A modified polypropylene foam material and preparation method thereof

Abstract

The present invention provides a modified polypropylene foam material and a preparation method thereof. The modified polypropylene resin composition comprises the following raw materials: polypropylene, terminal hydroxyl polybutadiene, a curing agent, a crosslinking modifier, a foaming agent, a lubricant, and an antioxidant; wherein the curing agent is a polyisocyanate curing agent; and the crosslinking modifier is a multi-arm star polymer crosslinking modifier. The modified polypropylene resin composition of the present invention has a significantly improved temperature resistance while improving the hardness of the material, has excellent thermal stability, and has broad application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of foaming materials, in particular to a modified polypropylene foaming material and a preparation method thereof. Background Art

[0002] Polyolefin foam material is one of the traditional foam materials. It is mainly made of polyethylene and is prepared by adding a foaming agent. The main problem with polyolefin foam materials is that the heat resistance and strength performance are relatively low, so the application field is limited. Especially with the development and application of polyolefin foam materials in automobile door panels, engines and other parts, it is usually required that the foam material can withstand the use temperature of 100°C, which puts higher requirements on the heat resistance and strength of polyolefin foam materials.

[0003] Polypropylene foam material is a type of polyolefin foam material. Due to the presence of tertiary carbon in its molecular structure, it is easy to remove hydrogen atoms during high-temperature processing to generate tertiary carbon free radicals, resulting in the degradation of the polypropylene molecular chain. At the same time, the melt strength of polypropylene is relatively low, which increases the difficulty of foaming and the control requirements of bubble uniformity. Therefore, modifying polypropylene to improve foaming performance is a problem that needs to be solved urgently.

[0004] Chinese patent document CN112280170A discloses a polypropylene composition for automotive interior parts and a preparation method thereof, which uses polypropylene, polyethylene and polybutadiene as a resin matrix and polypropylene glycol glycidyl ether as a curing agent to prepare a polypropylene foam product. Although the above method improves the mechanical strength of the polypropylene material to a certain extent, it has limited effect on improving the melt strength of the polypropylene. Summary of the invention

[0005] The purpose of the present invention is to provide a modified polypropylene foam material and a preparation method thereof, so as to solve the technical problem of poor strength of polypropylene foam materials in the prior art.

[0006] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0007] A modified polypropylene foam material comprises the following raw materials: polypropylene, terminal hydroxyl polybutadiene, a curing agent, a cross-linking modifier, a foaming agent, a lubricant, and an antioxidant;

[0008] Wherein, the curing agent is a polyisocyanate curing agent; and the cross-linking modifier is a multi-arm star polymer cross-linking modifier.

[0009] Preferably, the polyisocyanate curing agent is one or more of toluene diisocyanate, hexamethylene diisocyanate, 4,4′-diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, and isophorone diisocyanate.

[0010] Preferably, the multi-arm star polymer cross-linking modifier is one or more of polyethylene glycol-b-poly 4-vinylpyridine, polyethylene glycol-b-polystyrene, polystyrene-b-polyacrylic acid-b-polystyrene, polyacrylic acid-b-polystyrene-b-polyacrylic acid, and poly 4-vinylpyridine-b-polystyrene-b-poly 4-vinylpyridine.

[0011] Preferably, the multi-arm star polymer cross-linking modifier is polyacrylic acid-b-polystyrene-b-polyacrylic acid.

[0012] Preferably, the hydroxyl-terminated polybutadiene is a hydroxyl-terminated polybutadiene having a number average molecular weight of 2800-3600.

[0013] Preferably, the lubricant is ethylene bisstearamide.

[0014] Preferably, the blowing agent is azodicarbonamide.

[0015] Preferably, the antioxidant is one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and dilauryl thiodipropionate.

[0016] Preferably, the modified polypropylene foam material comprises the following raw materials in parts by weight:

[0017]

[0018] The present invention also provides a method for preparing the modified polypropylene foam material, comprising the following steps: taking polypropylene, terminal hydroxyl polybutadiene, a curing agent, a cross-linking modifier, a foaming agent, a lubricant, and an antioxidant, mixing them uniformly, and then granulating, extruding, irradiating, and foaming to obtain the modified polypropylene foam material.

[0019] Preferably, the method for preparing the modified polypropylene foam material comprises the following steps:

[0020] (1) taking polypropylene, hydroxyl-terminated polybutadiene, a curing agent, a cross-linking modifier, a lubricant, and an antioxidant, and mixing them uniformly to obtain a mixed material;

[0021] (2) subjecting the mixed material to internal kneading, extrusion and granulation at 140-160° C. to obtain a first granular material;

[0022] (3) melt-extruding and granulating the first granular material at 180-200° C. to obtain a second granular material;

[0023] (4) adding a foaming agent to the second granular material, mixing uniformly, and performing melt extrusion granulation at 145-165° C. to obtain a third granular material;

[0024] (5) stirring and drying the third particulate material at 140-160° C. for 30-90 min, and then extruding at 150-170° C. to obtain an extruded master sheet;

[0025] (6) placing the extruded mother sheet under irradiation conditions for irradiation cross-linking, and then foaming the irradiation cross-linked extruded mother sheet at 205-225° C. to obtain a product.

[0026] The modified polypropylene foam material of the present invention can also be processed by cutting and the like according to the requirements. The uses of the modified polypropylene foam material include but are not limited to: automobile roof, steering wheel, luggage compartment lining and air conditioner steam damping plate, side guard plate, door inner panel energy absorption protection pad, instrument insulation board, door inner side insulation, 100-135°C heat carrier circulation battery insulation material, engine room insulation material, indoor or automobile and other places sound insulation material.

[0027] The above solution of the present invention includes at least the following beneficial effects:

[0028] (1) The modified polypropylene resin composition of the present invention comprises the following raw materials: polypropylene, terminal hydroxyl polybutadiene, curing agent, crosslinking modifier, foaming agent, lubricant, and antioxidant; wherein the curing agent is a polyisocyanate curing agent; and the crosslinking modifier is a multi-arm star polymer crosslinking modifier. The modified polypropylene resin composition has a high polypropylene content. By adding terminal hydroxyl polybutadiene and polyisocyanate curing agent to the polypropylene matrix resin for chemical reaction modification, on the one hand, the double bonds in the molecular structure of polybutadiene can effectively improve the efficiency of radiation crosslinking, and on the other hand, the terminal hydroxyl polybutadiene is a terminal hydroxyl polybutadiene, and its functional terminal hydroxyl group can react with isocyanate to form a local hyperbranched structure. The terminal hydroxyl polybutadiene after polyisocyanate curing has high melt strength, which can effectively improve the melt strength of polypropylene and is also easy to achieve the regulation of the foaming process, thereby regulating the mechanical properties and sealing application performance of the product. At the same time, by adding a multi-arm star polymer cross-linking modifier, the cross-linking efficiency can be improved by using the star polymer. In addition, the heterogeneous components in the star polymer, such as polystyrene blocks, exist as heterogeneous nucleation points in the polypropylene melt, and can achieve phase separation from the polypropylene continuous phase. As a bubble nucleation point, it helps the bubble nucleation and stabilization.

[0029] (2) The modified polypropylene resin composition of the present invention, according to the structural characteristics of the tertiary carbon atoms of polypropylene, effectively reduces the processing difficulty of polypropylene, improves the crosslinking degree, and optimizes the foaming pore structure and its performance by adding components such as terminal hydroxyl polybutadiene. While improving the hardness of the material, the temperature resistance is greatly improved, and it has excellent thermal stability, product dimensional stability at high temperatures, a smooth and soft surface, and a comfortable feel. The maximum use temperature can reach 135°C, and it is resistant to boiling water and has good thermal insulation performance. It has good elasticity and thermoforming performance and excellent environmental protection. It can be used as a heat-resistant automotive interior foam material and has broad application prospects.

[0030] (3) The preparation method of the modified polypropylene resin composition of the present invention comprises the following steps: taking polypropylene, terminal hydroxyl polybutadiene, curing agent, cross-linking modifier, foaming agent, lubricant, antioxidant, mixing evenly, and then granulating, extruding, irradiating, and foaming to obtain. Among them, granulation can be carried out by melt extrusion and blending granulation with a twin-screw extruder, and then extruding a mother sheet through a conical twin-screw extruder, cross-linking is achieved by irradiation, and then, in a horizontal foaming furnace, the foaming agent is decomposed under high temperature conditions to prepare a foamed material. The above preparation method is simple to operate. Due to the presence of polystyrene blocks in the material, the bubble nucleation and stability are good, and the microporous structure of the polypropylene foam material can be effectively regulated. DETAILED DESCRIPTION

[0031] In the embodiments of the present invention, if the specific conditions are not specified, the conventional conditions or the conditions recommended by the manufacturer are followed. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially. Raw materials of different manufacturers and models do not affect the implementation of the technical solution of the present invention and the realization of the technical effects.

[0032] Example 1

[0033] The modified polypropylene foam material of this embodiment includes the following raw materials in parts by weight:

[0034]

[0035] Wherein, the polypropylene may be F800E; the curing agent is a polyisocyanate curing agent; the crosslinking modifier is a multi-arm star polymer crosslinking modifier. The polyisocyanate curing agent is toluene diisocyanate. The multi-arm star polymer crosslinking modifier is polyethylene glycol-b-poly 4-vinyl pyridine. The hydroxy-terminated polybutadiene is a hydroxy-terminated polybutadiene with a number average molecular weight of 2800, which may be Polybd CS-15 in this embodiment. The lubricant is ethylene bis stearic acid amide. The foaming agent is azodicarbonamide (AC-3). The antioxidant is a mixture of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] pentaerythritol ester (antioxidant 1010) and dilauryl thiodipropionate (DLTP) in a weight ratio of 2:1.

[0036] In this embodiment, the preparation method of the modified polypropylene foam material comprises the following steps:

[0037] (1) taking polypropylene, hydroxyl-terminated polybutadiene, a curing agent, a cross-linking modifier, a lubricant, and an antioxidant, and mixing them uniformly to obtain a mixed material;

[0038] (2) subjecting the mixed material to internal kneading, extrusion and granulation to obtain a first granular material; wherein, the internal kneading, extrusion and granulation can be carried out using an internal mixer. In this embodiment, an internal mixer is used to perform internal kneading, extrusion and granulation at a feeding speed of 30 r / min, an outlet temperature of 140°C, an extrusion speed of 50 r / min and an extrusion temperature of 140°C.

[0039] (3) The first granular material is melt-extruded and granulated at 180° C. to obtain a second granular material; wherein the melt-extrusion granulation can be performed using a twin-screw extruder.

[0040] (4) Adding a foaming agent to the second granular material, mixing them evenly, and performing melt extrusion granulation at 165° C. to obtain a third granular material; wherein the melt extrusion granulation can be performed using a twin-screw extruder.

[0041] (5) Stirring and drying the third granular material at 160° C. for 90 minutes, and then extruding and molding at 150° C. to obtain an extruded mother sheet; wherein the stirring and drying can be performed using a heated mixer.

[0042] (6) placing the extruded mother sheet under irradiation conditions for irradiation crosslinking, and then foaming the irradiated crosslinked extruded mother sheet at 225° C. to obtain a product; wherein, during the irradiation crosslinking, the web speed of the extruded mother sheet is 2.5 m / min, and the irradiation dose is 5.5 MeV; and the foaming can be carried out in a 145-190-215 three-stage horizontal furnace.

[0043] The modified polypropylene foam material obtained in this embodiment can also be processed by cutting and the like according to the needs. The uses of the modified polypropylene foam material include but are not limited to: automobile roof, steering wheel, luggage compartment lining and air conditioner steam damping plate, side guard plate, door inner plate energy absorption protection pad, instrument insulation board, door inner insulation, 100-135℃ heat carrier circulation battery insulation material, engine room insulation material, indoor or automobile and other places sound insulation material.

[0044] Example 2

[0045] The modified polypropylene foam material of this embodiment includes the following raw materials in parts by weight:

[0046]

[0047] Wherein, the polypropylene may be F800E; the curing agent is a polyisocyanate curing agent; the crosslinking modifier is a multi-arm star polymer crosslinking modifier. The polyisocyanate curing agent is hexamethylene diisocyanate. The multi-arm star polymer crosslinking modifier is polyethylene glycol-b-polystyrene. The hydroxy-terminated polybutadiene is a hydroxy-terminated polybutadiene with a number average molecular weight of 3600, which may be Polybd CS-15 in this embodiment. The lubricant is ethylene bis stearic acid amide. The foaming agent is azodicarbonamide (AC-3). The antioxidant is a mixture of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (antioxidant 1010) and dilauryl thiodipropionate (DLTP) in a weight ratio of 2:1.

[0048] In this embodiment, the preparation method of the modified polypropylene foam material comprises the following steps:

[0049] (1) taking polypropylene, hydroxyl-terminated polybutadiene, a curing agent, a cross-linking modifier, a lubricant, and an antioxidant, and mixing them uniformly to obtain a mixed material;

[0050] (2) subjecting the mixed material to internal kneading, extrusion and granulation to obtain a first granular material; wherein, the internal kneading, extrusion and granulation can be carried out using an internal mixer. In this embodiment, an internal mixer is used to perform internal kneading, extrusion and granulation at a feeding speed of 30 r / min, an outlet temperature of 160°C, an extrusion speed of 50 r / min and an extrusion temperature of 160°C.

[0051] (3) Melt-extrusion granulation is performed on the first granular material at 200° C. to obtain a second granular material; wherein the melt-extrusion granulation can be performed using a twin-screw extruder.

[0052] (4) Adding a foaming agent to the second granular material, mixing them evenly, and performing melt extrusion granulation at 145° C. to obtain a third granular material; wherein the melt extrusion granulation can be performed using a twin-screw extruder.

[0053] (5) Stirring and drying the third granular material at 140° C. for 30 minutes, and then extruding and molding at 170° C. to obtain an extruded mother sheet; wherein the stirring and drying can be performed using a heating mixer.

[0054] (6) placing the extruded mother sheet under irradiation conditions for irradiation crosslinking, and then foaming the irradiated crosslinked extruded mother sheet at 205° C. to obtain a product; wherein, during the irradiation crosslinking, the web speed of the extruded mother sheet is 2.5 m / min, and the irradiation dose is 5.5 MeV; and the foaming can be carried out in a 145-190-215 three-stage horizontal furnace.

[0055] Example 3

[0056] The modified polypropylene foam material of this embodiment includes the following raw materials in parts by weight:

[0057]

[0058] Wherein, the polypropylene may be F800E; the curing agent is a polyisocyanate curing agent; and the crosslinking modifier is a multi-arm star polymer crosslinking modifier. The polyisocyanate curing agent is a mixture of 4,4′-diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, and isophorone diisocyanate in a weight ratio of 1:1:1. The multi-arm star polymer crosslinking modifier is a mixture of polystyrene-b-polyacrylic acid-b-polystyrene, polyacrylic acid-b-polystyrene-b-polyacrylic acid, and poly-4-vinylpyridine-b-polystyrene-b-poly-4-vinylpyridine in a weight ratio of 1:1:1. The hydroxy-terminated polybutadiene is a hydroxy-terminated polybutadiene with a number average molecular weight of 2800-3600, which may be Polybd CS-15 in this embodiment. The lubricant is ethylene bis stearic acid amide. The foaming agent is azodicarbonamide (AC-3). The antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1010).

[0059] In this embodiment, the preparation method of the modified polypropylene foam material comprises the following steps:

[0060] (1) taking polypropylene, hydroxyl-terminated polybutadiene, a curing agent, a cross-linking modifier, a lubricant, and an antioxidant, and mixing them uniformly to obtain a mixed material;

[0061] (2) subjecting the mixed material to internal kneading, extrusion and granulation to obtain a first granular material; wherein, the internal kneading, extrusion and granulation can be carried out using an internal mixer. In this embodiment, an internal mixer is used to perform internal kneading, extrusion and granulation at a feeding speed of 30 r / min, an outlet temperature of 150°C, an extrusion speed of 50 r / min and an extrusion temperature of 150°C.

[0062] (3) The first granular material is melt-extruded and granulated at 180° C. to obtain a second granular material; wherein the melt-extrusion granulation can be performed using a twin-screw extruder.

[0063] (4) Adding a foaming agent to the second granular material, mixing them evenly, and performing melt extrusion granulation at 145° C. to obtain a third granular material; wherein the melt extrusion granulation can be performed using a twin-screw extruder.

[0064] (5) Stirring and drying the third granular material at 140° C. for 60 min, and then extruding and molding the third granular material at 170° C. to obtain an extruded mother sheet; wherein the stirring and drying can be performed using a heating mixer.

[0065] (6) placing the extruded mother sheet under irradiation conditions for irradiation crosslinking, and then foaming the irradiated crosslinked extruded mother sheet at 205° C. to obtain a product; wherein, during the irradiation crosslinking, the web speed of the extruded mother sheet is 2.5 m / min, and the irradiation dose is 5.5 MeV; and the foaming can be carried out in a 145-190-215 three-stage horizontal furnace.

[0066] Example 4

[0067] The modified polypropylene foam material of this embodiment includes the following raw materials in parts by weight:

[0068]

[0069] Wherein, the polypropylene may be F800E; the curing agent is a polyisocyanate curing agent; the crosslinking modifier is a multi-arm star polymer crosslinking modifier. The polyisocyanate curing agent is toluene diisocyanate. The multi-arm star polymer crosslinking modifier is polyacrylic acid-b-polystyrene-b-polyacrylic acid. The hydroxy-terminated polybutadiene is a hydroxy-terminated polybutadiene with a number average molecular weight of 3200, which may be Polybd CS-15 in this embodiment. The lubricant is ethylene bis stearic acid amide. The foaming agent is azodicarbonamide (AC-3). The antioxidant is a mixture of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] pentaerythritol ester (antioxidant 1010) and dilauryl thiodipropionate (DLTP) in a weight ratio of 2:1.

[0070] In this embodiment, the preparation method of the modified polypropylene foam material comprises the following steps:

[0071] (1) taking polypropylene, hydroxyl-terminated polybutadiene, a curing agent, a cross-linking modifier, a lubricant, and an antioxidant, and mixing them uniformly to obtain a mixed material;

[0072] (2) subjecting the mixed material to internal kneading, extrusion and granulation to obtain a first granular material; wherein, the internal kneading, extrusion and granulation can be carried out using an internal mixer. In this embodiment, an internal mixer is used to perform internal kneading, extrusion and granulation at a feeding speed of 30 r / min, an outlet temperature of 150°C, an extrusion speed of 50 r / min and an extrusion temperature of 150°C.

[0073] (3) The first granular material is melt-extruded and granulated at 190° C. to obtain a second granular material; wherein the melt-extrusion granulation can be performed using a twin-screw extruder.

[0074] (4) Adding a foaming agent to the second granular material, mixing them evenly, and performing melt extrusion granulation at 155° C. to obtain a third granular material; wherein the melt extrusion granulation can be performed using a twin-screw extruder.

[0075] (5) Stirring and drying the third granular material at 150° C. for 60 min, and then extruding and molding the third granular material at 160° C. to obtain an extruded mother sheet; wherein the stirring and drying can be performed using a heating mixer.

[0076] (6) placing the extruded mother sheet under irradiation conditions for irradiation crosslinking, and then foaming the irradiated crosslinked extruded mother sheet at 215° C. to obtain a product; wherein, during the irradiation crosslinking, the web speed of the extruded mother sheet is 2.5 m / min, and the irradiation dose is 5.5 MeV; and the foaming can be carried out in a 145-190-215 three-stage horizontal furnace.

[0077] Comparative Example 1

[0078] The modified polypropylene foam material in this comparative example is prepared with the same raw materials and the same method as that in Example 4, except that the polyisocyanate curing agent is not included.

[0079] Comparative Example 2

[0080] The modified polypropylene foam material of this comparative example is prepared with the same raw materials and the same method as that of Example 4, except that the multi-arm star polymer cross-linking modifier is not included.

[0081] Comparative Example 3

[0082] The modified polypropylene foam material of this comparative example is prepared with the same raw materials and the same method as that of Example 4, except that it does not contain terminal hydroxyl polybutadiene.

[0083] Effect comparison ratio

[0084] In order to verify the technical effect of the determination method of the modified polypropylene foam material described in the present invention, the following test was carried out:

[0085] The modified polypropylene foam materials prepared in Examples 1-4 and Comparative Examples 1-3 were cut into the same size, and the longitudinal tensile strength, transverse tensile strength, longitudinal elongation, transverse elongation and heat resistance temperature were tested according to methods such as GBT 6344-2008.

[0086] After experimentation, the results are as follows:

[0087]

[0088] It can be seen from the above results that the modified polypropylene foam materials of Examples 1-4 are significantly superior to those of Comparative Examples 1-3 in longitudinal tensile strength, transverse tensile strength, longitudinal elongation, transverse elongation, and heat resistance temperature.

[0089] It is known from common technical knowledge that the present invention can be implemented by other embodiments that do not deviate from its spirit or essential features. Therefore, the above disclosed embodiments are only illustrative in all respects and are not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are included in the present invention.

Claims

1. A modified polypropylene foam material, characterized in that: The invention comprises the following raw materials in parts by weight: 50-85 parts of polypropylene, 5-15 parts of terminal hydroxyl polybutadiene, 1-3 parts of polyisocyanate curing agent, 1-5 parts of multi-arm star polymer cross-linking modifier, 7-13 parts of foaming agent, 0.5-1.5 parts of lubricant, and 1-2 parts of antioxidant; The multi-arm star polymer cross-linking modifier is one or more of polyethylene glycol-b-poly 4-vinylpyridine, polyethylene glycol-b-polystyrene, polystyrene-b-polyacrylic acid-b-polystyrene, polyacrylic acid-b-polystyrene-b-polyacrylic acid, and poly 4-vinylpyridine-b-polystyrene-b-poly 4-vinylpyridine.

2. The modified polypropylene foam material according to claim 1, characterized in that: The polyisocyanate curing agent is one or more of toluene diisocyanate, hexamethylene diisocyanate, 4,4′-diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, and isophorone diisocyanate.

3. The modified polypropylene foam material according to claim 1, characterized in that: The hydroxyl-terminated polybutadiene is a hydroxyl-terminated polybutadiene with a number average molecular weight of 2800-3600.

4. The modified polypropylene foam material according to claim 1, characterized in that: The lubricant is ethylene bis stearamide.

5. The modified polypropylene foam material according to claim 1, characterized in that: The foaming agent is azodicarbonamide.

6. The modified polypropylene foam material according to claim 1, characterized in that: The antioxidant is one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and dilauryl thiodipropionate.

7. A method for preparing the modified polypropylene foam material according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: taking polypropylene, terminal hydroxyl polybutadiene, a curing agent, a cross-linking modifier, a foaming agent, a lubricant and an antioxidant, mixing them uniformly, and then granulating, extruding, irradiating and foaming to obtain the product.

8. The method for preparing the modified polypropylene foam material according to claim 7, characterized in that: The steps include: (1) taking polypropylene, hydroxyl-terminated polybutadiene, a curing agent, a cross-linking modifier, a lubricant, and an antioxidant, and mixing them uniformly to obtain a mixed material; (2) subjecting the mixed material to internal kneading, extrusion and granulation at 140-160° C. to obtain a first granular material; (3) melt-extruding and granulating the first granular material at 180-200° C. to obtain a second granular material; (4) adding a foaming agent to the second granular material, mixing uniformly, and performing melt extrusion granulation at 145-165° C. to obtain a third granular material; (5) stirring and drying the third particulate material at 140-160° C. for 30-90 min, and then extruding at 150-170° C. to obtain an extruded master sheet; (6) placing the extruded mother sheet under irradiation conditions for irradiation cross-linking, and then foaming the irradiation cross-linked extruded mother sheet at 205-225° C. to obtain a product.

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