JPS6332102B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the photostability of polyurethane resin molded in a closed mold, and more specifically, the weather resistance of the surface of a light-colored molded product with high brightness due to the addition of a colorant, that is, the color of the polyurethane resin surface mainly due to ultraviolet rays and heat. It relates to a method for significantly improving yellowing and its deterioration. Polyurethane resin has excellent properties that allow it to be molded into a wide range of shapes from soft to hard depending on its formulation, so it can be used in vehicles, transportation, machinery, furniture, office, electrical and audio equipment, building materials and housing, sports and leisure, etc. It is used for various purposes. These are generally classified into integral skin foam, structural foam, microcellular foam, and solid (elastomer), and are molded into various shapes. When these molded products are left exposed to the atmosphere, there is a problem in that surface deterioration such as color change (yellowing), small cracks, and pinholes occur on the surface of the molded product mainly due to ultraviolet rays and heat. Generally, these problems have been solved by applying a coating with excellent light resistance to the surface of the molded product. However, coating a molded product requires many steps and equipment, such as removing the mold release agent from the surface of the molded product, drying it, applying the paint, and drying it to harden it. In addition, it requires a great deal of time, effort, energy, and even more sophisticated skill. This has led to a significant increase in costs, and there has been a strong demand for molded products that do not require a painting process, that is, molded products that are colored by directly adding a coloring agent to polyurethane resin and that are weather resistant themselves. As a result of various studies on the light resistance of polyurethane resins, the present inventors found that volatile non-halogen compounds (pentane, hexane, acetone, tetrahydrofuran, , saturated hydrocarbons such as methyl acetate and methyl formate, and oxygen-containing compounds without active hydrogen) were used as blowing agents to obtain molded products with outstanding light resistance. . In this method, general-purpose MDI, TDI and their prepolymers are used as polyisocyanates.
Pure MDI carbodiimide modified polyisocyanate etc. could be used. When a colorant is added to this to color the molded article, the light resistance is further improved due to the hiding power of the colorant. However, when the isocyanate itself is brownish like crude MDI, a dark coloring agent will hide the coloring of the isocyanate itself, so although the desired color could be achieved,
When using light colors such as cream, light yellow, and light green, the color becomes a mixture of the light coloring agent and the brownish brown of the isocyanate, making it impossible to achieve the desired color. In this case, the color of the polyisocyanate is colorless or pale yellow.
By using TDI, prepolymer, XDI (xylylene diisocyanate), carbodiimide-modified polyisocyanate, etc., it was possible to color the desired color by adding a light coloring agent. However, these polyisocyanates do not have sufficient light resistance and turn yellow over time, and the hiding power of the pale coloring agent is not strong enough to hide it, resulting in a color different from the desired color. In this way, when a volatile non-halogen compound is used as a blowing agent, if the surface of the molded product is colored in a dark color with a lightness of less than 5, which is represented by the Munsell symbol, it is possible to use a general-purpose polyisocyanate by adding the colorant. The light resistance is good and it is possible to make molded products without painting. On the other hand, light-colored products having a surface coloring with a lightness of 5 or more in the Munsell symbol have the disadvantage that the color changes over time due to ultraviolet irradiation, resulting in a color different from the desired color. The present invention has been made as a result of intensive studies in view of the above situation, and is based on the following: (a) Volatile non-halogen It is characterized by blending the compound (b) isophorone diisocyanate and (c) a coloring agent having a surface color of a molded article with a lightness of 5 or more expressed by the Munsell symbol. That is, a polyurethane resin composed of a compound system consisting of polyol, isophorone diisocyanate, catalyst, colorant, foam stabilizer, volatile non-halogen compound (foaming agent), and other stabilizers and auxiliary agents as necessary is molded in a closed mold. It's a method. Volatile non-halogen compounds include saturated hydrocarbons with boiling points in the range of 20 to 100°C under vapor pressure, such as pentane, hexane, heptane, petroleum ether, acetone, tetrahydrofuran, propylene oxide, methyl acetate, and methyl formate, and active hydrogen. Examples include oxygen-containing compounds that do not have These blowing agents may be used in combination of two or more types or in combination with a chemical blowing agent such as water. Stabilizers include antioxidants, ultraviolet absorbers, and hydrolysis inhibitors, and at least one selected from these is added and used, and the amount added is preferably 0.1 to 6% by weight. Antioxidants include hindered phenols, phenols, hindered amines, and phosphites. Among these, the relatively good ones are hindered phenols, especially 2,6 di-t-butyl.
4-methylphenol gave good results. Ultraviolet absorbers include benzophenones, salicylic acid esters, benzotriazoles, etc. Among these, benzotriazoles were good. The hydrolysis inhibitor is used to inhibit or prevent hydrolysis of polyurethane resin, and includes polymeric carbodiimide. These stabilizers can be used alone or in combination of two or more, and the amount added is preferably 0.1 to 6% by weight, and more preferably 0.5 to 2% by weight. If added alone, the amount used will be large in order to achieve the effect, and the stabilizer may have an adverse effect on the moldability of the polyurethane resin, so its selection is important. Preferably, the addition of two or more types is good, and in that case, the amount added is smaller than the case of adding only one type, and the same effect can be achieved. Examples of auxiliary agents include internal mold release agents and flame retardants, which can be added as necessary. How to mold polyurethane resin in a closed mold
The RIM (Reaction Injection Molding) method is a typical method, and it molds into integral skin foam, structural foam, microcellular, and solid (elastomer) forms using various formulations. integral skinned form,
Both structural foam and microcellular foam require a blowing agent during their formulation. Solids (elastomers) are used with a small amount, usually 0.1 to 3 parts, of a blowing agent added for the purpose of overpacking the resin in the mold. Polyurethane resins using these blowing agents that have extremely poor light resistance are integral skinned foams, particularly hard integral skinned foams (structural foams). This is thought to be because the foaming agent is trapped in the skin layer of integral skinned foam, which has skin layers on both sides of the foam layer, and this greatly affects the light resistance. This is clear from the following points. When a halogen-containing compound such as Freon 11 is used as a physical foaming agent, the light resistance deteriorates significantly, whereas when a non-halogen compound is used, the light resistance is significantly improved. Further, even if a halogen-containing compound is used, the light resistance can be improved to some extent by forcibly removing the foaming agent present in the skin layer by vacuum treatment or the like. The yellowing and deterioration mechanism of polyurethane resin is thought to be as follows. (Advances in Urethane Science and
Technology, Vol6, P103-172, Technomic
Pub., 1978) The decomposition products of polyurethane resins caused by ultraviolet rays are olefins, aldehydes, ketones, etc., and the mechanism of their formation is thought to be as follows. In the reaction shown by Beachell et al., polyurethane dissociates to produce isocyanate (1), and amine (2) is produced by decarboxylation of the urethane group. It is said that the reaction product of polycarbodiimide (3) and alcohol is added and the coloring increases. Schollenberger et al. reported that TDI and MDI-based polyurethanes yellow mainly due to the conversion of benzene rings into quinone and quinone imidization by ultraviolet rays. Conventional measures to prevent yellowing in the formulation of polyurethane resin include (1) adding ultraviolet absorbers and antioxidants, and (2) introducing an alkylene group between the benzene nucleus and -NCO group to suppress resonance between the two. Isocyanates such as XDI (xylylene diisocyanate)
method using (3) A method using an alicyclic polyisocyanate, such as hydrogenated MDI or IPDI (isophorone diisocyanate). (4) A common method is to use a lipophilic polyisocyanate that does not contain conjoint double bonds, such as HMDI (hexamethylene diisocyanate). (1) is a method of improving light resistance by adding a stabilizer, and (2) to (4) is a method of improving light resistance by using an isocyanate. In experiments conducted by the present inventors, the method (1) of adding a stabilizer was not very effective in preventing yellowing. In the methods (2) to (4) using isocyanates, when a halogen-containing compound was used as a blowing agent, no great effect was observed in preventing yellowing, and some yellowing occurred. This is thought to be because the foaming agent present in the skin layer is decomposed by ultraviolet rays to produce halogen, and the halogen causes oxidation reactions, radical reactions, etc., resulting in yellowing. Therefore, even if an isocyanate having a structure that is difficult to form a quinone or quinone imide structure is used, yellowing is thought to occur due to the reaction of Beachell et al. mentioned above. On the other hand, when a volatile non-halogen compound that does not contain a halogen element and is relatively stable against ultraviolet rays and heat is used as a blowing agent as in the present invention, there is nothing that promotes the yellowing reaction and the light resistance is extremely good. Become something. The difference in effectiveness when conventionally known isophorone diisocyanate is used in the light resistance formulation in the present invention is that the light resistance can be significantly improved by using a volatile non-halogen compound as a blowing agent. It is also highly effective in improving the light resistance of light-colored products with a brightness of 5 or more as represented by the Munsell symbol. This will be explained in more detail below with reference to Examples. For accelerated light resistance testing, test pieces were tested using a fade meter (carbon arc) at a black panel temperature of 63°C.
I did it at The evaluation was made by measuring the color before and after the test using a tristimulus value X, Y, Z system, and using Hunter color difference. Color measurement is done using “direct reading measurement color difference computer”
Measured using "CDE-SCH-4A" (Suga Test Instruments).For Hunter's dye ΔE (Lab), the smaller the value, the better; 3 or less indicates an inconspicuous color difference.Long-term UV rays The state of surface deterioration due to exposure was determined by visual inspection.In other words, when small cracks or pinholes were observed on the surface of the molded product in a certain measurement value, they were marked with an x symbol, and when they were not observed, they were marked with an ○ symbol. Reference examples 1 to 8 Reference examples 1 to 8 are reference examples of light resistance when the blowing agent and polyisocyanate are different for hard integral skinned foam. Yes.Reference Examples 1 to 4 use Freon 11 as a blowing agent, and Reference Example 5
-8 are cases where pentane is used as a blowing agent, and each is treated as a crude polyisocyanate.
This is a formulation using MDI, pure MDI carbodiimide modified polyisocyanate, XDI, and IPDI. After uniformly mixing the polyol components in advance with the formulation shown in Table 1, add polyisocyanate to this and quickly mix until uniform, then pour into a 30 x 30 x 1 cm metal mold (mold temperature approximately 45°C) and form a molded plate. Created. These molded plates are approximately 1mm thick on both sides with a foam layer in between.
It had a firm skin layer and an overall specific gravity of approximately 0.4. This was cut into test pieces of 2 x 15 x 1 cm and subjected to a light resistance test. The results are shown in Figure 1.

[Table] It is clear from this that the light resistance is greatly affected by the blowing agent, and when the halogen-containing compound Freon 11 is used as the blowing agent, the light resistance is extremely poor. In contrast, in the case of volatile non-halogen compounds, the light resistance is significantly improved. Even with the well-known XDI and IPDI (isophorone diisocyanate), which are said to have excellent light resistance, the light resistance deteriorates when Freon 11 is used. In the case of IPDI, the color difference △E (Lab) used for evaluating light resistance is around 8, which is expressed visually as "muck".
Indicates that the color will be much different from the initial color.
A value of ΔE (Lab) of 3 or less is good, indicating that it is not noticeable compared to the original color.
When using pentane for IPDI, △E (Lab) is 3 ~
4, indicating good light resistance. Comparative Examples 1 to 11 and Examples 1 to 5 Comparative Examples 1 to 11 and Examples 1 to 5 are comparative examples and examples in which different colorants are used for hard integral skinned foams. Comparative Examples 1 to 8 are comparative examples in which pure MDI carbodiimide-modified polyisocyanate and pentane were used and different colorants were used. The color of the isocyanate itself is pale yellow, and a desired color can be produced by adding a pale coloring agent to this. Comparative Examples 9 to 11 are comparative examples in which isophorone diisocyanate and Freon 11 were used to add a light coloring agent. Examples 1-5
This is an example in which isophorone diisocyanate and pentane were used to add a light coloring agent. After uniformly mixing the polyol components in advance with the formulation shown in Table 2, add polyisocyanate to this and quickly mix until uniform, then pour into a 30 x 30 x 1 cm metal mold (mold temperature approximately 45°C) and form a molded plate. Created. These molded plates are approximately 1mm thick on both sides with a foam layer in between.
It had a firm skin layer and an overall specific gravity of approximately 0.4. This was cut into test pieces of 2 x 15 x 1 cm and subjected to a light resistance test. The results are shown in FIGS. 2 and 3. In the systems of Comparative Examples 1 to 8 consisting of carbodiimide-modified polyisocyanate, pentane, and colorant, the light resistance is broadly classified into three types.
One type has a color difference △E (Lab) of 3 or less up to 200hys of ultraviolet irradiation. One is color difference △E (Lab) of 8 to 10.
The other one has a color difference ΔE (Lab) of 20 or more. These differ depending on the colorant, and the brighter the colorant, that is, the lighter the color, the worse the light resistance. Dark colors with a lightness of less than 5, represented by the Munsell symbol, have a strong shade of colorant, so their light resistance is △E (Lab).
is 3 or less, which is good. However, the higher the lightness value of 5 or more in the Munsell symbol, the worse the light fastness becomes, and the value of the color difference ΔE (Lab) increases, resulting in a color that is far different from the initial color. As shown in Examples 1 to 5, good results were obtained for the light resistance of molded products whose surface was created by adding a light colored colorant with a brightness of 5 or more expressed by the Munsell symbol. show. In this case, as shown in Comparative Examples 9 to 11, when Freon 11 is used as a foaming agent, the

[Table] The optical property deteriorates significantly and the use of isophorone diisocyanate becomes meaningless. Comparative Examples 12 to 16 and Examples 6 to 9 Comparative Examples 12 to 16 and Examples 6 to 9 are cases in which the types of stabilizers and blowing agents are different regarding rigid integral skinned foams. Comparative Examples 12 to 16 were obtained by adding a stabilizer to the formulation of Comparative Example 9, and Examples 6 to 10 were obtained by adding a stabilizer to the formulation of Example 1. Their formulations are shown in Table 3. Using these formulations, molded plates were made in the same manner as before and a light resistance test was carried out.

[Table] The surface deterioration state was observed and the results are shown in Table 4.
It was shown to.

[Table] 〓.
The addition of a stabilizer can significantly improve the deterioration of the surface of a molded article due to long-term exposure to ultraviolet rays, and the use of a volatile non-halogen compound as a blowing agent further improves this. In addition, it is more effective to use stabilizers in combination than to add them singly. As detailed above, the polyurethane resin molded according to the present invention does not require painting to supplement light resistance, and has excellent light resistance even if the surface color of the molded product is a light color with a lightness of 5 or more expressed by the Munsell symbol. ing. Furthermore, by adding a stabilizer to this formulation, it is possible to significantly improve surface deterioration such as fine cracks and pinholes caused by long-term exposure to ultraviolet rays.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the irradiation time and color difference △E (Lab) due to ultraviolet irradiation of hard integral skin foams using different polyisocyanates and blowing agents. Figure 2 is a diagram showing the relationship between color difference △E (Lab) using different coloring agents using carbodiimide-modified polyisocyanates. A diagram showing the relationship between irradiation time and color difference △E (Lab) due to ultraviolet irradiation of hard integral skinned foam. Figure 3 shows ultraviolet ray irradiation of hard integral skinned foam with different foaming agents and light coloring agent using isophorone diisocyanate. FIG. 3 is a diagram showing the relationship between irradiation time and color difference ΔE (Lab).

Claims (1)

[Claims] 1. When producing a foamed polyurethane resin molded product by reacting a polyol and a polyisocyanate in a closed mold, (a) a volatile non-halogen compound, (b) isophorone diisocyanate, and (c) Munsell symbol. 1. A method for photostabilizing polyurethane resin molded products, which comprises blending a colorant having a surface color of the molded product with a lightness of 5 or more. 2. Volatile non-halogen compounds at normal pressure from 20℃ to 100℃
The method for photostabilizing polyurethane resin molded articles according to claim 1, wherein the compound is selected from saturated hydrocarbons having a boiling point of 0.degree. C. and/or oxygen-containing hydrocarbons having no active hydrogen.