Process for improving the transverse break force of a stretch film

Abstract

The process for improving the transverse breaking force of wrapping film belongs to the technical field of wrapping film and is prepared by a film blowing method and comprises the following steps: S1. preparing and weighing raw materials of different layers of ABCBA according to a proportion, uniformly mixing the raw materials to obtain raw materials of different film layers; S2. pouring the raw materials of different film layers into corresponding feeding machines of different extrusion layers, melt plasticizing, and co-extruding into a tubular die via a five-layer die; S3. blowing and shaping the tubular die, a blowing ratio of 2.3-2.5, and a longitudinal traction ratio of 1.9-2.1; S4. after cooling, traction and winding, and placing at 25-28 DEG C for 4-8 h, a finished wrapping film is obtained. The application enables the molecular chain to be fully stretched and oriented in the transverse direction by designing a blowing ratio of 2.3-2.5 and a traction ratio of 1.9-2.1, while inhibiting excessive orientation in the longitudinal direction, so that the mechanical properties are more balanced; and the application enhances the overall transverse breaking force of the wrapping film by cooperating with a five-layer structure component enhancement system, thereby improving the tear resistance of the film and preventing the film from being easily torn during the packaging process.

Description

Technical Field

[0001] This invention belongs to the technical field of stretch film and relates to a process for improving the lateral tensile strength of stretch film. Background Technology

[0002] Stretch film, also known as cling film, has many important applications in industry and agriculture. For example, in agriculture, stretch film can be used to pack hay, allowing it to be stored stably for a long time. In my country, stretch film is mostly used for packaging, especially as a key material for modern logistics packaging. With its high tensile strength, tear resistance, and excellent self-adhesive properties, it can effectively wrap objects into a whole, preventing them from scattering or collapsing during transportation. It also provides triple protection against water, dust, and damage, making it widely used in pallet packaging.

[0003] In existing stretch film manufacturing processes, single-layer or three-layer co-extrusion blown film is commonly used. Issues such as the limited variety of raw material ratios, improper control of blowing and traction parameters, and unreasonable melt plasticizing temperatures are the main reasons for insufficient transverse tensile strength. Furthermore, some processes fail to emphasize the synergistic effect of each film layer, resulting in low material selection and performance matching for the surface and intermediate layers, further impacting the transverse mechanical properties of the stretch film. To address these technical challenges, improve the transverse tensile strength of stretch film, and meet the needs of the packaging industry, it is essential to develop an optimized stretch film manufacturing process. Summary of the Invention

[0004] The purpose of this invention is to improve the lateral tensile strength of stretch film and to provide a process for improving the lateral tensile strength of stretch film.

[0005] The technical solution adopted by this invention to achieve its purpose is as follows: The process for improving the lateral tensile strength of stretch film, prepared using the blown film method, includes the following steps: S1. Weigh and prepare the raw materials of different layers ABCBA according to the proportion, mix them evenly, and obtain the raw materials of different membrane layers; S2. The raw materials of different film layers are poured into the feeders corresponding to different extrusion layers, melted and plasticized, and then co-extruded into a tubular die blank through five-layer die heads; S3. The tubular mold blank is blown and shaped with a blow-up ratio of 2.3-2.5 and a longitudinal traction ratio of 1.9-2.1; S4. After cooling, pull and roll up the film, and place it at 25-28℃ for 4-8 hours to obtain the finished wrapping film.

[0006] Preferably, layer A, by weight parts, comprises: 100 parts C8 LLDPE, 8-12 parts VLDPE, 0.04-0.08 parts PPA, 0.1-0.2 parts antioxidant, and 0.2-0.3 parts silica. Layer A uses a blend of C8 LLDPE and VLDPE, which can reduce surface crystallinity and improve initial surface tack. Silica acts as an opening agent to prevent film roll adhesion, and the combined effect of multiple components enhances transverse toughness. Layer B, by mass parts, includes: 45-55 parts C8 mLLDPE, 45-55 parts C8 LLDPE, 12-18 parts LDPE, 0.03-0.05 parts PPA, and 0.1-0.2 parts antioxidant. Layer B, by introducing LDPE, utilizes its long-branched structure to achieve high melt strength, which helps stabilize the bubble tube during blown film production. At the same time, the blending of LDPE and LLDPE can control the molecular chain entanglement density and balance the longitudinal and transverse orientation differences. The C layer, by weight parts, includes: 70-80 parts C8 mLLDPE, 18-22 parts MDPE, 6-8 parts POE, 0.06-0.1 parts PPA, 0.1-0.2 parts antioxidant, and 0.4-0.6 parts HPN-20E. The C layer uses C8 mLLDPE as the main resin to provide high strength to the matrix, MDPE to improve modulus and tensile strength, POE to enhance impact and tear resistance, and HPN-20E to promote the formation of fine and uniform grains, reduce stress concentration, and enable uniform load transfer under lateral stress, thereby improving lateral tensile strength.

[0007] Preferably, the C8 LLDPE has a melt index of 1.5-1.8 g / 10min and a density controlled between 0.920-0.925 g / cm³. 3 VLDPE melt index 1.5-2.0 g / 10min, density controlled at 0.890-0.905 g / cm³. 3 C8 mLLDPE melt index 1.0-1.2 g / 10min, density controlled at 0.916-0.922 g / cm³ 3 LDPE melt index 0.3-0.5 g / 10min, density controlled at 0.919-0.922 g / cm³. 3 MDPE melt index 0.8-1.0 g / 10 min, density 0.930-0.935 g / cm³ 3 POE melt index 0.5-1.0 g / 10 min, density 0.862-0.880 g / cm³ 3 .

[0008] Preferably, in step S2, the melting temperature is controlled as follows: Layer A, feeding section 170-175℃, compression section 185-195℃, metering section 200-210℃, die head 210-220℃; Layer B: feeding section 175-180℃, compression section 195-205℃, metering section 210-220℃, die head 215-225℃; Layer C: feeding section 180-185℃, compression section 200-210℃, metering section 215-225℃, die head 215-225℃.

[0009] Preferably, dual-outlet air ring cooling is used, with a cooling temperature of 22-26℃.

[0010] Preferably, the antioxidant is antioxidant 1010 and antioxidant 168 in a mass ratio of 1:(1-2).

[0011] Preferably, the ratio of different layers ABCBA is 1.5:2:3:2:1.5, and the total thickness of the wrapping film is 20-30μm.

[0012] The beneficial effects of this invention are: This invention designs an inflation ratio of 2.3-2.5 and a draw ratio of 1.9-2.1 to achieve sufficient stretching and orientation of the molecular chains in the transverse direction while suppressing excessive orientation in the longitudinal direction, resulting in more balanced mechanical properties. Combined with a five-layer structural reinforcement system, this enhances the overall transverse tensile strength of the wrapping film, improves its tear resistance, and makes it less prone to tearing during packaging. Detailed Implementation

[0013] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0014] Example 1

[0015] A type of stretch film with improved lateral tensile strength has a ratio of different layers ABCBA of 1.5:2:3:2:1.5, a total film thickness of 25μm, and the component distribution is shown in the table below: Table 1 The process for improving the lateral tensile strength of stretch film, prepared using the blown film method, includes the following steps: S1. Weigh and prepare the raw materials of different layers ABCBA according to the proportion, mix them evenly, and obtain the raw materials of different membrane layers; S2. Raw materials with different film layers are poured into feeders corresponding to different extrusion layers, melted and plasticized, and then co-extruded into tubular preforms through five-layer die heads; the melt plasticization is as follows: Layer A, feeding section 170℃, compression section 190℃, metering section 205℃, die head 215℃; Layer B, feeding section 175℃, compression section 200℃, metering section 215℃, die head 220℃; Layer C: feeding section 180℃, compression section 205℃, metering section 220℃, die head 220℃.

[0016] S3. The tubular mold blank is blown and shaped with a blow-up ratio of 2.4 and a longitudinal traction ratio of 2.0. It is cooled by a dual-outlet air ring with a cooling temperature of 24℃. S4. After cooling, pull and rewind, and place at 25℃ for 8 hours to obtain the finished stretch film.

[0017] Example 2

[0018] A type of stretch film with improved lateral tensile strength has a ratio of different layers ABCBA of 1.5:2:3:2:1.5, a total film thickness of 20μm, and the component distribution is shown in the table below: Table 2 The process for improving the lateral tensile strength of stretch film, prepared using the blown film method, includes the following steps: S1. Weigh and prepare the raw materials of different layers ABCBA according to the proportion, mix them evenly, and obtain the raw materials of different membrane layers; S2. Raw materials with different film layers are poured into feeders corresponding to different extrusion layers, melted and plasticized, and then co-extruded into tubular preforms through five-layer die heads; the melt plasticization is as follows: Layer A, feeding section 172℃, compression section 188℃, metering section 202℃, die head 212℃; Layer B, feeding section 178℃, compression section 198℃, metering section 212℃, die head 218℃; Layer C: feeding section 182℃, compression section 202℃, metering section 218℃, die head 218℃.

[0019] S3. The tubular mold blank is blown and shaped with a blow-up ratio of 2.3 and a longitudinal traction ratio of 1.9. It is cooled by a dual-outlet air ring with a cooling temperature of 22℃. S4. After cooling, pull and wind up, and place at 28℃ for 4 hours to obtain the finished stretch film.

[0020] Example 3

[0021] A type of stretch film with improved lateral tensile strength has a ratio of different layers ABCBA of 1.5:2:3:2:1.5, a total film thickness of 30μm, and the component distribution is shown in the table below: Table 3 The process for improving the lateral tensile strength of stretch film, prepared using the blown film method, includes the following steps: S1. Weigh and prepare the raw materials of different layers ABCBA according to the proportion, mix them evenly, and obtain the raw materials of different membrane layers; S2. Raw materials with different film layers are poured into feeders corresponding to different extrusion layers, melted and plasticized, and then co-extruded into tubular preforms through five-layer die heads; the melt plasticization is as follows: Layer A, feeding section 175℃, compression section 192℃, metering section 208℃, die head 218℃; Layer B, feeding section 180℃, compression section 205℃, metering section 220℃, die head 225℃; Layer C: feeding section 185℃, compression section 210℃, metering section 225℃, die head 225℃.

[0022] S3. The tubular mold blank is blown and shaped with a blow-up ratio of 2.5 and a longitudinal traction ratio of 2.1. It is cooled by a dual-outlet air ring with a cooling temperature of 26℃. S4. After cooling, pull and wind up, and place at 26℃ for 6 hours to obtain the finished stretch film.

[0023] The tensile strength and puncture resistance of the stretch films prepared in Examples 1-3 were tested, and the test results are shown in Table 4 below.

[0024] Table 4 As shown in Table 4, the stretch film produced by the process of this application has a transverse tensile strength of 9.1-12.7 N / cm, a longitudinal tensile strength of 10.2-15.4 N / cm, and a tear resistance of 43.6-56.3 kN / m. The stretch film has good tensile strength and tear resistance.

[0025] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit them. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the scope of the technology disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention.

Claims

1. A process for improving the transverse tensile strength of stretch film, prepared using a blown film method, characterized in that, Includes the following steps: S1. Weigh and prepare the raw materials of different layers ABCBA according to the proportion, mix them evenly, and obtain the raw materials of different membrane layers. S2. The raw materials of different film layers are poured into the feeders corresponding to different extrusion layers, melted and plasticized, and then co-extruded into a tubular die blank through five-layer die heads; S3. The tubular mold blank is blown and shaped with a blow-up ratio of 2.3-2.5 and a longitudinal traction ratio of 1.9-2.1; S4. After cooling, pull and roll up the film, and place it at 25-28℃ for 4-8 hours to obtain the finished wrapping film.

2. The process for improving the lateral tensile strength of the stretch film according to claim 1, characterized in that, Layer A, by weight parts, includes: 100 parts C8 LLDPE, 8-12 parts VLDPE, 0.04-0.08 parts PPA, 0.1-0.2 parts antioxidant, and 0.2-0.3 parts silica; Layer B, by weight parts, includes: 45-55 parts of C8 mLLDPE, 45-55 parts of C8 LLDPE, 12-18 parts of LDPE, 0.03-0.05 parts of PPA, and 0.1-0.2 parts of antioxidant; Layer C, by weight, includes: 70-80 parts of C8 mLLDPE, 18-22 parts of MDPE, 6-8 parts of POE, 0.06-0.1 parts of PPA, 0.1-0.2 parts of antioxidant, and 0.4-0.6 parts of HPN-20E.

3. The process for improving the lateral tensile strength of the stretch film according to claim 1, characterized in that, C8 LLDPE melt index 1.5-1.8 g / 10min, density controlled at 0.920-0.925 g / cm³ 3 VLDPE melt index 1.5-2.0 g / 10min, density controlled at 0.890-0.905 g / cm³. 3 C8 mLLDPE melt index 1.0-1.2 g / 10min, density controlled at 0.916-0.922 g / cm³ 3 LDPE melt index 0.3-0.5 g / 10min, density controlled at 0.919-0.922 g / cm³. 3 MDPE melt index 0.8-1.0 g / 10 min, density 0.930-0.935 g / cm³ 3 POE melt index 0.5-1.0 g / 10 min, density 0.862-0.880 g / cm³ 3 .

4. The process for improving the lateral tensile strength of the stretch film according to claim 1, characterized in that, In step S2, the melting temperature is controlled as follows: Layer A: feeding section 170-175℃, compression section 185-195℃, metering section 200-210℃, die head 210-220℃; Layer B: feeding section 175-180℃, compression section 195-205℃, metering section 210-220℃, die head 215-225℃; Layer C: feeding section 180-185℃, compression section 200-210℃, metering section 215-225℃, die head 215-225℃.

5. The process for improving the lateral tensile strength of the stretch film according to claim 1, characterized in that, It adopts dual-outlet air ring cooling, with a cooling temperature of 22-26℃.

6. The process for improving the lateral tensile strength of the stretch film according to claim 1, characterized in that, The antioxidants mentioned are antioxidant 1010 and antioxidant 168 in a mass ratio of 1:(1-2).

7. The process for improving the lateral tensile strength of the stretch film according to claim 1, characterized in that, The ratio of different layers of ABCBA is 1.5:2:3:2:1.5, and the total thickness of the wrapping film is 20-30μm.

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