Aluminum foil for food soft package and preparation method of aluminum foil

Abstract

The invention belongs to the technical field of aluminum foils for soft food packages, and provides a preparation method of an aluminum foil for soft food packages, which comprises the following preparation steps: S1, smelting an aluminum ingot to obtain molten aluminum, degassing, slagging off and standing the molten aluminum, filtering, and adding titanium powder and a fluxing agent to obtain molten aluminum; s2, Fe3O4 is added into the molten aluminum, heating and stirring treatment is conducted firstly, then precipitation and cast rolling treatment are conducted after gradient cooling, and a cast-rolled plate is obtained; s3, the cast-rolled plate is subjected to cold rolling for the first time, and a formed aluminum foil blank is obtained; s4, the aluminum foil blank is subjected to annealing treatment, second-time cold rolling is carried out during annealing, and third-time cold rolling is carried out after annealing; and S5, the aluminum foil blank subjected to third-time cold rolling is subjected to withdrawal, straightening and cleaning, then a rolling agent is sprayed for foil rolling treatment, and the aluminum foil for the food soft package is obtained after aftertreatment. The aluminum foil for the food soft package, which is prepared by the method, has a small number of pinholes, can be ensured to have good mechanical properties, and can also be suitable for being stably compounded with polypropylene.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum foil for soft food packages, and in particular, relates to an aluminum foil for soft food packages and a preparation method thereof. Background Art

[0002] Soft-package aluminum foil plays an important role in the food packaging industry. It has good barrier properties, plasticity, corrosion resistance and recyclability, and is widely used in the packaging of various foods. It is specifically made into bagged or boxed liquid packaging materials through online lamination or compounding with plastic film. Therefore, the requirements on the pinholes, plate shape and mechanical performance indicators of aluminum foil are relatively strict, especially for those with too many pinholes or too large pinhole diameters, the sealing and preservation effect of the packaging material will be lost. At the same time, it is also necessary to ensure that it has good composite properties when compounded with polypropylene, etc., so that the prepared food soft packaging material has high peel strength.

[0003] Therefore, based on the above description, there is an urgent need for a method for preparing aluminum foil for food soft packaging that has a small number of pinholes, excellent mechanical properties such as elongation, and is easy to compound with polypropylene to prepare a food soft packaging material with high stability. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the first object of the present invention is to provide a method for preparing aluminum foil for food soft packaging, which can obtain a food packaging bag with good mechanical properties and is easy to be compounded with polypropylene to obtain good stability and not easy to delaminate.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing aluminum foil for food soft packaging comprises the following preparation steps:

[0007] S1, smelting aluminum ingots to obtain aluminum liquid, filtering the aluminum liquid after degassing, slagging, and standing treatment, and then adding titanium powder and flux to obtain aluminum liquid;

[0008] S2, adding Fe3O4 to the aluminum liquid, first heating and stirring, then gradually cooling, precipitating, and casting to obtain a cast-rolled plate;

[0009] S3, performing a first cold rolling on the cast-rolled plate to obtain a formed aluminum foil blank;

[0010] S4, annealing the aluminum foil blank, performing a second cold rolling during the annealing period, and performing a third cold rolling after the annealing;

[0011] S5. The aluminum foil blank after the third cold rolling is straightened and cleaned, and then sprayed with a rolling agent for foil rolling treatment, and after post-treatment, an aluminum foil for food soft packaging is obtained.

[0012] In the present invention, the aluminum ingot is melted into aluminum liquid in a high-temperature melting furnace to ensure the liquefaction and uniformity of the raw materials; then the aluminum liquid is degassed to remove the gas (such as hydrogen, etc.) therein to avoid the formation of pores in the subsequent processing; at the same time, a further slag removal operation is performed to remove the scum and impurities on the surface of the molten metal, thereby ensuring the purity of the aluminum liquid; further static treatment is performed to make the temperature and composition of the aluminum liquid more uniform, so that each component is evenly distributed after the subsequent addition of titanium powder and flux; the aluminum liquid that has been statically treated is further purified by a filter to remove tiny impurities, and then an appropriate amount of titanium powder and flux are added to perform the static treatment. Alloying treatment is carried out to adjust the chemical composition of the aluminum liquid and improve the mechanical properties and corrosion resistance of the aluminum foil; Fe3O4 is then added and evenly mixed with the aluminum liquid. After heating, part of the Fe3O4 acts as foreign heterogeneous particles to provide additional nucleation sites for the melt. After cooling, the heterogeneous particles further promote the formation of crystal nuclei, thereby increasing the number of crystal nuclei. Finally, the grains are fully refined, and the strength and toughness of the aluminum foil are significantly improved; after further gradient cooling, the residual Fe3O4 particles are precipitated and evenly settled at the bottom of the aluminum liquid. The temperature is further reduced, and after continuous casting and rolling, a cast-rolled plate with a certain thickness is obtained.

[0013] In the present invention, the first cold rolling pass is 1-2, and the cast-rolled plate is subjected to preliminary cold rolling processing to reduce its thickness and preliminarily shape it into an aluminum foil blank, thereby realizing the adjustment of the thickness and shape of the aluminum foil; the second cold rolling pass is 3-4, and the aluminum foil blank after the first cold rolling is annealed to eliminate work hardening and residual stress, improve its ductility and flexibility, and the second cold rolling is carried out during annealing to further reduce the thickness of the aluminum foil; after further annealing, the third cold rolling is carried out, and the third cold rolling pass is 4-5, and the final required aluminum foil thickness and surface quality are achieved.

[0014] In the present invention, the aluminum foil blank after the third cold rolling is subjected to a straightening treatment to correct its shape and dimensional accuracy; then a cleaning operation is performed to remove oil stains and impurities on the surface; then a proper amount of rolling agent is sprayed on the side of the aluminum foil blank where Fe3O4 is precipitated, the aluminum foil blank is turned over again, and the side where Fe3O4 is precipitated is foil rolled to obtain a smooth, flat aluminum foil surface with a small number of pinholes; finally, after post-treatment, i.e., slitting treatment is performed according to the size requirements of the finished product, and annealing treatment is performed again to stabilize the performance and structure of the aluminum foil, and finally an aluminum foil for soft food packaging is obtained.

[0015] In the present invention, in step S4, the annealing treatment includes the following steps:

[0016] S41 homogenization annealing, annealing temperature is 500-530℃, annealing time is 2-4h;

[0017] S42 intermediate annealing, annealing temperature is 370-400℃, annealing time is 2-4h.

[0018] Furthermore, in step S1, the flux comprises the following components in weight ratio: 70-85% magnesium oxide and 15-30% graphite powder.

[0019] In the present invention, by using graphite powder, the fluidity of the melt can be improved without affecting the effect of magnesium oxide, and the overall sintering temperature can be reduced, thereby further reducing the melting point.

[0020] Furthermore, in step S1, by weight, the aluminum liquid comprises 70-80%, the titanium powder comprises 10-20% and the flux comprises 10-15%.

[0021] Furthermore, in step S1, the hydrogen content is controlled to 0.08 mL / 100 gAl, and the filtration particle size is ≥5 um.

[0022] Furthermore, in step S2, by weight, the aluminum liquid is 90-95%, and the Fe3O4 is 5-10%.

[0023] Furthermore, in step S2, the temperature rise range is 800-850°C, the stirring speed is 100-150r / min, and the stirring time is 1-2h.

[0024] Furthermore, the gradient cooling includes a first stage cooling and a second stage precipitation cooling; the temperature range of the first stage cooling is 680-710°C, the cooling time is 30-60min, and the temperature range of the second stage precipitation cooling is 670-680°C, and the cooling precipitation time is 1-2h.

[0025] Furthermore, in step S2, the convexity of the cast plate is between 0.03-0.04 mm, and the edge difference of the cast plate is ≤0.01 mm.

[0026] Furthermore, in step S5, the foil rolling process uses a rolling roller, and the roughness of the rolling roller is 0.07-0.08 um.

[0027] Furthermore, in step S5, the rolling preparation comprises the following components in weight ratio: 0.2-0.5% polyacrylic acid, 7-8% ester synthetic fat, 5-6% monohydric alcohol, and 80-88% rolling oil.

[0028] In the present invention, the rolling oil is a main component of the rolling agent and plays a major role in lubrication and cooling during the rolling process; wherein the polyacrylic acid has good film-forming properties and plays a role in thickening, stabilization or auxiliary lubrication in the rolling agent, and can also be compounded with Fe3O4 deposited on the surface of the aluminum foil blank during the foil rolling process to improve the toughness and wear resistance of the aluminum foil blank, thereby reducing the number of pinholes and cracks during the foil rolling process, so that in the subsequent food packaging production and application stage, it can be composite-grafted with materials such as polypropylene to obtain a stable and non-stratified composite packaging material.

[0029] The second object of the present invention is to provide an aluminum foil for soft food packaging obtained by the above preparation method.

[0030] The beneficial effects of the present invention are:

[0031] (1) The present invention adds an appropriate amount of titanium powder and flux to perform alloying treatment to adjust the chemical composition of the aluminum liquid and improve the mechanical properties and corrosion resistance of the aluminum foil.

[0032] (2) The present invention further adds Fe3O4 and mixes it evenly with the aluminum liquid. After heating, part of the Fe3O4 acts as foreign heterogeneous particles to provide additional nucleation sites for the melt. After cooling, the heterogeneous particles further promote the formation of crystal nuclei, thereby increasing the number of crystal nuclei. Finally, the grains are fully refined, and the strength and toughness of the aluminum foil are significantly improved. After further gradient cooling, the remaining Fe3O4 particles are precipitated and evenly settled at the bottom of the aluminum liquid. The temperature is further lowered, and after continuous casting and rolling, a cast-rolled plate with a certain thickness is obtained.

[0033] (3) The present invention sprays an appropriate amount of rolling agent on the side of the aluminum foil blank where Fe3O4 is precipitated, flips the aluminum foil blank again, and performs foil rolling on the side where Fe3O4 is precipitated, thereby obtaining a smooth, flat aluminum foil surface with a small number of pinholes; after post-treatment, an aluminum foil suitable for compounding with polypropylene for soft food packaging is finally obtained. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0035] Example 1

[0036] This embodiment provides a method for preparing aluminum foil for food soft packaging, comprising the following preparation steps:

[0037] 1. Materials and Equipment Preparation

[0038] Raw materials: aluminum ingot (purity ≥ 99.7%), titanium powder, Fe3O4, flux (magnesium oxide 75%, graphite powder 25%), rolling agent (polyacrylic acid 0.3%, ester synthetic fat 7.5%, monohydric alcohol 5.5%, rolling oil 86.7%).

[0039] Equipment: high temperature furnace, degassing device, slag remover, static tank, filter, agitator, casting and rolling mill, cold rolling mill, annealing furnace, straightening machine, cleaning machine, rolling equipment.

[0040] 2. Preparation process

[0041] (1) Preparation of aluminum liquid

[0042] Put the aluminum ingot into a high-temperature furnace and heat it until it is completely melted to obtain aluminum liquid. Degas the aluminum liquid to remove hydrogen and other gases in it, so that the hydrogen content is controlled to below 0.08mL / 100gAl. Remove the scum and impurities on the surface of the aluminum liquid to ensure the purity of the aluminum liquid. Let the aluminum liquid stand for a period of time to make the temperature and composition more uniform. Further purify the aluminum liquid through a filter, and the filter particle size is ≥5μm. Add 15% titanium powder and 10% flux (75% magnesium oxide, 25% graphite powder) by weight to the aluminum liquid for alloying treatment to improve the mechanical properties and corrosion resistance of the aluminum foil.

[0043] (2) Fe3O4 addition and casting

[0044] Add 5% Fe3O4 by weight to the alloyed aluminum liquid and mix them evenly. Heat the mixed aluminum liquid to 825℃ and stir at 120r / min for 1.5h to disperse the Fe3O4 particles evenly. Implement gradient cooling: first cool to 700℃ for 45 minutes; then cool to 675℃ for 1.5h. The aluminum liquid after cooling is cast and rolled to obtain a cast plate with a convexity of 0.035mm and a side difference of ≤0.01mm.

[0045] (3) Cold rolling

[0046] The cast plate is cold rolled for the first time, with one pass, to obtain a preliminarily formed aluminum foil blank. The aluminum foil blank is annealed: first, homogenization annealing is performed at a temperature of 515°C and an annealing time of 3 hours; then intermediate annealing is performed at a temperature of 385°C and an annealing time of 3 hours. During the annealing, a second cold rolling is performed, with three passes, to further reduce the thickness of the aluminum foil. After annealing again, a third cold rolling is performed, with four passes, to achieve the final required aluminum foil thickness and surface quality.

[0047] (4) Straightening, cleaning and foil rolling

[0048] After the third cold rolling, the aluminum foil blank is subjected to a straightening treatment to correct its shape and dimensional accuracy. The surface of the aluminum foil is cleaned to remove oil stains and impurities. An appropriate amount of rolling agent is sprayed on the side of the aluminum foil blank where Fe3O4 is precipitated. After the aluminum foil is turned over, the side where Fe3O4 is precipitated is subjected to foil rolling. A roller with a roughness of 0.075μm is used for rolling to obtain a smooth, flat aluminum foil surface with a small number of pinholes.

[0049] (5) Post-processing

[0050] According to the size requirements of the finished product, the rolled aluminum foil is slit and the slit aluminum foil is finally annealed to stabilize its performance and structure to obtain the final aluminum foil product for food soft packaging.

[0051] Example 2

[0052] (1) Preparation of aluminum liquid

[0053] The aluminum liquid preparation process is similar to that of Example 1, but the flux ratio is adjusted to 75% magnesium oxide, 25% graphite powder, and the titanium powder addition amount is 18% of the aluminum liquid.

[0054] (2) Fe3O4 addition and casting

[0055] The proportion of Fe3O4 added to the aluminum liquid was adjusted to 6%, the temperature was raised to 830°C, the stirring speed was 130r / min, and the stirring time was 1h. The temperature of the first stage of gradient cooling was set to 690°C, and the cooling time was 50 minutes; the temperature of the second stage was set to 678°C, and the cooling precipitation time was 1h45 minutes. The convexity of the cast plate obtained by casting and rolling was 0.038mm.

[0056] (3) Cold rolling

[0057] The first cold rolling pass was 2 times, the second cold rolling pass was 4 times, the third cold rolling pass was 5 times, and the annealing conditions were the same as those in Example 1.

[0058] (4) Straightening, cleaning and foil rolling

[0059] The straightening and cleaning steps are the same as those in Example 1, and the rolling agent ratio is adjusted to 0.4% polyacrylic acid, 7.8% ester synthetic fat, 5.7% monohydric alcohol, and 85.1% rolling oil.

[0060] (5) Post-processing

[0061] The post-processing steps are the same as in Example 1.

[0062] Example 3

[0063] (1) Preparation of aluminum liquid

[0064] During the preparation of aluminum liquid, the flux ratio is 70% magnesium oxide, 30% graphite powder, and the amount of titanium powder added is 20% of the aluminum liquid. The hydrogen content is strictly controlled below 0.07mL / 100gAl.

[0065] (2) Fe3O4 addition and casting

[0066] The amount of Fe3O4 added was 10% of the aluminum liquid, the temperature was raised to 850℃, the stirring speed was 150r / min, and the stirring time was 2h. The temperature of the first stage of gradient cooling was set at 710℃, and the cooling time was 60 minutes; the temperature of the second stage was set at 680℃, and the cooling precipitation time was 2h. The edge difference of the cast plate obtained by casting and rolling was 0.008mm.

[0067] (3) Cold rolling

[0068] During the cold rolling process, the first cold rolling pass is 2 times, the second cold rolling pass is 3 times, and the third cold rolling pass is 5 times. The annealing temperature and time are fine-tuned according to the specific situation, but are kept within the range given in Example 1.

[0069] (4) Straightening, cleaning and foil rolling

[0070] The roughness of the roller was adjusted to 0.08 μm, and the rolling agent ratio was 0.5% polyacrylic acid, 8% ester synthetic fat, 6% monohydric alcohol, and 84% rolling oil. Other straightening, cleaning, and foil rolling steps were the same as those in Example 1.

[0071] (5) Post-processing

[0072] The post-processing steps are the same as in Example 1.

[0073] Example 4

[0074] (1) Preparation of aluminum liquid

[0075] The flux ratio is adjusted to 85% magnesium oxide, 15% graphite powder, and 12% titanium powder added to the aluminum liquid. The hydrogen content of the aluminum liquid is controlled below 0.06mL / 100gAl.

[0076] (2) Fe3O4 addition and casting

[0077] The amount of Fe3O4 added is 7% of the aluminum liquid, the temperature is raised to 800℃, the stirring speed is 100r / min, and the stirring time is 1h. During the gradient cooling process, the temperature of the first stage is set at 680℃, the cooling time is 30 minutes; the temperature of the second stage is set at 670℃, and the cooling precipitation time is 1h. The quality control of the cast plate is more stringent, the convexity is maintained at 0.032mm, and the edge difference is ≤0.005mm.

[0078] (3) Cold rolling

[0079] During the cold rolling process, in order to optimize processing efficiency, the first cold rolling pass is 1, but the number and conditions of subsequent annealing and cold rolling are carefully adjusted to ensure that the final performance of the aluminum foil meets the predetermined standards.

[0080] (4) Straightening, cleaning and foil rolling

[0081] A special rolling agent formula is used, with a polyacrylic acid content of 0.2%, ester synthetic fat 7%, monohydric alcohol 5%, and rolling oil 87.8%. The steps of straightening, cleaning and foil rolling are the same as those in the previous embodiment.

[0082] (5) Post-processing

[0083] The post-processing steps are the same as in Example 1.

[0084] Comparative Example 1

[0085] The difference between this comparative example and Example 1 is that (1) aluminum liquid preparation: aluminum ingots are smelted into aluminum liquid, and only conventional degassing, slag removal and static treatment are performed, and titanium powder and flux are not added. After direct filtration, it is ready to proceed to the next step.

[0086] Comparative Example 2

[0087] The difference between this comparative example and Example 1 is that (2) Fe3O4 addition and casting: after Fe3O4 is added to the aluminum liquid, the temperature is directly raised and stirred, and then the temperature is quickly lowered to the casting temperature without gradient cooling treatment. Then, casting is performed to obtain a cast-rolled plate.

[0088] Comparative Example 3

[0089] The difference between this comparative example and Example 1 is that (4) straightening, cleaning and foil rolling: before foil rolling, the aluminum foil is sprayed with a conventional rolling agent that does not contain polyacrylic acid. After the straightening and cleaning steps are completed, foil rolling is performed.

[0090] Test Example 1

[0091] According to the preparation methods provided in Examples 1-4 and Comparative Examples 1-3, aluminum foil samples with a thickness of 0.0063 mm were prepared, and the number of pinholes was detected. Specifically, a laser detection method was used. The penetrating property of the laser beam was utilized. The laser beam was emitted onto the aluminum foil through a transmitter, and the receiver collected the laser beam that passed through the pinholes in the aluminum foil, thereby calculating the number and diameter of the pinholes. The detection results are shown in Table 1 below.

[0092] Test Example 2

[0093] According to the preparation methods provided in Examples 1-4 and Comparative Examples 1-3, aluminum foil samples with a thickness of 0.0063 mm were prepared and subjected to elongation tests; wherein the elongation was tested using a longitudinal tensile test method, and the test results are shown in Table 1 below.

[0094] Test Example 3

[0095] According to the preparation method provided in Examples 1-4 and Comparative Examples 1-3, aluminum foil samples with a thickness of 0.0063 mm were prepared and subjected to a collapse test. Specifically, the aluminum foil samples were placed on a parallel roller system with a wheelbase of 1.5 m, and the collapse was measured under a tensile stress of 0.8 kg / mm2. The test results are shown in Table 1 below.

[0096] Test Example 4

[0097] According to the preparation method provided in Examples 1-4 and Comparative Examples 1-3, an aluminum foil sample with a thickness of 0.0063 mm was prepared, and the aluminum foil was compounded with polypropylene using a conventional high temperature and high pressure compounding process. Finally, the obtained composite finished product was subjected to a peel strength test, specifically by using a peel tester to peel the composite film sample along the composite interface.

[0098] Table 1

[0099]

[0100] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing aluminum foil for food soft packaging, characterized in that: The method comprises the following preparation steps: S1, smelting aluminum ingots to obtain aluminum liquid, filtering the aluminum liquid after degassing, slagging, and standing treatment, and then adding titanium powder and flux to obtain aluminum liquid; S2, adding Fe3O4 to the aluminum liquid, first heating and stirring, then gradually cooling, precipitating, and casting to obtain a cast-rolled plate; S3, performing a first cold rolling on the cast-rolled plate to obtain a formed aluminum foil blank; S4, annealing the aluminum foil blank, performing a second cold rolling during the annealing period, and performing a third cold rolling after the annealing; S5. The aluminum foil blank after the third cold rolling is straightened and cleaned, and then sprayed with a rolling agent for foil rolling treatment, and finally slitting and annealing to obtain aluminum foil for food soft packaging.

2. The method for preparing aluminum foil for food soft packaging according to claim 1, characterized in that: In step S1, the flux comprises the following components in weight ratio: 70-85% magnesium oxide and 15-30% graphite powder.

3. The method for preparing the aluminum foil for food soft package according to claim 2, characterized in that: In step S1, by weight, the aluminum liquid comprises 70-80%, the titanium powder comprises 10-20% and the flux comprises 10-15%.

4. The method for preparing aluminum foil for food soft packaging according to claim 1, characterized in that: In step S1, the hydrogen content is controlled to 0.08 mL / 100 gAl, and the filter particle size is ≥ 5 um.

5. The method for preparing aluminum foil for food soft packaging according to claim 1, characterized in that: In step S2, by weight, the aluminum liquid accounts for 90-95% and the Fe3O4 accounts for 5-10%.

6. The method for preparing the aluminum foil for food soft package according to claim 5, characterized in that: In step S2, the temperature rise range is 800-850°C, the stirring speed is 100-150r / min, and the stirring time is 1-2h.

7. The method for preparing aluminum foil for food soft packaging according to claim 5, characterized in that: The gradient cooling includes a first stage cooling and a second stage precipitation cooling; the temperature range of the first stage cooling is 680-710°C, the cooling time is 30-60min, and the temperature range of the second stage precipitation cooling is 670-680°C, the cooling precipitation time is 1-2h.

8. The method for preparing aluminum foil for food soft packaging according to claim 1, characterized in that: In step S2, the convexity of the cast plate is between 0.03-0.04 mm, and the edge difference of the cast plate is ≤0.01 mm.

9. The method for preparing the aluminum foil for food soft packaging according to any one of claims 1 to 8, characterized in that: In step S5, the rolling preparation comprises the following components in weight ratio: 0.2-0.5% polyacrylic acid, 7-8% ester synthetic fat, 5-6% monohydric alcohol, and 80-88% rolling oil.

10. An aluminum foil for soft food packages obtained by the method for preparing the aluminum foil for soft food packages according to any one of claims 1 to 9.

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