Low-temperature-resistant PET packaging material and preparation method thereof

Abstract

The invention discloses a low-temperature-resistant PET packaging material and a preparation method thereof. The low-temperature-resistant PET packaging material structurally comprises a PET top layer, a rubber middle layer and a PET bottom layer in sequence from top to bottom, and is prepared by a three-layer co-extrusion process. And the rubber layer contains an initiator which is used for in-situ crosslinking of rubber and PET to enhance the interface bonding force. The low-temperature-resistant PET packaging material disclosed by the invention can resist low-temperature impact of 40 DEG C below zero, can be used for low-temperature cold-chain transportation of food, medicines and the like, reduces the breakage rate of the packaging material, and reduces the loss of contents.

Description

Technical Field

[0001] This invention belongs to the field of functional polymer materials, specifically relating to a low-temperature resistant PET packaging material and its preparation method. Background Technology

[0002] Biaxially oriented polyethylene terephthalate (BOPET) film has a high tensile modulus (greater than 3000 MPa) and high transparency (greater than 90%). Therefore, packaging boxes made of BOPET film are widely used in the food and pharmaceutical packaging fields. However, the PET molecular structure contains a large number of benzene rings, which restricts the relaxation of PET molecules. Especially under conditions below room temperature, the relaxation of PET molecules deteriorates rapidly as the temperature decreases. This results in a sharp decrease in the low-temperature impact toughness of PET packaging materials, which manifests as PET packaging boxes becoming extremely brittle at low temperatures, such as -40°C, causing great trouble for cold chain transportation. In order to improve the low-temperature impact resistance of PET, aliphatic dicarboxylic acids can be used to synthesize modified PET. When the adipic acid content is 15%, it can be used in a low-temperature environment of -20°C [Rubber and Plastics Technology and Equipment, 2022, 48 (08): 24-26]. PET's low-temperature impact resistance can also be improved by blending it with polycarbonate [Plastics Industry, 2021, 49 (08): 145-148+31]. However, the method of modifying PET by synthesizing aliphatic diacids will reduce the tensile modulus of PET, impairing its application value as a packaging material. Blending with polycarbonate will significantly increase the production cost of PET packaging materials and may impair the transparency of PET packaging materials due to polymer incompatibility. Most importantly, there is currently no data indicating how to produce PET packaging materials that can withstand temperatures as low as -40°C. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a low-temperature resistant PET packaging material and its preparation method. This invention designs a three-layer structure, utilizing rubber with a low glass transition temperature as the interlayer. In-situ crosslinking enhances the interfacial bonding between the rubber interlayer and the top and bottom PET layers, thereby effectively improving the low-temperature impact resistance of the PET packaging material.

[0004] The present invention relates to a low-temperature resistant PET packaging material, the structure of which, from top to bottom, comprises a PET top layer, a rubber middle layer, and a PET bottom layer, and is made by a three-layer co-extrusion process.

[0005] The PET is extrusion-grade PET and meets food-grade safety requirements. The PET can be pure PET, or it can be antibacterial PET or UV-resistant PET. Antibacterial PET refers to PET with antibacterial properties obtained through chemical grafting or physical blending; UV-resistant PET refers to PET with UV-blocking function obtained through chemical grafting or physical blending.

[0006] The rubber includes one or more of natural rubber and synthetic rubber, namely natural rubber, polybutadiene rubber, styrene-butadiene rubber, nitrile rubber, chloroprene rubber, methyl vinyl silicone rubber, and polyurethane rubber, which are solid at room temperature.

[0007] The rubber also includes liquid polybutadiene rubber, liquid nitrile rubber or liquid chloroprene rubber, which accounts for 10% of the total mass of the rubber.

[0008] The rubber also includes approximately 0.5% by mass of an initiator, 2,4,6-trimethylbenzoyl-di(p-tolyl)phosphine oxide (TMO). The initiator is pre-dispersed in liquid rubber with a molecular weight of 2000-10000 and injected into the rubber extruder through a side feed port.

[0009] The method for preparing the low-temperature resistant PET packaging material of the present invention includes the following steps:

[0010] The process employs a three-layer co-extrusion combined with biaxial stretching. First, the PET is plasticized using a first extruder and then injected into the upper and lower dies of the three-layer co-extrusion die through a manifold. The rubber components are then mixed evenly using a second extruder and extruded into the middle die of the three-layer co-extrusion die. The resulting preform is then biaxially stretched to form a composite film material.

[0011] The temperature of the first extruder is controlled at 260 ℃~280 ℃; the temperature of the second extruder is controlled at 50-160 ℃.

[0012] In the composite film material, the thickness of the PET top layer and the PET bottom layer is 10-50 μm, and the thickness of the rubber layer is 20-150 μm.

[0013] During the biaxial stretching process, the preheating temperature is 105 ℃, the preheating time is 20 s, and the stretching speed is 100% / s.

[0014] The PET composite film prepared by this invention can be used to make food packaging or pharmaceutical packaging boxes, and can withstand a drop impact of 1 m without breaking in a low temperature environment of -40 degrees Celsius (-40 ℃).

[0015] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0016] 1. The present invention designs a multilayer PET composite film structure with rubber interlayer, using rubber with a very low glass transition temperature (Tg), such as natural rubber (Tg is about -70 ℃), to improve the low temperature (-40 ℃) impact resistance of the PET composite film.

[0017] 2. During the co-extrusion film formation process, the in-situ crosslinking reaction of the high-temperature initiator TMO is utilized to achieve a tight bond between the rubber layer and the PET layer at the interface, as well as intermolecular crosslinking within the rubber layer. The initial decomposition temperature of TMO is approximately 255 ℃, slightly lower than the extrusion molding temperature of PET (~280 ℃).

[0018] 3. It adopts a co-extrusion process, which does not use organic solvents, making it green and pollution-free. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive step are within the scope of protection of this invention.

[0020] In the embodiments of the present invention, the natural rubber used is a product of Shanghai Liankangming Chemical Co., Ltd., No. 1 smoked sheet rubber; the nitrile rubber used is a product of Lanzhou Petrochemical Co., Ltd., grade NBR1806; the polybutadiene rubber used is a product of Yanshan Petrochemical Co., Ltd., grade BR Nd40; the styrene-butadiene rubber used is a product of Yangzi Petrochemical Co., Ltd., grade 1502; the chloroprene rubber used is a product of Shanna Synthetic Rubber Co., Ltd., grade CR244; the methyl vinyl silicone rubber used is a product of Zhejiang Hengyecheng Organosilicon Co., Ltd., grade 110; the polyurethane rubber used is a product of Anhui Juli Petroleum Drilling Equipment Co., Ltd., grade 70A; the liquid polybutadiene rubber used is a product of Kunshan Castel Polymer Materials Co., Ltd., grade LPB-3000; the liquid nitrile rubber used is a product of Ruien Rubber & Plastics Technology Co., Ltd., grade XL2740; and the liquid chloroprene rubber used is a product of Shenzhen Masni Elastomer Co., Ltd., grade CR A-90.

[0021] Example 1:

[0022] 1. Weigh 1000 g of pure PET chips and dry them at 80 ℃ for 12 hours for later use.

[0023] 2. Weigh out 900 g of natural rubber and set aside.

[0024] 3. Weigh 5 g of initiator 2,4,6-trimethylbenzoyl-bis(p-tolyl)phosphine oxide and 100 g of liquid polybutadiene rubber. Mix the initiator and liquid rubber evenly and set aside.

[0025] 4. Feed the PET chips into the extruder, set the barrel temperature to 260℃~280℃, the screw speed to 50 rpm, and start the machine to extrude;

[0026] 5. Put the natural rubber into the extruder at a temperature of 50℃~90℃ and a screw speed of 10 rpm.

[0027] 6. Inject the liquid rubber mixed with the initiator into the rubber extruder through the side feed port.

[0028] 7. The co-extruded preform is biaxially stretched to form a composite film material, and synchronously stretched in the longitudinal (MD) and transverse (TD) directions at a preheating temperature of 105 ℃, a preheating time of 20s, and a stretching speed of 100% / s.

[0029] Example 2:

[0030] 1. Weigh 1000 g of pure PET chips and dry them at 80 ℃ for 12 hours for later use.

[0031] 2. Weigh out 900 g of nitrile rubber and set aside.

[0032] 3. Weigh 5 g of initiator 2,4,6-trimethylbenzoyl-bis(p-tolyl)phosphine oxide and 100 g of liquid nitrile rubber. Mix the initiator and liquid rubber evenly and set aside.

[0033] 4. Feed the PET chips into the extruder, set the temperature to 260℃~280℃, the screw speed to 50 rpm, and start the machine to extrude;

[0034] 5. Add the nitrile rubber to the extruder at a temperature of 80℃~95℃ and a screw speed of 10 rpm.

[0035] 6. Inject the liquid rubber mixed with the initiator into the rubber extruder through the side feed port.

[0036] 7. The co-extruded preform is biaxially stretched to form a composite film material, and synchronously stretched in the longitudinal (MD) and transverse (TD) directions at a preheating temperature of 105 ℃, a preheating time of 20s, and a stretching speed of 100% / s.

[0037] Example 3:

[0038] 1. Weigh 1000 g of pure PET chips and dry them at 80 ℃ for 12 hours for later use.

[0039] 2. Weigh 900 g of polybutadiene rubber and set aside.

[0040] 3. Weigh 5 g of initiator 2,4,6-trimethylbenzoyl-bis(p-tolyl)phosphine oxide and 100 g of liquid polybutadiene rubber. Mix the initiator and liquid rubber evenly and set aside.

[0041] 4. Feed the PET chips into the extruder, set the temperature to 260℃~280℃, the screw speed to 50 rpm, and start the machine to extrude;

[0042] 5. Add the butadiene rubber to the extruder at a temperature of 50℃~90℃ and a screw speed of 10 rpm.

[0043] 6. Inject the liquid rubber mixed with the initiator into the rubber extruder through the side feed port.

[0044] 7. The co-extruded preform is biaxially stretched to form a composite film material, and synchronously stretched in the longitudinal (MD) and transverse (TD) directions at a preheating temperature of 105 ℃, a preheating time of 20s, and a stretching speed of 100% / s.

[0045] Example 4:

[0046] 1. Weigh 1000 g of pure PET chips and dry them at 80 ℃ for 12 hours for later use.

[0047] 2. Weigh out 900 g of styrene-butadiene rubber and set aside.

[0048] 3. Weigh 5 g of initiator 2,4,6-trimethylbenzoyl-bis(p-tolyl)phosphine oxide and 100 g of liquid polybutadiene rubber. Mix the initiator and liquid rubber evenly and set aside.

[0049] 4. Feed the PET chips into the extruder, set the temperature to 260℃~280℃, the screw speed to 50 rpm, and start the machine to extrude;

[0050] 5. Put the styrene-butadiene rubber into the extruder at a temperature of 50℃~105℃ and a screw speed of 10 rpm.

[0051] 6. Inject the liquid rubber mixed with the initiator into the rubber extruder through the side feed port.

[0052] 7. The co-extruded preform is biaxially stretched to form a composite film material, and synchronously stretched in the longitudinal (MD) and transverse (TD) directions at a preheating temperature of 105 ℃, a preheating time of 20s, and a stretching speed of 100% / s.

[0053] Example 5:

[0054] 1. Weigh 1000 g of pure PET chips and dry them at 80 ℃ for 12 hours for later use.

[0055] 2. Weigh out 900 g of chloroprene rubber and set aside.

[0056] 3. Weigh 5 g of initiator 2,4,6-trimethylbenzoyl-bis(p-tolyl)phosphine oxide and 100 g of liquid chloroprene rubber. Mix the initiator and liquid rubber evenly and set aside.

[0057] 4. Feed the PET chips into the extruder, set the temperature to 260℃~280℃, the screw speed to 50 rpm, and start the machine to extrude;

[0058] 5. Add the neoprene rubber to the extruder at a temperature of 50℃~70℃ and a screw speed of 10 rpm.

[0059] 6. Inject the liquid rubber mixed with the initiator into the rubber extruder through the side feed port.

[0060] 7. The co-extruded preform is biaxially stretched to form a composite film material, and synchronously stretched in the longitudinal (MD) and transverse (TD) directions at a preheating temperature of 105 ℃, a preheating time of 20s, and a stretching speed of 100% / s.

[0061] Example 6:

[0062] 1. Weigh 1000 g of pure PET chips and dry them at 80 ℃ for 12 hours for later use.

[0063] 2. Weigh 900 g of methyl vinyl silicone rubber and set aside.

[0064] 3. Weigh 5 g of initiator 2,4,6-trimethylbenzoyl-bis(p-tolyl)phosphine oxide and 100 g of liquid polybutadiene rubber. Mix the initiator and liquid rubber evenly and set aside.

[0065] 4. Feed the PET chips into the extruder, set the temperature to 260℃~280℃, the screw speed to 50 rpm, and start the machine to extrude;

[0066] 5. Add methyl vinyl silicone rubber to the extruder at a temperature of 120℃~160℃ and a screw speed of 10 rpm.

[0067] 6. Inject the liquid rubber mixed with the initiator into the rubber extruder through the side feed port.

[0068] 7. The co-extruded preform is biaxially stretched to form a composite film material, and synchronously stretched in the longitudinal (MD) and transverse (TD) directions at a preheating temperature of 105 ℃, a preheating time of 20s, and a stretching speed of 100% / s.

[0069] Example 7:

[0070] 1. Weigh 1000 g of pure PET chips and dry them at 80 ℃ for 12 hours for later use.

[0071] 2. Weigh 900 g of polyurethane rubber and set aside.

[0072] 3. Weigh 5 g of initiator 2,4,6-trimethylbenzoyl-bis(p-tolyl)phosphine oxide and 100 g of liquid polybutadiene rubber. Mix the initiator and liquid rubber evenly and set aside.

[0073] 4. Feed the PET chips into the extruder, set the temperature to 260℃~280℃, the screw speed to 50 rpm, and start the machine to extrude;

[0074] 5. Put the polyurethane rubber into the extruder, with a temperature of 150℃~190℃ and a screw speed of 10 rpm.

[0075] 6. Inject the liquid rubber mixed with the initiator into the rubber extruder through the side feed port.

[0076] 7. The co-extruded preform is biaxially stretched to form a composite film material, and synchronously stretched in the longitudinal (MD) and transverse (TD) directions at a preheating temperature of 105 ℃, a preheating time of 20s, and a stretching speed of 100% / s.

[0077] Comparative Example 1:

[0078] 1. Weigh 2000 g of pure PET chips and dry them at 80 ℃ for 12 hours for later use.

[0079] 2. Put 1000g of PET chips into two extruders respectively, set the temperature to 260℃~280℃, the screw speed to 50 rpm, and start the machine to extrude;

[0080] 3. The co-extruded preform is biaxially stretched to form a composite film material, and synchronously stretched in the longitudinal (MD) and transverse (TD) directions at a preheating temperature of 105 ℃, a preheating time of 20s, and a stretching speed of 100% / s.

[0081] Comparative Example 2:

[0082] 1. Weigh 1000 g of pure PET chips and dry them at 80 ℃ for 12 hours for later use.

[0083] 2. Weigh out 900 g of natural rubber and set aside.

[0084] 3. Weigh 100 g of liquid polybutadiene rubber and set aside.

[0085] 4. Feed the PET chips into the extruder, set the barrel temperature to 260℃~280℃, the screw speed to 50 rpm, and start the machine to extrude;

[0086] 5. Put the natural rubber into the extruder at a temperature of 50℃~90℃ and a screw speed of 10 rpm.

[0087] 6. Inject the liquid rubber into the rubber extruder through the side feed port.

[0088] 7. The co-extruded preform is biaxially stretched to form a composite film material, and the longitudinal (MD) and transverse (TD) synchronous stretching is carried out at a preheating temperature of 105 ℃, a preheating time of 20s, and a stretching speed of 100% / s.

[0089] The composite film materials prepared in Examples 1-5 and Comparative Examples 1 and 2 were tested according to the national standard GB / T 1040.3-2006 Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets and the national standard GB / T 9639.1-2008 Test method for impact resistance of plastic films and sheets - Free fall dart method - Part 1: Step method. The results are as follows:

[0090]

[0091] The present invention will be further explained below with reference to embodiments and comparative examples.

[0092] As can be seen from Examples 1 to 7, the PET-rubber-PET sandwich composite packaging material of the present invention exhibits high tensile strength and impact toughness at room temperature. It can also be seen from Examples 1 to 7 that the PET-rubber-PET sandwich composite packaging material of the present invention also exhibits high tensile strength and impact toughness at -40 °C.

[0093] In contrast, Comparative Example 1, because its packaging material contains only PET and no rubber, exhibits high tensile strength and impact toughness at room temperature, but almost completely loses its impact toughness at -40°C. In Comparative Example 2, although the packaging material contains rubber, the lack of peroxides prevents the achievement of good PET-rubber interfacial bonding through in-situ crosslinking, resulting in lower impact toughness at -40°C compared to Examples 1-7.

Claims

1. A low-temperature resistant PET packaging material, characterized in that: The low-temperature resistant PET packaging material has a multi-layer structure, consisting of a PET top layer, a rubber middle layer, and a PET bottom layer from top to bottom, and is made by a three-layer co-extrusion process.

2. The low-temperature resistant PET packaging material according to claim 1, characterized in that: The PET is extrusion-grade PET and meets food-grade safety requirements.

3. The low-temperature resistant PET packaging material according to claim 2, characterized in that: The PET is pure PET, antibacterial PET, or UV-resistant PET.

4. The low-temperature resistant PET packaging material according to claim 1, characterized in that: The rubber includes one or more of natural rubber and synthetic rubber, and is solid at room temperature.

5. The low-temperature resistant PET packaging material according to claim 4, characterized in that: The rubber is selected from one or more of the following: natural rubber, polybutadiene rubber, styrene-butadiene rubber, nitrile rubber, chloroprene rubber, methyl vinyl silicone rubber, and polyurethane rubber.

6. The low-temperature resistant PET packaging material according to claim 5, characterized in that: The rubber also includes liquid rubber, which is liquid polybutadiene rubber, liquid nitrile rubber or liquid chloroprene rubber, and the mass of the liquid rubber accounts for 10% of the total mass of the rubber.

7. A method for preparing a low-temperature resistant PET packaging material according to any one of claims 1-6, characterized in that... Includes the following steps: The process employs a three-layer co-extrusion combined with biaxial stretching. First, the PET is plasticized using a first extruder and then injected into the upper and lower dies of the three-layer co-extrusion die through a manifold. The rubber components are then mixed evenly using a second extruder and extruded into the middle die of the three-layer co-extrusion die. The resulting preform is then biaxially stretched to form a composite film material.

8. The preparation method according to claim 7, characterized in that: The rubber component also includes the initiator 2,4,6-trimethylbenzoyl-bis(p-tolyl)phosphine oxide; the initiator is pre-dispersed in liquid rubber with a molecular weight of 2000~10000 and injected into the rubber extruder through the side feed port.

9. The preparation method according to claim 7, characterized in that: The temperature of the first extruder is controlled at 260 ℃~280 ℃; the temperature of the second extruder is controlled at 50-160 ℃.

10. The preparation method according to claim 7, characterized in that: During the biaxial stretching process, the preheating temperature is 105 ℃, the preheating time is 20 s, and the stretching speed is 100% / s.

Images