High-easy-to-tear PE film and preparation method thereof

Abstract

The invention discloses a PE film with high easy-to-tear performance. The PE film with high easy-to-tear performance adopts a three-layer co-extrusion structure; the outer layer comprises the following components in parts by weight: 0-40 parts of linear low-density polyethylene, 35-50 parts of low-density polyethylene, 0-35 parts of modified resin and 15-30 parts of high-density polyethylene; the middle layer comprises the following components in parts by weight: 10-40 parts of low-density polyethylene, 0-35 parts of modified resin and 15-30 parts of high-density polyethylene; the inner layer comprises the following components in parts by weight: 0-55 parts of linear low-density polyethylene, 15-95 parts of low-density polyethylene and 5-35 parts of metallocene polyethylene. According to the invention, different types and different models of polyethylene are selected, three-layer co-extrusion processing is adopted, and a directional stretching process is matched with a proper blow-up ratio and a proper stretch ratio, so that the prepared PE film has high easy-to-tear property and also has good sealing performance, pressure resistance and anti-falling performance.

Description

Technical Field

[0001] The invention belongs to the technical field of packaging, and particularly relates to a highly tearable PE film and a preparation method thereof. Background Art

[0002] Due to the molecular chain entanglement and semi-crystalline properties, the Elmendorf tear force of traditional PE film is generally higher than 30N, far exceeding the ergonomic comfortable tear force threshold of 1.5-4N, resulting in the need for scissors or serrated incisions to assist in opening the packaging bag.

[0003] Foreign research on highly tearable PE films focuses more on multi-layer composite structures. For example, Japanese companies have developed a PET12 / PE147 / PE45 / PET12 / AL20 / PE45 structure, which achieves a combination of high barrier properties and easy tearing through a pre-combination process. The outer PET layer provides strength, the middle PE layer enables easy tearing, and the aluminum foil layer enhances barrier properties. Another example is the Exceed? series of mPE films developed by Dow Chemical in the United States, which controls crystallization behavior through a narrow molecular weight distribution (PDI=2.1), stabilizing the tear force at 15±2N.

[0004] Domestic research on highly tearable polyethylene (PE) films focuses on the blending of LDPE (low-density polyethylene), LLDPE (linear low-density polyethylene) and HDPE (high-density polyethylene), improving tearability by regulating crystallinity and chain segment mobility.

[0005] At present, high-tear polyethylene (PE) film is mainly used in the medical field and has not yet been widely used in fast-moving consumer goods fields such as food and daily necessities packaging. In order to provide users with a better user experience in the food and daily necessities fields, a PE packaging film with high tearability, as well as good sealing performance, pressure resistance and drop resistance is proposed. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned prior art and provide a highly tearable PE film and a preparation method thereof, which can have high tearability while also having good sealing performance, pressure resistance and drop resistance.

[0007] The technical solution adopted by the present invention is: a highly tearable PE film, wherein the highly tearable PE film adopts a three-layer co-extrusion structure; The outer layer comprises the following components in parts by weight: 0-40 parts of linear low-density polyethylene, 35-50 parts of low-density polyethylene, 0-35 parts of modified resin and 15-30 parts of high-density polyethylene; The middle layer comprises the following components in parts by weight: 10-40 parts of low-density polyethylene, 0-35 parts of modified resin and 15-30 parts of high-density polyethylene; The inner layer comprises the following components in parts by weight: 0-55 parts of linear low-density polyethylene, 15-95 parts of low-density polyethylene and 5-35 parts of metallocene polyethylene.

[0008] Preferably, the high-tearability PE film adopts a three-layer co-extrusion structure, wherein the outer layer comprises 35 parts of linear low-density polyethylene, 40 parts of low-density polyethylene and 25 parts of high-density polyethylene in parts by weight; the middle layer comprises 35 parts of low-density polyethylene, 40 parts of modified resin and 25 parts of high-density polyethylene in parts by weight; and the inner layer comprises 50 parts of linear low-density polyethylene, 20 parts of low-density polyethylene and 30 parts of metallocene polyethylene in parts by weight.

[0009] Preferably, the high-tearability PE film adopts a three-layer co-extrusion structure, wherein the outer layer comprises 35 parts of linear low-density polyethylene, 40 parts of low-density polyethylene and 25 parts of high-density polyethylene in parts by weight; the middle layer comprises 15 parts of low-density polyethylene, 60 parts of modified resin and 25 parts of high-density polyethylene in parts by weight; and the inner layer comprises 50 parts of linear low-density polyethylene, 20 parts of low-density polyethylene and 30 parts of metallocene polyethylene in parts by weight.

[0010] Preferably, the high-tearability PE film adopts a three-layer co-extrusion structure, wherein the outer layer comprises 45 parts of low-density polyethylene, 30 parts of modified resin and 25 parts of high-density polyethylene by weight; the middle layer comprises 15 parts of low-density polyethylene, 60 parts of modified resin and 25 parts of high-density polyethylene by weight; and the inner layer comprises 89 parts of low-density polyethylene and 10 parts of metallocene polyethylene by weight.

[0011] Preferably, a method for preparing a highly tearable PE film comprises mixing the outer layer formula, the middle layer formula and the inner layer formula respectively through a mixer, and then extruding the mixed layers through a twin-screw extruder at an extrusion speed of 8-10 kg / min. The three-layer extrudate is blown through a die head, and transverse blowing and longitudinal stretching are adopted during the blow molding process, wherein the blowing ratio is 2-3 and the stretching ratio is 3-4. After blow molding, the film is cooled and rolled up.

[0012] Preferably, the temperatures of the feeding section, compression section and plasticizing section of the outer layer extrusion are 175-190°C, 175-190°C and 180-195°C respectively.

[0013] Preferably, the temperatures of the feeding section, compression section and plasticizing section of the middle layer extrusion are 180-195°C, 180-195°C and 175-190°C respectively.

[0014] Preferably, the temperatures of the feeding section, compression section and plasticizing section of the inner layer extrusion are 175-185°C, 175-185°C and 175-190°C respectively.

[0015] Preferably, the temperature of the neck area and the die mouth area of ​​the blow molding die head are both 170-185°C.

[0016] Preferably, the cooling includes natural cooling and forced cooling. The natural cooling is to extend the film path and increase the natural cooling time. The forced cooling is to add water-cooled guide rollers.

[0017] The beneficial effects of the present invention are: (1) By selecting polyethylene with a relatively short main chain, more side chains, and a narrow molecular weight distribution that is both tough and brittle, the molecular structure inside the film is ensured to be more neatly arranged, making it easier to propagate in a straight line in a certain direction when tearing, thereby improving the tearability of the film; (2) By adopting directional stretching, i.e. transverse blowing and longitudinal stretching process, the film can be torn along the preset direction, providing excellent linear tearing performance.

[0018] The present invention selects polyethylene of different types and models, adopts three-layer co-extrusion processing, and adopts a directional stretching process with a suitable blowing ratio and stretching ratio, so that the prepared PE film has high tearability and also has good sealing performance, pressure resistance and drop resistance. DETAILED DESCRIPTION

[0019] The present invention will be further described in detail below with reference to specific embodiments. Example

[0020] This embodiment provides a highly tearable PE film, wherein the highly tearable PE film adopts a three-layer co-extrusion structure; The outer layer comprises, by weight, 35 parts of linear low-density polyethylene, 40 parts of low-density polyethylene, and 25 parts of high-density polyethylene; the linear low-density polyethylene and low-density polyethylene have good strength and puncture resistance, while the high-density polyethylene has relatively easy-to-tear properties; the linear low-density polyethylene of the outer layer is 35B type, the low-density polyethylene is 6230 type, and the high-density polyethylene is 04660 type; The middle layer comprises 35 parts of low-density polyethylene, 40 parts of modified resin, and 25 parts of high-density polyethylene, by weight. The modified resin and high-density polyethylene have good tearability, while the low-density polyethylene provides certain puncture resistance and strength. The low-density polyethylene of the middle layer is 6230, the modified resin is 20 parts of SJ102 and 20 parts of 9009YX respectively, and the high-density polyethylene is 04660. The inner layer comprises 50 parts by weight of linear low-density polyethylene, 20 parts by weight of low-density polyethylene, and 30 parts by weight of metallocene polyethylene. The combination of linear low-density polyethylene, low-density polyethylene, and metallocene polyethylene gives the inner layer excellent heat-sealing properties. The linear low-density polyethylene of the inner layer is 35B type, the low-density polyethylene is 2426 type, and the metallocene polyethylene is 1520 type. The raw material ratio design of the three-layer structure above makes the outer layer have good strength and puncture resistance, the middle layer can provide good rigidity and easy tearing performance, and the inner layer can ensure good heat sealing performance, pressure resistance and drop resistance. The outer layer formula amount, the middle layer formula amount and the inner layer formula amount are mixed respectively by a mixer, and then the three-layer structure is extruded simultaneously by three twin-screw extruders, the temperatures of the feeding section, compression section and plasticizing section of the outer layer extruder are 175°C, 180°C and 185°C respectively, the temperatures of the feeding section, compression section and plasticizing section of the middle layer extruder are 180°C, 185°C and 190°C respectively, and the temperatures of the feeding section, compression section and plasticizing section of the inner layer extruder are 175°C, 180°C and 185°C respectively, and composite blow molding is carried out after co-extrusion, the temperature of the neck area of ​​the blow molding die head is 170°C, and the temperature of the die area is 180°C; The blow molding process uses a directional stretching process of transverse blowing and longitudinal stretching. By directional stretching and blowing the blown film in the longitudinal and transverse directions, the molecular chains are arranged in an orderly manner along the longitudinal or transverse direction, reducing the disordered area, increasing the orderly arranged crystal part, and improving the crystallinity. This can not only increase the tensile strength, transparency, barrier properties, etc. of the polyethylene film, but also change the tearing properties of the polyethylene blown film. Control the transverse molecular orientation and transverse crystallinity of the blown film. A higher blow-up ratio can increase the transverse tensile strength of the film and improve the barrier properties of the film. However, an excessively high blow-up ratio will result in uneven film thickness and reduce the transverse tearing performance of the film. Therefore, controlling the blow-up ratio to 2-3 can ensure a certain transverse strength while avoiding excessive crystallization that leads to increased brittleness, helping to maintain good tearing properties. Control the longitudinal orientation and longitudinal crystallinity of the blown film. A higher stretch ratio will lead to higher crystallinity, which can not only improve the longitudinal tensile strength and hardness of the film, but also improve the transparency of the film. However, an excessively high stretch ratio will reduce the longitudinal tearing performance of the film. At the same time, a lower stretch ratio can maintain a certain degree of flexibility, which helps to improve the tearing performance, but it will sacrifice the mechanical strength of the film. Therefore, the stretch ratio is controlled at 3-4; During the longitudinal stretching and transverse blowing process, the longitudinal stretching speed and the transverse blowing speed should be matched with each other to avoid stress concentration or uneven stretching; The effect of cooling rate after blow molding on crystallinity: rapid cooling will inhibit the crystallization process and maintain a higher proportion of amorphous state; slow cooling will help to improve crystallinity, and the effect of crystallinity on tearing: high crystallinity means that the orderly arranged molecular chains not only provide a stronger internal support structure, making the film have higher mechanical strength, but also make the film harder and more brittle, prone to cracks or tearing points; low crystallinity means more amorphous areas, because the molecules are more loosely arranged, it is easier to break in a specific direction, thereby improving the tearing performance; therefore, we use the "frost line" to accurately Control is used to control the inflation cooling rate, thereby controlling the molecular crystallinity of the film. By replacing the ordinary air ring with a high-efficiency air ring, the cooling efficiency is improved, and the extrusion speed is reduced from the conventional 10.5-12.5kg / min to 8-10kg / min. The frost line height can be well controlled at 250-300mm. By replacing the high-efficiency air ring and controlling the extrusion speed at 8-10kg / min, the film can obtain excellent physical and mechanical properties, and at the same time obtain better molecular crystallinity, thereby improving the film's tearability. After blow molding, when the film passes through one traction, before winding, an array of guide rollers can be added to extend the film's path and increase the natural cooling time. At the same time, a forced cooling device can be added. The cooling device is a water-cooled guide roller with a diameter of 300-400. This can further effectively control the crystallinity of the film, enable the film to further obtain excellent physical and mechanical properties and transparency, and further improve the film's tearability. Example

[0021] This embodiment is substantially the same as embodiment 1, except that the raw material ratios of the inner layer, the middle layer, and the outer layer are different, and the extrusion temperature and the blow molding temperature of the inner layer, the middle layer, and the outer layer are different; the outer layer comprises, by weight, 35 parts of linear low-density polyethylene, 40 parts of low-density polyethylene, and 25 parts of high-density polyethylene; the linear low-density polyethylene of the outer layer is of type 35B, the low-density polyethylene is of type 6230, and the high-density polyethylene is of type 04660; The middle layer comprises 15 parts of low-density polyethylene, 60 parts of modified resin and 25 parts of high-density polyethylene by weight; the low-density polyethylene of the middle layer adopts 6230 model, the modified resin adopts 30 parts of SJ102 model and 30 parts of 9009YX model respectively, and the high-density polyethylene adopts 04660 model; The inner layer comprises 50 parts of linear low-density polyethylene, 20 parts of low-density polyethylene and 30 parts of metallocene polyethylene by weight; the linear low-density polyethylene of the inner layer adopts 35B model, the low-density polyethylene adopts 2426 model, and the metallocene polyethylene adopts 1520 model; The temperatures of the feed section, compression section and plasticizing section of the extruder for the outer layer are 180°C, 185°C and 190°C respectively; the temperatures of the feed section, compression section and plasticizing section of the extruder for the middle layer are 185°C, 190°C and 190°C respectively; the temperatures of the feed section, compression section and plasticizing section of the extruder for the inner layer are 180°C, 185°C and 190°C respectively; after co-extrusion, composite blow molding is carried out, the temperature of the neck zone of the blow molding die is 180°C, and the temperature of the die mouth zone is 185°C. Example

[0022] This embodiment is substantially the same as embodiment 1, except that the raw material ratios of the inner layer, the middle layer, and the outer layer are different, and the extrusion temperature and the blow molding temperature of the inner layer, the middle layer, and the outer layer are different; the outer layer comprises, by weight, 45 parts of low-density polyethylene, 30 parts of modified resin, and 25 parts of high-density polyethylene; the low-density polyethylene of the outer layer is of type 6230, the modified resins are 15 parts of SJ102 and 15 parts of 9009YX respectively, and the high-density polyethylene is of type 04660; The middle layer comprises 15 parts of low-density polyethylene, 60 parts of modified resin and 25 parts of high-density polyethylene by weight; the low-density polyethylene of the middle layer adopts 6230 model, the modified resin adopts 30 parts of SJ102 model and 30 parts of 9009YX model respectively, and the high-density polyethylene adopts 04660 model; The inner layer comprises 89 parts of low-density polyethylene and 10 parts of metallocene polyethylene by weight; the low-density polyethylene of the inner layer adopts 44 parts of 6230 model and 45 parts of 2426 model respectively, and the metallocene polyethylene adopts 1520 model; The temperatures of the feed section, compression section and plasticizing section of the extruder for the outer layer are 185°C, 190°C and 195°C respectively; the temperatures of the feed section, compression section and plasticizing section of the extruder for the middle layer are 180°C, 185°C and 190°C respectively; the temperatures of the feed section, compression section and plasticizing section of the extruder for the inner layer are 175°C, 185°C and 190°C respectively; after co-extrusion, composite blow molding is carried out, the temperature of the neck zone of the blow molding die is 175°C, and the temperature of the die mouth zone is 180°C.

[0023] After testing, Examples 1, 2, and 3 were all able to achieve the following: no irregular tear path was produced when tearing in the longitudinal and transverse directions, and the offset angle was ≤10°; the highly tearable PE film produced had the following characteristics: tensile strength (longitudinal / transverse, MPa / 15mm) ≥20 / 18; elongation at break (longitudinal / transverse, %) ≥200 / 300; composite films and bags produced from the highly tearable PE film had the following characteristics: right-angle tearing force (transverse / longitudinal, N / 15mm) ≥3.0; tensile strength (transverse / longitudinal, N / 15mm) ≥40; elongation at break (longitudinal / transverse, %) ≥35; heat seal strength (transverse / longitudinal, N / 15mm) ≥30; and peel strength (transverse / longitudinal, N / 15mm) ≥3.0.

[0024] The present invention uses a polyethylene resin model with a relatively short main chain, more side chains, and a narrow molecular weight distribution that is both tough and brittle, ensuring that the molecular structure inside the film is arranged more neatly, making it easier to propagate in a straight line in a certain direction when torn, thereby improving the tearability of the film.

[0025] The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any modification and replacement based on the technical solution and inventive concept provided by the present invention should be covered by the protection scope of the present invention.

Claims

1. A highly tearable PE film, characterized by: The highly tearable PE film adopts a three-layer co-extrusion structure; The outer layer comprises the following components in parts by weight: 0-40 parts of linear low-density polyethylene, 35-50 parts of low-density polyethylene, 0-35 parts of modified resin and 15-30 parts of high-density polyethylene; The middle layer comprises the following components in parts by weight: 10-40 parts of low-density polyethylene, 0-35 parts of modified resin and 15-30 parts of high-density polyethylene; The inner layer comprises the following components in parts by weight: 0-55 parts of linear low-density polyethylene, 15-95 parts of low-density polyethylene and 5-35 parts of metallocene polyethylene.

2. The highly tearable PE film according to claim 1, characterized in that: The highly tearable PE film adopts a three-layer co-extrusion structure, wherein the outer layer comprises 35 parts of linear low-density polyethylene, 40 parts of low-density polyethylene and 25 parts of high-density polyethylene by weight; the middle layer comprises 35 parts of low-density polyethylene, 40 parts of modified resin and 25 parts of high-density polyethylene by weight; and the inner layer comprises 50 parts of linear low-density polyethylene, 20 parts of low-density polyethylene and 30 parts of metallocene polyethylene by weight.

3. The highly tearable PE film according to claim 1, wherein: The highly tearable PE film adopts a three-layer co-extrusion structure, wherein the outer layer comprises 35 parts of linear low-density polyethylene, 40 parts of low-density polyethylene and 25 parts of high-density polyethylene by weight; the middle layer comprises 15 parts of low-density polyethylene, 60 parts of modified resin and 25 parts of high-density polyethylene by weight; and the inner layer comprises 50 parts of linear low-density polyethylene, 20 parts of low-density polyethylene and 30 parts of metallocene polyethylene by weight.

4. The highly tearable PE film according to claim 1, wherein: The highly tearable PE film adopts a three-layer co-extrusion structure, wherein the outer layer comprises 45 parts of low-density polyethylene, 30 parts of modified resin and 25 parts of high-density polyethylene by weight; the middle layer comprises 15 parts of low-density polyethylene, 60 parts of modified resin and 25 parts of high-density polyethylene by weight; and the inner layer comprises 89 parts of low-density polyethylene and 10 parts of metallocene polyethylene by weight.

5. The method for preparing a highly tearable PE film according to any one of claims 1 to 4, characterized in that: The outer layer formula, the middle layer formula and the inner layer formula are mixed separately by a mixer, and then extruded by a twin-screw extruder at an extrusion speed of 8-10kg / min. The three-layer extrudate is blown through a die head. Transverse blowing and longitudinal stretching are adopted in the blow molding process, wherein the blowing ratio is 2-3 and the stretching ratio is 3-4. After blow molding, the product is cooled and rolled up.

6. The method for preparing a highly tearable PE film according to claim 5, wherein: The temperatures of the feeding section, the compression section and the plasticizing section of the outer layer extrusion are 175-190° C., 175-190° C. and 180-195° C. respectively.

7. The method for preparing a highly tearable PE film according to claim 5, wherein: The temperatures of the feeding section, the compression section and the plasticizing section of the middle layer extrusion are 180-195° C., 180-195° C. and 175-190° C. respectively.

8. The method for preparing a highly tearable PE film according to claim 5, wherein: The temperatures of the feeding section, the compression section and the plasticizing section of the inner layer extrusion are 175-185° C., 175-185° C. and 175-190° C. respectively.

9. The method for preparing a highly tearable PE film according to claim 5, wherein: The temperatures of the neck area and the die mouth area of ​​the blow molding die are both 170-185°C.

10. The method for preparing a highly tearable PE film according to claim 5, wherein: The cooling includes natural cooling and forced cooling. The natural cooling is to extend the film path and increase the natural cooling time. The forced cooling is to add water-cooled guide rollers.