Glass materials have good barrier properties, which can effectively prevent the invasion of oxygen and other gases into the contents, and can also prevent the volatile components of the contents from volatilizing into the atmosphere. At the same time, the glass bottle is safe and hygienic, has good corrosion resistance and acid etching ability, and is suitable for the packaging of acidic substances. Therefore, at present, the packaging of liquor in China is still dominated by glass bottles. The appearance of glass wine bottles is colorless and transparent, and the color is monotonous, which limits the development of product packaging differentiation to a certain extent.
In recent years, with the development of the national economy, people's material culture is more abundant, and the demand for alcohol consumption packaging continues to upgrade. Among them, roasting flowers and spraying glaze are the two main ways for current manufacturers to change the color of glass wine bottles. The roasting process is divided into low-temperature baking process and high-temperature baking process according to the different types of baking paper used. Correspondingly, baked flower paper is divided into low temperature flower paper and high temperature flower paper, the low temperature flower paper baking temperature is 160 200, and the high temperature flower paper baking temperature is 560 600. High and low temperature flower paper, also known as "water transfer printing decal paper", is the use of water pressure to carry out polymer hydrolysis printing of transfer paper with color patterns, that is, the process principle of indirect printing. The main flow of the baking process is shown in Figure 1.
With the increasing attention of the country and consumers to product quality and food safety, the phenomenon that has not been paid attention to in the production process in the past has been re-proposed for research, and the beads on the inner wall of the wine bottle are one of the important contents. According to relevant enterprises, some wine bottles will hang beads on the inner wall of the wine bottle after cleaning or after being placed for a period of time. The phenomenon of hanging beads is more pronounced in bottles that have been roasted (especially at low temperatures) or glazed. According to its severity, the phenomenon of hanging beads can be roughly divided into two categories: one is fogging and hanging beads, that is, a large number of droplets are hung on the inner wall of the glass bottle, and the phenomenon of hanging beads is obvious; One is the non-fogging beads, that is, there are a small number of droplets on the inner wall of the glass bottle, and the bead hanging phenomenon is much slower than that of fog beads. For the convenience of expression, hereinafter referred to as "glass wine bottle (fogging hanging beads)" and "glass wine bottle (non-fogging hanging beads)". Combined with the long-term and detailed observation of this phenomenon, this study believes that temperature difference, organic pollutants and surface defects are important factors causing beads, and verifies them by means of instrumental analysis and testing.
1 Materials and methods
1.1 Materials, Reagents and Instruments
Material: glass bottle for wine, the same batch of glass bottle is commercially available.
Main instruments: Milli-Q ultrapure water system, Millipore, USA; DHG-9123A Electric Blower Drying Oven, Shanghai Yiheng Technology***GDW JB-0150 High and Low Temperature Damp-Heat Alternating Test Chamber, Wuxi Nanya Science & Technology***7890B-5977A Gas Chromatography-Mass Spectrometry, AGILENT Company, USA; JSM6380-LV Scanning Electron Microscope (SEM EDS), JEOL Corporation, Japan.
Main reagents: N,N-dimethylformamide (DMF) (analytical pure), Chengdu Kelong Chemicals *** 95% ethanol, Chengdu Kelong Chemicals *** This experiment did not use finished wine for testing, but used a simulated solution similar to the main components of wine for testing, the simulated solution was 52% vol ethanol solution, prepared on site; Ultrapure water, homemade.
1.2 Test Methods
1.2.1 Temperature difference test.
20 glass wine bottles produced in the same batch were selected for testing. The bottles were washed and dried with ultrapure water, then injected with two-thirds of the nominal volume of 52 % vol ethanol solution, sealed and then simulated for a simulation test. The sealed wine bottles were placed in a high and low temperature humidity alternating test chamber with constant temperature (room temperature) and humidity (75%RH) for 3 4 h, and then cooled down (δt=10) for 30 min and then taken out for observation.
1.2.2 Inner wall surface organic contaminant test.
The inner surface of the glass bottle was rinsed with the organic solvent DMF and analyzed by gas chromatography-mass spectrometry. At the same time, in order to confirm the possibility of organic contamination of the inner wall of the bottle, tests were carried out on the roasting line. During the roasting process, the bottles are divided into two batches, one with an open mouth and the other with a cap that matches the bottle finish. After the roasting process is completed, the original liquor platform of the new liquor bottle is cleaned and dried with ultrapure water, and then two-thirds of the nominal capacity of 52% vol ethanol solution is injected and sealed, and placed in a high and low temperature damp-heat alternating test chamber, and the temperature and humidity control of the program is adopted to simulate the normal storage of the finished wine, and the continuous simulation test is taken out for observation after 7 days.
1.2.3. Inner wall surface defect test.
Electron microscopy analysis was performed on glass wine bottles (fogging beads) and glass wine bottles (non-fogging beads) to observe and compare the differences between the surface morphology of the two and the corresponding relationship between them and the phenomenon of beads. After pickling 105 drying, the surface morphology of the wine bottle and the change of the hanging bead phenomenon were observed.
2 Results and Analysis
2.1 Effect of ambient temperature difference
Through simulation tests, it was found that when the wine bottle was left for a short time, or the wine bottle was placed in an environment with little change in temperature difference, there was almost no hanging beads on the inner wall. However, as the time of the wine bottle is extended, when the ambient temperature changes greatly, the number of bottles with a little water mist on the inner wall begins to increase, because the hotter air is close to the cooler glass surface, the temperature drops, and the water vapor is oversaturated and condenses into water droplets. It can be shown that the temperature difference is one of the important factors that cause the beads on the inner wall of the wine bottle.
2.2 Effects of organic contaminants on the inner wall surface
The DMF organic extract of glass wine bottles (fogging beads) was analyzed by gas chromatography-mass spectrometry, and the detection spectrum is shown in Figure 2, and the analysis and detection results were not detected. There are two possibilities for this test result: first, the hanging beads on the inner wall of the wine bottle are indeed not caused by organic contamination; Second, there are organic pollutants on the inner wall of the bottle, but their content is lower than the detection limit of the instrument and cannot be detected.
However, there is a high potential for organic matter to contaminate the inner wall of the bottle. Baking paper in the production process uses more organic solvents, high-temperature flower paper can not be removed with "face oil", can be completely volatilized after baking at a high temperature of more than 400, and low-temperature flower paper uses "tearable film", although it can be removed (adding stripping agent in the ingredients), but can not be volatilized by baking. Therefore, compared with high-temperature flower paper, the use of low-temperature flower paper to produce baked vases is more likely to cause organic pollution. In the baking process, due to the low temperature, the volatile organic gases in the baking paper cannot be completely and quickly discharged from the relatively closed baking oven, and the negative pressure formed in the baking oven will cause the air flow to settle, resulting in a small amount of organic gas settling in the glass bottle. When a bottle contaminated with organic matter is used to contain the wine, there may be beads on the inner wall of the bottle on the new brewing platform. Through the test on the roasting production line, it was found that the two batches of wine bottles also had beads, but the sealing measures were significantly less than those that were not sealed. Therefore, the roasting process will indeed cause the wine bottle to be polluted by organic matter, and it is recommended that enterprises should seal the bottle mouth before proceeding when roasting.
The possibility of beading in the glazed bottle is that the tooling carrying the bottle is contaminated by paint during repeated use. When the mouth of the wine bottle is inverted and put into the tooling, the inside of the bottle is closed, and the organic matter on the contaminated tooling is volatilized by heat during the baking stage and exists in the entire internal space of the bottle. As the roasted bottle leaves the oven for cooling, organic gases settle and adsorb on the inner wall of the bottle. Figure 3 is the glaze process diagram of wine bottles. Therefore, in order to reduce the probability of organic contamination of wine bottles, it is recommended that enterprises carefully check the contamination of the tooling before spraying the glaze, and replace the polluted tooling in time.
2.3 Effect of inner wall surface defects
Normally, we all think that the surface of the glass is smooth and defect-free, but in fact, the glass that looks smooth on the surface is not as smooth as what we see with the naked eye, and if you put the glass under the microscope to observe, you will find that the glass surface has more bumps and depressions. These defects become so-called "condensation nuclei", which facilitate the aggregation of water molecules, which eventually appear in the form of water droplets. Therefore, the more defective the glass bottle, the more likely it is that there will be hanging beads on the inner wall.
Glass wine bottles (fogging beads) and glass wine bottles (non-fogging beads) were used for electron microscopy spectrum analysis, as shown in Figure 4. It can be seen from Figure 4 that there are more and more surface defects of the fogging bead bottle, and the surface defects of the non-fogging bead bottle are less and not obvious. According to the elemental analysis of the energy spectrum in Figure 5, it can be seen that both the atomized bead bottle and the non-fogging bead bottle have silica as the main component, and contain a small amount of sodium, and the element content is similar.
Fig.4. Electron microscope scanning topography of the inner surface of the glass wine bottle (before pickling).
After taking the glass wine bottle (fogging hanging beads) and drying it by pickling 105, the hanging bead phenomenon of the bottle was significantly improved, and the electron microscope energy spectrum analysis showed that the electron microscope scanning morphology of the glass surface was compared with that before pickling, and the surface defects were significantly improved, but the elements and contents of the energy spectrum analysis did not change significantly (as shown in Fig. 6 and Fig. 7). Therefore, we believe that the surface morphology defect of the inner wall is one of the important reasons for the hanging beads of glass bottles.
Fig.7. Electron microscope spectra of the inner surface of glass wine bottles (after pickling).
3 Conclusion
As a traditional and safe liquor packaging container, glass bottles have been adopted by many domestic liquor companies. However, with people's attention to product quality, the phenomenon of glass wine bottle beads has caused serious trouble to the production and use of wine bottles. In order to find out the cause, the parties involved conducted a long-term observation study. It has been observed that under the same temperature difference and humidity conditions, glass wine bottles that have been roasted or glazed are more likely to hang beads than glass bottles that have not been post-processed (roasted or glazed).
Therefore, we believe that the ambient temperature difference, organic pollutants on the inner wall surface, and inner wall surface defects are important factors causing the beads on the inner wall of glass wine bottles, and the organic pollutants on the inner wall surface are the main reasons. It is impossible for enterprises to produce glass wine bottles with a completely smooth surface, so it is the most suitable method to reduce the proportion of glass wine bottle beads by taking effective control measures, such as sealing the bottle mouth before the roasting process and replacing the contaminated tooling before the glaze spraying process, so as to reduce the existence of organic pollutants. At the same time, it should be clear that the phenomenon of wine bottle hanging beads in the actual production process is almost impossible to be caused by one of the independent factors, only one of the factors plays a leading role, and more often is caused by the joint action of several factors.
The results of this study clarify the direction for glass wine bottle manufacturers to analyze the phenomenon of hanging beads in wine bottles, and provide an important basis for them to take measures to control the phenomenon of hanging beads. According to the idea of this study, enterprises can check the production, storage, transportation and other links of wine bottles one by one, and control them in a targeted manner, which can effectively improve the yield rate.