Hot-melt adhesives are solids at room temperature. They gradually soften and become a viscous liquid with certain fluidity and permeability when heated, and can have a certain wetting affinity for the surface of the object. After cooling, they solidify and congeal. The wireless binding hot-melt adhesives for books and periodicals supplied in China's printing market are mainly EVA hot-melt adhesives. The production and promotion of EVA hot melt adhesives in China is not long. Because of the promotion of the binding process, the supply and demand of hot melt adhesives by printing companies has been rising, but most domestic manufacturers have weak equipment and backward equipment. , Lack of necessary detection and control methods, the technical content of the produced products is low, there is no stable and reliable quality support, the product quality is uneven, which seriously affects the quality of post-press processing and causes binding accidents, so the industry standard is used to regulate EVA thermal The production and use of melt adhesives are necessary. This article focuses on the characteristics of EVA hot melt adhesives and talks about several aspects covered by its technical standards.
1. Softening degree
The softening degree of hot melt adhesive is directly related to the fixing speed. When the softening degree is too low, its curing speed will be slower, which will cause the book to be deformed or unable to be cut during cutting, which will affect the production efficiency of the linkage line and increase it. Production cost; when the softening degree is too high, the curing speed will be accelerated, but it will affect the effective bonding time of the hot melt adhesive (that is, the opening time). If the opening time is too short, it will cause the book block to separate from the cover. The softening degree is between 80 ～ 90 ℃.
2. Adhesion, flow properties
Due to the special application of hot melt adhesives, hot melt adhesives are required to have a certain melt viscosity, so as to ensure that the hot melt adhesives have good fluidity and wettability at the melting temperature, and can have sufficient penetration and stickiness to paper fibers.接 Strength. If the melt viscosity of the hot melt adhesive is too low, the amount of glue on the back of the book will be insufficient; and if the melt viscosity is too high, the fluidity will be poor, which will affect the adhesion effect of the back of the book.
3. Adaptability to temperature
Hot-melt adhesives are relatively sensitive to temperature. Generally good hot-melt adhesives should have low-temperature, high-temperature resistance and thermal stability to temperature. The low-temperature resistance of hot-melt adhesives is directly related to the binding of staples in cold environments. The safety of use, and the high temperature resistance performance is directly related to the aging performance of the hot melt adhesive.
In general, the better the toughness of the hot melt adhesive, the better the low temperature performance, and vice versa. The low temperature performance test of hot melt adhesive is generally in a low temperature environment, because the colloid is not easy to crack at this time; the high temperature resistance of hot melt adhesive mainly refers to the hot melt adhesive at a certain temperature (generally slightly higher than the melting temperature) , Will not produce colloidal discoloration, viscosity reduction and other phenomena; the thermal stability of hot melt adhesive refers to its aging resistance, good thermal stability means that the hot melt adhesive will not cause discoloration of the glue during long-term heating At the same time, the surface does not skin during use. The thermal stability of general hot-melt adhesives should be expressed as: when heated under a certain constant temperature for a period of time, the increase in color and viscosity has a certain range. A simpler method is to process the glue sample at a constant temperature at a higher temperature, and the change of the glue with poor anti-aging properties will be very obvious and easy to check.
4. Tensile strength and hardness
In order to make the packaging of books and periodicals well formed, there will be no loose pages or falling pages during frequent reading, folding and flattening. Hot melt adhesives should have appropriate hardness (generally HS78 ° ~ 90 °) and appropriate toughness. . Under the premise of full penetration of paper fibers, it is necessary to have a high tensile strength and an appropriate elongation at break. Generally, the performance of hot melt adhesives is evaluated by two indicators of hardness and tensile strength. of.
The hardness of the hot melt adhesive is directly related to the flexural strength of the bound book. The hardness is high, the book pages can withstand a certain bending resistance between the seams, the back of the book is firm and beautiful. In addition, high hardness can also be properly considered to reduce the thickness of the adhesive layer and reduce the consumption of hot melt adhesive. On the contrary, if the hardness is low, it is necessary to increase the thickness of the glue layer to improve the strength, especially the large gram double-glue book pages or the thick printed books with good paper quality.
Under the premise that the hot melt adhesive is sufficiently compatible with the paper, that is, the hot melt adhesive has sufficient penetration into the paper fibers, the hot melt adhesive should also have a high tensile strength to ensure the adhesion and use of the hot melt adhesive to the book Strength, so that the book will not loose pages, drop pages and cracks during use. When the tensile strength of the hot melt adhesive is greater than 4 MPa, it is not only conducive to the quality control of the book binding, but also can reduce the overall cost of production. Toughness, hardness and strength are interrelated. When the elongation at break of hot-melt adhesive is less than 100%, the back of the book will be brittle due to failure to resist external impact. On the contrary, it will be elastic due to its too high elongation at break, resulting in a multi-directional affinity over colloid and paper fiber. The pages are degummed and the pages are deformed due to excessive flattening.
5. Chroma and odor
In terms of appearance of hot melt adhesives, in addition to the need to add corresponding color materials when used in color printing paper, the surface of general high-quality adhesive materials or films is smooth, shiny and free of rough foreign particles. Generally, the quality of high-quality hot-melt adhesive products is milky white or light yellow, with luster and softness, and the density is generally about 0.93g / cm3. A glossless glue indicates poor raw material miscibility. If the raw materials cannot be sufficiently melted, the raw material will lose its proper function. This kind of glue has poor permeability to the paper and poor adhesion. There is no guarantee for the quality of the glue binding. The gas emitted by the melt during the melting process should also be within the evaluation index. General operators tend to use non-toxic and odor-free hot melt adhesives, but in the process of selecting hot melt adhesives and evaluating hot melt adhesives, they are non-toxic The hot melt adhesive is the first to be guaranteed, so the color and smell of the hot melt adhesive should also be in its evaluation system.
6. Specific gravity
As long as the glue is placed in water, the specific gravity of the glue can be detected. High-quality glue should float for a long time without sinking. Generally, glue with a specific gravity greater than 1 will sink to the bottom of the water, while glue with a specific gravity less than 1 will float on the water. For adhesives with a specific gravity greater than 1, the overall performance index is lower than hot melt adhesives with a specific gravity of less than 1. In addition, the greater the specific gravity of the hot melt adhesive, the greater the weight of the single-use adhesive when the adhesive layer is the same, and this will also significantly increase production cost.
Compared with foreign markets, China's hot-melt adhesive market has certain gaps in internal quality, process methods, raw materials and production equipment performance. For the current domestic hot-melt adhesive market, a set of hot-melt adhesive quality assessment standards is It is necessary that the above only analyzes the performance of the hot melt adhesive based on the performance of the hot melt adhesive. It is hoped that it can help the majority of users better understand the hot melt adhesive and have a certain reference role in the process of selecting the hot melt adhesive. .
1. Softening degree
The softening degree of hot melt adhesive is directly related to the fixing speed. When the softening degree is too low, its curing speed will be slower, which will cause the book to be deformed or unable to be cut during cutting, which will affect the production efficiency of the linkage line and increase it. Production cost; when the softening degree is too high, the curing speed will be accelerated, but it will affect the effective bonding time of the hot melt adhesive (that is, the opening time). If the opening time is too short, it will cause the book block to separate from the cover. The softening degree is between 80 ～ 90 ℃.
2. Adhesion, flow properties
Due to the special application of hot melt adhesives, hot melt adhesives are required to have a certain melt viscosity, so as to ensure that the hot melt adhesives have good fluidity and wettability at the melting temperature, and can have sufficient penetration and stickiness to paper fibers.接 Strength. If the melt viscosity of the hot melt adhesive is too low, the amount of glue on the back of the book will be insufficient; and if the melt viscosity is too high, the fluidity will be poor, which will affect the adhesion effect of the back of the book.
3. Adaptability to temperature
Hot-melt adhesives are relatively sensitive to temperature. Generally good hot-melt adhesives should have low-temperature, high-temperature resistance and thermal stability to temperature. The low-temperature resistance of hot-melt adhesives is directly related to the binding of staples in cold environments. The safety of use, and the high temperature resistance performance is directly related to the aging performance of the hot melt adhesive.
In general, the better the toughness of the hot melt adhesive, the better the low temperature performance, and vice versa. The low temperature performance test of hot melt adhesive is generally in a low temperature environment, because the colloid is not easy to crack at this time; the high temperature resistance of hot melt adhesive mainly refers to the hot melt adhesive at a certain temperature (generally slightly higher than the melting temperature) , Will not produce colloidal discoloration, viscosity reduction and other phenomena; the thermal stability of hot melt adhesive refers to its aging resistance, good thermal stability means that the hot melt adhesive will not cause discoloration of the glue during long-term heating At the same time, the surface does not skin during use. The thermal stability of general hot-melt adhesives should be expressed as: when heated under a certain constant temperature for a period of time, the increase in color and viscosity has a certain range. A simpler method is to process the glue sample at a constant temperature at a higher temperature, and the change of the glue with poor anti-aging properties will be very obvious and easy to check.
4. Tensile strength and hardness
In order to make the packaging of books and periodicals well formed, there will be no loose pages or falling pages during frequent reading, folding and flattening. Hot melt adhesives should have appropriate hardness (generally HS78 ° ~ 90 °) and appropriate toughness. . Under the premise of full penetration of paper fibers, it is necessary to have a high tensile strength and an appropriate elongation at break. Generally, the performance of hot melt adhesives is evaluated by two indicators of hardness and tensile strength. of.
The hardness of the hot melt adhesive is directly related to the flexural strength of the bound book. The hardness is high, the book pages can withstand a certain bending resistance between the seams, the back of the book is firm and beautiful. In addition, high hardness can also be properly considered to reduce the thickness of the adhesive layer and reduce the consumption of hot melt adhesive. On the contrary, if the hardness is low, it is necessary to increase the thickness of the glue layer to improve the strength, especially the large gram double-glue book pages or the thick printed books with good paper quality.
Under the premise that the hot melt adhesive is sufficiently compatible with the paper, that is, the hot melt adhesive has sufficient penetration into the paper fibers, the hot melt adhesive should also have a high tensile strength to ensure the adhesion and use of the hot melt adhesive to the book Strength, so that the book will not loose pages, drop pages and cracks during use. When the tensile strength of the hot melt adhesive is greater than 4 MPa, it is not only conducive to the quality control of the book binding, but also can reduce the overall cost of production. Toughness, hardness and strength are interrelated. When the elongation at break of hot-melt adhesive is less than 100%, the back of the book will be brittle due to failure to resist external impact. On the contrary, it will be elastic due to its too high elongation at break, resulting in a multi-directional affinity over colloid and paper fiber. The pages are degummed and the pages are deformed due to excessive flattening.
5. Chroma and odor
In terms of appearance of hot melt adhesives, in addition to the need to add corresponding color materials when used in color printing paper, the surface of general high-quality adhesive materials or films is smooth, shiny and free of rough foreign particles. Generally, the quality of high-quality hot-melt adhesive products is milky white or light yellow, with luster and softness, and the density is generally about 0.93g / cm3. A glossless glue indicates poor raw material miscibility. If the raw materials cannot be sufficiently melted, the raw material will lose its proper function. This kind of glue has poor permeability to the paper and poor adhesion. There is no guarantee for the quality of the glue binding. The gas emitted by the melt during the melting process should also be within the evaluation index. General operators tend to use non-toxic and odor-free hot melt adhesives, but in the process of selecting hot melt adhesives and evaluating hot melt adhesives, they are non-toxic The hot melt adhesive is the first to be guaranteed, so the color and smell of the hot melt adhesive should also be in its evaluation system.
6. Specific gravity
As long as the glue is placed in water, the specific gravity of the glue can be detected. High-quality glue should float for a long time without sinking. Generally, glue with a specific gravity greater than 1 will sink to the bottom of the water, while glue with a specific gravity less than 1 will float on the water. For adhesives with a specific gravity greater than 1, the overall performance index is lower than hot melt adhesives with a specific gravity of less than 1. In addition, the greater the specific gravity of the hot melt adhesive, the greater the weight of the single-use adhesive when the adhesive layer is the same, and this will also significantly increase production cost.
Compared with foreign markets, China's hot-melt adhesive market has certain gaps in internal quality, process methods, raw materials and production equipment performance. For the current domestic hot-melt adhesive market, a set of hot-melt adhesive quality assessment standards is It is necessary that the above only analyzes the performance of the hot melt adhesive based on the performance of the hot melt adhesive. It is hoped that it can help the majority of users better understand the hot melt adhesive and have a certain reference role in the process of selecting the hot melt adhesive. .
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