A foaming agent, a composite packaging material having a scrubbing effect, and a method for preparing the same

Abstract

This application provides a foaming agent comprising: 15wt%–30wt% sodium bicarbonate, 15wt%–25wt% sodium citrate, 30wt%–50wt% oily solvent, and the balance being additives; the sum of the mass percentages of sodium bicarbonate and sodium citrate does not exceed 50wt%. This application also provides a composite packaging material with a frosted effect and a method for preparing the same. This application uses a mixture of sodium bicarbonate and sodium citrate in a total amount not exceeding 50wt%, combined with an oily solvent and additives, and foaming is performed at a dosage not exceeding 1.5wt% to form uniform and dense cells, resulting in a frosted effect on the surface of the composite packaging material. The process is simple and low-cost.

Description

Technical Field

[0001] This invention relates to the field of packaging materials technology, and in particular to a foaming agent, a composite packaging material with a frosted effect, and a method for preparing the same. Background Technology

[0002] Frosted film is a type of plastic film with a finely textured surface, which can give products a unique texture and aesthetic appeal.

[0003] Existing technologies typically use materials such as PET (polyester film), PP (polypropylene), PVC (polyvinyl chloride), and PC as substrates. Depending on the substrate, a suitable abrasive agent and solvent are selected to dissolve or disperse the plastic substrate and abrasive agent, forming a uniform coating solution. This solution is then uniformly coated onto the substrate using a coating machine (such as a roller coating machine or a screen coating machine), followed by drying to obtain a plastic film with a frosted effect. Existing technologies also disclose physical or chemical treatments of the film surface using mechanical or chemical abrasion processes to achieve a frosted effect. However, the above processes for producing frosted films are complex and costly. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is a foaming agent, a composite packaging material with a frosted effect and a method for preparing the same. The foaming agent provided in this application produces a material with a frosted effect when used in amounts of less than 1.5%, and the process is simple and the cost is low.

[0005] This application provides a foaming agent comprising: 15wt% to 30wt% sodium bicarbonate, 15wt% to 25wt% sodium citrate, 30wt% to 50wt% oily solvent, and the balance being an additive;

[0006] The sum of the mass percentages of sodium bicarbonate and sodium citrate shall not exceed 50 wt%.

[0007] This application uses sodium bicarbonate and sodium citrate in a total amount not exceeding 50 wt%, combined with alkane oil and additives, to form uniform and dense cells when foaming with a usage amount not exceeding 1.5 wt%. This results in a frosted effect on the surface of the composite packaging material. The process is simple, low-cost, and the resulting composite packaging material has minimal loss in basic strength.

[0008] The foaming agent provided in this application includes sodium bicarbonate and sodium citrate, wherein the content of sodium bicarbonate is 15wt% to 30wt%, preferably 16wt% to 29wt%, more preferably 17wt% to 28wt%; and the amount of sodium citrate is 15wt% to 25wt%, preferably 15.5wt% to 24.5wt%, more preferably 16wt% to 24wt%.

[0009] The foaming agent provided in this application also includes an oily solvent, which mainly functions as a dispersant, facilitating the full dispersion of the foaming components in the material. In some specific implementations, the oily solvent includes, but is not limited to, alkane oil, soybean oil, isoalkane oil, and diisopropyl adipate, and may be one or more of these. When multiple oily solvents are used, this application does not impose any special restrictions on the content of each specific substance.

[0010] The foaming agent provided in this application also includes additives, including but not limited to emulsifiers, fillers, plasticizers, dispersants, and stabilizers, which may be one or more of these. This application does not impose any special restrictions on the selection of the additives; those skilled in the art can select them as needed. In some specific implementations, the additives include glyceryl monostearate, hydrated magnesium silicate, and zinc oxide in a mass ratio of 1–5:1–3:0.002–0.05, which can provide nucleation, dispersibility, and stability, and is beneficial for controlling the size of the foam cells.

[0011] In the foaming agent provided in this application, the sum of the mass percentages of sodium bicarbonate and sodium citrate does not exceed 50 wt%, preferably not more than 48 wt%, and more preferably 30 wt% to 45 wt%. When foaming is carried out with a usage of no more than 1.5 wt%, the foaming ratio is 1.05 to 1.2 times, which can form uniform and dense cells and has little impact on the strength of the material.

[0012] This application also provides a composite packaging material with a frosted effect, including a microbubble film, wherein the microbubble film comprises a surface layer, a microbubble intermediate layer and a bottom layer that are sequentially laminated.

[0013] The microbubble intermediate layer is formed by foaming 0.1wt% to 1.5wt% of the foaming agent described in the above technical solution and the balance matrix resin;

[0014] Alternatively, the microbubble intermediate layer is formed by foaming 0.1wt% to 1.5wt% of foaming masterbatch and the balance of matrix resin; the foaming masterbatch includes 30wt% to 40wt% sodium citrate, 30wt% to 50wt% carrier resin, 3wt% to 8wt% inorganic filler and the balance of additives.

[0015] The composite packaging material provided in this application includes a microfoamed film, which comprises a surface layer, a microfoamed intermediate layer, and a bottom layer that are sequentially laminated. This not only creates a frosted glass-like appearance but also reduces the weight of the composite packaging material.

[0016] In some specific implementations, the microbubble intermediate layer is formed by foaming 0.1wt% to 1.5wt% of the foaming agent described in the above technical solution and the balance being a matrix resin. As mentioned above, the foaming agent is a compound of sodium bicarbonate and sodium citrate in a total amount not exceeding 50wt%, combined with alkane oil and additives. When foaming is carried out at a dosage not exceeding 1.5wt%, it can form uniform and dense cells, exhibiting a frosted effect on the surface of the composite packaging material. The process is simple, the cost is low, and the resulting composite packaging material has virtually no loss of strength.

[0017] In some specific implementations, the microbubble intermediate layer is formed by foaming 0.1wt% to 1.5wt% of foaming masterbatch and the balance being matrix resin; the foaming masterbatch includes 30wt% to 40wt% sodium citrate, 30wt% to 50wt% carrier resin, 3wt% to 8wt% inorganic filler, and the balance being additives. Experimental results show that foaming masterbatch formed from 30wt% to 40wt% sodium citrate can also form uniform and dense cells when foamed with a usage not exceeding 1.5wt%, exhibiting a frosted effect on the surface of the composite packaging material. The process is simple, low-cost, and the resulting composite packaging material has virtually no strength loss. The foaming masterbatch contains sodium citrate at a mass percentage of 30 wt% to 40 wt%, preferably 31 wt% to 49 wt%. The carrier resin includes, but is not limited to, polyethylene, ethylene-vinyl acetate copolymer, etc., and can be one or more of these, preferably polyethylene, with a mass percentage of 30 wt% to 50 wt%, preferably 35 wt% to 45 wt%. The inorganic filler includes, but is not limited to, calcium carbonate, titanium dioxide, talc, silica, etc., and can be one or more of these, preferably calcium carbonate, with a mass percentage of 3 wt% to 8 wt%, preferably 4 wt% to 7 wt%. The additives include, but are not limited to, emulsifiers, fillers, plasticizers, dispersants, and stabilizers, preferably glyceryl monostearate, magnesium silicate hydrate, and zinc oxide in a mass ratio of 1 to 5: 1 to 3: 0.002 to 0.05.

[0018] In some specific implementations, the matrix resin includes, but is not limited to, polyethylene (PE), polypropylene (PP), polylactic acid (PLA), or polystyrene (PS), and different matrix resins can be selected depending on the composite packaging material.

[0019] In some specific implementations, the surface layer and the bottom layer of the microbubble membrane can be configured according to usage requirements, and each layer independently includes a matrix resin and additives; this application does not impose any special restrictions on this. The matrix resin of the surface layer and the bottom layer can be the same as or different from the matrix resin of the microbubble intermediate layer, but is preferably the same as the matrix resin of the microbubble intermediate layer.

[0020] In practice, the microfoamed membrane can be a film or a sheet, such as a PE film, PP film, PP sheet, PS sheet, PLA sheet, etc., and this application has no particular limitation. In some specific implementations, the thickness of the microfoamed membrane is 30μm to 150μm, preferably 35μm to 145μm. Specifically, when the microfoamed membrane is a PE film or a PP film, compared with the unfoamed membrane, the density of the microfoamed membrane decreases by 5% to 55%, preferably by 10% to 30%; the thickness of the microfoamed membrane is 30μm to 90μm, preferably 35μm to 85μm. In some specific implementations, the microfoamed membrane is a PE film, and its thickness is preferably 40μm to 90μm; in some specific implementations, the microfoamed membrane is a PP film, and its thickness is preferably 20μm to 50μm. When the microfoamed film is PP sheet, PS sheet, or PLA sheet, compared with the unfoamed film, the density of the microfoamed film decreases by 5% to 20%, preferably by 10% to 15%; the thickness of the microfoamed film is 70 μm to 150 μm, preferably 80 μm to 140 μm.

[0021] The microfoamed membrane disclosed in this application has a microporous structure visible to the naked eye in a transparent state, and its surface is relatively rough and uneven in a colored state, with a visible frosted effect.

[0022] In some specific implementations, the composite packaging material further includes a functional layer laminated to the surface of the microfoamed film. The microporous structure in the microfoamed film allows the functional layer to create a frosted effect on the material surface. In this application, the functional layer includes at least one of a paper layer, a plastic layer, and an aluminized plastic layer. Specifically, if the functional layer is an aluminized plastic layer, the composite packaging material is an aluminum (aluminized) plastic composite packaging material; if the functional layer is a plastic layer, the composite packaging material is a plastic-plastic composite packaging material; if the functional layer is a paper layer, the composite packaging material is a paper-plastic composite packaging material. When the functional layer consists of two or three types of aluminized plastic, plastic, and paper layers, this application does not impose any special restrictions on the structure of the functional layer; it can be designed according to the intended use of the composite packaging material. In some specific implementations, the functional layer can be one, two, three, four, or five layers, etc. This application does not impose any special restrictions on its structure and thickness; it can be designed according to the intended use of the composite packaging material. In some specific implementations, the functional layer includes an aluminized PET layer and a PET layer sequentially laminated to the surface of the microfoamed film. In some specific implementations, the functional layer includes an aluminized PET layer, a printing layer, and a PET layer sequentially laminated onto the surface of the microfoamed film. Those skilled in the art will understand that when the functional layer is an ink layer or a printing layer, the ink, coating, etc., used are not opaque. In some specific implementations, the functional layer includes an aluminized BOPP layer and a BOPP layer sequentially laminated onto the surface of the microfoamed film. In some specific implementations, when the functional layer includes an aluminized plastic layer, the thickness of the aluminized layer does not exceed 5 μm. In some specific implementations, the functional layer includes a paper layer laminated onto the bottom layer of the microfoamed film, which does not affect the frosted effect of the appearance. To avoid affecting the frosted effect of the composite packaging material surface, the composite packaging material does not contain aluminum foil or an aluminized layer with a thickness exceeding 5 μm.

[0023] The composite packaging material provided in this application can be used to prepare packaging bags, such as milk powder packaging bags, cheese packaging bags and other food outer packaging bags, and can also be used to prepare packaging cups, such as yogurt cups, etc. This application does not have any special restrictions on it.

[0024] This application uses a foaming agent or foaming masterbatch at a dosage of less than 1.5 wt% to prepare a composite packaging material comprising a surface layer, an intermediate microbubble layer, and a bottom layer. The intermediate microbubble layer forms dense and uniform pores, giving the composite packaging material a frosted appearance and reducing the weight of the composite packaging material.

[0025] This application also provides a method for preparing a composite packaging material with a frosted effect, comprising the following steps:

[0026] The first resin forming the surface layer, the resin composition forming the microbubble intermediate layer, and the second resin forming the bottom layer are co-extruded and then molded to obtain a microbubble film.

[0027] The resin composition comprises 0.1 wt% to 1.5 wt% of the foaming agent described in the above technical solution and the balance matrix resin, which are formed by foaming.

[0028] Alternatively, the resin composition may be formed by foaming 0.1 wt% to 1.5 wt% of foaming masterbatch and the balance of matrix resin; the foaming masterbatch may be composed of 30 wt% to 40 wt% of sodium citrate, 30 wt% to 50 wt% of carrier resin, 3 wt% to 8 wt% of inorganic filler and the balance of additives.

[0029] This application employs a co-extrusion method to prepare microcellular membranes, which involves co-extruding a first resin forming the surface layer, a resin composition forming the microcellular intermediate layer, and a second resin forming the bottom layer, followed by molding. As mentioned above, the first resin forming the surface layer and the second resin forming the bottom layer can be selected as needed, and this application does not impose any special restrictions on them. The resin composition forming the microcellular intermediate layer is as described above and will not be repeated here.

[0030] This application does not impose any special restrictions on the mixing method of the foaming agent or foaming masterbatch with the matrix resin. It can be done manually by mixing and stirring, then adding intermittently; it can also be done online by vacuum suction; or it can be added online by extraction using a peristaltic pump or screw pump. Preferably, it is added online by extraction using a peristaltic pump or screw pump. Furthermore, the peristaltic pump or screw pump packing device used for adding the foaming agent in this invention is connected online below the main hopper. To ensure the uniformity of the mixture, after the foaming agent and the main material are mixed and stirred, a mixing screw can be added. Preferably, the mixing screw is arranged horizontally and its length is at least 50 cm.

[0031] Depending on the intended use of the composite packaging material, its forming method varies. For example, when the composite packaging material is a packaging bag, it can be extruded and formed using a blow molding machine; when the composite packaging material is made into a yogurt cup, it can be first extruded and then calendered to obtain a sheet, which is then thermoformed into a yogurt cup. This application does not impose any special restrictions on this. In some specific implementations, the co-extrusion temperature is 150℃~220℃, preferably 160℃~210℃.

[0032] After preparing the microfoamed membrane, this application further composites a functional layer onto the surface of the microfoamed membrane. The functional layer includes at least one of a paper layer, a plastic layer, and an aluminized plastic layer. This application does not impose any particular limitation on the composite method; it can be dry lamination, solvent-free lamination, extrusion (casting, coating), etc. During the lamination process, the tension of the microfoamed membrane needs to be adjusted to prevent wrinkles. In some specific implementations, a dry lamination method is used to composite the functional layer onto the surface of the microfoamed membrane; during dry lamination, the lamination tension of the microfoamed membrane is 8N to 15N, preferably 10N to 13N.

[0033] This application describes the preparation of a composite packaging material consisting of a surface layer, an intermediate microbubble layer, and a bottom layer using a foaming agent or foaming masterbatch at a dosage of less than 1.5 wt%. The intermediate microbubble layer forms dense and uniform pores, which can present a frosted appearance on the surface of the composite packaging material without significantly affecting the strength of the material. The preparation method provided in this application has no special requirements for the preparation process, can be applied to packaging in various fields, and can be colored or printed with color masterbatch, giving it more commodity attributes and meeting the diverse needs of consumers. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the layered structure of the packaging material provided in Embodiment 1 of this application;

[0035] Figure 2 A photograph of the packaging material provided in Embodiment 1 of this application;

[0036] Figure 3 This is a photograph of the micro-foamed PE film prepared in Example 2 of this application;

[0037] Figure 4 This is a SEM image of the micro-foamed PE film prepared in Example 2 of this application;

[0038] Figure 5 A photograph of the packaging material provided in Embodiment 2 of this application;

[0039] Figure 6 A photograph of the packaging material provided in Embodiment 3 of this application;

[0040] Figure 7 A photograph of the packaging material provided in Embodiment 4 of this application;

[0041] Figure 8 A photograph of the packaging material provided in Embodiment 5 of this application;

[0042] Figure 9 A photograph of the yogurt cup provided in Embodiment 6 of this application. Detailed Implementation

[0043] This invention provides a foaming agent, a composite packaging material with a frosted effect, and a method for preparing the same. Those skilled in the art can refer to this document and appropriately modify the process parameters to achieve the desired results. It is particularly important to note that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately alter and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0044] Example 1

[0045] A three-layer extrusion blown film was produced using 40:60 polyethylene 2426H and linear low-density polyethylene 1002BU as the bottom and top layers, respectively, and a mixture of polyethylene 2426H, linear low-density polyethylene 1002BU, and a liquid foaming agent in a mass ratio of 40:59:1 as the middle layer. The blown film temperature was set to 163℃ in zone 1, 168℃ in zone 2, 168℃ in zone 3, and 150℃ in zone 4, resulting in a PE film with a microbubble layer in the middle layer. The thickness ratio of the bottom, middle, and top layers was 1:7:2. The foaming agent used in the middle layer included: 20wt% sodium bicarbonate, 18wt% sodium citrate, 48wt% alkane oil, 3wt% glyceryl monostearate, 3wt% hydrated magnesium silicate, 3wt% calcium carbonate, 4.995wt% polyolefin wax and a dispersant of higher alcohols (mass ratio of 4:6), and 0.005wt% zinc oxide. Compared to PE films without microfoaming in the intermediate layer, those with microfoamed intermediate layers have an overall weight reduction of 26%.

[0046] After obtaining the PE film, a dry lamination method was used with Henkel UR 2885 as the binder to form a composite film of PET12 / printed layer / VMPET12 / PE80. The PET was Yizheng Chemical Fiber FG610, and the VMPET was Jiangyin Saisheng SH650. During the dry lamination process, the lamination tension of the PE film was 12N, the drying temperature was below 80℃, the process was stable, and there were no wrinkles after lamination.

[0047] After obtaining the composite film, it undergoes curing, quality inspection, slitting, and bag making to obtain packaging bags with a frosted effect. See the results below. Figure 1 and Figure 2 , Figure 1 This is a schematic diagram of the laminated structure of the packaging material provided in Embodiment 1 of this application, wherein 11 is a PE film, 12 is a first adhesive layer, 13 is a VMPET layer, 14 is a second adhesive layer, and 15 is a PET layer; Figure 2 A photograph of the packaging material provided in Embodiment 1 of this application. Figure 1 and Figure 2It can be seen that the packaging bag prepared in Example 1 has a uniform and dense pore surface with a frosted glass-like appearance and can be used as an outer packaging bag for milk powder.

[0048] Those skilled in the art will understand that, in the composite film prepared in this application, a printing layer may also be formed between the second adhesive layer 14 and the PET layer 15.

[0049] Example 2

[0050] A three-layer extrusion blown film was produced using 40:60 polyethylene 2426H and linear low-density polyethylene 1002BU as the bottom and top layers, respectively, and a mixture of polyethylene 2426H, linear low-density polyethylene 1002BU, and a liquid foaming agent in a mass ratio of 40:59:1 as the intermediate layer. The blown film temperature was set to 150℃ in zone 1, 168℃ in zone 2, 180℃ in zone 3, and 180℃ in zone 4, resulting in a PE film with a microbubble layer in the intermediate layer. The thickness ratio of the bottom, intermediate, and top layers was 1:7.5:1.5. The liquid foaming agent used in the intermediate layer included: 26wt% sodium bicarbonate, 23wt% sodium citrate, 42wt% alkane oil, 5wt% dispersant of polyolefin wax and higher alcohol (mass ratio 4:6), 2wt% calcium carbonate, 1.69wt% hydrated magnesium silicate, 0.3wt% glyceryl monostearate, and 0.01wt% zinc oxide. Compared to PE films without microfoaming in the intermediate layer, those with microfoamed intermediate layers show an overall weight reduction of 27%. (See also...) Figure 3 and Figure 4 , Figure 3 This is a photograph of the micro-foamed PE film prepared in Example 2 of this application. Figure 4 This is a SEM image of the microfoamed PE film prepared in Example 2 of this application. Figure 3 and Figure 4 It is known that the PE film prepared in this application has uniform and dense pores, exhibiting a frosted glass-like appearance.

[0051] After obtaining the PE film, a dry lamination method was used with Henkel UR 2885 as the binder to form a composite film of PET12 / VMPET12 / PE70, wherein PET is Yizheng Chemical Fiber FG610 and VMPET is Jiangyin Saisheng SH650. During the dry lamination process, the lamination tension of the PE film was 12N, the drying temperature was below 80℃, the process was stable, and there were no wrinkles after lamination.

[0052] After obtaining the composite film, it undergoes curing, quality inspection, slitting, and bag making to obtain packaging bags with a frosted effect. See the results below. Figure 5 , Figure 5 A photograph of the packaging material provided in Embodiment 2 of this application. Figure 5It can be seen that the packaging bag prepared in Example 2 has a uniform and dense pore surface with a frosted glass-like appearance and can be used as an outer packaging bag for milk powder.

[0053] Example 3

[0054] A three-layer extrusion blown film was produced using linear low-density polyethylene (LL0220AA) and low-density polyethylene (LDPE) 2420H (75:25) as the bottom and top layers, respectively, and a foaming agent as the intermediate layer, with a mass ratio of LL0220AA, LDPE 2420H, and foaming agent. The blown film temperature was set to 150℃ in zone 1, 168℃ in zone 2, 180℃ in zone 3, and 180℃ in zone 4, resulting in a PE film with a microbubble layer in the intermediate layer. The thickness ratio of the bottom, intermediate, and top layers was 1:7.5:1.5. The foaming agent used in the intermediate layer included: 15wt% sodium citrate, 12wt% sodium bicarbonate, 45.95wt% carrier PE, 20wt% carrier EVA, 3wt% calcium carbonate, 2wt% hydrated magnesium silicate, 2wt% glyceryl monostearate, and 0.05wt% zinc oxide. Compared to PE films without microfoaming in the intermediate layer, those with microfoamed intermediate layers have an overall weight reduction of 18%.

[0055] After obtaining the PE film, a dry lamination method was used with Henkel 7723 as the binder to form a composite film of PET12 / VMPET12 (reinforced) / PE50. The PET was produced by Guofeng Plastics Co., Ltd., and the VMPET was produced by Huangshan Yongxin Co., Ltd. During the dry lamination process, the lamination tension of the PE film was 11N, the drying temperature was below 80℃, the process was stable, and there were no wrinkles after lamination.

[0056] After obtaining the composite film, it undergoes curing, quality inspection, slitting, and bag making to obtain packaging bags with a frosted effect. See the results below. Figure 6 , Figure 6 A photograph of the packaging material provided in Embodiment 3 of this application. Figure 6 It can be seen that the packaging bag prepared in Example 3 has a uniform and dense pore surface with a frosted glass-like appearance and can be used as an outer packaging bag for cheese.

[0057] Example 4

[0058] A three-layer extrusion blown film was produced using linear low-density polyethylene (LL0220AA) and low-density polyethylene (LDPE) 2420H (75:25) as the bottom and top layers, respectively, and a foaming agent as the intermediate layer (75:24:1 by mass). The blown film temperature was set to 150℃ in zone 1, 168℃ in zone 2, 180℃ in zone 3, and 180℃ in zone 4, resulting in a PE film with a microbubble intermediate layer. The thickness ratio of the bottom, intermediate, and top layers was 1:8:1. The foaming agent used in the intermediate layer included: 10wt% sodium bicarbonate, 23wt% sodium citrate, 50wt% alkane oil, 6wt% polyolefin wax and a dispersant of higher alcohols (4:6 by mass), 8wt% titanium dioxide, and 3wt% calcium carbonate. Compared with a film without microbubble intermediate layer, the PE film with microbubble intermediate layer showed an overall weight reduction of 16%.

[0059] After obtaining the PE film, a dry lamination method was used with Henkel 7723 as the binder to form a composite film of BOPP19 / VMBOPP18 / PE50. The BOPP was produced by Guofeng Plastics Co., Ltd., and the VMBOPP was produced by Huangshan Yongxin Co., Ltd. During the dry lamination process, the lamination tension of the PE film was 12N, the drying temperature was below 80℃, the process was stable, and there were no wrinkles after lamination.

[0060] After obtaining the composite film, it undergoes curing, quality inspection, slitting, and bag making to obtain packaging bags with a frosted effect. See the results below. Figure 7 , Figure 7 A photograph of the packaging material provided in Embodiment 4 of this application. Figure 7 As can be seen, the packaging bag prepared in Example 4 has a uniform and dense pore surface with a frosted glass-like appearance and can be used as an ice cream packaging bag.

[0061] Example 5

[0062] A three-layer extrusion process was performed using polypropylene T30S (96:4 ratio) and white masterbatch as the bottom and top layers, respectively, and a liquid foaming agent (mass ratio 0.8:95.2:4), polypropylene T30S, and white masterbatch as the intermediate layer. After calendering and cooling, a PP sheet with a microbubble layer in the intermediate layer was obtained. The extruder temperatures were 205℃ in zones 1, 2, 3, 4, and 5. The thickness ratio of the bottom, intermediate, and top layers was 15:70:15. The liquid foaming agent used in the intermediate layer included: 16wt% sodium bicarbonate, 23wt% sodium citrate, 46wt% alkane oil, 6wt% dispersant of polyolefin wax and higher alcohol (mass ratio 4:6), 8.58wt% titanium dioxide, 0.4wt% hydrated magnesium silicate, and 0.02wt% zinc oxide. Compared to PP sheets without microfoaming in the intermediate layer, those with microfoamed intermediate layers result in an overall weight reduction of 16%.

[0063] After obtaining the PP sheet, it is vacuum-formed to obtain the PP cup. The material is stable during the vacuum forming process, without any blow-out or poor forming problems, and the surface has a distinct frosted effect.

[0064] After the PP cup is molded, curved surface printing is performed, resulting in a noticeable frosted effect. See the results below. Figure 8 , Figure 8 A photograph of the packaging material provided in Embodiment 5 of this application. Figure 8 It can be seen that the PP cup prepared in Example 5 has a uniform and dense pore surface with a frosted glass-like appearance and can be used for yogurt packaging.

[0065] Example 6

[0066] A four-layer sheet with an A1 / B / A2 / C structure was prepared using the formulation shown in Table 1, wherein layer A1 is a HIPS layer, layer B is a HIPS foam layer, layer A2 is a HIPS layer, and layer C is a GPPS glossy layer (layers A1 and A2 are made of the same material):

[0067] Table 1 Formulation of each layer in Example 6

[0068]

[0069] The thickness ratio of the four layers A1 / B / A2 / C is 12:75:8:5.

[0070] The above materials were co-extruded using a 7-segment heated A-screw extruder with the following heating temperatures: segment 1 202℃, segment 2 195℃, segment 3 215℃, segment 4 200℃, segment 5 217℃, segment 6 236℃, and segment 7 211℃.

[0071] The foaming agent includes: 10 wt% sodium bicarbonate, 26 wt% sodium citrate, 40 wt% alkane oil, 9 wt% polyolefin wax, a dispersant consisting of hydrocarbon paraffin and higher alcohol (mass ratio 2:3:5), 11 wt% titanium dioxide, 3.98 wt% silica powder, and 0.02 wt% zinc oxide.

[0072] After obtaining the sheet material, it is subjected to thermoforming to produce yogurt cups. The material remains stable during the thermoforming process, without any breakage or poor forming. See the results below. Figure 9 , Figure 9 A photograph of the yogurt cup provided in Embodiment 6 of this application, by [author's name]. Figure 9 It can be seen that the surface of the yogurt cup has a distinct frosted effect. After the yogurt cup is formed, curved surface printing is performed, resulting in a noticeable frosted effect.

[0073] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A foaming agent, comprising: 15wt%–30wt% sodium bicarbonate, 15wt%–25wt% sodium citrate, 30wt%–50wt% oily solvent and balance additives; The sum of the mass percentages of sodium bicarbonate and sodium citrate shall not exceed 50 wt%.

2. The foaming agent according to claim 1, characterized in that, The oily solvent is selected from one or more of alkane oil, soybean oil, isoalkane oil, and diisopropyl adipate; The additives include one or more of emulsifiers, fillers, plasticizers, dispersants, and stabilizers.

3. A composite packaging material with a frosted effect, comprising a microbubble film, wherein the microbubble film comprises a surface layer, a microbubble intermediate layer and a bottom layer sequentially laminated together; The microbubble intermediate layer is formed by foaming 0.1wt% to 1.5wt% of the foaming agent as described in claim 1 or 2 and the balance matrix resin; Alternatively, the microbubble intermediate layer is formed by foaming 0.1wt% to 1.5wt% of foaming masterbatch and the balance of matrix resin; the foaming masterbatch includes 30wt% to 40wt% sodium citrate, 30wt% to 50wt% carrier resin, 3wt% to 8wt% inorganic filler and the balance of additives.

4. The composite packaging material according to claim 3, characterized in that, The carrier resin includes one or more of polyethylene and ethylene-vinyl acetate copolymer; The inorganic filler is selected from one or more of calcium carbonate, titanium dioxide, talc, and silicon dioxide; The additives are selected from one or more of emulsifiers, fillers, plasticizers, dispersants and stabilizers.

5. The composite packaging material according to claim 3 or 4, characterized in that, The matrix resin is polyethylene, polypropylene, polylactic acid, or polystyrene; The thickness of the microbubble membrane is 30μm to 150μm.

6. The composite packaging material according to claim 5, characterized in that, It also includes a functional layer composited on the surface of the microfoamed membrane, the functional layer comprising at least one of a paper layer, a plastic layer, and an aluminized plastic layer.

7. The composite packaging material according to claim 6, characterized in that, The functional layer includes an aluminum-plated PET layer and a PET layer sequentially laminated onto the surface of the micro-foamed membrane; Alternatively, the functional layer may include an aluminum-plated BOPP layer and a BOPP layer sequentially laminated onto the surface of the microfoamed membrane.

8. The composite packaging material according to claim 6, characterized in that, The functional layer includes a paper layer composited on the bottom layer of the microfoamed membrane.

9. A method for preparing a composite packaging material with a frosted effect, comprising the following steps: The first resin forming the surface layer, the resin composition forming the microbubble intermediate layer, and the second resin forming the bottom layer are co-extruded and then molded to obtain a microbubble film. The resin composition comprises 0.1 wt% to 1.5 wt% of the foaming agent as described in claim 1 or 2 and the balance being a matrix resin formed by foaming. Alternatively, the resin composition may be formed by foaming 0.1 wt% to 1.5 wt% of foaming masterbatch and the balance of matrix resin; the foaming masterbatch may be composed of 30 wt% to 40 wt% of sodium citrate, 30 wt% to 50 wt% of carrier resin, 3 wt% to 8 wt% of inorganic filler and the balance of additives.

10. The preparation method according to claim 9, characterized in that, The co-extrusion temperature is 150℃~220℃.

11. The preparation method according to claim 9 or 10, characterized in that, Also includes: A composite functional layer is formed on the surface of the microfoamed membrane, the functional layer comprising at least one of a paper layer, a plastic layer, and an aluminized plastic layer.

12. The preparation method according to claim 11, characterized in that, A functional layer is laminated onto the surface of the micro-foamed membrane using a dry lamination method; During the dry lamination process, the lamination tension of the microfoamed membrane is 8N to 15N.

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