Flushable nonwoven fabric

Abstract

The present application discloses a flushable non-woven fabric, which comprises natural fibers and viscose fibers that are intertwined with each other, wherein the length of the natural fibers is 1.5-3 mm, the length-width ratio is 80-160, and the wall-cavity ratio is greater than or equal to 1; the length of the viscose fibers is 4-10 mm, and the proportion of the viscose fibers is 20%-25%; and the proportion of the fibers with a length less than 1 mm in the natural fibers is 4-10%. Through the above proportioning, the flushable non-woven fabric formed can also achieve good flushability and good strength, and can meet the use performance requirements.

Description

Technical Field

[0001] This invention relates to a washable nonwoven fabric. Background Technology

[0002] With rapid economic development and increasing pursuit of quality of life, non-woven fabric products (face towels, makeup remover wipes, cotton wipes, etc.) have become an indispensable part of daily life in recent years. Non-woven fabrics have advantages such as a wide range of raw material sources, diverse varieties, and a soft, fluffy feel. As consumers' environmental awareness grows, non-woven fabrics are gradually developing towards a green and environmentally friendly direction.

[0003] To address this, the North American Nonwovens Industry Association (INDA) and the European Nonwovens Association (EDANA) jointly developed the "Washable Guidelines" in 2008, which defined "washableness." Prior to and since then, the industry has developed various washable nonwoven products and technologies. For example, patent document CN101984177A, entitled "Washable and Degradable Wood Pulp Composite Nonwoven Fabric," proposes a nonwoven fabric with a 2-5mm wood pulp fiber layer and a nonwoven fiber layer bonded together by hydroentangling, which possesses washability. Similarly, patent document CN108474153A, entitled "Hydrolytic Nonwoven Fabric and its Manufacturing Method," presents another washable nonwoven fabric and its preparation method.

[0004] Furthermore, numerous industry research papers, such as "Problems and Development Directions of Ruptureable Wipes" published in the November 2019 issue of "Household Paper," combine various existing technologies and research literature to find that the industry proposes to use longer fibers as much as possible. For example, patent document US5384189A, Water-decomposable non-woven fabric, mentions that the fiber length should not be shorter than 5mm, and preferably between 5-20mm. Considering the characteristics of softwood pulp fiber, current rinseable nonwoven fabrics all use softwood pulp + viscose fiber pulp form. However, there are still many other natural fibers on the market, and these natural fibers still hope to meet the requirements of rinseability.

[0005] Therefore, a new technical solution is needed to address the aforementioned technical problems. Summary of the Invention

[0006] Therefore, the present invention provides a washable nonwoven fabric to solve the above-mentioned technical problems.

[0007] A washable nonwoven fabric includes intertwined natural fibers and viscose fibers, wherein the natural fibers have an average length of 1.5-3 mm, an aspect ratio of 80-160, and a wall-to-cavity ratio greater than or equal to 1, the viscose fibers have a length of 4-10 mm, and the viscose fibers account for 20%-25% of the total, and the natural fibers with a length less than 1 mm account for 4-10% of the total number of natural fibers.

[0008] The natural fiber mentioned above is bamboo pulp fiber.

[0009] The viscose fiber is a flat viscose fiber, and the length of the flat viscose fiber is 4-7 mm.

[0010] Before forming the washable nonwoven fabric, the natural fibers are first screened to separate the natural fiber raw materials into a first slurry with a length of less than 1.0 mm and a second slurry with a length of more than 1.0 mm. Then, the ratio of the first slurry to the second slurry is adjusted to form a mixed slurry, so that the proportion of fibers with a length of less than 1.0 mm in the mixed slurry is 4 to 10% of the natural fibers.

[0011] The bamboo pulp fiber is a mixture of at least two types of bamboo pulp fiber, and the aspect ratio of the mixed bamboo pulp fiber is 80 to 100, and the wall-to-cavity ratio is 1 to 3.

[0012] The bamboo pulp fiber is a mixture of moso bamboo fiber and mixed bamboo fiber, and the ratio of moso bamboo fiber to mixed bamboo fiber is 50:50 to 70:30.

[0013] The bamboo pulp fiber is composed of 60% moso bamboo and 40% mixed bamboo, with an average fiber length of 1.72 mm, an average length-to-width ratio of 92, and an average wall-to-cavity ratio of 2.45. Fibers with a length of less than 1 mm account for 7.6%.

[0014] The bamboo pulp fiber is 100% bamboo, with an average fiber length of 1.99 mm, an average length-to-width ratio of 139, and an average wall-to-cavity ratio of 1.9. Fibers with a length of less than 1 mm account for 9.6%.

[0015] The bamboo pulp fiber is made of 100% moso bamboo, with an average fiber length of 1.8 mm, an average length-to-width ratio of 85, and an average wall-to-cavity ratio of 2.1. Fibers with a length of less than 1 mm account for 6.5% of the total.

[0016] Beneficial effects: This invention provides a washable nonwoven fabric comprising intertwined natural fibers and viscose fibers. The natural fibers have a length of 1.5–3 mm, an aspect ratio of 80–160, and a wall-to-cavity ratio greater than or equal to 1. The viscose fibers have a length of 4–10 mm and account for 20%–25% of the total composition. Furthermore, the proportion of natural fibers with a length less than 1 mm is 4–10% of the total natural fibers. Through the above proportions, the resulting washable nonwoven fabric achieves both good washability and good strength, meeting the performance requirements. Detailed Implementation

[0017] This invention provides a flushable nonwoven fabric with good water dispersibility. When discarded in environments such as toilets, it can be quickly flushed away by the water flow in those environments, thereby avoiding blockages in toilets or pipes or reducing the risk of blockages.

[0018] The washable nonwoven fabric includes intertwined natural fibers and viscose fibers. It is understood that the washable nonwoven fabric is not bonded by adhesives, but is formed by the intertwining of fibers. In addition, the intertwining can be the intertwining of natural fibers with natural fibers, the intertwining of natural fibers with viscose fibers, or the intertwining of viscose fibers with viscose fibers.

[0019] The natural fiber has a length of 1.5–3 mm, an aspect ratio of 80–160, and a wall-to-cavity ratio greater than or equal to 1. More specifically, the natural fiber is bamboo pulp fiber, such as bamboo, moso bamboo, wood bamboo, green bamboo, and nan bamboo. Preferably, the length of the bamboo pulp fiber is 1.6–2.5 mm, for example: 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, 2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm, 2.5 mm, etc. Furthermore, preferably, the wall-to-cavity ratio is 1.2–6.5, and more preferably, it is 1.6–5.0.

[0020] Furthermore, the bamboo pulp fiber is a mixture of at least two types of bamboo pulp fiber, and the aspect ratio of the mixed bamboo pulp fiber is 80-100, and the wall-to-cavity ratio is 1-3.

[0021] Furthermore, the bamboo pulp fiber is a mixture of moso bamboo fiber and mixed bamboo fiber, and the ratio of moso bamboo fiber to mixed bamboo fiber is 50:50 to 70:30.

[0022] It is understood that the lengths mentioned in the following descriptions are average lengths, the aspect ratios are average aspect ratios, and the wall-to-cavity ratios are average wall-to-cavity ratios.

[0023] The length of the viscose fiber is 4-10 mm, preferably 4-7 mm, such as 4 mm, 5 mm, 6 mm, 7 mm, etc. In this embodiment, the denier of the viscose fiber is preferably below 16 denier, and more preferably, the denier of the flat viscose fiber is 5-15 denier. The "denier" is an industrial weight unit called "denier" or "denier", which is expressed in grams of weight of 9000m of fiber and can reflect the thickness of the fiber.

[0024] Furthermore, the viscose fiber can be either flat viscose fiber or round viscose fiber. Flat viscose fiber is obtained by dissolving natural fibers in a suitable solvent and then wet spinning. Studies have shown that the bending stiffness of the fiber has a significant impact on its entanglement properties. The lower the bending stiffness, the easier it is for the fiber to entangle. Since flat viscose fiber has a lower bending stiffness, it is easier for it to entangle during fiber processing. When the same energy (such as water jet energy) is applied, the nonwoven material formed by flat viscose fiber has better entanglement properties. In other words, to achieve the same entanglement effect, flat viscose fiber requires less entanglement energy than ordinary viscose fiber. On the other hand, unlike external reinforcement energy, the entanglement obtained by the fiber through its own physical properties is a frictional cohesion property, which is more easily dispersed by external forces in water. Therefore, nonwoven materials processed from flat viscose fiber have better water washability. That is, compared with round viscose fiber, flat viscose fiber has better entanglement ability and water washability. Therefore, the preferred viscose fiber is flat viscose fiber.

[0025] In addition, the viscose fiber accounts for 20% to 25% of the total fiber mass.

[0026] Furthermore, the viscose fiber includes both flat viscose fiber and round viscose fiber, and the ratio of flat viscose fiber to the original viscose fiber is 5:5 to 9:1.

[0027] It is understood that the viscose fiber may include Lyocell fiber.

[0028] In the field of washable nonwoven fabrics, washable nonwoven fabrics need to simultaneously meet the requirements of washability and strength. However, washability and strength are inversely related; higher strength may result in poorer washability, and vice versa. Current research typically uses wood pulp and viscose fiber, especially softwood pulp and viscose fiber, as the main materials. This is because softwood pulp fibers have a relatively long length (usually greater than 3.6 mm, even exceeding 4 mm), a low aspect ratio (usually below 80), and a small wall-to-cavity ratio (usually less than 1). The relatively long length of coniferous wood fibers allows for more entanglement points with viscose fibers. Due to their low aspect ratio and thin-walled, large-cavity structure, they have a large surface area exposed to water flow and can easily disentangle and disperse, thus simultaneously meeting the requirements for strength and water-dispersible properties. Furthermore, it is generally believed in the art that other fibers struggle to simultaneously meet the requirements for both water-dispersible properties and strength. The applicant's research found that, for bamboo pulp fibers, when using conventional methods such as selecting relatively longer fibers or screening to form fibers predominantly of long fibers, the slender shape of the fibers and the thick walls and small cavities of bamboo fibers make it difficult for them to achieve the desired water-dispersible properties and strength. After the fibers and viscose fibers become entangled, on the one hand, the entanglement between the fibers is relatively tight, messy, and has many bonding points. On the other hand, due to the finer texture and thinner wall and smaller cavity of the viscose fibers compared to wood pulp, it is not easy for water flow to break up the entanglement. This is especially true when these fibers are shorter. When strength requirements need to be met, it is more difficult to simultaneously meet the requirements of strength and washability, requiring the addition of more viscose fibers or the use of longer viscose fibers. The applicant's further research found that when there are some short fibers among the long and thin fibers, the short fibers can either crowd out the entanglement positions or first become entangled with the long and thin fibers, and then... The fibers are then entangled with viscose fibers, which reduces the bending shape of these long fibers during entanglement. On the other hand, these short fibers are easily detached under the impact of water flow. During the detachment process, the porosity of the nonwoven fabric increases. The increase in porosity further increases the flow velocity and pressure of water at the pores, causing the fibers at the pores to be lost with the water flow, thus disintegrating and dispersing. However, when these fine fibers are in a dry state or not under the action of water flow, the nonwoven fabric can remain intact. Further research has found that among the natural fibers, fibers with a length of less than 1.0 mm account for more than 4% of the total number of natural fibers.

[0029] Furthermore, the proportion of fibers with a length of 1.0 mm or less to natural fibers is 4 to 10%, so that the strength and washability of the washable nonwoven fabric meet the requirements for use or at least meet the national standards.

[0030] Furthermore, before forming the nonwoven fabric, the natural fibers are first screened to separate the raw material fibers into a first slurry with a length of less than 1.0 mm and a second slurry with a length of more than 1.0 mm. Then, the ratio of the first slurry to the second slurry is adjusted to form a mixed slurry, so that the proportion of fibers with a length of less than 1.0 mm in the mixed slurry is 4 to 10% of the natural fibers.

[0031] Meanwhile, the washable nonwoven fabric of the present invention is prepared in the following manner: first, natural fibers are prepared to form a natural fiber slurry, viscose fibers are prepared to form a viscose fiber slurry, the natural fiber slurry and viscose fiber slurry are mixed in a certain proportion to form a mixed slurry, the mixed slurry is formed into a wet fiber web by wet web forming, the wet fiber web is transferred to a hydroentangled screen for hydroentanglement reinforcement, and then dried to form the washable nonwoven fabric.

[0032] In addition, since the natural fibers used in this application are longer and thinner, they are more prone to twisting, allowing for the use of relatively lower hydroentanglement pressure during the hydroentanglement process.

[0033] To more clearly describe the hydroentanglement pressure during hydroentanglement reinforcement, the hydroentanglement reinforcement process will be described in further detail below:

[0034] In hydroentanglement reinforcement, a wet fiber web is laid on a continuously movable hydroentangled mesh curtain and moves with the curtain. The hydroentangled nozzles spray high-pressure water jets onto the wet fiber web in a direction approximately perpendicular to the web, allowing the jets to pass from the surface to the bottom of the web. Under the action of the high-pressure water jets, some fibers bend, twist, and entangle, forming a substrate for the nonwoven fabric. Understandably, the properties of the nonwoven fabric obtained by this hydro-jet treatment vary depending on parameters such as the unit area weight of the wet fiber web, the nozzle orifice diameter, the number of nozzle orifices, and the processing speed (processing speed) when treating the fiber web.

[0035] Typically, the amount of work done by the water flow should be between 0.05 and 0.5 KW / ㎡. If the amount of work is greater than the upper limit, there will be too much entanglement between the fibers, which will reduce their hydrolytic properties. At the same time, it may also cause damage to the wet fiber web during the hydroentangling process. Meanwhile, if the amount of work is less than the lower limit, its bulkiness will be worse.

[0036] Therefore, in practice, multiple sets of water jet nozzles are usually used. In this embodiment, there are at least five sets of water jet nozzles, and the pressure of the multiple sets of water jet nozzles increases in a stepwise manner. In addition, the pressure of the first set of water jet nozzles located upstream is less than or equal to 50% of the pressure of the last set of water jet nozzles located downstream.

[0037] Furthermore, this hydroentanglement reinforcement treatment can be applied to only one side of the wet fiber web or to both sides simultaneously. For example, by performing several hydro-jet treatments at 0.05–0.5 kW / m² on one side of the wet fiber web, a washable nonwoven fabric with excellent hydrolytic properties and wet strength can be obtained. Alternatively, several hydro-jet treatments at 0.05–0.5 kW / m² can be performed on both sides of the wet fiber web, that is, on its bottom and top surfaces.

[0038] The washable nonwoven fabric of this application will be further described below through specific embodiments:

[0039] Example 1:

[0040] Natural fiber: 60% bamboo + 40% mixed bamboo, average fiber length: 1.72mm, average length-to-width ratio: 92, average wall-to-cavity ratio: 2.45, of which fibers with a length of less than 1mm account for 6.6%;

[0041] Viscose fiber: Morphology: flat, length 5mm, viscose fiber accounts for 25%.

[0042] Example 2:

[0043] Natural fiber: 100% bamboo, average fiber length: 1.99mm, average length-to-width ratio: 139, average wall-to-lumen ratio: 1.9, of which fibers with a length of less than 1mm account for 7.6%;

[0044] Viscose fiber: Shape: round, length 5mm, viscose fiber accounts for 20%.

[0045] Example 3:

[0046] Natural fiber: 100% bamboo, average fiber length: 1.8mm, average length-to-width ratio: 85, average wall-to-lumen ratio: 2.1, of which fibers with a length of less than 1mm account for 4.5%;

[0047] Viscose fiber: Morphology: flat, length 5mm, viscose fiber accounts for 25%.

[0048] Comparative Example 1:

[0049] Natural fiber: 100% bamboo, average fiber length: 2.6mm, average length-to-width ratio: 189, average wall-to-lumen ratio: 2.2, of which fibers with a length of less than 1mm account for 0.1%;

[0050] Viscose fiber: Shape: round, length 5mm, viscose fiber accounts for 20%.

[0051] In this embodiment, the natural fibers are pre-treated by sieving to remove natural fibers with a length of less than 1 mm.

[0052] Comparative Example 2:

[0053] Natural fiber: Eucalyptus, average fiber length: 1.05mm, average length-to-width ratio: 66, average wall-to-cavity ratio: 0.75;

[0054] Viscose fiber: Shape: round, length 12mm, viscose fiber accounts for 30%.

[0055] Comparative Example 3:

[0056] Natural fiber: Masson pine, average fiber length: 3.7mm, average length-to-width ratio: 72, average wall-to-lumen ratio: 0.64;

[0057] Viscose fiber: 8mm in length, viscose fiber accounts for 50%.

[0058] Comparative Example 3:

[0059] Natural fiber: Masson pine, average fiber length: 3.9mm, average length-to-width ratio: 68, average wall-to-lumen ratio: 0.7;

[0060] Viscose fiber: 10mm in length, viscose fiber accounts for 30%.

[0061] The above embodiments and comparative examples were subjected to tests for basis weight, dry-CDT, dry-MDT, wet-CDT, wet-MDT, and dispersibility. The results are as follows, and the requirements for washable nonwoven fabrics in GB / T 41244-2022 Washable Spunlace Nonwoven Materials and Products are listed in the table below:

[0062]

[0063] in,

[0064] The test methods for longitudinal and transverse dry tensile forces refer to the test methods in GB / T24218.3-2010 Textiles - Nonwovens - Test Methods - Part 3: Determination of breaking strength and elongation at break, wherein the sample width is 50 mm, the clamping distance is 100 mm, and the tensile speed is 100 mm / min.

[0065] The longitudinal and transverse wet strength references adopt the test method 5.2 of "GB / T 40181-2021 Test method and evaluation of washability of disposable sanitary nonwoven materials", wherein the sample width is 50mm, the clamping distance is 100mm, and the tensile speed is 100mm / min.

[0066] The water dispersibility test was conducted using the test procedure of the shaking chamber decomposition test in GB / T 40181-2021 Test Method and Evaluation of Disposable Sanitary Nonwoven Materials.

[0067] From the above comparison, compared with Comparative Examples 3 and 4 which use the prior art, Examples 1-3 are still weaker in terms of strength, but they can meet the requirements of GB / T 41244-2022, which is far better than using only eucalyptus short fiber. Compared with screened bamboo pulp fiber, their dispersion performance is far superior to that of screened bamboo pulp, achieving a balance between dispersibility and strength.

[0068] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A washable nonwoven fabric comprising intertwined natural fibers and viscose fibers, characterized in that, The natural fibers mentioned herein have an average length of 1.5–3 mm, an aspect ratio of 80–160, and a wall-to-cavity ratio greater than or equal to 1. The viscose fibers have a length of 4–10 mm and account for 20%–25% of the total. Furthermore, the natural fibers with a length less than or equal to 1.0 mm account for 4%–10% of the total natural fibers. The natural fibers are bamboo pulp fibers. Before forming the washable nonwoven fabric, the natural fibers are first screened to separate the raw materials into a first pulp with a length less than 1.0 mm and a second pulp with a length greater than 1.0 mm. Then, the ratio of the first pulp to the second pulp is adjusted to form a mixed pulp, such that the mixed pulp contains fibers with a length less than 1.0 mm accounting for 4%–10% of the total natural fibers.

2. The washable nonwoven fabric as described in claim 1, characterized in that, The viscose fiber is a flat viscose fiber, and the length of the flat viscose fiber is 4-7 mm.

3. The washable nonwoven fabric as described in claim 1, characterized in that, The bamboo pulp fiber is a mixture of at least two types of bamboo pulp fiber, and the aspect ratio of the mixed bamboo pulp fiber is 80 to 100, and the wall-to-cavity ratio is 1 to 3.

4. The washable nonwoven fabric as described in claim 3, characterized in that, The bamboo pulp fiber is a mixture of moso bamboo fiber and mixed bamboo fiber, and the ratio of moso bamboo fiber to mixed bamboo fiber is 50:50 to 70:

30.

5. The washable nonwoven fabric as described in claim 1, characterized in that, The bamboo pulp fiber is composed of 60% moso bamboo and 40% mixed bamboo, with an average fiber length of 1.72 mm, an average length-to-width ratio of 92, and an average wall-to-cavity ratio of 2.

45. Among them, the fiber length is less than 1 mm, accounting for 7.6%.

6. The washable nonwoven fabric as described in claim 1, characterized in that, The bamboo pulp fiber is 100% bamboo, with an average fiber length of 1.99 mm, an average length-to-width ratio of 139, and an average wall-to-cavity ratio of 1.

9. Among them, the fiber length is less than 1 mm, accounting for 9.6%.

7. The washable nonwoven fabric as described in claim 1, characterized in that, The bamboo pulp fiber is made of 100% moso bamboo, with an average fiber length of 1.8 mm, an average length-to-width ratio of 85, and an average wall-to-cavity ratio of 2.

1. Among them, fibers with a length of less than 1 mm account for 6.5%.

8. The washable nonwoven fabric according to any one of claims 1-7, wherein the water dispersibility of the washable nonwoven fabric is greater than or equal to 90%.

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