A microporous membrane is made by a dry-stretch process and has substantially round shaped pores and a ratio of machine direction tensile strength to transverse direction tensile strength in the range of 0.5 to 5.0. The method of making the foregoing microporous membrane includes the steps of: extruding a polymer into a nonporous precursor, and biaxially stretching the nonporous precursor, the biaxial stretching including a machine direction stretching and a transverse direction stretching, the transverse direction stretching including a simultaneous controlled machine direction relax.

Bi-axially orientated polypropylene film having a thickness of between 10 m and 120 m, suitable to make packing, flexible packages, laminated products and labels, where the film is obtained by means of flat die co-extrusion and sequential stretching respectively in the machine direction and in a direction transverse to the machine direction.

The inventive label is prepared from a polyester with an intrinsic viscosity of 0.58 dl/g or more. The label has a base film with a thickness of 8-30 m and a difference in specific heat capacity Cp between temperatures lower and higher than Tg of 0.2 J/(g.Math. C.) or more. The label has a tensile elongation at break of 5% or more in both a main shrinkage direction and an orthogonal direction. A difference between the absorbancy ratio (absorbancy at 1340 cm.sup.1/absorbancy at 1410 cm.sup.1) in the main shrinkage direction of the label and the absorbancy ratio in the direction orthogonal to the main shrinkage direction of the label is 0.2 or more. The label has a difference between a maximum value and a minimum value of a length in a vertical direction of the label of 3 mm or less.

Disclosed herein is an improved membrane, separator and/or method for forming a multilayer microporous membrane for use in an improved battery separator, particularly a battery separator for a lithium ion secondary battery. Also disclosed herein is the multilayer microporous membrane formed by this method, which has properties that compete with or exceed those of wet process, coated or uncoated, membranes that are also useable in battery separators. Also disclosed are battery separators comprising the multilayer microporous membrane and batteries, vehicles, or devices comprising the separators. The method may comprise at least the following steps: (1) forming a stretched first non-porous precursor film that has pores due to the stretching of a first non-porous precursor film; (2) separately forming a second stretched non-porous precursor film that has pores due to the stretching of a second non-porous precursor film; and then (3) laminating the stretched first non-porous precursor and the stretched second non-porous precursor.

A biaxially oriented thermoplastic resin film has at least one surface of which has protrusions each having a height of 1 nm or more and less than 2 nm at a density of 110.sup.7 to 110.sup.9 protrusions per mm.sup.2. The thermoplastic resin film is capable of suppressing generation of coarse protrusions and contaminants, and defects in a processing process while having slipperiness.

Novel or improved microporous single or multilayer battery separator membranes, separators, batteries including such membranes or separators, methods of making such membranes, separators, and/or batteries, and/or methods of using such membranes, separators and/or batteries are provided. In accordance with at least certain embodiments, a multilayer dry process polyethylene/polypropylene/polyethylene microporous separator which is manufactured using the inventive process which includes machine direction stretching followed by transverse direction stretching and a subsequent calendering step as a means to reduce the thickness of the multilayer microporous membrane, to reduce the percent porosity of the multilayer microporous membrane in a controlled manner and/or to improve transverse direction tensile strength. In a very particular embodiment, the inventive process produces a thin multilayer microporous membrane that is easily coated with polymeric-ceramic coatings, has excellent mechanical strength properties due to its polypropylene layer or layers and a thermal shutdown function due to its polyethylene layer or layers. The ratio of the thickness of the polypropylene and polyethylene layers in the inventive multilayer microporous membrane can be tailored to balance mechanical strength and thermal shutdown properties.

Disclosed are compositions and methods for multilayer films, which, in one embodiment may comprise a core layer comprising at least 50 wt. % of high-density polyethylene. Further, the multilayer film may include a first skin layer comprising at least 80 wt. % of high-density polyethylene, and a second skin layer comprising either: (i) one or more low-density polyethylenes; or (ii) one or more polypropylene-based copolymers. The multilayer film may be oriented in at least one direction.

A method is for producing a coextruded and biaxially stretched composite film using a novel combination of stretching and relaxation steps. A corresponding composite film has little or no shrinkage.

A method for manufacturing a crosslinked polyolefin separator and the crosslinked polyolefin separator obtained therefrom are provided. The method includes non-grafted polyolefin having a weight average molecular weight of 300,000 or more and silane-grafted polyolefin having a weight average molecular weight of 300,000 or more. The method minimizes gel formation, a side reaction occurring in an extruder during the manufacture of a-the separator, and provides a-the separator having a uniform surface.

A polyester film according to an embodiment includes a polyester resin. The polyester resin includes a repeating unit having a cyclohexane skeleton and a repeating unit having a benzene ring. The polyester film has a base peak related to bending vibration of the benzene ring and a first peak related to CO stretching vibration in a spectrum measured using a Fourier transform infrared spectrometer (FT-IR). The base peak is a peak at a wavenumber of 788 cm.sup.1 to 798 cm.sup.1. The first peak is a peak at a wavenumber of 1129 cm.sup.1 to 1139 cm.sup.1. The intensity of the base peak and the intensity of the first peak differ by 0.05 to +0.05. According to an embodiment, a polyester resin having a controlled degree of crystallization can be applied to a film to impart excellent heat resistance, mechanical properties, and the like to the film.