JP4948224B2 - Polypropylene foam sheet and method for producing the same - Google Patents

Description

  The present invention relates to a polypropylene foam sheet having a pearly luster suitable for containers such as cosmetics and stationery products, packaging materials, label materials, display wallpaper, and the like, which require a high-class feeling, and a method for producing the same.

  Conventionally, a plastic molding having a fine and uniform anisotropic gloss (hereinafter referred to as pearly gloss) is obtained by melt molding a resin composition in which a pearl pigment containing mica or the like is added to a thermoplastic resin. Yes. However, pearl pigments have the disadvantage that they are expensive and expensive.

  Therefore, as a method not using an expensive pearl pigment, for example, a resin composition of a thermoplastic polyester resin (A) and an incompatible resin (B) is extruded and injection molded, and a plastic having a specific internal structure There has been proposed a method for obtaining a pearly luster that further enhances the sense of quality by forming a molded body (Patent Document 1).

Japanese Patent Laid-Open No. 06-080789

  However, it is difficult to stably obtain the specific internal structure in a single process such as extrusion or injection, and it is necessary to perform a stretching process or the like in a subsequent process.

  The present invention has been made in view of the above-described circumstances, and is a high-quality polypropylene foam sheet that provides a good pearly luster, and is stable and good at a low cost in a single step such as extrusion. It is an object of the present invention to provide a method for producing a polypropylene foam sheet capable of obtaining a pearly luster.

  As a result of various studies to achieve the above object, the present inventors have obtained a high-quality, high-quality, pearly glossy polypropylene foam sheet having the following characteristics, and It has been found that a method for producing a polypropylene foam sheet having the following characteristics can stably supply the polypropylene foam sheet capable of obtaining the good pearly luster at low cost.

  That is, the polypropylene foam sheet according to claim 1 is an ethylene-propylene block copolymer having an ethylene content of 5 to 20% by weight, a melt flow rate of 0.1 to 10 g / 10 minutes, and a melt tension at 190 ° C. of 15 to 25 g. Mixing of 20 to 80% by weight with 20 to 80% by weight of ethylene-propylene block copolymer or / and ethylene-propylene random copolymer having an ethylene content of 5 to 20% by weight and a melt flow rate of 5 to 20 g / 10 min Polypropylene foam having a pearly luster that is foamed by extrusion molding from a die of an extruder after injecting an inorganic gas into a resin composition containing 2 to 5 parts by weight of a foam nucleating agent for 100 parts by weight of the product A center line average roughness based on JIS B0601 on the surface of the polypropylene foam sheet is 0.5 to .0Myuemu, the maximum height based on JIS B0601 is characterized in that it is a 5 to 25 [mu] m.

  According to the polypropylene foam sheet of the present invention, which has the above composition and the surface roughness of the polypropylene foam sheet falls within the above specified values, a high-quality and good pearly gloss can be obtained.

  The polypropylene foam sheet according to claim 2 is the polypropylene foam sheet according to claim 1, wherein the center line average roughness in the longitudinal direction and the width direction of the polypropylene foam sheet surface is 0.5 to 2.0 μm. And the said maximum height in the longitudinal direction and the width direction of the said polypropylene foam sheet surface is 5-25 micrometers, It is characterized by the above-mentioned.

  Furthermore, the polypropylene foam sheet according to claim 3 is the polypropylene foam sheet according to claim 1 or 2, wherein the polypropylene foam sheet has an average cell diameter of 20 to 80 μm.

  According to the polypropylene foam sheet of the present invention in which the surface roughness, average cell diameter and the like of the polypropylene foam sheet are within the above specified values, a high-quality and good pearly gloss can be obtained with certainty.

  And the manufacturing method of the polypropylene foam sheet which concerns on Claim 4 is an ethylene-propylene block whose ethylene content is 5-20 weight%, melt flow rate is 0.1-10 g / 10min, and melt tension in 190 degreeC is 15-25 g Copolymer 20 to 80 wt%, ethylene content 5 to 20 wt%, melt flow rate 5 to 20 g / 10 min ethylene-propylene block copolymer and / or ethylene-propylene random copolymer 20 to 80 wt% After injecting an inorganic gas into a resin composition containing 2 to 5 parts by weight of a foam nucleating agent with respect to 100 parts by weight of the admixture, and then extruding and foaming from a die provided at the tip of the extruder Features.

  According to the method for producing a polypropylene foam sheet of the present invention, it is possible to produce a polypropylene foam sheet capable of stably obtaining a good pearly luster without performing a treatment such as stretching after a process such as extrusion.

  The polypropylene foam sheet according to the present invention configured as described above can obtain a high-quality and good pearly gloss, and its manufacturing method is low cost in a single process such as extrusion. It has an excellent effect of being able to supply a polypropylene foam sheet capable of stably obtaining a good pearly luster.

  Hereinafter, the polypropylene foam sheet of the present invention will be described in more detail.

  The polypropylene foam sheet of this embodiment has an ethylene content of 5 to 20% by weight, a melt flow rate of 0.1 to 10 g / 10 min, and an ethylene-propylene block copolymer 20 to 80 having a melt tension at 190 ° C. of 15 to 25 g. 100 wt.% Of a blend of 20 wt.% And 20 to 80 wt.% Ethylene-propylene block copolymer or / and ethylene-propylene random copolymer having an ethylene content of 5 to 20 wt.% And a melt flow rate of 5 to 20 g / 10 min. The surface of the polypropylene foam sheet is manufactured by pressing an inorganic gas into a resin composition containing 2 to 5 parts by weight of a foam nucleating agent and then extruding and foaming from a die of an extruder. The center line average roughness based on JIS B0601 is 0.5 to 2.0 μm, and the maximum height based on JIS B0601 is 5 There is a 5μm.

  The ethylene-propylene block copolymer used in the present invention has an ethylene content of 5 to 20% by weight, preferably 7 to 15% by weight, a melt flow rate of 0.1 to 10 g / 10 minutes, and a melting at 190 ° C. Tensile strength is 15 to 25 g (melting tension is 4 m / min of molten resin extruded at a test temperature of 190 ° C. and an extrusion speed of 10 mm / min using a capillary meter equipped with an orifice having a diameter of 2.1 mm and a length of 8 mm. Measure the tension when pulled at a speed of min). By using at least 20% by weight of such a block copolymer, a foam sheet having excellent foamability can be obtained. In addition, an ethylene-propylene block copolymer having such an ethylene content and melt flow rate exhibits viscoelasticity suitable for foaming of the resin composition at the time of extrusion, so that a good foamed structure can be easily formed. Because it can. Outside the above range, a high-magnification foamed sheet cannot be obtained, and excellent physical properties cannot be obtained.

  In this embodiment, an ethylene-propylene block copolymer or / and an ethylene-propylene random copolymer 20 to 80% by weight with an ethylene content of 5 to 20% by weight and a melt flow rate of 5 to 20 g / 10 minutes were blended. The reason is that an increase in the resin temperature in the extruder is suppressed, and the variation of the expansion ratio in the longitudinal direction of the sheet is also reduced, and a foam sheet that is stable for a long time can be obtained.

  Examples of the foam nucleating agent include foaming aids such as sodium bicarbonate, ammonium bicarbonate, sodium bicarbonate citrate, and azodicarbonamide. As a commercially available product, Polyslen series manufactured by Eiwa Chemical Industry Co., Ltd. is preferably used. Further, examples of the foaming agent include inorganic gases such as nitrogen gas and carbon dioxide gas. In the gas foaming method in which these are injected and foamed, there is no heat generation due to the decomposition of the foaming agent, so that the resin temperature can be easily controlled and a suitable resin viscosity is easily maintained. Moreover, there is no harmful residue in the obtained foamed sheet, which is preferable in terms of hygiene.

  Add appropriate amounts of known additives such as nucleating agents, other modifying polymers and inorganic fillers, flame retardants, conductivity-imparting agents such as carbon black, antistatic agents, colorants, and UV absorbers. May be.

  The resin composition melt-kneaded in the extruder is injected with an inorganic gas from the middle of the extruder, then extruded through a die provided at the tip of the extruder and foamed to produce the desired polypropylene foam sheet.

  At this time, at least one set of forming rolls is installed in the horizontal direction from the tip of the foaming die, and the extruded foam sheet surface that passes between the rolls and the internal temperature are maintained at 70 to 130 ° C. without being crushed. When formed into a sheet and then cooled, a polypropylene foam sheet having a uniform cell diameter, a high closed cell ratio, and excellent surface smoothness and impact resistance can be obtained.

  It is important to maintain the sheet surface and internal temperature at 70 to 130 ° C. When the temperature is less than 70 ° C., foaming of the resin is suppressed, and it is difficult to obtain the desired wall thickness and expansion ratio. The above causes a problem that gas easily escapes from the surface.

  Next, although the Example of the polypropylene foam sheet of this invention is shown, this invention is not limited to the following example.

[Example]
In an extruder with a cylinder diameter of 65 mm, an ethylene content of 10% by weight, a melt flow rate of 0.5 g / 10 minutes, an ethylene-propylene block copolymer of 40 g by weight with a melt tension at 190 ° C. of 23 g, an ethylene content of 7% by weight, a melt 60-5 parts by weight of an ethylene-propylene random copolymer having a flow rate of 9 g / 10 min and 2-5 parts by weight of Polyslene EE207E (manufactured by Eiwa Kasei Kogyo Co., Ltd.) as a foam nucleating agent as shown in Table 1 below 2 parts by weight in Example 1, 3 parts by weight in Example 2, and 5 parts by weight in Example 3), and carbon dioxide as an inorganic gas is 7 kg / cm from the cylinder part in the middle of the extruder. after press-fitted in the ^second pressure, set up two sets of molding Rorudai horizontally from the center of the tip of the T-type foaming die width 400 mm, the Rorudai When passing through, the sheet surface temperature is maintained at 110 ° C. and extrusion foamed, and the thickness shown in the table is 0.75 to 1 mm (specifically, 0.75 mm in Example 1, Examples 2 to Example) A polypropylene foam sheet of 4 mm was prepared.

[Comparative example]
Of the composition ratios in the examples, Polyslen EE207E (manufactured by Eiwa Kasei Kogyo Co., Ltd.) as a foam nucleating agent is 1 part by weight in Comparative Examples 1 and 2, 10 parts by weight in Comparative Example 3, and extrusion foaming. The polypropylene foam sheet was produced by changing the thickness of the polypropylene foam sheet to be used in Comparative Example 1 only to 0.80 mm and in Comparative Example 2 and Comparative Example 3 to 1.0 mm.

[Evaluation]
1) Surface Roughness Centerline average roughness (Ra) based on JIS B0601 of the surface of the polypropylene foam sheet and the maximum height for the obtained six samples of Examples 1 to 3 and Comparative Examples 1 to 3 The thickness (Rmax) was measured. In addition, the measurement was measured about the longitudinal direction (machine direction) and width direction of the foam sheet using Tokyo Seimitsu Handy Surf E-30A.
2) Average bubble diameter According to ASTM D3576-77, SEM photographs of the cross section of the sheet were taken for the above six samples, straight lines were drawn in the horizontal and vertical directions on the SEM photograph, and the length of the bubble chord that the straight lines crossed The average t was averaged. Assuming that the magnification of the photograph is M, the average bubble diameter d was determined by substituting it into the following equation.
d = t / (0.616 × M)
3) Appearance evaluation of recording medium The appearance was evaluated visually for the recording quality of the six samples. In Table 1, those having a good pearly luster were shown as ◯, and those having no pearly luster were shown as x.

[Discussion]
All of the samples of Examples 1 to 3 were able to obtain a good pearly luster, and a high-class feeling was felt. On the other hand, in Comparative Example 1 and Comparative Example 2, no pearly luster was observed, and the appearance of a simple white plastic sheet was exhibited. In Comparative Example 3, pearly luster was not observed, but white was very strong.

  As a result, the gloss of good pearl tone is the composition ratio of the polypropylene foam sheet, the thickness of the polypropylene foam sheet, the center line average roughness (Ra) based on JIS B0601, and the maximum height based on JIS B0601 ( Rmax) and the average bubble diameter can be reliably obtained by making them within the specified values as in the present embodiment. Moreover, according to the manufacturing method of the present embodiment, the process can be stably performed in a single process of extrusion molding. It was confirmed that it could be manufactured.

Claims (4)

An ethylene-propylene block copolymer of 20 to 80% by weight having an ethylene content of 5 to 20% by weight, a melt flow rate of 0.1 to 10 g / 10 min, and a melt tension at 190 ° C. of 15 to 25 g; The foam nucleating agent is added to 100 parts by weight of a blend of 20% by weight of an ethylene-propylene block copolymer or / and an ethylene-propylene random copolymer having a melt flow rate of 5-20 g / 10 min. A polypropylene foam sheet having a pearly luster that is extruded and foamed from a die of an extruder after injecting an inorganic gas into a resin composition containing 2 to 5 parts by weight. Centerline average roughness based on B0601 is 0.5 to 2.0 μm, maximum height based on JIS B0601 is 5-2 Polypropylene foam sheet which is a [mu] m. The center line average roughness in the longitudinal direction and the width direction of the polypropylene foam sheet surface is 0.5 to 2.0 μm, and the maximum height in the longitudinal direction and the width direction of the polypropylene foam sheet surface is 5 to 25 μm. The polypropylene foam sheet according to claim 1, wherein: The polypropylene foam sheet according to claim 1 or 2, wherein the polypropylene foam sheet has an average cell diameter of 20 to 80 µm. An ethylene-propylene block copolymer of 20 to 80% by weight having an ethylene content of 5 to 20% by weight, a melt flow rate of 0.1 to 10 g / 10 min, and a melt tension at 190 ° C. of 15 to 25 g; The foam nucleating agent is added to 100 parts by weight of a blend of 20% by weight of an ethylene-propylene block copolymer or / and an ethylene-propylene random copolymer having a melt flow rate of 5-20 g / 10 min. A method for producing a polypropylene foam sheet, comprising: injecting an inorganic gas into a resin composition containing 2 to 5 parts by weight, and then extruding and foaming from a die provided at the tip of an extruder.