The influence factors of floor coating adhesion are discussed

China Coatings Online News Information: For floor coating production, adhesion quality control is a primary task of floor coating quality control. Because no matter how well the floor coating is done, as long as there is an attachment problem, for the flooring products, everything else will lose value. How to do a good job in the process of floor coating adhesion control, this paper will be from the principle of floor attachment, the impact of various factors on floor adhesion, and then come up with an effective control of floor coating adhesion feasibility program.。 Principle of UV coating and substrate adhesionthe adhesion of primer and substrate is one of the key problems of UV wood floor coating. General wood substrates have a wealth of corrugated structure, UV coatings with esters, ether structure main, wood substrates have sufficient affinity. When the viscosity of the primer is not high, it can penetrate into the porous substrate, and form an anchoring structure after cross-link curing, which is very beneficial to improve adhesion.From the point of view of surface stress, the overall surface strength of UV coatings is often lower than the surface stress of polar high, hydro-friendly wood, so that UV coatings are easy to wet wood substrates, and under the thinness of wood fibers and micro-pores, rapid spread, this physical penetration is very beneficial to attachment improvement. On the other hand, wood structure contains a large number of hydroxyl, ether bonds, UV coating esters, ether structures may and wood fiber hydroxyl to form a "hydrogen bond" force, to promote adhesion. This hydrogen bond can be between the chemical bond energy and molecules between Van der Wally, the traditional PU coating in many substrates have a good attachment, there is a great reason for the role of hydrogen bond.from the above two aspects, UV coating on the wood flooring material attachment should be no difficulty, but why the real production practice process, will often occur the problem of poor attachment? This is to say that the UV coating curing process occurred in the contraction stress.。 UV before curing is mainly active monomer and lymer, relative density between 0.8-0.9, when it is exposed to ultraviolet light, cross-curing occurs, the density of the membrane layer generally increased, membrane volume contraction. Because in-film curing contraction does not occur uniformly, there is both a contraction in the direction of film thickness and a lateral contraction. The specific shrinkage process is shown in Figure 1-1 as follows: In fact, the contraction of UV coatings in the curing process does not necessarily lead to problems between UV coatings and wood substrates. UV coating from receiving ultraviolet light exposure began to carry out free-based polymerization, after the initial 0.2 seconds or so of induction period, the paint internal polymer and monomer began to quickly cross-link, this crosslink is three-dimensional network format cross-linking, because all reaction chain segments in the coating The beginning of the membrane is free to swim, as "fish in the water" free contact with the new cross-linking chain segment, molecular weight continues to increase, this initial stage due to the paint viscosity is low, the chain segment of the "swimming is not hindered, so the reaction speed is very fast; Cross-linking reaction to the medium
period, the system viscosity began to increase, in the coating film began to form a number of mesh-like nodes, in these nodes, the coating film began to initially harden, the chain segment swim here, will be hindered, UV curing process, paint The tendency to increase the volume of the membrane will be limited at these points, and a large number of "internal stresses" will gradually gather inside the coating film, which, if not released during the curing process, will continue to release excess internal stress after curing is completed, and this "internal stress" Late release is very harmful to the attachment of UV coatings to wood substrates. This is also many early floor customers reflect the "just finished floor, test UV coating and wood substrate attachment is able, why put overnight, retest adhesion is worse?" "The root cause.reduce the negative effects of internal stress on attachment during UV coating curing?, how to prevent or UV coating curing process to produce internal stress on the negative impact of attachment?First of all, from the formulation point of view of coating products, from the formulation design stage of UV coatings, according to the curing shrinkage rate of different UV lymers and active monomers, the rigid and flexible groups are reasonably matched; And multi-official monomer, balance the system viscosity, paint film hardness and other physical and chemical indicators requirements, so that UV coatings in more time to have greater cross-linking freedom and stress release space, so that in the reaction stage, not to a collection of excessive internal stress resulting in poor attachment., measures can be taken to reduce the internal stress caused by UV curing from the on-site construction phase. For example, for some UV coatings, can be used in turn half-dry, and finally all-dry curing mode, in order to reduce the internal stress of UV curing, UV coating can also be heated and infrared heating, so that the temperature of the coating increases, when the coating temperature exceeds the glass transition temperature Tg of the micropolymer node, these mesh nodes are no longer solid, but more fluid semi-fluid, UV coating curing resulting in internal stress can be effectively released, so as to get better properties. This is also why the floor coating and wood substrate adhesion obtained by summer UV coatings are significantly better than winter adhesion. Winter due to lower ambient temperature, coating temperature, roller coating equipment temperature is significantly lower than in summer, which will make the "micro-cluster nodes" of the degree of hardening, these nodes on the chain segment growth of the blocking effect is more obvious, resulting in the final curing of the coating after the collection of internal stress rapidly increased, coating rigidity is too large, and wood substrate adhesion due to the "internal stress" of the late release and difference.The adhesion factors and response measures of the floor UV coating process From the current process of wood flooring UV coating, most flooring production enterprises have reached the standardized configuration of the coating line on nine floors, this coating configuration can meet the production requirements of most floor products (whether it is flat products, antique products, or brushed floor products), we take this nine-bottom three-sided production process as an example. For floor UV coating, the effect on the final product adhesion of the floor is the greatest, the highest frequency problems are mainly three types of problems:
1) UV coating on the substrate attachment is not good, 2) UV coating between the poor attachment, 3) water-based color layer and wood substrate attachment is not good.below, we analyze these three issues: 1, UV coating and wood substrate attachment adverse causes and response measuresIn this case, water-based colorants and UV coatings do not penetrate and adhere to the wood surface easily, resulting in poor UV coating and wood substrate attachment. For this situation, it is generally appropriate to control the moisture content of wood in the front-end process (8-12), specifically to the floor products to the customer geographical balance water content is accurate; Attached reinforced primer to solve
floor front polishing is also
to be appropriate, not suitable for excessive polishing, excessive polishing will lead to a large increase in the concentration of water-like coloring in the back channel when coloring, cost increases, attachment difficulties also greatly increased.the concentration of colors (including water-like coloring and slurry) in water-dependent colorants is too large, resulting in poor attachment. When the wood is lightly colored, the incoming ultraviolet light can pass through the UV coating, except for the part absorbed by the light trigger, about 50% of the UV light can still be re-reflected back by the substrate, so that the UV attachment primer can be accepted to about 1 50% of the UV incoming light energy, so that the bottom layer attached to the primer and the surface layer to accept the UV light energy gap will not be very large, the bottom can also achieve a better
cross-linking degree; The suction color is heavier, wood and UV contact part of the color is close to black, at this time, the incoming UV, light energy through the UV coating, as shown in Figure 2, in addition to the light energy consumed by the light trigger molecules, there is still about 50% of the light energy can reach the dark wood, but because of At this time the wood part of the color is very dark, absorbing most of the UV light energy, resulting in the UV light energy should be reflected back to the UV coating is gone, thus directly affecting the bottom of the UV attached primer can not absorb enough UV light energy, cross-linking degree is seriously weakened, the bottom curing is insufficient, Thus, the final performance of the same in the light-color substrate UV attachment primer, in the dark substrate, attachment significantly worse.primer is not selected properly. Floor processing manufacturers sometimes in order to meet customer requirements for flooring product hardness or wear resistance, in the selection of the first UV primer, only hardness support or wear support as the only consideration factor, then, the brittleness of the primer is too large, failed to provide considerable flexibility to adapt to the wood floor in the end consumer's home may change, most likely to bring paint peeling from the floor substrate or the risk of collapse.for the above three factors, in floor production, it is necessary to start from the front-end process control, including moisture content, coloring process, the choice of attached primer and other aspects of comprehensive consideration. Wood moisture content is controlled within 8-12%, when producing dark flooring, choose UV attachment primers with better attachment and deep curing, and for heavier tree species, you can choose the attachment primer corresponding to which the wood can have an effective cross-linking reaction, and if necessary, add 1-2% UV hardener to the UV attachment primer to enhance the deep curing effect and cross-linking degree to obtain a more stable flooring.2, UV coating layer between the causes of poor attachment and response measures the bottom / paint curing degree is not appropriate UV primer in UV curing, if the process does not require sand curing excessive, the surface is too dry, will lead to the rear UV coating between the layer binding problems. This is because, at this time, after the forecor UV primer over-curing, the reactive substrate of the surface of the paint film is basically gone, the UV coating of the rear channel can not produce a chemical bonding reaction with the front channel UV primer, the inter-layer binding force is only the inter-molecular force, far less than the chemical bonding force inside the coating film, thus prone to poor inter-layer attachment. In the process of sanding, if the primer is not dry well, sand belt sanding a certain square floor, gravel is not completely dry paint particles, these paint particles in the sand belt sanding behind the floor will be covered in the floor surface, these paint particles will become a bad point of interlayer attachment, resulting in poor interlayer attachment. In the process that requires sanding, if the primer cures too much, the paint film is too hard, the sand belt wears out very quickly, resulting in a period of time, the sand belt on the primer basically loses the polishing effect, resulting in poor inter-layer attachment.Response:
For these factors, it is recommended that the primer remain sufficiently sticky in the non-sanding process, while in the process where sanding is required, the drying degree of the primer is not sticky, the nails are lightly scratched white marks is appropriate, of course, these recommendations are generally referred to, depending on the product and process, depending on the actual situation at the coating site.or improper dust removal. After the sand primer curing is completed, the primer sander is required to sand the primer surface, remove the particles, get a smoother surface effect, and at the same time, the paint film surface to maintain sufficient microscopic roughness to benefit the penetration attachment of the next UV coating. And when the sander is not properly manipulated or the sand belt is not replaced in time, the floor sand is not sufficient or the dust produced by the sand is not cleared in time and effectively, it will be easy to produce poor inter-layer attachment.Response measures:
regularly check the effect of the sand plate surface, the sander parameters to be corrected in a timely manner to ensure good sand, and can be installed after the sander 3 axis dust removal device, and equipped with artificial blowing dust, to avoid the surface sand after the powder particles affect the back channel attachment.amount of UV primer coating after the wear-resistant substrate is not enough.
UV wear primer is a product developed to improve the long-term durability of floor products, the product also has a large number of large particle size inorminated particles, these particles on the floor even distribution is the guarantee of floor wear resistance. These wear-resistant particles need to be completely covered by the back primer, can be sanded, otherwise, when the wear-resistant particles are not covered by the rear UV primer resin, sand, these inorderable particles will be completely exposed to the surface of the paint film, in these exposed inorminated particle points, the rear UV coating can not be chemically bonded with it, so that these points, the adhesion layer of the paint film is significantly reduced, resulting in poor attachment.response:
After wear-resistant primers, it is best to ensure that there are 2 to UV sand primer coating, the ratio of the amount of coating is best controlled at ≥1:1.8, i.e. if wear-resistant The amount of primer coating is 20g/m2, then the coating volume of the UV sand primer in the back two lanes is best controlled at (36-40) g/m2, otherwise, the risk of poor inter-layer attachment will be greatly increased.· UV substrate/face paint for coloring, color addition ratio is not right.
UV color repair refers to some floor manufacturers in order to the effect of floor color, in UV primer or finish to add color refinement to secondary coloring to achieve a better color effect of the process. General UV coloring is the use of color, coloring addition ratio from 5% to 30% or more indeterminate. This technique was most prevalent in the 1990s and is becoming less common. Color fine particles are very easy to absorb UV light, for the need to absorb UV light to produce free-based light triggers, these fine particles are huge competitors, when the UV primer or paint added color essence content of more than a certain ratio, such as 10%, the underlying trigger molecules can not absorb enough UV light, and then the bottom coating can trigger UV cross-linking reaction activity free The base concentration is much lower than the coating surface, which will lead to the colored UV coating surface has been dried, while the bottom layer is only very low cross-linking density, so that the color-added bottom and its cross-linking strength with the previous primer is much lower than the surface cross-linking strength, thus forming the obvious internal stress shown in Figure 1, the final performance of the color coating and its substrate layer attachment is poor.Response:
Avoid one-time coloring too heavy, each color adder is not easy to add more than 8%, in the case of must add color and color ratio is high, you can add 3-5% of the deep curing agent in the paint, supplemented by the drying of the lamp and mercury lamp, using the penetration capacity of long-wave UV to enhance the finisher / paint bottom curing process