Weakening-free polypropylene foam for air bag blasting, preparation method, application and layered skin material

Abstract

The invention discloses weakening-free polypropylene foam for air bag blasting, a preparation method, application and a layered skin material, relates to the technical field of automotive interior skin, and aims to solve the problem that the polypropylene foam in the skin material is irregularly torn during air bag blasting. The cohesive force of the polypropylene foam is 20-25 N / 1.5 cm. The polypropylene foam is prepared from the following raw materials in parts by weight: 50-80 parts of homo-polypropylene, 20-30 parts of block copolymerized polyethylene, 5-10 parts of ethylene propylene diene monomer, 1-2 parts of a cross-linking agent, 1-2 parts of an antioxidant and 4-8 parts of an ADCA foaming agent. The cohesive force of the polypropylene foam is improved, the prepared layered skin material can be applied to an automotive trim safety air bag area, and it is guaranteed that the skin material is regularly torn according to the shape of an air bag box when the air bag is exploded and unfolded.

Description

Technical Field

[0001] The invention relates to the technical field of automobile interior skin, in particular to a copolymer layered product, specifically a weakening-free polypropylene foam for airbag explosion, a preparation method, an application and a layered skin material. Background Art

[0002] In recent years, for considerations such as the feel and aesthetics of car interiors, more and more large-area interiors such as car dashboards and door panels have been designed as one-piece. In particular, the airbag area also adopts an integral skin design and uses non-weakening airbag explosion materials. The TPO dashboard has better tensile strength and is more likely to rupture under the impact of an explosion, ensuring the normal deployment of the airbag.

[0003] Polypropylene foam is compressible. After bonding with the plastic frame, it can effectively cover up some burrs and defects on the plastic frame. At the same time, it can improve the soft touch of support and obtain a good blasting effect without weakening the surface. For this reason, polypropylene foam has become an excellent choice for the skin material of the automotive interior airbag.

[0004] However, a large number of new technical problems have emerged in practical applications, such as Figure 3 As shown in the figure, the deployment direction of the airbag explosion deviates, resulting in an angular deviation in the deployment direction of the airbag. When the vehicle collides and the occupants need the airbag to protect them properly, this deviation is likely to cause the airbag to fail to achieve the designed safety effect. Figure 4 As shown, when the airbag explodes, excessive splashes are generated under the huge impact force, which may also lead to safety failure and may cause accidental injuries to people in the car facing the airbag.

[0005] After analysis, it is found that there is usually no problem with the adhesion between polypropylene foam and the TPO skin layer and substrate. However, when the airbag explodes and deploys, there will still be a situation where the skin material is not torn regularly along the direction specified by the airbag box. After a more in-depth detailed analysis and research, it was found that the irregular tearing starts from the inside of the polypropylene foam itself. In addition to the above two problems, when the polypropylene foam is torn irregularly, the huge impact force of the airbag explosion may also interrupt or break the weak parts of the skeleton; there are two possible ways to solve this problem in the prior art. One is to increase the density of the polypropylene foam, but this method will increase a lot of production costs in addition to poor results; the second is to increase the hardness of the polypropylene foam, but nowadays automobile interiors pursue soft touch, and hard ones have gradually been eliminated. Therefore, there is an urgent need for a non-weakening polypropylene foam for airbag explosion, a preparation method, an application, and a layered skin material to solve this problem. Summary of the invention

[0006] The purpose of the present invention is to provide a non-weakening polypropylene foam for airbag explosion, a preparation method, an application and a layered skin material to solve the problem of irregular tearing of the polypropylene foam in the skin material when the airbag explodes.

[0007] To achieve the above object, the present invention provides the following technical solution: a weakening-free polypropylene foam for airbag explosion, the cohesive force of the polypropylene foam is 20-25N / 1.5cm, and the raw materials of the polypropylene foam include 50-80 parts of homopolymer polypropylene, 20-30 parts of block copolymer polyethylene, 5-10 parts of ethylene propylene diene monomer rubber, 1-2 parts of cross-linking agent, 1-2 parts of antioxidant, and 4-8 parts of ADCA foaming agent in parts by weight; The melt index of homopolymer polypropylene is 1-8 g / 10 min at 230 ° C and a load of 2.16 kg, and the density is 0.89-0.91 g / cm 3 , softening temperature ≥135℃; The melt index of the block copolymer polyethylene is 1 to 3 g / 10 min when measured at 190° C. and a load of 2.16 kg, the melting point is 105 to 115° C., and the hardness is 55 to 65A.

[0008] Preferably, the main body of the above block copolymer polyethylene is C2, and the comonomer is C8.

[0009] Preferably, the melt index of the EPDM rubber is 1-3 g / 10 min at 190°C and a load of 2.16 kg, the Mooney viscosity is 20-40, and the density is 0.89-0.91 g / cm 3 .

[0010] Preferably, the viscosity of the cross-linking agent at room temperature is 40-70 mPa.s, the antioxidant is a hindered phenol antioxidant, the water content of the ADCA foaming agent is ≤1%, and the gas release volume is 140-160 mL / g.

[0011] Preferably, the thickness of the polypropylene foam is 1.5 to 3.0 mm, and the density is 50 to 100 kg / m 3 ; Tensile strength MD1200~1800kPa, CD 200~700kPa; Elongation at room temperature MD≥300%, CD≥250%; Elongation at 120℃ MD≥800%, CD≥600%; 25% compression strength is 80~150kPa.

[0012] Another technical solution provided by the present invention: a method for preparing polypropylene foam, comprising the following contents: feeding the above raw materials into an extruder according to a set ratio, fully plasticizing and mixing, and then extruding them into sheets through a mold, during which the melt temperature is controlled to ensure that the foaming agent does not decompose in the extruder; irradiating the sheet to allow the cross-linking agent to fully react and cross-link; using a vertical foaming furnace for foaming production, wherein the horizontal section is used to preheat the sheet, and the vertical section is a foaming section, and cooling and shaping are performed after foaming.

[0013] Preferably, in the above preparation method, the melt temperature in the extruder is ≤180°C; double-layer irradiation is adopted, and the dosage is 30-40KGy; the preheating section temperature is 200-240°C, and the preheating is 40-60 seconds; the foaming section temperature is 300-400°C, and the heating is 10-20 seconds.

[0014] Another technical solution provided by the present invention is that a polypropylene foam is applied to the skin material of the airbag area of ​​the automobile interior, so as to ensure that when the airbag explodes and deploys, the skin material is torn according to the shape of the airbag box.

[0015] Another technical solution provided by the present invention is a layered skin material, comprising a polypropylene foam layer and a TPO skin layer attached to a substrate, wherein the polypropylene foam layer adopts the above-mentioned polypropylene foam and is located between the substrate and the TPO skin layer.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The non-weakening polypropylene foam, preparation method, application and layered skin material for airbag explosion achieve the improvement of the cohesive force of the polypropylene foam by targetedly adjusting the properties of homopolymer polypropylene and block copolymer polyethylene to a suitable range, combined with corresponding improvements in other ingredients and preparation methods. After the polypropylene foam of the present invention is made into a layered skin material, it can be applied to the safety airbag area of ​​automobile interior to ensure that when the airbag is exploded and deployed, the skin material is torn according to the shape rules of the airbag box, ensuring that the safety measures can effectively achieve their designed effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the structure of the layered material of the present invention; Figure 2 The results of the airbag explosion test of Example 1 of the present invention; Figure 3 The results of the airbag explosion test of Comparative Example 1 are as follows; Figure 4 This is the result of the airbag explosion test for comparative example 2.

[0018] In the figure: 1. TPO skin layer; 2. Polypropylene foam layer; 3. Base material. DETAILED DESCRIPTION

[0019] See also Figure 1 A non-weakening layered skin material for airbag explosion, including a polypropylene foam layer and a TPO skin layer attached to a substrate. The substrate can generally be a plastic frame. The polypropylene foam layer is located between the substrate and the TPO skin layer, and is bonded to the TPO surface on one side, usually by softening the TPO material at high temperature, and then hot-pressing and bonding it to the polypropylene foam layer, and bonding it to the frame on the other side. The bonding method can be to pre-spray glue on the plastic frame, and then vacuum-form the heated composite material onto the plastic frame on a vacuum forming machine, activate the glue at high temperature, and shape it after cooling; the TPO skin layer can use conventional TPO skin materials, such as modified polypropylene, low-density polyethylene and EPDM rubber, which are mixed on a co-rotating twin-screw extruder and extruded from a die to form a film material.

[0020] In the present invention, the most important thing is that the cohesion of the polypropylene foam layer must be 20-25N / 1.5cm (most of the polypropylene foam in the prior art is 10-15N / 1.5cm). Through experiments, it can be achieved that regular tearing can be achieved. The cohesion is tested by the following method: take a strip sample with a width of 15mm and a length of 200mm, and then cut it from the middle of one end of the strip with a knife, pre-peel 20mm, and then use upper and lower clamps to clamp the two ends of the peeled part, and use a speed of 50mm / min on the stretching machine. The material is stretched to a certain degree and the force value in N is recorded. In order to achieve this target characteristic, the raw materials of the polypropylene foam layer include 50-80 parts of homopolymer polypropylene, 20-30 parts of block copolymer polyethylene, 5-10 parts of EPDM rubber, 1-2 parts of crosslinking agent, 1-2 parts of antioxidant, and 4-8 parts of ADCA foaming agent by weight. The melt index of homopolymer polypropylene is 1-8 g / 10 min at 230 ° C and a load of 2.16 kg, and the density is 0.89-0.91 g / cm 3 , softening temperature ≥135℃; the melt index of the block copolymer polyethylene is measured at 190℃ and a load of 2.16kg to be 1-3g / 10min, the melting point is 105-115℃, and the hardness is 55-65A.

[0021] For reference, the main body of the above-mentioned block copolymer polyethylene is C2, and the comonomer can be C8, wherein C8 is regularly arranged on the main chain of the C2 polymer, and it has the characteristics of high strength, low hardness and high melting point, but this is only a feasible solution. The implementer can adjust the structure of the block copolymer polyethylene according to the above-mentioned specific cohesion and MFR and other parameters. Under the idea provided by the present invention, the purpose of regular tearing can also be achieved, but the choice provided by the present invention also has the following advantages for reference when selecting other block copolymer polyethylenes: better toughness; due to the longer side chains of C8, it is easier to react with the crosslinking agent during radiation crosslinking, and it is easy to achieve a higher reasonable crosslinking degree at a low radiation dose; high melting point, which is conducive to the high temperature (85°C) burst test of the airbag.

[0022] Optionally, the melt index of the EPDM rubber is 1-3 g / 10 min at 190° C. and a load of 2.16 kg, the Mooney viscosity is 20-40, and the density is 0.89-0.91 g / cm 3 .

[0023] Optionally, the viscosity of the cross-linking agent at room temperature is 40-70 mPa.s, the antioxidant is a hindered phenol antioxidant, the water content of the ADCA foaming agent is ≤1%, and the gas release volume is 140-160 mL / g.

[0024] In a preferred embodiment, the thickness of the polypropylene foam layer can be 1.5 to 3.0 mm; the density can be 50 to 100 kg / m 3 ; The tensile strength can be MD 1200~1800kPa, CD 200~700kPa; the elongation at room temperature can be MD≥300%, CD≥250%; the elongation at 120℃ can be MD≥800%, CD≥600%; the 25% compressive strength can be 80~150kPa.

[0025] In the above-mentioned layered skin material, the preparation method of polypropylene foam comprises: Put all raw materials (homopolymer polypropylene, block copolymer polyethylene, EPDM rubber, crosslinking agent, antioxidant, ADCA foaming agent) into the extruder according to the set ratio, preferably a co-rotating twin-screw extruder, and the liquid crosslinking agent is preferably fed with a high-precision liquid feeding pump. After being fully plasticized and mixed, it is extruded into a sheet through a die. During the process, the melt temperature is controlled to ensure that the foaming agent will not decompose in the extruder. For reference, the melt temperature in the extruder should be below 180°C; Irradiate the material, preferably double-layer irradiation, the dose is preferably controlled at 30-40 KGy, specifically, an electron irradiation accelerator can be used to allow the crosslinking agent to fully react and crosslink; A vertical foaming furnace is used for foaming production, in which the horizontal section is used to preheat the sheet, and the vertical section is the foaming section. Natural gas heating and infrared heating can be used as heat sources. For reference, the preheating section temperature is 200-240°C, preheating for 40-60 seconds, and the foaming section temperature is 300-400°C, heating for 10-20 seconds; after foaming, it is cooled and set.

[0026] In the following embodiments, homopolymer polypropylene is made of Korea Petrochemical, brand HJ4006; block copolymer polyethylene is made of C2 (ethylene) as the main body and C8 (octene) as the comonomer, wherein C8 is regularly arranged on the main chain of the C2 polymer, specifically Dow Chemical, brand 9107; EPDM is made of Dow Chemical, brand 4820P; the crosslinking agent is made of >99.9% trimethylolpropane trimethacrylate, specifically BASF, brand TMPTMA, the antioxidant is made of >99.9% pentaerythritol tetrakis (3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate), specifically BASF, brand IRGANOX 1010, and the ADCA foaming agent is calculated by weight percentage, 50-55% azodicarbonamide, and 45-50% low-density polyethylene carrier, specifically Lei Fus, brand 5038.

[0027] Embodiment 1: 60 parts of homopolymer polypropylene, 30 parts of block copolymer polyethylene, 5 parts of ethylene propylene diene monomer rubber, 1 part of cross-linking agent, 1 part of antioxidant and 5 parts of ADCA foaming agent are weighed by weight, and the materials except the cross-linking agent are put into a co-rotating twin-screw extruder, and the cross-linking agent is fed by a high-precision liquid feeding pump. After being fully plasticized and mixed, the sheet is extruded through a mold; an electron irradiation accelerator is used to irradiate the sheet so that the cross-linking agent fully reacts and cross-links; a vertical foaming furnace is used for foaming production, with a preheating stage of 220°C for 40 seconds and a foaming stage of 350°C for 20 seconds; after foaming, the sheet is shaped by a cooling guide roller to obtain a polypropylene foam.

[0028] Its two sides are bonded to the plastic skeleton substrate and TPO skin layer respectively, and an airbag is installed under the substrate. The burst test results are as follows Figure 2 As shown; the cohesive force of the polypropylene foam is measured to be about 24N / 1.5cm.

[0029] Embodiment 2: 70 parts of homopolymer polypropylene, 30 parts of block copolymer polyethylene, 10 parts of ethylene propylene diene monomer rubber, 2 parts of crosslinking agent, 2 parts of antioxidant and 6 parts of ADCA foaming agent are weighed by weight, and the materials except the crosslinking agent are put into a co-rotating twin-screw extruder, and the crosslinking agent is fed by a high-precision liquid feeding pump. After being fully plasticized and mixed, the sheet is extruded through a mold; an electron irradiation accelerator is used to irradiate the sheet so that the crosslinking agent fully reacts and crosslinks; a vertical foaming furnace is used for foaming production, with a preheating stage of 200°C for 50 seconds and a foaming stage of 300°C for 20 seconds; after foaming, the sheet is shaped by a cooling guide roller to obtain a polypropylene foam.

[0030] Its two sides are bonded to the plastic skeleton substrate and the TPO skin layer respectively, and an air bag is installed under the substrate. The bursting test results are basically the same as those in Example 1; the cohesive force of the polypropylene foam is measured to be about 21N / 1.5cm.

[0031] Embodiment 3: 50 parts of homopolymer polypropylene, 20 parts of block copolymer polyethylene, 5 parts of ethylene propylene diene monomer rubber, 2 parts of crosslinking agent, 1 part of antioxidant and 4 parts of ADCA foaming agent are weighed by weight, and the materials except the crosslinking agent are put into a co-rotating twin-screw extruder, and the crosslinking agent is fed by a high-precision liquid feeding pump. After being fully plasticized and mixed, the sheet is extruded through a mold; an electron irradiation accelerator is used to irradiate the sheet so that the crosslinking agent fully reacts and crosslinks; a vertical foaming furnace is used for foaming production, with a preheating stage of 220°C for 40 seconds and a foaming stage of 400°C for 10 seconds; after foaming, the sheet is shaped by a cooling guide roller to obtain polypropylene foam.

[0032] Its two sides are bonded to the plastic skeleton substrate and the TPO skin layer respectively, and an air bag is installed under the substrate. The bursting test results are basically the same as those in Example 1; the cohesive force of the polypropylene foam is measured to be about 23N / 1.5cm.

[0033] Comparative Example 1: According to the weight fraction, 86 parts of EPDM rubber (Kumho, 570P), 20 parts of polypropylene (ExxonMobil, 7032), 15 parts of ethylene-acrylate copolymer (BASF, VMX5020), 22 parts of paraffin oil (Wantai Chemical, paraffin oil) and 7 parts of talc (Xinda Talc, 92876) were plasticized at a roller temperature of 75°C and a plasticizing speed of 2min / kg, and then refined into sheets at a refining temperature of 60°C and a refining speed of 2min / kg, and then granulated to obtain modified EPDM rubber; By weight, 80 parts of polypropylene (Sinopec, 1806), 2.5 parts of nano calcium carbonate (Liangjiang Chemical, 400 mesh), 6 parts of ethylene-octene copolymer (Dow, 8480), and 12 parts of ethylene-acrylate copolymer (BASF, VMX5020) were put into a mixer and mixed at 180°C for 10 minutes, extruded at 180°C, and granulated to obtain modified polypropylene; The polypropylene foam raw materials are calculated by weight: 21 parts of the above-mentioned modified polypropylene, 70 parts of the above-mentioned modified EPDM rubber, 27 parts of low-density polyethylene (Formosa Plastics, 3224), 2.5 parts of AC foaming agent (Jie Shang Jie, LD50S), and 2 parts of masterbatch (Aomekai, 6006); A preparation process as close as possible to that of the embodiment is adopted, the materials are put into a co-rotating twin-screw extruder, and after being fully plasticized and mixed, they are extruded into sheets through a mold; a vertical foaming furnace is used for foaming production, with a preheating stage of 220° C. for 40 seconds and a foaming stage of 350° C. for 20 seconds; after foaming, the polypropylene foam is shaped by a cooling guide roller.

[0034] Its two sides are respectively bonded with the same plastic skeleton substrate and TPO skin layer as in the embodiment, and an air bag is installed under the substrate. The explosion test results are as follows: Figure 3As shown; the cohesive force of the polypropylene foam is measured to be about 13N / 1.5cm.

[0035] Comparative Example 2: Polypropylene resin (Sinopec, 1806), rubber (Dawn, D85), toughening agent (Dow Chemical, 8842), foaming agent (Jieshangjie, LD50S), lubricant (Kline, 4201), and antioxidant (BASF, brand IRGANOX 1010) are added into the hopper of a twin-screw extruder for melting, mixing, and extrusion. The screw temperature of the twin-screw extruder is controlled at 250°C. The raw materials extruded from the twin-screw extruder are pulled, cooled, and dried to obtain polypropylene foam.

[0036] Its two sides are respectively bonded with the same plastic skeleton substrate and TPO skin layer as in the embodiment, and an air bag is installed under the substrate. The explosion test results are as follows: Figure 4 shown.

[0037] It can be seen from the airbag explosion test results of the embodiments and comparative examples that the tearing edges of the method of the present invention are regular and are all torn along the edge of the airbag box, with significant effects. The principle is mainly to improve the cohesive force of the polypropylene foam through special raw materials and proportions, combined with a suitable preparation method, so that it is not easy to break from the middle of the foam layer. In summary, after the polypropylene foam of the present invention is made into a layered skin material, it can be applied to the automotive interior safety airbag area to ensure that when the airbag explodes and deploys, the skin material is torn according to the shape of the airbag box, thereby ensuring that the safety measures can effectively achieve their designed effects.

[0038] The above are only preferred embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope defined by the claims.

[0039] The matters not described in detail in the present invention are all known technologies to those skilled in the art.

Claims

1. A non-weakening polypropylene foam for airbag explosion, characterized in that: The cohesive force of the polypropylene foam is 20-25N / 1.5cm, and the raw materials of the polypropylene foam include 50-80 parts of homopolymer polypropylene, 20-30 parts of block copolymer polyethylene, 5-10 parts of EPDM rubber, 1-2 parts of crosslinking agent, 1-2 parts of antioxidant, and 4-8 parts of ADCA foaming agent in parts by weight; The melt index of the homopolymer polypropylene is 1-8 g / 10 min at 230° C. and a load of 2.16 kg, and the density is 0.89-0.91 g / cm 3 , softening temperature ≥135℃; The block copolymer polyethylene has a melt index of 1-3 g / 10 min measured at 190° C. and a load of 2.16 kg, a melting point of 105-115° C., and a hardness of 55-65A.

2. The weakening-free polypropylene foam for airbag explosion according to claim 1, characterized in that: The main body of the block copolymer polyethylene is C2, and the comonomer is C8, wherein C8 is regularly arranged on the main molecular chain of C2.

3. The weakening-free polypropylene foam for airbag explosion according to claim 1, characterized in that: The EPDM rubber has a melt index of 1-3 g / 10 min at 190° C. and a load of 2.16 kg, a Mooney viscosity of 20-40, and a density of 0.89-0.91 g / cm 3 .

4. The weakening-free polypropylene foam for airbag explosion according to claim 1, characterized in that: The viscosity of the cross-linking agent at room temperature is 40-70 mPa.s, the antioxidant is a hindered phenol antioxidant, the water content of the ADCA foaming agent is ≤1%, and the gas release volume is 140-160 mL / g.

5. The weakening-free polypropylene foam for airbag explosion according to claim 1, characterized in that: The thickness of the polypropylene foam is 1.5-3.0 mm; the density is 50-100 kg / m 3 ; Tensile strength MD 1200~1800kPa, CD 200~700kPa; Elongation at room temperature MD ≥300%, CD ≥250%; Elongation at 120℃ MD ≥800%, CD ≥600%; 25% compression strength is 80~150kPa.

6. A method for preparing polypropylene foam according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: feeding the raw materials into an extruder according to a set ratio, fully plasticizing and mixing, and then extruding the raw materials into sheets through a mold, during which the melt temperature is controlled to ensure that the foaming agent does not decompose in the extruder; irradiating the sheet to allow the cross-linking agent to fully react and cross-link; and using a vertical foaming furnace for foaming production, wherein the horizontal section is used to preheat the sheet, and the vertical section is a foaming section, which is cooled and shaped after foaming.

7. The preparation method according to claim 6, characterized in that: The melt temperature in the extruder is ≤180°C; double-layer irradiation is adopted, and the dosage is 30-40KGy; the preheating section temperature is 200-240°C, and the preheating is 40-60 seconds; the foaming section temperature is 300-400°C, and the heating is 10-20 seconds.

8. A polypropylene foam as claimed in any one of claims 1 to 5 used as a skin material in the airbag area of ​​an automobile interior, characterized in that: Used to ensure that when the airbag explodes and deploys, the skin material is torn regularly according to the shape of the airbag box.

9. A layered skin material, characterized in that: It comprises a polypropylene foam layer and a TPO skin layer attached to a substrate, wherein the polypropylene foam layer adopts the polypropylene foam described in any one of claims 1 to 5 and is located between the substrate and the TPO skin layer.

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