Breathable digital printing fabric based on bio-based spandex fiber and preparation method thereof

Abstract

The application discloses a breathable digital printing fabric based on bio-based spandex fiber and a preparation method thereof, and belongs to the field of textile materials and digital printing technology. The application first provides a bio-based spandex fiber prepared through specific prepolymerization, chain extension, end capping and spinning process, and realizes in-situ covalent coloring by introducing an anthraquinone-containing dye monomer chain extender; finally, the colored bio-based spandex fiber is used as an elastic component to weave a three-layer structure fabric body, and after pretreatment, digital direct jet printing and post-finishing, a breathable digital printing fabric is obtained. The application solves the technical problems that traditional bio-based spandex fiber has poor coloring stability, and the breathability and printing quality of the digital printing fabric are difficult to be considered, and the prepared fabric has excellent elasticity, coloring fastness, breathability and environmental protection, the process is simple and controllable, and is suitable for large-scale production, and has a wide application prospect in the fields of high-end sportswear, close-fitting underwear and the like.

Description

Technical Field

[0001] This invention relates to the field of textile materials and digital printing technology, and in particular to breathable digitally printed fabrics based on bio-based spandex fibers and their preparation methods. Background Technology

[0002] Spandex (polyurethane elastic fiber) is widely used in elastic fabrics such as sportswear and compression garments. Traditional spandex production primarily uses petroleum-based polytetramethylene ether glycol (PTMEG) as its raw material, resulting in low bio-based content, which is detrimental to sustainable development. In recent years, research and development of bio-based spandex has made some progress. For example, patent CN115233331A discloses a cationic dyeable bio-based spandex fiber, which uses a reaction between bio-based polyester diol and diisocyanate, and utilizes lysine as a chain extender. However, this technology only improves the affinity of spandex for cationic dyes and does not solve the problem of permanent dye fixation in the fiber; the risk of color migration and fading still exists after dyeing.

[0003] In the field of digital printing, water-based polyurethane-based polymer dye inks have attracted attention due to their combination of color fastness and breathability. However, existing digital printing technologies mostly use physical adhesion to attach dyes to the fiber surface. For highly elastic spandex fabrics, under repeated stretching conditions, white showing can easily occur, meaning that the stretched areas are exposed due to insufficient dye coverage, revealing the fabric's base color, which seriously affects the appearance and performance.

[0004] Regarding stretch-sensitive color-changing fabrics, patent CN106042494A discloses an elastic fabric that changes color with stretching deformation. It employs a double-layer structure with an outer and inner layer bonded together and capable of interlocking. When stretched, the outer layer's openings reveal the inner layer's color. However, this technology relies solely on the physical obstruction of the fabric's weave structure to achieve color change, and the interlocking of the outer and inner layers requires connecting threads. This results in a complex structure, significant thickness, and unsuitability for tight-fitting sportswear. Furthermore, the interlocking between the two layers compromises wearing comfort. Patent CN108950850A discloses a method for manufacturing a stretch-sensitive color-changing polyester-cotton-spandex blended knitted fabric. This method requires first preparing color-changing spandex fibers and combining them with various yarns. The process is complex, and the color-changing effect depends on the external coating of color-changing dyes, limiting durability.

[0005] Furthermore, in the field of tight-fitting sportswear such as gymnastics suits, athletes and coaches rely primarily on subjective observation and experience to judge the standardization of movements and the degree of force exertion, lacking intuitive, real-time, and quantifiable proprioceptive feedback methods. Existing smart clothing mostly depends on electronic sensors, which suffers from problems such as complex wiring, poor water resistance, and the need for an external power source.

[0006] Based on the above technical shortcomings, it is necessary to develop a breathable fabric technology solution that takes into account the environmental protection characteristics of bio-based materials, permanent color fastness, stretch color change feedback function, simple structure, and comfortable wear. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by proposing a breathable digital printing fabric based on bio-based spandex fibers and its preparation method.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention first proposes a bio-based spandex fiber, wherein the bio-based spandex fiber is in-situ colored using a chain extender containing chromophores, and the chromophores are covalently embedded in the polyurethane molecular backbone;

[0010] The bio-based spandex fiber is prepared by prepolymerization, chain extension, end-capping and spinning of bio-based polyester diol or bio-based polyether diol, diisocyanate compound, chain extender and end-capping agent;

[0011] The molar ratio of the diisocyanate compound, bio-based polyester diol or bio-based polyether diol, chain extender and capping agent is 1.65-1.85:1:0.2-0.6:0.02-0.1; the chain extender is prepared by mixing a chromophore chain extender and a conventional chain extender in a molar ratio of 1:2.

[0012] Preferably, the bio-based polyester diol or bio-based polyether diol is derived from at least one renewable biomass resource selected from vegetable oils, starch, or cellulose, and has a molecular weight of 1000-4000; the diisocyanate compound is selected from one or more of 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, or hexamethylene diisocyanate; and the end-capping agent is one or more of glycine, glutamic acid, aspartic acid, lysine, or alanine.

[0013] Preferably, the conventional chain extender is one or more of ethylenediamine and 1,2-propanediamine;

[0014] The chromophore chain extender is formed by reacting 1,4-diaminoanthraquinone with ethylene oxide, and its molecular weight is between 300 and 500 g / mol.

[0015] This invention also proposes a method for preparing a breathable digitally printed fabric based on bio-based spandex fiber, comprising the following steps:

[0016] S1: Preparation of outer layer blended yarn: Using bio-based spandex fiber as core yarn and nylon or polyester filament as outer yarn, spandex core-spun yarn is made through core-spun spinning process, which is used as outer layer blended yarn, wherein the spandex content is 12wt%~18wt%;

[0017] S2: Preparation of intermediate layer yarn: Bio-based spandex fiber is used to make high-count, high-density core-spun yarn or twisted yarn as intermediate layer yarn. Its color is a dark tone in the same color family as the background color of the unprinted area of ​​the outer layer.

[0018] S3: Outer layer negative digital printing: The outer layer blended yarn is woven into a greige fabric and negative digital printing is performed so that the printed pattern covers 90% to 95% of the fabric area, while only unprinted areas with matching shapes are reserved at the locations corresponding to specific muscle groups of the human body; after printing, steaming, washing and setting treatments are performed to obtain the printed greige fabric.

[0019] S4: Three-layer integrated weaving: Using a double-needle bed warp knitting machine, two layers of printed greige fabric are used as the outer and inner layers respectively, and the greige fabric woven from the middle layer yarn is used as the middle layer. The three layers are woven into a whole fabric through weft connecting yarns. During the weaving process, the warp feed of the middle layer yarn is controlled so that its weaving tension is 20% to 30% higher than that of the outer layer yarn, so that the middle layer is tightly covered by the outer layer in a natural relaxed state, resulting in a composite greige fabric.

[0020] S5: Finishing: The composite fabric is pre-shaped, washed and finally set to obtain a breathable digital printed fabric.

[0021] Preferably, when the breathable digitally printed fabric is stretched, the pores in the unprinted area increase with the stretching rate, exposing the dark-colored bio-based spandex fibers in the underlying middle layer, causing the color of this area to gradually deepen with the stretching rate; while the printed area, being covered by printing dye, does not show obvious color change when stretched.

[0022] Preferably, in step S3, the specific implementation of negative digital printing includes: in the image processing software of the digital printing machine, a preset muscle group outline graphic is used as a mask for reverse processing, so that the printhead only prints ink in the area outside the mask; the shape of the unprinted area corresponds to the specific human muscle group, which is the surface projection shape of at least one muscle group among the deltoid, pectoralis major, latissimus dorsi, and quadriceps femoris.

[0023] Preferably, in S4, the outer layer is woven with a plain warp weave or a satin warp weave to provide elasticity; the middle layer is inserted as a float through a weft guide bar and does not participate in loop formation; the weft connecting yarn is fine denier nylon or polyester monofilament, used to bind and connect the inner, middle and outer layers.

[0024] Preferably, in step S4, the knitting tension of the intermediate layer is 20% to 30% higher than that of the outer layer, which is achieved by controlling the warp feed of the double needle bed warp knitting machine: the warp feed of the outer layer is 1700 to 1900 mm / rack, and the warp feed of the intermediate layer is 1300 to 1500 mm / rack.

[0025] At the same weaving speed, the amount of warp feed is strictly inversely proportional to the yarn weaving tension. The tension difference caused by the difference in the amount of warp feed between the outer layer and the middle layer corresponds to the aforementioned technical feature that the weaving tension of the middle layer is 20% to 30% higher than that of the outer layer.

[0026] When the fabric is unstretched, the CIE Lab colorimetric value L in the unprinted area is ≥70; when the stretch rate is 30%, the L value in this area decreases to 50-60; when the stretch rate is 50%, the L value in this area... Value ≤ 45.

[0027] During the weaving process, the middle layer yarns are pre-stretched by 20% to 30% due to their small warp feed, and are in a state of high elastic potential energy; while the outer layer yarns have a large warp feed and are almost unstretched, and are in a naturally relaxed state. When the fabric falls off the warp knitting machine and the tension is released, the middle layer yarns, due to their high elastic recovery ability, will undergo significant elastic shrinkage, attempting to return to their original length, while the outer layer yarns, because they are almost unstretched, shrink very little and basically maintain their length at the time of weaving.

[0028] Because the three layers are bound together by weft yarns, the shrinkage of the middle layer is restricted by the outer layer, ultimately forming a stable structure in which the outer layer is loosely pleated and the middle layer is tightly wrapped by the outer layer:

[0029] Outer fabric: exhibits a natural micro-wrinkled state, with tightly arranged yarns and extremely low porosity;

[0030] Middle layer fabric: bound in a contracted state by the outer layer, and in a slightly tense state;

[0031] Interlayer interface: The outer layer and the middle layer are completely bonded together without any gaps;

[0032] This structure is the key to achieving the effect of no color showing when unstretched, but color showing when stretched. In a naturally relaxed state, even if the middle layer is very dark, it will be completely covered by the tightly packed outer layer, and the fabric as a whole will only show the color and pattern of the outer layer.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] 1. This invention precisely controls the interlayer tension difference through the warp feed amount of a double-needle bed warp knitting machine, forming an integrated three-layer structure that is loose on the outside and tight on the inside. This solves the problems of easy separation between layers, poor air permeability, and low elastic recovery rate caused by the use of adhesives in existing technologies. The middle layer yarn is pre-stretched by 20% to 30% and then tightly wrapped by the outer layer. The hysteresis effect during stretching and the short response time of color change can reflect the instantaneous force exerted by the muscle in real time.

[0035] 2. This invention innovatively combines negative digital printing with a color development mechanism based on pore change and color superposition, achieving precise regional control of the stretch-induced color-changing effect. The dye in the printed area fills the fabric pores, so the color of the middle layer will not be exposed even when stretched; only the unprinted muscle group areas will show color as the stretching rate increases, avoiding the visual confusion and inability to locate the stress points of existing overall color-changing fabrics. Furthermore, it is seamless, significantly improving wearing comfort.

[0036] 3. This invention uses a chain extender containing chromophores to prepare in-situ colored bio-based spandex. The chromophores are embedded in the polyurethane molecular backbone through covalent bonds, which solves the problems of easy dye migration, precipitation and poor color fastness in traditional pigment blending or post-dyeing processes, making it suitable for repeated washing and wearing of high-intensity sportswear.

[0037] This invention utilizes a double-needle bed warp knitting machine to precisely control interlayer tension, forming an adhesive-free, integrated three-layer structure. This solves the problems of easy layer separation and poor breathability in traditional composite fabrics, while also providing fast color response and resistance to repeated stretching. The innovative combination of negative digital printing enables precise positioning of muscle groups for the stretch-and-change color effect, avoiding visual confusion. Furthermore, it employs covalently bonded in-situ dyed bio-based spandex, offering excellent colorfastness, high bio-based content, and environmental friendliness, making it suitable for professional sportswear needs. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the structure of the breathable digital printing fabric proposed in this invention.

[0039] In the diagram: outer blended yarn 1, middle layer yarn 2, weft connecting yarn 3. Detailed Implementation

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0041] Example 1:

[0042] Preparation of bio-based spandex: 1 mol of bio-based polytetrahydrofuran glycol (molecular weight 2000 g / mol, derived from corn fermentation) was vacuum dehydrated and reacted with 1.75 mol of MDI at 90℃ for 100 min to obtain a prepolymer. A mixed chain extender consisting of 0.2 mol of color-developing chain extender (molecular weight 344 g / mol) and 0.4 mol of conventional chain extender (ethylenediamine) (molar ratio 1:2) was added, followed by end-capping with 0.05 mol of glycine. Blue bio-based spandex fiber was obtained by dry spinning.

[0043] Fabric preparation: The outer layer blended yarn 1 consists of 15% bio-based spandex fiber and 85% 40D nylon core-spun yarn; the middle layer yarn 2 is 100% dark blue bio-based spandex 40D core-spun yarn of the same system. The outer layer fabric is digitally printed in the negative direction, covering 92% of the area, leaving unprinted areas for the outlines of the rectus abdominis and quadriceps muscles. It is woven on a double-needle bed warp knitting machine, with a warp feed of 1800mm / rack for the outer layer and 1400mm / rack for the middle layer (tension difference approximately 22%). The weft connecting yarn 3 is 20D nylon, with one yarn inserted every 3 rows. The fabric is obtained by pre-setting at 188℃ for 45 seconds, washing, and final setting at 178℃ (overfeed rate 7.5%).

[0044] Example 2:

[0045] Preparation of bio-based spandex: The bio-based polyol was replaced with 1 mol of polylactic acid diol (molecular weight 2000 g / mol, corn starch source), and the remaining raw material ratios, reaction conditions and spinning process were the same as in Example 1, to obtain light yellow bio-based spandex fiber.

[0046] Fabric preparation: The spandex content of the outer layer blended yarn was adjusted to 16%, and the warp feed of the middle layer was adjusted to 1380mm / rack (tension difference of about 24%). The remaining weaving, printing and finishing processes were the same as in Example 1.

[0047] Example 3:

[0048] Preparation of bio-based spandex: The mixed chain extender was adjusted to 0.24 mol color-developing chain extender + 0.48 mol ethylenediamine, and the end-capping agent was replaced with 0.06 mol alanine. The rest was the same as in Example 1, and a slightly darker light yellow bio-based spandex fiber was obtained.

[0049] Fabric preparation: The outer layer warp feed is adjusted to 1750mm / rack, and the middle layer warp feed is adjusted to 1450mm / rack (tension difference of about 17%, close to the lower limit). The biceps brachii outline is added to the unprinted area. The rest of the process is the same as in Example 1.

[0050] The following comparison model was also set:

[0051] Comparative Example 1:

[0052] Ordinary petroleum-based spandex fibers are used, and light yellow and dark blue spandex are produced by high-temperature and high-pressure dyeing with disperse dyes. The rest of the fabric preparation process (three-layer structure, warp feed, negative printing, and finishing) is exactly the same as in Example 1.

[0053] Comparative Example 2:

[0054] A single-layer fabric structure is adopted, with the yarn being a blend of 15% bio-based spandex and 85% 40D nylon from Example 1. The same negative digital printing is performed, and the remaining finishing processes are the same as in Example 1. There is no intermediate layer or tension difference design.

[0055] Comparative Example 3:

[0056] The three-layer structure and raw materials are the same as in Example 1, but the warp feed of the middle layer and the outer layer during weaving is 1800mm / rack (without tension difference). The remaining printing and finishing processes are the same as in Example 1.

[0057] Comparative Example 4:

[0058] The three-layer structure, raw materials, and weaving process are the same as in Example 1, but the outer layer of fabric is digitally printed in full width with no unprinted area. The remaining finishing processes are the same as in Example 1.

[0059] Performance testing:

[0060]

[0061] Data Analysis:

[0062] The intermediate layer fibers (in-situ covalently dyed) in Examples 1-3 showed varying degrees of color change after 20 washes. The attenuation rate is only 1.8% to 2.3%, while the attenuation rate of Comparative Example 1 (traditional dyed spandex) reaches 15.6%. This directly proves that the permanent coloring effect brought about by "covalently embedding the chain extender containing chromophores into the main chain" is unattainable by traditional physical adsorption dyeing, constituting a fundamental technological breakthrough.

[0063] Stretch color change range of Example 1 The color change reached 33.9, while Comparative Example 3 (no tension difference, same warp feed) was only 15.6. The color change range of the two schemes differed by more than double (33.9 vs 15.6), which proves that the process feature of "the knitting tension of the middle layer being 20% ​​to 30% higher than that of the outer layer" is not a simple optimization, but can bring about unexpected technical effects—the tension difference causes the outer layer to produce micro-wrinkles in a relaxed state and tightly cover the middle layer. During stretching, the pores open and the intermediate layer exhibits "emergent" color development. This achieves high-contrast color change. When there is no tension difference, the three layers are of equal length. In the relaxed state, the color of the middle layer has already partially penetrated through the outer layer, resulting in a low color change starting point and a small range.

[0064] Comparative Example 4, with full-width positive printing and no reserved unprinted areas, received a visual evaluation score of only 1.0 (completely no color-changing effect). This demonstrates from the opposite perspective that "negative digital printing + muscle group contour reservation" is a necessary technical path to achieve localized, fixed-point color changing. Full-width printing covers the entire fabric surface, and regardless of stretching, the color remains unchanged, failing to achieve the function of visualizing force exertion.

[0065] Comparative Example 2 has a single-layer structure with no intermediate layer or tension differential design. When stretched by 50%, it exhibits a slight color change solely due to the molecular chain orientation of the single-layer spandex. The color change is almost imperceptible to the naked eye, and the function is completely lost. This proves that the color-changing mechanism of the present invention does not rely on the stretching color change of the spandex fiber itself (comparative example 2 has ruled out this possibility), but rather on the physical masking-revealing mechanism in the three-layer structure. A single-layer structure cannot achieve this function.

[0066] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A bio-based spandex fiber, characterized in that, The bio-based spandex fiber is in-situ colored using a chain extender containing chromophores, wherein the chromophores are covalently embedded in the polyurethane molecular backbone. The bio-based spandex fiber is prepared by prepolymerization, chain extension, end-capping and spinning of bio-based polyester diol or bio-based polyether diol, diisocyanate compound, chain extender and end-capping agent; The molar ratio of the diisocyanate compound, bio-based polyester diol or bio-based polyether diol, chain extender and capping agent is 1.65-1.85:1:0.2-0.6:0.02-0.1; the chain extender is prepared by mixing a chromophore chain extender and a conventional chain extender in a molar ratio of 1:

2.

2. The bio-based spandex fiber according to claim 1, characterized in that, The bio-based polyester diol or bio-based polyether diol is derived from at least one renewable biomass resource selected from vegetable oils, starch, or cellulose, and has a molecular weight of 1000-4000; the diisocyanate compound is selected from one or more of 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, or hexamethylene diisocyanate; the end-capping agent is one or more of glycine, glutamic acid, aspartic acid, lysine, or alanine.

3. The bio-based spandex fiber according to claim 1, characterized in that, The conventional chain extender is one or more of ethylenediamine and 1,2-propanediamine; The chromophore chain extender is formed by reacting 1,4-diaminoanthraquinone with ethylene oxide, and its molecular weight is between 300 and 500 g / mol.

4. A method for preparing a breathable digitally printed fabric based on bio-based spandex fiber, characterized in that, Includes the following steps: S1: Preparation of outer layer blended yarn: Using bio-based spandex fiber as core yarn and nylon or polyester filament as outer yarn, spandex core-spun yarn is made through core-spun spinning process, which is used as outer layer blended yarn, wherein the spandex content is 12wt%~18wt%; S2: Preparation of intermediate layer yarn: Bio-based spandex fiber is used to make high-count, high-density core-spun yarn or twisted yarn as intermediate layer yarn. Its color is a dark tone in the same color family as the background color of the unprinted area of ​​the outer layer. S3: Outer layer negative digital printing: The outer layer blended yarn is woven into a greige fabric and negative digital printing is performed so that the printed pattern covers 90% to 95% of the fabric area, while only unprinted areas with matching shapes are reserved at the locations corresponding to specific muscle groups of the human body; after printing, steaming, washing and setting treatments are performed to obtain the printed greige fabric. S4: Three-layer integrated weaving: Using a double-needle bed warp knitting machine, two layers of printed greige fabric are used as the outer and inner layers respectively, and the greige fabric woven from the middle layer yarn is used as the middle layer. The three layers are woven into a whole fabric through weft connecting yarns. During the weaving process, the warp feed of the middle layer yarn is controlled so that its weaving tension is 20% to 30% higher than that of the outer layer yarn, so that the middle layer is tightly covered by the outer layer in a natural relaxed state, resulting in a composite greige fabric. S5: Finishing: The composite fabric is pre-shaped, washed and finally set to obtain a breathable digital printed fabric.

5. The preparation method according to claim 4, characterized in that, When the breathable digitally printed fabric is stretched, the pores in the unprinted area increase with the stretching rate, exposing the dark-colored bio-based spandex fibers in the underlying middle layer, causing the color of this area to gradually deepen with the stretching rate; while the printed area, because it is covered by printing dye, does not show obvious color change when stretched.

6. The preparation method according to claim 4, characterized in that, In S3, the specific implementation of negative digital printing includes: in the image processing software of the digital printing machine, the preset muscle group outline graphic is used as a mask for reverse processing, so that the print head only prints ink in the area outside the mask; the shape of the unprinted area corresponds to the specific human muscle group, which is the surface projection shape of at least one muscle group among the deltoid, pectoralis major, latissimus dorsi, and quadriceps femoris.

7. The preparation method according to claim 4, characterized in that, In S4, the outer layer is woven with a plain weave or a satin weave to provide elasticity; the middle layer is inserted as a float through a weft guide bar and does not participate in loop formation; the weft connecting yarn is fine denier nylon or polyester monofilament, used to bind and connect the inner, middle and outer layers.

8. The preparation method according to claim 4, characterized in that, In S4, the knitting tension of the middle layer is 20% to 30% higher than that of the outer layer. This is achieved by controlling the warp feed of the double needle bed warp knitting machine: the warp feed of the outer layer is 1700 to 1900 mm / rack, and the warp feed of the middle layer is 1300 to 1500 mm / rack.

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