Microporous breathable film and its preparation method and application

Abstract

The present application relates to a microporous breathable film, the microporous breathable film is formed by a polymer composition, and the microporous breathable film is liquid impermeable under atmospheric pressure, the thickness of the microporous breathable film is 5 μm to 50 μm.Based on 100 parts by weight of the polymer composition, the polymer composition comprises: (a) 30-40 parts by weight of polyethylene; (b) 40-60 parts by weight of ethylene-butene polymer; (c) 10-20 parts by weight of poly (ethylene-co-1,2-butene) glycol.The present application also relates to a preparation method of the microporous breathable film, and application of the microporous breathable film.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, and in particular to a microporous breathable membrane, a method for preparing the microporous breathable membrane, and applications of the microporous breathable membrane. Background Technology

[0002] This section provides background information relevant to this application, which does not necessarily constitute prior art.

[0003] Existing sanitary napkins generally include a top layer, an absorbent material layer, and a backing material layer that are layered and bonded together in sequence. The top layer is in contact with the wearer's skin, the absorbent material layer is used to absorb excrement, and the backing material layer is used to cover the absorbent material layer and prevent leakage of fluid excrement.

[0004] Current sanitary napkins generally use a porous polyolefin membrane for the backing layer, which is breathable and moisture-permeable. However, in order to improve the user experience, sanitary napkins are becoming thinner (current ultra-thin sanitary napkins are only about 1mm to about 3mm thick). Therefore, the thickness of the backing layer tends to decrease, which makes the porous membrane, which is not strong enough, prone to rupture, resulting in insufficient leakage prevention performance.

[0005] Therefore, as a measure to avoid the above-mentioned drawbacks, there is a strong need for a backing material layer with excellent breathability as well as improved strength and leak-proof performance.

[0006] It should be noted that the term "microporous breathable membrane" refers to a polymer membrane layer with micropores, and the term "micropore" refers to a porous material in which the pores are not easily visible to the naked eye, and the maximum pore size is usually no more than a few micrometers. These pores are small enough that the microporous breathable membrane is impermeable to liquids under atmospheric pressure. Summary of the Invention

[0007] The purpose of this invention is to provide another type of microporous breathable membrane, specifically, a microporous breathable membrane with excellent breathability and continuous through-pores, suitable for use as the backing material layer of sanitary napkins. This microporous breathable membrane possesses excellent breathability, excellent strength, and leak-proof performance, and sanitary napkins made using this microporous breathable membrane can achieve a thinner and lighter design.

[0008] Specifically, the present invention provides the following solutions.

[0009] A microporous breathable membrane with excellent air permeability and strength, the microporous breathable membrane being formed from a polymer composition and being impermeable to liquids under atmospheric pressure.

[0010] Although the thickness of the microporous breathable membrane provided according to the invention can be suitably adjusted according to the application requirements, when considering breathability, softness, mechanical strength, and leak-proofness, the thickness of the microporous breathable membrane used in sanitary napkins is preferably from about 5 μm to about 50 μm, more preferably from about 10 μm to about 15 μm. When the thickness is less than 5 μm, it tends to be difficult to obtain sufficient mechanical strength and leak-proofness, and when the thickness exceeds 50 μm, it tends to be difficult to obtain a good texture with sufficient breathability.

[0011] Based on 100 parts by weight of the polymer composition, the polymer composition comprises:

[0012] (a) 30-40 parts by weight of polyethylene;

[0013] (b) 40-60 parts by weight of ethylene-butene polymer;

[0014] (c) 10-20 parts by weight of poly(ethylene-co-1,2-butene) diol.

[0015] The polyethylene includes at least one of ultra-low density polyethylene, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, and cross-linked polyethylene. Preferably, the polyethylene is cross-linked polyethylene, chosen to balance both the softness and mechanical strength of the microporous breathable membrane.

[0016] The manufacturing method of the microporous breathable membrane includes the following steps:

[0017] The process of mixing the polymer composition and the diluent to obtain a mixture;

[0018] The process of extruding the mixture through a die to obtain an extrudate;

[0019] The process of removing diluent from the extrudate to manufacture the microporous breathable membrane.

[0020] The polymer composition and diluent are premixed by dry mixing or melt mixing before being mixed to produce the mixture. Based on the weight of the mixture, the content of the polymer composition in the mixture ranges from about 10% by weight to about 40% by weight. The diluent is an organic solvent, such as one or more aliphatic, alicyclic, or aromatic hydrocarbons such as nonane, decane, naphthane, p-xylene, undecane, and dodecane; liquid paraffin; and mineral oil distillates with the same boiling point as the aforementioned hydrocarbons. Preferably, the diluent is liquid paraffin. Without affecting the technical effect of the present invention, the mixture may also contain one or more additives such as antioxidants, the amount of which does not exceed 1% by weight based on the weight of the mixture.

[0021] The polymer composition and the diluent are mixed and then extruded from a die using an extruder to form an extrudate. If necessary, the extrudate can be exposed to an ambient temperature of approximately 15°C to approximately 25°C to form a cooled extrudate. To produce a final film with a desired thickness, the extrudate or cooled extrudate should have a suitable thickness. For example, the extrudate may have a thickness in the MD direction ranging from approximately 10 μm to approximately 20 μm. It should be noted that the MD direction is defined as the direction from which the extrudate is manufactured from the die, and the TD direction is the direction perpendicular to both the MD direction and the thickness direction of the extrudate.

[0022] The method for removing the diluent from the extrudate to form a film can employ any method capable of removing volatile substances, including existing methods such as heat drying and air drying. Removing the diluent increases the porosity of the final microporous permeable membrane.

[0023] Without affecting the technical effect of the present invention, additional steps that are generally useful in the manufacture of films may be selectively used. Depending on the desired outcome, selective extrudate stretching, selective heat setting (one or more heat treatments of the film), selective crosslinking using ionizing radiation, and selective hydrophilic treatment steps may be performed. The number and order of these selective steps are not important. For example, depending on the desired outcome, a stretched extrudate may be manufactured by stretching or cooling the extrudate in at least one direction (e.g., at least one planar direction such as MD or TD).

[0024] In one or more embodiments, the polymer composition and the diluent are mixed using a mixer (e.g., a Henschel mixer, tumbling mixer, V-mixer, ribbon mixer, Banbury mixer, etc.). The mixing temperature is generally from room temperature to about 100°C, and the mixing time varies depending on the rotational speed of the equipment, but is generally preferred to be from about 1 to about 20 minutes.

[0025] In one or more embodiments, the mixture is melt-kneaded using a single or twin-screw extruder and then extruded from a T-die or blown die to prepare a film material, wherein the temperature during melt kneading is preferably from about 220°C to about 280°C.

[0026] A backing for absorbent articles, characterized in that it comprises the aforementioned microporous breathable membrane having excellent breathability and strength.

[0027] An absorbent article, characterized in that it comprises the aforementioned backing material used as a backing material. The absorbent article can be a hygiene product, such as a disposable diaper, shorts-type diaper, sanitary napkin, incontinence pad, etc.

[0028] The absorbent articles of the present invention can be readily manufactured using methods commonly used in the art. In one or more embodiments, an absorbent article comprises a liquid-permeable face material layer, a leak-proof back material layer, and an absorbent material layer located between the face material layer and the back material layer, wherein a backing composed of a microporous breathable membrane provided by the present invention serves as the back material layer. Preferred examples of liquid-permeable face material layers include nonwoven fabrics made of polyolefins such as polyethylene and polypropylene, porous polyethylene sheets, etc. Preferred examples of absorbent material layers include soft pulp, absorbent paper, and superabsorbent polymers such as starch-based or cellulose-based grafted polymers, carboxymethylated polymers, polyacrylate polymers, polysulfonate polymers, polyvinyl alcohol polymers, polyvinyl alcohol / polyacrylate copolymer polymers, polyacrylamide polymers, polyoxymethylene polymers, and other synthetic polymers. Generally, the aforementioned superabsorbent polymers, soft pulp, and absorbent paper are used as multilayer and / or mixed systems.

[0029] The microporous breathable membrane provided by this invention not only has excellent breathability, but also excellent leak-proof properties and mechanical strength. Absorbent products using the microporous breathable membrane provided by this invention as a backing can achieve a reduction in thickness without the problem of backing material layer cracking. The absorbent products have excellent breathability, moisture permeability, and good texture, allowing for comfortable wear without causing stuffiness, and significantly improving the consumer's user experience.

[0030] The following description is based on specific embodiments. Detailed Implementation

[0031] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0032] It should be noted that the components disclosed in the embodiments of the present invention are all commercially available products.

[0033] The microporous breathable membrane provided in this embodiment of the invention is formed from a polymer composition. Based on 100 parts by weight of the polymer composition, the polymer composition comprises:

[0034] (a) 30-40 parts by weight of cross-linked polyethylene;

[0035] (b) 40-60 parts by weight of ethylene-butene polymer;

[0036] (c) 10-20 parts by weight of poly(ethylene-co-1,2-butene) diol.

[0037] The microporous breathable membrane formed by the polymer composition allows water vapor to pass through but prevents water droplets from passing through through its microporous structure and surface properties, thus achieving the function of being breathable but not permeable to liquid.

[0038] The microporous breathable membrane provided by the present invention is a membrane composed of the above-mentioned polymer composition and having continuous through pores. When the thickness of the microporous breathable membrane is about 10 μm to about 15 μm, the microporous breathable membrane has the following characteristics:

[0039] (1) The porosity of the microporous breathable membrane is about 35% to about 40%. The porosity of the microporous breathable membrane is determined using existing methods. Specifically, the porosity is calculated using the following formula:

[0040] Porosity (%) = (w2-w1) / w2×100, where "w1" is the actual weight of the microporous breathable membrane and "w2" is the weight of an equivalent non-porous membrane of 100% polyethylene with the same size and thickness.

[0041] (2) The Gurley permeability of the microporous breathable membrane, as determined by ISO 5636-5:2013 "Paper and paperboard - Determination of air permeability and air resistance (medium range). Part 5: Gurley method", is about 4000 seconds / 100cc to about 4200 seconds / 100cc;

[0042] (3) The moisture permeability of the microporous breathable membrane, as determined by GB 1037-88 "Test Method for Water Vapor Permeability of Plastic Films and Sheets", is approximately 4900 g / m³. 2 • 24 hours or longer;

[0043] (4) The softness of the microporous breathable membrane, as determined according to GB / T 8942-2016 "Determination of Paper Softness", is about 7.1 mN to about 7.5 mN;

[0044] (5) The tensile strength of the microporous breathable membrane, as determined by GB / T16491-2008 "Standard Test Method for Measuring Mechanical Properties of Thin Films", is between about 55 MPa and about 60 MPa, and the elongation at break is between about 180% and about 190%.

[0045] (6) The hydrostatic pressure of the microporous breathable membrane measured according to GB / T 4744-2013 "Test and evaluation of waterproof performance of textiles - hydrostatic method" is about 300 kPa or higher.

[0046] When the Gurley breathability and moisture permeability of the microporous breathable membrane of the present invention are within the above-mentioned range, absorbent articles using the microporous breathable membrane of the present invention can be worn comfortably without causing a stuffy feeling. When the hydrostatic pressure of the microporous breathable membrane is about 380 kPa to about 400 kPa, the microporous breathable membrane easily obtains the desired Gurley breathability and moisture permeability.

[0047] The microporous breathable membrane of the present invention possesses the aforementioned air permeability, moisture permeability, and leak-proof properties. It has been found that if the porosity of the microporous breathable membrane is less than 30%, it cannot possess the air permeability and moisture permeability within the aforementioned range; and if the porosity of the microporous breathable membrane is greater than 40%, it cannot achieve the hydrostatic pressure within the aforementioned range. When the softness and mechanical strength (including tensile strength) of the microporous breathable membrane of the present invention are within the aforementioned range, absorbent articles using the microporous breathable membrane of the present invention can still prevent rupture and possess excellent leak-proof performance even with a total thickness not exceeding 3 mm.

[0048] [Methods for manufacturing microporous breathable membranes]

[0049] The preparation of the microporous breathable membrane in this embodiment of the invention includes the following steps:

[0050] Step 1: 25% by weight of the polymer composition is filled into a strong mixing twin-screw extruder with an inner diameter of 58 mm and an L / D of 42. 75% by weight of liquid paraffin is fed into the twin-screw extruder through a side feeder, thereby preparing the mixture.

[0051] Step 2: After the mixture is melted at 250°C and 200 rpm, it is fed from the twin-screw extruder to the extrusion T-die, from which it is extruded. The extrudate is then cooled by a cooling roller controlled at 20°C to produce a sheet.

[0052] Step 3: Immerse the sheet in a 25°C dichloromethane bath for 3 minutes to remove the liquid paraffin, and dry it under airflow at room temperature to create a dry film.

[0053] Step four: The dried film is stretched at high temperature using a tenter frame, and then the film is exposed to 120°C for 10 minutes for heat treatment to produce the final microporous breathable membrane. High temperature stretching and heat treatment can ensure the dimensional stability of the film.

[0054] [Examples 1-3]

[0055] Examples 1-3 all provide a microporous breathable membrane. The specific component ratios of the polymer compositions corresponding to the microporous breathable membranes are shown in Table 1.

[0056] The thickness, porosity, air permeability, moisture permeability, softness, mechanical strength, and hydrostatic pressure of the microporous breathable membranes provided in Examples 1-3 are shown in Table 3.

[0057] [Comparative Examples 1-8]

[0058] Comparative Examples 1-8 all provide a microporous breathable membrane, and the specific component ratios of the polymer compositions corresponding to the microporous breathable membranes are shown in Table 2. The preparation methods of the microporous breathable membranes provided in Comparative Examples 1-8 are the same as those of the microporous breathable membranes provided in Examples 1-3.

[0059] The thickness, porosity, air permeability, moisture permeability, softness, mechanical strength, and hydrostatic pressure of the microporous breathable membranes provided in Comparative Examples 1-8 are shown in Table 4.

[0060] Table 1

[0061]

[0062] Table 2

[0063]

[0064] It should be noted that:

[0065] The thickness of the microporous breathable membrane was measured using a Mahr C1200M-AT thin film thickness gauge.

[0066] According to ISO 5636-5:2013 "Paper and paperboard - Determination of air permeability and air resistance (medium range). Part 5: Gurley method", the Gurley permeability was tested using a TAPPI T460 Gurley method air permeability tester.

[0067] The moisture permeability was determined according to GB 1037-88 "Test Method for Water Vapor Permeability of Plastic Films and Sheets" using a Labthink W3 / 130 water vapor transmission rate tester.

[0068] The softness of paper was determined according to GB / T 8942-2016 "Determination of Softness of Paper". The instrument used was a Thwing-Albert Instrument softness tester (the test result is the sum of the maximum vector of the bending resistance of the sample itself and the friction between the sample and the gap; the smaller the instrument reading, the softer the sample).

[0069] Mechanical strength was determined according to GB / T16491-2008 "Standard Test Methods for Measuring Mechanical Properties of Thin Films". The instrument used was the Instron 5900 dual-column electronic universal tensile testing machine.

[0070] The hydrostatic pressure was determined according to GB / T 4744-2013 "Test and Evaluation of Waterproof Performance of Textiles - Hydrostatic Pressure Method". The instrument used was the YLA060 hydrostatic pressure tester from Dongguan Youli Precision Machinery Co., Ltd.

[0071] Liquid leakage tests were conducted on the microporous breathable membranes provided in Examples 1-3 and Comparative Examples 1-8, respectively. This test simulates the leakage performance of breathable membranes in sanitary napkins, and the specific steps are as follows:

[0072] Step 1: Place the microporous breathable membrane to be tested on a piece of filter paper, place an absorbent pad on the microporous breathable membrane, and then add 10 ml of solution to the absorbent pad with a syringe and let it stand for 30 seconds. The solution contains 100 ml of distilled water, 2 g of urea, 0.9 g of sodium chloride, 0.06 g of calcium chloride and 0.11 g of magnesium sulfate hydrate. Adjust the solution with a surfactant (such as ammonium lauryl sulfate) to obtain a surface tension of 29 dynes / cm.

[0073] Step 2: Apply a non-porous membrane of 100% polyethylene to the absorbent pad, and then apply a 5 kg weight to the polyethylene membrane. After 15 minutes, remove the weight, the polyethylene membrane, and the microporous breathable membrane. Compare this filter paper with a standard filter paper to determine whether the microporous breathable membrane is qualified or unqualified.

[0074] The test results are as follows: the microporous breathable membranes provided in Examples 1-3 and Comparative Examples 1-6 are qualified and no leakage was found; the microporous breathable membranes provided in Comparative Examples 7-8 are unqualified and leakage was found.

[0075] Table 3

[0076]

[0077] According to the test results in Table 3, the microporous breathable membranes prepared in Examples 1-3 showed significantly increased mechanical strength, Gurley permeability, moisture permeability and hydrostatic pressure, and also had excellent softness.

[0078] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0079] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A microporous breathable membrane, characterized in that, The microporous breathable membrane is formed from a polymer composition and is impermeable to liquids under atmospheric pressure. The thickness of the microporous breathable membrane is 5 μm to 50 μm. Based on 100 parts by weight of the polymer composition, the polymer composition comprises: (a) 30-40 parts by weight of polyethylene, wherein the polyethylene is cross-linked polyethylene; (b) 40-60 parts by weight of ethylene-butene polymer; (c) 10-20 parts by weight of poly(ethylene-co-1,2-butene) diol.

2. The microporous breathable membrane according to claim 1, characterized in that: The thickness of the microporous breathable membrane is 10 μm to 15 μm.

3. A method for preparing the microporous breathable membrane according to claim 1 or 2, characterized in that, The process includes the following steps: The process of mixing the polymer composition and the diluent to obtain a mixture; The process of extruding the mixture through a die to obtain an extrudate; The process of removing diluent from the extrudate to manufacture the microporous breathable membrane; The polymer composition and the diluent are premixed by dry mixing or melt mixing before being mixed with the diluent to produce the mixture. Based on the weight of the mixture, the content of the polymer composition in the mixture ranges from 10% by weight to 40% by weight; The diluent includes liquid paraffin.

4. The method according to claim 3, characterized in that, The mixture is melt-kneaded using a single or twin-screw extruder and then extruded from a T-die or blown die to prepare the extrudate in the shape of a film, with the temperature during melt-kneading being 220°C to 280°C.

5. A backing for absorbent articles, characterized in that, The microporous breathable membrane according to claim 1 or 2.

6. An absorbent article, characterized in that, The backing as described in claim 5 is used as the backing material.

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