Traditionally, summer clothes are made from fabrics light colors. It is believed that light-colored clothing reflects Sun rays, and the person is not so hot in the sun. However, experts strongly recommend wearing dark clothes on hot sunny days. It is she who protects our skin from harmful effects. ultraviolet rays capable of causing skin cancer.

People who want to protect themselves from harmful ultraviolet rays should dress in dark clothes, not bright Hawaiian shirts, experts say. Yellow shirts provide the least protection from the sun. Few would think of wearing black or navy on a hot sunny day, but scientists from the University of Catalonia, Spain, advise choosing these colors. “The color of the fabric has a tremendous influence on its protective properties from ultraviolet radiation”, - says the author of the study, Dr. Ascension Riva (Ascension Riva).

Traditional warm weather white and yellow colors put a person at greater risk of developing skin cancer, scientists say. And darker and more saturated colors absorb the sun's rays better. Dark blue and red colors are especially good in this aspect - they protect the skin best of all. The scientists wrote about this in the pages of the journal Industrial and Engineering Chemistry. In the course of work, they dyed the same cotton fabric in various shades red, blue and yellow flowers and then measured the ability of each sample to absorb ultraviolet rays.

Most people who go to resorts rely on clothing to protect themselves from the scorching sun, although regular sunscreen would suffice. Keep in mind that white T-shirts and tight-fitting tank tops, as well as wet bathing suits, do not protect well from ultraviolet rays. Scientists believe that this information can be useful not only to consumers, but also to clothing manufacturers to create products that can effectively protect from the sun.

Guzhenko Artyom

In this work, the student is trying to find out whether the black color really attracts the sun's rays more strongly, and the white one repels them.

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Research work on the topic "Black or White?"

Head: Ovsyannikova M.N.,

Primary school teacher

One hot summer day, Mom and Dad and I decided to go for a walk. I put on a black T-shirt and a dark cap, but my mother said that I would be hot in these clothes, since the black color attracts the sun's rays more. I, of course, listened to my mother and changed into light clothes, but decided to think about this issue. Why then do people with black skin color live in African countries, because they must be very hot. And why do polar bears live in the cold north, probably they are cold?

Problem

Is not it White color reflects the sun's rays, and black "attracts" them?

Hypotheses

Perhaps the rays "do not see" the white color?

Let's assume that dark clothes are just brighter and more noticeable.

Let's assume that this is just a superstitious omen.

Target

Find out if the black color really attracts the sun's rays more strongly, and the white one repels them.

Tasks

Get acquainted with additional literature and Internet materials on this issue;

Contact a physics teacher for advice;

Conduct an experiment to confirm or refute this issue;

Prepare a presentation - a report on the work done.

Theoretical part

First, I decided to find out why people with black skin live in Africa. If black attracts the sun's rays more strongly, then you will not envy these people ...

From books and encyclopedias, I learned that according to an ancient legend, before all people had black skin. One day they discovered a lake with water that stained a person white, which was no longer washed off after. People went to this lake and, having plunged into it, acquired a white skin color. When the turn came to the inhabitants of Africa, there was already so little water left in the lake that they could dip only the palms of their hands and feet into the water. That's why Africans are black.

There is another explanation why there are people with black skin in hot countries, which is more like truth than legend.

It turns out that the skin of such people is rich in melanins, that is, substances that are found in the skin, human tissues, hair, and even the retina of the eye. Melanins are widely distributed in plant and animal tissues. They determine the color of the skin and hair, for example, the color of horses, the color of bird feathers, and fish scales. Melanins also absorb ultraviolet rays and, accordingly, protect tissues from burns. That is, nature itself figured out how to protect the inhabitants of hot countries from burns and made them black .... So, people with dark skin color are better protected from ultraviolet radiation, and not from light or heat. That's the whole question...

But why do polar bears live in the cold north? It is very cold in the habitat of these predators, so every ray of sunlight that gives warmth is valuable. BUT white color bears' fur must reflect light well - dark wool would heat up much better. But then the bear among the ice and snow would be visible from afar. There is no one to be afraid of a predator - with its size, it simply has no enemies. After the ban on hunting polar bears, they stopped being afraid of people. But camouflage on the hunt is very much needed. Indeed, among the snow-white landscape, only black eyes, nose and lips give out a bear approaching prey.

It turns out that the skin polar bear black! But how does light make its way to the body through a thick fur coat? In fact, the hairs are hollow (empty) inside, and the rays easily reach the black skin, to which they transfer heat.

From additional literature and from a physics teacher, I learned that all colors found in nature are divided into achromatic (colorless) and chromatic (colored).

Achromatic include white and black, as well as all gray colors, which are obtained by mixing white and black colors. There are no achromatic colors in the spectrum. In nature, there are no such bodies that would completely reflect the entire light flux falling on them, and all bodies absorb light to one degree or another.

Black and white colors reflect light differently. Magnesium oxide powder, which is the whitest object, has the strongest reflection.

But black velvet absorbs light best, it seems to us the blackest object.

Practical part

In order to make sure that dark-colored surfaces absorb light better, we will conduct an experiment.

We will need two plastic bottles with screw caps. We paint one bottle black, wrap the other with white tape. Let's hang the bottles with their necks down, put them between them. table lamp. It should be located quite close to the bottles, on equal distance from each.

With an awl, we will make holes in the plugs, insert transparent hoses into them. We hang the free ends of the hoses at the level of the bottom of the bottles. As a result, each bottle with a hose should resemble English letter U.

Now the resulting structure must be filled with water. Remove the bottles, disconnect the hoses. Pour water into the first hose to half, pour it into a bottle. For clarity, add potassium permanganate to the water. We twist the cork, insert the hose and hang the bottle. Fluid will fill the bottom of the hose. We will do the same with the second bottle. When the whole structure takes its initial position, the liquids in the two hoses should be at the same level. Turn on the lamp and see what happens.

Result

After turning on the lamp, almost immediately the water began to move in the hose, which is connected to the black bottle. She climbed up the hose and began to go outside. The water from the tube attached to the white bottle rose slightly. What follows from this? The switched on lamp heats the bottles and the air in them. When heated, the air expands and pushes against the water in the hose. Under air pressure, it rises and reaches the tip of the hose the faster, the faster the air heats up, and, consequently, the surface of the bottle itself. From experience it can be seen that the first to reach the finish line was water from a hose connected to a black bottle. In addition to color, the bottles did not differ in anything, the experimental conditions for them were the same. It follows that black surfaces heat up faster.

conclusions

Thus, the hypotheses that the rays "do not see" the white color, that dark clothes are simply brighter and more noticeable, or that this is just a superstitious omen, have not been confirmed.

As a result of the experiment, I found out that black absorbs light better than white. So really hot sunny weather you need to wear light-colored clothes.

Practical significance

The materials of the work can be used in the lessons of the surrounding world and for conversations on the prevention of sun or heat stroke with children in a summer health camp. ;

It is known that surfaces painted with ordinary black paint absorb about 85% of the light falling on them. But a newly developed metamaterial with a complex surface can absorb about 99% of the light falling on it, so the term “blacker than black” is quite usable in relation to this material.

This metamaterial, which has optical properties described by hyperbolic dependencies, has a very low reflectance, which can be used to create highly efficient solar panels, photo sensors and new stealth technologies.

Researchers from Purdue University and Norfolk state university(Norfolk State University), headed by Evgeny Narimanov, made new material using silver nanowires grown on the surface of an aluminum plate. After examining the optical properties of the resulting metamaterial, the scientists found that, despite the fact that both silver and aluminum absorb light poorly, the surface of the material absorbs about 80% of the incident light.

After that, applying some technological tricks, the scientists made it so that the strictly ordered surface of the material was covered in abundance with cracks and defects, which, as it was calculated, drastically reduced the reflection coefficient. Further experiments showed that such a “grooved” metamaterial is capable of absorbing 99% of the incident light, but moreover, such a radiation absorption coefficient is preserved in almost the entire range of electromagnetic waves.

As the scientists explained, the low reflectivity of the new material is due to the superposition of the hyperbolic optical properties of the original material with the unpredictable properties of defects, which greatly increased the “depth” of the hyperbolic law.

The researchers believe that the new metamaterial will serve as a prototype for the creation of new materials that will effectively absorb all types of electromagnetic radiation. Since light absorption plays a key role in the efficiency of solar cells and other technologies, the researchers plan to conduct further work, focusing on the direction of solar energy.

Comments:

UV curing ink contains substances that react to exposure to ultraviolet radiation and therefore air dry. Such a colorful material is used for various kinds printing, for example, offset, flex, screen, to reproduce raster graphics. It is applied to any surface - paper, plastic, polyethylene, thick or thin layer.

During the printing process, UV lamps are used, which fix the ink applied to the product. Some colorful materials, which cure when exposed to ultraviolet rays, are toxic and should not be printed on food packaging. But during drying, they do not emit solvents into the air, unlike solvent formulations. However, when using lamps, ozone is released, which can be toxic if its concentration in the air is high.

Paint features

UV-curing paint differs from conventional solvent-based formulations in its ability to dry and "set" almost instantly. Other Features of UV Coloring Materials:

• rigid structure;
• more viscous, sticky;
• resistant to moisture;
• does not rub off as quickly as solvent paints;
• hardens (dries) only under the influence of UV radiation.

As part of UV-curable inks:

• a pigment or dye that gives the base color to the coating;
• specialized liquid binder, which turns into a solid film, polymerizes under the influence of UV rays;
• photoinitiator involved in chemical reaction polymerization or curing of the paint layer;
• UV hardener are oligomers, which are viscous substances that harden under the influence of ultraviolet light;
• monomers - solvents, vegetable oils;
• additives, waxes and fillers.

On a note! The coloring composition is a powder of curable polymers that is heated, melted and forms a strong film on paper, plastic or wood.

An interesting feature of ultraviolet curing paints is that the layer is fixed faster on a white material, and slower on a dark one, because a light background repels UV radiation, while a black one, on the contrary, absorbs it.

Curing methods

The last stage in obtaining a layer of paintwork material is drying. The dispersed medium in the process of drying powder varnishes and paints is air. The film is obtained because the solid polymer particles in the composition of the material form a strong bond, first melt, then cure. The coloring composition heats up to 110 degrees and hardens in a matter of seconds.

UV Sources

The optimization of the curing process depends on the choice of UV emitter. Sources of UV light can be:

• electrodeless, LED, quartz emitters;
• mercury lamps;
• fluorescent, xenon lighting devices;
• Led UV drying lamps.

The main rule when choosing a paint curing machine is that the frequency of the device's radiation must match the absorption frequency of the photoinitiator, which is responsible for the optimal dose of UV rays and the ability of coloring materials to enter into a chemical reaction.

For powder curing paintwork materials wide spectrum lamps can also be used, but they have significant drawbacks:

• energy consumption;
• toxicity.

Attention! These devices, when heated, release a large amount of ozone into the air, which adversely affects health.

Coating quality

The curable polymers in the composition of paints and varnishes form a durable film during the drying process. The thickness of the layer does not affect the quality of the result. paint material:

• lies flat;
• does not spread beyond the boundaries of the image;
• distributed evenly.

Quality is affected by:

• a coloring composition, which includes a pigment, a diluent, a resin, a photoinitiator, fillers, a synergist;
• painted surface;
• the conditions under which painting takes place;
• radiation dose;
• type of UV device;
• the distance between the lamps and from the radiation source to the substrate.

The colorful coating is durable, resistant to moisture, does not fade under the influence of sunlight, other radiation, so even full-color images applied with UV-curable inks come out of high quality.

Advantages and disadvantages of UV curing technology

The UV curing method is environmentally friendly. Other advantages of modern technology:

• short drying time of varnish or paint;
• high performance;
• economy because drying finished products does not take time;
• application in parts, for example, painting a specific area of ​​\u200b\u200bthe surface;
• reuse of the rest of the paintwork materials or the stacked paintwork material;
• applying a thin layer is sufficient for High Quality finished product;
• strength and durability of the painted surface;
• low explosiveness;
• health safety.

UV curing technology also has disadvantages:

• use on automatic lines pays off only in case of high production volumes;
• the price of paints and varnishes is higher than similar solvent or folic;
• if you need to paint non-flat surfaces, drying takes longer;
• to achieve high quality, the curing process must be slowed down.

In addition, if layer defects, such as smudges, drops, have formed on the surface to be painted, most often they cannot be eliminated.

There are several types of paints and varnishes on the market. coloring compositions which dry out under the influence of ultraviolet light.

Specificity of UV curing inks

The pressrooms use acrylic, waterborne, polyester varnishes and UV-cured inks.

Acrylic

These paints dry in just a few minutes and are highly reactive with almost 100% dry residue. Contains no UV hardener. The hardness and strength of the resulting layer makes it possible to use the material for painting parquet flooring. They are environmentally friendly, in the process of drying they almost do not emit fumes. However, upon contact with open skin, they harm the epidermis, so it is necessary to work with acrylic coatings with gloves, a respirator and goggles. Due to their high viscosity, acrylic coatings cannot be applied by spraying.

Polyester

These paints and varnishes are inexpensive, but require blowing to dry completely. Cures upon impact a large number ultraviolet lamps. Suitable for spray application. Coatings tend to turn yellow during UV curing.

Waterborne

Characteristics of these paints and varnishes:

• environmental friendliness;
• high quality;
• safety.

Waterborne coatings do not yellow and are suitable for spraying. When dried, they form durable pigment layers of high quality. Absolutely harmless in contact with open skin. They are more expensive than acrylic and polyester, require convective drying.

Comparison Chart for Acrylic, Polyester and Waterborne UV Inks

UV inks in printing

UV curing technology is used in almost all printing methods:

• screen printing of all kinds;
• flexo printing;
• silk screen printing;
• offset sheet and roll;
• polygraphy;
• wide format, inkjet printers.

Thanks to unique properties coloring materials almost instantly cure, you can print with UV inks on different materials:

• paper;
• wood;
• plastic;
• film;
• plastic.

If you are printing on non-absorbent materials such as polyethylene films, it is necessary to control the tension of the surface, because the problem of adhesion of the ink layer to the film or plastic can be a time bomb. Defects will become visible later, and it will be impossible to fix the marriage, so the tension is checked with special ink or test pencils.

During printing, the following climatic conditions must be observed:

• temperature from 18 to 24 degrees;
• humidity from 50 to 60%.

Important! Light from fluorescent lamps and sunlight should not fall on the printing press, cans of coloring materials. For window protection, yellow filters and lamps of a safe yellow and white spectrum should be used.

Finished products can be coated with UV curing varnishes that protect the product and create special effects such as glossy or matt surfaces. UV varnishing is considered an environmentally friendly, safe and cost-effective technology.

In general, UV-cured inks and varnishes are popular in Moscow printing shops, because they give good results even when printing on “capricious” materials.

Administrator

Reflective paints

reflective paint coatings extend the life of your roof in three ways: by reflecting sunlight off the surface and therefore reducing heat transfer in the building, by reducing thermal contraction and expansion of the roof membrane (such as with Superec Flex Bedec), and by helping to manage and stop roof leaks. Solar reflective paint can help reduce energy costs and simply improve roof aesthetics. The price of reflective paint varies by brand and type.

Reflective roof paint

Generally, white reflective coatings are water based and are more suitable for new roofs due to their low cost and ease of use. Coo-Var Solar Reflective White Paint is a bright white acrylic coating that reduces heat build-up inside and outside of a building. It can be used on concrete, wood, brick and other surfaces, and is also an excellent choice as a solar reflective paint for flat roofs in good condition, but not recommended for roofs where standing water often collects.

Reflective paint for weathered surfaces

Because older roofs need more waterproofing to keep watertight, aluminum roofing paint tends to be used quite often. Since these products are usually solvent based heat reflective paints and are used in thicker coatings, they are a more expensive option.

There are a number of reasons to apply reflective roofing to your roof, whether it's a mobile home, a camping trailer, or just a shed, reflective roofing will extend the life of your roof by reducing heat transfer to the structure, thereby reducing thermal shock (roof expansion and contraction). as the weather warms and cools) and by limiting the amount of leaks that dot the surface. Although almost any type of roof can be covered with this paint, the most common are metal, polyurethane, single-layer and built-in roof systems. There are several various types roofing to choose from. You should choose the most ideal type for your situation.

Paint GacoRoof silicone reflective roof coating

It is one of the most durable reflective roof coatings on the market. GacoRoof's Rolex Silicone Reflective Coating comes with a 50-year material warranty, thanks in large part to the 100 percent silicone elastomer construction. This product is great for flat roofs because it is strong enough to withstand water. GacoRoof is resistant to sunlight, rain, snow and extreme temperatures.

Black Jack Paint Elastomeric Reflective Coating

Black Jack reflective coating is a white silicone elastomeric roof coating, which means that it is a polymer that has elastic properties. These qualities lead to the fact that the paint always returns to its original shape if it is deformed. Its flexible properties allow it to resist cracking and maintain a seal throughout the roof. It is best used on metal, tile or built-in roofing.