or more mixtures of cellulose acetate butyrate, cellulose acetate propionate, and cellulose nitrate.

[0032] Furthermore, the present invention provides a method for preparing the above-mentioned waterproof varnish, which includes: mixing the raw materials evenly.

[0033] The process of mixing the raw materials evenly includes the following steps: (1) The hard transparent microspheres and slippery wax are dispersed in a portion of an organic solvent to obtain the first slurry; the hard transparent microspheres and slippery wax are stirred and dispersed at a speed of 1500-2000 r / min for 30-60 min.

[0034] (2) Dissolve acrylic resin, chloroether resin or cellulose resin in the remaining organic solvent to obtain a second slurry; based on the total organic solvent in the raw materials being 100%, the mass percentage of some organic solvent and the remaining organic solvent is 10%-90%: 60%-40%.

[0035] (3) Mix the first slurry and the second slurry to obtain the final product.

[0036] In this invention, rigid transparent microspheres and slippery wax are first dispersed in a portion of an organic solvent to ensure that the rigid transparent microspheres and slippery wax are fully dispersed. Then, they are mixed with a resin system so that the rigid transparent microspheres and slippery wax can be embedded in the adhesive layer to maintain support stability. The whole operation is simple and easy to implement, and the waterproof varnish prepared is easy to apply.

[0037] Furthermore, this invention also provides a waterproof heat-shrink label, which is made by applying the aforementioned waterproof varnish to the adhesive surface of a transparent heat-shrink film, with a wet film thickness of 10-15 μm, and drying it in an oven at 40-60°C. Through the supporting effect of rigid transparent microspheres, an air gap with an average height of 4 μm is formed between the label and the bottle body. The coating process includes, but is not limited to, gravure coating or differential coating; the transparent heat-shrink film is one of PETG, PVC, or BOPP.

[0038] Please see Figure 4The waterproof heat shrink label prepared in the above manner can be widely used in the field of beverage packaging. The waterproof heat shrink label of the present invention can avoid the generation of false water stains and prevent the formation of real water stains. While solving the water stain problem, it can ensure the high transparency and adhesion of the varnish, reduce the friction noise between the label and the bottle, and improve product quality.

[0039] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0040] Example 1 This embodiment provides a waterproof heat-shrinkable label with the following formulation composition (by weight percentage): ethyl acetate 68.5%, acrylic resin (Bolier BM66) 25.4%, cellulose acetate butyrate (Eastman CAB381-0.5) 3%, hollow glass microspheres (3M Im16K, diameter 5.5μm, particle size distribution variation coefficient 8%) 2.6%, and polyethylene wax powder (Clariant 3620) 0.5%.

[0041] Preparation method: (1) Disperse hollow glass microspheres and polyethylene wax powder in a portion of ethyl acetate (accounting for 20% of the total ethyl acetate) and stir at a high speed of 1800 r / min for 40 min to form a uniform slurry; (2) Dissolve acrylic resin and cellulose acetate butyrate in the remaining ethyl acetate (accounting for 80% of the total ethyl acetate) and stir until completely dissolved to obtain a resin solution; (3) Mix the slurry and resin solution, stir thoroughly until uniform, and obtain a waterproof varnish; (4) The coating is evenly applied to the adhesive surface (inner side) of the transparent PETG heat shrink film by gravure coating method. The wet film thickness is 12μm. After drying in a 50℃ oven, a waterproof heat shrink label is obtained.

[0042] Example 2 This embodiment provides a waterproof heat-shrinkable label with the following formulation (by weight percentage): ethyl acetate 50%, n-propyl acetate 18.2%, acrylic resin (Mitsubishi BR-116) 25%, nitrocellulose (Luzhou Beifang H1 / 2) 2.5%, solid glass microspheres (Shenglait MC-10, diameter 5μm, particle size distribution variation coefficient 7%) 3.0%, and polyethylene wax powder (Tianshi PEW-0601) 0.5%.

[0043] Preparation method: It is basically the same as in Example 1, except that the stirring speed in step (1) is 1600 r / min and the time is 35 min; the thickness of the wet film in step (4) is 10 μm.

[0044] Example 3 This embodiment provides a waterproof heat-shrinkable label with the following formulation (by weight percentage): ethyl acetate 20%, n-propyl acetate 49%, acrylic resin (Rohm Chemical DEGALAN® 64 / 12N) 20%, chloroprene resin (Hangzhou Electric Machinery MP45) 8%, PMMA microspheres (Sekisui MBX-12, Japan, 6μm in diameter, 9% particle size distribution variation coefficient) 2.5%, and polyethylene wax powder (BASF Luwax AF31) 0.5%.

[0045] Preparation method: It is basically the same as in Example 1, except that the stirring speed in step (1) is 2000 r / min and the time is 50 min; the wet film thickness in step (4) is 15 μm.

[0046] Comparative Example 1 This comparative example is basically the same as Example 1, except that 2.6% of hollow glass microspheres (3MIm16K, diameter 5.5μm, particle size distribution variation coefficient 8%) and 0.5% of polyethylene wax powder (Clariant 3620) are omitted in this comparative example, and their corresponding masses are replaced by the organic solvent ethyl acetate.

[0047] Comparative Example 2 This comparative example is basically the same as Example 1, except that 2.6% of the hollow glass microspheres (3MIm16K, diameter 5.5μm, particle size distribution variation coefficient 8%) were omitted in this comparative example, and their corresponding mass was replaced by the organic solvent ethyl acetate.

[0048] Comparative Example 3 This comparative example is basically the same as Example 1, except that 0.5% of polyethylene wax powder (Clariant 3620) was omitted in this comparative example, and its corresponding mass was replaced by the organic solvent ethyl acetate.

[0049] Comparative Example 4 This comparative example is basically the same as Example 1, except that the amount of hollow glass microspheres used in this comparative example is 0.5% and the amount of polyethylene wax powder is 2.6%.

[0050] Comparative Example 5 This comparative example is basically the same as Example 1, except that the particle size of the hollow glass microspheres in this comparative example is 4 μm.

[0051] Comparative Example 6 This comparative example is basically the same as Example 1, except that the hollow glass microspheres in this comparative example are replaced with silica microspheres with a particle size of 1μm.

[0052] Experimental Example The waterproof heat-shrink labels provided in Examples 1-3 and Comparative Examples 1-6 were applied to 500ml PET beverage bottles for comparative testing. The test items and methods are as follows: (1) Water stain resistance: Test method for manual water spray sealing test (35℃ oven accelerated drying): First, manually wet the outside of the blank beverage bottle, heat and shrink the test label onto the beverage bottle, and place the sample in a constant temperature oven at 35℃ to observe the time required for the water stains to disappear; Condensation environment label shrinkage test (bottle temperature 20℃, workshop temperature 33℃): Test method: Place a beverage bottle with a body temperature of 20℃ in an environment with a workshop temperature of 33℃ and a relative humidity of 75-80%. A layer of water vapor (small water droplets) will quickly condense on the surface of the bottle. At this time, heat shrink the labels of different test samples onto the bottle. Subsequently, place the test samples in a room temperature warehouse (based on a summer temperature of 30℃ and an ambient humidity of 70%) and observe the time required for the water stains to disappear. (2) Optical performance: Interference observation testing methods include visual observation (which requires bright full-spectrum ambient light); The testing methods for haze and transmittance include haze meter measurement. Transmittance (T, %): Total transmitted light flux / Incident light flux × 100%; Haze (H, %): Scattered light flux deviating from the incident direction > 2.5° / Total transmitted light flux × 100%. Transparency is measured visually. The judgment criteria are as follows: "Best" refers to a blank film without coating where the change in transparency after printing the coating is almost imperceptible in various scenarios; "Good" refers to a film that is discernible when placed on a black substrate but indistinguishable when compared closely to a reference blank film suspended in the air; "Average" refers to a film where a difference is discernible when compared closely to a reference blank film suspended in the air but indistinguishable when laid flat on a light-colored table; and "Poor" refers to a film where a difference is discernible even when laid flat on a light-colored table.

[0053] (3) Friction and tactile properties: The method for testing friction noise is as follows: in a quiet environment, the bottle is kneaded and squeezed by hand, with the decibel meter placed 10cm away from the bottle. This test needs to be repeated three times, and the average of the noise peak values ​​is recorded. The tactile testing method involved a direct comparison of the feel of multiple samples, using a standard sample (product name: OPI-PP waterproof varnish, batch number 2601850260) as a reference, and recording the comparative impressions. The tactile evaluation was categorized into the following levels: smooth to the touch (only the bottle body deforms when squeezed, with no obvious resistance from the label), relatively smooth to the touch (the main sensation during squeezing comes from the deformation of the bottle body, with slight resistance from the label), slightly rough to the touch (in addition to the deformation of the bottle body, there is noticeable friction and wrinkling from the label when squeezing), and very rough to the touch (in addition to the deformation feedback force of the bottle body, there is a very obvious feeling of restraint and friction from the label when squeezing).

[0054] Please refer to Tables 1-3 below for the test results: Table 1. Statistical Table of Water Repellency Performance Test Results

[0055] Table 2. Statistical Table of Optical Performance Test Results

[0056] Table 3. Statistical Table of Friction and Hand Feel Performance Test Results

[0057] As can be seen from Tables 1, 2, and 3 above, Examples 1-3 are significantly superior to Comparative Examples 1-6 in terms of comprehensive evaluation of water stain dissipation rate, condensation environment scaling test, interference observation, haze and transmittance, friction noise, and tactile feel. Specifically, Comparative Example 1 and Comparative Example 2 omitted hollow glass microspheres and polyethylene wax powder, respectively. It can be seen that their water stains were difficult to dissipate, and colored interference patterns were present; both also had a very rough feel. Comparative Example 3 omitted polyethylene wax powder, and it can be seen that it improved water stain dissipation to some extent, proving that adding hollow glass microspheres can significantly improve water stain and interference problems, but its friction noise and tactile feel are inferior to Example 1. Through the above Comparative Examples 1-3, it can be seen that the simultaneous addition of hollow glass microspheres and polyethylene wax powder in this invention has a synergistic effect.

[0058] In Comparative Example 4, the amount of hollow glass microspheres and polyethylene wax powder was changed, which resulted in water stains that were difficult to dissipate and a significant increase in haze. The light transmittance and transparency were significantly lower than those of Example 1, but the friction noise and tactile feel were inferior to those of Example 1.

[0059] In Comparative Example 5, the small particle size of the hollow glass microspheres resulted in poor support between the label and the bottle, uneven air gaps, and consequently, difficulty in removing water stains. Slight colored interference patterns were visible at certain angles, and the friction noise and tactile feel were also inferior to Example 1. In Comparative Example 6, 1μm silica microspheres were used instead of hollow glass microspheres. Due to their smaller particle size and the significantly lower compressive strength of silica microspheres compared to hollow glass microspheres, the water stain removal was even worse than in Comparative Example 5, with noticeable colored interference patterns, higher noise levels, and a rougher feel when squeezed. Comparative Examples 5 and 6 demonstrate that the choice of particle size and material for hollow glass microspheres is crucial.

[0060] In summary, the waterproof varnish provided by this invention uses an organic solvent, acrylic resin, and chloroprene resin (or cellulose resin) to form a solvent system, effectively ensuring the varnish's adhesion strength and film-forming properties, and matching the refractive index of the microspheres and bottle materials. The varnish has a light transmittance >90% and a haze <2%, maintaining the label's high transparency while ensuring coating adhesion. By adding hard, transparent microspheres with a diameter of 5-6 μm and a particle size distribution variation coefficient ≤10% to the raw materials of the waterproof varnish, the microspheres can act as "micro-pillars" to support the label and bottle body, creating a uniform air gap. This facilitates the formation of a stable gap of about 4 μm between the label and bottle body, disrupting light interference conditions, and providing a channel for water vapor to escape, completely solving the three types of water stain mechanisms. Simultaneously, this invention also incorporates a slippery wax, which helps reduce the coefficient of friction between the label and bottle body. Combined with the microspheres to reduce the contact area, it significantly reduces frictional noise (≤35dB) when squeezing the bottle body, improving tactile smoothness and reducing the "plastic feel." By selecting the aforementioned raw materials, the micro-gap light interference effect between the label and the bottle can be fundamentally eliminated, avoiding the formation of false water stains. A stable micron-level fluid channel is constructed, enabling the rapid escape of moisture trapped between the label and the bottle, preventing the formation of true water stains. While solving the water stain problem, the high transparency and adhesion of the varnish are ensured, and friction noise between the label and the bottle is reduced, improving product quality. The varnish formula is highly compatible with existing label production lines, requiring no major equipment modifications and enabling industrial application. Its preparation method is simple and easy to operate, and the resulting waterproof varnish can be widely used on heat-shrink labels in the beverage packaging industry.

[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A waterproof varnish, characterized in that, The raw materials, by mass percentage, include 50-70% organic solvent, 20-30% acrylic resin, 1-10% chloroether resin or cellulose resin, 0.1-3% rigid transparent microspheres, and 0.1-3% slip wax; the rigid transparent microspheres have a diameter of 5-6 μm and a particle size distribution variation coefficient ≤10%.

2. The waterproof varnish according to claim 1, characterized in that, The rigid transparent microspheres are one or more of the following: solid glass microspheres, hollow glass microspheres, and cross-linked PMMA microspheres.

3. The waterproof varnish according to claim 1, characterized in that, The mass ratio of the rigid transparent microspheres to the slippery wax is 5-6:1; And / or, the slippery wax is polyethylene wax powder.

4. The waterproof varnish according to claim 1, characterized in that, The organic solvent is one or a mixture of two of ethyl acetate and n-propyl acetate; And / or, the acrylic resin is one of the following: a copolymer of methyl methacrylate and butyl methacrylate, a copolymer of methacrylate resin and butyl acrylate, or a copolymer of methyl methacrylate, butyl methacrylate, and butyl acrylate. And / or, the chloroether resin is a copolymer resin of vinyl chloride and ethylene isobutyl ether; And / or, the cellulose resin is one or more of cellulose acetate butyrate, cellulose acetate propionate, and cellulose nitrate.

5. A method for preparing a waterproof varnish as described in any one of claims 1-4, characterized in that, It includes: Mix the raw materials evenly.

6. The method for preparing the waterproof varnish according to claim 5, characterized in that, Mixing the raw materials evenly includes: The rigid transparent microspheres and the slippery wax are dispersed in a portion of the organic solvent to obtain a first slurry; The acrylic resin, the chloroether resin, or the cellulose resin are dissolved in the remaining organic solvent to obtain a second slurry; The first slurry and the second slurry are mixed to obtain the final product.

7. The method for preparing the waterproof varnish according to claim 6, characterized in that, The rigid transparent microspheres and the slippery wax were stirred and dispersed at a speed of 1500-2000 r / min for 30-60 min.

8. The method for preparing the waterproof varnish according to claim 6, characterized in that, Based on the total organic solvent content of the raw materials being 100%, the mass percentage of a portion of the organic solvent and the remaining organic solvent is 10%-90% : 60%-40%.

9. A water-resistant heat-shrinkable label, characterized in that, The waterproof varnish according to any one of claims 1-4 is applied to the adhesive surface of a transparent heat shrink film, the wet film thickness is 10-15μm, and it is then dried in an oven at 40-60℃. Preferably, the coating includes gravure coating or differential coating; Preferably, the transparent heat-shrinkable film is one of PETG, PVC, or BOPP.

10. The application of the waterproof heat shrink label as described in claim 9 in the field of beverage packaging.

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