JPWO2007142260A1 - Thermoplastic resin foam - Google Patents

Abstract

The present invention provides a thermoplastic resin foam having high reflectivity and UV resistance, and suitable as a light reflector for an electric signboard, a lighting fixture, a display backlight, an illumination box, and the like. At least one surface has a large number of fine irregularities (10, 12), and at least one of an average value of distances between adjacent convex parts and an average value of distances between adjacent concave parts When the value of d is d, a thermoplastic resin foam that satisfies 0.01 μm ≦ d ≦ 20 μm is obtained. [Selection] Figure 1

Description

  The present invention relates to a thermoplastic resin foam, and more particularly to a sheet-like thermoplastic resin foam having a number of fine irregularities on the surface. The thermoplastic resin foam of the present invention can impart UV resistance without causing a significant increase in cost even when a resin that is likely to be deteriorated by UV is originally used. It can be suitably used as a light reflector such as a backlight or an illumination box.

  Conventionally, a light reflector made by processing a synthetic resin film or sheet that reflects light into a three-dimensional shape has been proposed as a light reflector used in electrical signs, lighting fixtures, display backlights, lighting boxes, etc. (For example, refer to Patent Document 1).

  Light emitted from a light source used for an electric signboard, a lighting fixture, a display backlight, a lighting box, and the like includes light in the ultraviolet region (ultraviolet rays) with high energy. Therefore, among resin members used in electrical signs, lighting fixtures, display backlights, lighting boxes, etc., those that are likely to deteriorate due to ultraviolet light will deteriorate with long-term use. Since the device has been devised to weaken the irradiation intensity, the deterioration rate is much slower than that of resin members exposed and used outdoors.

  However, resin members used in electrical signs, lighting fixtures, display backlights, lighting boxes, etc., even if the strength is sufficient to withstand the use, because of their use, surface In many cases, it is evaluated that the quality has deteriorated by a slight change in color, and the use limit has been exceeded. This is a much stricter requirement in consideration of the UV resistance required for ordinary resin products.

  On the other hand, the demand for cost reduction has been increasing in recent years for resin-made members used in electrical signs, lighting fixtures, display backlights, lighting boxes, etc. It is necessary to satisfy the severe UV resistance.

  On the other hand, Patent Document 2 discloses a method of imparting ultraviolet resistance to the resin reflector by providing a coating layer containing a light stabilizer on the surface of the resin reflector. However, in this method, since a special light stabilizer is used to provide UV resistance, a significant increase in cost is inevitable.

  Patent Document 3 discloses a technique for imparting ultraviolet resistance characteristics to a resin product without adding an ultraviolet absorber by devising the composition of the resin composition. However, this technique relates to a resin container, and its purpose is to protect the contents of the container from ultraviolet deterioration. That is, in the invention of Patent Document 3, the deterioration rate of the resin product itself due to ultraviolet rays does not slow down.

  Japanese Patent Application Laid-Open No. H10-228667 discloses a light reflecting plate having irregularities formed on the surface thereof. However, the object of the invention of Patent Document 4 is to make the reflection uniform by forming the unevenness, and does not mention at all the improvement of the ultraviolet resistance property due to the unevenness. The object of the present invention is to improve the ultraviolet resistance by fine unevenness, and is completely different from the object of the invention of Patent Document 4.

JP 2002-122863 A JP 2002-90515 A JP-A-12-85037 JP 2003-270415 A

  As described above, in recent years, excellent ultraviolet resistance is required for a resin film or sheet having a high reflectance.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a thermoplastic resin foam that can be produced at low cost while having both high reflectance and excellent ultraviolet resistance.

  As a result of intensive studies to solve the above-described problems, the present inventors have found that when a large number of fine irregularities are provided on the surface of the thermoplastic resin foam, even if the resin is originally susceptible to UV degradation, It has been found that UV resistance can be imparted to a plastic resin foam at a low cost.

This invention is made | formed based on the knowledge mentioned above, and provides the thermoplastic resin foam shown to following (1)-(8).
(1) At least one of the surfaces has a large number of fine irregularities, and at least one of the average value of the distance between adjacent convex portions and the average value of the distance between adjacent concave portions is d The thermoplastic resin foam is characterized in that 0.01 μm ≦ d ≦ 20 μm.
(2) After producing a fine foam, at least one surface portion of the fine foam is removed to expose an internal fine foam portion, thereby forming the numerous fine irregularities. The thermoplastic resin foam of (1).
(3) The thermoplastic resin foam according to (1) or (2), wherein the thermoplastic resin foam contains an ultraviolet absorber.
(4) The thermoplastic resin foam according to any one of (1) to (3), wherein a coating layer is formed on a surface having a large number of fine irregularities of the thermoplastic resin foam.
(5) The thermoplastic resin foam according to (4), wherein the coating layer contains an ultraviolet absorber.
(6) The thermoplastic resin foam according to any one of (1) to (5), wherein the thermoplastic resin foam is a polyester resin foam.
(7) The thermoplastic resin foam according to any one of (1) to (6), wherein the specific gravity of the thermoplastic resin foam is 0.7 or less.
(8) Any one of (1) to (7), wherein an average reflectance of light in a wavelength region of 400 nm to 700 nm on the surface having a large number of fine irregularities of the thermoplastic resin foam is 90% or more Such thermoplastic resin foam.

  The thermoplastic resin foam of the present invention has a high light reflectivity and can be produced at low cost while having excellent UV resistance, and even with a resin that is originally susceptible to UV degradation, it is resistant to fine irregularities on the surface. Since the ultraviolet characteristics can be strengthened, it can be suitably used as a light reflector such as an electric signboard, a lighting fixture, a display backlight, or an illumination box.

  The reason why the above effect is obtained by the thermoplastic resin foam of the present invention is not clear, but the presence of many fine irregularities on the surface seems to cause complicated behavior such as reflection, interference and diffraction on the surface. It is expected that it becomes difficult to enter the resin. In addition, the thermoplastic resin foam of the present invention has a smaller resin volume near the surface than a resin foam that does not have fine irregularities on the surface. It may be possible to be suppressed.

It is a figure showing evaluation of d in case only a convex part can be confirmed in the foam surface. It is a figure showing evaluation of d when only a crevice can be checked in a foam surface. It is a figure showing evaluation of d when both a convex part and a recessed part can be confirmed in the foam surface. It is a schematic sectional drawing when the surface layer of a fine foam is cut with a slicer.

  Hereinafter, the present invention will be described in more detail. In the present invention, at least one of the average value of the distance between the adjacent convex portions and the average value of the distance between the adjacent concave portions on the surface having a large number of fine irregularities of the thermoplastic resin foam is set to at least one value. Let d. That is, as in the surface shown in FIG. 1, when the convex portion 10 can be recognized but the concave portion 12 cannot be recognized, the average value of the distances between all the adjacent convex portions 10 is defined as d. When the concave portion 12 can be recognized but the convex portion 10 cannot be recognized as in the surface shown in FIG. 2, the average value of the distances between all the adjacent concave portions 12 is defined as d. When both the convex portion 10 and the concave portion 12 can be recognized as in the surface shown in FIG. 3, the average value of the distances between all the adjacent concave portions 12 is d1, and the average of the distances between all the adjacent concave portions 12 The value is d2, and both d1 and d2 are d.

  In the present invention, the value of d described above is set to 0.01 μm ≦ d ≦ 20 μm. More preferably, 0.01 μm ≦ d ≦ 10 μm, and most preferably 0.01 μm ≦ d ≦ 5 μm. The smaller d, the finer the surface uneven structure, which is desirable from the standpoint of enhancing ultraviolet resistance. However, if d is smaller than 0.01 μm, d becomes too small compared with the wavelength of ultraviolet rays, and ultraviolet rays enter the resin. When d is larger than 20 μm, good ultraviolet resistance characteristics cannot be obtained.

  The kind of resin that is a main constituent of the thermoplastic resin foam of the present invention is not particularly limited, and polyester, polycarbonate, polyamide, polyolefin, polystyrene, acrylic resin, and the like are used. In the present invention, a polyester-based resin can be preferably used among these because the surface structure has UV resistance. The kind of polyester resin is not particularly limited, and polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and the like can be appropriately selected. These may be used individually by 1 type, and may mix and use 2 or more types. Among polyester resins, polyethylene terephthalate is particularly preferable in terms of foamability and heat resistance.

  In the present invention, a crystallization nucleating agent, a crystallization accelerator, an aerated nucleating agent, an oxidizing agent are added to the thermoplastic resin foam material before foaming within a range that does not significantly increase the cost and does not affect the characteristics. Inhibitor, antistatic agent, ultraviolet absorber, light stabilizer, fluorescent whitening agent, pigment, dye, compatibilizer, lubricant, reinforcing agent, flame retardant, crosslinking agent, crosslinking aid, plasticizer, thickener, Various additives such as a viscosity reducer may be blended, and it is particularly preferable to blend an ultraviolet absorber or a light stabilizer. Examples of UV absorbers and light stabilizers include organic UV absorbers and stabilizers such as hindered amine, salicylic acid, benzophenone, benzotriazole, cyanoacrylate, triazine, benzoate, and oxalate anilide, or Inorganic ultraviolet absorbers and light stabilizers such as sol-gel and metal oxide can be used. In the present invention, the UV resistance is enhanced by the surface structure, but it is preferable to appropriately use these UV absorbers and light stabilizers depending on the use environment. However, if the amount of the organic ultraviolet absorber or light stabilizer is too large, the foam becomes yellowish, so the amount is preferably 0.01 to 1% by weight. Inorganic ultraviolet absorbers and light stabilizers are not limited thereto, but the blending amount is preferably 0.01 to 10% by weight in view of demands for other characteristics such as foam strength. Moreover, you may laminate | stack the resin layer containing the said additive on the obtained thermoplastic resin foam.

  In this invention, a coating layer can be formed on the surface which has many fine unevenness | corrugations of a thermoplastic resin foam. This is because, depending on the use environment, the irregularities may adsorb dust in the atmosphere, which may impair the function as a light reflecting plate. In addition, this coating layer has an antioxidant, antistatic agent, ultraviolet absorber, light stabilizer, fluorescent whitening agent, pigment, dye, compatibilizing agent, lubricant, and reinforcement within a range that does not cause a significant increase in cost. Various additives such as an agent, a flame retardant, a cross-linking agent, a cross-linking aid, a plasticizer, a thickener, and a thinning agent may be blended, and it is particularly preferable to blend an ultraviolet absorber or a light stabilizer.

  In the present invention, when the specific gravity of the thermoplastic resin foam increases, that is, when the foaming ratio of the thermoplastic resin foam decreases, as a result, the reflectivity decreases due to the decrease in the bubble rate, the moldability decreases, and the weight reduction effect. Since it leads to a reduction | decrease, it is preferable that the specific gravity of the obtained thermoplastic resin foam is 0.7 or less. More preferably, it is 0.65 or less, More preferably, it is 0.5 or less.

  In the present invention, the bubble diameter of the bubbles contained in the resin foam is not particularly limited, but is preferably 0.01 to 20 μm. Especially preferably, it is 0.01-10 micrometers. When the bubble diameter is smaller than 0.01 μm, the bubble diameter becomes too small compared to the wavelength of visible light, so that light easily passes through the resin foam, and the characteristics as a light reflecting plate become insufficient. On the other hand, if the bubble diameter exceeds 20 μm, the reflectance of the entire light reflecting plate is lowered, and as a result, the characteristics as the light reflecting plate are also insufficient.

  In the present invention, the average reflectance of light in the wavelength region of 400 nm to 700 nm on the surface of the thermoplastic resin foam having a large number of fine irregularities is preferably 90% or more. More preferably, it is 94% or more, and most preferably 98% or more. If the average reflectance is less than 90%, it cannot be said that the light energy emitted from the light source is sufficiently utilized, and more energy than necessary is wasted in order to obtain desired brightness and brightness. In general, a light reflector is incorporated into a design on the assumption that not only light from the light source (primary light) but also light that has returned from the exit surface (secondary light and return light) will be reflected. This is because the light energy loss from the actual light source becomes large.

  The method for producing the thermoplastic resin foam of the present invention is not particularly limited, but considering the mass productivity, for example, the following method is preferably used. That is, a resin sheet made of a thermoplastic resin composition is prepared, a roll is formed by winding the resin sheet and a separator, and the roll is held in a pressurized inert gas atmosphere so that the resin sheet is not It is preferable to use a method in which an active gas is contained and a resin sheet further containing an inert gas is heated to a temperature equal to or higher than the softening temperature of the thermoplastic resin under normal pressure.

  Examples of the inert gas include helium, nitrogen, carbon dioxide, and argon. The inert gas permeation time and the inert gas permeation amount until the resin sheet is saturated vary depending on the type of resin to be foamed, the type of inert gas, the permeation pressure, and the thickness of the sheet. In consideration of gas permeability (rate, solubility) to the resin, carbon dioxide is more preferable.

  Moreover, in the said method, before hold | maintaining the roll which consists of a resin sheet and a separator in a pressurization inert gas atmosphere, and making an inert gas contain in a resin sheet, you may make the resin sheet contain an organic solvent. Examples of the organic solvent include benzene, toluene, methyl ethyl ketone, ethyl formate, acetone, acetic acid, dioxane, m-cresol, aniline, acrylonitrile, dimethyl phthalate, nitroethane, nitromethane, and benzyl alcohol. Of these, acetone is more preferable from the viewpoints of handleability and economy.

  The thermoplastic resin foam obtained by the method described above contains a large number of fine bubbles inside. The method for providing fine irregularities on the surface of the foam is not limited. For example, the following method can be used. That is, the surface of the foam is cut with a sharp blade, the surface of the foam is cut with a slicer perpendicular to the thickness direction, or the surface of the foam is bonded to a jig, and then the entire surface of the foam is peeled off. By removing the bubbles, the bubbles inside the foam are exposed. Since the internal fine bubbles are exposed on the surface by these methods, at least one of the average value of the distance between the adjacent convex portions and the average value of the distance between the adjacent concave portions is defined as d. In this case, a large number of irregularities that satisfy 0.01 μm ≦ d ≦ 20 μm can be easily formed on the surface. Of course, the method is not limited to the above method as long as the above condition can be achieved.

Hereinafter, the present invention will be described by way of examples. In addition, the measurement and evaluation of various characteristics of the obtained thermoplastic resin foam were as follows.
(specific gravity)
The specific gravity (ρf) of the foam sheet was measured by an underwater substitution method.
(Foaming ratio)
The ratio was calculated as a ratio ρs / ρf between the specific gravity (ρf) of the foam sheet and the specific gravity (ρs) of the resin before foaming. However, ρs was calculated as 1.34 for polyethylene terephthalate.
(Evaluation method of fine uneven structure on the surface)
An SEM photograph of the surface of the foam sheet is taken. In the photograph of the surface, when the convex portion 10 is independent and can be recognized as shown in FIG. 1 and the concave portion 12 cannot be recognized, the distance between all the adjacent convex portions 10 within the photographed range is measured, Get the average value. This is d. On the contrary, as shown in FIG. 2, when the convex portion 10 cannot be recognized and the concave portion 12 is independent and can be recognized, the distance between all the adjacent concave portions 12 in the photographed range is measured, and the average value thereof is measured. Get. This is d. When both the convex portion 10 and the concave portion 12 can be recognized as shown in FIG. 3, the average distance between all the adjacent convex portions 10 is d1, and the average distance between all the adjacent concave portions 12 is d2. To do. Both of these values d1 and d2 are evaluated as d. In addition, when there is a coating layer or when another substance is laminated, an SEM photograph of a cross section is taken. When the surface structure of the foam is confirmed in the photograph and both the convex portions and the concave portions can be recognized, the average distance between all adjacent convex portions is d1, and the average distance between all adjacent concave portions is d2. . Both of these values d1 and d2 are evaluated as d. When only one of the convex portion and the concave portion can be recognized, the average value of the distances between all adjacent convex portions or the concave portions is evaluated as d.
(Reflectance)
The reflectance in the wavelength range of 400 to 700 nm was measured using a spectrophotometer (UV-3101PC, manufactured by Shimadzu Corporation). This reflectance was converted to a relative value with the diffuse reflectance of a white plate obtained by solidifying fine barium sulfate powder as 100%, and averaged over this wavelength range.
(Evaluation of UV resistance)
Using a foam sheet as a sample, using an iSuper UV tester (SUV-W151, manufactured by Iwasaki Electric Co., Ltd.), a wavelength range of 300 nm to 400 nm, an irradiation intensity of 100 mW / cm ² , a test temperature of 63 ± 3 ° C., and a humidity of 50 ± 10 UV irradiation was performed under the conditions of% RH and irradiation time of 15 hours. Before and after this test, L ^* , a ^* , b ^* values were measured according to JIS Z8730 using a color difference meter (CR-300, manufactured by Minolta), and ΔE ^* values were calculated from the following formulas. The smaller this value ΔE ^{*, the} better the UV resistance.
ΔE ^* = (ΔL ² + Δa ^{* 2} + Δb ^{* 2} ) ^0.5

(Example 1)
Polyethylene terephthalate (grade: C-0312, manufactured by Unitika) was molded into a sheet of 0.6 mm thickness × 300 mm width × 60 m length. This resin sheet is overlaid with an olefin-based nonwoven fabric separator (grade: FT300, manufactured by Nippon Vilene Co., Ltd.) having a thickness of 160 μm × 290 mm width × 60 m length and a basis weight of 55 g / m ^2. It was rolled into a roll shape so that there was no part to do. Then, this roll was put into a pressure vessel, pressurized to 6 MPa with carbon dioxide gas, and carbon dioxide gas was infiltrated into the resin sheet. The penetration time of carbon dioxide gas into the resin sheet was 72 hours. Next, the roll was taken out from the pressure vessel, and while removing the separator, the resin sheet alone was continuously supplied to a hot-air circulating foaming furnace set at 220 ° C. so that the foaming time was 1 minute, and foamed.

  The cross section of the obtained foam was as shown in FIG. The obtained foam was uniformly foamed, and the average cell diameter was as very fine as 10 μm. The thickness of the foam was 1.0 mm, and the average reflectance of the foam was as high as 97.0%.

Further, the surface of the obtained foam was cut with a slicer (trade name FORTUNA, manufactured by Reader Co., Ltd.) in a plane perpendicular to the thickness direction, and the surface layer was removed by 0.2 mm. A schematic view of the cross section of the obtained foam is shown in FIG. In FIG. 4, 14 is a foam, 10 is a convex portion, 12 is a concave portion, and 16 is a bubble. When the irregularities on the surface of the foam were confirmed and d was measured, the average distance d1 between adjacent convex portions was 11 μm. Moreover, when the ultraviolet-ray resistant property of this foam was evaluated, ΔE ^* was 24.4.

(Example 2)
A master batch (Nanomax EZ153, manufactured by Showa Denko) containing polyethylene oxide terephthalate (grade: C-0312, manufactured by Unitika Ltd.) containing an inorganic oxide filler (zinc oxide) having ultraviolet shielding properties and a filler content of 0.5 mass. After adding and kneading so as to be part, it was molded into a sheet of 0.6 mm thickness × 300 mm width × 60 m length, and this sheet was foamed under the same conditions as in Example 1.

The obtained foam was uniformly foamed, and the average cell diameter was very fine at 7 μm. The thickness of the foam was 1.0 mm, and the average reflectance of the foam was as high as 97.8%. A surface layer of this foam was removed by 0.2 mm by the same method as in Example 1. When the unevenness of the surface of this foam was confirmed and d was measured, d was 8 μm. Further, when the ultraviolet resistant property of this foam was evaluated, ΔE ^* was 10.4, and the ultraviolet resistant property was improved.

(Comparative Example 1)
The foam obtained in Example 1 was used as Comparative Example 1 without removing the surface layer. This foam had a flat surface. When the UV resistance of this foam was evaluated, ΔE ^* was 46.8.

(Comparative Example 2)
The foam obtained in Example 2 without removing the surface layer was used as Comparative Example 2. When the UV resistance of this foam was evaluated, ΔE ^* was 42.2.

(Comparative Example 3)
To polyethylene terephthalate (grade: C-0312, manufactured by Unitika Ltd.), an inorganic oxide filler (two types of zinc oxide, manufactured by Shodo Chemical Industry Co., Ltd.) was added and kneaded so that the filler content was 2.0 parts by mass. Thereafter, the sheet was formed into a sheet of 0.6 mm thickness × 300 mm width × 60 m length, and the sheet was foamed under the same conditions as in Example 1. As a result, a foam having a large surface was obtained. When d was evaluated, it was 500 μm and ΔE ^* was 29.9.

The results are shown in Table 1. The evaluation criteria for ultraviolet resistance in Table 1 are as follows.
(Double-circle): The ultraviolet-ray resistant characteristic is very good.
○: UV resistance is good.
×: UV resistance is poor.

  As described above, when Example 1 and Comparative Example 1 are compared with each other, it can be seen that the deterioration of ultraviolet rays is reduced due to the unevenness of the surface without performing ultraviolet resistant prescription with an inorganic oxide filler. Moreover, as shown in Example 2, it can be seen that the UV resistance is further improved by the surface unevenness effect and UV resistance prescription. In addition, although the comparative example 2 is an example which does not scrape the surface of the foam of Example 2, since the kneaded inorganic oxide filler is difficult to be distributed in the vicinity of the foam surface, the effect does not occur. As can be seen from Example 2.

Claims (8)

  When at least one surface has a large number of fine irregularities, and at least one of the average value of the distance between adjacent convex portions and the average value of the distance between adjacent concave portions is d And a thermoplastic resin foam characterized by satisfying 0.01 μm ≦ d ≦ 20 μm.   2. The fine foam is produced by removing at least one surface portion of the fine foam and exposing an internal fine foam portion to form the numerous fine irregularities. The thermoplastic resin foam described in 1.   The thermoplastic resin foam according to claim 1 or 2, wherein the thermoplastic resin foam contains an ultraviolet absorber and / or a light stabilizer.   The thermoplastic resin foam according to any one of claims 1 to 3, wherein a coating layer is formed on the surface of the thermoplastic resin foam having a large number of fine irregularities.   The thermoplastic resin foam according to claim 4, wherein the coating layer contains an ultraviolet absorber and / or a light stabilizer.   The thermoplastic resin foam according to any one of claims 1 to 5, wherein the thermoplastic resin foam is a polyester resin foam.   The specific gravity of a thermoplastic resin foam is 0.7 or less, The thermoplastic resin foam of any one of Claims 1-6 characterized by the above-mentioned.   8. The average reflectance of light in a wavelength region of 400 nm to 700 nm on the surface having a large number of fine irregularities of the thermoplastic resin foam is 90% or more. Thermoplastic resin foam.

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