Method for preparing digital printing paste from modified straw cellulose

Abstract

The invention relates to the technical field of textile printing and dyeing, in particular to a method for preparing digital printing paste from modified straw cellulose. The modified straw cellulose is used as a core, carboxymethyl cellulose, sodium sulfate, an auxiliary agent S60, hydrophobic filler modified carboxymethyl starch, a complexing agent sodium hexametaphosphate and a biological inhibitor BR are compounded, the formula and the preparation process are optimized, the raw material cost is remarkably reduced by 30% or above, and meanwhile the water holding property, rheological property and dye fixation effect of the paste are improved. The obtained paste is bright in color, soft in hand feeling, clear in outline and high in color fastness, and is particularly suitable for deep color digital printing of cotton fabrics. The method disclosed by the invention is simple and easy to implement, mild in condition and easy for large-scale production, and meets the requirements of the market on the efficient and environment-friendly digital printing paste.

Description

Technical Field

[0001] This invention relates to the field of textile printing and dyeing technology, specifically to a method for preparing digital printing paste from modified straw cellulose. Background Technology

[0002] With the rapid development of digital printing technology, its application in the textile printing and dyeing field is becoming increasingly widespread, significantly increasing the demand for digital printing pastes. Digital printing processes require printing pastes to penetrate the fabric quickly during printing while maintaining pattern clarity and color yield, while also placing higher demands on hand feel and desizing performance. However, existing digital printing pastes still have significant shortcomings in terms of raw material cost, environmental friendliness, and overall performance. Currently, commercially available digital printing pastes mainly use sodium alginate as the base material, but the high and fluctuating price of sodium alginate limits its large-scale application. Furthermore, pastes using sodium alginate as the base material perform poorly in printing with dark dyes, exhibiting low color yield and failing to meet the market's demand for high-precision printing. While pastes using carboxymethyl starch (CMS) as the main base material are lower in cost, they suffer from poor hand feel, unsatisfactory penetration and color fastness, resulting in low cost-effectiveness and difficulty in fully meeting the stringent requirements of digital printing.

[0003] Existing printing pastes also have other problems. For example, when using dark dyes, the reaction between conventional pastes and dyes may affect the hand feel of the print, leading to blurred print outlines, insufficient color intensity, and decreased color fastness. Furthermore, the desizing performance of the printing paste directly affects the hand feel and final quality of the printed product. Existing pastes have low desizing efficiency in the washing process, easily leaving residues, which in turn affects the hand feel and appearance of the fabric. Therefore, developing a low-cost, environmentally friendly digital printing paste with excellent overall performance has become an urgent technical challenge to be solved.

[0004] To address the aforementioned problems, this invention proposes a method for preparing digital printing paste using modified straw cellulose as the core. The modified straw cellulose, through carboxymethylation treatment, exhibits excellent water-holding capacity, rheological properties, and stability, significantly reducing raw material costs while simultaneously improving the overall performance of the paste. Summary of the Invention

[0005] This invention addresses the technical problems of existing digital printing pastes, such as high raw material costs, low color yield, poor hand feel, and insufficient penetration, by proposing a method for preparing digital printing paste using modified straw fiber. The method uses modified straw cellulose as the core component, combined with the synergistic effects of carboxymethyl cellulose, sodium sulfate, auxiliary agent S60, hydrophobic filler modified carboxymethyl starch, complexing agent sodium hexametaphosphate, and bioinhibitor BR, to provide a highly efficient, environmentally friendly, and economical digital printing paste and its preparation process.

[0006] This invention provides a digital printing paste, which is composed of the following components in weight percentage: 20-50% modified straw cellulose (carboxymethylated, DS = 1.5-2.0), 10-30% carboxymethyl cellulose (CMC, DS = 1.5-2.0), 30-50% sodium sulfate (Na2SO4), 1-2% auxiliary agent S60, 1.5-3.5% hydrophobic filler modified carboxymethyl starch, 2-5% complexing agent sodium hexametaphosphate, and 3% bioinhibitor BR. The specific selection and compounding ratio of each component have been optimized to ensure that the paste exhibits excellent comprehensive performance in practical applications.

[0007] The modified straw cellulose has a mass percentage of 20-50% and a degree of substitution (DS) of 1.5-2.0. This component is prepared through alkali treatment and etherification, exhibiting significant water-holding capacity and stability. As the core component, the high degree of substitution of modified straw cellulose endows it with excellent hydrophobicity and electrolyte resistance, while the hydroxyl groups on the molecular chain retain a certain degree of hydrophilicity, ensuring good compatibility with aqueous dye systems. During the printing process, the modified straw cellulose forms a stable three-dimensional network structure, providing a basic viscosity for the paste and effectively inhibiting the free migration of dyes, ensuring the clarity of the printed pattern outline.

[0008] Furthermore, the carboxymethyl cellulose has a mass percentage content of 10-30% and a degree of substitution (DS) of 1.5-2.0. The anionic properties of carboxymethyl cellulose promote uniform dye dispersion and prevent dye particle aggregation through electrostatic repulsion. Synergistically, it works with modified straw cellulose to optimize the rheological properties of the paste and the dye fixation effect. By controlling the blending ratio between 20-50% and 10-30%, the thixotropic properties of the paste can be precisely controlled, allowing it to exhibit good flowability under high shear conditions and rapidly recover viscosity under low shear conditions, thereby effectively preventing dye diffusion and penetration.

[0009] Specifically, the sodium sulfate has a mass percentage of 30-50%, a particle size ≤50μm, and a purity ≥99.5%. Sodium sulfate stabilizes the cellulose molecular chain through charge shielding, preventing viscosity fluctuations caused by excessive swelling of carboxymethyl cellulose, while simultaneously reducing the system's conductivity to protect the printing nozzle. Its dosage is matched to the high-substitution components to avoid a decline in paste performance due to salting-out effects.

[0010] Furthermore, the auxiliary agent S60 has a mass percentage of 1-2%, is a polyoxyethylene ether nonionic surfactant, and has an HLB value of 12-15. Auxiliary agent S60 adjusts the wetting balance between the paste and the fabric, promoting dye penetration without bleeding. Auxiliary agent S60 can be added by pre-dissolving it in a small amount of water and then spraying it in, with the dosage not exceeding 5% of the total water volume, to reduce dust impact.

[0011] The hydrophobic filler modified carboxymethyl starch has a mass percentage of 1.5-3.5% and a degree of substitution of 0.8-1.2. The modified carboxymethyl starch fills the gaps in the paste network, improving film density and reducing the risk of cracking after printing, while maintaining appropriate bulkiness to ensure sufficient dye fixation. Its introduction prevents the paste from cracking due to excessive shrinkage after drying, while also ensuring the color yield and color fastness of the printed fabric sample.

[0012] Furthermore, the complexing agent, sodium hexametaphosphate, has a mass percentage of 5% and is a food-grade additive. Sodium hexametaphosphate chelates calcium, magnesium, and other metal ions in water, preventing the cross-linking reaction between polyvalent metal ions and anionic carboxymethyl cellulose, which would otherwise lead to gelation of the paste.

[0013] The bioinhibitor BR, comprising 3% by mass, is an isothiazolinone compound. BR inhibits microbial growth and prolongs the storage stability of the paste, exhibiting particularly excellent performance under high temperature and humidity conditions. Its broad-spectrum antibacterial properties, combined with the inherent resistance to microbial degradation of the highly substituted component, provide dual protection, significantly enhancing the long-term stability of the paste.

[0014] The preparation method of the present invention includes the following steps:

[0015] S1 weighs the modified straw cellulose, carboxymethyl cellulose, modified carboxymethyl starch and sodium sulfate according to the formula ratio, and mixes them in a three-dimensional mixer at 30 rpm for 15 minutes until uniform, to obtain a dry powder mixture.

[0016] Add additive S60, sodium hexametaphosphate, and bio-inhibitor BR sequentially to the dry powder mixture. Mix at low speed (20 rpm) for 5 minutes, avoiding dust generation. Additive S60 can be pre-dissolved in a small amount of water and then sprayed in, with the amount not exceeding 5% of the total water volume.

[0017] S3 mixes the dry powder mixture with deionized water at a ratio of 1:20, stirs at 600-1800 rpm for 30 minutes, and then matures in a 40℃ constant temperature water bath for 20 minutes (600 rpm) to release the viscosity of all substances and remove air bubbles. After maturation, filter through a 150-mesh screen to remove impurities.

[0018] When the carboxymethyl cellulose content is ≥25%, segmented high-shear dispersion is adopted: first, disperse at 800 rpm for 15 minutes, then stop the machine and scrape off the gel clumps on the agitator and the vessel wall, then add modified carboxymethyl starch and continue dispersion at 1500 rpm for 10 minutes. This operation breaks the colloidal coating through mechanical shearing, ensuring that the hydrophobic starch is fully dispersed and functions properly.

[0019] When the modified straw cellulose content is ≥50%, the dry powder mixture is first pre-wetted with 5% anhydrous ethanol, then dissolved in water at a ratio of 1:20 at room temperature, and cured in stages from 40℃ to 60℃. During the curing process, 0.5% sodium sulfate is added to inhibit excessive thickening. This process alleviates the problem of rapid oxygen consumption when high-content straw cellulose comes into contact with water, and at the same time prevents the formation of microcrack networks caused by shrinkage stress during drying.

[0020] Through the above technical solution, the present invention achieves the following technical effects:

[0021] Raw material innovation: Modified straw cellulose is used as the core component to replace sodium alginate, reducing raw material costs by more than 30% and significantly improving environmental performance.

[0022] Excellent performance: Through the synergistic effect of each component, the resulting paste has excellent water retention, rheology and dye fixation effect. The printed fabric sample has high color strength (significant improvement in K / S value), soft hand feel, clear outline and high color fastness, and is especially suitable for dark digital printing on cotton fabrics.

[0023] Process advantages: The preparation method is simple, the operating conditions are mild, and it is easy to scale up production, meeting the market demand for high-performance digital printing pastes.

[0024] In summary, this invention, through reasonable formula design and optimized preparation process, has developed a high-efficiency, environmentally friendly, and economical digital printing paste, filling the market gap for high-performance digital printing pastes. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall process flow for preparing digital printing paste from modified straw cellulose according to the present invention; Detailed Implementation

[0026] This invention provides a method for preparing digital printing paste from modified straw fibers, as illustrated in the accompanying drawings. Figure 1 The specific implementation methods are described in detail.

[0027] First, the modified straw cellulose, carboxymethyl cellulose, sodium sulfate, and the hydrophobic filler modified carboxymethyl starch were weighed according to the formula ratio and placed in a three-dimensional mixer for initial mixing. The three-dimensional mixer was operated at a low speed of 30 rpm for 15 minutes to ensure the dry powder mixture reached a homogeneous state. During the mixing process, the components were fully dispersed by mechanical force, and the synergistic effect of modified straw cellulose and carboxymethyl cellulose was initially observed. Subsequently, adjuvant S60, sodium hexametaphosphate, and bio-inhibitor BR were added to the dry powder mixture in sequence, and the mixture was mixed at a low speed of 20 rpm for 5 minutes to avoid dust generation. It is particularly important to note that adjuvant S60 can be pre-dissolved in a small amount of deionized water and then sprayed in, and its amount should not exceed 5% of the total water volume, thereby reducing the inconvenience caused by powder flying.

[0028] After the dry powder mixture is completed, it is dissolved in deionized water at a ratio of 1:20 in a stirring device. The stirring speed is set to 600-1800 rpm for 30 minutes. This process aims to ensure that all components are fully dissolved and form a stable paste system. During stirring, modified straw cellulose, as the core component, exhibits significant water-holding properties, forming a three-dimensional network structure with carboxymethyl cellulose, which imparts the paste with its basic viscosity and rheological properties. Simultaneously, sodium sulfate stabilizes the cellulose molecular chains through charge shielding, preventing viscosity fluctuations caused by excessive swelling of carboxymethyl cellulose. After stirring, the paste is transferred to a curing device and cured at 600 rpm for 20 minutes in a 40°C constant temperature water bath. The main purpose of curing is to release the viscosity of all substances and remove air bubbles, ensuring the paste exhibits excellent overall performance in subsequent use. After curing, the paste is filtered through a 150-mesh screen filter to remove impurities, ultimately yielding the finished digital printing paste.

[0029] When the carboxymethyl cellulose content is ≥25%, a segmented high-shear dispersion technique is required. Specifically, the dry powder mixture is first added to a stirring device at a ratio of 1:20 with deionized water and dispersed at 800 rpm for 15 minutes using high shear. This stage uses high shear force to break down the colloidal encapsulation formed by the carboxymethyl cellulose, preventing the inhibition of the function of the hydrophobic filler-modified carboxymethyl starch. Afterwards, the stirring paddle and vessel walls are scraped off, and the modified carboxymethyl starch is added again, with dispersion continuing at 1500 rpm for 10 minutes. This operation ensures that the hydrophobic starch is fully dispersed and functions effectively, further improving the film density of the paste and the dye fixation effect.

[0030] When the modified straw cellulose content is ≥50%, a special oxygen absorption-resistant process is required. First, pre-wet the dry powder mixture with 5% anhydrous ethanol (by weight of the total paste), manually stir for 5 minutes, and then let it stand for 10 minutes. The introduction of anhydrous ethanol effectively alleviates the problem of rapid oxygen consumption when a large amount of modified straw cellulose comes into contact with water, preventing molecular chain oxidative breakage that leads to a significant decrease in paste viscosity. Then, fully dissolve the pre-wetted dry powder mixture with deionized water at a ratio of 1:20 at room temperature. A stepped curing process is used during dissolution: first, stir at 1000 rpm for 10 minutes at 40℃, then raise the temperature to 60℃ and stir at 1000 rpm for 10 minutes. This process design effectively prevents the formation of microcrack networks due to shrinkage stress during drying, thereby improving the outline clarity and color fastness of the printed fabric sample. If the paste thickens too quickly during curing, immediately add 0.5% sodium sulfate to inhibit excessive thickening and ensure the stability of the paste system.

[0031] To further verify the technical effects of the present invention, three examples and three comparative examples were prepared for comparative testing. The examples mainly used modified straw cellulose as the main raw material, while the comparative examples used a commonly used formulation in the industry with sodium alginate and CMC as the main raw materials.

[0032] Example 1 uses a formulation ratio of 20% modified straw cellulose, 20% carboxymethyl cellulose, 48.5% sodium sulfate, 2.0% additive S60, 1.5% hydrophobic filler modified carboxymethyl starch, 5% sodium hexametaphosphate, and 3% bioinhibitor BR.

[0033] Example 2 uses a formulation ratio of 25% modified straw cellulose, 25% carboxymethyl cellulose, 39.2% sodium sulfate, 1.0% additive S60, 1.8% hydrophobic filler modified carboxymethyl starch, 5% sodium hexametaphosphate, and 3% bioinhibitor BR.

[0034] Example 3 uses a formulation ratio of 50% modified straw cellulose, 10% carboxymethyl cellulose, 27.5% sodium sulfate, 1.0% additive S60, 3.5% hydrophobic filler modified carboxymethyl starch, 5% sodium hexametaphosphate, and 3% bioinhibitor BR.

[0035] Comparative Example 1 uses a formulation ratio of commercially available low-viscosity pure sodium alginate (90%), sodium hexametaphosphate (5%), additive S60 (2%), and biological inhibitor BR (3%).

[0036] Comparative Example 2 uses a formulation ratio of sodium carboxymethyl cellulose (CMC, 30%), sodium sulfate (50%), modified carboxymethyl starch (10%), sodium hexametaphosphate (5%), adjuvant S60 (3%), and biological inhibitor BR (2%).

[0037] Comparative Example 3 was formulated with carboxymethyl starch (CMS, 20%), sodium carboxymethyl cellulose (CMC, 15%), sodium sulfate (55%), sodium hexametaphosphate (5%), adjuvant S60 (3%), and biological inhibitor BR (2%).

[0038] The total mass of dry powder in each example and comparative example is 100g, to facilitate experimental proportioning. See Table 1 for details:

[0039] Table 1: Dry Powder Formulations for Examples and Comparative Examples (Unit: g)

[0040] Components Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Modified straw cellulose 20.0g 25.0g 50.0g Carboxymethyl cellulose (CMC) 20.0g 25.0g 10.0g 30.0g 15.0g Sodium alginate (low viscosity, 95% pure) 90.0g Carboxymethyl starch (CMS) 1.5g 1.8g 3.5g 10.0g 20.0g <![CDATA[Sodium sulfate (Na2SO4)]]> 48.5g 39.2g 27.5g 50.0g 55.0g Sodium hexametaphosphate 5.0g 5.0g 5.0g 5.0g 5.0g 5.0g Additive S60 2.0g 1.0g 1.0g 2.0g 3.0g 3.0g Biological inhibitor BR 3.0g 3.0g 3.0g 3.0g 2.0g 2.0g total 100.0g 100.0g 100.0g 100.0g 100.0g 100.0g

[0041] The digital printing pastes obtained in the above examples and comparative examples were respectively prepared with resist salt, sodium sulfate, urea, baking soda, and water to form sizing pastes. The formulation of the printing paste is as follows: 2-6% printing paste, 1% resist salt, 3% sodium sulfate, 10-15% urea, 3% baking soda, and water to make up the balance. The test fabric samples were pre-treated cotton fabrics to remove surface impurities and improve their water absorption. After the prepared printing paste was evenly coated on the surface of the cotton fabric, the printing operation was carried out using digital printing equipment. The printing process includes the following steps: fabric padding, drying, digital inkjet printing, drying, steaming, washing, and drying.

[0042] To comprehensively evaluate the technical advantages of this invention, multiple performance tests were conducted on the obtained printed fabric samples, and the test results are shown in Table 2.

[0043] Table 2: Performance Test Table of Printing Paste

[0044]

[0045] illustrate:

[0046] 1. Paste viscosity: Unit mPa·s (millipascal-seconds), fill in the measured value.

[0047] 2. Outline sharpness: 1-5 points (1 = worst, 5 = best)

[0048] 3. Feel: on a scale of 1 to 10 (1 = rough, 10 = very soft)

[0049] 4. Colorfastness: 1-5 points (1 = severe fading, 5 = no fading)

[0050] 5. All tests were conducted under standard environmental conditions, and the expert evaluation was based on the average score of 10 people.

[0051] First, the viscosity of the paste was measured directly using a rotational viscometer (MPa·s). The results showed that the viscosity range of Examples 1-3 of this invention was controlled between 30-50 MPa·s, meeting the spraying requirements of digital printing equipment. Color fastness testing employed a manual visual colorimetric method (grey gauge method) to evaluate the color change and staining degree of the fabric under conditions such as friction, washing, perspiration, and light exposure. The results showed that the color fastness rating of Examples 1-3 of this invention all reached level 4 or above, significantly better than Comparative Examples 1-3. The hand feel score was blind-tested by 10 industry experts, with a maximum score of 10. The hand feel score of Examples 1-3 of this invention was above 8, showing no significant difference from Comparative Examples 1-3. The outline sharpness score was also evaluated by 10 experts, with a maximum score of 5. The score of Examples 1-3 of this invention was 4-5, completely reproducing the original image with sharp edges, while the score of Comparative Examples 1-3 was below 4, showing slight blurring or bleeding.

[0052] Secondly, the color strength (K / S value) and color difference (DE*) of the printed fabric samples were tested using a Datacolor 600 colorimeter. Based on the actual processes of the dyeing and printing factory, test combinations of red, blue, dark blue, green, black, and gray were conducted, forming a highly comprehensive evaluation system.

[0053] Blue / Dark Blue: Tests the ability to process macromolecular dyes.

[0054] Black: Test depth and color matching compatibility.

[0055] Green: Tests the synchronization of two-color mixing.

[0056] Red: Tests hue reproduction accuracy.

[0057] Gray: This is the ultimate test for the compatibility of mixing the three primary colors, and it has the highest sensitivity.

[0058] Table 3: Performance Test Data of Printing Paste

[0059]

[0060]

[0061] illustrate:

[0062] 1. Standard Sample: High-purity (≥95%), low-viscosity (20-100 mPa.s) sodium alginate raw material is boiled with deionized water to prepare a paste of a specific concentration, which is defined as the reference (color strength 100%, color difference DE*0.00).

[0063] 2. Objective: To evaluate the color strength (K / S value) and color accuracy (DE value) of printing paste under different colors.

[0064] 3. Testing instrument: Datacolor; Light source / observer: D65 standard light source / 10° standard observer

[0065] 4. Test fabric: 100% cotton plain weave semi-finished fabric that has undergone scouring treatment.

[0066] 5. Printing process: Digital inkjet printing

[0067] 6. Evaluation index: Color strength (K / S value %): Sample K / S value ÷ Standard sample K / S value × 100%

[0068] Color difference (DE*): CIELAB (1976) standard, the smaller the value, the better.

[0069] According to the colorimeter test, the patented formula of this invention (Examples 1-3) showed excellent performance in the two key performance indicators of color strength and color difference. Its overall data performance is comparable to commercially available printing pastes (Comparative Examples 1-3), especially Example 1, which has obvious advantages.

[0070] Regarding color strength, the formulation of this invention exhibits stronger coloring performance, with the color strength values ​​of each embodiment outperforming the best performance of commercially available products. Regarding color difference, the formulation of this invention exhibits better color accuracy, with the color difference values ​​of each embodiment lower than the best level of commercially available products.

[0071] It is particularly noteworthy that these performance improvements were achieved under the premise of a significant reduction in raw material costs. Through formula innovation, this invention significantly reduces production costs while maintaining excellent performance, demonstrating remarkable technological advancement and practical value.

[0072] The test results above demonstrate that the modified straw cellulose digital printing paste provided by this invention achieves significant breakthroughs in raw material cost, environmental performance, and overall performance. Modified straw cellulose, as the core component, replaces traditional sodium alginate, not only reducing raw material costs by more than 30% but also improving the paste's water-holding capacity and stability.

[0073] In summary, this invention, through rational formulation design and optimized preparation process, has developed a high-efficiency, environmentally friendly, and economical digital printing paste. This paste not only significantly reduces raw material costs but also achieves multi-dimensional performance improvements in color strength, hand feel, and color fastness, making it particularly suitable for digital printing of dark-colored dyes on cotton fabrics. Its preparation method is simple and easy to implement, with mild and easily controllable conditions, enabling industrial application and filling the market gap for high-performance digital printing pastes.

Claims

1. A digital printing paste, characterized in that... It is composed of the following components in the indicated mass percentages: 20-50% modified straw cellulose, 10-30% carboxymethyl cellulose, 30-60% sodium sulfate, 1-2% auxiliary agent S60, 1.5-3.5% hydrophobic filler modified carboxymethyl starch, 0.2-0.5% complexing agent sodium hexametaphosphate, and 0.3% bioinhibitor BR. The modified straw cellulose is prepared by alkaline treatment and etherification reaction.

2. The digital printing paste as described in claim 1, characterized in that... The mass ratio of modified straw cellulose to carboxymethyl cellulose is 2:1 to 5:

3.

3. The digital printing paste as described in claim 1, characterized in that... Sodium sulfate has a particle size of less than or equal to 50 μm and a purity of greater than or equal to 99.5%.

4. The digital printing paste as described in claim 1, characterized in that... Additive S60 is a polyoxyethylene ether nonionic surfactant with an HLB value of 12-15.

5. A method for preparing the digital printing paste as described in claim 1, characterized in that... Includes the following steps: S1 Weigh the modified straw cellulose, carboxymethyl cellulose, modified carboxymethyl starch and sodium sulfate according to the formula ratio, and mix them in a three-dimensional mixer at 30 rpm for 15 minutes until uniform to obtain a dry powder mixture; S2 Add the auxiliary agent S60, sodium hexametaphosphate and biological inhibitor BR to the dry powder mixture in sequence, and mix at low speed (20 rpm) for 5 minutes; S3 mixes the dry powder mixture with deionized water at a ratio of 1:20, stirs at 600-1800 rpm for 30 minutes, and then matures in a constant temperature water bath at 40℃ for 20 minutes (600 rpm) to release the viscosity of all substances and remove air bubbles. After maturation, filter through a 150-mesh screen to remove impurities.

6. The preparation method according to claim 5, characterized in that... When the carboxymethyl cellulose content is greater than or equal to 25%, a segmented high-shear dispersion process is adopted. First, disperse at 800 rpm for 15 minutes, stop the machine and remove the glue blocks on the agitator and the vessel wall, then add modified carboxymethyl starch and continue to disperse at 1500 rpm for 10 minutes.

7. The preparation method according to claim 5, characterized in that... When the cellulose content of straw is ≥50%, the dry powder mixture is first pre-wetted with 5% anhydrous ethanol, then dissolved in water at a ratio of 1:20 at room temperature, and then matured in stages from 40℃ to 60℃.

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