Melt tension improver for polyolefin resins and process for producing the same

Abstract

A melt tension enhancer for polyolefin resins that contains polytetrafluoroethylene and a polymer of an alkyl (meth)acrylate of 5-30 carbon atoms, and a process for its production. Its addition to polyolefin resins enhances the melt tension of the polyolefin resins without impairing the surface appearance of their molds.

Description

[0001] The present invention relates to a melt tension enhancer for polyolefin resins that contains (A) polytetrafluoroethylene and (B) a polymer based on an alkyl (meth)acrylate of 5-30 carbon atoms, and to a process for its production.[0002] Polyolefin resins have been widely used in the past for a variety of molded products because of their low cost and excellent physical properties. However, because of low tension upon melting (hereunder referred to as "melt tension") in the case of polypropylene, for example, there are some disadvantages in terms of processability, including inferior vacuum moldability, blow moldability, foam moldability, extrusion moldability and calender moldability.[0003] Polyethylene and the like are often blended with polypropylene toward the aim of improving these processability, but since the improvement in processability is insufficient, large amounts of polyethylene are required and this leads to the disadvantage of lower rigidity of the resulting blen...

AI Technical Summary

Benefits of technology

[0012] It is an object of the present invention to provide a melt tension enhancer that increases the dispersability of polytetrafluoroethylene in polyolefin resins and improves the molding processability of polyolefins without impairing the surface appearance of molded products.

[0021] The amount of the polytetrafluoroethylene in the melt tension enhancer of the invention is preferably 0.05-40 wt % based on the total weight of the melt tension enhancer. At less than 0.05 wt % it will have to be added in too large amount to achieve sufficient melt tension, and the rigidity and heat resistance of the polyolefin resin may be impaired. At greater than 40 wt % the dispersability of the polytetrafluoroethylene may be reduced.

[0029] The polyolefin resin composition containing the melt tension enhancer of the invention has increased tension when melted, improves the drawing properties upon calendering, the draw down of melted resins for thermoforming or blow molding, and the open cell formation upon foam molding, and improves the general processability for calendering, thermoforming, blow molding, foam molding and the like. It also improves the discharge volume for extrusion molding and the surface condition of extrusion molded articles such as sheets and films, as well as the extrusion processability. There is also no macro-aggregation of the polytetrafluoroethylene, so that the surface appearance of the molded products is excellent.

Problems solved by technology

However, because of low tension upon melting (hereunder referred to as "melt tension") in the case of polypropylene, for example, there are some disadvantages in terms of processability, including inferior vacuum moldability, blow moldability, foam moldability, extrusion moldability and calender moldability.

Polyethylene and the like are often blended with polypropylene toward the aim of improving these processability, but since the improvement in processability is insufficient, large amounts of polyethylene are required and this leads to the disadvantage of lower rigidity of the resulting blend.

It has been attempted to raise the melt tension by increasing the molecular weight of the polyolefin, but higher molecular weight is a problem because it reduces the melt flow property which is one parameter of the processability, thus making it impossible to achieve a suitable balance between the melt tension and the melt flow property.

However, because this type of polypropylene requires a special treatment method or synthesis method involving electron beam irradiation or peroxide addition in order to produce the free-ended long-chain branched structure, it has the disadvantage of greatly increased production costs for the resin.

Polyolefins obtained by metallocene catalysts have excellent heat seal properties and hot tackiness, but their narrow molecular weight distribution results in a low melt tension and they are hence known to have problems in terms of molding processability; an improvement in melt tension, therefore, is still desired.

However, polytetrafluoroethylene has the disadvantage of poor dispersability in common thermoplastic resins including no halogen atoms, and as taught in Japanese Unexamined Patent Publication No. 5-214184 and Japanese Unexamined Patent Publication No. 6-306212, it fails to uniformly disperse by simple blending and thus notably lowers the surface appearance of molded products.

Even with the process of Japanese Unexamined Patent Publication No. 7-324147, it is difficult to render all of the polytetrafluoroethylene fibrous by shear force, and the fibrous polytetrafluoroethylene therefore also aggregates in the matrix resin making it impossible to obtain a homogeneous composition.

Moreover, while the process of Japanese Unexamined Patent Publication No. 9-25420 attempts to improve affinity with the matrix resin by encapsulation, there is no effect of improved dispersability in polyolefin resins.

In other words, all of these processes leave the problem of dispersability of polytetrafluoroethylene in polyolefin resins, with the disadvantages of requiring large amounts of polytetrafluoroethylene to exhibit the useful properties mentioned above, and giving molded products with impaired surface appearance.