Dulled stretched moulding and process for producing the same

Abstract: A dulled stretched molding of at most 30% in gloss value, which is useful as a general-purpose packaging material, printing paper, tracing paper, etc., is produced from a coposition comprising 100 parts by weight of a propylene-ethylene block copolymer and 3 to 40 parts by weight of a cyclopentadiene type petroleum resin having a ring and ball softening point of at leat 160°C, by the stages of melt extrusion and stretching of the resulting flat extrudate. There also is disclosed a heat-shrinkable foamed molding having a density of no more than 0.85 and a heat shrinkability at 100°C of at least 10% produced from a composition comprising a crystalline propylene-­ α-olefin copolymer having a crystal melting point of at most 150°C and 5 to 40 wt. %, based on the copolymer, of a hydrogenated cyclopentadiene type resin having a ring and ball softening point of at least 160°C, by the steps of melt extruding the composition and stretching the resulting flat extrudate.

Description: The present invention relates to a stretched moulding comprising a propylene-ethylene block copolymer as the main component, and a process for producing the same. More particularly, the invention relates to a surface-roughened stretched moulding of the kind as described above to which a dull tone has been imparted, and a process for producing the same which comprises stretching a flat moulding formed from a composition comprising a propylene-ethylene block copolymer and a specific petroleum hydrocarbon resin added thereto to form an innumerable number of microvoids on the inside and surface of the flat moulding. 2. Description of the Prior Art In general, surface-roughened flat plastic mouldings, for example, in the form of a monoaxially or biaxially stretched film, are widely used as polychromatic paper, tracing paper, release paper, general-purpose packaging paper, etc. Conventional processes for roughening the surface of a molding include a filler addition method wherein a large amount of an inorganic filler such as calcium carbonate, silica or sodium silicate is added to a moulding material; a post-treatment method wherein a moulding is treated with a solvent or a chemical to be dulled; and a coating method wherein a moulding is coated with a matte coating film. The filler addition method is defective in that addition of a large amount of an inorganic filler to a moulding material is liable to cause sharp reduction in the flowability, during extrusion, of the material, clogging of a screen bag, failure in obtaining products having a roughened surface with a high density of unevenness because of its liability to cause moisture absorption and foaming of the material attributable to the inorganic filler as well as poor dispersion of the inorganic filler, etc. The post-treatment method is economically disadvantageous because of the necessity of a step of removing a solvent or a chemical from a molding after the treatment thereof with the solvent or the chemical, while the coating method is also economically disadvantageous because of the necessity of investment in coating equipment and facilities related thereto. Furthermore, the latter two methods are defective in that products are very liable to undergo damage due to wear because the improvement attained by these methods is directed only to the surfaces of moldings. Other known processes for modifying the surface of a film include a lamination method wherein a film of a blend composition comprising polypropylene and high-density or low-density polyethylene is laminated on a polypropylene film, and a lamination method wherein a film of a propylene-ethylene block copolymer alone is laminated on a polypropylene film (see Japanese Patent Publication No. 32,954/1982). However, lamination of either of the above-mentioned two types of films is defective, for example, in that the resulting laminated film has too rough a surface without a high density of unevenness. Japanese Patent Publication No. 90 734/1985 discloses films prepared by stretching resin compositions containing 95-77 wt% of polypropylene and 5-27 wt% of a petroleum resin. The petroleum resin is preferably a cyclopentadiene resin. Japanese Patent Publication No 146 952/1988 discloses compositions comprising 70-99 parts by weight of polypropylene and 1-30 parts by weight of an hydrogenated resin of chain α-olefin and cyclopentadiene. The resin preferably has a softening point (by ring and ball test) of 90-200°C. The resin composition provides films used for packaging. As a result of extensive investigations with a view to eliminating the above-mentioned defects of the foregoing conventional processes and thereby providing a process for producing a low-gloss molding having a matte-tone roughened surface with a high density of unevenness, the authors of the present invention have found out that a flat molding formed from a blend composition comprising a propylene-ethylene block copolymer and a specific cyclopentadiene type petroleum resin at a specified weight ratio, when stretched under specified conditions, can provide a very beautiful dull-tone molding having a surface with a very high density of unevenness. Thus, the dulled stretched molding of the present invention has been materialized. SUMMARY OF THE INVENTION More specifically, in accordance with the present invention, there is provided a dulled stretched moulding produced by melt-kneading and melt-extruding a blend composition comprising 100 parts by weight of a propylene-ethylene block copolymer and 3 to 40 parts by weight of a hydrogenated or unhydrogenated cyclopentadiene type petroleum resin obtained by heat polymerization of a cyclopentadiene fraction obtained by steam cracking a petroleum naphtha, and having a ring and ball softening point of at least 160°C and stretching the resulting flat molding in at least one direction at a draw ratio of at least 2 at a stretching temperature of the cyclopentadiene type petroleum resin; in such a way as to make the resulting stretched molding have a roughened surface of at most 30% in gloss value with a high density of unevenness; DETAILED DESCRIPTION OF PREFERED EMBODIMENTS The propylene-ethylene block copolymer to be used in the dulled stretched molding of the present invention may generally be prepared either by a two-stage polymerization process comprising a first stage of propylene-rich polymerization which may involve copolymerization thereof with at most 1 wt. % of ethylene and a second stage of ethylene-rich polymerization, or by a multi-stage polymerization process wherein the above-mentioned first and second stages are repeated alternately. However, the preparation of the above-mentioned copolymer is not particularly restricted in respect of the method of polymerization thereof. For example, there are known such methods as respectively disclosed in Japanese Patent Laid-Open Nos. 69,215/1983, 116,716/1980, 29,811/1983 and 195,718/1982, which are all employable. The propylene/ethylene ratio is also not particularly restricted. For example, preferred is a propylene-ethylene block copolymer having a melt flow rate of 0.1 to 20 g/10 min and a block index of at least 0.6 in terms of the ratio of absorbance at 720 cm -1 to that at 731 cm -1 as determined using an infrared spectrophotometer when the ethylene unit content is 2 to 20 wt. %. If crystalline polypropylene is used instead of the propylene-ethylene block copolymer, a large amount of the cyclopentadiene type petroleum resin must be blended therewith in a molding composition in order to produce therefrom an opaque molding, which, however, is a highly brilliant product unlike the dulled stretched molding of the present invention, the aim of which is to give thereto a roughened surface with a dull tone. Even if the amount of the above-mentioned petroleum resin to be blended in the molding composition is decreased, molding of the composition can only provide a film product of low commercial value with an insufficient opaquness as well as with an uneven surface, which looks as if it contains nonuniform foreign particles. Thus, in this case, a desired low-gloss roughed surface with a matte tone cannot be secured unlike in the dulled stretched molding of the present invention. As the cyclopentadiene type petroleum resin to be used in the dulled stretched molding of the present invention, is a cyclopentadiene type petroleum resins prepared by at least a few hours of heat polymerization of a cyclopentadiene fraction obtained, for example, through steam cracking of petroleum naphtha or the like and comprising as the main component cyclopentadiene, dicyclopentadiene, a polymer thereof, an alkyl-substituted derivative(s) thereof or a mixture thereof in the presence or absence of a solvent under an atmosphere of an inert gas such as nitrogen gas at a temperature of preferably 220 to 320 °C under such a pressure as can at least keep the polymerization system in a liquid phase; hydrogenated cyclopentadiene type petroleum resins prepared from a cyclopentadiene type petroleum resin as mentioned above through hydrogenation thereof according to a known method wherein hydrogenation is effected in a solvent in the presence of a metallic or metallic oxide catalyst such as palladium, nickel, cobalt or an oxide thereof at a temperature of 150 to 320 °C under a hydrogen pressure of 10 to 150 kg/cm ; and mixtures thereof. The polymerization of the above-mentioned cyclopentadiene fraction may be done either continuously or batch-wise and either in one stage or in two or more stages. In the case of preparation of a hydrogenated cyclopentadiene type petroleum resin, the polymerization of the cyclopentadiene fraction and the subsequent hydrogenation of the resulting polymer may be done either continuously or batch-wise. The cyclopentadiene type petroleum resin to be used in the dulled stretched molding of the present invention is required to have a ring and ball softening point of at least 160 °C. When use is made of a cyclopentadiene type petroleum resin having a ring and ball softening point of lower than 160 °C, a glossy molding with insuficient dullness is obtained, which is not a stretched molding adapted for the purpose of the present invention. When use is made of a cyclopentadiene type petroleum resin having a ring and ball softening point of at most 150 °C, there cannot be obtained a characteristic dull-tone stretched molding having a roughened surface with a high density of unevenness, which is adapted for the purpose of the present invention, and there is instead obtained a high-gloss molding totally contrary to the aim of the present invention. A hydrogenated cyclopentadiene type petroleum resin having a ring and ball softening point of at least 160 °C is preferably used for the production of the dulled stretched molding of the present invention. Especially preferred are hydrogenated cyclopentadiene type petroleum resins having a ring and.ball softening point of 170 to 200 °C and a bromine number of at most 20. This is so because they are so excellent in compatibility with the propylene-ethylene block copolymer as to ensure a stable processability, and are capable of providing a stretched molding with an excellent dull tone. 100 parts by weight of the propylene-ethylene block copolymer is blended with 3 to 40 parts by weight of the cyclopentadiene type petroleum resin having a ring and ball softening point of at least 160 °C to prepare a composition for use in the production of the dulled stretched molding of the present invention. When the amount of the above-mentioned petroleum resin is smaller than 3 parts by weight, the dulling effect aimed at to obtain the dulled stretched molding of the present invention is unsatisfactory. When the amount of the petroleum resin exceeds 40 parts by weight, the productivity is unfavorably lowered to an extreme extent because extrusion molding tends to be accompanied by extrusion nonuniformity while rupture of the molding is liable to occur in the course of stretching. In order to produce dulled stretched moldings with high productivity, the aforementioned hydrogenated cyclopentadiene type petroleum resin having a ring and ball softening point of 170 to 200 °C is especially preferably used in an amount ranging from 5 to 30 parts by weight. In the composition for use in the production of the dulled stretched molding of the present invention, the propylene-ethylene block copolymer and the cyclopentadiene type petroleum resin as the essential components may be blended with any one(s) of various additives known in the art to be capable of being added to propylene-ethylene block copolymers, such as processing stabilizers, anti-oxidizing agents, slip agents, antistatic agents, and other various polymers, if necessary. The above-mentioned composition can be easily prepared by mixing the above-mentioned copolymer with the above-mentioned petroleum resin and, if necessary, other additive(s) by means of a common blender, a Henschel mixer (trade name) or the like. Alternatively, the use of an extruder, a Banbury mixer or the like capable of mixing the copolymer with the petroleum resin in a molten state is especially preferable since a composition in the serviceable form of pellets can be prepared. It also is efficient to blend the propylene-ethylene block copolymer or other resin(s) (e.g., HDPE, LDPE and L-LDPE) with a large amount of the petroleum resin to prepare a master batch, which is blended with the propylene-ethylene block copolymer in such a way as to prepare a composition in agreement with a predetermined formulation. The composition thus obtained is melt-extruded into a flat molding, or a raw sheet, which is then monoaxially or biaxially stretched by a known method to produce a dulled stretched molding according to the present invention. Employable stretching methods include known monoaxial stretching methods such as roll stretching, oven stretching, and hot plate stretching; and known simultaneous or consecutive biaxial stretching methods such as tubular stretching and tenter stretching. The temperature of the raw sheet during the course of stretching must be set lower than the ring and ball softening point of the petroleum resin contained in the composition thereof. A choice of such conditions enables the resulting stretched molding to have a dulled surface with a gloss value of at most 30 %. It is impossible to effect stretching or orientation at a temperature equal to or higher than the melting point of the propylene-ethylene block copolymer. In the case of stretching in an oven or in a similar case, nevertheless, the temperature of hot air may sometimes be set the same as or higher than the melting point of the propylene-ethylene block copolymer. This is possible because the actual stretching temperature does not reach the melting point of the propylene-ethylene block copolymer. This has much to do with the thickness of the raw sheet being stretched and the time of passage thereof through the oven or the like, associated with the thermal conductivity of the raw sheet. In this sense, the term "stretching temperature" used herein refers to the actual temperature of the raw sheet being stretched. The dulled stretched molding of the present invention can be obtained by stretching the raw sheet in at least one direction at a draw ratio of at least 2 at a temperature of at most the ring and ball softening point of the petroleum resin contained in the composition. The stretching is preferably effected at a draw ratio of at least 4. It is especially preferable to effect simultaneous or consecutive biaxial stretching of the raw sheet at a high draw ratio of about 10 to about 60. The dulled stretched molding of the present invention is characterized by a gloss value of at most 30 %. When the gloss value of a stretched molding exceeds 30 %, the stretched molding has some shininess with no dull tone. The gloss value of a stretched molding according to the present invention is especially preferably at most 20 % since such a molding has a roughened surface excellent in dull tone with a high density of unevenness. The dulled stretched molding of the present invention may further be surface-treated through a corona treatment, a plasma treatment or the like under an atmosphere of air, oxygen, nitrogen or the like if necessary. EXAMPLES AND COMPARATIVE EXAMPLES The following Examples will now illustrate the present invention in comparison with the following Comparative Examples, but should not be construed as limiting the scope of the invention. The methods of determination of characteristic values mentioned in the following Examples and Comparative Examples are as follows. (1) Ring and ball softening point: in accordance with JIS K2207; (unit: °C). (2) Bromine number: in accordance with JIS K2543 - 1979. It refers to how many grams of bromine is added to the unsaturated moeities of a substance contained in 100 g of the sample thereof. (3) Gloss value: in accordance with ASTM D523 (angle: 20°). (4) Melt flow rate (MFR): in accordance with JIS K7210 - 1976, Test Conditions 14 (230 °C, 2.16 kgf); (unit: g/10 min). (5) Ethylene unit content: calculated from an absorbance at 731 cm -1 which is measured using an infrared spectrophotometer (Perkin-Elmer Model 783). The block index is calculated from a ratio of absorption intensity at 720 cm -1 to absorption intensity at 731 cm -1 . (6) Density: The weight per m 2 of a molding is measured and is converted into the weight per cm 2 of the molding, which is divided by the thickness thereof in terms of cm to obtain the value of density (unit: g/cm 3 ) thereof. (7) Total light transmission: in accordance with JIS K6714. (8) Heat shrinkability: A molding is cut into a sample strip of 10 mm in width and 100 mm in length, which is then dipped in a silicone bath kept at 100 °C for 30 seconds, followed by the measurement of the length (L) of the sample strip. The heat shrinkability is calculated according to the following equation. heat shrinkability (%) = {(100 - L)/100} × 100 Examples 1 to 5 and Comparative Examples 1 to 4 (Examples 1, 2 and 3) 0.1 part by weight of a phenolic anti-oxidizing agent BHT, 0.1 part by weight of calcium stearate, and a predetermined amount of a hydrogenated cyclopentadiene type petroleum resin as listed in Table 1 were added to 100 parts by weight of a propylene-ethylene block copolymer powder having an MFR of 1.5, an ethylene unit content of 8 wt. % and a block index of 0.8, followed by mixing by means of a Henschel mixer. The resulting mixture was passed through an extruder to effect melt-mixing at 250 °C. The molten mixture was cooled and cut to prepare a composition in the form of pellets. The composition was melt-extruded through an extruder of 40 mm in cylinder diameter and a T die of 30 mm in width at a temperature of 250 °C and then quickly cooled with mirror-surfaced cooling rolls kept at 45 °C to form an unstretched raw sheet of 0.75 mm in thickness. Subsequently, the raw sheet was cut into a square piece, which was then preheated with a pantograph type biaxial stretcher at a temperature of 153 °C for 60 seconds. The preheated raw sheet was stretched with the above-mentioned stretcher five-fold in each of longitudinal and lateral directions simultaneously in both directions at a temperature of 153 °C, followed by a heat treatment under tension at 153 °C for 20 seconds. According to the foregoing procedure, nine kinds of biaxially stretched films were obtained. The characteristic values of these biaxially stretched films are listed in Table 1. Additionally stated, cyclopentadiene type petroleum resins as starting materials of hydrogenated cyclopentadiene type petroleum resins were prepared by customary polymerization of cyclopentadiene, dicyclopentadiene or the like obtained by steam cracking of naphtha, and hydrogenated in the presence of a nickel type catalyst under a hydrogen pressure of 80 kg/cm 2 at a temperature of 250 °C to prepare the respective hydrogenated cyclopentadiene type petroleum resins, which were used as starting materials for the production of the above-mentioned biaxially stretched films. (Examples 4 and 5) In Examples 4 and 5, biaxially stretched films were formed according to substantially the same procedure as in Examples 1, 2 and 3 except that the propylene-ethylene block copolymer used in Examples 1, 2 and 3 was replaced with a propylene-ethylene block copolymer having an MRF of 1.0, an ethylene unit content of 12 wt. % and a block index of 1.6 which was used in combination with respective hydrogenated cyclopentadiene type petroleum resins having a ring and ball softening point and a bromine number, at least one of which was different from those of the petroleum resins used in Examples 1, 2 and 3, to prepare respective compositions. (Comparative Examples 1 and 2) In Comparative Examples 1 and 2, a propylene homopolymer having an MFR of 2.5 was used instead of the propylene-ethylene block copolymer used in Example 2. In Comparative Example 1, 5 parts by weight of the same petroleum resin as used in Example 2 was used instead of 10 parts by weight thereof used in Example 2. In Comparative Example 2, the same amount of the same petroleum resin as used in Example 2 was used. Substantially the same procedure as in Example 2 except for the foregoing conditions was repeated. Thus, two kinds of biaxially stretched films were formed. (Comparative Examples 3 and 4) Petroleum resins of substantially the same type as uused in the present invention except that the ring and ball softening points thereof were below the range as specified in the present invention were respectively used in an amount of 15 parts by weight in Comparative Examples 3 and 4. Substantially the same procedure as in Example 2 except for the foregoing conditions was repeated. Thus, two kinds of biaxially stretched films were formed. As is apparent from Table 1, the biaxially stretched films of Examples 1 to 5 according to the present invention were greatly lowered in gloss value with a peculiar low-brightness dull-tone hand. In contrast, both of the biaxially stretched films of Comparative Examples 1 and 2 with the use of the propylene homopolymer in combination with the same pertoleum resin as in Example 2, even when used in the same amount as in Example 2, had a gloss value exceeding 60%. The same is true of both of the biaxially stretched films of Comparative Examples 3 and 4 with the use of the respective petroleum resins having a ring and ball softening point lower than that specified in the present invention, which films in particular had a gloss value conspicuously much higher than those of the stretched films according to the present invention. Thus, it will be understandable that the use of a starting material(s) other than those specified in the present invention cannot give a stretched film product a desired performance adapted for the purpose of the present invention. The stretched films of Examples 1 to 5 were all roughened in the surface with a high density of unevenness to have a gloss value lower than 20 % and a peculiar beautiful dull-tone hand without shininess. Thus, they were excellent films. The dulled stretched molding of the present invention in the form of a film, a yarn, a filament, a hollow container formed through stretching blow molding, etc. is useful in a wide variety of use applications, including a general-purpose packaging material, printing paper, tracing paper and a packing material, wherein the peculiar, beautiful, opaque, dull-tone roughened surface thereof with a high density of unevenness can be made the most of.

Claims: A dulled stretched molding produced by melt-kneading and melt-extruding a blend composition comprising 100 parts by weight of a propylene-ethylene block copolymer and 3 to 40 parts by weight of a hydrogenated or unhydrogenated cyclopentadiene type petroleum resin obtained by heat polymerization of a cyclopentadiene fraction obtained by steam cracking of petroleum naptha, and having a ring and ball softening point of at least 160°C; and stretching the resulting flat molding in at least one direction at a draw ratio of at least 2 at a stretching temperature of not more than the ring and ball softening temperature of the cyclopentadiene type petroleum resin so that the resulting stretched molding has a roughened surface of at most 30% in gloss value.

Inventors: ISHIBASHI TADAO, KURODA TAKASHI, YAMADA KAZUHIRO, ISHIBASHI, TADAO, KURODA, TAKASHI, YAMADA, KAZUHIRO
Applicants: CHISSO CORP, CHISSO CORPORATION
Application year: 1990
Main classification: C08J5
IPC codes: C08J5, C08J9, C08L57, B29C55, B29C61