JP2006095944A - Thermoplastic resin foam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoplastic resin foam which is suitable for a backlight and an illumination box such as an illumination fascia, a lighting equipment, a display or the like, and which has a high reflectance ratio. <P>SOLUTION: The thermoplastic resin foam is manufactured by a manufacturing method comprising: a process which makes a thermoplastic resin sheet contain inert gas by keeping it in a pressurized inert gas atmosphere; a process which heats the thermoplastic resin sheet containing inert gas and makes it to foam under an ordinary pressure; and a process which draws the foamed thermoplastic resin in at least uniaxial direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a thermoplastic resin foam sheet suitable for backlights and lighting boxes such as electric signboards, lighting fixtures, and displays.

2. Description of the Related Art Conventionally, a light reflecting plate obtained by processing a synthetic resin film or sheet that reflects light into a three-dimensional shape has been proposed as a light reflecting plate used for backlights of electric signs, lighting fixtures, and displays. (For example, refer to Patent Document 1).

As a film or sheet made of a synthetic resin that reflects light, a film or sheet of a thermoplastic resin foam having a large number of fine bubbles or pores therein (see, for example, Patent Document 2), or a thermoplastic resin containing a filler A film is known in which a large number of voids are formed using a filler as a core (see, for example, Patent Document 3).

The former foam with a large number of fine bubbles or pores is made by bringing the molten or solid thermoplastic resin into contact with an inert gas under pressure, then depressurizing and softening the resin under normal pressure. It can be obtained by foaming by heating above the temperature. The obtained thermoplastic resin foam film or sheet has an average cell diameter as fine as 50 μm or less, and thus has high reflectivity and excellent shape retention. A film or sheet alone can be processed into a three-dimensional shape. In general, the light reflectance of a thermoplastic resin foam film or sheet tends to decrease as the thickness of the film or sheet decreases. Therefore, there is a need for a thermoplastic resin foam that is thin but has high reflectivity.

On the other hand, the film of the thermoplastic resin containing the latter filler is formed by forming an unstretched film containing a filler such as calcium carbonate or barium sulfate, and stretching the unstretched film, so that a large number of voids with the filler as a core are formed. Is obtained. Since the obtained film is as thin as less than 200 μm, the film alone does not have shape retaining property, and more light leaks to the back of the film. Therefore, a plate having sufficient strength and light shielding property is disposed on the back side of the film.

Incidentally, a binding band obtained by stretching a foamed polyester sheet is known (see, for example, Patent Document 4). However, this only describes that a binding band having sufficient tensile strength and appropriate flexibility can be obtained by stretching the foam.
Moreover, the white film obtained by extending | stretching a melt-extrusion foam is known (for example, refer patent document 5 and patent document 6). However, as described in Patent Document 5, since the foam obtained by the melt extrusion method has a large bubble diameter of 15 to 400 μm (80 to 350 μm in the examples), it is highly reflective even when it is stretched. Rate film can not be obtained. As described in Patent Documents 5 and 6, maintaining the pressure of the die is a necessary condition for obtaining fine bubbles by the melt extrusion method, but not only that, but also increasing the pressure drop rate at the outlet. It is also necessary to take. These techniques are known in various literatures, but although this method can be carried out with a narrow film, it is very difficult to carry out a wide product level (for example, about 600 mm to 1500 mm width). Although it is possible to widen a narrow film by stretching in a subsequent process, in that case, only a very thin film can be obtained. In the case of a thin film, it is difficult to obtain a high reflectance, and shape retention property, handling property, and assembly workability are inferior. In particular, there is a problem when used as a light reflecting plate.

JP 2002-122863 A WO97 / 01117 Publication Japanese Patent Laid-Open No. 4-296619 Japanese Patent Laid-Open No. 10-101127 Japanese Patent Laid-Open No. 2004-195685 JP-A-11-300814

In recent years, power saving has been demanded, and a resin film or sheet having higher reflectivity has been demanded. Further, particularly in the field of electric signboards and displays, there is an increasing need for space saving, and a thin resin film or sheet that reflects light is required. However, as described above, when the film or sheet is made thinner, the reflectivity decreases as the film or sheet becomes thinner, and it tends to be difficult to obtain a reflector satisfying the recent requirements for high luminance and high reflectivity. In addition, as the thickness is reduced, there is a problem that the shape retainability is lowered and the secondary workability such as bending and punching is lowered. Further, in the case of a thin film or sheet, there is a problem in that it is difficult to align when incorporated in a display backlight or the like, and the work efficiency is lowered. An object of the present invention is to provide a thermoplastic resin foam that is not only thin and has a higher reflectance, but also has excellent processability and shape retention.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have held a thermoplastic resin sheet in a pressurized inert gas atmosphere to contain an inert gas (hereinafter referred to as “first step”). ), A step of heating and foaming a thermoplastic resin sheet containing an inert gas under normal pressure (hereinafter referred to as “second step”), and a step of stretching the foamed thermoplastic resin sheet (hereinafter referred to as “third”). It has been found that a thermoplastic resin foam having a higher reflectivity can be obtained by producing by a production method consisting of “process”. That is, the present invention
(1) A step of holding the thermoplastic resin sheet in a pressurized inert gas atmosphere to contain the inert gas, and a step of heating and foaming the thermoplastic resin sheet containing the inert gas under normal pressure, and A thermoplastic resin foam produced by a production method comprising a step of stretching a foamed thermoplastic resin sheet at least uniaxially;
(2) The thermoplastic resin according to (1), wherein the thermoplastic resin foam has an expansion ratio of 2 times or more, and a thickness of the thermoplastic resin foam sheet is 250 μm or more. Resin foam,
(3) The thermoplastic resin foam according to (1) or (2), wherein an average reflectance in a wavelength range of 400 to 700 nm is 90% or more,
(4) The thermoplastic resin foam according to any one of (1) to (3), wherein the thermoplastic resin is polyester.
Is to provide.

The thermoplastic resin foam obtained by the present invention can be thinned and has a smaller cell diameter than a thermoplastic resin foam sheet obtained by stretching a melt-extruded foam. High reflectivity not obtained. In addition, the thermoplastic resin foam obtained by the present invention has excellent shape-retaining properties despite being thin, and the thermoplastic resin foam film or sheet alone is processed into a three-dimensional shape. Is possible. Therefore, the work efficiency of incorporation into the backlight of the display is good. Furthermore, since the thermoplastic resin foam obtained by the present invention has superior tensile elongation characteristics compared to conventional thermoplastic resin foams, defects such as sheet cracking occur when processed into a three-dimensional shape. Hateful.
That is, the thermoplastic resin foam obtained by the present invention can be suitably used as a backlight of an electric signboard, a lighting fixture, a display, or a light reflecting plate of an illumination box.

In the first step of the present invention, first, a roll is formed by winding a thermoplastic resin sheet and a separator, and the roll is held in a pressurized inert gas atmosphere so that the inert gas is supplied to the thermoplastic resin sheet. Contain.
Examples of the inert gas include helium, nitrogen, carbon dioxide, argon, and compressed air. The inert gas permeation time and the inert gas permeation amount until the thermoplastic resin is saturated vary depending on the type of thermoplastic resin to be foamed, the type of inert gas, the permeation pressure, and the thickness of the sheet.

In addition, you may make it contain in the organic solvent before hold | maintaining the roll which consists of a thermoplastic resin sheet and a separator in a pressurization inert gas atmosphere, and making this thermoplastic resin sheet contain an inert gas.
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.

  When the thermoplastic resin is polyethylene terephthalate, it is preferable that the degree of crystallinity of the thermoplastic polyester resin sheet after containing the inert gas is 30% or more. If the crystallinity is 30% or more, more uniform and fine bubbles can be obtained.

In the second step of the present invention, the thermoplastic resin sheet containing the inert gas through the first step is foamed by heating under normal pressure. Examples of the heating means in this step include a hot air circulation type foaming furnace, an oil bath, a molten salt bath, and the like.

More specifically, for example, a method is used in which a roll is taken out from the pressure vessel and only the resin sheet is passed through a hot-air circulating foaming furnace while separating the thermoplastic resin sheet and the separator. The foaming conditions are set to be equal to or higher than the softening temperature of the thermoplastic resin. Thereafter, the foamed sheet coming out of the furnace is immediately formed flat with a forming roll.

  In the third step of the present invention, the thermoplastic resin sheet foamed through the first step and the second step is stretched at least uniaxially. In the case of performing biaxial stretching, any of sequential biaxially oriented stretching, simultaneous biaxially oriented stretching, and stretching combining them may be used. Further, the stretching may be single-stage stretching or multi-stage stretching. The stretching is preferably performed at a temperature not lower than the glass transition temperature of the thermoplastic resin and not higher than the melting temperature. For example, when the thermoplastic resin is polyethylene terephthalate, the stretching is preferably performed at 70 to 220 ° C, preferably 80 to 200 ° C. Further, after stretching, the thermoplastic resin foam sheet may be heat-set by heat treatment. The temperature for the heat treatment is generally from the glass transition temperature of the thermoplastic resin to the melting point or less, but is appropriately set so as to satisfy various properties finally required as a product.

Although the stretching method is not particularly limited, an example is a method of stretching by a predetermined ratio by a tenter method. At this time, the draw ratio is not particularly limited. For example, when the thermoplastic resin is polyethylene terephthalate, it is 1.1 times or more in the longitudinal direction in the case of uniaxial stretching, 1.1 times or more in the longitudinal direction or in the transverse direction in the case of biaxial stretching. Less than is preferable. More preferably, it is 1.2 to 4 times, and further preferably 1.2 to 3 times. If the draw ratio is 1.1 times or more and less than 5 times, a sufficient drawing effect can be obtained, and there is no problem such as an increase in thermal shrinkage or a decrease in tear propagation resistance, and a heat with higher reflectivity. A plastic resin foam can be obtained.

  Further, the expansion ratio of the thermoplastic resin foam obtained in the present invention is not particularly limited, but is preferably 2 times or more. More preferably, it is 2.5 times or more, more preferably 3 times or more. In particular, when the foaming ratio of the thermoplastic resin foam is 1.3 times or less, the bubble distribution tends to be sparse, and as a result, the reflectance tends to decrease. When the expansion ratio is 2 times or more, there is an effect of reducing the weight, and in the secondary processing such as bending and punching, folding back and defective punching hardly occur and the productivity is excellent.

  The thickness of the thermoplastic resin foam obtained in the present invention is not particularly limited, but is preferably 250 μm or more. More preferably, it is 300 micrometers or more, More preferably, it is 350 micrometers or more. When the thickness of the thermoplastic resin foam is 250 μm or more, it exhibits high reflectivity and is excellent in shape retention, secondary workability, and assembly workability.

  The average reflectance of light in the wavelength region of 400 nm to 700 nm of the thermoplastic resin foam obtained in the present invention is preferably 90% or more. More preferably, it is 95% or more, more preferably 97% or more, and particularly preferably 98% or more. When the reflectance is less than 90%, the reflection characteristics required as a light reflecting plate are not sufficiently satisfied, and as a result, a sufficient brightness improvement effect as a product incorporating the light reflecting plate tends not to be obtained.

  The surface glossiness of the thermoplastic resin foam obtained in the present invention is not particularly limited, but is preferably 50% or more. More preferably, it is 60% or more, More preferably, it is 65% or more. When the surface glossiness is 50% or more, the diffuse reflection component is reduced, and particularly when used for a backlight, the amount of light reflected on the front surface increases, and the luminance tends to be further improved.

  The thermoplastic resin used in the present invention is not particularly limited, but is a general-purpose resin such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polychlorinated biphenyl, polyethylene terephthalate, polyvinyl alcohol, polycarbonate, polybutylene terephthalate, polyamide, polyacetal, polyphenylene ether. , Engineering plastics such as ultrahigh molecular weight polyethylene, polysulfone, polyethersulfone, polyphenylene sulfide, polyarylate, polyamideimide, polyetherimide, polyetheretherketone, polyimide, polytetrafluoroethylene, liquid crystal polymer, fluororesin, or these Or a copolymer thereof. Among these, polyester, polycarbonate, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, and cyclopolyolefin are preferable because of good heat resistance and impact resistance, and polyester is particularly preferable. Furthermore, among polyesters, polyethylene terephthalate is particularly preferable.

In the present invention, to the thermoplastic resin before foaming, the crystallization nucleating agent, the crystallization accelerator, the bubbling nucleating agent, the antioxidant, the antistatic agent, the ultraviolet ray preventing agent, the light stabilizing agent, as long as the properties are not affected. Various additives such as additives, fluorescent brighteners, pigments, dyes, compatibilizers, lubricants, reinforcing agents, flame retardants, cross-linking agents, cross-linking aids, plasticizers, thickeners, thickeners, etc. good. Moreover, the resin containing the said additive may be laminated | stacked on the obtained thermoplastic resin foam, and the coating material containing the said additive may be coated.

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to the following examples. In addition, the measurement and evaluation of the various characteristics of the obtained thermoplastic resin foam were as follows.
(density)
The density (ρf) of the thermoplastic foam was determined by a water displacement method using an electronic balance (AE240 manufactured by METTER).
(Foaming ratio)
The density (ρf) of the foam sheet was measured by an underwater substitution method and calculated as a ratio ρs / ρf with respect to the density (ρs) of the resin before foaming. However, when the thermoplastic resin was polyethylene terephthalate, ρs was calculated as 1.34.
(thickness)
The thickness of 5 points in the width direction of the obtained thermoplastic resin foam was measured using Teclock SM-112 (measuring element shape Φ10 mm, measuring force 2.5 N or less), and the average value was measured for the thermoplastic resin foam. The thickness was taken.
(Reflectance)
Using a spectrophotometer (UV-3101PC: manufactured by Shimadzu Corporation), the reflectance in the wavelength range of 400 to 700 nm was measured, the reflectance was read at 1 nm intervals from the obtained chart, and the average value was calculated. In Table 1, the diffuse reflectance of each thermoplastic resin foam is shown as a relative value, assuming that the diffuse reflectance of the white plate in which the fine powder of barium sulfate is hardened is 100%.
(Whiteness)
It calculated | required according to JIS-L-1015. That is, when the reflectance at wavelengths of 450 nm and 550 nm measured using a spectrophotometer (UV-3101PC: manufactured by Shimadzu Corporation) was B% and G%, respectively, whiteness was obtained by substituting into the following formula.
Whiteness = 4B-3G
(Surface gloss)
The surface gloss was measured with a gloss meter (GM-268 manufactured by Minolta) at an incident angle of 60 ° and a light receiving angle of 60 °. All measurements were performed with the number of samples n = 5, and the average value was obtained.
(Shape retention)
The resulting thermoplastic resin foam was thermoformed with a vacuum molding machine into a hemispherical light reflector having an opening diameter of 100 mm and a depth of 70 mm as shown in FIG. The obtained light reflection plate was held by hand and force was applied to observe the presence or absence of deformation to evaluate shape retention.

Example 1
A roll of polyethylene terephthalate sheet (C-0312 grade, manufactured by Unitika Co., Ltd.) having a thickness of 0.6 mm × 300 mm width × 60 m and a separator having a thickness of 160 μm thickness × 290 mm width × 60 m length and a basis weight of 55 g / m 2 An olefin-based non-woven roll (FT300 grade, manufactured by Nippon Vilene Co., Ltd.) was prepared. The rolls were overlapped and wound so that there was no portion where the surfaces of the polyethylene terephthalate sheet contacted each other, and a new roll was produced.

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 polyethylene terephthalate sheet. The carbon dioxide gas permeation time into the polyethylene terephthalate sheet was 72 hours.

Next, the roll is taken out from the pressure vessel, and only the polyethylene terephthalate sheet infiltrated with carbon dioxide gas is continuously supplied to a hot-air circulating foaming furnace set at 220 ° C. so that the foaming time is 1 minute while removing the separator. Foamed. The obtained foam had a thickness of 1000 μm and an average cell diameter of 9 μm.

Next, the sheet was stretched in a uniaxial direction at 180 ° C. using a tenter method stretching apparatus so that the stretching ratio was 2.0 times, heat-treated at 200 ° C. as it was, and then gradually cooled to room temperature. .
Although the stretched foam was thinned to 35% of the thickness before stretching, the reflectivity showed a value of 101.1%, which could not be considered by the conventional method. The whiteness was 107.5. The obtained results are shown in Table 1.

(Example 2)
The conditions were the same as in Example 1 except that the draw ratio was 1.4. The obtained results are shown in Table 1.

(Example 3)
The conditions were the same as in Example 1 except that the draw ratio was 2.4 times. The obtained results are shown in Table 1.

Example 4
The conditions were the same as in Example 1 except that the stretching temperature was 200 ° C. and the stretching ratio was 2.5 times. The obtained results are shown in Table 1.
The stretched foam showed a value of 102.7%, which was unthinkable by the conventional method, although the thickness was reduced to 32% compared to the thickness before stretching. The whiteness was 110.9. The obtained results are shown in Table 1.

(Example 5)
The conditions were the same as in Example 1 except that the drawing temperature was 80 ° C. and the draw ratio was 1.5 times. The obtained results are shown in Table 1.

(Example 6)
The conditions were the same as in Example 1, except that the stretching direction was biaxial, the stretching temperature was 180 ° C., the stretching ratio was 1.4 times in the longitudinal direction, and 1.4 times in the transverse direction. The obtained results are shown in Table 1.

(Example 7)
The conditions were the same as in Example 1 except that the stretching direction was biaxial, the stretching temperature was 100 ° C., the stretching ratio was 1.6 times in the longitudinal direction, and 1.6 times in the transverse direction. The obtained results are shown in Table 1.

(Comparative Example 1)
The conditions were the same as in Example 1 except that the stretching process was not performed and a polyethylene terephthalate sheet having a length of 0.33 mm thickness × 300 mm width × 60 m was used. The obtained results are shown in Table 1.
The obtained sheet had a thickness of 470 μm, a reflectance of 96.6%, and a whiteness of 98.8.

Sectional drawing which shows the light reflecting plate produced in the Example of this invention

Explanation of symbols

1 Thermoplastic foam

Claims (4)

The step of holding the thermoplastic resin sheet in a pressurized inert gas atmosphere to contain an inert gas, the step of heating and foaming the thermoplastic resin sheet containing the inert gas under normal pressure, and foaming A thermoplastic resin foam produced by a production method comprising a step of stretching a thermoplastic resin sheet at least uniaxially. 2. The thermoplastic resin foam according to claim 1, wherein a foaming ratio of the thermoplastic resin foam is 2 times or more and a thickness of the thermoplastic resin foam sheet is 250 μm or more. . The thermoplastic resin foam according to claim 1 or 2, wherein an average reflectance in a wavelength range of 400 to 700 nm is 90% or more. The thermoplastic resin foam according to any one of claims 1 to 3, wherein the thermoplastic resin is polyester.

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