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While it is common to add anti-blocking agents to biaxially oriented polypropylene (BOPP) films for general use in order to prevent blocking against each other, the technology of crater-like film surface roughness formed on the BOPP films without any additives is well known in the industrial BOPP film areas. Numerous studies have been reported on the crater-like film surface roughness on the BOPP films since the 1980s, but its formation mechanism and the controlling method of the crater-like film surface roughness are yet to be clarified. In our previous reports, we presented a new hypothesis of crater formation mechanism from a new point of view on sheet morphology and crater shape on the BOPP film surface. It was strongly influenced by the crystal grain shape in the surface layer of PP sheet. In this report, it was clarified that a nucleator has a big influence on the formation of the crystal grains in the surface layer of PP sheets and on the formation of craters. In addition, craters did not form on the BOPP films stretched from the sheet of which the skin layer with crystal grain was shaved, even though β crystal still remained. It was clarified that the crystal grain is trans-crystal from the observation using TEM. Therefore, it is concluded that the existence of β crystals in the surface layer of PP sheets is not essential in order to produce craters on BOPP films, but trans-crystals are necessary to form the craters. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3555–3564, 2013

Biaxially oriented polypropylene (BOPP) films are used in a variety of areas around the world. They are especially well suited for food packaging and industrial usages because of their high productivity. Many studies on the stretchability with regard to crystal structure changes have been reported by various researchers because the machine speed has been increasing and the demand to produce thinner films has been becoming more important. Furthermore, a number of studies on the surface structure of BOPP films with craterlike roughnesses have been reported since the 1980s. Although a craterlike surface roughness was formed under specific film process conditions, the formation mechanism and the controlling method of the craterlike film surface are yet to be clarified. In this report, we demonstrated a new hypothesis for the craterlike film surface roughness formation mechanism by analyzing the morphology of the surface layer of polypropylene (PP) sheets and by investigating the relationship between the surface structural changes and the changes in the entire structure. As a result, we found that an overcritical crystallization time was needed to form the crater on the surface of the BOPP film, and the crater formation mechanism was closely related not only to the surface structure changes but also to the deformation phenomenon of the spherulite in the PP sheet during stretching. Furthermore, this report shows the controlling factors in the formation of the crater structure from the viewpoint of the production conditions. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012 Copyright © 2012 Wiley Periodicals, Inc.

Biaxially oriented polypropylene (BOPP) film accounts for a large amount of polypropylene since it is well suited for food packaging films or industrial films, because of its high performance in terms of mechanical and optical properties. Recently machine speed has been increasing to obtain higher production rate and film thickness has become thinner to reduce the environmental load. To meet the demands, many researchers have been investigating stretchability of PP by connecting the stretching force at the yield point and crystalline structure. Many other studies have been conducted regarding the surface structure of BOPP. Although there were some cases that crater-like film surface roughness was formed on BOPP films, the formation mechanism of craters has not been clarified. In this report, new hypothesis of the crater-like film surface roughness formation mechanism is proposed by observing the transformation of crater from sheet to BOPP film and by investigating the relationship between the stress–strain curve and surface roughness change. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Unique deterioration with a striped pattern caused by thermal heating is reported for injection molding comprising polypropylene/ethylene–α-olefin rubber blends. This stripe is due to the formation of glossy and cloudy parts in alternation approximately perpendicular to the flow direction of the molten resin. On the surface of the cloudy part, a number of micro-objects appear. They have a dome shape about 10 μm in diameter and 2 μm height. Some experimental evidence indicates that the objects are composed of the rubber contained in the blends. On the other hand, only a few objects appear in the glossy region after heating. This is the reason that the stripe with the micro-objects (migrating rubber to the surface) is examined in terms of a higher order structure of injection molding with laser scanning microscopy, wide-angle X-ray scattering, and microhardness (Martens hardness). Consequently, we have concluded that this thermally deteriorated stripe depends on periodic changes in the crystallinity along the flow direction. The evidence indicates that a snakelike flow occurs during the injection process of the molding. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

金沢大学大学院自然科学研究科, 出光興産㈱ 先進技術研究所 解析技術センター 第二解析技術室, Many additives are commercially used to add more favorable qualities to films. The bleeding process by which the additive in a film comes to the surface is considered. A new bleeding model of additives in a polypropylene film under atmospheric pressure was investigated. Solubility and diffusion are found to be important for explaining this bleeding process. It was found that the experimental results were explained more precisely by assuming a twostep transport process between the crystalline regions and the amorphous ones. The solubilities and diffusion coefficients of UV-stabilizers such as 2-(2H-benzotriazol-2-yl)-4(l,l,3,3-tetramethylbutyl)phenol and 2-(2H-benzotriazol-2yl)-4-methylphenol were determined at 4O°C. The difference between the saturation solubilities and the diffusion coefficients of UV-stabilizers was discussed by comparing with the results of molecular dynamics (MD) simulation. © 2007 Wiley Periodicals, Inc.

Unique deterioration with a periodical striped pattern on the injection moldings of polypropylene/rubber blends is reported. After exposure to ultraviolet irradiation with a sunshine fade meter, striped patterns appeared on the injection moldings along the flow direction of the molten resin during the filling process of injection molding, even though the initial specimen showed no sign of any stripe pattern on its surface. The stripe was carefully observed with ultrasonic echo imaging, scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. As a result, a number of microvoids were observed inside the injected body at a depth of 50–100 μm from the surface. It became clear that the difference in the number of voids along the flow direction formed the stripe pattern. Surprisingly, these voids occurred in domains comprising a rubber phase. The distribution of voids in depth indicated the existence of a trace of a snakelike flow caused inside the injected body during the injection-molding process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007