MXPA00010202A - Methods and compositions for protecting polymers from uv light - Google Patents

Abstract

A polymeric article, such as an extruded or molded article or a biaxially oriented tape of film, and a method of stabilizing such a polymeric article to protect the article from degradation due to exposure to UV light. The article is formed by blending a polymeric material with from about 50to about 5,000 ppm of at least one ortho hydroxy tris-aryl triazine light absorber and from about 500 ppm to about 1.25 percent of at least one oligomeric, polymeric, or high molecular weight HALS having a molecular weight of at least about 500, wherein the weight ratio of HALS to triazine light absorber is from about 3:1 to about 20:1, to form a stabilized polymeric composition, and forming an extruded or molded article or a biaxially oriented tape or film from the stabilized polymeric composition.

Description

FLEXIBLE POLYURETHANE MATERIAL FIELD PE J? INVENTION This invention relates to a flexible polyurethane material, more particularly, to a solvent-free, two-component polyurethane and, even more particularly, to a polyurethane which is transparent and exhibits flexibility, durability and degradation characteristics to the Improved weather. The present invention also includes an article that uses polyurethane as a topcoat, and a method for making such a topcoat of polyurethane.

BACKGROUND OF THE INVENTION Decorative articles often use a polyurethane top coating to cover or protect a base substrate and any decorative symbol or feature located on the substrate. The articles may include various substrates on which printed or profiled graphics have been applied. The polyurethane material is generally clear or optically transparent and functions as a lens in order to exhibit the substrate or any symbol applied thereto. The decorative items have Ref: 124262 a wide variety of uses in both indoor and outdoor applications. For example, model names for automobiles often demonstrate in a decorative manner on an exterior vehicle surface. The polyurethane covers and protects the symbols displayed on the name plate of the model. Polyurethanes are generally applied to articles or substrates as a solution or a flowable reaction mass which then cures to form a lens. The flow characteristics of the uncured polyurethane are important in the development of a polyurethane coating with sufficient and desired thickness when curing. Some polyurethanes, when curing, are rigid and non-flexible polymers. The rigidity of the article is often due to the chemical structure of the components used in the polyurethane formulation. Rigid polyurethanes are susceptible to abrasion and scraping. Additionally, the materials do not demonstrate an appropriate level of self-policing. Autocitration describes the ability of polyurethane to return to its original shape or appearance after being deformed, for example by scraping. Polyurethanes are applied on various types of substrates. However, some specific substrates are not suitable for use with conventional polyurethanes. Some substrates are capable of absorbing a quantity of moisture which can react with the polyurethane to form bubbles in the cured polyurethane. The formation of bubbles in the polyurethane is called gas evolution. For polyurethanes containing an isocyanate, gas evolution can also occur when certain porous substrates, for example polyvinyl chloride, are placed as backing with adhesives containing carboxyl groups. The porous substrate allows the reaction of the isocyanate in the polyurethane with the carboxyl groups in the adhesive. This reaction results in the release of carbon dioxide, which is generally trapped in the polyurethane. The presentation of gas evolution in a cured polyurethane is aesthetically undesirable. Conventional two-component polyurethanes typically rely on solvent or use polyethers as the primary hydroxyl source. The solvent-based polyurethanes are generally sufficiently non-viscous to provide a desired thickness to the polyurethane lens. Additionally, solvent based polyurethanes, when applied as top coatings, do not allow complete evaporation of the polyurethane solvent. Incomplete evaporation can produce streaks, split lines or bubbles in the polyurethane and thus result in an aesthetically unacceptable topcoat. Polyether-based polyurethane blends can provide suitable flexible properties. Nevertheless, they tend to degrade and yellow when exposed to sunlight. Therefore, existing polyurethane compositions and the methods for producing them, with frequencies result in undesirable finished properties or are not suitable for outdoor applications. There is a need to provide a polyurethane that is flexible, durable and weather resistant. Additionally, such polyurethane should be applicable to various substrates without experiencing a substantial amount of gas evolution. A polyurethane having the indicated properties could be suitable for use as a protective coating on various substrates in both indoor and outdoor applications.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a two component polyurethane, an article using the polyurethane, and a method for making the polyurethane. The cured polyurethane is flexible, durable and resistant to the weather. The optically clear polyurethane is suitable for use as a protective coating on various substrates.

The polyurethane of the present invention has a crosslinking of primary aliphatic isocyanate. Polyurethane is the reaction product of two reaction components. The first reaction component includes one or more polyols. The polyol portion of the first component has an equivalent weight in the range of about 28 to about 3000. The first component also includes one or more diols having an equivalent weight in the range of about 30 to about 4000. The desired diol is a combination of a short-chain diol, having an equivalent weight in the range of about 30 to about 400, and a polymeric diol, having an equivalent weight in the range of about 400 to about 4000. Suitable polyol and diol compounds for Use in the first component may include polyesters, polycarbonates, polyacrylates, polyalkylenes and polyethers, and combinations thereof. Additionally, a catalyst is included in the first component. The second component includes a primary aliphatic polyisocyanate crosslinker. The indicated polyisocyanate preferably represents at least about 50 percent by weight of total isocyanate present in the second component. The first and second components combine to form a solvent-free mixture which can then be applied to a substrate and cured. The viscosity of the mixture is generally in the range of about 400 cps to about 500 cps at 25 ° C. The viscosity of the material allows the formation of a lens, or meniscus, on the substrate. The cured polyurethane, optically transparent, is flexible, durable and resistant to the weather. The flexibility of the polyurethane is demonstrated by the Shore A hardness test, the flexural modulus test, and the storage module test. The polyurethane has a Shore hardness of less than 94, a storage modulus of 1.0 x 108 Pascals or less, and a flexural modulus of 1.0 x 108 Pascals or less. The durability and weathering properties of the present invention are demonstrated by tests such as the Hoffman scrap resistance test and the heat aging test. The polyurethane of the present invention has a surface with a test result of Hoffman scraping hardness of 2 to less. Additionally, the polyurethane shows a color shift value of 1 or less when subjected to the heat aging test. It would be an advantage to provide a polyurethane that is flexible, durable and weather resistant. A polyurethane having the indicated properties would be suitable for use as a protective layer for indoor and outdoor applications. It would be an additional advantage to provide a polyurethane that prevents gas evolution when applied to a substrate. The ability to prevent gas evolution would allow the use of polyurethane in various substrates of decorative articles.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description, when considered in light of the accompanying drawings, in which: Figure 1 is a cross-sectional view of a shaped article using the polyurethane of the present invention; Figure 2 is a cross-sectional view of another article formed using the polyurethane of the present invention; and Figure 3 is a cross-sectional view of an article using a three-dimensional substrate and the polyurethane of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The preferred polyurethane of the present invention has a primary aliphatic isocyanate crosslinking. Polyurethane is the reaction product of a two component system. The reaction mass resulting from the two components is generally free of solvents. According to the invention, solvent-free means that the reaction mass contains an amount of water or organic solvents at concentrations that do not adversely affect the viscosity of the reaction mass and therefore could prevent the formation of a lens. Additionally, the amount of water or organic solvent must be sufficient to evaporate when curing in order to avoid the formation of stretch marks, dividing lines or bubbles in the cured polyurethane. Preferably, solvent-free means that there is less than about 5 percent by weight of water or organic solvents in the combined mixture of the reaction components. More preferably, the solvent content in the combined reaction components is less than about 1 percent by weight. The first reaction component contains one or more polyols, optionally one or more diols, and a catalyst. The polyols used according to the present invention are compounds having three or more hydroxyl groups. The polyols are generally selected from the group consisting of polyesters, polycarbonates, polyacrylates, polyalkylene and polyethers, or combinations thereof. The combined polyol or polyols have an equivalent weight in the range of about 28 to about 3000. In the present invention, the equivalent weight corresponds to the molecular weight of the material divided by the number of hydroxyl groups. The combinations of polyols within the limitation of the indicated equivalent weight may be suitable for use with the invention. However, the amount of polyether in the first reaction component, whether provided as a polyol or a diol, preferably should not exceed about 40 percent by weight of the first component. The amounts of polyesters that exceed the stated limitation may adversely affect the transparency or weathering properties of the present invention. Desirably, polyols and diols based on polyester, which form more than about 20 weight percent of the polyester in the first reaction component, are used in the present invention in order to improve the outer durability. The polyol comprises a range from more than about 10 weight percent of the first reaction component. Optionally, one or more diols are included in the first reaction component. Diols are compounds that have two hydroxyl groups. In addition to the polyester diols, polycarbonate, polyacrylate, polyalkylene and polyether diols or combinations of the indicated compounds can be used in the present invention. One or more diols have a combined weight equivalent in the range of about 30 to about 4000. Additionally, the diols comprise a range of up to about 65 weight percent of the first reaction component. Desirably, the diols include the combination of a short chain diol having an equivalent weight in the range of about 30 to about 400, and a long chain diol having an equivalent weight in the range of about 400 to about 4000 Additionally, it has been found that when a polyester and a polyether are used in the first reaction component, the combined amount of polyether, provided it is provided as a polyol or a diol preferably should not exceed about 40 weight percent of the first reaction component. The first reaction component of the present invention also requires a catalyst. The isocyanate groups of the second component react with the hydroxyl groups of the first component under the influence of the catalyst to form urethane linkages. Catalysts are conventionally recognized for use in the polymerization of urethanes and may be suitable for use in the present invention. For example, catalysts based on aluminum, bismuth, tin, vanadium, zinc, or zirconium can be used with the present invention. Although not desired, due to its potential toxicity, a mercury-based catalyst can also be used. The desired catalysts are tin-based catalysts. It has been found that a tin-based catalyst significantly reduces the amount of gas evolution present in the polyurethane. The most desirable are dibutyltin compounds. Even more desirable are the catalysts which are selected from the group consisting of dibutyltin diacetate, dibutyltin dilaurate, dibutyltin diacetylacetonate, dibutyltin dimercaptide, dibutyltin dioctoate, dibutyltin dimaleate, dibutyltin acetonylacetonate, and dibutyltin oxide. The catalyst is preferably included at concentrations of at least 200 ppm in the first component, and more preferably 300 ppm or greater. Optionally, the first reaction component of the present invention may include various additives. For example, leveling agents may be used in the first reaction component to ensure a uniform finish of the exposed surface of the polyurethane. It can be used in the present invention as a polymethylsiloxane triblock modified with polyethylene oxide. However, other leveling agents generally recognized by those ordinarily skilled in the art are also suitable for use with the invention. The leveling agents desirably are included in a range of about 0.01 weight percent to about 1 weight percent. Another additive to the first component may include substances that absorb UV radiation which improve the weathering of the polyurethane topcoat. Substances that absorb UV radiation are generally recognized in the art which may be suitable for use with the invention. Alternatively, a hindered amine radical scavenger may be included in the first reaction component or may be combined with a substance that absorbs UV radiation. The free radical scavengers of hindered amine are generally recognized in the art to contribute to the photostabilization of the polyurethane by trapping alkoxy and hydroxy radicals produced by the dissociation of hydroperoxides, induced by light. The amount of substance that absorbs UV radiation in the first component desirably is in the range of about 0.1 weight percent to about 4 weight percent. The amount of hindered amine radical scavenger in the first component is desirably in the range of about 0.1 percent by weight to about 2 percent by weight. Additionally, moisture scavengers, antioxidants and antifoaming agents may be included with the first reaction component. Conventional compounds of the indicated categories generally recognized by those skilled in the art may be suitable for use in the present invention to improve the finishing properties of the polyurethane. Desirably, moisture scavengers are included at concentrations in the range of about 0.1 weight percent to about 3 weight percent. The antioxidant is desirably included in a range of about 0.1 percent by weight to about 2 percent by weight. The defoaming agents desirably are included in an amount of percent by weight 0.2 percent by weight or less. Other compounds, such as coloring agents and decorative solids, can be added to the first component to improve the aesthetics of the finished polyurethane. Coloring agents, such as pigments or dyes, are included at various concentrations to obtain a desired effect. Decorative solids may include items such as metal flakes, polymeric flakes, tinsel, spheres or other materials that provide decorative features to the finished polyurethane. Decorative solids are also included in various amounts to obtain a desired effect on the finished article. In accordance with the present invention, a second component is provided which includes a primary aliphatic isocyanate crosslinker, and preferably a primary aliphatic polyisocyanate crosslinker. A primary isocyanate is defined as having one carbon atom having one -NCO group and two hydrogen atoms attached to the carbon atom. The primary isocyanate is an important factor in providing a flexible polyurethane that does not show a substantial amount of gas evolution. Gas evolution may occur when the isocyanate component of the polyurethane reacts undesirably with a water source or carboxyl groups and not with the hydroxyl groups present in the first component. In the present invention, it is preferred that the second reaction component includes a primary polyisocyanate in an amount of about 50 percent by weight or greater. This generally corresponds to a polyisocyanate crosslink of about 25 percent by weight or more in the cured polyurethane. The primary aliphatic polyisocyanate may be the sole source of isocyanate in the component or it may be combined with other primary aliphatic isocyanates, such as monomeric isocyanates. The use of secondary isocyanates can result in rigid polyurethanes or polyurethanes which show gas evolution. The conventional primary aliphatic polyisocyanate crosslinkers may be suitable for use in the present invention. For example, Desmodur XP-7100 and Desmodur N-3300 from Bayer Chemical of Pittsburgh, PA are the two polyisocyanates suitable with the invention. Additionally, the polyisocyanate can be a blocked polyisocyanate to further improve the reduction of gas evolution in the cured polyurethane. The blocked polyisocyanates will not react until the desired curing temperature is obtained, whereby additionally they prevent the undesired reaction of the isocyanate with water or with carboxyl groups. The polyisocyanate levels of at least about 50 percent by weight of the total isocyanate present in the second component can substantially reduce the evolution of gas in the cured polyurethane. The crosslink density of the polyurethane is calculated by dividing the weight of the reaction components having a functionality of 3 or greater between the total weight of the polyurethane and multiplying by 100. Generally, the rigid polyurethanes have relatively high crosslinking densities of 30. percent or greater. In accordance with the present invention, the use of a primary aliphatic polyisocyanate results in a flexible polyurethane having a high crosslink density. When the polyisocyanate content of the second reaction component is about 50 weight percent or greater, the crosslinking densities are 30 percent or greater, and preferably 40 percent or greater. The flexibility of the resulting urethanes, according to the flexure modulus test, are generally 1.0 x 108 or less. The first and second reaction components combine to form a solvent-free mixture having an NCO: OH ratio of about 0.75 to about 1.25. The reaction components, before mixing, are desirably maintained at specified viscosity ranges. The viscosity measurements for the present invention are divided into a Brookfield viscometer model RV with a rod number 4, at about 20 rpm. The viscosity of the first component is desirably maintained in the range of about 200 cps to about 5000 cps at 25 ° C. The viscosity of the second reaction component is desirably maintained in the range of about 100 cps to about 5000 cps at 25 ° C. When mixing, the viscosity of the mixture is in the range of about 400 cps to about 5000 cps at 25 ° C, and desirably in the range of about 600 cps to about 4000 cps.

The viscosity of the uncured polyurethane is important to obtain a desired thickness and continuity in the cured polyurethane lens when applied to a substrate. The viscosity limitation also provides a pourable reaction mass, which flows on a substrate. It is desired that the reaction mass flows to the edge of the substrate and forms a radius of curvature, without actually exceeding the substrate. The viscosity limitation also improves the ability to obtain the desired layer thickness. A viscosity greater than the indicated limitation may result in streaks or dividing lines in the finished polyurethane. A lower viscosity will not allow the polyurethane to form the desired meniscus or lens on the substrate. The polyurethane of the present invention is capable of obtaining thicknesses greater than 0.13 mm, and preferably greater than 0.25 mm. In accordance with the present invention, the mixture is applied to a substrate and cured to form a polyurethane coating. The curing of the polymer can be carried out by heating the material, applying infrared radiation or curing at room temperature. Other conventional curing techniques recognized by those skilled in the art may be suitable for use with the present invention. Desirably, the polyurethane is cured in a convection oven at 52 ° C for about 10 hours. An advantage of the present invention over conventional polyurethane s is that the polyurethane is adhesion free after about 1 hour of curing at about 52 ° C. The adhesion-free polyurethane can then be handled without being fully cured. Upon curing, the polyurethane of the present invention shows flexibility, durability and weathering properties that are desired. Preferably, the polyether segments, which result from the use of polyether-based polyols and diols in the first component, represent a maximum of 20 percent by weight in the cured polyurethane. More preferably, the polyether segments in the cured polyurethane are about 15 percent by weight or less. A polyether content exceeding the stated limitation may have an adverse impact on the clarity and weathering properties of the cured polyurethane. The flexibility of the present invention allows the use of polyurethane in various articles. For example, the present invention can be used as a protective layer on a substrate supported with adhesive. The flexibility of the polyurethane of the present invention allows the application of the coated article on curved or non-planar surfaces. Flexibility significantly reduces the tendency of polyurethane to return to its originally cured form after it joins a surface.

The flexibility of the polyurethane is demonstrated by the Shore A hardness properties, the storage modulus and the flexural modulus. The Shore A hardness test of the polyurethane of the present invention is generally less than 94, and preferably less than 92. Shore A hardness levels exceeding 94 are considered rigid. The storage module indicates the stiffness of the polyurethane under tension. The polyurethanes of the present invention have a storage modulus of 1.0 x 108 or less. The flexure module measures the flexibility of polyurethanes under torsional stress. The polyurethanes of the present invention have a flexural modulus of 1.0 x 108 or less. Additionally, polyurethane flexibility is often indicated by its self-healing characteristics, or the ability to return to its original shape after deformation. The durability and weathering properties of the present invention are important characteristics which allow the use of polyurethane in various environments. For polyurethane applications in outdoor environments, polyurethane should not yellow or change color significantly when exposed to environmental conditions. The present invention, when subjected to a heat aging test according to ASTM D2244-79, shows a color shift within a delta E. Other environmental tests used to indicate acceptable exterior performance are the salt spray test, the test of humidity resistance and thermal shock test. A polyurethane should remain transparent and without turbidity or opacity when completing the indicated tests. The durability of a polyurethane topcoat is measured by Hoffman's scrap resistance test which indicates the abrasion resistance of the material. The present invention generally has a Hoffman scraping resistance of 2 or less. The polyurethane of the present invention can be applied to several substrates to form a layer on the substrate, or a portion of substrate. The substrate may include wood, polymeric material, fiber reinforced polymers, metal or combinations thereof. The choice of substrate depends on the desired end use. Some examples of combined substrates include polymeric films coated with metal and wood sealed with polymer or veneered wood. The polyurethane of the present invention is ideally suited for applications with substrates containing moisture or applications that allow direct or indirect contact of the isocyanate with carboxyl groups. For example, a porous substrate with an adhesive backing allows indirect contact of the isocyanate in the reaction mass of the polyurethane with carboxyl groups in the adhesive.

The polyurethane of the present invention is ideally suited for use in the shaping of decorative articles that require a transparent layer. Some decorative items use a substrate with signs applied on the substrate. Signs include any distinctive mark or representation. According to the present invention, the polyurethane can be applied directly on the substrate and the signs. In the present invention, the signs may include items such as printed graphics or three-dimensional graphics. Signs printed on the substrate can be applied, for example, with solvent-based inks, water-based inks, UV inks, or powdered inks. The printed signs can be applied through various processes that include screen printing, flexo printing, printing by engraving, digital printing, off-set printing and pad printing. You can also apply three-dimensional graphics on the substrate or they can serve, on their own, as the substrate. The three-dimensional graphics may include, for example, a cured polyurethane body with a link layer bonded to the polyurethane. An adhesive is then applied to the opposite surface of the bonding layer. An example of the three-dimensional graphics may include those described in EP 0392847, incorporated herein by reference. Other types and styles of signs may also be used with the present invention. Alternatively, the article may include several different types or styles of signs applied, or stratified on the substrate. The polyurethane of the present invention is suitable for this type of application because it does not allow a substantial amount of gas evolution. This style of stratified signs can directly expose an adhesive to the top urethane coating. This type of application with a conventional polyurethane often results in a significant amount of gas evolution in the cured polyurethane. The present invention does not experience a substantial amount of gas evolution, thereby allowing direct exposure of the adhesive to the polyurethane. Figure 1 illustrates an article manufactured in accordance with the present invention. The article 10 includes a substrate 12 of polymeric base on which an upper coating 14 of polyurethane of the present invention is applied. The polymeric base substrate 12 may desirably include polyvinyl chloride, polyester, acrylic polymers, polycarbonates, polyurethanes, polyethylene acrylic acid copolymer, polyvinyl acetates and reflective laminates. An adhesive 16 may be attached to a surface 18 of the substrate 12 opposite the surface 20 on which the polyurethane 14 is applied. The adhesive may include various adhesive bonding systems, for example, pressure sensitive adhesives, contact adhesives, hot melt adhesives and structural adhesives. A release liner 22 is attached to the adhesive 16 until it is removed before the final application of the article 10 to a desired surface (not shown). The substrate 12 includes signs 24 applied on the surface 20 of the substrate 12. The signs 24 are covered by the top coating 14 of polyurethane. Another embodiment of the present invention is shown in Figure 2. Figure 2 generally includes an article 30 having a base substrate 32 and an upper coating 34 of polyurethane applied to the substrate. Fixed to the substrate 32 is an adhesive 36. A removable release liner 38 is attached to the adhesive. A first layer of signs 40 is applied to a surface of the substrate 32. A second article containing signs 42 is then applied to the first sign layer 40. The second article 42 includes a substrate 44, an adhesive 46 and signs 48 applied to the substrate 44 opposite the adhesive 46. The upper polyurethane coating 34 of the present invention is applied on the base substrate 32 and the second article 42. Figure 3 illustrates another embodiment of the present invention. Article 50 includes three-dimensional substrate 52. An upper coating 54 of polyurethane is applied to the three-dimensional substrate 52. A release coating 56 is applied to a surface of the substrate opposite the top coating 54 of polyurethane. The following non-limiting examples further illustrate the present invention. Unless otherwise indicated, the following test procedures are used in the examples. The particular materials and amounts mentioned in these examples, as well as other conditions and details, should be broadly construed in the art and should not be construed as unduly restricting or limiting the invention in any way.

TEST METHODS Test sis scraped d = Hoffman and wear resistance usual The usual scraping and wear of the polyurethanes is measured by a balanced beam shaving decaller described in ASTM-2197-86. The Hoffman stylet is held at 45 ° from the vertical with the top inclined in the direction of displacement of the test sample. The stylet is held in place by a fulcrum raised to 22 °. A weight of 1000 grams is placed on the weight support. The beam is lowered until the circuit rests on the upper part of the test sample, after which the sliding platform is pushed slowly through the sample. The scraping test is carried out at 25 ° C. A successful test will result in the polyurethane coating showing no permanent damage, scraping or defect after 1 hour.

Resistance to humidity Polyurethanes are applied on a polyester film coated with tin steam and cured. Each sample is placed in a humidity condensation chamber with 100% relative humidity at 38 ° C for 7 days. Samples are observed to determine turbidity and corrosion when removed from the chamber.

Aging in heat Polyurethanes are applied on a polyester substrate coated with standard tin printed with white ink, and cured. The samples are placed in an oven at 80 ° C for 7 days. When it is removed, polyurethane coating is observed to determine any significant yellowing in the color. The difference or change of color is measured by the standard test ASTM D2244-79. The color difference (Delta E) is calculated by CIÉ 1976 L * a * b * Uniform Color Space and Color-Difference Equation. For successful results, the Delta E value does not exceed 1.

Salt spray The polyurethanes are applied on a tin-coated polyester substrate and cured. The samples are placed in a salt spray chamber, which has a 5% NaCl solution atomized at 35 ° C. When they are removed after 10 days, the samples are observed to determine turbidity and corrosion.

Shore A hardness The Shore A hardness is measured by a Shore A durometer, in accordance with ASTM D-2240.

Thermal shock The polyurethanes are applied on polyester coated with tin and are cured. Each sample is tested at 10 cycles of the following tests: - 4 hours at -30 ° C. - 5 minutes immersion in water at 85 ° C.

The samples for turbidity and corrosion are observed.

Storage module test The value of E '(storage module) is a measure of the flexibility of a material. The storage module is measured at 25 ° C under tension using a Rheometric Solids Analyzer (RSA II) at a frequency of 6.28 rad / second. The voltage is maintained at a voltage of 0.03%. The test sample, at a thickness of 1.8 mm and with a variation in size from 3.5 mm to 6.5 mm, are clamped and tightened. The oscillatory flow is applied to the sample a periodic voltage of a predetermined amplitude and frequency, and the voltage response of the material is measured. The real part of the Fourier transform of the response provides the elastic modulus, E '(storage module).

Bending module test The flexural modulus at 25 ° C is measured using Seiko DMS 110 at a frequency of 6.28 rad / second. It is mounted on a double cantilever device, a sample strip having a thickness of 1.8 mm and varying from 10 mm to 13 mm in width and 20 mm in length. HE. It uses a voltage amplitude of 30 micrometers to determine the flexural modulus of the sample.

Substrates used in the examples The substrate (1) is prepared by Scotchcal * 7900 Series solvent-based phosphorescent ink screen printing using a 110 mesh screen on a Scotchlite * reflective engineering sheet, both supplied from the Minnesota Mining and Manufacturing Company of St. Paul Minnesota. The ink is dried for 30 minutes at 80 ° C. Substrates (2) - (4) are standard p ScotchcalMR series films Minnesota Mining and Manufacturing Company. The substrate (5) is prepared by digitally printing standard powdered organic pigment on a white PVC film. The substrate (6) is produced by rotary printing of a black metallic ink based on Scotchcal ^ 7900 Series solvent with a carbon fiber pattern on a PVC and silver film. The substrate (7) is made by applying plots of PVC cut by die on a hologram polyester film substrate. The substrate (8) is a three-dimensional standard graphics not rinsed and uncut from Minnesota Mining and Manufacturing Co. The substrate (9) is made by applying a three-dimensional unclarified graph of a laser-cut beam on a wood grain film of PVC The substrate (10) is prepared by screened white ink based on Scotchcal solvent "1 7900 Series" with a 230 mesh screen on a thin metallized film The substrate (11) is a thin metallized film.

Example 1 The first component, which is based on polyester polyols / diols, is prepared by mixing 31.9 grams of Formrez-55-225, 30 grams of Formrez-55-112 and 30 grams of Tone-301 in a round bottom flask and it is heated to 70 ° C. The mixture is stirred and degassed for 4 hours under vacuum (below about 762 mmHg (30 inches of Hg)) until the bubbles are removed. The temperature of the mixture is cooled to approximately 50 ° C and then 0.06 grams of T-12, 0.2 grams of Silwet L-7607, 1.5 grams of Uvinul N-539 and 1 gram of Tinuvin-292 are added to the mixture. The mixture is stirred for 15 minutes. The formulation of the first reaction component, in percent by weight, is included in table 2. The second reaction component includes 100 grams of polyisocyanate (Desmodur XP-7100). The first and second reaction components are mixed in a volume ratio of 1 to 1 and poured over the 11 substrates indicated above. The polyurethanes are cured for 10 hours at 52 ° C in a convection oven. The cured polyurethane does not release gas on any of the substrates and has excellent optical clarity and flexibility.

Comparative examples 1-4 The first component in the comparative examples 1 to 4 includes different polyethers based on polyols and diols. The examples are prepared according to the same procedure described in Example 1. In Table 1 the polyols and diols used for each example are indicated. The second component for the comparative example 1 is prepared by reacting 30 grams of Pluracol TP-4040 and 70 grams of Desmodur W for 4 hours at 80 ° C. The second resulting component is a mixture of a secondary polyisocyanate and a monomeric isocyanate (Desmodur W). The second component using in the comparative example 2 is prepared by reacting 73.5 grams of Desmodur I, with 23.5 grams of Desmophen L951, and 3 grams of Multranol-4011 for 4 hours at 80 ° C. The resulting part B comprises a mixture of polyisocyanate with primary and secondary isocyanate functional groups and monomeric Desmodur I. The polyurethanes are prepared by mixing the first and second reaction components in a volume ratio of 1 to 1 and then pouring on the substrates indicated (1) to (11). The polyurethanes are cured for 10 hours at 52 ° C. The polyurethanes in comparative examples 1, 2 and 4 are still adherent when cured 1 hour at 52 ° C in a convection oven or 10 minutes in an IR oven, and have a strong gas evolution on the substrates (1) to ( 9). The polyurethanes are very rigid. The polyurethane in comparative example 3 is opalescent.

Examples 2-6 The first components used in examples 2-6 are prepared according to the same procedure described in example 1. The composition of the first component for each example is included in table 1. The second component used in example 2 is prepared when reacting 30 grams of Pluracol-538, and 70 grams of Vestanat IPDI for 4 hours at 80 ° C. The second resulting component includes a mixture of polyisocyanate with primary and secondary isocyanate groups and monomeric Vestanat IPDI. The second component used in example 3 is the same as that used in comparative example 1. The second component in example 3 comprises a mixture of secondary polyisocyanate and monomeric Desmodur W. The second component used in example 4 is prepared by mixing 70 grams of polyisocyanate and 30 Desmodur H. The second component used in example 5 is prepared by mixing 50 grams of polyisocyanate and 50 grams of Desmodur H. Polyurethanes are prepared by mixing the first component and the second component in a ratio in volume 1 to 1 and then applied to the substrates (1) to (11). The polyurethanes are cured for 10 hours at 52 ° C. The polyurethanes in examples 2 and 3 show severe gas evolution on the substrates (1) to (9). Although not indicated in the table, the weathering properties of Examples 2 and 3 are improved with respect to conventional polyurethanes. Additionally, examples 2 and 3 are rigid. The flexible polyurethane in Examples 4 and 6 is transparent and shows no gas evolution in any of the substrates. The polyurethane in example 5 shows gas evolution on the substrates (1), (5) and (9).

Comparative examples 5-8 and examples 7-12 The first polyol / diol polyester based components in Examples 5 to 12 are prepared according to the first procedure desed in Example 1. The ingredients and amounts used for each example are summarized in Table 4. The type of catalyst varies for each example. The various catalysts are indicated in the table. Polyurethanes are prepared by mixing the first and second reaction components in a volume ratio of 1 to 1 and then pouring on the substrates (1) to (9). The polyurethanes are cured for 10 hours at 52 ° C. The polyurethane in Examples 7, 9, 10 and 12 does not release gas and is flexible and optically transparent. Comparative examples 7 and 8 show severe gas evolution in all tested substrates.

Examples 13-19 The first components used in Examples 13-17 are prepared according to the same procedure desed in Example 1. The ingredients vary in order to demonstrate the effect of the variation in the polyester content on the cured polyurethane. Table 5 summarizes the ingredients and amounts used. Additionally, Example 18 includes a black pigment added to the first reaction component. The second component in example 16 is the same as that used in comparative example 2. The second component in example 17 is the same used in comparative example 1. Examples .13 to 15 and 18 use a polyisocyanate. Table 5 includes the quantity of the second component used in each example. The polyurethanes of Examples 13-17 are prepared by mixing the first and second components in a volume ratio of 1 to 1 and then pouring onto the substrates (1) to (11). The polyurethanes are cured for 10 hours at 52 ° C. The polyurethane with black pigment in example 18 is only cast on the substrate (4), a black PVC film. The polyurethane in Example 18 is cured in the same manner as desed in Examples 13-17. The polyurethane in example 13 is cloudy and therefore unacceptable. The polyurethane in Examples 14 and 15 does not release gas and is transparent and flexible. The polyurethanes in examples 15 and 16 show gas evolution in all tested substrates. Both examples are rigid. The polyurethane pigmented in Example 18 is flexible and does not show any gas evolution.

Table 1. Materials used in the invention Table 2. Polyether-based polyurethanes cured on various substrates Table 3. Polyester-based polyurethanes cured on various substrates Table 4. Polyurethanes made of polyester polyols / diols comprising different catalysts in the first component and curing on various substrates. 15 - Table 5. Clarity of polyurethanes made from a mixture of polyester / polyether polyols / diols in the first component and cured by primary and secondary polyisocyanates. é6 - Table 6. Specification of test results, 15 Discussion of examples and tables 2-6 Tables 2 and 3 illustrate the impact of the primary and secondary isocyanates on the flexibility of the resulting polyurethanes. Examples using a primary isocyanate result in flexible polyurethanes. Examples using secondary isocyanates, or a combination of primary and secondary isocyanates, result in a rigid polyurethane. Additionally, the examples indicate that the use of secondary isocyanates results in gas evolution in the cured polyurethane. Comparative Example 3 in Table 2 indicates that the use of polyester compounds in an amount of about 50 percent by weight results in a poorly transparent polyurethane. Additionally, the tables indicate that the examples using primary aliphatic polyisocyanate result in flexible polyurethanes with crosslinked densities at the same level or higher than that of rigid polyurethanes. Table 4 represents the results of bismuth-based catalysts, tin and zinc on the polyurethane of the present invention. The catalysts based on bismuth and zinc result in the evolution of gas in the cured polyurethane. Those based on tin work much better and show only gas evolution in some types of substrates. The dibutyltin compounds show no gas evolution. The results of the polyether / polyester mixed polyurethanes are included in table 5. The results indicate that the secondary isocyanates produce rigid polyurethanes. Additionally, the use of secondary isocyanates results in gas evolution. In Example 13, with a polyether content exceeding 20 percent by weight, they become milky white. Examples that use a primary polyisocyanate are flexible and do not release gas.

Example 18 demonstrates the use of a black pigment in the first reaction component. Table 6 illustrates the properties of flexibility, durability and weather resistance of polyurethanes. Examples 1, 6, 13 and 14 indicate that the polyurethanes produced according to the present invention show improved flexibility and durability properties over the comparative examples. The flexibility and durability of polyurethanes is demonstrated through Hoffman's Shore A hardness, storage modulus, flexural modulus and scraping tests. Additionally, polyester based polyurethanes show improved weathering properties, represented through salt spray, moisture resistance and heat shock test.

In accordance with the provisions of the patent statutes, the present invention has been described in what it considers to represent its preferred embodiment. However, it should be noted that the invention can be brought into practice in a different manner to that illustrated and described specifically, without departing from its spirit and scope. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention

Claims (1)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. A polyurethane characterized in that it contains a primary aliphatic isocyanate crosslinker and at least about 25% by weight of the primary polyisocyanate crosslinker. . The polyurethane according to claim 1, characterized in that the polyurethane is based on at least one of the polymers selected from the group consisting of polyesters, polycarbonates, polyacrylates and polyethers. 3. The polyurethane according to claim 2, characterized in that the polyurethane is based on polyester. 4. The polyurethane according to claim 2, characterized in that the polyurethane is based on a copolymer of at least two such polymers. 5. The polyurethane according to claim 4, characterized in that the polyurethane is based on a polyester copolymer and up to about 20% by weight of polyether. 6. A flexible polyurethane, characterized in that it comprises: a reaction product of: (a) a first component that includes one or more polyols having an equivalent weight in the range of about 28 to about 3000, optionally one or more diols having a weight equivalent in the range of about 30 to about 4000, and a catalyst; and (b) a second component that includes a primary aliphatic isocyanate crosslinker, wherein the first and second components together are solvent-free. The polyurethane according to claim 6, characterized in that the reaction product has a viscosity in the range of about 400 cps to about 5000 cps at 25 ° C. The polyurethane according to claim 6, characterized in that the reaction product has a viscosity in the range of about 600 cps to about 4000 cps at 25 ° C. The polyurethane according to claim 6, characterized in that one or more polyols and one or more diols are selected from the group consisting of polyesters, polycarbonates, polyacrylates and polyethers, or combinations thereof. The flexible polyurethane according to claim 6, characterized in that the primary aliphatic isocyanate crosslinker is a polyisocyanate of at least about 50% by weight of the second component. The polyurethane according to claim 6, characterized in that the reaction product, upon curing, has a Shore A hardness of about 94 or less at room temperature. 12. The polyurethane according to claim 6, characterized in that the catalyst is included in the first component in an amount of at least about 200 ppm. The polyurethane according to claim 6, characterized in that the catalyst is a tin-based catalyst. The polyurethane according to claim 6, characterized in that the tin-based catalyst is selected from the group consisting of dibutyltin diacetate, dibutyltin dilaurate, dibutyltin diacetylacetonate, dibutyltin dimercaptide, dibutyltin dioctoate, dibutyltin dimaleate, acetonylacetonate of dibutyltin and dibutyltin oxide. 15. The polyurethane according to claim 6, characterized in that the first component comprises in the range of more than about 10% by weight of one or more polyols. 16. The polyurethane according to claim 6, characterized in that the first component comprises in the range of up to about 65% by weight of one or more diols. 17. A flexible polyurethane, according to claim 6, characterized in that one or more diols include a short chain diol having an equivalent weight in the range of about 30 to about 400, and a polymeric diol having an equivalent weight in the range from about 400 to about 000. 18. The polyurethane according to claim 6, characterized in that the isocyanate is a blocked isocyanate. 19. The polyurethane according to claim 6, characterized in that the first component includes one or more compounds that are selected from the group consisting of antioxidants, moisture scavengers, antifoaming agents, ultraviolet light absorbing substances, amine free radical scavengers hindered, leveling agents, decorative solids and coloring agents. 20. The polyurethane according to claim 6, characterized in that the polyurethane has a surface with a test result of Hoffman scraping hardness of two or less. 21. The polyurethane according to claim 6, characterized in that the polyurethane has a storage modulus of 1.0 x 108 pascals or less. 22. The polyurethane according to claim 6, characterized in that the polyurethane has a flexural modulus of 1.0 x 108 pascals or less. 23. The polyurethane according to claim 13, characterized in that the reaction product, upon exposure to moisture or carboxyl groups, does not show a substantial amount of gas evolution in the cured polyurethane. 24. The polyurethane according to claim 6, characterized in that the reaction product has polyether segments of about 20% by weight or less. 25. An article, characterized by comprising: (a) a substrate, and (b) a polyurethane applied as a layer on a substrate surface, the polyurethane is a reaction product of, (i) a first component that includes one or more polyols having an equivalent weight in the range from about 28 to about 3000, optionally one or more diols having an equivalent weight in the range from about 30 to about 4000, and a catalyst; and (ii) a second component that includes a primary isocyanate crosslinker, wherein the first and second components, together, are free of solvents. 26. The article according to claim 25, characterized in that the substrate is a polymeric material, wood, cloth, reinforced polymers, metal or combinations thereof. 27. The article according to claim 25, characterized in that an adhesive is applied on an opposite side of the substrate. 28. The article according to claim 25, characterized in that it comprises signs applied on a surface of the substrate and covered by the polyurethane. 29. The article according to claim 25, characterized in that the signs are three-dimensional. 30. The article according to claim 25, characterized in that the polyurethane layer covers the entire surface of the substrate and the signs. 31. The article according to claim 29, characterized in that the three-dimensional signs comprise a cured polyurethane body having a mounting surface, a tie layer attached to the mounting surface of the cured polyurethane body, and a bonded adhesive body. to the junction layer. 32. The article according to claim 25, characterized in that the substrate is a base substrate and one or more secondary articles are applied on the base substrate, each of the secondary articles comprises an adhesive bonding system, a substrate and a sign. 33. The article according to claim 32, characterized in that the base substrate includes signs and the secondary articles are applied on the signs of the base substrate. 34. The article according to claim 32, characterized in that one or more secondary articles include three-dimensional articles. 35. The article according to claim 25, characterized in that the catalyst is a tin-based catalyst, and the polyurethane, upon exposure to moisture or carboxyl groups, does not show a substantial amount of gas evolution. 36. A method for producing a polyurethane, characterized in that it comprises: reacting a first component and a second component, wherein the first component includes a polyol having an equivalent weight in the range from about 28 to about 3000, optionally, one or more diols having an equivalent weight in the range of from about 30 to about 4000, and a catalyst, and the second component includes a primary aliphatic isocyanate crosslinker, wherein the first and second components together are free of solvents.