How should my country's fiberglass paper industry make breakthroughs and strategic plans for the future?
In recent years, with economic development and social progress, the demand for new materials in both industrial production and daily life has been continuously expanding, both in terms of variety and functionality. In the paper industry, the range of raw materials for specialty paper has also broadened. Glass fiber, as a typical representative of inorganic fibers, has gradually attracted widespread attention in the paper industry due to its unique properties compared to plant fibers and other synthetic fibers, becoming a new raw material for developing and producing specialty paper products.
1. Characteristics of Fiberglass
Fiberglass is a new type of functional and structural material among inorganic non-metallic materials. Its main component is silicon dioxide, and it also contains oxides of many other macronutrients, such as calcium, boron, sodium, potassium, and aluminum. Currently, the main manufacturing methods for glass fiber are the crucible method and the tank furnace method. Typically, glass fiber has a transparent and smooth cylindrical appearance with a perfectly circular cross-section. Its density is generally around 2.50–2.70 g/cm³, mainly depending on the glass composition. The tensile strength of glass fiber far exceeds that of other natural fibers, synthetic fibers, and various alloy materials, while its water absorption is much lower than that of natural and man-made fibers. Glass fiber also possesses high heat resistance, with a softening temperature of 550–750℃. It also exhibits excellent electrical insulation and dielectric properties, making it suitable for various insulating materials, radomes, etc. Furthermore, its excellent sound insulation and absorption properties allow its products to be used in various acoustic devices. However, glass fiber is a brittle material with very low elongation at break, resulting in relatively low flexibility or high brittleness – a key characteristic.
Fiberglass can be classified according to its alkali content into alkali-free fiber (commonly known as E-glass), medium-alkali fiber, high-alkali fiber, and special glass fiber. The first three types are commonly used in the paper industry. Alkali-free glass fiber is suitable for epoxy copper-clad laminates and electrical insulation products; medium-alkali glass fiber is suitable for continuous machine operation or hand lay-up to produce sheets, pipes, tanks, vessels, bathtubs, etc.; high-alkali glass fiber is suitable for battery separators, roofing waterproofing materials, etc.
2. Production of Fiberglass Paper
2.1 Forming Process of Fiberglass Paper
Fiberglass-based thin functional materials produced by wet papermaking can also be called glass fiber paper. The manufacturing process of this paper differs somewhat from ordinary papermaking. It uses glass fibers, which are lightly loosened, and binders are added, or some chemical wood pulp is added. It is then formed on a fourdrinier or cylinder papermaking machine. Silica gel or colloidal alumina can also be added to improve the strength of the finished paper. Usually, glass fiber paper does not require pulping during production; only dispersion is needed. Due to the relatively brittle nature of glass fibers, pressing is usually not required after forming the paper.
Under a microscope, glass fibers resemble glass rods; each fiber is stiff, slender, and has a large length-to-width ratio. The surface of these fibers also carries an electrical charge. Therefore, before papermaking, when preparing the pulp, the fibers easily entangle, forming a large number of difficult-to-disperse fiber clumps. Even after a short period of settling, flocculation occurs, affecting the uniformity of the glass fiber paper. To ensure good dispersion of the glass fiber slurry during papermaking, the following measures can generally be taken: (1) Adjust the pH of the suspension using dilute acid, generally pH=2.5~3.0 is suitable; (2) Reduce the slurry concentration to about 0.2%; (3) Improve the wetting condition of the glass fiber surface using dispersants or other chemicals; (4) Adjust the white water circulation system.
Fiberglass has a smooth surface, no fiber fracturing, and no -OH groups that can form hydrogen bonds on the fiber surface. Therefore, it cannot naturally generate strength in the paper during forming and drying. To ensure that the glass fiber can be firmly interwoven with the mixed fibers during papermaking, the glass fiber is often pretreated, or the formed paper web is sprayed or impregnated with glue. The main function of pretreatment is to give the glass fiber paper good uniformity, uniform thickness, and no protruding fiber clusters on the surface. Post-treatment such as spraying or impregnation mainly imparts better strength or other special properties to the paper. Liao He et al. studied different physical and chemical methods for surface treatment of glass fibers, and simultaneously reinforced glass fiber paper by adding acid, pulped plant fibers, and reinforcing agents. Adding pulped plant fibers and reinforcing agents significantly strengthened the glass fiber paper. Luo Guo et al. explored the performance of glass fiber and plant fiber blends and derived the optimal relationship between the concentration of the treatment agent, the blending ratio of glass fibers, and the physical properties of the finished paper.
2.2 Drying Process of Fiberglass Paper
Because glass fibers are brittle and fragile, glass fiber paper rarely undergoes a pressing process. This results in a wet paper web with a large amount of moisture entering the drying process. To address the problem of high moisture content during drying, vacuum suction is typically used to remove some moisture before the wet paper web enters the drying process.
To improve strength or meet other special application performance requirements, glass fiber paper often requires the addition of binders during the papermaking process or resin impregnation after forming, making the composition of the wet paper web more complex. To remove a large amount of moisture from fiberglass paper in a short time while ensuring a smooth, strong paper with uniform distribution and high retention of binders or resins, special drying methods are required. Microwave drying and hot air penetration drying are two commonly used methods for drying fiberglass paper.
Microwave drying can quickly achieve a certain degree of dryness within the wet paper web. This is because during microwave drying, the temperature gradient and moisture gradient are in the same direction, resulting in consistent heat and mass transfer. This promotes rapid evaporation of moisture within the fiberglass paper, creating an internal pressure gradient that allows moisture to quickly diffuse to the surface and evaporate, significantly shortening the drying time. However, it is important to note that microwave drying time should not be too long, typically within 30 seconds, as prolonged microwave exposure can cause paper shrinkage and deformation, leading to surface wrinkles and affecting the quality of the finished paper. Fiberglass is hydrophobic, and the resulting paper is porous and a poor conductor of heat. Based on the actual conditions of glass fiber paper, taking advantage of its low air permeability resistance, hot air is allowed to penetrate the paper web and directly contact the moisture adsorbed on the surface of the glass fiber paper. The hot air, at a certain speed, lowers the vapor partial pressure at the interface, facilitating moisture evaporation. The hot air immediately carries away the evaporated moisture, and there is no saturated vapor layer at the interface that hinders moisture evaporation; this is known as "penetration drying," resulting in high drying efficiency. The selection of the hot air temperature is also extremely important during hot air drying. To ensure the optimal effect of different binders or reinforcing resins, the drying temperature varies for different types of glass fiber paper. Generally, the drying temperature for glass fiber paper is not lower than 130℃, and some even require 180-200℃.
3. Common Fiberglass Papers
Fiberglass mat, also known as glass fiber paper, is made from short strands of glass fiber filaments randomly and evenly distributed into continuous glass fiber sheets using a papermaking process, and then bonded together with an emulsion.
3.1 Ultrafine Glass Fiber Filter Paper
Ultrafine glass fiber filter paper is a new type of high-tech filter paper. Unlike ordinary filter paper made primarily from plant fibers, glass fiber filter paper is a specialty paper made mainly from ultra-fine glass fibers using a special papermaking process and subsequent processing. It is primarily used for air purification. Glass fiber filter paper features good isotropy, uniform pore size distribution, small basis weight deviation, heat resistance, flame retardancy, water resistance, and high dirt-holding capacity.
Glass fiber air filter paper is made primarily from glass fibers using a wet-forming process, making it an ideal air filtration material. Products are categorized into three main series based on filtration efficiency: ventilation (ASHRAE); medium and high efficiency (HEPA); and ultra-high efficiency (ULPA). General ventilation glass fiber filter paper and medium efficiency air glass fiber filter paper are mainly used in general air conditioning systems, gas turbines, and air compressors. This type of glass fiber filter paper is produced by treating the fiber surface with chemical additives and combining precise pulp formulation. The resulting products exhibit high efficiency, low resistance, and folding resistance. Especially at low resistance, the filtration efficiency can reach 60%–95%, and it also has a certain degree of water resistance, making it suitable for high-humidity environments. High-efficiency particulate air (HEPA) air filter paper is mainly used in cleanrooms or workbenches ranging from Class 10,000 to Class 100,000, nuclear power plant exhaust systems, high-end household vacuum cleaners, air purifiers, and respirators. This product has excellent moisture and water resistance, with a filtration efficiency of 99.9% to 99.9999%. Ultra-high-efficiency particulate air (UHEPA) air filter paper is mainly used in chip factories and Class 100, Class 10, and Class 1 cleanrooms.
Ordinary plant fiber filter paper has a filtration efficiency of only 16% to 87%, with a best permeability of 13%. In contrast, ultra-fine glass fiber filter paper has a filtration efficiency of 99.99995% and a permeability of 0.00005%. Therefore, the filtration efficiency of ultra-fine glass fiber filter paper is exceptionally high.
3.2 Glass Fiber Battery Separator Paper
Fiberglass separator paper is composed of ultra-fine glass fibers with a diameter of 0.5 to 4 μm that do not contain any organic binders. The uncompressed glass fiber paper, produced by the papermaking process, has a multi-layered felt-like structure formed by randomly arranged glass fibers creating relatively small, high-torque free channels. This separator exhibits significantly superior performance compared to ordinary battery separators in many aspects, such as high liquid absorption capacity, fast liquid absorption speed, good hydrophilicity, absorption and retention of the electrolyte required for the battery's rated capacity, and maintenance of its high liquid absorption rate throughout its lifespan. Meanwhile, glass fiber separators possess a large surface area, high porosity, small pore size, high chemical purity, and few harmful impurities, exhibiting excellent acid resistance and oxidation resistance. Related patents disclose the use of glass fiber composite materials as the substrate for battery separator paper, fully leveraging the corrosion resistance of glass fiber and the good pore size of the glass fiber substrate, allowing for ample electrolyte permeation.
The performance of glass fiber separator paper is closely related to the characteristics of the glass fiber itself. Ultrafine glass fibers have small diameters, large surface areas, and high wettability, resulting in a high liquid absorption rate and small pore size in the separator, providing strong resistance to dendrite penetration. However, this also increases the resistivity, necessitating the selection of an optimal combination. The length of the glass fibers also affects the separator's performance; excessively long fibers are difficult to disperse and may flocculate, leading to an uneven separator. If the diaphragm is too short, the uniformity of the diaphragm is improved, but the strength is low; therefore, an optimal length range should be selected.
3.3 Glass Fiber Copper Clad Laminate Paper
Fiberglass copper clad laminate paper is mainly used as the substrate for copper clad laminates. It has a uniform appearance, excellent electrical properties, heat resistance, solvent resistance, and excellent compatibility with epoxy resin. Copper clad laminates produced using glass fiber paper can achieve performance levels comparable to glass cloth laminates, making them suitable for industrial electronic products. In particular, glass fiber paper's superior post-processing properties make it even more popular in the market. Impregnation with epoxy resin is a crucial process in the production of glass fiber copper clad laminate paper. The impregnation involves two steps: first, the resin aggregates on the surface of the glass fiber paper with a certain degree of dryness; then, the resin aggregated on the paper surface gradually flows towards the glass fibers. The process of sizing involves the penetration of the sizing solution into the glass fiber paper, displacing moisture from the wet paper web. The penetration process has a significant impact on the sizing properties. Experiments have shown that the penetration rate is inversely proportional to the cube of the fiber thickness; therefore, increasing the penetration rate of the sizing solution into the glass fiber paper is the fundamental method to improve the sizing effect. The "vacuum-assisted sizing method" is currently a relatively advanced technology. The core of this method lies in the special equipment used in the pre-impregnation stage. Its principle is: during pre-impregnation, vacuum suction is used to rapidly penetrate the sizing solution from the surface of the glass fiber paper into the paper, while simultaneously removing air bubbles from the sizing solution and fibers.
4. Development of New Fiberglass Paper
Fiberglass is combined with softwood fiber, with the glass fiber acting as a skeleton to improve the strength properties of the finished paper. Experiments have shown that adding 10% glass fiber to softwood pulp can significantly improve the strength of the paper. High-quality paper exhibits excellent tensile and tear strength. Further processing, such as adhesive spraying, impregnation, and multilayer lamination, allows it to be used as a building filler material.
Fiberglass paper possesses good sound absorption properties. Coating the surface of the base glass fiber paper with pigments, adhesives, flame retardants, and coupling agents, followed by drying and curing, allows it to be used as a sound-insulating and flame-retardant material in building walls and interior decoration. Dyed glass fiber paper also offers enhanced decorative properties. Research has found that by improving the Johns On-Allard model, the sound absorption effect of glass fiber paper mats with different porosities and even different fiber lengths can be measured.
A Japanese company has successfully developed a glass fiber paper using a papermaking process that can be used as a sealing material in automobiles and industrial equipment. This paper is composed of calcium carbonate whiskers with diameters of 6 μm and 0.16 μm. Composed of μm glass fibers, sepiolite, cellulose pulp, etc., and reinforced with styrene-butadiene rubber and flocculants.
Another Japanese company has developed a porous glass fiber reinforced plastic tube using a wet papermaking process. The production process involves dispersing chopped glass fibers in resin-containing water, dehydrating them into sheets, winding them onto a tube, inserting it into a cylindrical mold, heating it to expand, and then using it to obtain a porous glass fiber reinforced plastic tube. This glass fiber reinforced plastic tube exhibits excellent strength properties and can be used in construction, filtration, and other fields.
Fiberglass reinforced flooring layers can effectively prevent flooring from cracking or shrinking during use. The formed glass... After being cut into sheets, fiberglass paper is bonded together with a polymer adhesive. In practical applications, the fiberglass paper increases the strength, hardness, and stiffness of the flooring layer, while the polymer adhesive has a certain degree of elasticity, preventing deformation caused by thermal expansion and contraction. This makes it a novel and ideal flooring material.
A US patent discloses a method for using fiberglass paper-faced gypsum board for supporting decoration of house floors or ceilings. This fiberglass paper is made by blending glass fibers with an average diameter of 8–17 μm and other man-made fibers with a diameter of less than 5.5 μm, with the glass fiber required to account for more than 30% of the total product mass.
Mica is an important non-metallic mineral. Using pulping and papermaking technology, mica fragments can be used as raw materials to produce various... Various types of mica paper are available. However, currently produced mica paper generally has low strength, making it difficult to adapt to high-strength application environments. Patents have disclosed the use of aramid precipitated fibers, short aramid fibers, or the addition of bulk fibers between layers of powdered mica paper to reinforce it. Glass fiber itself has high insulation properties and high strength, making it an excellent reinforcing material and a potential substitute for aramid fibers. Research is being conducted on its reinforcing effect on mica paper.
5. Summary and Outlook
In the past decade, my country's glass fiber industry has developed rapidly, and China has consistently maintained its position as the world's largest producer and user of glass fiber. The application of glass fiber in the papermaking industry has gradually gained popularity with the rapid development of the glass fiber industry. This has garnered significant public attention. my country's "12th Five-Year Plan" for the development of the glass fiber industry specifically emphasizes the need to vigorously develop the application areas of glass fiber products, continuously expanding the application scope of glass fiber, especially in areas such as fire resistance, heat resistance, and reinforcement. The plan calls for developing various forms of products to facilitate use, fundamentally improving the quality of the glass fiber industry by expanding the application market, and broadening and deepening the application fields. This will facilitate the connection between glass fiber enterprises and downstream industries, promoting the development and growth of the glass fiber industry chain. This places higher demands on the development and quality optimization of glass fiber paper types.
Functionally leveraging the inherent properties of glass fiber and exploring its combination with various papermaking raw materials will enable it to achieve greater success in specialty paper products.
