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| Analysis on the absorption and antifouling of polished tile |
Analysis on the absorption and antifouling of polished tile
Currently, common porcelain tiles in market have the same water absorption, but there still a big difference among them on antifouling. It shows the antifouling ability of polished tiles not only depend on closed porosity, but also other performance in terms of the construction of air hole, shape distribution and connect condition and so on. The reasons that make the antiflourin ability decrease is the following 2 aspects:
1. residual air hole in embryo
Polished porcelain tile is a combination of various crystal, crystal boundary, air hole and glass phase. It is burned through kiln to increase the density of embryo, but finally leave some air hole in it. When polished porcelain tile is made, the true porosity, apparent porosity and closed porosity in embryo will change along with the burning temporature.
As a result, when burned, the apparent porosity of polished porcelain will decline to 0, but the closed porosity will still above 8%. If we increase the burning temporature, we can only low down the apparent porosity, the closed porosity will even up after the disappear of apparent porosity. Then after polished, these closed porosity will exposed on the surface of bricks. So some pollutants will penetrate into the closed porosity and become a spot when they touch the surface of polished tiles.
2. small crack on the surface of polished tile
Among bricks which are rapidly burned under low temporature, glass phrase account for 50% to 60%, the others are Sio, Mullite and air hole. Since the expansion coefficient of Sio and glass phrase are largely different, glass phrase will generate crack under deep tensile stress when cooling if Sio particles are too large, the crack will even generated through the whole embryo. That¡¯s why there are some cracks in embryo when Sio contains too much water. In the process of polishing, embryo should be acted through preliminary grinding,fine grinding and polishing, then with large stress of snoop head, little cracks will expand to different level (eg. If the former cracks are too large, the embryo will break ). As a result, the surface of polished tile is full of small cracks and absorb pullutants.
At present, with the above defect, domestic manufacturing polished tile should apply a repellent to promot the ability of antifouling. As different repellent has different quality and ability of antifouling, it¡¯s necessary to fully realize repellent for polished tiles.
1. species
According to different solvent, repellent can be divided into oil-based anti-fouling agents and water-based anti-fouling agents and by appearance, repellent can be divided into liquid anti-fouling agents and solid anti-fouling agents. Currently, as wax-polishing machine become very common, makers prefer to use liquid and oil-base anti-fouling agents.
According to different product, antiflourin agent can be divided into WAXES, Latex and Silicones products. WAXES used to be popular because of low price, but it cant prevent pullution for long time, so its no longer popular now. Latex products belongs to water base, many makers cannot accept this product because the technology is not mature enough and the ability of antifouling cant catch up with oil-based antifouling agent. Silicones products solve the problems having in WAXES and Latex , so Silicones products become more and more popular now. For silicones product, it uses synthetic polymer to form a useful solid film along the open pore, then finally achieve antifouling by efficient pressure on surface.
2. function
The functions of antifouling agent are the following two aspects.
Keep tiles away from MTc and rubber mark when under construction. On the process of construction, sometimes MTc will penetrate into the surface of brick , when that happens , this brick is hard to clean.
Keep tiles away from ink, tea and shoe mark in daily life. Currently, many antifouling agents have ablitity to prevent ink, but most of them cant prevent PVc , shoe and rubber mark, and shoe mark is a problem must be solved under construction. When at work, workers usually use rubber hammer to knock bricks so as to balance the bricks, but this step will leave black mark onto them which similar as shoe marks. So antifouling agent with ability of preventing shoe mark is very necessary.
3. Quality and performance
To choose a good antifouring agent, we can follow these aspects:
(1). Antifouring effect. This aspect is the key one.
(2). The performance of preventing shoe mark, rubber mark and PVc.
(3). The drying speed of antifouring agent. If products dry too fast, we cant operate them. And if too slow, the quality will be influenced.
(4). Glossiness of polished tile. A good antifouling agent can not only promote the product¡¯s ability to prevent pollution, but also improve the glossiness of products.
(5). No harm to human body. Some markets use antifouling agent contains harmful chemical materials(eg. TOL,THMS...) which have irritative smell and harm effect to workers.
(6). No erosion effect to foam packaging materials. Some antifouling agents will have chemical reaction with foam packaging materials which will damage the appearance and performance of packaging materials.
Antifouling technic of polished tile
The antifouling principle of polished tile uses the pinciple of solid surface modification, which means people use absorption characteristics to change brick¡¯s construction and features on various surfaces. Antifoulant which is also named surface reactive materials will form a adsorption film on the surface of brick after modification. These films have hydrophobic nature and make bricks well antifloured. Nowadays, in antifouling field of polished tile, people commonly use silicone rubber and fluoropolymers as they have the advantage of low surface tension, high weather resistance, durability and chemical reactivity.
anti-fouling technology on Waxes, Organic coatings and surface hydrophobicity of active agent
Waxes and organic coatings are usually used as antifouling agent of polished tile, but lack of effect. Waxes can prevent pollutant, but as a coating material, a gas-tight tisseel, it has big surface tension and can¡¯t last long. When coated, Waxes can stop water or moisture from outside into the bricks, so as to achieve the function of antifouling. But according to Waxes¡¯ easy abrasion and time limited, it is hard to be cleaned. So Waxes coating is not a good way to prevent pollutant. In addition, organic coating will impact the glaze of the surface of bricks.
surface hydrophobicity active agent has low surface tension. Small molecule hydrophobicity active agent includes SA, palmitic acid, oleic acid, Naphthenic acid mixtures, abietic acid and their alkali metal salt water with big tension between 30 and 40mN m. When dealed, there will be a thin water-repellent layer with some antifouling effect. Since this thin layer is not tight enough, it may drop under external force or current rush, if that happen, bricks will lose the effect of antifouling, durability and the efficient of antifouling.
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Silicone anti-fouling technology
Surface energies is an very important factor on the surface antifouling of polished tile. Silicone rubber is an ideal antifouling treatment agent because of low surface tension ( down to 21-22mN m). Silicone is different from other common surface agent in preventing pollutant, it works through chemical reation with structure materials, then form a hydrophobic film with a molecle layer which can not only own hydrophobic nature of anti-adhension and breathability. With this technology, bricks will have some excellent feactures like clean, no dust, easy cleaning and scrubbability.
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Fluorinated and low surface energy antifouling technic
Fluorochemicals have very low surface energies, such as CFA, its surface tension is 10mN m, and the contact angle is 110:101 compared with Silicone Rubber, so fluorochemicals perform better in preventing pollutants. But fluorochemicals is too expensive and lack technology in porcelain fields, so it is not very commonly used. We are looking forward for this technology¡¯s coming more and more mature.
To promote antifouling ability of polished tile
1. Fomulate suitable burning temporature
Not only porosity impact the ability of antifouling, but also the constroutional closeness of pore. In the burning process, the number of small pore( less than 5 ¦Ì) will decrease and the volume of big pore (more than 30 ¦Ì) will increase, if the temporature continues to rise, the embryo will inflate to produce big pore (which is more than 60 ¦Ì) to make the surface very poor. So we must use polished tile with minimun small pore ( less than 15 ¦Ì) and forbidden bigger or connected pore to appear. Generally speaking, we can get this construction under higer temperature (higer than dense sintering temperature). In addition, properly extend the time on temperaturez zone between 1051 to 1150 ¡æ, this step can improve the density of embryo, lower closeness porosity of embryo and avoid crystal¡¯s upscaling.
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Control the fineness of blank
In the ball-milling, we should seriously control the fineness of blank, usually 250 blank shorts in 1%, and most sio particle are less than 40 ¦Ì so as to minimun the stress generated by the difference between sio particle and low-coefficient glass and the cracks in embryo when cooling. In addition, we should avoid small cracks which may generated when sio particles produce strong stress under 573¡æ.
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Focus on formular of embryo and crystal transformation
Good brick sintering and low WA are basic conditions for a polished tile with excellent antifouling ability.
According to the entoplasm, antifouling ability is also contact to fomular and calcination condition. If only control WA under 0.2%, it just shows we limit micro structure¡¯s porosity to some extent, but crystalline transformation will also impact the products. Or if only consider the antifouling angle and under the same WA, when burns more time, crystalline transformation will changed more, and the antifouling ability will better, SIO2 and AI203 will increase , high-temperature glass phase will rise, Kaolin residue crystalline phase will decrease and finnal antifouling ability of product will be better.
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Reasonable choose anti-fouling agents
The most common way to prevent pollutant is coating antifouling agent after polished. Currently , there are various brands of antifouling agent with different performance, for instance, some are slightly acid, good to prevent cement but bad to human body; some have strong covering power, good for premary antifouling effect, but cant last long; soe have good penetration power with good durability, but hard to clean unless washing agent or chemical solvent. So we should reasonable choose antifouling agents. In addition, it is better to dry the water with proper temperature in the surface before coating antifouling agents, so as to have a nice coating effect and get excellent antifouling effect.
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