JP2013043413A - Method of manufacturing transparent fluororesin molded product and transparent fluororesin molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method by which a fluororesin molded product having excellent transparency and heat resistance is obtained at a relatively low cost and the transparent fluororesin molded product obtained by the manufacturing method and having excellent transparency and heat resistance.SOLUTION: The method of manufacturing the transparent fluororesin molded product has a pressing step of pressing a molded product of a resin composition containing fluororesin as a principal ingredient at pressure Y (MPa) satisfying a condition of a following formula (1): logY≥-0.0069T+2.3 (where, Y≤10^[5×(-0.0069T+2.3)]), at a temperature T (°C) below the melting point of the fluororesin. After the pressing step, it is preferable to provide a crosslinking step of crosslinking the fluororesin by irradiation with ionizing radiation.

Description

  The present invention relates to a fluororesin molded article suitably used as an optical member for electronic equipment parts and a method for producing the same.

  Various optical films are used as light guide plates, light diffusion sheets, light condensing sheets, and the like in electronic devices such as mobile phones, notebook computers, digital cameras, and liquid crystal televisions. Various optical lenses such as a pickup lens, a camera lens, a microarray lens, a projector lens, and a Fresnel lens are used. These optical films and optical lenses are required to have transparency, that is, high transmittance of visible light and near infrared light, and acrylic resins and polycarbonate resins are used for these applications.

  These optical films and optical lenses (hereinafter referred to as optical members) are also required to have heat resistance. This is because electronic components are mounted by solder reflow due to the downsizing and high performance of the electronic devices described above, and heat resistance that can maintain the shape without melting even at the reflow temperature is desired. Furthermore, it is also desired to withstand high temperature lead-free solder to cope with environmental problems.

  Optical members made of acrylic resin or polycarbonate resin have low heat resistance and are not suitable for such applications. Therefore, the use of a fluororesin having high heat resistance and excellent transparency as an optical member has been studied. However, general-purpose fluororesin molded articles are not sufficiently transparent, and various studies have been made to increase transparency.

  Patent Document 1 describes a transparent molded body made of a fluororesin composition using an amorphous fluororesin. A general-purpose fluororesin has crystallinity, and the crystal of the fluororesin causes a decrease in transparency. When an amorphous fluororesin is used, a fluororesin crystal is not generated, so that a highly transparent molded body can be obtained.

  In Patent Document 2, as a method for producing a fluororesin molded body having excellent transparency, a molding process for molding a resin composition made of a fluororesin, and a molded body obtained in the molding process in a temperature atmosphere below the melting point of the fluororesin. First irradiation step of irradiating ionizing radiation at least once to crosslink the resin composition, second irradiation of irradiating ionizing radiation at least once in a temperature atmosphere higher than the melting point of the fluororesin to crosslink the resin composition A method for producing a transparent resin molded product having a process is described. A molded body having high transparency can be obtained by heating to the melting point of the fluororesin or higher and performing the second irradiation. The reason for this is that the fluororesin crystals are melted in the temperature atmosphere above the melting point of the fluororesin and there are no crystals, and irradiation is generated in this state to produce crosslinks. It is described that it is considered that the transparency of is improved.

JP 2001-123034 A JP 2011-052063 A

  The molded body made of the amorphous fluororesin of Patent Document 1 is excellent in transparency, but is expensive and expensive, and is not practical.

  Since the molded body obtained by the manufacturing method of Patent Document 2 uses a general-purpose fluororesin, the material is relatively inexpensive. However, a process of irradiating ionizing radiation in an atmosphere having a temperature equal to or higher than the melting point of the fluororesin is required, and a complicated manufacturing facility is required, resulting in an increase in manufacturing cost.

  Therefore, the present invention provides a production method capable of obtaining a fluororesin molded article having excellent heat resistance and transparency at a relatively low cost, and a transparent fluororesin molded article having excellent heat resistance and transparency obtained by this production method. The issue is to provide.

The present invention provides a pressing step of applying a pressure Y (MPa) that satisfies the following formula (1) at a temperature T (° C.) below the melting point of the fluororesin to a molded body of a resin composition containing a fluororesin as a main component. It is a manufacturing method of the transparent fluororesin molded object which has (Claim 1).
log ₁₀ Y ≧ −0.0069T + 2.3 (1)
(However, Y ≦ 10 ^ [5 × (−0.0069T + 2.3)])

  The present inventors have found that the transparency of the fluororesin, which is a crystalline material, can be improved by applying a certain pressure to the molded body, and that the pressure required in that case correlates with the temperature. Was completed. As a result, a molded article with high transparency can be obtained even when a general-purpose fluororesin having a relatively low cost is used. Further, since processing at a temperature lower than the melting point of the fluororesin is possible, it is possible to manufacture at a low cost with less load on the manufacturing equipment.

  Preferably, after the pressing step, there is a crosslinking step of irradiating ionizing radiation to crosslink the fluororesin (Claim 2). The pressing process improves transparency while maintaining crystals in the fluororesin. When the molded body in this state is crosslinked, the state of the fluororesin is fixed, so that transparency can be maintained even if there is a subsequent temperature change. Moreover, the heat resistance of a molded object improves by bridge | crosslinking.

  The melting point of the fluororesin is preferably less than 300 ° C. (Claim 3). As the fluororesin, any resin that is a thermoplastic resin containing fluorine and can be molded by injection molding or the like to obtain a transparent molded body can be used, but if the melting point is less than 300 ° C., it is easy to mold. is there. More preferably, it is a fluororesin having a carbon-hydrogen bond and crosslinked by irradiation with ionizing radiation. As such a fluororesin, at least one resin selected from an ethylene-tetrafluoroethylene copolymer, an ethylene-tetrafluoroethylene-hexafluoropropylene copolymer, and a modified product thereof can be preferably used. 4).

  The molded body is formed by injection molding a resin composition containing a fluororesin as a main component, and it is preferable that the injection molding step and the pressing step are continuously performed by injection compression molding. ). By using such a process, the manufacturing time of a molded object can be shortened and cost can be reduced. Moreover, there is little dispersion | variation in the transparency of a molded object, and it can improve quality.

  A fluororesin molded article having excellent transparency can be obtained by the above production method. As the transparency index, the transmittance of light having a wavelength of 400 nm and the transmittance of light having a wavelength of 850 nm are used. The fluororesin molded body obtained by this production method has a light transmittance of 85% or more at both a wavelength of 400 nm and 850 nm at a converted thickness of 0.45 mm. In addition, when a crystalline fluororesin is used, the crystallinity is maintained even in a pressed molded body (transparent fluororesin molded body). Accordingly, the present invention is a transparent fluororesin molded body obtained by molding a resin composition containing a fluororesin as a main component, and the light transmittance when the thickness is 0.45 mm is any of the wavelength of 400 nm and 850 nm. Is 85% or more, and a transparent fluororesin molded product having a crystal calorie of 10 J / g or more is provided. The crystal calorie is measured by differential scanning calorimetry.

  Further, after the pressing step, the transparent fluororesin molded body obtained by irradiating ionizing radiation and cross-linking the fluororesin has a light transmittance after heating at 150 ° C. for 3000 hours at any wavelength of 400 nm and 850 nm. The transmittance is 95% or more, and excellent in long-term heat resistance (Claim 7).

  According to the present invention, a fluororesin molded product having excellent heat resistance and transparency can be obtained at a relatively low cost. Moreover, the transparent fluororesin molded object which is excellent in heat resistance and transparency is obtained by this manufacturing method.

  As the fluororesin used in the present invention, any resin that is a fluorine-containing thermoplastic resin that can be molded by injection molding or the like and can obtain a transparent molded body can be used. Further, a fluororesin that is cross-linked by irradiation with ionizing radiation is preferable. Specifically, an ethylene-tetrafluoroethylene copolymer, an ethylene-tetrafluoroethylene-hexafluoropropylene copolymer, a modified product thereof, a polyvinylidene fluoride, or the like can be used. It is preferable that the melting point is less than 300 ° C. to facilitate molding. Further, it is preferable that the transmittance of the molded body before irradiation with ionizing radiation is 20% or more in the molded body having a thickness of 2 mm.

  Examples of the modified body include a fluororesin having a reactive functional group at one or both of the main chain terminal and the side chain terminal. Here, examples of the reactive functional group include a carbonyl group, a carbonyldioxy group, a haloformyl group, a hydroxyl group, and an epoxy group. In addition, a modified product obtained by graft polymerization of other components on an ethylene site can also be used. An example is Neoflon RP-4020 (trade name) manufactured by Daikin Industries.

  A molded body is obtained by molding the resin composition containing the fluororesin as a main component. The phrase “main component” means that 50% by mass or more of the resin composition is a fluororesin. A plurality of fluororesins may be mixed and used. You may add another resin component to the resin composition in the range which does not impair the effect of this invention. Examples of other resin components include polyethylene, polypropylene, polystyrene, and thermoplastic elastomer.

  A polyfunctional monomer may be added to the resin composition in order to improve the crosslinking efficiency by irradiation with ionizing radiation. As the polyfunctional monomer, those having a molecular weight of 1000 or less and having two or more carbon-carbon double bonds in the molecule are preferable. When the molecular weight is 1000 or less, it is possible to obtain a fluororesin molded article having excellent heat resistance while maintaining transparency. Examples of such polyfunctional monomers include trimethylolpropane (tri) methacrylate, 1,6-divinyl (perfluorohexane), tris (acryloxyethyl) isocyanurate, tris (methacryloxyethyl) isocyanurate, and the like. It is done.

  The addition amount of the polyfunctional monomer is preferably 0.05 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the fluororesin. If the addition amount is less than 0.05 parts by mass, the effect of improving the crosslinking efficiency cannot be obtained, and a large amount of ionizing radiation is required. Moreover, when it exceeds 20 mass parts, the handling at the time of kneading | mixing at the time of producing a resin composition will become difficult.

  In addition to the above-described components, various additives such as antioxidants, flame retardants, ultraviolet absorbers, light stabilizers, heat stabilizers, and lubricants may be added to the resin composition. The resin composition can be produced by mixing these materials using a known mixing apparatus such as an open roll, a pressure kneader, a short-shaft mixer, or a twin-screw mixer. It is preferable to perform melt mixing at a temperature equal to or higher than the melting point of the fluororesin used.

  The molded body before pressing is obtained by molding the resin composition containing the fluororesin as a main component. As the molding method, existing methods such as injection molding, press molding, and extrusion molding can be employed. Of these, injection molding is preferably used. The melting point of the resin composition used in the present invention can be adjusted by the type of fluororesin, for example, the ratio of monomers constituting the fluororesin. When a fluororesin having a melting point of less than 300 ° C. is used, molding at a low temperature is possible and moldability is excellent. When a fluororesin having a melting point of 300 ° C. or higher is used, it is necessary to apply a hydrogen fluoride-resistant plating treatment to the part of the equipment in contact with the molded body in consideration of the corrosion of the equipment due to hydrogen fluoride.

Pressure is applied to the molded body (pressing step) to obtain a transparent fluororesin molded body. The pressure Y (MPa) required at this time depends on the temperature T (° C.), and it is necessary to satisfy the condition of the following formula (1). For example, the pressure required when pressing at 25 ° C. is 134 MPa or more, and when pressing at 100 ° C., the pressure is 41 MPa or more. However, if the pressure exceeds 5 times the predetermined pressure, the compact is destroyed, so the pressure Y (MPa) is set to 10 ^ [5 × (−0.0069T + 2.3)] or less.
logY ≧ −0.0069T + 2.3 (1)

  The temperature at which the pressure is applied is less than the melting point of the fluororesin. It is because a molded object will deform | transform if it exceeds melting | fusing point of a fluororesin. There is no particular lower limit to the temperature, but if the temperature is low, the pressure required in the pressing process increases and the load on the equipment increases, so it is preferable to set the temperature to 25 ° C. or higher. By applying a certain pressure under such temperature conditions, the crystal structure of the fluororesin, which is a crystalline resin, is changed and the transparency is improved. The pressure is applied for about 0.1 seconds to 5 minutes.

  The pressing step can be performed by any method. After producing a molded body by injection molding, when a pressure is applied by injection compression molding that clamps the mold and applies pressure, a transparent fluororesin molded body can be manufactured in a continuous process, and the manufacturing cost can be reduced. The quality of the finished compact is stable. In this case, first, the mold is filled with the resin composition melted by injection molding. A molded product is obtained by cooling the filled resin composition to a certain temperature. Thereafter, the mold is moved to apply pressure to the molded body. The pressure required in this case is calculated based on the mold temperature when the mold is moved.

  It is preferable that the transparent fluororesin molded body obtained by the pressing step is irradiated with ionizing radiation to crosslink the fluororesin because heat resistance is improved. Moreover, the structure of the fluororesin is fixed by irradiation crosslinking, and transparency can be maintained. In particular, a transparent fluororesin molded article that can maintain transparency even after being held for a long time in a high-temperature environment and has excellent long-term heat resistance is obtained.

  Examples of ionizing radiation sources include accelerated electron beams, gamma rays, X rays, α rays, ultraviolet rays, and the like. An accelerated electron beam is preferable from the viewpoint of industrial use, such as ease of use of the radiation source, transmission thickness of ionizing radiation, speed of crosslinking treatment, and the like. What is necessary is just to set the acceleration voltage of an acceleration electron beam suitably according to the thickness of a molded article. For example, in the case of a molded product having a thickness of about 2 mm, the acceleration voltage is selected between 100 kV and 10,000 kV. The greater the irradiation dose of ionizing radiation, the higher the degree of cross-linking of the fluororesin and the better the heat resistance. However, when the irradiation dose is too large, problems such as coloring of the molded product, white turbidity, and resin decomposition may occur. Therefore, the irradiation dose is preferably 100 kGy or more and less than 1500 kGy. Within this range, heat resistance that can withstand solder reflow using lead flow solder can be obtained. Specifically, even when exposed to heat at 260 ° C. for 60 seconds, deformation, shrinkage, etc. do not occur, and heat resistance is such that there is little change in transmittance of light having a wavelength of 850 nm.

The transparent fluororesin molded product can have any shape. In the case of a plate-shaped molded body, the thickness is preferably 0.05 mm to 1.5 mm. More preferably, it is 0.1 mm-1 mm. The light transmittance X (%) at a converted thickness of 0.45 mm can be obtained by the following equation.
X (%) = 100 * 10 ^ [(log ₁₀ (A / 100)) × 0.45 / t]
t: Measured thickness of molded product (mm)
A: Transmittance (%) at thickness t (mm)

  Next, the present invention will be described in more detail based on examples. The examples are not intended to limit the scope of the invention.

(Examples 1-10, Comparative Examples 1-4)
(Preparation of resin composition pellets)
Using a biaxial mixer (30 mmφ, L / D = 30), the barrel temperature is set to 190 ° C. to 330 ° C., and the resin and additives shown in Table 1 are melt mixed at a screw rotation speed of 100 rpm. After preparing the resin composition, resin composition pellets were prepared with a strand cut pelletizer. The barrel temperature was appropriately selected so as to be 10 ° C. or higher than the melting point of the resin.

(Production of molded body)
The obtained resin composition pellets were put into an injection molding machine (manufactured by Nissei Plastic Co., Ltd.) having a clamping force of 40 t class, and injection molding was performed using a mold made of SUS304 polished with a surface roughness Ra = 1.6a level. It carried out and produced the plate of predetermined thickness. Table 1 shows the thickness of the obtained molded body.

(Pressing process)
The molded body was pressed at the temperature and pressure shown in Table 1 to produce a transparent fluororesin molded body. The pressing time was 1 minute preheating and 20 seconds pressurization. Table 1 shows the thickness of the transparent fluororesin molded body after pressing. In Comparative Example 1 and Comparative Example 4, no pressing process was performed.

(Transparency evaluation)
The color of the sample cut at 10 mm × 10 mm square from the plate of the transparent fluororesin molded product was visually confirmed. The light transmittance was measured at wavelengths of 400 nm and 850 nm. The thickness of the measurement sample is the “thickness after pressing” in Table 1.

(Electron beam irradiation)
The plate of the transparent fluororesin molded body was irradiated with an acceleration electron beam having an acceleration voltage of 200 kV at a dose shown in Table 1. The temperature at the time of irradiation is room temperature.

(Melting point measurement)
The melting point of the transparent fluororesin molded body after irradiation with the electron beam (Examples 8 to 10 are unirradiated transparent fluororesin molded bodies) was measured by differential scanning calorimetry. When a peak having a calorific value of 1 J / g or more was observed in the vicinity of the original melting point of the resin, this was judged as the melting point peak, and the peak temperature was taken as the melting point.

(Heat resistance evaluation)
The plate of the transparent fluororesin molded body that had been irradiated with the electron beam was cut into a 30 mm × 30 mm square, and the color after being heated in a constant temperature bath at 270 ° C. for 60 seconds was visually confirmed. The transmittance was measured at wavelengths of 400 nm and 850 nm.

(Long-term heat resistance evaluation)
The plate of the transparent fluororesin molded body that had been irradiated with the electron beam was cut into a 30 mm × 30 mm square, and the color after being heated in a constant temperature bath at 150 ° C. for 3000 hours was visually confirmed. The transmittance was measured at wavelengths of 400 nm and 850 nm. The results are shown in Table 1.

(footnote)
(* 1) An ethylene-tetrafluoroethylene copolymer. (Product name Fullon LM-ETFE LM730AP, manufactured by Asahi Glass Co., Ltd.)
(* 2) Ethylene-tetrafluoroethylene copolymer. (Asahi Glass Co., Ltd., trade name Fullon ETFE C-88AP)
(* 3) A copolymer of ethylene-tetrafluoroethylene-hexafluoropropylene. (Product name: Neoflon RP4020, manufactured by Daikin Industries, Ltd.)
(* 4) Tetotafluoroethylene-hexafluoropropylene copolymer. (Product name: Neoflon FEP NP-21, manufactured by Daikin Industries, Ltd.)
(* 5) Polycarbonate. (Made by Mitsubishi Engineering Plastics, trade name Iupilon S3000)
(* 6) Trimethylolpropane trimethacrylate

  The relationship between temperature and pressure satisfies the formula (1), and the transparent fluororesin molded bodies of Examples 1 to 7 in which the fluororesin is crosslinked by irradiating an electron beam have high initial transmittance and good transparency. It is. Further, the transmittance after heating at 270 ° C. for 60 seconds is almost the same as the initial transmittance, and is excellent in reflow resistance. Further, it can be seen that the transmittance after a long-term heat test at 150 ° C. for 3000 hours is almost unchanged at both wavelengths of 400 nm and 850 nm, and excellent in long-term heat resistance.

  The transparent fluororesin moldings of Examples 8 and 9 are not irradiated with an electron beam. Therefore, the initial transparency was good, but after heating at 270 ° C. for 60 seconds, it became cloudy and the transparency deteriorated. The transparent resin molded body of Example 10 was not irradiated with an electron beam, but because PFA having a high melting point was used, not only the initial transparency but also after heating at 270 ° C. for 60 seconds and after heating at 150 ° C. for 3000 hours. Transparency is also excellent. Moreover, the crystal calorie | heat amount after irradiation of the transparent fluororesin molding of Examples 1-9 is all 10 J / g or more, and it turns out that crystallinity is maintained.

  Comparative Examples 1 to 3 are formed using the same fluororesin as in Examples 1 and 4 to 5, and the pressing conditions are changed. In Comparative Example 1 in which the pressing process was not performed at all, the initial transparency was poor, and although the thickness was as thin as 0.5 mm, it was visually turbid, and the transmittance at 400 nm wavelength light and 850 nm wavelength light was also the same thickness. This is lower than that of Example 1. Although the comparative example 2 is performing the press process, since it is pressing at a pressure lower than the required pressure (134 MPa) at a temperature of 25 ° C., the transparency is not sufficient. In Comparative Example 3, since the pressure is too high, the molded body is broken. In Comparative Example 4, a molded body is produced using polycarbonate instead of fluororesin. Polycarbonate is excellent in transparency and has high initial transmittance but low heat resistance. When heated at 270 ° C. for 60 seconds, the molded body melted. Moreover, although it did not melt | dissolve by heating at 150 degreeC for 3000 hours, the molded object turned yellow and the transmittance | permeability also fell.

Claims (7)

Transparent fluorine having a pressing step of applying a pressure Y (MPa) satisfying the following formula (1) to a molded body of a resin composition containing a fluororesin as a main component at a temperature T (° C.) below the melting point of the fluororesin Manufacturing method of resin molding.
logY ≧ −0.0069T + 2.3 (1)
(However, Y ≦ 10 ^ [5 × (−0.0069T + 2.3)])   The manufacturing method of the transparent fluororesin molding of Claim 1 which has a bridge | crosslinking process of irradiating ionizing radiation and bridge | crosslinking the said fluororesin after the said press process.   The manufacturing method of the transparent fluororesin molding of Claim 1 or 2 whose melting | fusing point of the said fluororesin is less than 300 degreeC.   The said fluororesin is 1 or more types chosen from ethylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene-hexafluoropropylene copolymer, and these modified bodies, The any one of Claims 1-3 The manufacturing method of the transparent fluororesin molded object of description.   The molded body is formed by injection molding a resin composition containing a fluororesin as a main component, and the injection molding step and the pressing step are continuously performed by injection compression molding, The manufacturing method of the transparent fluororesin molded object of any one of Claims 1-4.   A transparent fluororesin molded body obtained by molding a resin composition containing a fluororesin as a main component, and the light transmittance at a converted thickness of 0.45 mm is 85% or more at both wavelengths of 400 nm and 850 nm, A transparent fluororesin molded product having a crystal calorie of 10 J / g or more.   A transparent fluororesin molded product obtained by the method for producing a transparent fluororesin molded product according to claim 2, wherein the light transmittance after heating at 150 ° C. for 3000 hours is heated at both wavelengths of 400 nm and 850 nm. A transparent fluororesin molded body having a transmittance of 95% or more with respect to the previous light transmittance.