Water-based container coating standards, performance requirements, construction technology and development status quo.

Since its inception in China in the 1980s, container manufacturing industry after more than 30 years of development, has become a mature industry, each year there are 2.5 million to 3 million TEU of new container demand, the amount of paint required is 180,000 to 220,000 tons, basically solvent-based coatings, about 95%. The traditional industrial coating contains a large number of organic solvents, solvents in the construction and drying process are mostly waved out, which not only seriously pollutes the environment and harms human health, but also caused a great waste of resources. According to the data, steel products and their facilities in the coating process volatile VOC total of about 20% to 25% of the global VOC total, has become one of the main sources of air pollution

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years, under the impetus of national policies, various places have promulgated environmental protection policies on "oil-to-water". As for the container coatings industry, in 2017 China Container Industry Association in the industry to enforce the "no oil push water" policy and set industry standards, "box paint" has since entered the era of water-based coatings. After nearly two years of development, "box paint" has also been developed from the "two strong stand-by" to the "group male" era, which refers to Dewey and KCC, group male refers to Zhong Tu chemical industry, COSCO Kansi, Mecca, Settai, Haihong, Haoli, Chenyang and other enterprises.
water-based container coating matching
according to industry standards, the current body paint system is generally used in the "3 plus 2" supporting way, of which "3" refers to the outer supporting three-way paint, respectively, two-part epoxy-rich zinc primer, single/double-part epoxy intermediate paint and acrylic exterior paint; For intermediate paint, there is a choice of single parts, there are two parts.
water-based epoxy zinc-rich coating
due to the presence of zinc powder, water-based epoxy zinc-rich coating can effectively cathode protection of the box, delay the progress of tank corrosion, to prevent the paint film caused by bumps off, so the system has been unanimously recognized by the east of the box.
water-based epoxy zinc-rich coatings, the main components include epoxy resin, curing agents, zinc powder and a variety of additives, lively metal zinc powder can be chemically react with water, so there is zinc powder in the components, can not contain moisture, and Epoxy resins and curing agents in epoxy coatings are also not allowed in one part, so there are 2 ideas for designing the formula (zinc powder and epoxy resin in one part; zinc powder and amine curing agent in one part).
because the water-based epoxy zinc-rich coating is the main coating to provide corrosion protection to the box, so the anti-corrosion performance of the product, mechanical performance as the main point of formulation design, while focusing on the construction performance.
water-based interior paint
the main formulation system of water-based inner paint is: water-based epoxy interior paint, water-based acrylic epoxy interior paint 2 kinds.
water-like epoxy interior paint. The system is the original solvent-based system of paint water-based solutions, the main groups are divided into water-based epoxy emulsion, water-based epoxy curing agent, rust-proof fillers, pigments, functional fillers and so on. Considering the stability of the system, the general use of self-emulsified epoxy emulsion, but at present it seems that most of the resin produced by domestic enterprises have some room for improvement.
water-based curing agents, the current paint suppliers are very different, but from the perspective of corrosion protection, water solubility is very good, low reaction activity of curing agents are not suitable for water-based container paint. Due to the introduction of hydro-based groups, the corrosion resistance of water-based coatings is not as good as solvent-based under the same conditions.
water-based acrylic epoxy interior paint. The system generally uses special acrylic resin as the main resin, and then introduces liquid epoxy for hybridization. The advantages of the formulation system is relatively low cost, but considering the anti-corrosion factors, the current market share of more than 80% of the mainstream paint suppliers, did not choose the system.
water-based intermediate paint
the main formulation system of water-based intermediate paint are: water-based epoxy intermediate paint, water-based acrylic epoxy intermediate paint, water-based acrylic intermediate paint 3 kinds.
water-based epoxy intermediate paint, water-based acrylic epoxy intermediate paint formula design ideas and water-based interior paint similar. The main resin of water-based acrylic intermediate paint is a high relative molecular quality acrylic emulsion, because acrylic emulsion and epoxy emulsion cost difference is huge, the cost advantage of the formulation system is obvious, but with the improvement of domestic epoxy emulsion performance, the cost advantage has a tendency to decrease.
acrylic finish
water-based acrylic finish is divided into pure acrylic emulsion, silicone emulsion and phenylpropyl emulsion due to differences in acrylic emulsion monosomes.
water-based acrylic paint is mainly to give the paint film excellent appearance, high weather resistance and water resistance and other properties. The weather resistance, water resistance and soil resistance of silicone propylene emulsion are better than the other 2 kinds of emulsions, but because of the introduction of silane, the cost is higher;
acrylic paint in addition to emulsion parts, pigments are also an important part of the group. From an environmental point of view, the pigments currently used are heavy metal-free products, but some pigment stability has certain requirements for pH, so the formulation design needs to confirm and process the pH requirements of each pigment.
water-based container coating performance requirements and related standards
long-term paint film performance
long-term paint film performance mainly includes corrosion resistance, mechanical performance, weather resistance 3 aspects. The more authoritative test standard is the IICL test carried out by KTA laboratory, and the requirements for the long-term performance of paint film in JH/TE08-2015 "Container Water-based Coating Testing Methods and Acceptance Standards" developed by the China Container Association (CCIA) are mainly referenced for the long-term performance of the paint film.
different from the internal and external supporting systems, the test process method is also different, the specific process is shown in the following diagram.
paint film acceptance standards and initial water resistance requirements
paint film acceptance is mainly on the paint film hanging state, pinhole / dark bubble state, color appearance, dew, etc. to investigate. The JH/TE08-2015 organization of the Container Association has made specific specifications for the requirements of film thickness, adhesion, appearance, etc., as the industry's key reference standards, and some of the box east also has their own company's specific acceptance standards, respectively, the internal control indicators set. This article describes only the key items encountered in the actual application.
pinholes, dark bubbles
because of the emulsifying agent and other surfactants, water-based coatings are more likely to produce bubbles, the performance of the film is pinholes, dark bubbles; At present, the main treatment method is to rely on the addition of additives to achieve, so that the cost of coatings has been greatly increased.
water resistance in the
mainly includes the initial water resistance outside the box and the water splashing experiment in the tank 2 aspects. Among them, the initial water resistance outside the box mainly for the container after the line of the weather continued to rain, the dryness of the paint film, the initial cross-link density, paint film water-soluble substance content, etc. put forward higher requirements;
water-based container coating construction process introduction
"three-point paint, seven-point construction", there is no good construction of water-based paint, even if the anti-corrosion performance is very good will not be received by the market, for water-based container coatings, especially so.
solvent-based container coating into water-based container coating, the biggest change is: three spray one baking into three spray three baking, at the same time because the water-based coating on the construction of temperature, humidity, wind speed and other requirements are higher, so the overall layout of the spray line changes greatly. Typical coating line layout (sometimes adjusted according to the actual situation of the coating position order) is: workshop sanding, primer coating and baking→ (forming, parting, assembly) → (secondary sanding, de-oiling) →heated and pre-coated primer→ watery epoxy zinc-rich primer coating → primer flat→ primer → cooling→ And interior paint coating →low flat→ middle paint oven →coaling→ paint coating→ cooling→ online repair →coal oven→ cooling → (wood flooring and finished work station) →strate paint coating →low flat→ rack drying → cooling→ finish inspection.
problems that can be encountered in each station are as follows.
heating and cooling work space
is mainly to ensure that the box temperature before spraying can not be too high or too low, such as more than 40 degrees C spraying, very easy to occur rough and other problems, such as less than 15 degrees C, but also very easy to occur hanging and other problems.
flattening work
can make the wet film part of the moisture volatile, to avoid direct access to the oven high temperature heating. Therefore, in order to ensure the volatilization of part of the water, the position needs to ensure a certain wind speed and temperature, wind speed and temperature too low or too high are very easy to produce bubbles, pinholes, hanging and other paint diseases.
basting room work place
oven temperature is best for the gradient rise mode, the optimal way is to set low, high temperature oven, to avoid just finished construction of water-based paint directly into the high temperature oven, the appearance of paint film is scorched, the internal generation of honeycomb pinholes and other paint diseases;
Coating station
because water-based paint atomization is not solvent-based paint good, so need to choose a small caliber nozzle, spray pressure needs to be appropriately improved, while spray gun distance control in more than 35cm, otherwise the paint film is very easy to produce pinholes, dark bubbles and other paint diseases, thereby negatively affecting corrosion prevention.
The main problem of water-based container coatings
the supply of raw materials
resins, additives and other high-value-added raw materials are mainly supplied by large foreign companies, because large international companies in water-based coatings technology for decades of technical accumulation, have some application experience, but this also provides a domestic technical enterprises a "sky high bird fly" market environment.
problem of high energy consumption
Compared with the use of three-spray-one-baking and fast-drying thinners in the original solvent-based system, the water-based system can only adjust the temperature and humidity by external heating and energy consumption. However, with the further promotion of clean energy in China, the application prospects of water-based coatings with low VOC emissions are more broad.
water treatment
because water-based coatings contain a certain amount of water-soluble substances, wastewater from water-based spraying processes is more difficult to treat than solvent-based wastewater. However, relatively speaking, container coating concentration is very high, sewage can be centralized treatment.
The control problem of paint disease
because water-based paint is more sensitive to temperature, humidity, gun mouth wear, etc. , with the change of temperature if not timely adjustment of the painting process, it is very easy to occur rough and hanging phenomenon. But at present, the mainstream water-based container coating suppliers have found a set of on-site control means to predict related problems, to prevent the occurrence of batch problems, resulting in greater losses.
Conclusion
The current large-scale use of water-based container coatings, for the large-scale application of industrial coatings water-based, with the gradual accumulation of technical knowledge of coating research and development engineers, the expansion of raw materials technical performance, the further improvement of the coating process, water-based industrial coatings will further mature, thus making a great contribution to the greening of the coating industry.
source: Water-based large platform
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