Method for preparing diamond-like film in PET bottle and application thereof

Abstract

The invention provides a method for preparing a diamond-like film in a PET bottle and application of the diamond-like film in the PET bottle, and belongs to the technical field of film plating. The method comprises the following steps: S1, introducing a hydrocarbon-containing gas into a film forming cavity, and then introducing the hydrocarbon-containing gas into a PET bottle through a gas conduit; s2, starting a microwave generator, and performing microwave chemical vapor deposition on the inner wall of the PET bottle; and S3, a vacuum pump is started, residual gas in the PET bottle is pumped out, then the vacuum pump is closed, and the PET bottle with the diamond-like film loaded on the inner wall is obtained. The PET bottle with the diamond-like film loaded on the inner wall prepared by the method is low in water vapor and oxygen transmittance and good in preservation effect, and can be widely applied to the field of food.

Description

Technical Field

[0001] The present invention belongs to the technical field of coating, and particularly relates to a method for preparing diamond-like film inside a PET bottle and its application. Background Art

[0002] Under the background of the booming development of the current food industry, food preservation has always been a key link in ensuring food quality and safety. At present, the food preservation field mainly relies on two major types of preservation methods, namely physical and chemical methods. They each play an important role, but they also have disadvantages that cannot be ignored.

[0003] Chemical preservation methods mainly rely on chemical preservatives to play their roles. Such as sulfites, imazalil, carbendazim, etc. These preservatives can effectively inhibit the growth and reproduction of microorganisms and prevent food from spoiling, and were once widely used in the food industry. For example, adding sulfites to some pickled foods can extend the shelf life of the food and maintain its color and flavor. However, as people's attention to food safety and health has increased day by day, the disadvantages of chemical preservatives have gradually emerged. The use of chemical preservatives will inevitably bring the problem of residual toxic and harmful chemicals. These residual substances may gradually accumulate in the human body and pose a potential threat to human health. For example, they may affect the human body's metabolism and damage the functions of organs such as the liver and kidneys. Therefore, the use of chemical preservatives has been increasingly restricted, and many regions have formulated strict standards for their scope of use and residue levels.

[0004] With the continuous progress of materials science, high water vapor barrier films made by advanced coating technologies have brought new hope to the food preservation field. High water vapor barrier films have excellent properties. They can effectively prevent the transmission of water vapor and oxygen. At the microscopic level, their special molecular structure is like a tight barrier, and it is very difficult for water molecules and oxygen molecules to penetrate through. In the process of food preservation, water vapor and oxygen are important factors leading to food oxidation and spoilage. The emergence of high water vapor barrier films effectively solves this problem and slows down the process of food oxidation and spoilage. The application range of this kind of film is extremely wide, covering from the field of advanced semiconductor coating, such as organic thin film solar cells and OLED displays, to the field of food preservation. The application in different fields mainly depends on different requirements for the oxygen transmission rate and water vapor transmission rate. In the semiconductor field, extremely high requirements are placed on the barrier performance of the film to ensure the stable performance of electronic components; while in the food preservation field, although the requirements are relatively low, it is also necessary to precisely control the oxygen and water vapor transmission rates of the film according to the characteristics of different foods.

[0005] At present, for the preservation treatment inside PET bottles, there is still a lack of an efficient, safe and environmentally friendly preservation method. Due to its advantages such as light weight, transparency and low cost, PET bottles are widely used in the food packaging field. Many of the beverages and edible oils we drink daily are packaged in PET bottles. However, PET bottles have obvious deficiencies in terms of preservation. Its material properties determine that the transmittance of water vapor and oxygen is relatively high during the preservation process. External oxygen and water vapor easily enter the bottle, accelerating the oxidation and deterioration of food, resulting in poor preservation effect. This not only affects the taste and quality of food, but also may cause food waste, bringing economic losses to food enterprises.

[0006] At present, for the preservation treatment inside PET bottles, there is still a lack of an efficient, safe and environmentally friendly preservation method. During the preservation process of PET bottles, the transmittance of water vapor and oxygen is high, and the preservation effect is poor. Summary of the Invention

[0007] The present invention provides a method for preparing a diamond-like film inside a PET bottle and its application, so as to solve the problem that the transmittance of water vapor and oxygen is high and the preservation effect is poor when PET bottles store food and beverages in the prior art.

[0008] To achieve the above-mentioned invention purpose, the present invention provides a method for preparing a diamond-like film inside a PET bottle, including the following steps; S1. Introduce a hydrocarbon gas into the film-forming cavity, and then introduce it into the PET bottle through a gas conduit; S2. Turn on the microwave generator with a microwave power of 300 - 350 W, and perform microwave chemical vapor deposition on the inner wall of the PET bottle; S3. Turn on the vacuum pump, evacuate the residual gas inside the PET bottle, and then turn off the vacuum pump to obtain a PET bottle with a diamond-like film on its inner wall.

[0009] Preferably, the hydrocarbon gas in S1 is a mixed gas of C 2 H 2 and CH 4 .

[0010] Preferably, the volume ratio of C 2 H 2 and CH 4 in the hydrocarbon gas is 2 - 3:6 - 7.

[0011] A suitable ratio can provide a suitable ratio of carbon source and hydrogen source during the microwave chemical vapor deposition process, which is beneficial to the formation of a diamond-like film with uniform structure and good performance.

[0012] Preferably, the flow rate of the hydrocarbon gas in S1 is 100 - 200 sccm.

[0013] Preferably, the gas pressure in the film-forming cavity in S1 is 1-10 Pa.

[0014] Preferably, the time of the microwave chemical vapor deposition in S2 is 2-5 s.

[0015] Preferably, the thickness of the diamond-like film in S3 is 20-50 nm.

[0016] The present invention also provides a PET bottle prepared by the method described above.

[0017] Preferably, the oxygen transmission rate of the PET bottle at 23 °C is 0.73 cc / m² / 24 h / atm.

[0018] In microwave CVD, microwaves are used to generate plasma. The mechanism is that microwaves cause high-frequency oscillation of electrons, and these electrons collide with gas molecules and atoms. These collisions ionize the gas, generating highly reactive plasma, and this plasma can enhance the chemical reactions required for deposition. The plasma provides a high-energy material source, including ions, electrons, and free radicals. Compared with traditional CVD, they can initiate and maintain chemical reactions at lower temperatures. In the present invention, a hydrocarbon gas is introduced into the film-forming cavity, and the carbon-containing gas is then introduced into the PET bottle through a gas conduit, and then microwave chemical vapor deposition is carried out on the inner wall of the PET bottle to complete the coating inside the PET bottle. The film-forming method of the present invention is different from another kind of plasma, namely inductive coupled Plasma (ICP). The principle of generating ICP plasma is to apply 13.56 MHz radio frequency power to a helical coil antenna through a matching network to generate radio frequency magnetic flux. Electrons in the vacuum chamber are accelerated by the induced electric field, and the electrons accelerated by the electric field collide violently and frequently with gas molecules, causing the gas molecules to be excited, ionized, and dissociated to form ICP plasma. The microwave plasma has a large processing area, is a non-polar power source, and has no pollution source. In the present invention, SiN or SiOx coating inside the PET bottle can be achieved by replacing the hydrocarbon gas with other gases.

[0019] Diamond-like-carbon (DLC) has both diamond SP3 and graphite SP2 structures, possessing excellent mechanical properties (high hardness), including 1) smoothness; 2) insulation; 3) super hardness; 4) corrosion resistance; 5) good wear resistance (low friction and wear); 6) resistance to oxygen, water, and ultraviolet rays; 7) biocompatibility, etc. During the microwave chemical vapor deposition process, hydrocarbon-containing gases decompose under the action of microwaves, and carbon atoms, etc., will deposit on the inner wall of the PET bottle in a specific manner, forming a continuous film with almost no pores or defects. For oxygen and water molecules to permeate through the PET bottle, they must pass through this dense diamond-like film, and its dense structure greatly hinders the passage of oxygen and water molecules. The diamond-like film has good chemical stability, with low chemical activity on its surface, and is not easily chemically reactive with substances such as oxygen and water. It will not, like the PET material itself, possibly generate some channels or defects that are conducive to the permeation of gases or liquids due to interactions with oxygen, etc. The diamond-like film usually has a certain degree of hydrophobicity. There is a hydrogen bond interaction between water molecules, which tend to aggregate with each other. The hydrophobic surface of the diamond-like film makes it difficult for water molecules to adhere to and spread on its surface, thus reducing the adsorption and diffusion of water molecules on the film surface and lowering the water permeability. For oxygen molecules, the hydrophobic surface is also not conducive to their adsorption and dissolution on the film surface, thereby reducing the oxygen permeability.

[0020] In the present invention, hydrocarbon-containing gases are introduced into the film-forming chamber and then into the PET bottle through a gas conduit. Here, the hydrocarbon-containing gases are preferably a mixed gas of C 2 H 2 and CH 4 , and the mixing ratio of the two is carefully adjusted to provide suitable carbon and hydrogen sources for the subsequent film-forming reaction. When controlling the gas flow rate, the flow rate of the hydrocarbon-containing gases is set at 10 - 200 sccm. If the flow rate is too small, it may lead to insufficient reaction raw materials, slow film-forming speed or even ineffective film formation; if the flow rate is too large, the reaction may be too intense and it will be difficult to control the film quality. At the same time, the gas pressure in the film-forming chamber is maintained at 1 - 10 Pa. This pressure range not only ensures that gas molecules have sufficient space to move in the chamber but also allows the gas to maintain an appropriate diffusion speed when introduced into the PET bottle, which is conducive to uniform film formation on the inner wall of the bottle subsequently.

[0021] Turn on the microwave generator and perform microwave chemical vapor deposition on the inner wall of the PET bottle. The microwave generator can generate high-frequency microwaves. Under the action of the microwaves, hydrocarbon gas molecules are excited and a series of complex chemical reactions occur. The active groups generated by these reactions continuously deposit and polymerize on the inner wall of the PET bottle, gradually forming a diamond-like film. During this process, the frequency and power of the microwaves need to be precisely controlled to ensure the smooth progress of the chemical reaction and the quality and performance of the film. Different microwave parameters will affect the generation rate and reaction path of the active groups, and thus affect the structure and performance of the film.

[0022] Turn on the vacuum pump to pump out the residual gas in the PET bottle and then turn off the vacuum pump to obtain a PET bottle with a diamond-like film on its inner wall. During the pumping process, it is necessary to ensure the working efficiency and pumping time of the vacuum pump to completely remove the unreacted gas and reaction by-products remaining in the bottle to avoid their adverse effects on the performance and stability of the diamond-like film. The thickness of the diamond-like film obtained here is 20 - 50 nm. This thickness can not only ensure that the diamond-like film has good barrier properties, effectively blocking water vapor and oxygen, but also will not affect the transparency and flexibility of the PET bottle due to excessive thickness, while also taking into account the cost and feasibility of the preparation process.

[0023] Compared with the prior art, the present invention has the following beneficial effects; 1. The inner wall coating technology coats the inner surface of the object. A gas guide tube is used to cause microwave plasma to occur inside the bottle, and DLC film is formed on the inner wall of the PET bottle.

[0024] 2. The diamond-like carbon film is used as a high water vapor barrier film in food / drink packaging, which can enhance the ability of the product to isolate oxygen and water vapor, and at the same time enhance its ability to resist ultraviolet rays.

[0025] 3. During the coating process, strictly control the volume ratio of C 2 H 2 and CH 4 , deposition time and temperature to ensure the uniformity of the coating, and form a continuous film with almost no pores or defects on the inner wall of the PET bottle, enhancing the effect of the film in isolating oxygen and water vapor.

[0026] 3. Adopt microwave CVD coating technology to improve the productivity of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of a method for preparing a diamond-like film inside a PET bottle provided in the specific embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions of the embodiments of the present invention in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0029] Embodiment 1 As Figure 1 shown, in this embodiment, a method for preparing diamond-like film inside a PET bottle is provided, including the following steps; S1. First, use high-purity nitrogen to purge the film-forming cavity and the gas conduit for 15 minutes with a purge flow rate of 50 sccm to remove residual impurities and moisture inside. Then, evacuate the film-forming cavity to 1×10 -4 Pa to ensure the initial environment of the cavity is clean. Introduce the hydrocarbon gas into the film-forming cavity and then into the PET bottle through the gas conduit. The hydrocarbon gas is a mixed gas of C 2 H 2 and CH 4 with a flow rate of 100 sccm. The gas pressure inside the film-forming cavity is 1 Pa, and the volume ratio of C 2 H 2 and CH 4 is 1:3; S2. Turn on the microwave generator. The operating frequency of the microwave generator is set to 2.45 GHz, and the microwave power is 300 W. Perform microwave chemical vapor deposition on the inner wall of the PET bottle for 2 s; S3. Turn on the vacuum pump, evacuate the residual gas inside the PET bottle, and then turn off the vacuum pump to obtain a PET bottle with a diamond-like film on its inner wall. The thickness of the diamond-like film is 20 nm.

[0030] For a 500 ml PET bottle, at room temperature of 23°C, its oxygen transmission rate is 0.03 cc / bottom / day = 0.09 ppm / day. Assuming that the critical value of the oxygen intrusion amount in the PET bottle that can cause the deterioration of the food and beverage inside the bottle is 1 ppm, it means its shelf life is only 12 days; if a diamond-like film is used as the water vapor barrier film, its oxygen transmission rate is reduced by one order of magnitude (10 times). As a result, the shelf life can be increased by 120 days. The oxygen transmission rate is the main factor affecting the preservation of food and beverages. The application of a high water vapor barrier film in food packaging solves the actual problems of short shelf life and lack of freshness in current domestic food and beverage packaging.

[0031] Adopt advanced coating technology to coat a high water vapor barrier film on the surface of PET bottles or films, which is mainly used in beverage fresh-keeping packaging, including large PET bottles for beer packaging, PET bottles as substitutes for wine glass bottles, and PET bottles for edible oil to prevent plasticizers. PET bottles containing a high water vapor barrier film for beer can achieve freshness preservation (preventing the internal CO of beer from 2 overflowing) and quality preservation (preventing external oxygen from invading). PET bottles containing a high water vapor barrier film for wine as substitutes for glass bottles not only guarantee quality but also greatly reduce transportation costs. PET bottles containing a high water vapor barrier film for edible oil can prevent plasticizers from invading the edible oil and eliminate unhealthy hidden dangers.

[0032] Take PET bottles with no diamond-like film on the inner wall and PET bottles with diamond-like film on the inner wall prepared by the method of this embodiment for testing the oxygen transmission rate and water vapor transmission rate. The test results are shown in Table 1.

[0033] Table 1 Test results of oxygen transmission rate and water vapor transmission rate

[0034] It can be seen that the oxygen transmission rate of the PET bottle in the film-free state is 19 [cc / m 2 / 24hr / 0.1mm / atm]. After coating, the oxygen transmission rate is reduced to 0.73 [cc / m 2 / 24h / atm], a reduction of 26 times; the water vapor transmission rate is reduced from 9.2 [g / m 2 / 24hr / 0.1mm] to 0.69 [g / m 2 / 24h], a reduction of 13 times. It can be seen that by coating the inner wall of the PET bottle, its freshness preservation ability can be effectively improved.

[0035] Example 2 In this embodiment, a method for preparing a diamond-like film in a PET bottle is provided, including the following steps; S1. Introduce a hydrocarbon gas into the film-forming cavity and then into the PET bottle through a gas conduit. The hydrocarbon gas is a mixed gas of C 2 H 2 and CH 4 , with a flow rate of 200 sccm, the gas pressure in the film-forming cavity is 10 Pa, and the volume ratio of C 2 H 2 and CH 4 is 3:7; S2. Turn on the microwave generator with a microwave power of 350 W and perform microwave chemical vapor deposition on the inner wall of the PET bottle for 3 s; S3. Turn on the vacuum pump, evacuate the residual gas in the PET bottle, and then turn off the vacuum pump to obtain a PET bottle with diamond - like carbon film on its inner wall. The thickness of the diamond - like carbon film is 30 nm.

[0036] Example 3 In this example, a method for preparing diamond - like carbon film in a PET bottle is provided, including the following steps: S1. Introduce the hydrocarbon - containing gas into the film - forming chamber, and then pass it into the PET bottle through the gas conduit. The hydrocarbon - containing gas is a mixed gas of C 2 H 2 and CH 4 . The flow rate is 150 sccm, the gas pressure in the film - forming chamber is 5 Pa, and the volume ratio of C 2 H 2 to CH 4 is 2.5:6.3. S2. Turn on the microwave generator with a microwave power of 340 W, and perform microwave chemical vapor deposition on the inner wall of the PET bottle. The time for microwave chemical vapor deposition is 5 s. S3. Turn on the vacuum pump, evacuate the residual gas in the PET bottle, and then turn off the vacuum pump to obtain a PET bottle with diamond - like carbon film on its inner wall. The thickness of the diamond - like carbon film is 50 nm.

[0037] The oxygen permeability and water vapor permeability of the PET bottles with diamond - like carbon film prepared in Example 2 and Example 3 are similar to those in Example 1.

[0038] The specific embodiments of the present invention described above do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and deformations made according to the technical concept of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a diamond-like film in a PET bottle, characterized in that: The steps include: S1, passing hydrocarbon-containing gas into the film-forming cavity, and then into the PET bottle through the gas conduit; S2, turning on the microwave generator, the microwave power is 300-350W, and performing microwave chemical vapor deposition on the inner wall of the PET bottle; S3, turning on the vacuum pump, pumping out the residual gas in the PET bottle, and then turning off the vacuum pump to obtain a PET bottle with a diamond-like film on the inner wall.

2. The method for preparing a diamond-like film in a PET bottle according to claim 1, characterized in that: The carbon-hydrogen-containing gas in S1 is a mixed gas of C2H2 and CH4.

3. The method for preparing a diamond-like film in a PET bottle according to claim 2, characterized in that: The volume ratio of C2H2 to CH4 in the carbon-hydrogen-containing gas is 2-3:6-7.

4. The method for preparing a diamond-like film in a PET bottle according to claim 1, characterized in that: The flow rate of the carbon-containing hydrogen gas in S1 is 100-200 sccm.

5. The method for preparing a diamond-like film in a PET bottle according to claim 1, characterized in that: The gas pressure in the film forming chamber described in S1 is 1-10Pa.

6. The method for preparing a diamond-like film in a PET bottle according to claim 1, characterized in that: The time of the microwave chemical vapor deposition in S2 is 2-5s.

7. The method for preparing a diamond-like film in a PET bottle according to claim 1, characterized in that: The thickness of the diamond-like film in S3 is 20-50 nm.

8. A PET bottle prepared by the method according to any one of claims 1 to 7.

9. The PET bottle according to claim 8, characterized in that: The oxygen permeability of the PET bottle at 23°C is 0.73cc / m² / 24h / atm.

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