Low-temperature heat-shrinkable material, heat-shrinkable sleeve, manufacturing method of heat-shrinkable sleeve and safety air bag

Abstract

The invention provides a low-temperature heat-shrinkable material, a heat-shrinkable sleeve, a manufacturing method of the heat-shrinkable sleeve and a safety air bag, and the low-temperature heat-shrinkable material comprises the following components in parts by weight: 100 parts of ethylene-vinyl acetate copolymer; 3-5 parts of a copolymer compatilizer; 60 to 80 parts of a flame retardant; 2-5 parts of color master batch; 4 parts of an antioxidant; 1-4 parts of a lubricant; and 2-5 parts of an acid neutralizer. The low-temperature thermal shrinkage material can be shrunk at a lower temperature, meets the processing temperature requirement of the safety air bag, has no peculiar smell, meets the smell experiment standard, and can conveniently design a directional blasting defect. According to the novel heat-shrinkable sleeve, the material and labor cost is reduced, and the safety and the reliability of the safety air bag are improved.

Description

Technical Field

[0001] This application relates to the technical field of polymer materials, and particularly to a low-temperature heat-shrinkable material, a heat-shrinkable sleeve, a manufacturing method thereof, and an airbag. Background Art

[0002] As a heat-shrinkable sleeve made of polyolefin material, heat-shrinkable sleeves are widely used in protecting metal and non-metal components due to their property of shrinking upon heating and tightly fitting on the surface of the protected object. They provide functions such as insulation, protection, and identification. In the field of automobile manufacturing, as a key safety component, the fixing method of the airbag poses special requirements for the material selection and processing technology.

[0003] In the existing technology, the airbag is wrapped with felt to play a fixing role, but this method has high material costs and labor costs.

[0004] In addition, heat-shrinkable sleeves face several problems when applied to airbags:

[0005] 1. Processing temperature limitation: Since the airbag contains explosives, the processing temperature during the wrapping process cannot exceed 100°C, while conventional heat-shrinkable sleeves require a temperature above 130°C to fully shrink.

[0006] 2. Odor problem: Heat-shrinkable sleeves with an ethylene-vinyl acetate copolymer substrate have a sour smell because it is difficult to completely remove small molecules such as vinyl acetate, which does not meet the customer's requirement that the odor test is less than or equal to level 3.0.

[0007] 3. Directional blasting requirement: The airbag needs to be directionally blasted when subjected to external force. Therefore, artificial defects need to be designed in the heat-shrinkable sleeve to facilitate directional blasting.

[0008] In view of the above problems, it is necessary to develop a new type of heat-shrinkable sleeve that can shrink at a lower temperature, meet the processing temperature requirements of the airbag, have no peculiar smell and meet the odor test standard, and can conveniently design directional blasting defects. This new type of heat-shrinkable sleeve will reduce material and labor costs and improve the safety and reliability of the airbag. Summary of the Invention

[0009] In view of this, in order to solve the technical problem that heat-shrinkable sleeves cannot be used in airbags due to the above problems in the prior art, the present invention provides a low-temperature heat-shrinkable material, which includes the following components by weight:

[0010]

[0011] Furthermore, the ethylene-vinyl acetate copolymer has a melt index of 2-4 grams per minute (g / min), a vinyl acetate (VA) content of 15%-30%, and a melting point of 60-90°C.

[0012] Furthermore, the copolymer compatibilizer is maleic anhydride grafted ethylene-vinyl acetate copolymer, and the content of the maleic anhydride comonomer is 0.4-1%wt (weight percentage).

[0013] Furthermore, the flame retardant comprises the following components by weight: montmorillonite, organic diethylaluminum hypophosphite and melamine cyanurate, and the ratio is 1:1:2.

[0014] Furthermore, the antioxidant comprises the following components by weight: hindered phenol and phosphite, in a ratio of 1:2.

[0015] Furthermore, the lubricant is a silicone masterbatch, wherein the effective content of silicone is 50%.

[0016] Furthermore, the acid neutralizer comprises the following components by weight: hydrotalcite and magnesium oxide in a ratio of 1:1.

[0017] The present invention also provides a heat shrinkable sleeve, characterized by using any of the low-temperature heat shrinkable materials described above.

[0018] The present invention also provides a method for manufacturing a heat shrinkable sleeve, comprising: taking the low-temperature heat shrinkable material described in any one of the above items and subjecting it to blending and granulation in a twin-screw extruder to obtain a modified masterbatch; extruding the masterbatch through a single-screw extruder, irradiating and cross-linking, and expanding and molding to obtain a finished heat shrinkable sleeve.

[0019] The present invention further provides a safety airbag, characterized in that the safety airbag is covered with the heat shrinkable tube as claimed in claim 8, and a side wall of the heat shrinkable tube has a plurality of openings.

[0020] Furthermore, the opening is elliptical, with a long diameter of 10±1 mm, a short diameter of 8±0.8 mm, and a distance between adjacent holes of 10±1 mm.

[0021] The low-temperature heat shrink material provided by the present invention can shrink at a relatively low temperature, meet the processing temperature requirements of the airbag, and has no odor, meets the odor test standards, and can conveniently design directional explosion defects. This new type of heat shrink tubing will reduce material and labor costs and improve the safety and reliability of the airbag. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings used in the description of the embodiments are briefly introduced below.

[0023] Figure 1 Schematic diagram of the heat-shrinkable sleeve structure applied to the airbag provided by the embodiment of the present application. Specific embodiments

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the specific embodiments of the present application will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to these drawings, and other embodiments can be obtained.

[0025] In the description of the present application, the terms "first", "second", etc. are only used to distinguish the described associated objects, and cannot be understood as indicating or implying the relative importance or order between the associated objects. The term "including: a combination of one or more of a1, a2,..., an" (n is a positive integer greater than 2) means any object in the described object, any combination of any two objects, any combination of any three objects, any combination of n objects. For example, "including a combination of one or more of a1, a2, a3" includes a1, a2, a3, a1 and a2, a1 and a3, a2 and a3, a1, a2 and a3.

[0026] In the field of automobile manufacturing, as a key safety component, the fixing method of the airbag has special requirements for the material selection, resulting in the inability to use heat-shrinkable sleeves and processing techniques in the prior art.

[0027] To solve these problems, the embodiments of the present application propose a new heat-shrinkable material development solution. Through specific component design, this material can shrink at a lower temperature, meet the processing temperature requirements of the airbag, have no peculiar smell, meet the odor test standard, and can conveniently design directional blasting defects. This new heat-shrinkable sleeve will reduce material and labor costs and improve the safety and reliability of the airbag.

[0028] The components and preparation process of this heat-shrinkable material will be described separately below.

[0029] The low-temperature heat-shrinkable material provided by this embodiment includes the following components by weight:

[0030]

[0031] In the embodiment of the present invention, the ethylene-vinyl acetate copolymer has a melt index of 2-4 g / min (grams per minute), a vinyl acetate (VA) content of 15%-30%, and a melting point of 60-80 °C.

[0032] In the embodiment of the present invention, the ethylene-vinyl acetate copolymer grade is Hanwha EVA1828 from South Korea, with a melt index of 3-4 g / min, a VA content of 27%-29%, and a melting point of 75°C.

[0033] The technical solution provided in this embodiment requires the selection of a main substrate with a low melting point. Since there is explosive in the airbag, the shrinkage temperature of the heat shrinkable tube cannot exceed 100°C. Through experimental verification, the melting point of the selected main substrate needs to be lower than 80°C to ensure complete shrinkage at 100°C. In addition, for convenient assembly, there are certain requirements for the hardness of the heat shrinkable tube, and more fillers need to be added to ensure the stiffness of the tube. Therefore, a main substrate with a relatively high VA content needs to be selected, and the resin has a strong powder absorption ability.

[0034] In the embodiment of the present invention, the copolymer compatibilizer is maleic anhydride grafted ethylene-vinyl acetate copolymer, and the content of the maleic anhydride comonomer is 0.4-1% wt (weight percentage).

[0035] In an embodiment of the present invention, the flame retardants are montmorillonite, aluminum diethyl phosphite, and melamine cyanurate. When using aluminum diethyl phosphite and melamine cyanurate, aluminum diethyl phosphite can generate acid sources such as phosphoric acid and carbon sources such as carbon dioxide and carbon monoxide during combustion to form a dense carbon layer, and melamine cyanurate can provide acid sources such as cyanuric acid and gas sources during combustion; the inventor found that when montmorillonite is added, it can not only greatly increase the hardness of the tube, but also have a synergistic effect with aluminum diethyl phosphite and melamine cyanurate, reducing the addition amount of aluminum diethyl phosphite, thereby reducing the cost of the entire formulation.

[0036] In an embodiment of the present invention, the flame retardants are montmorillonite, aluminum diethyl phosphite, and melamine cyanurate, and the ratio is 1:1:2 by weight.

[0037] In an embodiment of the present invention, the antioxidant is composed of a hindered phenol and a phosphite ester compounded, and the ratio is 1:2 by weight.

[0038] Research has found that when a hindered phenol and a phosphite ester are used together, their antioxidant performance can be greatly improved. Because the hindered phenol can form a stable molecule with free radicals, and the phosphite ester can reduce peroxides to alcohols, preventing the occurrence of a new oxidation cycle, and the effect is the best when the ratio is 1:2.

[0039] In an embodiment of the present invention, the acid neutralizer is composed of hydrotalcite and magnesium oxide compounded, and the ratio is 1:1 by weight.

[0040] When ethylene-vinyl acetate copolymer is synthesized, it is inevitable that there will be some small molecule residues of acetic acid type, so it smells sour. When conducting the odor experiment, it cannot meet the customer's requirement of less than or equal to grade 3.0. Through experiments, it is found that only when the acid neutralizers hydrotalcite and magnesium oxide are added can the requirement be met. Adding only one of them still cannot meet the requirement because magnesium oxide has adsorption and oxidation reactions with acidic substances and can convert acidic substances into corresponding oxides. Hydrotalcite is a layered structure with alternating silicon tetrahedrons and magnesium ions, and its surface has static charges, which can adsorb substances with opposite charges. The hydroxyl groups and metal ions on the surface can chemically react with acidic substances to form chemical bonds. The researchers found that when magnesium oxide and hydrotalcite are used together, the adsorption effect is better, and the adsorption effect on odor is the best. The heat shrinkable tube made can meet the customer's requirement of less than or equal to grade 3.0 when conducting the odor experiment.

[0041] The embodiment of the present invention also provides a preparation method of a heat shrinkable tube, including the following steps:

[0042] (1) Mixing ethylene-vinyl acetate copolymer, copolymer compatibilizer, flame retardant, color masterbatch, antioxidant, lubricant, and acid neutralizer in a twin-screw extruder under the condition of 130 - 140 °C to obtain modified masterbatch by melt granulation;

[0043] (2) Extruding the above masterbatch through a single-screw extruder at 110 - 130 °C, and obtaining the finished heat shrinkable tube through irradiation cross-linking and expansion molding;

[0044] After the finished heat shrinkable tube prepared in the embodiment of the present invention is cut into a certain length according to requirements, it is punched with a single line into an elliptical shape. The size of the hole is 10 mm ± 1 mm for the long diameter and 8 mm ± 0.8 mm for the short diameter, and the distance between two holes is 10 mm ± 1 mm. Finally, it shrinks and wraps the airbag at 100 °C and can pop open the airbag directionally under specific conditions. The hole is punched into an elliptical shape because the heat shrinkable tube is an extruded product and is prone to longitudinal cracking. The elliptical shape can avoid this defect while ensuring that the airbag can pop open smoothly along the opening direction when being impacted.

[0045] The following provides several specific examples, comparative examples and performance test results:

[0046] Example 1

[0047] The formula and manufacturing method of a low-temperature shrinkable heat shrinkable tube in this example include the following components by weight: 100 parts of ethylene-vinyl acetate copolymer, 3 parts of copolymer compatibilizer, 70 parts of flame retardant, 4 parts of color masterbatch, 3 parts of antioxidant, 2 parts of lubricant, and 5 parts of acid neutralizer;

[0048] The ethylene-vinyl acetate copolymer mentioned above is Hanwha EVA1828 from South Korea, with a VA content of 27%-29% and a melting point of 75°C;

[0049] The copolymer compatibilizer mentioned above is Nanjing Juxing JX-15;

[0050] The flame retardant is montmorillonite, aluminum diethyl phosphite, and melamine cyanurate, and the ratio is 1:1:2;

[0051] The masterbatch can be customized in various colors according to customer needs;

[0052] The antioxidant is composed of a hindered phenol and a phosphite, and the optimal ratio is 1:2;

[0053] The lubricant is a silicone masterbatch, and the effective content of silicone is 50%;

[0054] The acid neutralizer is composed of hydrotalcite and magnesium oxide, and the optimal ratio is 1:1;

[0055] An embodiment of the present invention also provides a method for preparing a heat shrinkable tube, which includes the following steps:

[0056] (1) Mix the ethylene-vinyl acetate copolymer, copolymer compatibilizer, flame retardant, masterbatch, antioxidant, lubricant, and acid neutralizer in a twin-screw extruder at 130°C to obtain a modified masterbatch by melt granulation;

[0057] (2) Extrude the above masterbatch through a single-screw extruder at 120°C, and obtain the finished heat shrinkable tube through irradiation cross-linking and expansion molding.

[0058] In an embodiment of the present invention, after the prepared finished heat shrinkable tube is cut to a certain length as required, elliptical holes are drilled in a single line on the side wall. The size of the holes is 10mm±1mm in long diameter and 8mm±0.8mm in short diameter, and the distance between two holes is 10mm±1mm. Finally, it shrinks and wraps the airbag at 100°C, and can pop open the airbag directionally under specific conditions.

[0059] Example 2

[0060] A formula and manufacturing method of a low-temperature shrinkable heat shrinkable tube in an embodiment of the present invention, the components by weight include: 100 parts of ethylene-vinyl acetate copolymer, 5 parts of copolymer compatibilizer, 60 parts of flame retardant, 2 parts of masterbatch, 1 part of antioxidant, 1 part of lubricant, and 2 parts of acid neutralizer;

[0061] The ethylene-vinyl acetate copolymer mentioned above is Hanwha EVA1828 from South Korea, with a VA content of 27%-29% and a melting point of 75°C;

[0062] The copolymer compatibilizer is of the brand Nanjing Juxing JX-15;

[0063] The flame retardant is montmorillonite, aluminum diethyl phosphite, and melamine cyanurate, and the optimal ratio is 1:1:2;

[0064] The masterbatch can be customized in various colors according to customer needs;

[0065] The antioxidant is composed of a hindered phenol and a phosphite ester, and the optimal ratio is 1:2;

[0066] The lubricant is a silicone masterbatch, and the effective content of silicone is 50%;

[0067] The acid neutralizer is composed of hydrotalcite and magnesium oxide, and the optimal ratio is 1:1;

[0068] An embodiment of the present invention further provides a method for preparing a heat shrinkable tube, including the following steps:

[0069] (1) Mix ethylene-vinyl acetate copolymer, copolymer compatibilizer, flame retardant, masterbatch, antioxidant, lubricant, and acid neutralizer in a twin-screw extruder at 140 °C to obtain a modified masterbatch by granulation;

[0070] (2) Extrude the above masterbatch through a single-screw extruder at 110 °C, and obtain a finished heat shrinkable tube through irradiation crosslinking and expansion molding;

[0071] Please refer to Figure 1 , which shows a schematic structural diagram of a heat shrinkable tube applied to an airbag provided by an embodiment of the present invention. After cutting the obtained finished heat shrinkable tube to a certain length as required, make single-line holes in an elliptical shape on the side wall, with the size of the holes being a major diameter of 10 mm ± 1 mm and a minor diameter of 8 mm ± 0.8 mm, and the distance between two holes being 10 mm ± 1 mm. Finally, shrink-wrap the airbag at 100 °C and can pop open the airbag directionally under specific conditions.

[0072] To more clearly illustrate the beneficial technical effects achieved by the technical solution provided in this application, the following comparative examples are given for comparison:

[0073] Comparative Example 1

[0074] The difference between this example and Example 1 is that the ethylene-vinyl acetate copolymer has the brand Beijing Organic EVA14-2, the VA content is 13% - 16%, and the melting point is 85 °C.

[0075] Comparative Example 2

[0076] The difference between this example and Example 1 is that no acid neutralizer is added.

[0077] Comparative Example 3

[0078] The difference between this example and Example 1 is that only 2 parts of hydrotalcite are added as the acid neutralizer.

[0079] Comparative Example 4

[0080] The difference between this example and Example 1 is that only 2 parts of magnesium oxide are added as the acid neutralizer.

[0081] Comparative Example 5

[0082] The difference between this example and Example 1 is that no antioxidant is added.

[0083] Comparative Example 6

[0084] The difference between this example and Example 1 is that only 1 part of hindered phenol is used as the antioxidant.

[0085] Comparative Example 7

[0086] The difference between this example and Example 1 is that only 20 parts of the flame retardant are added, and the ratio is 1:1:2.

[0087] Comparative Example 8

[0088] The difference between this example and Example 1 is that montmorillonite is not added to the flame retardant, and only 60 parts of aluminum diethyl phosphinate and melamine cyanurate are added, and the ratio is 1:2.

[0089] Performance Test

[0090] Performance Test 1

[0091] Referring to the ASTM D2671 standard, the tensile strength of the samples obtained in Examples 1-2 and Comparative Examples 1-6 was tested. When the tensile strength > 12 MPa, it was recorded as A; when the tensile strength was 10-12 MPa, it was recorded as B; when the tensile strength < 10 MPa, it was recorded as C.

[0092] Performance Test 2

[0093] The samples obtained in Examples 1-2 and Comparative Examples 1-8 were placed in an oven at 158 °C for 168 h according to the UL224 standard, and then the tensile strength of the samples was tested according to the ASTM D2671 standard. When the tensile strength > 8.0 MPa, it was recorded as A; when the tensile strength was 6-8 MPa, it was recorded as B; when the tensile strength < 6 MPa, it was recorded as C.

[0094] Performance Test 3

[0095] Referring to the UL94 standard, for the flame retardant performance of the samples obtained in Examples 1-3 and Comparative Examples 1-8 of the 3mm tablet test, if it self-extinguishes within 15S without igniting absorbent cotton and meets the V-0 requirement, it is recorded as A; if the burning time is within 10-30s without igniting absorbent cotton, it is recorded as B; if the burning time is within 10-30s and ignites absorbent cotton, it is recorded as C.

[0096] Performance Test Four

[0097] For the tubes cut from the samples obtained in Examples 1-2 and Comparative Examples 1-8, check whether they can be recovered in place at 100°C. If they can be shrunk in place, it is recorded as "able"; if they cannot be shrunk in place, it is recorded as "not able".

[0098] Performance Test Five

[0099] Carry out an odor experiment on the samples obtained in Examples 1-2 and Comparative Examples 1-8 according to the Volkswagen VW50180 standard. The odor level is from 1 to 6 levels, and the requirement is ≤ 3 levels.

[0100] Performance Test Table

[0101] Strength before aging Strength after aging Flame retardancy Retraction in place Odor level Example 1 A A A Yes Level 3 Example 2 A A A Yes Level 3 Comparative Example 1 B B A No Level 3 Comparative Example 2 A A A Yes Level 6 Comparative Example 3 A A A Yes Level 4 Comparative Example 4 A A A Yes Level 4 Comparative Example 5 C C A Yes Level 3 Comparative Example 6 B B A Yes Level 3 Comparative Example 7 A A C Yes Level 3 Comparative Example 8 A A B Yes Level 3

[0102] From the above test data, it can be seen that: in the technical solution provided by the embodiments of the present invention, by using ethylene-vinyl acetate copolymer with low melting point and high VA content, not only can the heat shrinkable tube be shrunk at 100°C, but also the mechanical properties of the material can be significantly improved; by using a suitable flame retardant compounding, when montmorillonite is added, not only can the hardness of the tube be greatly increased, but also it has a synergistic effect with aluminum diethylphosphinate and melamine cyanurate, reducing the addition amount of aluminum diethylphosphinate, thereby reducing the cost of the whole formula; by using a suitable antioxidant compounding and addition ratio, the mechanical strength of the heat shrinkable tube after aging can be effectively improved; by using a suitable acid neutralizer compounding and addition ratio, the adsorption effect on odor is the best, and the heat shrinkable tube made can meet the customer requirement of less than or equal to 3.0 level in the odor experiment. After the finished heat shrinkable tube of the present invention is cut into a certain length according to requirements, it is in the shape of an ellipse with a single-line hole, and finally shrinks to wrap the airbag, and can pop open the airbag directionally under specific conditions. This solution is a brand-new application field, which can reduce material and labor costs and improve the degree of automation of assembly.

[0103] The low-temperature heat shrinkable material provided by the embodiments of the present invention can shrink at a lower temperature, meet the processing temperature requirements of the airbag, have no peculiar smell, meet the odor experiment standard, and can conveniently design a directional blasting defect. This new type of heat shrinkable tube will reduce material and labor costs and improve the safety and reliability of the airbag.

[0104] The above are only some embodiments of the present invention. For those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A low-temperature heat-shrinkable material, characterized in that, By weight, it includes the following components:

2. The low-temperature heat-shrinkable material according to claim 1, wherein The ethylene-vinyl acetate copolymer has a melt index of 2-4 grams per minute (g / min), a vinyl acetate (VA) content of 15%-30%, and a melting point of 60-90°C.

3. The low-temperature heat-shrinkable material according to claim 1, characterized in that, The copolymer compatibilizer is maleic anhydride grafted ethylene-vinyl acetate copolymer, and the content of the maleic anhydride comonomer is 0.4-1% wt (weight percentage).

4. The low-temperature heat-shrinkable material according to claim 1, characterized in that, By weight, the flame retardant includes the following components: montmorillonite, aluminum diethylphosphinate, and melamine cyanurate, and the ratio is 1:1:

2.

5. The low-temperature heat-shrinkable material according to claim 1, characterized in that, By weight, the antioxidant includes the following components: hindered phenol and phosphite, and the ratio is 1:

2.

6. The low-temperature heat-shrinkable material according to claim 1, characterized in that, The lubricant is a silicone masterbatch, and the effective content of silicone is 50%.

7. The low-temperature heat-shrinkable material according to claim 1, characterized in that, By weight, the acid neutralizer includes the following components: hydrotalcite and magnesium oxide, and the ratio is 1:

1.

8. A heat-shrinkable sleeve, characterized in that, Use the low-temperature heat-shrinkable material according to any one of claims 1-7.

9. A method for manufacturing a heat-shrinkable sleeve, characterized in that, It includes: Take the low-temperature heat-shrinkable material according to any one of claims 1-7 and conduct melt blending and pelletizing in a twin-screw extruder to obtain a modified masterbatch; Extrude the above masterbatch through a single-screw extruder, irradiate and crosslink, and expand and mold to obtain a finished heat-shrinkable sleeve.

10. An airbag, characterized in that, The safety airbag is coated with the heat-shrinkable sleeve according to claim 8, and a plurality of openings are provided on one side wall of the heat-shrinkable sleeve.

11. The airbag according to claim 10, wherein, The openings are oval, with a long diameter of 10±1 mm, a short diameter of 8±0.8 mm, and the spacing between adjacent holes is 10±1 mm.

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