Varieties of bottle glass
There are many types of bottle glass, and there are many classification methods.
(1) According to the shape, there are round, oval, square, rectangular, flat, and special-shaped bottles (other shapes), among which round ones are the most common.
(2) According to the size of the bottle mouth, there are wide-mouth, small-mouth, and spray-mouth bottles. Bottles with an inner diameter of less than 30 mm are called small-mouth bottles, which are often used to hold various fluids. Bottles with an inner diameter of more than 30 mm and no or few shoulders are called wide-mouth bottles, which are often used to hold semi-fluids, powdered or blocky solids.
(3) According to the molding method, there are molded bottles and tube bottles. Molded bottles are made directly from glass liquid in a mold; tube bottles are made by first pulling glass liquid into a glass tube and then processing it into shape (small-capacity penicillin bottles, tablet bottles, etc.).
(4) According to the color of bottles, there are colorless, colored, and opalescent bottles. Most glass bottles are clear and colorless, which can keep the contents in a normal image. Green bottles are usually used to hold beverages; brown bottles are used to hold medicines or beer. They can absorb ultraviolet rays, which is beneficial to the preservation of the contents. The United States stipulates that the average wall thickness of colored glass bottles and jars should make the transmittance of light waves with a wavelength of 290~450nm less than 10%. A few cosmetics, vanishing creams and ointments are stored in opalescent glass bottles and jars. In addition, there are colored glass bottles such as amber, light cyan, blue, red, and black.
(5) According to the purpose, there are beer bottles, white wine bottles, beverage bottles, cosmetic bottles, condiment bottles, tablet bottles, canned bottles, infusion bottles, and educational bottles.
(6) According to the use requirements of bottles and jars, there are disposable bottles and jars and recycling bottles and jars. Disposable bottles and jars are used once and then discarded; recycled bottles and jars can be recycled multiple times and used in rotation.
The above classification is not very strict. Sometimes the same bottle can often be classified into several types, and according to the development of the functions and uses of glass bottles and jars, the variety will increase day by day.
Performance of bottle glass
Various glass products have different requirements for glass performance due to their different application ranges and functions. There are many types of bottle glass and a wide range of applications. For bottle glass products, the main performance requirements include mechanical properties, chemical properties, thermal properties, optical properties, surface properties and other requirements.
Mechanical properties of bottle glass
(1) Bottle glass should have a certain mechanical strength Bottle glass will be subject to different stresses due to different use conditions. Generally, it can be divided into internal pressure strength, heat shock resistance, mechanical impact strength, bottle tipping strength, vertical load strength, etc. However, from the perspective of causing glass bottles to break, the direct cause is almost always mechanical impact, especially when glass bottles are repeatedly scratched and impacted during transportation and filling. Therefore, glass bottles should be able to withstand general internal and external stresses, vibrations, and impacts encountered during filling, storage, and transportation. The strength of bottle glass varies slightly depending on whether it is a gas-filled bottle or a non-gas-filled bottle, a disposable bottle, or a recycled bottle, but it must be safe to use and not burst. Not only should the pressure resistance be checked before leaving the factory, but the strength reduction problem of recycled bottles during recycling should also be considered. According to foreign data, after 5 uses, the strength is reduced by 40% (only 60% of the original strength); after 10 uses, the strength is reduced by 50%. Therefore, when designing the bottle shape, it is necessary to consider that the glass strength has a sufficient safety factor to avoid the bottle from "exploding" and injuring people.
(2) Factors affecting the mechanical strength of bottle glass The unevenly distributed residual stress in the bottle glass greatly reduces the strength. The internal stress in glass products mainly refers to thermal stress, and its existence will lead to reduced mechanical strength and poor thermal stability of glass products.
Macro and micro defects in glass, such as stones, bubbles, streaks, etc., often cause internal stress due to inconsistent composition with the main glass composition and different expansion coefficients, thereby causing cracks, which seriously affect the strength of glass products.
In addition, scratches and wear on the glass surface have a great influence on the strength of the product. The larger and sharper the scars, the more significant the reduction in strength. Cracks formed on the surface of bottle glass are mainly caused by scratches on the glass surface, especially surface scratches between glass and glass. For bottle glass that needs to withstand high pressure, such as beer bottles and soda bottles, the decrease in strength will cause the product to burst during processing and use, so collision, abrasion and wear should be strictly prohibited during transportation and filling.
The thickness of the bottle wall is directly related to the mechanical strength of the bottle and its ability to withstand internal pressure. If the thickness ratio of the bottle wall is too large and the thickness of the bottle wall is uneven, the bottle wall will have weak links, thus affecting the impact resistance and internal pressure resistance performance. The national standard GB4544-1996 "Beer Bottle" strictly stipulates that the thickness ratio of the bottle wall is <2:1. The optimal annealing temperature, insulation time and cooling time are different for different bottle wall thicknesses. Therefore, in order to avoid deformation or incomplete annealing of the product and ensure the quality of the bottle, the thickness ratio of the bottle wall should be strictly controlled.
Thermal properties of bottle glass
During the disinfection and sterilization process, bottle glass needs to withstand drastic temperature changes. When the tensile stress exceeds the strength of the glass, it will break. Therefore, the thermal stability of bottle glass must meet the requirements, have a certain degree of thermal shock resistance, and be able to withstand heating and cooling processes such as washing and sterilization.
The main factors affecting the thermal stability of bottle glass are as follows.
The linear expansion coefficient a of glass changes greatly with the change of composition, so the linear expansion coefficient has a decisive significance for the thermal stability of glass. The smaller the thermal expansion coefficient of glass, the better its thermal stability, and the greater the temperature that the sample can withstand, and vice versa. Therefore, any component that can reduce the thermal expansion coefficient of glass can improve the thermal stability of glass, such as SiO2, B2O3, Al2 03, ZrO2, ZnO, Mg0, etc. Alkali metal oxide R20 can increase the thermal expansion coefficient of glass, so glass containing a large amount of alkali metal oxides has poor thermal stability.
The thermal stability of glass is also related to the thickness of the product. The thicker the wall of a glass product is, the smaller the sudden temperature difference it can withstand. When subjected to thermal shock, compressive stress is generated on the surface of the glass, while when it is rapidly cooled, tensile stress is formed on the surface of the glass. The compressive strength of glass is 10 times greater than its tensile strength. Therefore, when measuring the thermal stability of glass, the experiment is usually conducted under the condition of rapid cooling.
Quenching can increase the thermal stability of glass by 1.5 to 2 times. This is because after quenching, the surface of the glass has uniformly distributed compressive stress, which can offset the tensile stress generated on the surface of the product when it is rapidly cooled.
Chemical properties of bottle glass
During use, glass products are subject to corrosion by water, acid, alkali, salt, gas, and various chemical reagents and liquid medicines. The ability of glass to resist these corrosions is called the chemical stability of glass. Various glass bottles and cans are generally used in people's daily lives. For bottles and cans containing wine, beverages and food, they should have a certain chemical stability, especially for saline bottles and ampoule bottles used in medicine. The chemical stability requirements are higher, otherwise, the components in the glass will dissolve in the liquid medicine, and even peeling will occur, causing certain harm to the human body.
With the formulation of green product evaluation standards and the improvement of testing technology, the detection of harmful substances in bottle glass has become more and more stringent, especially the EU often uses green barriers to restrict the export of Chinese products, affecting the entry of products into the international market. To this end, the General Administration of Quality Supervision, Inspection and Quarantine and the State Administration of Standardization have added the allowable limit values of arsenic and antimony based on the allowable limit values of lead and cadmium in IS07086-2:2000 "Hollow glass products in contact with food--allowable limit values of lead and cadmium dissolution" according to China's situation (Table 2-1).
The factors affecting the chemical stability of glass are as follows.
① The water resistance and acid resistance of silicate glass are mainly determined by the content of silicon oxide and alkali metal oxide. The higher the silicon dioxide content, the greater the degree of interconnection between silicon oxide tetrahedrons, and the higher the chemical stability of the glass. As the content of alkali metal oxide increases, the chemical stability of the glass decreases. And as the radius of the alkali metal ion increases and the bond strength weakens, its chemical stability generally decreases, that is, water resistance Li+>Na+>K+.
② When two alkali metal oxides exist in the glass at the same time, the chemical stability of the glass reaches an extreme value due to the "mixed alkali effect", and this effect is more obvious in lead glass.
③ When alkaline earth metals or other divalent metal oxides replace silicon and oxygen in silicate glass, the chemical stability of the glass will also be reduced. However, the effect of reducing stability is weaker than that of alkali metal oxides. Among divalent oxides, BaO and PbO have the strongest effect in reducing chemical stability, followed by MgO and CaO.
④ In the base glass with a chemical composition of 100SiO2+(33.3-x)Na2O+xRO(R2O3 or RO2), after replacing part of Na2O with oxides such as CaO, MgO, AlO3, TiO2, ZrOz, and BaO in sequence, the order of water resistance and acid resistance is as follows.
Water resistance: ZrO2>AlO3>TiOz>ZnO>MgO>CaO>BaO.
Acid resistance: ZrO2>Al2O3>ZnO>CaO>TiOz>MgO>BaO.
Among glass compositions, ZrO₂ has the best water and acid resistance, as well as the best alkali resistance, but is difficult to melt. BaO is not good in both cases.
Among trivalent oxides, aluminum oxide and boron oxide will also have a "boron anomaly" phenomenon in terms of the chemical stability of glass.
In sodium-lime silicate glass xNa2O·yCaO·zSiO2, if the oxide content meets the relationship (2-1), a fairly stable glass can be obtained.
In summary, any oxide that can strengthen the glass structure network and make the structure complete and dense can improve the chemical stability of the glass; otherwise, it will reduce the chemical stability of the glass.
Optical properties of bottle glass
Bottle glass can effectively cut off ultraviolet rays and prevent the deterioration of the contents. For example, beer will produce an odor after being exposed to light with a wavelength below 550nm (blue light or green light), which is the so-called sunlight smell. The quality of foods such as wine and sauce will also be affected after being exposed to ultraviolet rays below 250nm. German scholars proposed that the photochemical effect of visible light gradually weakens from green light to long waves and ends at about 520nm. In other words, 520nm is the critical wavelength. Light shorter than this wavelength will have a photochemical effect on the contents of the bottle, causing beer to be damaged. Therefore, bottle glass is required to absorb light below 520nm, and brown bottles have the best effect.
When milk is exposed to light, it produces "light smell" and "odor" due to the generation of peroxides and subsequent reactions. Vitamin C and ascorbic acid are also reduced. Vitamin A, vitamin B2 and vitamin D also have similar situations. If a component that absorbs ultraviolet rays but has little effect on color is added to the glass composition, the impact of light on milk quality can be avoided.
For bottles and cans containing medicines, 2mm thick glass is required to absorb 98% of the wavelength of 410nm and transmit 72% at 700nm, which can prevent photochemical reactions and observe the contents of the bottle.
Except for quartz glass, most ordinary soda-lime-silica glass can filter most ultraviolet rays. Soda-lime-silica glass cannot transmit ultraviolet light (200~360nm), but can transmit visible light (360~1000nm), which means that ordinary soda-lime-silica glass can absorb most ultraviolet rays.
In order to meet consumers' requirements for the transparency of glass bottles and cans, it is best to make the bottle glass absorb ultraviolet rays without making it dark in color. Adding CeO2 to the composition can meet this requirement. Cerium can exist in two forms, Ce3+ or Ce4+, and both ions produce strong ultraviolet absorption. Japanese patents report that a glass composition contains 0.01%~1.0% vanadium oxide and 0.05%~0.5% cerium oxide. When exposed to ultraviolet light, the following reaction occurs:
Ce3++V3+-Ce4++V2+
As the exposure time increases, the ultraviolet radiation dose increases, the V2+ ratio increases, and the glass color deepens. For example, sake is easy to deteriorate when exposed to ultraviolet light, and using colored glass bottles affects transparency, making it difficult to observe the contents. When CeO2 and V203 are added, the glass is colorless and transparent when the storage time is short and the ultraviolet radiation dose is small, but when the storage time is long and the ultraviolet radiation dose is too high, the glass changes color. The depth of the color change can be used to judge the length of the storage time.