The so-called gloss of the printed matter refers to the brightness of the printed matter on the surface of the printed matter under a certain background and lighting conditions and the contrast relationship between the brightness of the printed matter and the distribution of light in all directions. The optical characteristics related to gloss mainly include surface reflected light and internal reflected light.
Gloss and color are collectively called color. Because color is more intuitive and has a direct impact on many mental factors such as people's mental state and emotions, people began to study color early. This research work is basically mature and is obtained in daily life. Has been widely used. The gloss is the same as the color, and it can also respond to people's psychology, especially in the quality evaluation of prints.
1. Surface reflected light, which is composed of surface regular reflection light and surface diffused light.
Regular reflected light: Light that conforms to the law of reflection is called regular reflected light. In addition to the reflectance of the substance, the intensity of the regular reflected light is mainly related to the state of the light-receiving surface of the object. In general, the smoother the surface, the stronger the reflected light. The specular reflection light is a special kind of information in the reflected light of an object, which has special significance for the study of gloss. In the past, gloss research has attached great importance to specular reflection light. For example, for the determination of the gloss of general smooth surface objects, most of the industrial standards in Japan and the United States use specular gloss directly related to specular reflection light. The specular reflection light is basically reflected on the surface of the object, so the object has little selective absorption of this part of the light, and its spectral composition is basically the same as the original incident light.
Diffuse light on the surface: the actual mirror surface is not an ideal mirror surface, so it will produce light diffusion. At this time, it can be considered that the light intensity reflected by many small mirrors is superimposed. When the brightness of the diffusion surface is a constant, it is called a cosine diffuser.
2. Internally reflected light. After the light refracts into the object, it is re-entered into the original medium by the internal reflection of the object. This part of light is called internal reflected light. The internal reflected light is subject to selective absorption by the substance, so that its spectral composition changes. If the incident light is white, the internal reflected light will become colored light and show the color of the object.
Matte print is one of the quality marks of the printed matter. If it is rich, it can increase the vividness of the printed color of the printed matter; enhance the three-dimensional sense of the image, especially the reproduction of the actual photo, with gloss, more realistic. There are many factors that affect the gloss of the imprint, which can be summarized in the following aspects.
1. The nature of the paper
The structural state of the paper has a decisive influence on the printing gloss, which is the most basic condition. The three indicators of paper surface smoothness, gloss and ink absorption will have an impact on the gloss of the printed products.
1. The effect of the surface smoothness of the paper on the gloss of the printed product. In order to make the printed products form mirror reflection, bright colors and good gloss, they must be printed on smooth paper. Paper with a rough surface is difficult to make the print shiny. Even if the flatness is good, capillary holes are formed between the coating particles of the paper, and the penetration of the binder is large, and high-gloss products cannot be obtained. The surface smoothness of various papers is different, and the level of smoothness has a greater impact on the gloss of the finished product. The paper with high smoothness has good contact speed with the ink, which can guarantee the complete reproduction of the dots and make the finished product have better gloss. Because the gloss of the ink film on the paper depends on whether the incident light can be specularly reflected, only the paper with high smoothness can produce specular reflection after the ink film is leveled. On the contrary, the paper with poor smoothness and rough surface has uneven level of imprinted ink film, which can only form diffuse reflection to the light, and the finished product will have no gloss. Therefore, in order to obtain a good gloss for the exquisite and high-end products, the paper with high smoothness must be selected for printing.
2. The effect of paper ink absorption on gloss. The paper's ink absorption actually refers to the paper's absorption performance of the ink binder. The paper's absorption is one of the main conditions that determine the amount of penetration. The gloss should be reduced, or even dull. The rougher the paper, the larger the fiber gap, the stronger the absorption capacity of the binder. The linking material is absorbed by the fiber most before drying, and the remaining part of the linking material and ink particles adhere to the surface of the paper, and lose the leveling performance that it should have, and cannot form a smooth ink film layer. The product is dull and dull. For coated paper (coated paper), there are two main reasons that affect the absorption of ink: one is the variety and materials used in the coating and the mysterious tablet. The lower the ratio of adhesive to pigment, the higher the paper's absorption of ink. If the coating concentration is low, the adhesive and water in the coating can easily penetrate into the thick paper, which reduces the amount of adhesive in the coating, thereby increasing the absorbency of the ink. Second, the variety of pigments and particle size in the paint are also related to ink absorption. The finer the pigment particles, the less easily the glue in the coating is transferred to the paper base. The pigment particles are coarse, the gap between the particles is large, and the absorption of ink is also large. It is difficult to obtain the ideal gloss effect in the finished product.
3. The effect of paper gloss on the gloss of printed products. The gloss of the paper itself has a considerable effect on the gloss of the finished product. The gloss of the coated paper surface mainly depends on the glossing materials used in papermaking and the processing accuracy of the paper. Brightening materials include aluminum stearate, paraffin wax, insect wax, etc. The finishing method is super calendering. The paper processed by the above method has a smooth surface, and forms the specular reflection (unidirectional reflection) of light on itself. When printed with a higher transparency ink, the gloss effect of the finished product will be better.
4. The effect of paper strength on the gloss of printed products. The strength of the paper is low, and the phenomenon of powder loss and hair loss is serious. During printing, the binding force between the ink and the paper is not high, and the glossiness of the printed product is low or even dull.
5. The effect of paper pH on the gloss of printed products. The pH of the paper affects the drying speed of the ink film, and the drying speed of the ink film affects the glossiness of the printed product. Alkaline paper can accelerate the drying of the ink film, thereby relatively reducing the penetration time and the penetration of the binder, so the gloss of the printed product is better; acid paper is second.
2. Ink properties
1. Ink leveling, in the printing process, the ink leveling is good, the gloss is good; the leveling is poor, easy to draw, poor gloss.
2. The fluidity of the ink, the fluidity of the ink is large, the size of the imprint is enlarged, the dots are enlarged, the ink layer is thin, the gloss is poor, the fluidity of the ink is small, the penetration can be reduced, the ink film is easily flattened, and the glossiness of the printed product high. But the fluidity of the ink is too small, the ink is not easy to transfer, which is not conducive to printing. Therefore, in order to obtain a better gloss, the fluidity of the ink should be controlled, and other printing conditions must be considered to increase the viscosity or reduce the fluidity, otherwise simply emphasizing the printing gloss will cause other quality problems.
3. The fineness of the ink, the roughness of the ink particles, prone to faults such as stacking during printing, the prints are also rough, diffuse reflection, and poor gloss. On the contrary, the gloss is better, and you should pay attention when choosing ink (especially gold ink and silver ink).
4. The viscosity of the ink can not be too large or too small, too large will peel off the blanket and the surface of the printed matter, drawing; too small, the imprint size will expand, the ink layer will become thin, affecting the gloss.
5. The drying form of the ink, the same ink volume uses different drying forms, and its gloss is also different. Generally, the oxidized conjunctival drying has a higher gloss than the permeation drying, because the ink condensate dried on the surface of the ink print has more connection material, and the permeation drying The ink printing material has less connection material on the surface. After the ink is transferred to the paper, the solvent part of the binder will penetrate into the paper at a faster speed. At the same time, the coating and paper fibers must absorb the binder. The rougher the paper, the greater the absorption capacity of the binder. The stronger. The binder is absorbed by the paper fiber before the oxidized conjunctiva is dried, and the remaining binder and pigment particles adhere to the surface of the paper, making the product dull and dull.
6. The amount of driers added to the ink. In addition to the drying performance of the ink itself, the amount of driers added to the ink is also a factor that determines the gloss of the blot. As the driers increase, the drying speed can be increased accordingly and the penetration time of the ink layer can be reduced. For example, the cobalt drier is mainly used to promote the oxidation of the conjunctiva. It should be properly selected. It dries quickly, the surface conjunctiva is smooth, and has the effect of increasing gloss. The loss of gloss is often due to the excessive drying time. The absorption of ink by the paper and the penetration of ink into the paper increase, resulting in the separation of the binder and the pigment. Some of the binder in the ink penetrates into the capillary holes of the paper, so that the binder is in The proportion on the paper surface is reduced, and if the penetration stage is ended as soon as possible, the gloss state of the dried ink layer can be improved. On the contrary, the surface of the ink film is diffused and dull.
7. Transparency of ink, ink with high transparency forms the ink film color layer, part of the incident light is reflected by the surface of the ink film, and the other part reaches the surface of the paper, and then reflected out, forming two color filters, this complex reflection mechanism is rich In order to achieve the effect of color, the gloss of the chromatic ink film formed by opaque pigments is only reflected by the surface, and the gloss effect is definitely not as good as that of transparent ink.
8. The gloss of the binder, the main components of the ink are the binder and the pigment. The gloss of the linking material is the main factor of whether the ink blot can produce gloss. The early ink binders were made of vegetable oils such as linseed oil, tung oil, catalpa oil, etc. The smoothness of the surface after the imprinted conjunctiva was not high, and it could only present a fatty film surface, forming diffuse reflection of the incident light, and the gloss of the imprint was more difference. The connecting material of the ink now uses resin as the main component, the surface smoothness after the imprinted conjunctiva is high, and the diffuse reflection of the incident light is reduced, so the gloss of the imprint is several times higher than that of the grease ink.
9. The viscosity of the ink is related to the adsorption force between the binder and the pigment. The viscosity of the ink is related to the adsorption force between the binder and the pigment. Increasing the viscosity will increase the adsorption between the two, so that the paper will adhere to the binder The absorption will be reduced accordingly, and the penetration will be reduced, the better the gloss, so the appropriate increase in viscosity in the ink can increase the gloss of the imprint.
10. The thickness of the ink layer, the total thickness of the ink layers on the surface of the printed sheet is closely related to the gloss. Generally, monochrome prints rarely have gloss. If they are overprinted, they will show gloss, so the thickness of each color ink layer is correct. Gloss has an effect. For example, a thicker ink layer can lay a foundation for the improvement of gloss, and more color registration can fill the paper surface, which can improve the gloss.
11. The emulsification of ink, emulsified ink must start to dry after the water evaporates, so the drying is delayed, and many small holes are formed on the surface of the ink layer, reducing the gloss of the imprint.
3. Printing pressure
Pressure is the key to good transfer of imprinting. Excessive pressure will enlarge the imprinting and weaken the gloss; too low pressure will make the imprinting unclear, which will cause dullness of the printed product. Therefore, under the premise of ensuring that the ink on the blanket can be correctly transferred to the printing material during offset printing, the minimum pressure should be used as far as possible to print out the print with good gloss.
Under the same paper and ink conditions, due to problems in the operation process, the gloss of the finished product after printing is often quite different. Under the premise of not considering the post-print glazing treatment, the following methods can be used to improve the gloss of the printed product:
1. Improve acidic wetting fluid. The acidic wetting fluid used in China for decades is mainly chromic acid and phosphoric acid. Although it has been diluted, the PH value is still between 3.5 and 5.6. The stronger the acidity, the greater the decomposition and corrosion of the ink binder and pigment, resulting in a rough surface of the imprinted film and reduced gloss. The research and development of the wetting fluid has made breakthroughs in recent years, such as Shanghai's "Lead Wetting Powder", which can be said to have a good effect. Today, China's offset printing wetting fluid has entered a new stage, but some printing The factory is still using the old formula.
2. Reduce ink emulsification. The excessive emulsification of ink in offset printing is mostly caused by water and ink in operation. The imprint looks very thick, but the ink molecules become oil-in-water. After drying, the gloss is extremely poor, and a series of other malfunction. Water ink is the most taboo practice in offset printing. To change this situation, in addition to the quality and technical education of the operator, it is recommended to use "Lead Wetting Powder" because the agent has better wetting performance. Even if the moisture content of the layout is small, it is not easy to get dirty. Not only facilitates operation, but also makes the finished product shiny.
3. Add auxiliary agent appropriately in the ink. Adding appropriate auxiliary agent in the ink can adjust the printing suitability of the ink, so as to print smoothly. Most of the adjuvants will have an adverse effect on the gloss of the finished product. For example: anti-sticking agent, the main raw material is six grain powder, after adding ink, the surface of the imprinted film layer becomes rough due to the precipitation of corn flour, and the gloss of the finished product is poor. Another example is the addition of No. 6 thinning ink, which not only increases the fluidity, but also increases the permeability of the blot on the paper, and also reduces the dryness, which is not good for the gloss of the blot. Therefore, the amount of the auxiliary agent added to the ink should not exceed 5%. If the gloss effect is considered, it should be placed less or not. But the fluorocarbon surfactant is different, it can prevent the surface defects such as orange peel and wrinkle in the ink layer, and can also improve the gloss of the printed surface.
4. Use dry oil correctly. For advanced high-gloss quick-drying inks, under normal temperature and humidity conditions, they already have sufficient drying capacity. Dry oil should be added in the following situations: one is when the temperature and humidity are low in winter; the other is that anti-sticking agent, de-tackifier, thin-adjusting ink, etc. should be added in the ink. Dry oil. In the process operation, the correct use of dry oil is very beneficial to the formation of gloss in the finished product. This is because it takes a certain amount of time for the paper to absorb the linking material. In this process, the linking material is coagulated as soon as possible until the conjunctiva is dry, which is the key to good gloss of the finished product.
5. Pay attention to dusting. Powder spraying, like ink, can also cause cohesion, especially in bags or barrels that are not well sealed. After spraying powder is wet, it aggregates into larger particles and sprays onto wet ink marks, making the surface of the ink layer rough and reduced In addition to the original gloss, pay attention to moisture protection. In addition, there is a heating device on the mechanism of the powder spraying device. When using powder spraying, it should be checked whether the heating device is malfunctioning.
6. Adjust the machine correctly. Whether the thickness of the imprinted ink layer reaches the standard also has an influence on the gloss. For example, the pressure regulation is poor, the dot expansion rate is high, the thickness of the ink layer does not reach the standard, and the gloss of the finished product is slightly worse. Therefore, it is necessary to adjust the pressure so that the expansion rate of the dots is controlled at about 15%. The printed ink layer of the product is thick, the layers are opened, and the gloss is also available.
7. Add Fan Lishui (No. 0 oil). This oil has a high viscosity and is thick in itself. It can adjust the ink concentration to thicken the thin ink and increase the gloss of the printed product.
8. Add bright light paste. The gloss paste is made of raw materials with high gloss, which can increase the gloss of the ink, but the amount should not be too large, otherwise it will reduce the drying speed of the ink, and the phenomenon of stickiness and drawing will occur, affecting the gloss.
9. Add desalting agent. When some inks are too dark and do not meet the requirements of spot color printing, they need to be lightened, which not only makes the ink lighter, but also improves the gloss of the printed product.
10. Add 19 # resin oil. When the ink fluidity and transfer performance are not good, it can be directly transferred into 19 # resin oil, which not only can improve the gloss of the ink, but also does not affect the multi-color overprint printing.
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