Adhesive resin for heat-sealing PS (polystyrene) easy-to-uncover film as well as preparation method and application of adhesive resin

Abstract

The invention discloses adhesive resin for a heat-sealing PS easy-to-uncover film as well as a preparation method and application of the adhesive resin. The adhesive resin for the heat-sealing PS easy-to-uncover film comprises the following components: an ethylene-vinyl acetate copolymer graft, an ethylene-vinyl acetate copolymer with low VA content, an ethylene-vinyl acetate copolymer with medium VA content, tackifying resin, a slipping agent and an antioxidant. After being packaged, the easy-to-uncover film prepared from the adhesive resin has the advantages of being capable of being opened once being torn, labor-saving and free of splashing, meanwhile, good sealing performance can be kept, and the easy-to-uncover film has the characteristics of being free of opening and air leakage after being stored at low temperature for a long time; the problems that in the prior art, packaging materials need to be opened violently and splash out, long-time low-temperature refrigeration cannot be achieved, and the sealing performance is poor can be effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of food packaging, and specifically relates to an adhesive resin for heat-sealing PS easy-open lid film, its preparation method, and its application. Background Technology

[0002] Heat-sealable PS (polystyrene) easy-open lid film is a high-performance packaging material. It is not just a simple sealing layer; it provides the key function of "easy-opening," offering consumers a good packaging experience by being "easy to open with a single tear, without effort or splashing," while simultaneously balancing airtightness (ensuring product safety during transportation and shelf life). It is mainly used for packaging cup and bowl-shaped foods made of PS material, such as dairy products (packaging of cup-shaped products like yogurt, pudding, and cheese), snack foods (packaging of jelly, desserts, salads, and jams), fast food and takeout (packaging of ready-to-eat meals such as soups, rice, and snacks), and pre-prepared meals (packaging of emerging refrigerated / frozen pre-prepared dishes).

[0003] Currently, demand for heat-sealed PS easy-open lid film continues to grow in both the global and Chinese markets. According to industry data, the global market's compound annual growth rate (CAGR) is projected to remain between 5% and 7%. The Chinese market, due to its large food consumption base and rapidly developing new retail formats, is experiencing a growth rate higher than the global average, with a projected CAGR of 8%-10%.

[0004] However, current heat-sealed PS cap films often suffer from a "sealed-off" phenomenon, requiring consumers to use tools or force to open them to access food, resulting in a poor user experience. Alternatively, in pursuit of "easy-open" performance, insufficient sealing can lead to adhesion failure during transportation and low-temperature storage, resulting in problems such as delamination and air leakage. This severely impacts consumers' experience with this packaging method and hinders the application of easy-open cap films in food packaging. Summary of the Invention

[0005] The primary objective of this invention is to provide an adhesive resin for heat-sealing PS easy-open film that has good processing performance, can be "torn open easily without effort or splashing", maintains good sealing performance, can be stored at low temperatures for a long time without opening, and has excellent sealing performance.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned adhesive resin for heat-sealing PS easy-open film. The preparation method is a twin-screw melt graft extrusion two-stage method: in the first stage, a graft of ethylene-vinyl acetate copolymer (EVA) is obtained by twin-screw reactive extrusion technology; in the second stage, the obtained ethylene-vinyl acetate copolymer (EVA) graft is effectively compounded with other components, extruded and granulated by a twin-screw extruder, and then dried in a storage tank to obtain the adhesive resin for heat-sealing PS easy-open film.

[0007] Another object of the present invention is to provide the application of the adhesive resin for the above-mentioned heat-sealing PS easy-open cover film.

[0008] The objective of this invention is achieved through the following technical solution: An adhesive resin for heat-sealing PS easy-open cover film comprises the following components in parts by weight: 10-30 parts of ethylene-vinyl acetate copolymer (EVA) graft, 40-70 parts of low-VA content ethylene-vinyl acetate copolymer (EVA), 5-15 parts of medium-VA content ethylene-vinyl acetate copolymer (EVA), 5-15 parts of tackifying resin, 0.5-1.0 parts of slip agent, and 0.1-0.3 parts of antioxidant; preferably comprising the following components in parts by weight: 15-25 parts of ethylene-vinyl acetate copolymer (EVA) graft, 50-70 parts of low-VA content ethylene-vinyl acetate copolymer (EVA), 10-15 parts of medium-VA content ethylene-vinyl acetate copolymer (EVA), 5-10 parts of tackifying resin, and slip agent. 0.8 to 1.0 parts, antioxidant 0.2 to 0.3 parts; more preferably, it includes the following components by mass parts: 20 to 25 parts of ethylene-vinyl acetate copolymer (EVA) graft, 57 to 62 parts of low VA content ethylene-vinyl acetate copolymer (EVA), 10 parts of medium VA content ethylene-vinyl acetate copolymer (EVA), 7 parts of tackifying resin, 0.8 parts of slip agent, antioxidant 0.2 parts; most preferably, it is prepared from the following raw materials by mass parts: 20 parts of ethylene-vinyl acetate copolymer (EVA) graft, 62 parts of low VA content ethylene-vinyl acetate copolymer (EVA), 10 parts of medium VA content ethylene-vinyl acetate copolymer (EVA), 7 parts of tackifying resin, 0.8 parts of slip agent, antioxidant 0.2 parts.

[0009] The grafted ethylene-vinyl acetate copolymer (EVA) is preferably prepared by the following method: 1.0 to 3.0 parts by weight of polar monomer and 0.10 to 0.30 parts by weight of initiator are dissolved in an organic solvent, then mixed with 100 parts by weight of ethylene-vinyl acetate copolymer (EVA), and then subjected to reactive extrusion, granulation, and drying using a twin-screw extruder to obtain the grafted ethylene-vinyl acetate copolymer (EVA).

[0010] The polar monomer is at least one selected from maleic anhydride (MAH), methyl methacrylate, methacrylic acid, acrylic acid, acrylamide, glycidyl methacrylate (GMA), fumaric acid, itaconic acid, itaconic anhydride, and methyl maleic anhydride; more preferably, maleic anhydride (MAH), acrylic acid, or glycidyl methacrylate (GMA); and most preferably, maleic anhydride (MAH).

[0011] The preferred amount of the polar monomer is 1.0 to 2.0 parts by mass; more preferably 1.5 to 2.0 parts by mass.

[0012] The initiator is at least one of dicumyl peroxide (DCP), benzoyl peroxide, di-tert-butyl peroxide (DTBP), tert-butyl peroxide, tert-butyl peracetate, tert-butyl hydroperoxide, and hydroisopropylbenzene; preferably dicumyl peroxide (DCP) or di-tert-butyl peroxide (DTBP); most preferably dicumyl peroxide (DCP).

[0013] The preferred amount of the initiator is 0.15 to 0.25 parts by weight; the most preferred amount is 0.2 to 0.25 parts by weight.

[0014] The organic solvent is preferably acetone, which serves as a reaction carrier and does not participate in the reaction.

[0015] The preferred amount of organic solvent is the sum of the mass of the polar monomer and the initiator.

[0016] The preferred density of the ethylene-vinyl acetate copolymer (EVA) is 0.940–0.965 g / cm³. 3 The ethylene-vinyl acetate copolymer (EVA) has a melt flow rate (MI) of 1–30 g / 10 min at 190 °C and 2.16 kg, and a VA content of 25%–35%; more preferably, it has a density of 0.950–0.952 g / cm³. 3 An ethylene-vinyl acetate copolymer (EVA) with a melt flow rate (MI) of 2.5–20 g / 10 min and a VA content of 28% was selected at 190 °C and 2.16 kg; the optimal density was 0.952 g / cm³. 3 An ethylene-vinyl acetate copolymer (EVA) with a melt flow rate (MI) of 20 g / 10 min and a VA content of 28% under the conditions of 190 ℃ and 2.16 kg.

[0017] The mixing speed is preferably 150-250 rpm; more preferably 200 rpm.

[0018] The processing temperature of the twin-screw extruder is preferably 140–160 °C; more preferably 140–150 °C; and most preferably 140 °C.

[0019] The screw speed of the extruder is preferably 350-500 rpm; more preferably 350-400 rpm; and most preferably 400 rpm.

[0020] The preferred density of the low-VA-content ethylene-vinyl acetate copolymer (EVA) is 0.915–0.935 g / cm³. 3The ethylene-vinyl acetate copolymer (EVA) with a low VA content and a melt flow rate (MI) of 0.5–8 g / 10 min at 190 °C and 2.16 kg is preferred; more preferably, the density is 0.929–0.932 g / cm³. 3 The preferred ethylene-vinyl acetate copolymer (EVA) has a melt flow rate (MI) of 0.8–7 g / 10 min at 190 °C and 2.16 kg, and a low VA content of 9%–9.5%; its optimal density is 0.929 g / cm³. 3 A low-VA ethylene-vinyl acetate copolymer (EVA) with a melt flow rate (MI) of 0.8 g / 10 min and a VA content of 9.5% at 190 °C and 2.16 kg.

[0021] The ethylene-vinyl acetate copolymer (EVA) with a medium VA content preferably has a density of 0.930–0.950 g / cm³. 3 The ethylene-vinyl acetate copolymer (EVA) with a melt flow rate (MI) of 8–25 g / 10 min and a VA content of 15%–20% is preferred, and the VA content is 15%–20%. More preferably, the VA content is 0.935–0.945 g / cm³. 3 The ethylene-vinyl acetate copolymer (EVA) with a melt flow rate (MI) of 15–20 g / 10 min and a VA content of 18% is selected at 190 °C and 2.16 kg; the most preferred density is 0.939 g / cm³. 3 An ethylene-vinyl acetate copolymer (EVA) with a melt flow rate (MI) of 16 g / 10 min and a VA content of 18% at 190 °C and 2.16 kg.

[0022] The tackifying resin is at least one of rosin resin, hydrogenated rosin resin, terpene resin and hydrogenated petroleum resin; preferably hydrogenated petroleum resin; more preferably hydrogenated petroleum resin with a ring and ball softening point of 100-120 °C; most preferably hydrogenated petroleum resin with a ring and ball softening point of 110-120 °C.

[0023] The slip agent is at least one of erucamide, oleamide, stearyl erucamide, silica and pentaerythritol stearate; preferably erucamide or stearyl erucamide; most preferably erucamide.

[0024] The antioxidant is preferably at least one of antioxidant 168, antioxidant 1010 and antioxidant B215; more preferably a mixture of antioxidant B215 and antioxidant 168; and most preferably a mixture obtained by mixing antioxidant 168 and antioxidant B215 in a mass ratio of 1:2.

[0025] The preparation method of the adhesive resin for the heat-sealable PS easy-open cover film specifically includes the following steps: S1. Mix the low-VA content ethylene-vinyl acetate copolymer, the medium-VA content ethylene-vinyl acetate copolymer (EVA), the tackifying resin, the slip agent, and the antioxidant evenly to obtain mixture A; S2. The mixture A obtained in step S1 and the grafted ethylene-vinyl acetate copolymer (EVA) are placed in different loss-in-weight hoppers respectively. The loss-in-weight feeding technology is used to stabilize the feeding through double weighing. The mixture is then extruded, granulated, and dried by a twin-screw extruder to obtain the adhesive resin for heat-sealing PS easy-open film.

[0026] The mixing speed in step S1 is preferably 150 to 250 rpm; more preferably 200 rpm.

[0027] The preferred processing conditions for the twin-screw extruder in step S2 are: a processing temperature of 120–150 °C and a screw speed of 350–500 rpm; more preferably, a processing temperature of 140–150 °C and a screw speed of 400–450 rpm; and most preferably, a processing temperature of 140 °C and a screw speed of 450 rpm.

[0028] The above-mentioned adhesive resin for heat-sealing PS easy-open cover film is used in the production of heat-sealing PS easy-open cover film.

[0029] The typical process for heat-sealing PS easy-open cover film is as follows: first, a pre-made film is obtained by using a three-layer co-extrusion blown film process; then, the pre-made film is combined with aluminum foil, aluminized PET or PET by a dry composite process to obtain heat-sealing PS easy-open cover film.

[0030] The preferred three-layer co-extrusion blown film process includes the following steps: using a heat-sealable PS easy-open cover film adhesive resin as the easy-open layer to be heat-sealed with PS; melting and plasticizing the heat-sealable PS easy-open cover film adhesive resin through a single-screw extruder, and simultaneously extruding it through a three-layer superimposed die along with the other two layers of resin melted through the single-screw extruder; finally, after further processing, a three-layer pre-formed film is obtained.

[0031] The preferred melting temperature is 160 °C.

[0032] The other two resin layers are preferably polyethylene (PE).

[0033] The structure of the pre-formed membrane is preferably polyethylene / polyethylene / easy-peel layer.

[0034] The processing includes the following steps: inflation, traction, thickness measurement, cooling, slitting, and winding.

[0035] The dry lamination process involves using dry lamination equipment to bond aluminum foil, aluminized PET or PET with the pre-made film obtained by the above three-layer co-extrusion blown film process using polyurethane adhesive, thereby forming a heat-sealable PS easy-open cover film.

[0036] The present invention has the following advantages and effects compared with the prior art: 1. The adhesive resin for the heat-sealing PS easy-open cover film provided by the present invention is in the form of transparent granules.

[0037] 2. The adhesive resin for the heat-sealing PS easy-open film provided by the present invention has good processing performance. After encapsulation, it can be "torn open easily, without effort, and without splashing", while maintaining good sealing performance. It has the characteristics of long-term low-temperature storage without opening and without air leakage.

[0038] 3. The adhesive resin for heat-sealing PS easy-open cover film provided by the present invention has a simple manufacturing process and is easy to process. Attached Figure Description

[0039] Figure 1 This is a flow chart of the heat-sealed PS easy-open cover film prefabricated film three-layer co-extrusion blown film forming process.

[0040] Figure 2 This is a flow chart of the dry composite molding process of heat-sealed PS easy-open cover film preform and other base films. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. It should be noted that, without conflict, the various embodiments described below can be arbitrarily combined to form new embodiments; the equipment and raw materials used can be purchased from the market or are commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0042] Example 1 (1) First, dissolve 1.6 parts by weight of maleic anhydride (MAH) and 0.22 parts by weight of dicumyl peroxide (DCP) in 1.82 parts by weight of acetone, and then add 100 parts by weight of ethylene-vinyl acetate copolymer (EVA) (density 0.952 g / cm³). 3The melt flow rate (MI) was 20 g / 10 min at 190℃ and 2.16 kg, and the VA content was 28%. The mixture was added to a high-speed mixer (speed 200 rpm) and mixed evenly. Then it was extruded and granulated by a twin-screw extruder (processing conditions: extrusion temperature 140℃, screw speed 400 rpm). Finally, it was dried in a storage tank at 60℃ to obtain the ethylene-vinyl acetate copolymer (EVA) graft (EVA-g-MAH). The grafting rate of this graft was determined to be 1.3% by acid-base titration (Gao Yongzhi, Zhang Jianbin, Liu Jianwei. Determination of maleic anhydride content in maleic anhydride grafted polypropylene by acid-base titration [J]. Engineering Plastics Application, 2005, 33(5):3.).

[0043] (2) First, the ethylene-vinyl acetate copolymer with low VA content (density 0.932 g / cm³) 3 62 parts by weight of ethylene-vinyl acetate copolymer with medium VA content (density 0.939 g / cm³) were obtained under the following conditions: melt flow rate (MI) of 7.0 g / 10 min at 190 ℃ and 2.16 kg; VA content of 9.0%; and melt flow rate (MI) of 7.0 g / 10 min at 190 ℃ and 2.16 kg. 3 10 parts by weight of a mixture A (melt flow rate (MI) of 16 g / 10 min and VA content of 18%), 7 parts by weight of a tackifying resin (hydrogenated petroleum resin with a ring and ball softening point of 115 ℃), 0.8 parts by weight of a slip agent (erucamide), and 0.2 parts by weight of an antioxidant (a mixture of antioxidant 168 and antioxidant B215 in a mass ratio of 1:2) were added together into a high-speed mixer (speed of 200 rpm) and mixed evenly to obtain 80 parts by weight of mixture A.

[0044] (3) Place mixture A in loss-in-weight weigher No. 1; then place 20 parts by mass of the grafted product (EVA-g-MAH) of ethylene-vinyl acetate copolymer (EVA) obtained in step (1) in loss-in-weight weigher No. 2; then feed the material stably by loss-in-weight feeding technology (80% of the material is fed from weigher No. 1 and 20% of the material is fed from weigher No. 2), extrude and granulate it through a twin-screw extruder (the processing conditions of the twin-screw extruder are a processing temperature of 150 ℃ and a screw speed of 400 rpm), and finally dry it in a storage tank at 60 ℃ to obtain adhesive resin granules for heat-sealing PS easy-open film.

[0045] Example 2 (1) First, dissolve 1.6 parts by weight of maleic anhydride (MAH) and 0.22 parts by weight of dicumyl peroxide (DCP) in 1.82 parts by weight of acetone, and then add 100 parts by weight of ethylene-vinyl acetate copolymer (EVA) (density 0.950 g / cm³). 3The ethylene-vinyl acetate copolymer (EVA) graft (EVA-g-MAH) was added to a high-speed mixer (200 rpm) at 190℃ and 2.16 kg, with a melt flow rate (MI) of 2.5 g / 10 min and a VA content of 28%. The mixture was then extruded and granulated using a twin-screw extruder (processing conditions: extrusion temperature 140℃, screw speed 400 rpm). Finally, the mixture was dried in a storage tank at 60℃ to obtain the grafted product (EVA-g-MAH). The grafting rate of this graft was determined to be 1.3% by acid-base titration.

[0046] (2) First, the ethylene-vinyl acetate copolymer with low VA content (density 0.929 g / cm³) 3 57 parts by weight of ethylene-vinyl acetate copolymer with medium VA content (density 0.939 g / cm³) were obtained under the following conditions: melt flow rate (MI) of 0.8 g / 10 min at 190 ℃ and 2.16 kg; VA content of 9.5%; and melt flow rate (MI) of 0.8 g / 10 min at 190 ℃ and 2.16 kg. 3 10 parts by mass of a mixture A (melt flow rate (MI) of 16 g / 10 min and VA content of 18%), 7 parts by mass of a tackifying resin (hydrogenated petroleum resin with a ring and ball softening point of 115 ℃), 0.8 parts by mass of a slip agent (erucamide), and 0.2 parts by mass of an antioxidant (a mixture of antioxidant 168 and antioxidant B215 in a mass ratio of 1:2) were added together into a high-speed mixer (speed of 200 rpm) and mixed evenly to obtain 75 parts by mass of mixture A.

[0047] (3) Place mixture A in loss-in-weight weigher No. 1; then place 25 parts by mass of the grafted product (EVA-g-MAH) of ethylene-vinyl acetate copolymer (EVA) obtained in step (1) in loss-in-weight weigher No. 2; then feed the material stably by loss-in-weight feeding technology (75% of the material is fed from weigher No. 1 and 25% of the material is fed from weigher No. 2), extrude and granulate it through a twin-screw extruder (the processing conditions of the twin-screw extruder are a processing temperature of 140 ℃ and a screw speed of 450 rpm), and finally dry it in a storage tank at 60 ℃ to obtain adhesive resin granules for heat-sealing PS easy-open film.

[0048] Example 3 (1) First, the ethylene-vinyl acetate copolymer with low VA content (density of 0.929 g / cm³) is used. 3 62 parts by weight of ethylene-vinyl acetate copolymer with medium VA content (density 0.939 g / cm³) were obtained under the following conditions: melt flow rate (MI) of 0.8 g / 10 min at 190 ℃ and 2.16 kg; VA content of 9.5%; and melt flow rate (MI) of 0.8 g / 10 min at 190 ℃ and 2.16 kg. 310 parts by weight of a mixture (melt flow rate (MI) of 16 g / 10 min and VA content of 18%), 7 parts by weight of a tackifying resin (hydrogenated petroleum resin with a ring and ball softening point of 115 ℃), 0.8 parts by weight of a slip agent (erucamide), and 0.2 parts by weight of an antioxidant (a mixture of antioxidant 168 and antioxidant B215 in a mass ratio of 1:2) were added together into a high-speed mixer (speed of 200 rpm) and mixed evenly to obtain 80 parts by weight of mixture A.

[0049] (2) Place mixture A in loss-in-weight weigher No. 1; then place 20 parts by mass of the grafted product (EVA-g-MAH) of ethylene-vinyl acetate copolymer (EVA) obtained in step (1) of Example 1 in loss-in-weight weigher No. 2; then feed the material stably by loss-in-weight feeding technology (80% of the material is fed from weigher No. 1 and 20% of the material is fed from weigher No. 2), extrude and granulate it through a twin-screw extruder (the processing conditions of the twin-screw extruder are a processing temperature of 140 ℃ and a screw speed of 450 rpm), and finally dry it in a storage tank at 60 ℃ to obtain adhesive resin granules for heat-sealing PS easy-open film.

[0050] Comparative Example 1 The only difference from Example 3 is that the grafting material is changed from ethylene-vinyl acetate copolymer (EVA) grafting material (EVA-g-MAH) to low-density polyethylene grafting material (LDPE-g-MAH), as detailed below: (1) First, dissolve 1.6 parts by weight of maleic anhydride (MAH) and 0.22 parts by weight of dicumyl peroxide (DCP) in 1.82 parts by weight of acetone, and then add 100 parts by weight of low-density polyethylene (density 0.918 g / cm³). 3 The melt flow rate (MI) was 7 g / 10 min at 190 ℃ and 2.16 kg. The mixture was added to a high-speed mixer (200 rpm) and mixed evenly. Then, it was extruded and granulated by a twin-screw extruder (processing conditions: extrusion temperature 160 ℃, screw speed 400 rpm). Finally, it was dried in a storage tank at 60 ℃ to obtain low-density polyethylene graft (LDPE-g-MAH). The grafting rate of this graft was determined to be 1.3% by acid-base titration.

[0051] (2) First, the ethylene-vinyl acetate copolymer with low VA content (density 0.929 g / cm³) 3 62 parts by weight of ethylene-vinyl acetate copolymer with medium VA content (density 0.939 g / cm³) were obtained under the following conditions: melt flow rate (MI) of 0.8 g / 10 min at 190 ℃ and 2.16 kg; VA content of 9.5%; and melt flow rate (MI) of 0.8 g / 10 min at 190 ℃ and 2.16 kg. 310 parts by weight of a mixture (melt flow rate (MI) of 16 g / 10 min and VA content of 18%), 7 parts by weight of a tackifying resin (hydrogenated petroleum resin with a ring and ball softening point of 115 ℃), 0.8 parts by weight of a slip agent (erucamide), and 0.2 parts by weight of an antioxidant (a mixture of antioxidant 168 and antioxidant B215 in a mass ratio of 1:2) were added together into a high-speed mixer (speed of 200 rpm) and mixed evenly to obtain 80 parts by weight of mixture A.

[0052] (3) Place mixture A in loss-in-weight weigher No. 1; then place 20 parts by weight of the low-density polyethylene graft (LDPE-g-MAH) obtained in step (1) in loss-in-weight weigher No. 2; then feed the material stably using loss-in-weight feeding technology (80% of the material is fed from weigher No. 1 and 20% of the material is fed from weigher No. 2), extrude and granulate it through a twin-screw extruder (the processing conditions of the twin-screw extruder are a processing temperature of 150 ℃ and a screw speed of 450 rpm), and finally dry it in a storage tank at 60 ℃ to obtain adhesive resin granules for heat-sealing PS easy-open film.

[0053] Comparative Example 2 The only difference from Example 3 is that the grafting material is changed from ethylene-vinyl acetate copolymer (EVA) grafting material (EVA-g-MAH) to POE grafting material (POE-g-MAH), as detailed below: (1) First, dissolve 1.6 parts by mass of maleic anhydride (MAH) and 0.22 parts by mass of dicumyl peroxide (DCP) in 1.82 parts by mass of acetone, and then add 100 parts by mass of POE (density 0.870 g / cm³). 3 The POE graft (POE-g-MAH) was added to a high-speed mixer (200 rpm) at 190 ℃ and 2.16 kg with a melt flow rate (MI) of 5.0 g / 10 min and mixed evenly. Then, it was extruded and granulated by a twin-screw extruder (processing conditions: extrusion temperature 160 ℃, screw speed 400 rpm). Finally, it was dried in a storage tank at 60 ℃ to obtain the POE graft (POE-g-MAH). The grafting rate of this graft was determined to be 1.3% by acid-base titration.

[0054] (2) First, the ethylene-vinyl acetate copolymer with low VA content (density 0.929 g / cm³) 3 62 parts by weight of ethylene-vinyl acetate copolymer with medium VA content (density 0.939 g / cm³) were obtained under the following conditions: melt flow rate (MI) of 0.8 g / 10 min at 190℃ and 2.16 kg; VA content of 9.5%; and melt flow rate (MI) of 0.8 g / 10 min at 190℃ and 2.16 kg. 310 parts by weight of a mixture (melt flow rate (MI) of 16 g / 10 min and VA content of 18%), 7 parts by weight of a tackifying resin (hydrogenated petroleum resin with a ring and ball softening point of 115 ℃), 0.8 parts by weight of a slip agent (erucamide), and 0.2 parts by weight of an antioxidant (a mixture of antioxidant 168 and antioxidant B215 in a mass ratio of 1:2) were added together into a high-speed mixer (speed of 200 rpm) and mixed evenly to obtain 80 parts by weight of mixture A.

[0055] (3) Place mixture A in loss-in-weight weigher No. 1; then place 20 parts by mass of the grafted product (EVA-g-MAH) of ethylene-vinyl acetate copolymer (EVA) obtained in step (1) in loss-in-weight weigher No. 2; then feed the material stably by loss-in-weight feeding technology (80% of the material is fed from weigher No. 1 and 20% of the material is fed from weigher No. 2), extrude and granulate it through a twin-screw extruder (the processing conditions of the twin-screw extruder are a processing temperature of 140 ℃ and a screw speed of 450 rpm), and finally dry it in a storage tank at 60 ℃ to obtain adhesive resin granules for heat-sealing PS easy-open film.

[0056] Comparative Example 3 The only difference from Example 3 is that POE replaces the ethylene-vinyl acetate copolymer with low VA content, as detailed below: (1) First, POE (density is 0.902 g / cm³) 3 62 parts by weight of ethylene-vinyl acetate copolymer with medium VA content (density 0.939 g / cm³) were obtained at 190 °C and 2.16 kg with a melt flow rate (MI) of 1 g / 10 min. 3 10 parts by weight of a mixture (melt flow rate (MI) of 16 g / 10 min and VA content of 18%), 7 parts by weight of a tackifying resin (hydrogenated petroleum resin with a ring and ball softening point of 115 ℃), 0.8 parts by weight of a slip agent (erucamide), and 0.2 parts by weight of an antioxidant (a mixture of antioxidant 168 and antioxidant B215 in a mass ratio of 1:2) were added together into a high-speed mixer (speed of 200 rpm) and mixed evenly to obtain 80 parts by weight of mixture A.

[0057] (2) Place mixture A in loss-in-weight weigher No. 1; then place 20 parts by mass of the grafted product (EVA-g-MAH) of ethylene-vinyl acetate copolymer (EVA) obtained in step (1) of Example 1 in loss-in-weight weigher No. 2; then feed the material stably by loss-in-weight feeding technology (80% of the material is fed from weigher No. 1 and 20% of the material is fed from weigher No. 2), extrude and granulate it through a twin-screw extruder (the processing conditions of the twin-screw extruder are a processing temperature of 150 ℃ and a screw speed of 450 rpm), and finally dry it in a storage tank at 60 ℃ to obtain adhesive resin granules for heat-sealing PS easy-open film.

[0058] Comparative Example 4 The only difference from Example 3 is that the slip agent is removed and the amount of ethylene-vinyl acetate copolymer (EVA) graft (EVA-g-MAH) is increased, as follows: (1) First, the ethylene-vinyl acetate copolymer with low VA content (density of 0.929 g / cm³) is used. 3 62 parts by weight of ethylene-vinyl acetate copolymer with medium VA content (density 0.939 g / cm³) were obtained under the following conditions: melt flow rate (MI) of 0.8 g / 10 min at 190 ℃ and 2.16 kg; VA content of 9.5%; and melt flow rate (MI) of 0.8 g / 10 min at 190 ℃ and 2.16 kg. 3 10 parts by mass of a melt flow rate (MI) of 16 g / 10 min and a VA content of 18% under the conditions of 190 ℃ and 2.16 kg, 7 parts by mass of a tackifying resin (hydrogenated petroleum resin with a ring and ball softening point of 115 ℃), and 0.2 parts by mass of an antioxidant (a mixture of antioxidant 168 and antioxidant B215 in a mass ratio of 1:2) were added together into a high-speed mixer (speed of 200 rpm) and mixed evenly to obtain 79.2 parts by mass of mixture A.

[0059] (2) Place mixture A in loss-in-weight weigher No. 1; then place 20.8 parts by weight of the grafted product (EVA-g-MAH) of ethylene-vinyl acetate copolymer (EVA) obtained in step (1) of Example 1 in loss-in-weight weigher No. 2; then feed the material stably by loss-in-weight feeding technology (80% of the material is fed from weigher No. 1 and 20% of the material is fed from weigher No. 2), extrude and granulate it through a twin-screw extruder (the processing conditions of the twin-screw extruder are a processing temperature of 140 ℃ and a screw speed of 450 rpm), and finally dry it in a storage tank at 60 ℃ to obtain adhesive resin granules for heat-sealing PS easy-open film.

[0060] Performance testing: First, the adhesive resin particles for the heat-sealable PS easy-open film obtained in Examples 1-3 and Comparative Examples 1-4 were used in a three-layer co-extrusion blown film process. The process involved extrusion and blown film production using three single-screw extruders to obtain a pre-formed film containing an easy-open layer (structure: easy-open layer / PE / PE, where the thickness of the easy-open layer is 18 micrometers and the total thickness is 20 micrometers). Then, the pre-formed film was bonded to aluminized PET using a dry lamination process to prepare a heat-sealable PS easy-open film with a total thickness of 80 micrometers.

[0061] Heat-sealing performance test: The heat-sealing PS easy-open cover film prepared above was cut into 15mm×200mm strips, and then heat-sealed with PS using heat-sealing equipment. The heat-sealing process was 180℃, 0.45 MPa, and 1 s. The heat-sealed strips were then peeled off at 180℃ using a microcomputer-controlled electronic universal testing machine (tensile speed 300mm / min). The heat-sealing strength between the heat-sealed PS easy-open cover film and PS was tested.

[0062] Easy-open performance test: The heat-sealing PS easy-open lid film prepared above was cut into 60 mm × 60 mm samples, and then heat-sealed with a PS material cup (filled with water) with a diameter of 50 mm and a height of 40 mm. The heat-sealing process was 210 ℃, 0.45 MPa and 3 s. Then, the lid film was torn open by hand to feel the tearing force and observe whether any liquid splashed out.

[0063] Low-temperature refrigeration test at 8 ℃: The heat-sealing PS easy-open lid film prepared above was cut into 60 mm × 60 mm sample pieces, and then heat-sealed with a cup (filled with water) with a diameter of 50 mm and a height of 40 mm. The heat-sealing process was 210 ℃, pressure of 0.45 MPa, and time of 3 s. Then it was placed in a low-temperature chamber, and the test program was set as follows: temperature 8 ℃ and time 180 days. Finally, it was observed whether there were any openings or leaks at the seal of the cup.

[0064] Sealing performance test: The heat-sealing PS easy-open cover film prepared above was cut into 60 mm × 60 mm samples, and then heat-sealed with a cup (empty cup) with a diameter of 50 mm and a height of 40 mm. The heat-sealing process was 210 ℃, 0.45 MPa, and 3 s. The sealing performance was tested using a negative pressure sealing tester (test program settings: pressure -0.4 MPa, time 60 s).

[0065] The test data of the multilayer co-extruded film prepared above are shown in Table 1 below.

[0066] Table 1. Test results of hot melt adhesives in Examples 1-3 and Comparative Examples 1-4

[0067] Application Examples The process of using the adhesive resin for the heat-sealing PS easy-open cover film of the present invention in heat-sealing PS products includes the following steps (such as...). Figure 1 and Figure 2 As shown): Heat-sealable PS easy-open lid film is produced using adhesive resin granules as raw material. A three-layer co-extrusion blown film process is employed, using three single-screw extruders for extrusion and blown film production to obtain a pre-formed film containing an easy-open layer (structure: easy-open layer / PE / PE, where the thickness of the easy-open layer is 18 micrometers, and the total thickness is 20 micrometers). Then, a dry lamination process is used to bond the pre-formed film to aluminized PET to prepare a heat-sealable PS easy-open lid film with a total thickness of 80 micrometers. Finally, the prepared heat-sealable PS easy-open lid film is heat-sealed and packaged with cup-shaped or bowl-shaped PS. Testing in Examples 1-3 showed that the heat-sealable PS easy-open lid film, when sealed with PS cups, exhibits "easy to open with a single tear, no effort, and no splashing," while maintaining good sealing performance. It also has the characteristics of long-term low-temperature storage without opening or leakage. This effectively solves the problems of existing technologies, such as the need for "forceful opening" leading to spillage, inability to withstand long-term low-temperature storage, and poor sealing performance.

[0068] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An adhesive resin for heat-sealing PS easy-open cover film, characterized in that... It includes the following components by weight: 10-30 parts of grafted ethylene-vinyl acetate copolymer, 40-70 parts of ethylene-vinyl acetate copolymer with low VA content, 5-15 parts of ethylene-vinyl acetate copolymer with medium VA content, 5-15 parts of tackifying resin, 0.5-1.0 parts of slip agent, and 0.1-0.3 parts of antioxidant; The grafted product of the ethylene-vinyl acetate copolymer was prepared by the following method: 1.0 to 3.0 parts by weight of polar monomer and 0.10 to 0.30 parts by weight of initiator were dissolved in an organic solvent, then mixed with 100 parts by weight of ethylene-vinyl acetate copolymer, and then subjected to reactive extrusion, granulation and drying by a twin-screw extruder to obtain the grafted product of ethylene-vinyl acetate copolymer. The aforementioned low-VA-content ethylene-vinyl acetate copolymer has a density of 0.915–0.935 g / cm³. 3 An ethylene-vinyl acetate copolymer with low VA content, having a melt flow rate of 0.5–8 g / 10 min and a VA content of 8%–12%, under conditions of 190 °C and 2.16 kg. The ethylene-vinyl acetate copolymer with medium VA content has a density of 0.930–0.950 g / cm³. 3 An ethylene-vinyl acetate copolymer with a medium VA content of 15%-20% and a melt flow rate of 8-25 g / 10min at 190 ℃ and 2.16 kg.

2. The adhesive resin for heat-sealing PS easy-open cover film according to claim 1, characterized in that... It includes the following components by weight: 15-25 parts of grafted ethylene-vinyl acetate copolymer, 50-70 parts of ethylene-vinyl acetate copolymer with low VA content, 10-15 parts of ethylene-vinyl acetate copolymer with medium VA content, 5-10 parts of tackifying resin, 0.8-1.0 parts of slip agent, and 0.2-0.3 parts of antioxidant.

3. The adhesive resin for heat-sealing PS easy-open cover film according to claim 2, characterized in that... It includes the following components by weight: 20-25 parts of ethylene-vinyl acetate copolymer graft, 57-62 parts of ethylene-vinyl acetate copolymer with low VA content, 10 parts of ethylene-vinyl acetate copolymer with medium VA content, 7 parts of tackifying resin, 0.8 parts of slip agent, and 0.2 parts of antioxidant.

4. The adhesive resin for heat-sealing PS easy-open cover film according to any one of claims 1 to 3, characterized in that: In the preparation of grafts of ethylene-vinyl acetate copolymer: The polar monomer is at least one of maleic anhydride, methyl methacrylate, methacrylic acid, acrylic acid, acrylamide, glycidyl methacrylate, fumaric acid, itaconic acid, itaconic anhydride and methyl maleic anhydride. The initiator is at least one selected from dicumyl peroxide, benzoyl peroxide, di-tert-butyl peroxide, tert-butyl peroxide, tert-butyl peracetate, tert-butyl hydroperoxide, and cumyl hydroperoxide. The organic solvent is acetone; The ethylene-vinyl acetate copolymer has a density of 0.940–0.965 g / cm³. 3 An ethylene-vinyl acetate copolymer with a melt flow rate of 1-30 g / 10 min and a VA content of 25%-35% under the conditions of 190 ℃ and 2.16 kg. The aforementioned low-VA-content ethylene-vinyl acetate copolymer has a density of 0.929–0.932 g / cm³. 3 A low-VA-content ethylene-vinyl acetate copolymer with a melt flow rate of 0.8–7 g / 10 min and a VA content of 9%–9.5% under conditions of 190 °C and 2.16 kg. The ethylene-vinyl acetate copolymer with medium VA content has a density of 0.935–0.945 g / cm³. 3 An ethylene-vinyl acetate copolymer with a medium VA content of 18% and a melt flow rate of 15-20 g / 10min at 190 ℃ and 2.16 kg. The tackifying resin is at least one of rosin resin, hydrogenated rosin resin, terpene resin, and hydrogenated petroleum resin; The slip agent is at least one of erucamide, oleamide, stearyl erucamide, silica, and pentaerythritol stearate; The antioxidant is at least one of antioxidant 168, antioxidant 1010 and antioxidant B215.

5. The adhesive resin for heat-sealing PS easy-open cover film according to claim 4, characterized in that: In the preparation of grafts of ethylene-vinyl acetate copolymer: The ethylene-vinyl acetate copolymer has a density of 0.950–0.952 g / cm³. 3 An ethylene-vinyl acetate copolymer with a melt flow rate of 2.5–20 g / 10 min and a VA content of 28% under conditions of 190 °C and 2.16 kg. The tackifying resin is a hydrogenated petroleum resin with a ring and ball softening point of 100-120 °C. The antioxidant is a mixture of antioxidant 168 and antioxidant B215 in a mass ratio of 1:

2.

6. The adhesive resin for heat-sealing PS easy-open cover film according to any one of claims 1 to 3, characterized in that: The amount of the polar monomer used is 1.0 to 2.0 parts by weight; The amount of the initiator used is 0.15 to 0.25 parts by weight; The amount of organic solvent used is the total mass of the polar monomer and the initiator; The processing temperature of the twin-screw extruder is 140–160 °C; The screw speed of the extruder is 350-500 rpm.

7. The method for preparing the adhesive resin for heat-sealing PS easy-open film according to any one of claims 1 to 6, characterized in that... Includes the following steps: S1. Mix the low-VA content ethylene-vinyl acetate copolymer, the medium-VA content ethylene-vinyl acetate copolymer, the tackifying resin, the slip agent, and the antioxidant evenly to obtain mixture A; S2. The mixture A obtained in step S1 and the grafted ethylene-vinyl acetate copolymer are placed in different loss-in-weight hoppers respectively. The loss-in-weight feeding technology is used to stabilize the feeding through double weighing. The mixture is then extruded, granulated, and dried by a twin-screw extruder to obtain the adhesive resin for heat-sealing PS easy-open film.

8. The application of the adhesive resin for heat-sealing PS easy-open film according to any one of claims 1 to 6 in the production of heat-sealing PS easy-open film.

9. The application according to claim 8, characterized in that: The heat-sealable PS easy-open cover film is prepared by the following steps: First, a pre-formed film is obtained by a three-layer co-extrusion blown film process; then, the pre-formed film is combined with aluminum foil, aluminized PET or PET by a dry composite process to obtain the heat-sealable PS easy-open cover film. The three-layer co-extrusion blown film process includes the following steps: using the adhesive resin for heat-sealable PS easy-open cap film as described in any one of claims 1 to 6 as the easy-open layer for heat-sealing with PS; melting and plasticizing the adhesive resin for heat-sealable PS easy-open cap film as described in any one of claims 1 to 6 through a single-screw extruder, and simultaneously extruding it through a three-layer superimposed die along with the other two layers of resin melted through the single-screw extruder; finally, after further processing, a three-layer pre-formed film is obtained. The dry lamination process involves using dry lamination equipment to bond aluminum foil, aluminized PET or PET to a three-layer pre-made film using polyurethane adhesive, resulting in a heat-sealable PS easy-open cover film.

10. The application according to claim 9, characterized in that: The other two resin layers are polyethylene; The structure of the pre-formed membrane is polyethylene / polyethylene / easy-peel layer.

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