New light curing resin and formula for the hottest

2022-10-01
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New UV curing resins and formulas for plastic hard coatings

due to the growth of plastic materials in automotive, electronics, communications and other industries, plastic coatings have also developed rapidly in recent years

some common functions of plastic surface coatings are: coatings can play a good protective role on plastic surfaces and prevent mechanical wear; Paint can give plastic surface many decorative effects (high gloss, matte, hammer pattern, etc.); Coatings can also bring many functional effects to plastics, such as anti reflection, anti-static, etc. When emphasizing the protective function of coatings on plastic surfaces, it is necessary to develop corresponding high hardness coatings

due to the highly crosslinked structure and good physical and mechanical properties of the cured system, UV coating technology has been more and more applied in the fields of wood, furniture, architecture, printing and electronics, so as to provide a film with good performance and protect the substrate. But in general, the application of UV coatings in plastics is still relatively limited

at present, among plastic coatings, UV coatings are mainly used in, computers, MP3 players, cameras, household appliances and cosmetics packaging. In Asia, the demand for coatings in these application fields has reached about 16000 tons/year, with an annual growth rate of%. In Asia, Japan still dominates the market of UV plastic coatings, followed by China, which has become the second largest application market. However, at present, imported coating products still occupy the mainstream position in the Chinese market. Chinese local coating manufacturers are actively using the resources provided by raw material suppliers and equipment suppliers to independently develop coating systems with their own characteristics. South Korea has developed a very successful coating system in the field of vacuum coating for cosmetics packaging

the purpose of this paper is to put forward some typical problems encountered by coating manufacturers in the process of developing coatings, and to test the service performance of some new resin products in combination with these practical problems. Some common methods to evaluate the mechanical properties of paint film

pencil hardness

this method is most commonly used in testing because of the simple and convenient characteristics of pencil hardness. The pencils used in the test range from the hardest 9h to the softest 9b. H stands for hard, B for black, and Hb for hard and black pencils. The hardest is 9h, which is 8h, 7h, 6h, 5h, 4h, 3h, 2h and H. F means medium hardness; Then Hb, B, 2b, 3b, 4b, 5b, 6b, 7b, 8b, 9B are the softest pencils

when two different topcoats are applied to the same system, whether directly on the substrate or on the primer, pencil hardness can be used as a comparison means to measure the hardness of the paint film. However, the measurement result of pencil hardness is not absolute, and the part under the topcoat will also affect the final test result. For example, when the same paint is coated on different substrates, the hardness will be very different, so the pencil hardness test should be carried out under the same conditions, such as the same substrate and film thickness

rca detection

rca (coating wear resistance) detection is a relatively soft wear-resistant detection method (compared with the wear-resistant detection method used for wood floors or PVC gusset plates). The detection principle is that the weight of an object with a specific weight (usually 175g) is transferred to the paper tape contacting the object through a rubber wheel, and finally the wear test of the object is carried out by the paper tape. The test result is expressed by the accumulated number of turns of the paper bag when the primer is worn through. Since both primer and substrate often have colors, it is easy to distinguish directly with eyes

rca abrasion resistance test method is also very sensitive to the thickness of the paint film, so the two coatings must be compared under the same conditions

the medical community has long thought of the existence of silk fibroin paint. Generally speaking, the wear resistance requirements of RCA are between turns, and some manufacturers with high requirements will also reach 1000 turns

in the Chinese paint market, RCA testing is necessary, and sometimes other testing methods will be applied together. In other Asian countries, the most commonly used is the Taber wear test. RCA tester used for abrasion resistance testing of plastic coatings

Taber abrasion test

Taber abrasion tester is composed of a horizontal test disk for holding objects and two abrasion wheels. During the test, the horizontal test plate will rotate at a constant speed, and the wear of the tested object is detected by two wear wheels. Due to the constant speed and weight, the wear wheel can maintain a constant wear detection on the tested object. The commonly selected wear wheel is CS 10F model with a weight of 1000g

for plastic paint, Taber wear results are usually reflected in two ways: first, the number of revolutions required to wear through the paint film; Second, under a fixed number of revolutions, the change of paint film conditions, such as: the reduction of gloss, the degree of fog shadow, and the weight loss of paint film

steel ball detection

this is a fast detection method. By scratching the tested object back and forth with a steel ball at a constant force and speed, observe the changes of the surface

the judgment standard can be the change of the transparency of the paint film surface after a certain number of scratches, or the number of scratches when the paint film surface changes. Therefore, this method is often used when the substrate is transparent, such as PS, pet, TAC, etc

other internal testing methods

each manufacturer may have some testing standards formulated by itself. For example, some manufacturers may use rubber to wipe the surface of the paint film to characterize the strength of the film, but all these testing methods are trying to imitate the external conditions in actual application, so as to evaluate the performance of the paint. Flexibility and brittleness

the simple test of flexibility and brittleness is to bend the coated test sample and then observe whether there are cracks on the surface

other key requirements

adhesion

obtaining good adhesion on various substrates or primers is indeed a great challenge for coating manufacturers. Coating developers always hope to develop a coating product with good adhesion on common plastic substrates such as ABS, PC, BMC or polyolefins, as well as various primers (thermoplastic primer or two-component Pu primer). According to our experimental results, Various aluminum foundation make-up paints have particularly high requirements for adhesion. The test of adhesion is generally based on ISO 2409 standard, that is, the cross cut method, which means that the paint will not fall off. The adhesion test is generally carried out after UV curing, or a series of durability tests are carried out after UV curing, such as moisture resistance and heat resistance. In addition, observing whether the surface of the paint film has embrittlement or other changes after these durability tests can also reflect the adhesion from another side. Of course, the solvent in the spraying formula also has a great impact on the adhesion

the color of the coating does not change before and after curing

since the top coat is mostly varnish, the most ideal situation is that there is no color difference between the object before and after coating the top coat. The change of color mainly depends on three points:

-- the color of the coating system itself: the change of color can be measured by colorimeter before and after coating, which is usually expressed by labvalues. In the process of resin production, antioxidants, stabilizers, catalysts and other substances will have a great impact on the final product color. Therefore, for resin manufacturers, reducing the color of the resin itself is an important topic and the focus of future work

-- color change after long-term storage or exposure to light: that is, the so-called non yellowing has the characteristics of COFCO biochemical, Dacheng Group and other leading enterprises or outdoor durability. This is mainly due to the fact that the resin itself has some unstable structures to light, which will cause color changes after being irradiated by light. Generally, resins containing aromatic ring structures should be avoided, and aliphatic polyurethane acrylates have excellent performance in this regard. In addition, photoinitiators should also be carefully selected

-- on metal primers, some color darkening is caused by the bite of monomers in the formula such as HDDA, TPGDA or TMPTA on the primer. Therefore, in order to obtain good final effect, the current trend is to develop prepolymers without monomers. In addition, the solvent in the formula will also have an erosive effect on the primer, which should also be considered by DSM to create a sustainable solution worldwide. Surface condition

spraying requires a lot of adjustment skills to obtain a good surface effect. Formulation design and coating users need to deal with many surface defects, such as orange peel, fish eyes, and holes. The solution of all these problems requires a very fine adjustment of the coating system, such as adjusting the volatilization speed of the solvent system in the spraying process, not too fast to achieve a good leveling, but not too slow to prevent the incomplete volatilization of the solvent before light curing, which will affect the performance of the paint film

for the current plastic topcoat, physical drying and crosslinking curing are in two completely different stages. The first stage is usually the flash drying of the solvent at 60-80 degrees; The second stage is the crosslinking and curing of the coating itself at a lower temperature. Therefore, the surface condition of the coating in the first stage will also be maintained until after UV curing, which means that it is impossible to remove the surface defects produced in the first stage in the second stage

at present, the common surface defects in UV coatings, such as pitting, can be solved to the greatest extent by using oligomers 1, 2, 3, and satisfactory leveling can be achieved by selecting the appropriate solvent combination

to sum up, it is necessary to develop resin products with good spray workability, leveling and surface defects prevention, so as to facilitate the formulation development

conclusion: the hard coating used for plastic surface is a high-performance coating, which requires a comprehensive balance of color, hardness, wear resistance, flexibility and adhesion. In addition, the final construction method is spraying, and good surface effects such as leveling and gloss must be obtained

reprinted from: paint and ink

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