A high-resilience film having a multi-layer structure and a method for preparing the same

Abstract

This invention discloses an elastic film with an ABA three-layer structure and its preparation method. The core layer of the elastic film comprises an SBC-type material, and the surface layer comprises low-modulus PE as the main component, modified by blending with EVA, TPEE, or POE. The total thickness of a single surface layer is 1-5 μm, accounting for 2% to 10% of the total thickness of the elastic film, while the two surface layers account for 4% to 15% of the total thickness. The permanent deformation rate of the elastic film of this invention is within 12%, and the elongation at break is above 500%. The surface layer of the elastic film provides anti-stick properties and has a soft feel, while minimizing the constraint of the surface layer on the elastic layer. No pretreatment is required before use, and it can be widely used in the clothing and hygiene product industries, such as waistbands, elastic cuffs, and elastic waistbands for diapers. Due to its good elasticity and softness, it provides a comfortable fit for the wearer.

Description

Technical Field

[0001] This invention relates to a high-resilience film with a multilayer structure and a method for preparing the same; more specifically, this invention relates to an elastic film with a soft surface layer that requires no pretreatment and a method for preparing the same. Background Technology

[0002] Elastic film products are characterized by high resilience and generally use single elastomers or mixtures thereof, such as TPU, EVA, TPEE, POE, SIS, SBS, SEBS, and SEPS, as the main raw materials. However, because these elastomers generally have high viscosity, when processed into films, the films tend to stick together, rendering them unusable.

[0003] In existing technologies, the industry generally employs two types of technical solutions to address this problem. The first type involves adding agents such as calcium carbonate, silica, erucamide, oleamide, and silicone as opening agents. These agents reduce film adhesion by forming a lubricating layer or micro-protrusions on the film surface, thus reducing contact between films. However, to achieve the desired opening effect, these agents typically require a high proportion, which not only weakens the film's resilience but also leads to problems such as failure to laminate later. The second type involves coating or co-extruding a non-adhesive polymer layer to encapsulate the core elastic layer, thereby solving the adhesion problem. When using coating, the composite layer needs to be torn off and discarded upon use, which is cumbersome and wasteful. When using co-extrusion, the surface layer does not need to be peeled off.

[0004] US Patent Application US 2003 / 0181120 A1 discloses a breathable, progressively stretched elastic composite material comprising an inner elastic film and an outer nonwoven web extruded and laminated to each surface of the film. The inner elastic film has large pores formed by random incremental stretching and substantially no filler forming the pores. In one embodiment, this elastic composite material comprises an elastic film and a nonwoven web extruded and laminated to one or both surfaces of the film. Methods of manufacturing the elastic composite material include extrusion lamination and incremental stretching, and it can be used to form garments and disposable articles.

[0005] US Patent 7,879,452 B2 discloses a non-block multilayer film comprising a first brittle polymer film layer and a second elastic polymer film layer, wherein the first brittle polymer film layer cannot be stretched beyond 110% of its original size without breaking, and the first brittle polymer film layer can be attached to a first surface of the second elastic polymer film layer by co-extrusion, extrusion coating, adhesive bonding, thermal bonding, ultrasonic bonding, calendering bonding, spot bonding, etc.; the multilayer film can be activated by stretching the first brittle polymer film layer to stretch it to at least 150% of its original size and recover to no more than 120% of its original size; the brittle polymer can be selected from polystyrene, acrylate polymers, polycarbonate and combinations thereof, especially polystyrene, and the elastic polymer can be selected from block copolymers of vinyl aromatics and conjugated diene monomers, natural rubber, polyurethane rubber, polyester rubber, elastomeric polyolefins, elastomeric polyamides and mixtures thereof.

[0006] US Patent 9,669,606B2 discloses an elastic membrane that may comprise a first layer consisting of: (i) at least 50% of at least one non-styrene elastic polymer selected from copolymers of polypropylene and polyethylene and mixtures thereof; and (ii) at least one draw-down polymer, comprising 5%-25% of the layer, selected from linear low-density polyethylene, high-density polyethylene, polypropylene homopolymers and mixtures thereof; the basis weight of the elastic membrane not exceeding about 25 gsm, and the permanent deformation rate after being stretched twice to its original size not exceeding about 14%. The elastic membrane of this patent may further comprise a second layer consisting of: (a) at least one elastomeric polymer, and (b) a second draw-down polymer, in which case the basis weight of the elastic membrane does not exceed 40 gsm, and the permanent deformation rate after being stretched twice does not exceed about 14%. The second layer of elastomer polymer can be a non-olefin-based elastomer polymer, such as block copolymers of vinyl aromatics and conjugated dienes, natural rubber, polyester rubber, polyamide elastomers, polyether elastomers, polyisoprene, polychloroprene rubber and mixtures thereof, especially block copolymers of styrene, such as styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene block copolymers, styrene-isoprene-butadiene-styrene block copolymers, styrene-ethylbutene-styrene block copolymers, styrene-ethylene-propylene block copolymers, styrene-ethylene-propylene-styrene block copolymers, styrene-ethylene-ethylene-propylene-styrene block copolymers and mixtures thereof. The second pull polymer can be selected from polystyrene, high-impact polystyrene, linear low-density polyethylene, high-density polyethylene, polypropylene homopolymers and mixtures thereof.

[0007] US Patent 10,239,295B2 (family including Chinese Patent 201680009617.7, Publication No. CN107454870 B) discloses a split-layer thermoplastic film having a structure A-(BC)nBA, where n≥1, A and C are inelastic layers each having a thickness and each independently comprising at least one of polymer compositions A and C; B is an elastic layer containing polymer composition B, wherein: a) the layer containing (BC)nB has a combined thickness x; b) polymer compositions A and C comprise inelastic polymers; c) polymer composition B comprises an elastic polymer; d) the thickness of C is less than or equal to 5% of the total thickness of the film; wherein the notched Elmendorf tear strength of the film is at least twice that of a contrasting thermoplastic film having a structure ABA, A and B comprise substantially the same polymer compositions A and B as thermoplastic films, and wherein the thickness y of the B-layer in the contrasting thermoplastic film is substantially equal to x. Among them, the inelastic polymer is selected from polyolefins, styrene polymers, acrylic polymers, polyamides and their mixtures, and the polyolefin is selected from polyethylene, polypropylene, linear low-density polyethylene, low-density polyethylene, high-density polyethylene, their homopolymers, their copolymers and their mixtures; the elastomer polymer is selected from styrene-based block copolymers, elastomer olefin block copolymers or their mixtures, and the styrene block copolymer is selected from styrene-butadiene-styrene, styrene-isoprene-styrene, styrene-ethylbutene-styrene, styrene-ethylene-propylene, styrene-ethylene-propylene-styrene, styrene-ethylene-ethylene-propylene-styrene, polystyrene, high-impact polystyrene and their mixtures.

[0008] Chinese Invention Patent 201880022360.8 discloses a structure for use in clothing, protective gear, socks, or shoes, comprising a low-resilience member 1 made of thermoplastic elastomer (X) and a high-resilience member 2 made of thermoplastic elastomer (Y). The thermoplastic elastomer (X) and thermoplastic elastomer (Y) are each independently formed from a resin composition comprising the following components: (a) 100 parts of a hydrogenated block copolymer formed by hydrogenating a block copolymer consisting of at least two polymer blocks A and at least one polymer block B, and having a weight average molecular weight of less than 200,000 for 50-100% of the polymer blocks A being formed from structural units derived from vinyl aromatic compounds and polymer blocks B being formed from structural units derived from conjugated diene compounds; (b) 50-300 parts of a hydrocarbon softener; and (c) 3-50 parts of a polyolefin resin relative to the total 100 parts of (a) and (b). Hydrocarbon softeners can be paraffinic oils, naphthenic oils, aromatic oils, etc.; polyolefin resins can be propylene polymers, ethylene polymers, and copolymers of olefins. In this patent, the thermoplastic elastomer (X) has a modulus of 1.0 MPa or less at 100% elongation and a hysteresis loss rate of 70% or more, and the thermoplastic elastomer (Y) has a modulus of 1.0 MPa or less at 100% elongation and a hysteresis loss rate of 40% or less.

[0009] US Patent Application US 2021 / 0386904 A1 discloses a multilayer thermoplastic film comprising an inner layer and two outer layers. The inner layer polymer composition comprises: (a) 50%-95% of a non-hydrogenated styrene block copolymer selected from SBS, SIS, and SIBS; and (b) an olefin block copolymer. The outer layers comprise polypropylene and polyethylene, with polypropylene comprising at least 20% of the outer layers. The thickness of each outer layer is 5%-15% of the total film thickness. The film of this application is particularly suitable for fasteners, belts, and cuffs of absorbent articles.

[0010] It is evident that when using co-extrusion to form elastic films, existing technologies typically use LDPE and PP as surface materials. However, these materials have high hardness and no elasticity, resulting in a hard feel, strong plasticity, high permanent deformation rate, and severe necking during pre-stretch activation. Special processes are required before use to stretch and tear the surface layer to release elasticity, making the process relatively complex.

[0011] Therefore, in view of the problems existing in the prior art, it is necessary to provide an elastic film prepared by co-extrusion process, which has an anti-sticking surface, good hand feel and low binding characteristics. Summary of the Invention

[0012] The purpose of this invention is to provide an elastic film with a soft surface layer that does not require pretreatment, has an ABA three-layer structure, and is formed by three-layer co-extrusion.

[0013] To achieve the aforementioned objectives, the present invention provides an elastic film with a soft surface layer that requires no pretreatment. This elastic film has an ABA three-layer structure. The core layer of the elastic film comprises an SBC-type material, which serves as the elastic layer providing elasticity. The surface layer comprises a low-modulus PE as the main component, such as PE with an elastic modulus below 100 MPa, and is modified by blending with EVA, TPEE, or POE to give the surface a soft feel. Each surface layer has a thickness of 1-5 μm, accounting for 2% to 10% of the total thickness of the elastic film. The combined thickness of the two surface layers accounts for 4% to 15% of the total thickness of the elastic film, thereby minimizing the constraint of the surface layers on the elastic layer and eliminating the need for pretreatment during use. The permanent deformation rate of the elastic film is less than 12%, preferably less than 10%, and the elongation at break is greater than 500%, preferably greater than 600%. When stretched by 300%, the necking is small, preferably less than 40%.

[0014] In the elastic film of the present invention, since the surface layer uses low-modulus PE and is modified by blending with EVA, TPEE or POE, the surface layer of the elastic film has a soft feel. By controlling the thickness of the surface layer to make it a small proportion of the total thickness of the elastic film, the constraint of the surface layer on the elastic layer is minimized, and no pretreatment or preactivation is required during use. At the same time, the surface layer does not form a fracture structure under normal stretching conditions, the permanent deformation rate of the entire elastic film is very small, and the elongation at break is high.

[0015] In this invention, the term modulus refers to the ratio of stress to strain of a material under stress. Note that the modulus may have different names depending on the stress state, such as tensile modulus (E), shear modulus (G), bulk modulus (K), longitudinal compression modulus (L), etc. In this invention, modulus specifically refers to the elastic modulus, which is the proportionality coefficient between stress and strain during the elastic deformation stage of a material (i.e., it conforms to Hooke's law). The tensile elastic modulus E is also called Young's modulus.

[0016] In this invention, the term permanent deformation rate refers to the percentage of the permanent deformation size of a material after the stress is relieved, compared to its original size. In practical standards, it generally refers to the percentage of the deformation size of a material after the stress is relieved and it is left to stand for a certain period of time, compared to its original size.

[0017] In this invention, the term elongation at break refers to the ratio of the displacement of a material at break to its original length, expressed as a percentage.

[0018] In this invention, the term necking refers to the phenomenon that a material may experience localized reduction in cross-sectional area under tensile stress.

[0019] In the elastic membrane of the present invention, the SBC-type material in the core layer refers to styrene block copolymer, preferably SIS, SBS, SEBS, SEPS and / or SEEPS, more preferably SIS, SBS, SEBS, or SEPS, especially SEBS.

[0020] In the elastic film of the present invention, the core layer can be composed of SBC-type material and elastomer. The elastomer can be EVA, TPEE, or POE, and its proportion in the core layer of the elastic film is no more than 20 wt%, preferably no more than 10 wt%, and more preferably no more than 5 wt%.

[0021] In the elastic film of the present invention, the low-modulus PE in the surface layer can be LLDPE, MLDPE, and / or ULDPE. These low-modulus PEs have a soft feel and also have a high elongation at break.

[0022] In the elastic film of the present invention, the proportion of EVA, TPEE or POE in the surface layer is 5wt%-30wt%, preferably 10wt%-25wt%, and more preferably 15wt%-25wt%.

[0023] It is particularly important to note that the surface layer of the elastic film of the present invention does not contain rigid polymers such as PP.

[0024] In one specific embodiment of the present invention, the surface layer may further include 5 wt%-15 wt% of open-cell masterbatch, which may be formed by adding inorganic powder to low-modulus PE. For example, the open-cell masterbatch contains 2 wt%-12 wt% silica, more preferably, the open-cell masterbatch contains 3 wt%-8 wt% silica, and the silica used may be silica powder with an average particle size of 2.5 μm.

[0025] In this invention, the basis weight of the entire elastic membrane is preferably 20-80 gsm, more preferably 30-60 gsm; and the thickness, measured without pressure, is preferably 22-88 μm, more preferably 33-66 μm.

[0026] In addition, it should be noted that in the elastic membrane with the ABA three-layer structure of the present invention, the two surface layers are not necessarily the same in thickness and are not necessarily completely identical in composition.

[0027] On the other hand, in order to achieve the purpose of the invention, the present invention also provides the use of the above-mentioned elastic membrane in the preparation of clothing, surgical gowns or absorbent hygiene products.

[0028] In this invention, absorbent hygiene products can be diapers or other forms of products, especially disposable hygiene products. In this invention, the term "disposable" means that the product is discarded after limited use without being washed or repaired for reuse.

[0029] The elastic film of this invention has ultra-high resilience and is particularly suitable for making waistbands, elastic cuffs, or elastic waistbands for diapers.

[0030] Furthermore, to achieve the objective of this invention, the present invention also provides a method for preparing the aforementioned elastic film, wherein the ABA three-layer structure of the elastic film is formed using a true three-layer co-extrusion die structure. In this method, the polymer or polymer mixture of each layer in the elastic film is melted separately, the molten polymer layers within the co-extrusion die, and is extruded substantially simultaneously from the die, with no adhesive between each co-extruded layer.

[0031] Traditional ABA co-extrusion processes are achieved by splitting the flow using a distributor, which can easily lead to cross-layering between layers A and B, resulting in unstable performance. However, this invention, by using a true three-layer die head process, achieves higher thickness uniformity and more stable performance.

[0032] This invention features an elastic membrane with an ABA three-layer structure, exhibiting ultra-high resilience. It can be widely used in the apparel and hygiene product industries, such as in waistbands, elastic cuffs, and elastic waistbands for diapers. Its excellent elasticity and softness provide a comfortable fit for the wearer.

[0033] Compared to existing technologies, the surface layer of the elastic film of this invention is non-brittle. It uses low-modulus PE and is blended and modified with elastomers to give it a soft feel and an elongation at break of over 500%. In contrast, the surface layer of US 7,879,452 B2 uses brittle polymers selected from polystyrene, acrylate polymers, polycarbonate, and combinations thereof, with an elongation at break of less than 110%. US 9,669,606 B2, US 10,239,295 B2, and US 2021 / 0386904 A1 use polypropylene homopolymers. Therefore, the elastic film of this invention recovers to less than 110% after being stretched to 150%, exhibiting a lower permanent deformation rate and better elastic recovery. The surface layer of the elastic film of this invention provides an anti-sticking effect while possessing a good feel and low binding characteristics.

[0034] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. However, these specific embodiments are merely descriptions of certain specific implementations of the present invention and are not intended to limit the present invention. Attached Figure Description

[0035] Figure 1The cross-sectional surface morphology of the elastic membrane prepared in Example 2 of this invention;

[0036] Figure 2 The cross-sectional surface morphology of the elastic membrane prepared in Comparative Example 5 of the present invention; Detailed Implementation

[0037] The polymer raw materials used in this invention are:

[0038] LLDPE is linear low-density polyethylene (LLDPE) 7042 produced by Maoming Petrochemical.

[0039] LDPE is low-density polyethylene LDPE 0274 produced by Qatar Petrochemicals Ltd.

[0040] POE refers to ENGAGE 8150, 8003, etc., manufactured by Dow Chemical Company.

[0041] SIS is the D1114 manufactured by Kraton Pharmaceuticals, Inc.

[0042] SEBS G1657 manufactured by Kraton S.p.A.

[0043] PP is HP 510 produced by CNOOC Shell Petrochemicals Co., Ltd.

[0044] The open-face masterbatch is LLDPE 7042 + silica (Japan Fuji Silicon Chemical SY530) formulated by the applicant itself.

[0045] In the following embodiments and comparative examples, the test methods and instruments for weight, permanent deformation rate, tensile strength, elongation at break, necking, and thickness are as follows:

[0046] (1) Gram weight testing standards:

[0047] A) Testing instrument: Analytical balance, accuracy 0.001g;

[0048] B) Sampling standard: Samples are taken approximately every 60mm from the edge in the width direction, starting 15mm from the edge, and every 300mm in the length direction. The sample size is 100x100mm, and a total of 100 samples are taken in both the width and length directions.

[0049] (2) Permanent deformation rate:

[0050] A) Testing Standards: Company Standards

[0051] B) Testing instrument: Tensile testing machine

[0052] C) Sampling criteria:

[0053] C1. Wash your hands before testing to remove dust or oil that may affect the results;

[0054] C2. When samples are obtained from large quantities (such as material rolls), remove several layers of sample or box to ensure that the sample used for testing is free from contamination and damage;

[0055] C3. Use scissors to cut samples from the roll. The material sample should be large enough to allow at least one sample 2.54 cm wide and 15.0 cm long to be cut in the desired direction, either CD or MD. If you want the average value of the sample, cut a sample large enough to allow an appropriate number of test samples to be cut (each 2.54 cm wide and 15.0 cm long).

[0056] C4. Before cutting individual samples from each sample:

[0057] i. Determine that the sample is arranged in the desired test orientation (CD or MD) before cutting;

[0058] ii. Ensure the cutting shears are sharp so that the sample edges are free of defects or tears during cutting. Visually inspect the cut samples for any defects and discard any defective samples, especially at the edges;

[0059] C5. Using precise cutting shears, cut at least one sample 2.54 cm wide and 15 cm long from the original sample in the desired orientation (CD or MD). If the sample width is less than 2.54 cm, use the width of the material as the sample width for calculation. To obtain the average sample size, cut an appropriate number of test samples from the original sample. Avoid gripping the area of ​​the sample to be tested (gripping the end of the sample to be clamped);

[0060] C6. Adjust the sample condition to 23℃±2℃ and relative humidity of 50%±2%, and keep it for at least two hours before testing;

[0061] D) Detection method:

[0062] Test steps:

[0063] D1. Tested in an air-conditioned room at 23℃±2℃ and relative humidity of 50%±2%;

[0064] D2. Set the initial jaw air pressure based on the test material. A typical setting is 550 kPa (approximately 80 psi). If the sample slips, increase the jaw air pressure.

[0065] D3. Insert one end of the sample into the upper jaw and close the jaws. Straighten the sample between the stationary and moving jaws. Insert the other end of the sample into the lower jaw and apply sufficient force to eliminate slack, but less than 0.05N of preload to the load cell. After loading the sample, zero the elongation and force readings of the tensile testing machine.

[0066] D4. Adjust the clamp spacing length L0 to 50.8mm, check that the jaws are accurately aligned and parallel to ensure that the applied force does not cause angular deviation, set the constant elongation rate of the stretching machine to 254mm / min, and set the pre-tension of the stretching machine to 0.1N;

[0067] D5. Start the tensile testing machine and stretch the specimen to 200% elongation at the set speed, pause for one minute, and return to the initial position at the same speed;

[0068] D6. Repeat step 5 to read the sample length L1 under a pre-tension of 0.1N;

[0069] Results and representation:

[0070] Calculate the permanent deformation rate (%) using the following formula.

[0071]

[0072] B represents the permanent deformation rate, in %.

[0073] L0 is the initial clamping distance length, in millimeters (mm).

[0074] L1 is the length of the sample after it has returned to the zero position and been held for a predetermined time before the pretension is applied, in millimeters (mm).

[0075] (3) Tensile strength and elongation at break:

[0076] A) Testing Standards: Company Standards

[0077] B) Testing instrument: Tensile testing machine

[0078] C) Sampling criteria:

[0079] The same sampling standard as the aforementioned permanent deformation rate

[0080] D) Detection method:

[0081] Test steps:

[0082] D1. Tested in an air-conditioned room at 23℃±2℃ and relative humidity of 50%±2%;

[0083] D2. Set the initial jaw air pressure based on the test material. A typical setting is 550 kPa (approximately 80 psi). If the sample slips, increase the jaw air pressure.

[0084] D3. Insert one end of the sample into the upper jaw and close the jaw. Straighten the sample between the stationary and moving jaws. Insert the other end of the sample into the lower jaw and apply sufficient force to eliminate slack, but less than 0.05N of preload to the load cell. Do not zero the device after loading the sample;

[0085] D4. Turn on the tensile tester and data collection equipment simultaneously according to the manufacturer's instructions;

[0086] D5. Observe the sample during testing to check for slippage. If slippage is observed during testing, the jaw air pressure should be gradually increased, and a new sample should be tested until no slippage is detected. Report the jaw pressure used with the test results;

[0087] Note: Slippage of the sample in the jaws can cause inaccurate elongation values. To help confirm whether slippage has occurred, immediately mark the upper jaw contact claw with a pen after loading (do not mark the test area of ​​the sample between the two jaws);

[0088] D6. Ensure the instrument does not stop testing until the entire sample breaks. If the test stops prematurely, or continues after the sample has broken, the fracture detector should be adjusted. This result should be discarded, and another sample should be tested.

[0089] Note: If a sample breaks at the jaws or nodal line, it should be discarded and a new sample tested. Data from this sample should not be used, as elongation and maximum strength data may not be accurate. If the sample consistently breaks at the jaws, the air pressure may be too high and should be reduced.

[0090] D7. Remove the sample from the jaws and return the cross jaws of the device to the starting position to prepare for testing the next sample;

[0091] Calculations and Reporting:

[0092] The basic output of a tensile testing instrument is a force-elongation or force-strain curve; where:

[0093] Elongation at break % = (Crosshead distance x 100) / Clamp spacing

[0094] Fracture strength = Peak maximum strength (N) (reported to an accuracy of 0.01N)

[0095] Tensile strength = breaking strength (N) / sample width (cm) (report accurate to 0.01 N / cm)

[0096] (4) Neck retraction:

[0097] A) Testing Standards: Company Standards

[0098] B) Testing instrument: Necking tester (this instrument has two clamps, which are tightened and loosened by nuts, and the clamp spacing is controlled by rotating threaded rods. The clamp spacing is displayed in real time by a rangefinder).

[0099] C) Sampling criteria:

[0100] The sampling standard for permanent deformation rate is the same as mentioned above, except that the sample taken is at least 100 mm wide and 200 mm long;

[0101] D) Detection method:

[0102] Test steps:

[0103] D1. Tested in an air-conditioned room at 23℃±2℃ and relative humidity of 50%±2%;

[0104] D2. Accurately cut a sample 100mm wide and 200mm long;

[0105] D3. Adjust the clamp spacing to 100mm, clamp the long end of the sample to both ends of the clamp, slightly tighten the film to prevent it from loosening, and tighten the clamp;

[0106] D4. Adjust the clamp spacing to 300mm by rotating the threaded rod, and measure the sample width L at the midpoint between the two clamps at this time;

[0107] Calculations and Results:

[0108] The necking rate (%) is calculated using the following formula.

[0109]

[0110] In the formula, X is the necking rate, %

[0111] L represents the width of the sample at the middle position when the clamp spacing is adjusted to 300 mm, in millimeters / mm.

[0112] (5) Thickness:

[0113] A) Testing standard: This method is technically the same as ASTM D645.

[0114] B) Testing instrument: Scissors or blade: can cut samples to the required size;

[0115] Thickness gauge: Sensitivity up to 0.001 mm;

[0116] C) Sampling criteria:

[0117] - Before testing, allow the sample to equilibrate for 2 hours at 23℃ (±2℃) and 50% (±2%) relative humidity;

[0118] - Use scissors / knife to cut a strip from the sample that is larger than the size of the indenter in contact with the sample;

[0119] - The test sample should be selected from the transverse direction of the entire sample.

[0120] D) Detection method:

[0121] Test steps:

[0122] D1. Prepare a micrometer with the specified anvil and weights;

[0123] D2. Zero the thickness measuring instrument before testing each sample;

[0124] D3. Before using the micrometer, ensure that the presser foot and anvil are clean, the instrument has been calibrated, and the instrument is mounted on a solid, level surface without significant vibration.

[0125] D4. With the presser foot in the upward position, place the sample underneath. Release the presser foot using the handle; it will slowly descend on its own.

[0126] 5. Record the measurement data after the preset hysteresis time, accurate to 0.01 mm, or 0.001 mm for thin films.

[0127] Calculations and Reporting:

[0128] Report the mean and standard deviation to 0.01 mm; for films <0.10 mm: report to 0.001 mm.

[0129] Preparation of open-face masterbatch

[0130] 1. Accurately weigh 100 parts resin and 5 parts silica powder; 2. Pour them into a mixer and mix for 30 minutes to ensure thorough and uniform mixing; 3. Feed the mixed material into a twin-screw extruder for melt extrusion granulation; 4. Place the prepared masterbatch in an oven and dry it at 80°C for later use.

[0131] Preparation method of elastic membrane

[0132] 1. Accurately weigh the required quantities of materials for layers A and B according to their respective proportions, and mix them thoroughly in a mixer for thirty minutes. The proportions for layer A are 70 kg LLDPE (7042, Maoming Petrochemical), 20 kg POE (8150, Dow), and 10 kg open-face masterbatch, while layer B consists of 100 kg SIS (D1114, KTE).

[0133] 2. The single-screw extruder is divided into two parts: extruder A and extruder B. The die head is a true three-layer die head with three cavities (ABC). Extruder A is connected to cavity A and cavity C of the die head through a Y-shaped flow channel, while extruder B is directly connected to cavity B of the die head.

[0134] 3. The A layer material is fed into the A extruder and the B layer material is fed into the B extruder. The A layer material and the B layer material are melted and extruded into the die head to form an ABA three-layer structure. The material is then cast and shaped by a casting roller and cooled and shaped by a cooling roller to finally produce an elastic film with an ABA three-layer structure.

[0135] Example 1

[0136] According to the aforementioned elastic film preparation method, the ABA three-layer elastic film of this embodiment was prepared, wherein the A layer is composed of 70wt% LLDPE (7042, Maoming Petrochemical) + 20wt% POE (8150, Dow) + 10wt% open masterbatch; the B layer is SIS (D1114, Kronentech).

[0137] According to the above testing method, the basis weight, permanent deformation rate, elongation at break, tensile strength, necking, and thickness of the elastic membrane prepared in Example 1 were tested, and the data are shown in Table 1.

[0138] Example 2

[0139] According to the aforementioned elastic film preparation method, the ABA three-layer elastic film of this embodiment was prepared, wherein the A layer is composed of 70wt% LLDPE (7042, Maoming Petrochemical) + 20wt% POE (8150, Dow) + 10wt% open masterbatch; the B layer is SEBS (G1657, Kronen).

[0140] According to the above test method, the basis weight, permanent deformation rate, elongation at break, tensile strength, necking, and thickness of the elastic membrane prepared in Example 2 were tested. The data are shown in Table 1.

[0141] Comparative Example 1

[0142] According to the aforementioned elastic film preparation method, an ABA three-layer elastic film of this comparative example was prepared, wherein layer A is composed of 70wt% LLDPE (7042, Maoming Petrochemical) + 20wt% PP (HP510, CNOOC Shell Petrochemical Co., Ltd.) + 10wt% open-cell masterbatch; layer B is SIS (D1114, Kertész).

[0143] Following the above testing method, the basis weight, permanent deformation rate, elongation at break, tensile strength, necking, and thickness of the elastic membrane prepared in Comparative Example 1 were tested, and the data are shown in Table 1.

[0144] As can be seen from the data in Table 1, compared with Example 1, the addition of PP to the surface layer, although having no significant effect on the elongation at break and even slightly improving the tensile strength, resulted in a significantly worse permanent deformation rate and a markedly worse necking at 300% stretch. This indicates that the modification of the surface layer with POE reduces the elastic constraint on the elastic layer, thereby allowing the resulting elastic film to significantly reduce the permanent deformation rate.

[0145] Comparative Example 2

[0146] According to the aforementioned elastic film preparation method, an ABA three-layer elastic film of this comparative example was prepared, wherein layer A is composed of 70% LLDPE (7042, Maoming Petrochemical) + 20% POE (8150, Dow) + 10% open-cell masterbatch; layer B is composed of 90wt% SIS (D1114, Kraton) + 10wt% LDPE (LDPE 0274, Qatar Petrochemical).

[0147] Following the above testing method, the basis weight, permanent deformation rate, elongation at break, tensile strength, necking, and thickness of the elastic membrane prepared in Comparative Example 2 were tested, and the data are shown in Table 1.

[0148] As can be seen from the data in Table 1, compared with Example 1, the addition of LDPE to the core layer slightly improved the tensile strength and only slightly reduced the elongation at break, but significantly worsened the permanent deformation rate and the necking at 300% stretch. This indicates that adding PE to the intermediate core layer improves the tensile strength of the elastic film, but reduces its elastic recovery performance.

[0149] Comparative Example 3

[0150] According to the aforementioned elastic film preparation method, an ABA three-layer elastic film of this comparative example was prepared, wherein layer A is composed of 70% LLDPE (7042, Maoming Petrochemical) + 20% POE (8150, Dow) + 10% open-cell masterbatch; layer B is composed of 80wt% SIS (D1114, Kraton) + 20wt% LDPE (LDPE 0274, Qatar Petrochemical).

[0151] Following the above testing method, the basis weight, permanent deformation rate, elongation at break, tensile strength, necking, and thickness of the elastic membrane prepared in Comparative Example 3 were tested, and the data are shown in Table 1.

[0152] As can be seen from the data in Table 1, compared with Example 1, the addition of LDPE to the core layer significantly improved the tensile strength, but also greatly deteriorated the permanent deformation rate, significantly reduced the elongation at break, and exhibited a more pronounced decrease in necking at 300% stretch. This also indicates that adding PE to the intermediate core layer increases the tensile strength of the elastic film, but reduces its elastic recovery performance.

[0153] Comparative Example 4

[0154] Following the aforementioned elastic film preparation method, an ABA three-layer elastic film of this comparative example was prepared, wherein layer A consists of 70wt% LLDPE (7042, Maoming Petrochemical) + 20wt% PP (HP510, CNOOC Shell Petrochemical Co., Ltd.) + 10wt% open-cell masterbatch; layer B is SEBS (G1657, Kraton).

[0155] Following the above testing method, the basis weight, permanent deformation rate, elongation at break, tensile strength, necking, and thickness of the elastic membrane prepared in Comparative Example 4 were tested. The data are shown in Table 1.

[0156] As can be seen from the data in Table 1, compared with Example 2, the addition of PP to the surface layer resulted in a slight decrease in elongation at break and even a slight increase in tensile strength, but a significant deterioration in permanent deformation and necking at 300% stretch. This further indicates that POE modification of the surface layer can reduce the permanent deformation of the entire film.

[0157] Comparative Example 5

[0158] Following the aforementioned elastic film preparation method, an ABA three-layer elastic film of this comparative example was prepared, wherein layer A consists of 40wt% LLDPE (7042, Maoming Petrochemical) + 50wt% POE (8150, Dow) + 10wt% open-cell masterbatch; layer B is SEBS (G1657, Kronen).

[0159] Following the above testing method, the basis weight, permanent deformation rate, elongation at break, tensile strength, necking, and thickness of the elastic membrane prepared in Comparative Example 5 were tested, and the data are shown in Table 1.

[0160] As can be seen from the data in Table 1, compared with Example 2, after significantly increasing the POE content in the surface layer, only the tensile strength decreased slightly, the elongation at break increased slightly, and the permanent deformation rate and necking at 300% tension were both quite excellent. However, unfortunately, there was some stickiness between the layers (see Table 1). Figure 1 , Figure 2 (These are the cross-sectional surface morphologies of the elastic films of Example 2 and Comparative Example 5, respectively). This fails to solve the adhesion problem between films, leading to significant difficulties or even unusability in practical applications. This indicates that increasing the amount of POE added to the surface layer reduces the decrease in permanent deformation rate, but severely reduces tensile strength. Therefore, the optimal amount of POE added is approximately 20%.

[0161] Table 1

[0162]

[0163] Example 3

[0164] According to the aforementioned elastic film preparation method, the ABA three-layer elastic film of this embodiment was prepared, wherein the A layer is composed of 70wt% LLDPE (7042, Maoming Petrochemical) + 20wt% POE (8150, Dow) + 10wt% open masterbatch; the B layer is SEBS (G1657, Kronen).

[0165] According to the above testing method, the basis weight, permanent deformation rate, elongation at break, tensile strength, necking, and thickness of the elastic membrane prepared in Example 3 were tested, and the data are shown in Table 2.

[0166] Comparative Example 6

[0167] The same formulation as in Example 3 is used: Layer A consists of 40wt% LLDPE (7042, Maoming Petrochemical) + 50wt% POE (8150, Dow) + 10wt% open-face masterbatch; Layer B is SEBS (G1657, Kronen). The ABA structure elastic film of this comparative example is prepared by conventional co-extrusion through a distributor.

[0168] Following the above testing method, the basis weight, permanent deformation rate, elongation at break, tensile strength, necking, and thickness of the elastic membrane prepared in Comparative Example 6 were tested, and the data are shown in Table 2.

[0169] As can be seen from the comparison of the test data of Example 3 and Comparative Example 6 in Table 2, after using the true three-layer co-extrusion die head process, the various performance data are more stable and the film basis weight is more uniform.

[0170] Table 2

[0171]

[0172] Influence of surface layer thickness

[0173] In a set of experiments shown in Table 3 below, with the composition of layer A and layer B (formulation of Example 2) fixed, the effect of the thickness variation of the surface layer (layer A) on permanent deformation rate, tensile strength, elongation at break, and necking at 300% stretch was investigated:

[0174] Table 3

[0175]

[0176] The data in Table 3 shows that:

[0177] When the thickness of a single surface layer accounts for only 5% of the total thickness and the thickness of two surface layers accounts for 10% of the total thickness, the permanent deformation rate of the resulting elastic film is 8.1%, which is less than 10%. The elongation at break and necking after stretching are also relatively ideal. This indicates that the surface layer of this thickness has a relatively small constraint on the elastic layer and does not require the influence of pretreatment.

[0178] When the thickness of a single surface layer accounts for 10% of the total thickness and the thickness of two surface layers accounts for 20% of the total thickness, the permanent deformation rate of the resulting elastic membrane is 12.5%, which is slightly greater than 10%. Its elongation at break and necking after stretching also deteriorate slightly. This indicates that as the thickness of the surface layer increases, its constraint on the elastic layer begins to increase.

[0179] When the thickness of a single surface layer exceeds 10% of the total thickness, and the thickness of two surface layers exceeds 25% of the total thickness, although the tensile strength of the resulting elastic film increases slightly, its permanent deformation rate is much greater than 10%. Moreover, its elongation at break and necking after stretching are also significantly worse. This indicates that the surface layer of this thickness restricts the elastic layer too much and requires pretreatment.

[0180] Based on the data collected from multiple repeated experiments, the inventors believe that in the elastic film of the present invention, the thickness of each surface layer is preferably 1-5 μm, which preferably accounts for 2% to 10% of the total thickness of the elastic film. When the thickness of the two surface layers preferably accounts for 4% to 15% of the total thickness of the elastic film, the constraint of the surface layer on the elastic layer can be minimized, and no pretreatment is required during use.

[0181] Influence of POE content in the surface layer

[0182] Layer A was prepared using LLDPE (7042, Maoming Petrochemical), POE (8150, Dow) and open-face masterbatch from Example 2, and layer B was prepared using SEBS (G1657, Kraton). The effect of changes in POE content in layer A on the elastic film properties and production process was investigated, and the data obtained are listed in Table 4.

[0183] Table 4

[0184]

[0185] The data in Table 4 shows that:

[0186] When the POE content in the surface layer increases, the permanent deformation rate of the resulting elastic membrane decreases slightly, the elongation at break increases slightly, and the necking after stretching also decreases slightly. These changes in performance are beneficial to the elastic membrane, but the benefits are not very obvious.

[0187] However, when the POE content in the surface layer increases, the tensile strength of the resulting elastic film decreases significantly, which is detrimental to the performance of the elastic film.

[0188] When the POE content in the surface layer reaches about 30%, the interlayer shows signs of stickiness; when the POE content in the surface layer reaches about 40%, slight stickiness occurs between the layers; when the POE content in the surface layer reaches about 50%, more obvious stickiness occurs between the layers.

[0189] For the purposes of this invention, interlayer stickiness is unacceptable. Therefore, in the elastic film of this invention, the proportion of EVA, TPEE or POE in the surface layer can be 5wt%-30wt%, preferably 10wt%-25wt%, and more preferably 15wt%-25wt%.

[0190] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An elastic membrane having a soft surface layer and requiring no pretreatment, the elastic membrane having an ABA three-layer structure; in, The core layer of the elastic membrane includes an SBC-type material, which is an elastic layer that provides elasticity to the elastic membrane; the SBC-type material in the core layer is SIS, SBS, SEBS, SEPS and / or SEEPS; The surface layer of the elastic film comprises low-modulus PE as the main component, and is modified by blending with EVA, TPEE or POE to give the surface layer a soft feel; wherein the low-modulus PE in the surface layer is LLDPE, MLDPE and / or ULDPE, the proportion of EVA, TPEE or POE in the surface layer is 5wt%-30wt%, and the surface layer does not contain rigid polymers; Each of the aforementioned surface layers has a thickness of 1-5 µm, accounting for 2% to 10% of the total thickness of the elastic film, and the thickness of the two aforementioned surface layers accounts for 4% to 15% of the total thickness of the elastic film, thereby minimizing the constraint of the surface layers on the elastic layer and requiring no pretreatment during use; The elastic membrane has a permanent deformation rate of less than 12%, an elongation at break of more than 500%, and a necking rate of less than 40% when stretched by 300%.

2. The elastic membrane as described in claim 1, wherein, The core layer is composed of SBC-type material and elastomer, wherein the elastomer is EVA, TPEE or POE, and its proportion in the core layer does not exceed 20 wt%.

3. The elastic membrane as described in claim 1, wherein, The surface layer further comprises 5wt%-15wt% open-cell masterbatch, which is formed by adding inorganic powder to the low-modulus PE.

4. The elastic membrane as described in claim 3, wherein, The open-cell masterbatch contains 2wt%-12wt% silicon dioxide.

5. Use of the elastic membrane as described in any one of claims 1-4 in the preparation of clothing or absorbent hygiene products.

6. A method for preparing an elastic membrane as described in any one of claims 1-4, wherein, The elastic membrane's ABA three-layer structure is formed using a three-layer co-extrusion die structure.

7. The use as described in claim 5, wherein, The clothing mentioned is a surgical gown.

8. The use as described in claim 5, wherein, The elastic membrane is used to prepare waistbands, elastic cuffs, or elastic waistbands for diapers.

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