Abstract: A continuous, preferably counter-current, extraction process that can be used to significantly reduce the concentrations of residual monomers, residual catalyst, undesired solvents, and other impurities in polymer compositions. The invention is particularly beneficial for extracting residual monomers and other impurities from viscous, sticky polymer solutions, such as solutions of PSAs and low cohesive strength polymer compositions that phase change during extraction (i.e., change from liquid to solid, or precipitate), in a continuous manner. The polymer composition can be extruded into an extraction solvent as fibers in a vertical extraction column, under conditions such that at least a portion of an impurity is extracted from the polymer into the extraction solvent.

Abstract: Rod-like aromatic heterocyclic polymers having repeating units of the formula --(--Q--Ar--).sub.m --(--Q--Ph--).sub.n)-- where Q is ##STR1## X is --O--, --S--, or --NH--; m is 0.05 to 1.0; n is 1.0-m; Ph is 1,4-phenylene; Ar is ##STR2## R.sub.1 and R.sub.2 are the same and are either H or CH.sub.3 ; and R.sub.3 and R.sub.4 are CH.sub.3.

Abstract: Graft copolymer particles comprising an elastomeric base polymer such as polybutadiene and grafted chains of a thermoplastic, non-elastomeric polymer such as styrene-acrylonitrile are coagulated for isolation from aqueous emulsion by subjecting the emulsion to mechanical shear in the absence of chemical coagulants at a temperature greater than or equal to the glass transition temperature of the thermoplastic, non-elastomeric portion of the copolymer.

Abstract: A method for the synthesis of TFPX-dichloride is disclosed. The method involves reacting hexachloro-p-xylene with anhydrous HF in an inert organic solvent. The reaction is advantageous in that it produces relatively high yields of TFPX-dichloride, provides little waste, and is carried out as a simple, one-step process.

Abstract: Melt processed linear polyethylenes which may optionally contain an elastomer, are shown to exhibit improved processability through the addition of certain surfactants. Among the melt processing parameters improved are reduced head pressure, reduced torque, reduced motor load, reduced or eliminated melt fracture, or combinations of these parameters. The surfactants can be chosen from a non-aromatic alkyl sulfonate or sulfate salt wherein a cation of the salt is selected from the group consisting of Na, K, Li, and other alkali cations and quaternary ammonium cations, said surfactant being essentially free of halogens.

Abstract: Melt processed linear polyethylenes are shown to exhibit improved processability through the addition of certain surfactants. Among the melt processing parameters improved are reduced head pressure, reduced torque, reduced motor load, reduced or eliminated melt fracture, or combinations of these parameters. The surfactants can be chosen from a non-aromatic alkyl sulfonate or sulfate salt wherein a cation of the salt is selected from the group consisting of Na, K, Li, and other alkali cations and a quaternary ammonium cations, said surfactant being essentially free of halogens.

Abstract: Processes for producing free flowing, Mannich and glyoxal polyacrylamide water soluble and water-swellable granules from a water-in-oil emulsion and compositions comprising such dry polymer granules are disclosed.

Abstract: There is a need for polymers which are utilized in automotive interiors which offer increased heat and ultraviolet light resistance. It is particularly critical for polymers which are utilized in making skin compounds for automotive instrument and door panels to display excellent heat and ultraviolet light resistance. This invention discloses a continuous process for preparing a rubbery polymer which can be blended with polyvinyl chloride to make leathery compositions having good heat and ultraviolet light resistance. This technique involves utilizing a multiple continuous reactor system wherein a first phase monomer solution containing butyl acrylate, an acrylic monomer, acrylonitrile and a crosslinking agent is continuously charged into at least three initial reactors. To attain a small particle size, it is necessary to limit the solids content in each of these initial reactors.

Abstract: A novel process for the production of degraded polyolefin is described. The process involves introducing polyolefin into one end of a vented multi-screw extruder, in the substantial absence of free radical initiator and oxidizing agent, and removing degraded polyolefin from the opposite end of the extruder.

Abstract: A process for recovering the resin contained in optical information recording media having either a thin metal film layer or a printed coating film layer, coated on at least one side of a resin substrate,which comprises the following steps of:(1) rolling the recording media,(2) bringing the rolled recording media into contact with hot water,(3) separating the coating film peeled from the recording media,(4) grinding the resulting recording media,(5) bringing the obtained small pieces of the recording media into contact with hot water to detach the thin metal film component, and(6) separating the detached thin metal film component from the small pieces of the recording media to recover and obtain the small pieces of the recording media.With this process, the coating layer can be removed effectively from the optical information recording media and the resin component in the recording media can be selectively recovered advantageously in industry.

Abstract: Processability of non-fluorinated melt-processible polymers is improved by introducing a process aid comprising a fluoroelastomer latex or aqueous fluoropolymer dispersion to the non-fluorinated polymer and extruding the blend.

Abstract: A biocompatible, heterofunctional, star-shaped poly(ethylene glycol) is described. Methods of making the heterofunctional star-shaped poly(ethylene glycol) and using it for conjugation with proteins are also described.

Abstract: A method of forming a urea formaldehyde resin includes the step of heating solid paraformaldehyde to a temperature of 60 to 120.degree. C. Urea is added to the heated paraformaldehyde to form a urea mixture, which is dry mixed and heated until a temperature of 80 to 110.degree. C. has been reached. After this, a methanolic quanine base is added to the urea mixture to form a quanine-urea-formaldehyde mixture, which is heated until the quanine-urea-formaldehyde mixture is liquefied and cooled to 65.degree. C. Then, the quanine-urea-formaldehyde mixture is heated until it boils, at which point it is condensed for a period of 30 to 100 minutes. After this, additional urea is added to the liquified urea mixture to form a urea enriched mixture. The urea enriched mixture is condensed for 90 to 180 minutes. After condensation, the urea enriched mixture is buffered with lactic acid to form a buffered mixture. This buffered mixture is cooled.

Abstract: The presently claimed process for the production of a solid pigment/resin dispersion comprises the steps of mixing together a particulate pigment, a solid resin carrier, a water-immiscible organic solvent in which the carrier is at least partially soluble, water, and, optionally, a water miscible solvent until the mixture separates into an aqueous phase and a coherent phase comprising resin, pigment and organic solvent; separating water from the coherent phase; and continuing to mix the coherent phase while removing the organic solvent under the action of heat and/or reduced pressure until a dry particulate material comprising a pigment and resin is formed.

Abstract: Acetals are produced from the reaction of aldehydes and alcohols, e.g. methylal by the reaction of methanol and formaldehyde, by the reaction in a reaction distillation column of the alcohol and aldehyde in the presence of a catalyst and the concurrent fractional distillation of the reaction mixture to separate the reaction products, water and acetal.

Abstract: The specification discloses a method for the manufacture of a fluorescent polyphenolic product with high UV absorbance, its subsequent epoxidation as well as polyphenolic products and epoxidized derivatives and compositions thereof. The polyphenolic products are prepared by heating glyoxal at a temperature of about 80.degree. C. to about 100.degree. C. with a molar excess of a phenol in the presence of an acidic catalyst which is eliminated from the reaction mixture at a temperature below about 170.degree. C. The total mole ratio of glyoxal to phenol charged to the reaction mixture is about 0.15 to 0.22 moles of glyoxal for each mole of phenol. The glyoxal is added continuously or by stepwise additions to the phenol so as to keep the aldehyde units in the reaction mixture to less than about 70% of the aldehyde units in the total quantity of glyoxal to be charged for making the polyphenol. Water is distilled stepwise or continuously from the reaction mixture.

Abstract: To provide a polytetrafluoroethylene granular powder for molding and a process for preparing the granular powder, in which the granular powder contains only a small number of coarse particles, is obtained with good tumbling efficiency and further no organic liquid is required to be used.

Abstract: A method of treating polyolefin comprises (i) a ligand-decomposition step of contacting polyolefin, which is obtained by the use of a transition metal compound containing ligands having cyclopentadienyl skeleton, with a ligand decomposer, such as water, oxygen, alcohol, alkylene oxide or peroxide, to decompose the ligands contained in the polyolefin, and (ii) a ligand-removal step of heating the polyolefin contacted with the ligand decomposer to remove the decomposed ligands from the polyolefin. According to this method, the residual ligands having cyclopentadienyl skeleton, which are contained in the polyolefin produced by the use of a transition metal compound containing ligands having cyclopentadienyl skeleton, are decomposed and removed from the polyolefin, whereby polyolefin diminished in odor development in the molding process can be obtained.

Abstract: The present invention provides a method for producing a film forming, fractionated novolak resin having consistent molecular weight and superior performance in photoresist composition, by isolating such novolak resin fractions without high temperature distillation. A method is also provided for producing photoresist composition from such a fractionated novolak resin and for producing semiconductor devices using such a photoresist composition.

Abstract: Composites which include a polymer matrix having natural free volume therein and an inorganic or organic material disposed in the natural free volume of the polymer matrix are disclosed. In addition, methods for making a composite are described. A polymer matrix having free volume therein is provided. The free volume is evacuated, and inorganic or organic molecules are infused into the evacuated free volume of the polymer matrix. The inorganic or organic molecules can then be polymerized under conditions effective to cause the polymerized inorganic or organic molecules to assemble into macromolecular networks. Alternatively, where the polymer matrix contains a functionality, the inorganic or organic molecules can be treated underconditions effective to cause the inorganic or organic molecules to interact with the polymer matrix's functionality.

Abstract: A process for finishing latex to form a dry resin and the resulting product. The process includes coagulating a latex of a thermoplastic polymer at a temperature at or just above the agglomeration temperature of the resin, dewatering the resin slurry to form a resin cake, drying the resin cake using extrusion technology to form a resin melt and solidifying the resin melt to form the resin. Preferred processes of the invention also include finishing the resin, such as by pelletizing and/or grinding it. More preferred processes of the invention include collecting and neutralizing the aqueous liquid byproducts from the dewatering and drying steps of the process. One embodiment of the invention includes utilizing water to solidify the resin melt, pelletizing the resin and drying the pellets.

Abstract: A method of forming polymer beads comprising forming an aqueous solution comprising a cross-linkable water soluble polymer and a water-soluble crosslinking agent, adding said solution with mixing to a thixotropic oil gel comprising an oil in which said polymer is insoluble and a silica or silicate, continuing said mixing for a time sufficient and under conditions sufficient to form a water-in-oil dispersion having individual water/polymer droplets dispersed in said thixotropic oil gel, stopping mixing, and when the droplets are in the form of solid beads recovering the beads from the thixotropic oil gel.

Abstract: A polyketone is provided wherein the polyketone is water soluble and curable. A method to make a such a polymer is also disclosed, the method including the steps of: providing a polyketone, the polyketone comprising 1,4-diketone units; contacting the polyketone with a diamine wherein the diamine comprises one nitrogen which is more reactive than another of the nitrogens under conditions effective to incorporate the more reactive nitrogen in the polyketone; contacting the polyketone having the diamine incorporated into the polyketone with maleic anhydride under conditions effective to react the less reactive nitrogen with the maleic anhydride; contacting the polyketone having maleic anhydride incorporated thereto with a strong base; and recovering a functionalized polyketone wherein the functionalized polyketone is water soluble and curable.

Abstract: The present invention provides methods for solutions having a very low level of metal ions, utilizing a specially designed Ion Exchange Pack. A method is also provided for producing photoresist composition having a very low level of metal ions from novolak resins purified in a process using such an Ion Exchange Pack.

Abstract: A method and apparatus for product recovery of polyolefins, particularly high molecular weight amorphous poly alphaolefins, wherein the use of water during the method is significantly decreased and wherein the intermediate stage of storing and drying the chunk form of the polyolefin is eliminated. Polyolefins produced in a reactor are heated and mixed by sigma blades in a kneader-extruder to remove any unreacted monomer(s). The polyolefin material in a liquid form is then transferred directly to an extruder to further remove any unreacted monomer(s) and catalyst(s). The invention further includes a method of measuring the inventory in a vessel using a gas of known quantity and known thermodynamic properties.

Abstract: A process for the devolatilization of a thermoplastic polymer containing gaseous impurities in an apparatus having a melting zone, a mixing zone, and a reduced pressure zone, comprising:(a) (i) adding a granular blowing agent directly or via a masterbatch to the polymer prior to the introduction of the polymer into the melting zone, said blowing agent being added in an amount of about 1 to about 4 percent by weight based on the weight of the polymer or (ii) adding a gaseous blowing agent to the mixing zone;(b) melting the polymer in the melting zone;(c) mixing the molten polymer and blowing agent in the mixing zone under sufficient pressure to maintain the blowing agent in the mixture;(d) at a temperature sufficient for decomposition or expansion, (i) decomposing the granular blowing agent in the mixing zone and/or in the reduced pressure zone or (ii) expanding the gaseous blowing agent in the reduced pressure zone wherein the blowing agent in its decomposed or expanded state develops froth cells in the molte

Abstract: The present invention relates to a process for recovering polyhydroxyalkanoate from a biological source material containing the polyhydroxyalkanoate, the process comprising: a) comminuting the biological source material; b) suspending the comminuted biological source material in a fluid; c) partitioning the polyhydroxyalkanoate from the other components of the biological source material by centrifugal fractionation to form a solid-solid separation; and d) recovering the polyhdroxyalkanoate.

Abstract: Impurities dissolved in a solid polymer and/or trapped in the spacial volume of the polymer can be removed quickly and efficiently in one or more relatively short pressurization/depressurization cycles, using a penetrant fluid (e.g. carbon dioxide) having at least some solubility in the polymer. Polymers with inherently slow or delayed elastic recovery at the temperature or temperatures at which the cycle is carried out (e.g. within the range of 20 to 200.degree. C.) or polymers with a high T.sub.g are the ones most efficiently treated. The penetrant is used to expand the polymer matrix, increasing its spacial volume. The pressure is then decreased rapidly, so that the impurities will migrate out of the polymer matrix before the matrix has a chance to relax or return to substantially its original volume. Each complete cycle should last seconds or minutes rather than hours.

Abstract: Polyester is depolymerized by methanolysis and methanol is recovered in a process that uses methyl benzoate and/or p-methyltoluate as an azeotropic agent while the methanol is present.

Abstract: The present invention provides a method for producing a film forming, fractionated novolak resin having consistent molecular weight and superior performance in photoresist composition, by isolating such novolak resin fractions without high temperature distillation. A method is also provided for producing photoresist composition from such a fractionated novolak resin and for producing semiconductor devices using such a photoresist composition.

Abstract: The present invention relates to a process for recovering polyhydroxyalkanoate from biological source material containing the polyhydroxyalkanoate, the process comprising: a) comminuting the biological source material; b) suspending the comminuted biological source material in a fluid; c) partitioning the polyhydroxyalkanoate from the other components of the biological source material by centrifugal fractionation to from a solid-solid separation; and d) recovering the polyhydroxyalkanoate.

Abstract: The invention relates to a method of producing partially aromatic copolyamides from polymeric esters of aromatic dicarboxylic acids by amidation of the ester groups with diamines, removal of the split-off alcohols or diols and after-condensation of the low-molecular precondensates as well as by the following compounding to polyamide molding materials.

Abstract: The invention relates to a method for forming a composition comprising a thermoplastic composite in the form of a linear profile extrudate. Such a profile comprises a structural member having improved tensile strength, flex modulus, impact resistance and other improved structural properties. The invention involves a unique extruder configuration having a change in direction for the resin and fiber that optimizes the composite strength by promoting the random orientation of the fibers resulting in improved structural properties. Further, because of the change in direction, the extruder can include a cooling feature that cools the profile interior as the profile leaves the exit die thus increasing the physical properties, productivity and quality of the product.

Abstract: A method for producing a polylactic acid includes the steps of (a) crystallizing polylactic acid pellets obtainable by direct polymerization of lactic acid or ring-opening polymerization of lactide; and (b) removing low-molecular components having a weight-average molecular weight of 1,000 or less in the resulting crystallized, solid polylactic acid pellets by gasifying the low-molecular components to obtain polylactic acids with substantially no low-molecular components. In this method, an apparatus for removing low-molecular components in polylactic acid pellets includes a crystallizing means for maintaining a temperature between equal to or higher than a glass transition temperature of polylactic acid pellets and equal to or lower than the melting point thereof, while fluidizing the polylactic acid pellets; and a reactor for allowing a heated inert gas and/or heated air to pass through the resulting crystallized, solid polylactic acid pellets obtained by the crystallizing means.

Abstract: The residual level of monomer in a polymer may be reduced by passing a melt of the polymer through a devolatilizer column which contains an array of two or more trays having voids comprising from 15 to 50% of the surface of the tray which are offset so the voids in the upper tray are spaced over the solid areas of the tray below.

Abstract: The present invention provides a method enabling segregation of the various ingredients making up the polymer based products into component product streams and collection of these component streams so as to form individual product streams. Thus, according to this invention there is provided a process for purposefully segregating polymer-polymer and polymer-additive mixtures. The process for segregating the various combinations of components may be advantageously used on the one hand for the production of separate product streams from a mixture of polymers or polymer-additives in, for example, recycling of waste plastic based products, or on the other hand, in the production of polymer-polymer or polymer-additive layered structures exhibiting preselected spatial segregation of the various components. In its simplest form, the polymer segregation part of the process consists of a tube added to an extruder. During segregation, polymer layers containing different blend compositions are formed.

Abstract: A process is provided for preparing a resin composition for coloring which comprises the steps of a phase replacement and dehydration of a pigment (a); water (b); a thermoplastic resin (c), an aqueous dispersion or solution of a thermoplastic resin (d) or an aqueous compound (e) in a twin screw extruder. Also, there is provided a resin composition for coloring prepared by such a process. It is possible to efficiently manufacture a resin composition for coloring (master batch) which has excellent pigment dispersibility and which is capable of uniform coloring without causing color unevenness.

Abstract: A pressure-sensitive adhesive comprises an elastomer having a partially oriented and partially crystallized elastomer component. Articles comprising the pressure-sensitive adhesive on a backing or substrate are also disclosed, as are methods of preparing the adhesive and the articles.

Abstract: A process for compounding polymer dispersions, which comprises circulating the polymer dispersion from a vessel (7) having a stirring device (6) through a line (3) having a mixing device (2) by means of a pump (4) which is located in the line (3), and, before the entry of the circulated polymer dispersion into the mixing device (2), metering at least one solution or dispersion of at least one compounding material from at least one stock container (5) via a supply line (9) into the circulated polymer dispersion.

Abstract: To prepare nitrogen-containing polycondensates, a starting substance which still contains reactive end groups is dispersed in a high-boiling inert solvent, preferably in the presence of a dispersing auxiliary, low molecular weight by-products are distilled off at elevated temperature, the batch is cooled and the dispersed polycondensate is isolated. To prepare the starting substance, a mixture of at least two monomers which react with one another is heated up to a constant reaction temperature, a melt being formed at least in part, but initially no homogeneous melt occurring. The reaction is continued until a homogeneous melt is present. The precondensate formed is then dispersed in the high-boiling inert solvent and the condensation reaction is brought to completion.

Abstract: Processes for spray drying water-soluble and water-swellable vinyl-addition polymer-containing dispersions, emulsions and microemulsions to obtain substantially dry water-soluble or water-swellable polymer particles, compositions of substantially dry water-soluble or water-swellable polymer particles, methods of agglomerating spray-dried polymer particles, and methods of using spray-dried polymer particles and agglomerates in water-treating, mining, paper, food processing, soil conditioning, solution thickening, biotechnological, and oil recovery applications are disclosed.

Abstract: A method for particles agglomeration and enlargement of a diene type polymer rubber latex, which comprises subjecting a diene type polymer rubber latex produced by emulsion polymerization, to particles agglomeration and enlargement to obtain a particles-enlarged diene type polymer rubber latex (A), wherein the particles enlargement is allowed to take place by agglomeration based mainly on Brownian coagulation; a graft copolymer (B) of a particles-enlarged diene type polymer rubber latex (A) obtained by the above method; and a thermoplastic resin composition comprising said graft copolymer (B).

Abstract: A method for improving consolidation of powder resin is provided. The method broadly includes the steps of: (1) sorting particles of the powder resin according to their diameter; (2) combining the sorted particles having a first diameter D1 with the sorted particles having a second diameter D2 so as to form a particle mixture; (3) applying a vibration to the particle mixture; (4) heating the particle mixture; and (5) delivering the particle mixture through a nozzle or into a mold. The particle diameters D1 and D2 are chosen so that once combined there is optimal close packing of the three-dimensional spaces between the powder resin particles.

Abstract: Methods of preparing granules which contain a water soluble or water dispersable polymer suitable for use in detergents are disclosed, in which a solution of the polymer in a liquid or a dispersion of the polymer in a liquid is formed into granules, in a single drying and granulation stage, wherein the polymer solution or dispersion is introduced into a substantially horizontal drum containing a multiplicity or rotating arms proximate its internal surface, which internal surface has an elevated temperature, and a gas is introduced into the drum at an elevated temperature via a gas inlet. Granules prepared by such methods may be used in detergent compositions, water treatment compositions, agrochemical compositions, adhesive compositions and cosmetic compositions, and may be used as pigment dispersants, mineral dispersants, cement additives, oil field additives, textile additives and paper additives.

Abstract: The invention relates to a process for drying polymeric powders and polymeric agglomerates, in particular thermoplastic aromatic polycarbonate or other thermoplastic polymers such as, for example, acrylonitrile-butadiene-styrene copolymer, in the melt, whereby thermoplastic polymeric powders or polymeric agglomerates containing water or solvent or both are freed from adhering moisture and contained solvent, accompanied by melting, in an apparatus provided with rotating baffles for cleaning the walls of the apparatus and for distribution and transport of the material being dried, by heat input through the walls or through the rotating baffles or both as well as by heat input as a result of shearing action. The process of drying and that of melting for the subsequent granulation are thereby combined.

Abstract: The invention relates to a process and an arrangement for the three-dimensional forming of a fabric. The process comprises the steps of providing a countermold; preparing a complex sheet by superimposing a sheet of plastics, hot-melt material and a fabric; die-cutting the complex sheet; superimposing the die cut complex sheet over the fabric; attachment of the die cut complex sheet to the fabric by pressing and heating until the fabric is impregnated by melting of the hot-melt material; and application of the ensemble of the complex sheet and fabric to the countermold by blowing pressurized air. The arrangement comprises a frame receiving the fabric to be formed and which is movable through various workstations wherein the process steps take place.

Abstract: Disclosed are a method for producing a polyamide resin which comprises the steps of extracting with water a polyamide resin obtained by polymerizing caprolactam in the presence of water; condensing the extracted aqueous solution containing unreacted caprolactam and its low polymerized materials; and polymerizing the condensate by adding an additional amount of caprolactam, the improvement wherein(a) among the low polymerized materials of caprolactam, a cyclic dimer is supplied to a polymerization reactor after subjecting it to ring-opening reaction to give a chain structure material in an amount of 15% by weight or more based on the total amount of the cyclic dimer, or(a') a condensate obtained by condensing said aqueous solution until reaching a water partial pressure of 10 kg/cm.sup.2 G or more and a temperature of 230.degree. C.

Abstract: A process for preparing a styrenic resin is herein disclosed which comprises the step of volatilizing-extruding a styrenic polymer (SPS) powder having a syndiotactic configuration in the presence of water, an alcohol or an antioxidant by the use of an extruder to obtain pellets. According to this process, the operation of volatilization-extrusion is done in the presence of water, the alcohol or the antioxidant to stably and efficiently prepare the SPS pellets in which yellowing is inhibited, and the operation of the volatilization-extrusion is carried out in the presence of water to stably and efficiently prepare the SPS pellets containing a less amount of a remaining volatile component such as an unreacted monomer.

Abstract: A styrenic resin is prepared by a method which comprises extruding a styrenic polymer powder having a syndiotactic configuration at a molding temperature of from the melting point of the polymer to 400.degree. C. at an extrusion rate meeting the equation Q/(D.times.H.times.V)=2.0.times.10.sup.4 to 6.0.times.10.sup.5, by the use of an extruder provided with one or more vents having an internal pressure of 0 to 760 Torr, wherein Q is an extrusion rate (kg/hr), D is a screw diameter (m), H is a screw groove depth (m), and V is a screw peripheral speed (m/sec); a residual volatile component, such as a monomer in the styrenic polymer powder having the syndiotactic configuration, can economically and efficiently be decreased at the time of extrusion, whereby a molding material having a good shape and containing a reduced amount of the residual volatile component can efficiently be prepared to prevent the emission of an objectionable odor at the time of the extrusion or molding.

Abstract: A process which combines a calender with a stretching system and a set of heating rolls is provided in this invention to produce films of polypropylene resin of wide thickness range. The polypropylene films which have cavities distributed in the film and on the surfaces are suitable for writing or printing and have a low density. The films have surface qualities of each side of surface within .+-.2.times.10.sup.-6 inch of the average depth of the cavities, .+-.2% of the average of the gloss at 45.degree. angle and .+-.0.02 of the average of coefficient of friction. Such a film is obtained by passing the molded film from the calender through a set of heating rolls at temperatures revealed in this invention before entering the stretching system. The obtained polypropylene film has superior printability, low density and high stiffness, and thus is suitable for use as a paper substitute.