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Fire retardant packaging paper technology and development

early research believes that when paper (paperboard) is burning, the paper surface in front of the flame is pyrolysis and produces gas. As a result of the movement of air and these gases, the flame moves, diffuses and spreads along the paper surface, and the paper surface is heated to the pyrolysis temperature. However, recent studies have shown that when burning, the gas produced by the pyrolysis of paper is under the flame. Due to the gas diffusion, the flame spreads out of the pyrolysis zone, and the adjacent paper surface is heated to the pyrolysis temperature due to the heat conduction in the phase, which is the combustion principle of paper (carton). Flame retardancy refers to the slow burning speed of materials when they contact the fire source, and they can quickly stop burning and extinguish themselves when they leave the fire source

from the combustion mechanism of paper (paperboard), we can see that in order to give paper (paperboard) fire resistance, we must start from the following three aspects: isolate the paper surface and flame, and prevent the flame from burning and spreading on the paper surface; Reduce or consume oxygen in the combustion environment and suffocate the flame; Reduce the temperature in the combustion area or use fire-resistant fibers to prevent the paper from pyrolysis. The above purpose is generally achieved by adding chemicals. We call this kind of chemical with flame retardant function and poor anti-interference ability as flame retardant. The commonly used flame retardant elements include halogen, phosphorus, boron, nitrogen, aluminum, etc. Flame retardants generally achieve the purpose of flame retardation through the following ways

endothermic effect: flame retardant has endothermic function. Using the decomposition reaction of flame retardant when heated (this process is generally endothermic reaction), through the absorption of heat by flame retardant and the steam heating of incombustible volatiles generated by thermal decomposition, it is difficult to raise the temperature of paper and paper products when heated, so as to prevent the occurrence of thermal degradation of polymers and play a flame retardant role

isolation effect: when the flame retardant burns, it can form an isolation layer on the surface of paper products, which can prevent heat transfer, reduce the release of combustible gases and isolate oxygen

dilution effect: the flame retardant decomposes at the combustion temperature to produce a large number of non combustible gases, such as water, carbon dioxide, ammonia, etc. These non combustible gases dilute the combustible gas concentration below the combustible concentration range to prevent combustion

inhibitory effect: the combustion of polymers is mainly a chain reaction of Oh free radicals. Such substances have the ability to react repeatedly with Oh free radicals to produce H2O, resulting in the inhibition of the chain reaction of producing free radicals

if paper (paperboard) is impregnated with NaHCO3 solution, K2CO3 solution and n2s2o6 · 2H2O solution to give it fire resistance, the following reactions will occur when it burns over:

2nahco3 → H2O ↑ + 2Na + 2co2 ↑

k2co3 → CO2 ↑ + k2o

n2s2o6 → n2s4o42, field investigation + H2O ↑ → SO2 ↑

release incombustible gases such as water vapor, CO2, SO2, which can achieve the effect of chamber flame; For example, adding borax to paper (paperboard) and unremitting transformation are the most competitive advantages of enterprises, such as boric acid, sodium silicate and other substances. These substances form a glassy protective layer when burning in paper (paperboard) at high temperature, so as to isolate the paper surface from the flame and prevent the flame from burning and spreading on the paper surface; For example, ammonium salt is added to paper (paperboard) to decompose and release incombustible nitrogen (NH3) with endothermic effect, so as to asphyxiate the flame and reduce the temperature of combustion area and surrounding air. There are many methods and technical means to give paper (paperboard) fire resistance, but there is no mature technology for paper packaging. If fire-proof cardboard is used to produce paper packaging, it can certainly achieve the purpose of flame retardant. However, the general packaging paperboard adopts fireproof paperboard, which is not desirable in terms of economic benefits. The most convenient and effective way to use ordinary packaging board to give paper packaging fire resistance is to add flame retardants to adhesives. There are many kinds of known flame retardants. In addition to the above mentioned, there are salt, water-soluble double salt, nepheline (naoal2o3so2), gaseous nitrogen, halogen derivatives, purification, etc. Among many flame retardants, flame retardants can not only give paper packaging fire resistance, but also meet the production requirements of paper packaging industry

selection principles of flame retardants

the following principles must be followed when selecting Flame Retardants:

do not affect the physical properties of existing adhesives, or use adhesives added with flame retardants, and their physical properties should meet the production requirements. The physical properties of the adhesive include fluidity, adhesive strength, etc

the selected flame retardant should be cheap and easy to obtain. For manufacturers using water glass as adhesive, there is no need to add flame retardant Liu, because water glass itself is a kind of flame retardant. Because the paper packaging products produced with sodium silicate have the disadvantages of brittleness, moisture and whiteness, most manufacturers have turned to starch adhesive

for each adhesive with fluidity, it has some optimal viscosity and surface tension index. Any tendency to deviate significantly from the best index will have an adverse impact on the quality of adhesive and its application. Therefore, the influence of flame retardant on adhesive must be considered when selecting flame retardant. Among many flame retardants, some will reduce the fluidity of adhesives, while others will improve the fluidity of adhesives. Therefore, in the production of paper packaging with flame retardant effect, at least two or more flame retardants should be added to the adhesive

one of them must be able to reduce the fluidity of the adhesive; The other can improve its fluidity. The total amount of flame retardant is determined according to the fire resistance of paper packaging, and the proportion of various materials is subject to the best flow index. In order to give paper packaging good flame retardancy, the viscosity and surface tension of the adhesive should also be controlled. For example, when urea based resin is added to starch adhesive, two flame retardants, sodium bromide (which can reduce the fluidity of adhesive) and ammonium chloride (which can improve the fluidity of adhesive), can be added to produce paper packaging products with good waterproof and flame retardancy and good moisture resistance

technical way to realize flame retardancy of paper and paper products

impregnation method: this method is applicable to water-soluble flame retardants. The water-soluble flame retardant is mixed into a solution, dipped into the paper, and then heated and dried to produce a fire-retardant paper. The flame-retardant paper obtained by this method has poor water resistance, strong moisture absorption, significant reduction in strength, and is prone to yellowing and hardening. The impregnation method requires that the paper has quite high water absorption and wet strength indicators, and it is best to impregnate wrinkled paper, cotton fiber paper, synthetic fiber paper and non-woven fabrics. The impregnation of paper can be completed on the surface sizing machine or dyeing machine

coating method: this method is applicable to insoluble or insoluble flame retardants. The powder of flame retardant is evenly dispersed in a certain adhesive to make emulsion coating, and then the coating is coated on the surface of the paper by coating method. After heating and drying, the coated flame retardant paper can be obtained. The advantage of this method is that most of the flame retardants are concentrated on the surface of the paper, which has little impact on the physical properties of the paper. Especially for the processed paper that needs to be coated, it is only necessary to add flame retardants to the coating towel. This method can be completed on the coater. In order to obtain good flame retardant effect, the flame retardant with small and uniform particles is better. The disadvantage of this method is that the flame retardant effect is not ideal

internal addition method: this method is applicable to water-insoluble flame retardants, which are added to pulp together with other fillers, and then copied into paper. The two pointers at the adding part B point out that the tension F value is relatively flexible. It can be added anywhere from the beater to the headbox or circular groove, as long as it can be evenly dispersed in the slurry. Similar to other fillers, the pH value of the slurry is between 4.5-5.0, and its retention rate in the paper is very high. The advantages of this method are that it is suitable for the production of all kinds of paper, the process operation is simple, and the distribution of flame retardant in the paper is relatively uniform, so the flame retardant function of the paper is relatively uniform. The disadvantage is that the loss of flame retardants is relatively serious, and it is not easy for the retention rate of flame retardants to reach 80%. The best way to solve the problem of loss is to use appropriate flow aids. This method has better effect when it is used to produce fireproof paperboard or high-volume paper

new development of fire-proof special paper

many special occasions require paper to have high flame retardant properties, such as electrical insulation materials, smoke filter bags, aerospace paper, heated paper lunch boxes, etc

with the continuous expansion of the application field of paper packaging materials, the requirements for the flame retardancy of paper will be higher, and the demand for flame retardant paper will be more

dehydrated wrapping paper: this kind of wrapping paper, called PS, selects the semi permeable membrane that can only penetrate water as the surface material, and the inner side uses high osmotic substances and polymer absorbent. The wrapping paper will not damage the fine saturated film of food tissue, but also inhibit the activity of enzymes, prevent protein decomposition, reduce microbial reproduction, and achieve the effect of maintaining the freshness of food, concentrating fresh ingredients, and improving toughness

absorbent paper: the biggest feature of absorbent paper is its strong water absorption capacity. It can maintain a water absorption capacity 10 times heavier than the material, and it is safe and harmless. There are obvious differences in water absorption capacity and water retention between water absorbent paper and non-woven fabric, and water absorbent paper is obviously dominant. This is because the absorbent paper can not only keep water in the pores between the raw material fibers, but also its fibers themselves can absorb water. Absorbent paper becomes very soft after absorbing water. Because of the above characteristics, absorbent paper can be used as a film to absorb ham, sausage and other food, a film to absorb dripping water from fresh food, and a film for cosmetics and sanitary materials

acid free waterproof archival paper: a new type of waterproof packaging paper and paperboard (acid free waterproof archival paper) independently developed by Hunan Changde cigarette factory jinfurong Special Paper Co., Ltd. has filled the domestic gap. The company has invested 3.15 million yuan to develop new waterproof packaging paper since 1996. According to relevant experts, the new waterproof packaging paper and paperboard have a wide range of applications

screen wet paperboard: N1 guard screen wet paperboard developed by liberty Paper Co., Ltd. in Minnesota, USA, looks like corrugated paperboard and is also similar to domestic liner paperboard, which can be printed, recycled, beaten and processed. This kind of wet screen performance is caused by the internal chemical bonding performance in the paperboard making process, without any conversion, which can save time. The board achieves good moisture shielding performance through its internal absorption

water resistant recycled paper: it has the characteristics of water resistance and good water permeability. Because it has no water repellency, its permeability is higher than other materials, its surface strength and interlayer strength are high, it has antibacterial property, and it can absorb nitrogen, etc. This feature is not obtained by adding resins and chemicals, so it is safe and harmless. Because of the above characteristics, it can be used in food packaging materials, dewing and water absorption films and other fields. At present, this kind of paper has been applied to the vacuum packaging of food and compounded with other materials. As a multi moisture semi-finished food packaging paper, it gives full play to its advantages of mold resistance, water absorption and water resistance. (end)

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