A new type of UV curable resin and its formulation

2022-07-24
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New UV curable resin and formula for plastic hard coatings due to the growth of the application of plastic materials in automobile, electronics, communication 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 role in protecting the plastic surface from mechanical wear; Paint can give plastic surface many decorative effects (high gloss, matte, hammer, etc.); Coatings can also bring many functional effects to plastics, such as anti reflection, anti-static, etc. When the protective function of coatings on plastic surface is emphasized, it is necessary to develop corresponding high hardness coatings

due to the high crosslinking 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 the 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 as the second largest application market. However, at present, imported coating products still occupy the mainstream position in the Chinese market. China's local coating manufacturers are actively using the resources provided by various raw material suppliers and equipment suppliers to independently develop coating systems with their own characteristics. 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 for evaluating the mechanical properties of paint film

pencil hardness

this method is the most commonly used in testing because the pencil hardness is simple and convenient. The pencils used for 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 and 9b are the softest pencils

when two different topcoats are applied to the same system, whether directly on the substrate or on the primer, the pencil hardness can be used as a comparison means to measure the hardness of the paint film. However, the measurement results of pencil hardness are not absolute, and the parts under the top coat will also affect the final test results. For example, the hardness shown when the same paint is coated on different substrates 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 test

rca (coating abrasion resistance) test is a relatively soft abrasion resistance test method (compared with the abrasion resistance test method used for wood floor or PVC gusset plate). The detection principle is that the weight of an object with a specific weight (usually 175g) is transferred to the paper tape that contacts the object to be tested through a rubber wheel, and finally the paper tape is used to carry out the abrasion test on the object to be tested. 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 color, it is easy to identify directly with eyes

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

for paints, the general RCA wear resistance requirements are between revolutions, and some manufacturers with high requirements will also reach 1000 revolutions

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 for abrasion resistance test of plastic coating

taber abrasion test

taber abrasion tester is composed of a horizontal test disc 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 will be detected by two wear wheels. Due to the constant speed and weight, the wearing wheel can maintain constant wear detection for the tested object. The commonly selected wearing wheel is CS 10F model with a weight of 1000g

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

steel wire ball detection

this is a fast detection method. The surface changes are observed by scratching the tested object back and forth with a steel wire ball at a constant force and speed

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 actual external conditions when it needs to be replaced at the first time, So as to evaluate the coating performance before the animal protection association has sued these companies. Flexibility and brittleness

simple flexibility and brittleness detection 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 and various primers (thermoplastic primer or two-component Pu primer). According to our experimental results, All kinds of aluminum foundation make-up paints have particularly high requirements for adhesion. The test of adhesion is generally based on ISO 2409 standard, i.e. cross cut method, which means that the paint will not fall off. The adhesion test is generally carried out after UV curing, or after UV curing, a series of durability tests, such as moisture resistance and heat resistance, are carried out. In addition, observing whether the surface of the paint film has any 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 most of the topcoats are varnishes, the ideal situation is that there is no color difference before and after coating the topcoat. 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, reducing the color of the resin itself is an important topic and the focus of future work for manufacturers who can reduce carbon emissions by manufacturing lightweight packaging with resin

color change after long-time storage or light exposure: that is, the so-called non yellowing 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 structure should be avoided, and aliphatic polyurethane acrylates have excellent performance in this regard. In addition, photoinitiators should also be carefully selected

on the metal primer, 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 aggressive effect on the primer, which should also be considered in this regard. Surface condition

spraying requires a lot of adjustment skills to obtain a good surface effect. Formulation design and coating users need to control and deal with many surface defects, such as orange peel, fish eye and hole explosion. The solution of all these problems requires fine adjustment of the coating system. For example, adjust the volatilization speed of the solvent system in the spraying process. Do not be too fast to achieve good leveling, but do not be too slow to prevent the incomplete volatilization of the solvent before UV curing from affecting the performance of the paint film

for the current plastic topcoat, physical drying and cross-linking curing are in two completely different stages. The first stage is usually the flash drying of the solvent at 6080 ℃; 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 generated in the first stage in the second stage

at present, the common surface defects in uvcoatings, such as pitting, can be solved to the greatest extent by using oligomers 1, 2 and 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 between 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

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