Plastic-free coated paperboard container and manufacturing method thereof

Abstract

The plastic-free coated paperboard container comprises a side wall and a bottom wall which are composed of plastic-free coated paperboards, the inner surface of each plastic-free coated paperboard is provided with a plastic-free water-based coating, micron-sized wrinkles are arranged on the plastic-free water-based coating through a controlled photocuring process, and the wrinkles on the surface of the coating of the side wall are perpendicular to a bottom opening of the container and are uniform in width; on the basis, the coating is mainly composed of organic silicon modified polyurethane acrylate. The plastic-free coated paperboard container is high in hydrophobicity, water resistance and corrosion resistance, less liquid is hung on the inner surface of the side wall, pouring is convenient, and the plastic-free coated paperboard container can be safely used in the field of food packaging materials.

Description

Technical Field

[0001] The present invention relates to the field of food packaging materials, and more particularly to a plastic-free coated paperboard container and a manufacturing method thereof. Background Art

[0002] In response to the severe situation of plastic pollution, countries around the world have introduced plastic bans and restrictions, and people have also proposed various plastic reduction plans in various fields of life. Among them, "replacing plastic with paper" is one of the most popular choices in the field of food packaging. In order to make paper products have the good mechanical and chemical properties of plastics, it is often necessary to add a layer of water-proof coating on the surface of the base paper. The traditional coating materials are non-degradable plastics such as PP and PE, which reduces the environmental advantages of paper containers. Therefore, relatively degradable acrylate / polyurethane coatings have come into people's view. How to improve the performance of coatings while controlling costs is the key factor for the widespread use of such environmentally friendly coatings in packaging materials.

[0003] Silicone modification is one of the effective methods to increase the hydrophobicity of coatings. In acrylic resin coatings with added silicone monomers, silicon-containing groups tend to aggregate on the coating surface, giving it a lower surface energy. Zhang Zhao et al. studied a silicone-modified acrylic antifouling coating. With the increase of silicone monomer content, the static contact angle of seawater on the coating surface increased from 80.4° to 104.6°. The contact angle increased fastest when the silicone monomer content was between 0 and 10%. This is because the enrichment of silicon on the coating surface gradually reached saturation. The same literature also shows that SiO 2 Nanoparticles also promote the hydrophobicity of coatings.

[0004] Compared with the more studied chemical modification methods, the method of using physical means to change the surface properties of the coating has not been widely used. Inspired by the surface structure of rice leaves, SGLee et al. synthesized a polydimethoxysilane film with an anisotropic wavy surface, in which the wavy structure with a period of about 41 μm makes the water on the surface of the film have different static contact angles in two vertical directions, 112° and 130°, respectively, which makes the water tend to diffuse in a specific direction. Depending on the initial hydrophobicity of the material, the modification method and the scale of the stripes / folds, its surface hydrophobicity may increase or decrease. There is no shortage of coatings / inks / coating technologies with surface wrinkles in the prior art, but their purpose is to enhance the beauty of the material or to use the wrinkle pattern to store information. Limited by the control of cost, safety and material properties, the prior art lacks methods for applying the above-mentioned modification methods to the coating of food packaging materials to improve their performance. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention discloses a plastic-free coated paperboard container and a method for manufacturing the same. Micro-wrinkles are arranged on the surface of the water-based coating by controlled photocuring to increase the hydrophobicity, water resistance and friction of the container wall surface, and the flow state of the liquid on the inner surface of the container is regulated by anisotropic wrinkles to reduce wall hanging and improve pouring performance. In addition, the silicone modification of the polyurethane polyacrylate coating further promotes the improvement of its hydrophobic barrier properties.

[0006] One of the objects of the present invention is to provide a plastic-free coated paperboard container.

[0007] It includes a side wall and a bottom wall, wherein the side wall and the bottom wall together form an inner cavity of the container, and the edge where the side wall and the bottom wall are connected is the bottom opening of the container;

[0008] The side wall and the bottom wall are made of plastic-free coated paperboard, the plastic-free coated paperboard includes a bottom paper layer, and an inner coating layer arranged on the surface of the bottom paper layer facing the inner cavity of the container, and the inner coating layer is formed by coating and curing a light-cured plastic-free water-based paint;

[0009] The inner coating surface of the plastic-free coated paperboard has micron-level wrinkles, wherein the inner coating surface of the side wall has a series of wrinkles that are perpendicular to the bottom of the container and have uniform width.

[0010] In a further technical solution, the solid component of the photocurable plastic-free water-based coating includes silicone-modified polyurethane acrylate.

[0011] Another object of the present invention is to provide a method for preparing the plastic-free coated paperboard container, comprising the following steps:

[0012] (1) coating the light-curable plastic-free water-based coating on the surface of the base paper layer, including first coating along the conveying direction of the base paper layer, second coating in the opposite direction of the conveying direction of the base paper layer, and smoothing the coating with a scraper to obtain a wet coated paperboard;

[0013] (2) pre-drying the wet coated paperboard, then curing it by exposing it to an excimer laser and ultraviolet light twice in succession, and cutting it according to the unfolded shape of the bottom wall and the side wall to obtain a plastic-free coated paperboard;

[0014] (3) The plastic-free coated paperboard is enclosed to form the side wall and the bottom wall, and the side wall is rolled and sealed at the seam and the seam between the side wall and the bottom wall by hot pressing to obtain the plastic-free coated paperboard container.

[0015] The technical solution of the present invention has the following beneficial effects:

[0016] 1. The inner coating surface of the side wall of the plastic-free coated paperboard container of the present invention has a series of micron-level wrinkles perpendicular to the bottom of the container and with uniform width, which increases the roughness of the coating surface. At the same time, the nitrogen-containing monomer can reduce the surface energy of the coating, thereby increasing its hydrophobicity and enhancing its water barrier property.

[0017] 2. Due to the presence of the wrinkles on the inner surface of the side wall of the plastic-free coated paperboard container of the present invention, the static contact angle of water in the direction perpendicular to the bottom of the container is 10-20° smaller than that in the horizontal direction; the wrinkles enhance the fluidity of the liquid in the vertical direction on the inner surface of the side wall, making it less likely for the liquid to stick to the wall, and at the same time, the wetting line is sharper when pouring, which is beneficial to reduce leakage of liquid when pouring / drinking.

[0018] 3. The main component of the photocurable plastic-free water-based coating of the present invention is silicone-modified polyurethane acrylate oligomer, in which the silicon groups contained in the silicone monomers aggregate to the surface of the container coating after polymerization, further reducing its surface energy, enhancing its hydrophobicity and water barrier properties, and also having stronger chemical resistance to common corrosive substances such as ethanol and acetic acid.

[0019] 4. In some embodiments of the present invention, the outer side of the plastic-free coated paperboard container also has a coating with the wrinkles on the surface, which increases the hydrophobicity and friction of the outer surface of the container, allowing it to contain cold liquids without being penetrated by water condensed on the outer wall, and is easier to hold. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a vertical section and an enlarged view of the side wall of the plastic-free coated paperboard container obtained in Examples 1 to 3;

[0021] Figure 2 It is a vertical section and an enlarged view of the side wall of the plastic-free coated paperboard container obtained in Example 4;

[0022] Figure 3 It is an enlarged view of the mask part used for the side wall part and the inner coating layer of the wet coated paperboard obtained in Examples 1 to 4 under the excimer laser;

[0023] Figure 4 This is a microscopic photograph of the wrinkles on the inner surface of the side wall of the plastic-free coated paperboard obtained in Example 1;

[0024] Figure 5 This is a microscopic photograph of the wrinkles on the inner surface of the bottom wall of the plastic-free coated paperboard obtained in Example 1. DETAILED DESCRIPTION

[0025] In order to make the technical means, creative features, objectives and effects of the present invention easy to understand, the present invention is further described below in conjunction with specific embodiments and drawings. Obviously, the described embodiments are only part of the implementation methods of the present invention and should be understood as an explanation of the technical solution of the present invention rather than a limitation.

[0026] The present invention provides a plastic-free coated paperboard container, comprising a side wall and a bottom wall, wherein the side wall and the bottom wall are combined to form a container inner cavity, and the edge position where the side wall and the bottom wall are connected is the container bottom opening; the side wall and the bottom wall are composed of plastic-free coated paperboard, and the plastic-free coated paperboard comprises a bottom paper layer, and an inner coating layer arranged on the surface of the bottom paper layer on the side facing the container inner cavity, and the inner coating layer is formed by coating and curing a light-cured plastic-free water-based paint; the inner coating layer surface of the plastic-free coated paperboard has micron-level wrinkles, wherein the inner coating layer surface of the side wall has a series of wrinkles perpendicular to the container bottom opening and uniform in width.

[0027] Preferably, the inner coating has an average thickness of 40 to 50 μm.

[0028] The series of microfolds perpendicular to the bottom of the container and with uniform width does not mean that all microfolds are strictly perpendicular to the bottom of the container. Specifically, 70-85% of the area of ​​the inner coating surface of the side wall irradiated by the excimer laser has wrinkles that are substantially perpendicular to the bottom of the container, so that the direction perpendicular to the bottom of the container is the direction with the extremely low static contact angle of water.

[0029] Furthermore, the solid content of the photocurable plastic-free water-based coating is between 30 and 45%, and its solid components include: 65 to 85 parts by weight of silicone-modified polyurethane acrylate (Si-PUA), 15 to 20 parts by weight of active diluent, 10 to 15 parts by weight of tertiary amino acrylate, 1 to 3 parts by weight of photoinitiator, and 1 to 4 parts by weight of additives.

[0030] Polyurethane acrylate (PUA) has both the mechanical strength and adhesion of polyurethane and the weather resistance of polyacrylate, and is a photocurable coating component with excellent comprehensive performance. The present invention preferably uses multifunctional PUA to prepare the photocurable plastic-free coating; and the organosilicon modification can greatly improve the water resistance, solvent resistance and mechanical properties of PUA. The reactive diluent is a multifunctional acrylate monomer, which can greatly increase the crosslinking speed of the coating. The tertiary amino acrylate monomer can consume oxygen during the curing process, further reducing oxygen inhibition, thereby improving the degree of curing and shortening the curing time.

[0031] Furthermore, in the organosilicon-modified polyurethane acrylate, the mass ratio of polyurethane to polyacrylate is 1 to 3:1, and the organosilicon monomer accounts for 3 to 6% (mass fraction); preferably, the organosilicon monomer is siloxane.

[0032] The silicone modification of polyurethane acrylate materials mainly includes several methods such as silicone oil, siloxane or silicone monomers containing unsaturated double bonds. Among them, the resin obtained by polycondensation of PUA materials containing active groups and siloxane is the most stable in storage and not easy to gel. If the content of silicone monomers is too high, not only will the hydrophobicity not be significantly improved, but it will also affect the adhesion, transparency and mechanical strength of the coating.

[0033] Furthermore, the active diluent is trimethylolpropane triacrylate (TMPTA), tripropylene glycol diacrylate (TPGDA) or a mixture of the two; the tertiary amino acrylate is dimethylaminoethyl acrylate (DMAEA), dimethylaminoethyl methacrylate (DMAEMA) or a mixture of the two; and the additive includes a defoamer and / or a dispersant.

[0034] Furthermore, the photoinitiator is a combination of one or more of an aliphatic α-keto acid and an α-keto ester. The aliphatic α-keto ester includes but is not limited to 2-ketobutyric acid (2-KBA) and 2-octanone acid (2-OOA), and the aliphatic α-keto ester includes but is not limited to ethyl pyruvate (EP), ethyl 3-methyl-2-oxobutyrate (EMOB) and 4,4-dimethyldihydrofuran-2,3-dione (DDFD).

[0035] Furthermore, the plastic-free coated paperboard further comprises an outer coating disposed on the surface of the side of the bottom paper layer facing away from the inner cavity of the container, and the outer coating is also formed by coating and curing the light-curable plastic-free coating, and has micron-level microfolds on its surface. The light-curable plastic-free coating of the outer coating also satisfies the condition of being able to form micron-level microfolds under light radiation, but is not necessarily identical to the inner coating material; for example, the photoinitiator of the light-curable plastic-free coating of the outer coating can be a combination of one or more conventional photoinitiators such as initiator 1173, initiator 819, initiator BP, initiator ITX, etc., to meet the needs of ink printing, etc.

[0036] Preferably, the outer coating has an average thickness of 30 to 40 μm.

[0037] The present invention also provides a method for preparing the plastic-free coated paperboard container, which is characterized by comprising the following steps:

[0038] (1) coating the light-curable plastic-free water-based coating on the surface of the base paper layer, including first coating along the conveying direction of the base paper layer, second coating in the opposite direction of the conveying direction of the base paper layer, and smoothing the coating with a scraper to obtain a wet coated paperboard;

[0039] (2) pre-drying the wet coated paperboard, then curing it by exposing it to an excimer laser and ultraviolet light twice in succession, and cutting it according to the unfolded shape of the bottom wall and the side wall to obtain a plastic-free coated paperboard;

[0040] (3) The plastic-free coated paperboard is enclosed to form the side wall and the bottom wall, and the side wall is rolled and sealed at the seam and the seam between the side wall and the bottom wall by hot pressing to obtain the plastic-free coated paperboard container.

[0041] The wavelength of the excimer laser emitted by the common excimer light source is less than 200nm, the energy of a single photon is extremely high, and the penetrating power is weak, so it can quickly cure the surface layer of the coating. The cured surface layer is affected by the surface tension of the uncured bottom layer, forming a regular wrinkle structure. The ultraviolet light is emitted by an ultraviolet broadband light source, which has high power and high penetrating power, and can quickly cure the part of the coating that was not cured in the previous step. It should be noted that the first excimer laser irradiation is a fixed-point irradiation, and the second ultraviolet light fixed-speed transmission irradiation is immediately carried out before the resulting wrinkles relax.

[0042] Furthermore, the pre-drying temperature is between 60 and 85° C., and the drying time is between 40 and 90 seconds.

[0043] Furthermore, the excimer laser is emitted by a 172nm excimer lamp, and the irradiation power is 20-50mW / cm 2 , the irradiation time is 1.5 to 3 seconds, the surface of the wet coated paperboard is purged with nitrogen; a mask is arranged between the excimer lamp and the side wall of the wet coated paperboard, and its target pattern is a series of lines parallel to the upper and lower bottom edges of the side wall of the paperboard, wherein the unexposed area accounts for 15 to 30% of the total area.

[0044] In order to obtain wrinkles that are mainly perpendicular to the bottom of the container, the mask is set in a direction parallel to the bottom of the container. Due to the boundary effect of photocuring and the internal stress of the coating, stripe wrinkles that are parallel to each other and perpendicular to the unexposed area are formed in the exposed area. Depending on the coating monomer composition, the photoinitiator content, and the irradiation time and power of the excimer laser, the wrinkle width (wavelength) is between 15 and 40 μm, and the depth (amplitude) is between 5 and 12 μm.

[0045] Furthermore, the ultraviolet light is emitted by an ultraviolet mercury lamp, and the irradiation power is 0.8-1.5 W / cm 2 , the irradiation time is 4 to 7 seconds.

[0046] Since conventional aromatic photoinitiators have certain biological toxicity and migration pollution, the present invention uses aliphatic α-keto acids or α-keto esters as initiators, and their initiation cross-linking rate is not significantly different from that of conventional type II photoinitiators such as BP, BMS or ITX. However, due to the lack of aromatic structure, their absorbance is extremely low, especially in the UV-A and UV-B bands, the absorbance coefficient is more than two orders of magnitude lower than that of conventional initiators. Therefore, in order to achieve a thorough curing effect in a short time, a higher light intensity than conventional initiators is required.

[0047] The present invention is described in detail below with reference to the examples. The experimental methods are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0048] Coating Preparation Example 1

[0049] Prepare the light-curing plastic-free coating by the following steps:

[0050] 0.7 kg of silicone-modified polyurethane acrylate emulsion (solid content 36%, silicone monomer content 5%), 0.2 kg of TMPTA, and 0.1 kg of DMAEA were stirred at 50° C. for 30 min to obtain a prepolymer, and then 20 g of DDFD and 10 g of SRE-2020 silicone defoamer were added, stirred and dispersed for 30 min and cooled to room temperature to obtain a light-cured plastic-free coating 1.

[0051] The silicone-modified polyurethane acrylate emulsion is prepared by the following steps:

[0052] Under nitrogen protection, 0.4kg 2-hydroxyethyl acrylate (HEA), 0.27kg glycerol polyether (molecular weight 1000), 0.6g dibutyltin dilaurate (DBTDL) catalyst and 0.05g hydroquinone were stirred evenly at 60°C, and 0.25kg isophorone diisocyanate (IPDI) was slowly added dropwise within 1.5h, and then reacted for 2h; then 0.08kg γ-methacryloxypropyl trimethoxysilane was added, and the temperature was raised to 75°C, and reacted for 2h to obtain Si-PUA (trifunctionality). Deionized water was added to the obtained Si-PUA to adjust the solid content to 36%, and triethylamine was used to adjust the pH to 8.1, and finally shear emulsification was performed to obtain the silicone-modified polyurethane acrylate emulsion.

[0053] Coating Preparation Example 2

[0054] The only difference between this preparation example and coating preparation example 1 is that in the preparation step of the silicone-modified polyurethane acrylate emulsion, the amount of siloxane added is 0.048 kg, that is, the silicone monomer content of the silicone-modified polyurethane acrylate emulsion is 3%, and a photocurable plastic-free coating 2 is obtained.

[0055] Coating Preparation Example 3

[0056] Prepare the light-curing plastic-free coating by the following steps:

[0057] Take 0.8 kg of the silicone-modified polyurethane acrylate emulsion (solid content 36%, silicone monomer content 5%) obtained in Coating Preparation Example 1, 0.15 kg of TPGDA, and 0.1 kg of DMAEA, and stir at 50°C for 30 minutes to obtain a prepolymer. Then add 15 g of EP, 10 g of 2-OOA, 10 g of SRE-2020 silicone defoamer and 5 g of SRE-4190 water-based coating dispersant, stir and disperse for 30 minutes and cool to room temperature to obtain light-cured plastic-free coating 3.

[0058] Coating control example 1

[0059] Take 0.8 kg of the silicone-modified polyurethane acrylate emulsion (solid content 36%, silicone monomer content 5%) obtained in Coating Preparation Example 1 and 0.2 kg of TMPTA and stir at 50°C for 30 minutes to obtain a prepolymer, then add 20 g of DDFD and 10 g of SRE-2020 silicone defoamer, stir and disperse for 30 minutes and cool to room temperature to obtain a light-cured plastic-free coating 4.

[0060] Coating control example 2

[0061] Take 0.7 kg of silicone-modified polyacrylate emulsion (solid content 36%, silicone monomer content 5%) prepared in the same manner as in Coating Preparation Example 1, 0.2 kg of TMPTA, and 0.1 kg of DMAEA, and stir at 50°C for 30 min to obtain a prepolymer. Then add 20 g of DDFD and 10 g of SRE-2020 silicone defoamer, stir and disperse for 30 min and cool to room temperature to obtain light-curing plastic-free coating 5.

[0062] Coating control example 3

[0063] The only difference between this control example and coating example 1 is that the homemade silicone-modified polyurethane acrylate emulsion is replaced with an emulsion of the same solid content and pH prepared from a trifunctional aromatic polyurethane acrylate oligomer (YC2203, Jining Tangyi Chemical Co., Ltd.) to obtain a photocurable plastic-free coating 6.

[0064] Example 1

[0065] The following steps are used to prepare a plastic-free coated paperboard container, in this case a paper cup:

[0066] The obtained light-curable plastic-free coating 1 is coated on the surface A of the bottom paper of a 180g paper cup. The coating amount of the first coating is 18g / m 2 The second reverse coating amount is 25g / m 2 , use a scraper to smooth it out.

[0067] The wet coated paperboard was dried in an oven at 70°C for 60 seconds; then, under nitrogen purge, the paperboard was heated at 40 mW / cm2 through a mask (half-masking the predetermined position of the side wall). 2 The radiation intensity was 172nm excimer lamp, which was used for curing for 2.5s; then the 1.2W / cm 2 The medium-pressure mercury lamp irradiates within a range of 6 seconds; finally, the paperboard is cut according to the shape and predetermined position of the bottom wall and the side wall to obtain a plastic-free coated paperboard.

[0068] The obtained plastic-free coated paperboard side wall is rolled up so that the surface A is on the inside, and the seam is heat-pressed and sealed; the bottom opening side is connected to the bottom wall, and the seam is heat-pressed and sealed; the upper edge of the side wall is turned outward to form a curling edge, thereby obtaining the plastic-free coated paperboard container.

[0069] Example 2

[0070] The only difference between this example and Example 1 is that a light-curing plastic-free coating 2 is used for coating.

[0071] Example 3

[0072] The only difference between this example and Example 1 is that a light-curing plastic-free coating 3 is used for coating.

[0073] Example 4

[0074] The plastic-free coated paperboard container, in this case still a paper cup, is prepared by the following steps:

[0075] The obtained light-curable plastic-free coating 2 is coated on the surface A of the 180g paper cup bottom paper. The coating amount of the first coating is 15g / m 2 The second reverse coating amount is 22g / m 2 , use a scraper to smooth it out.

[0076] The A-side wet coated paperboard was dried in an oven at 70°C for 60 seconds; then, under nitrogen purge, the paperboard was heated at 40 mW / cm2 through a mask (half-masking the predetermined position of the side wall). 2 The radiation intensity was 172nm excimer lamp, which was used for curing for 2s; then the 1.2W / cm 2 The irradiation range of the medium-pressure mercury lamp is passed through for 5 seconds to obtain the A-side plastic-free coated base paper.

[0077] The obtained light-curable plastic-free coating 2 is coated on the other surface B of the paper cup bottom paper. The coating amount of the first coating is 12 g / m 2 The second reverse coating amount is 18g / m 2 , use a scraper to smooth it out.

[0078] The wet coated paperboard on the B side was dried in an oven at 70°C for 45 seconds; then, the paperboard was heated at 40 mW / cm 2The radiation intensity was 172nm excimer lamp, which was used for curing for 1.5s (without using a mask); then the 1.2W / cm 2 The medium-pressure mercury lamp irradiates within a range of 4 seconds; finally, the paperboard is cut according to the shape and predetermined position of the bottom wall and the side wall to obtain a plastic-free coated paperboard.

[0079] The obtained plastic-free coated paperboard side wall is rolled up so that the surface A is on the inside, and the seam is heat-pressed and sealed; the bottom opening side is connected to the bottom wall, and the seam is heat-pressed and sealed; the upper edge of the side wall is turned outward to form a curling edge, thereby obtaining the plastic-free coated paperboard container.

[0080] Example 5

[0081] Prepare a plastic-free coated paperboard container, in this case a paper bowl, by following the steps below:

[0082] The obtained light-cured plastic-free coating 2 was coated on the surface A of the bottom paper of the 320g paper bowl. The coating amount of the first coating was 20g / m 2 The second reverse coating amount is 25g / m 2 , use a scraper to smooth it out.

[0083] The wet coated paperboard was dried in an oven at 75°C for 60 seconds; then, under nitrogen purge, the paperboard was heated at 50 mW / cm2 through a mask (half-masking the predetermined position of the side wall). 2 The radiation intensity was 172nm excimer lamp, which was used for curing for 2.5s; then the 1.2W / cm 2 The medium-pressure mercury lamp irradiates within a range of 7 seconds; finally, the paperboard is cut according to the shape and predetermined position of the bottom wall and the side wall to obtain a plastic-free coated paperboard.

[0084] The obtained plastic-free coated paperboard side wall is rolled up so that the surface A is on the inside, and the seam is heat-pressed and sealed; the bottom opening side is connected to the bottom wall, and the seam is heat-pressed and sealed; the upper edge of the side wall is turned outward to form a curling edge, thereby obtaining the plastic-free coated paperboard container.

[0085] Comparative Example 1

[0086] The only difference between this example and Example 1 is that no excimer lamp is used for irradiation. After the wet coated paperboard is pre-dried, it is directly passed through a 1.2W / cm 2 Irradiate with a medium-pressure mercury lamp for 7 seconds.

[0087] Comparative Example 2

[0088] The only difference between this example and Example 1 is that nitrogen purge is not used during excimer lamp irradiation.

[0089] Comparative Example 3

[0090] The only difference between this example and Example 1 is that a light-curing plastic-free coating 4 is used for coating.

[0091] Comparative Example 4

[0092] The only difference between this example and Example 1 is that a light-curing plastic-free coating 5 is used for coating.

[0093] Comparative Example 5

[0094] The only difference between this example and Example 1 is that a light-curing plastic-free coating 6 is used for coating.

[0095] Figure 1 It is a vertical section and an enlarged view of the side wall of the plastic-free coated paperboard container obtained in Examples 1 to 3 of the present invention. Figure 2 The vertical section and side wall enlarged view of the plastic-free coated paperboard container obtained in Example 4 of the present invention. The plastic-free coated paperboard container includes a side wall 1 and a bottom wall 2, which together form a container cavity, and the edge position connected thereto is the container bottom opening 3; the side wall 1 and the bottom wall 2 are composed of plastic-free coated paperboard, including a bottom paper layer 10, and an inner coating layer 11 disposed on the surface of the bottom paper layer 10 facing the container cavity; in some embodiments of the present invention, the plastic-free coated paperboard further includes an outer coating layer 12 disposed on the surface of the bottom paper layer 10 facing away from the container cavity.

[0096] Figure 3 The side wall of the wet coated paperboard obtained in Examples 1 to 4 of the present invention and the enlarged view of the mask part used for the inner coating under the excimer laser are shown. The side wall 1 includes a bonding block 1' located at one side edge, and the position of the container bottom 3 is marked with a dotted line below it, and the oblique line represents the area irradiated by the excimer laser (including being blocked by the mask stripes); the circle 4 is an enlarged view of the mask part used for the inner coating under the excimer laser, including an exposed part 41 and an unexposed part 42, and the stripe boundary formed is parallel to the container bottom 3 (approximately a straight line due to the high magnification), and in these embodiments, the width of the exposed part is 200μm, and the width of the unexposed part is 50μm.

[0097] Figure 4 This is a microscopic photograph of the microfolds on the inner surface of the side wall of the plastic-free coated paperboard obtained in Example 1 of the present invention, wherein the blank part is the unexposed part in the excimer laser irradiation step, and the part with parallel stripes is the exposed part; the photograph shows that the spacing between the microfolds is about 20 μm.

[0098] Figure 5 This is a microscopic photograph of the microfolds on the inner surface of the bottom wall of the plastic-free coated paperboard obtained in Example 1 of the present invention, and it can be seen that the surface has irregular microfolds.

[0099] The following is a performance test of the plastic-free coated paperboard containers obtained from the various embodiments and comparative examples of the present invention.

[0100] (1) Water absorption test:

[0101] According to GB / T 1540 standard, the water absorption of plastic-free coated paperboard container samples was tested by Cobb method. Each sample was divided into two groups: the inner surface of the side wall and the inner surface of the bottom wall. The results are shown in Table 1.

[0102] Table 1 30-minute swell value of the inner surface of plastic-free coated paperboard container (g / m 2 )

[0103] Example Inner surface of side wall inner surface of bottom wall Comparative Example Inner surface of side wall inner surface of bottom wall Example 1 2.2 2.3 Comparative Example 1 4.6 4.5 Example 2 4.2 4.4 Comparative Example 2 4.3 4.3 Example 3 2.5 2.5 Comparative Example 3 3.9 4.0 Example 4 2.8 2.9 Comparative Example 4 5.4 5.2 Example 5 1.7 1.9 Comparative Example 5 9.6 10.1

[0104] (2) Hydrophobicity test:

[0105] The static contact angles of water on the surfaces of the plastic-free coated paperboard containers obtained in each embodiment and comparative example were tested, and the results are shown in Table 2.

[0106] Table 2 Static contact angle of water on the inner surface of plastic-free coated paperboard container (°)

[0107]

[0108]

[0109] (3) Liquid flowability in the vertical direction of the side wall:

[0110] The plastic-free coated paperboard containers obtained in Example 1 and Comparative Example 1 were used as comparison, and the two containers were filled with 2%, 5%, 10%, and 20% of pure water, respectively. At each water content, the minimum tilt angle required for pouring out the water was tested for the two containers, and the results are shown in Table 3.

[0111] Table 3 Minimum tilt angle for pouring water (°)

[0112] Example 1 Minimum tilt angle Comparative Example 1 Minimum tilt angle 2％ 82.4 2％ 84.7 5％ 79.5 5％ 81.2 10％ 74.2 10％ 75.3 20％ 67.8 20％ 68.4

[0113] Under the same container shape and water volume, the plastic-free coated paperboard container obtained in Example 2 can pour out water at a smaller tilt angle, indicating that under the condition of ensuring the overall hydrophobicity of the inner surface of the container side wall, the plastic-free coated paperboard container of the present invention can better overcome the surface tension to pour out water and reduce spillage.

[0114] (4) Water vapor transmission rate and corrosion resistance test:

[0115] According to GB / T 1037-2021 standard, the water vapor transmission rate (WVT) of the plastic-free coated paperboard containers obtained in each embodiment and comparative example was measured by cup weight gain method, and the results are shown in Table 4.

[0116] Table 4 Water vapor transmission rate of plastic-free coated paperboard containers (g / (m 2 ·24h))

[0117]

[0118]

[0119] The plastic-free coated paperboard containers obtained in each example were filled with 50% ethanol (volume) or 6% acetic acid (mass), respectively, and placed at 25° C. for 24 hours to simulate the corrosion of liquor and vinegar, then cleaned and dried, and the water vapor transmission rate was measured again. The results are shown in Table 5.

[0120] Table 4 Water vapor transmission rate of plastic-free coated paperboard containers before and after corrosion (g / (m 2 ·24h))

[0121] initial Ethanol Acetic acid Example 1 312.8 346.3 321.4 Example 2 486.2 512.0 501.6 Example 3 302.6 324.1 310.2 Example 4 107.1 123.8 112.9 Example 5 239.4 278.4 252.7

[0122] (5) Adhesion test:

[0123] The binding strength (adhesion) of the coatings on the surfaces of the plastic-free coated paperboard containers obtained in each embodiment and comparative example was tested by the cross-hatch method. The results showed that the binding strength of the coatings obtained on the surface of the 180g paper cup bottom paper was level 5 (including each comparative example).

[0124] (6) Safety testing:

[0125] According to the standard of GB 4806.8-2016, the food safety of the paper materials used in the plastic-free coated paperboard containers obtained in each embodiment was tested, and the results were all in compliance; it is worth mentioning that as a paper material using a light-curing coating, the test results of its fluorescent substances (wavelengths of 254nm and 365nm) were negative.

[0126] Obviously, the above embodiments are merely examples for clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description, and the obvious changes or modifications derived therefrom should still be considered as the protection scope of the present invention.

Claims

1. A plastic-free coated paperboard container, characterized in that: It includes a side wall and a bottom wall, wherein the side wall and the bottom wall together form an inner cavity of the container, and the edge where the side wall and the bottom wall are connected is the bottom opening of the container; The side wall and the bottom wall are made of plastic-free coated paperboard, the plastic-free coated paperboard includes a bottom paper layer, and an inner coating layer arranged on the surface of the bottom paper layer facing the inner cavity of the container, and the inner coating layer is formed by coating and curing a light-cured plastic-free water-based paint; The inner coating surface of the plastic-free coated paperboard has micron-level wrinkles, wherein the inner coating surface of the side wall has a series of wrinkles that are perpendicular to the bottom of the container and have uniform width.

2. The plastic-free coated paperboard container according to claim 1, characterized in that: The solid content of the photocurable plastic-free water-based coating is between 30 and 45%, and the solid components include: 65 to 85 parts by weight of silicone-modified polyurethane acrylate, 15 to 20 parts by weight of active diluent, 10 to 15 parts by weight of tertiary amino acrylate, 1 to 3 parts by weight of photoinitiator, and 1 to 4 parts by weight of additives.

3. The plastic-free coated paperboard container according to claim 2, characterized in that: In the organosilicon-modified polyurethane acrylate, the mass ratio of polyurethane to polyacrylate is 1 to 3:1, and the organosilicon monomer accounts for 3 to 6%; preferably, the organosilicon monomer is siloxane.

4. The plastic-free coated paperboard container according to claim 2, characterized in that: The active diluent is trimethylolpropane triacrylate, tripropylene glycol diacrylate or a combination of the two; the tertiary amino acrylate is dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate or a combination of the two; the additive includes a defoamer and / or a dispersant.

5. The plastic-free coated paperboard container according to claim 2, characterized in that: The photoinitiator is a combination of one or more of aliphatic α-keto acid and α-keto ester.

6. The plastic-free coated paperboard container according to claim 1, characterized in that: The plastic-free coated paperboard also includes an outer coating layer arranged on the surface of the bottom paper layer facing away from the inner cavity of the container. The outer coating layer is also formed by coating and curing a light-cured plastic-free water-based coating and has micron-level wrinkles on its surface.

7. A method for preparing the plastic-free coated paperboard container according to any one of claims 1 to 6, characterized in that: The steps include: The light-curable plastic-free water-based coating is applied on the surface of the base paper layer, including first coating along the conveying direction of the base paper layer, second coating in the opposite direction of the conveying direction of the base paper layer, and smoothing the coating with a scraper to obtain a wet coated paperboard; The wet coated paperboard is pre-dried, then exposed and cured twice by excimer laser and ultraviolet light, and cut according to the unfolded shape of the bottom wall and the side wall to obtain a plastic-free coated paperboard; The plastic-free coated paperboard is enclosed to form the side wall and the bottom wall, and the side wall is rolled and sealed at the seam and the seam between the side wall and the bottom wall by heat pressing to obtain the plastic-free coated paperboard container.

8. The method according to claim 7, characterized in that The pre-drying temperature is between 60 and 85° C., and the pre-drying time is between 40 and 90 seconds.

9. The method according to claim 7, characterized in that: The excimer laser is emitted by a 172nm excimer lamp, and the irradiation power is 20-50mW / cm 2 , the irradiation time is 1.5 to 3 seconds, the surface of the wet coated paperboard is purged with nitrogen; a mask is arranged between the excimer lamp and the side wall portion of the wet coated paperboard, the target pattern of the mask is a series of lines parallel to the upper and lower bottom edges of the side wall portion of the paperboard, wherein the unexposed area accounts for 15 to 30% of the total area.

10. The method according to claim 7, characterized in that The ultraviolet light is emitted by an ultraviolet mercury lamp, and the irradiation power is 0.8-1.5 W / cm 2 , the irradiation time is 4 to 7s.

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