Coextruded matte film

Abstract: A coextruded film having a matte surface layer is prepared by forming the layer from a blend of polyiso­ butylene and high density polyethylene. The film pre­ ferably has a heatseal layer on the other surface. In addition to having low gloss for consumer appeal, the matte surface layer has a medium coefficient of friction for good machinablility and excellent heat resistance to facilitate heatsealing. The film is especially useful as an overwrap for packaging consumer products.

Description: This invention is a coextruded plastic film having a nonembossed matte surface layer. As disclosed in US-A-3,843,478, coextruded films having a nonembossed matte surface layer are known in the art. However, such surface layers tend to have a high coefficient of friction, which limits their suitability for use in automatic packaging equipment. This invention provides a film having a matte surface layer having a coefficient of friction which renders the film especially suitable for processing in packaging equipment. The matte surface layer also imparts other desirable properties to the film. The film of this invention comprises a matte surface layer consisting essentially of a blend of from about ten to forty percent polyisobutylene, fifty to ninety percent high density polyethylene, and zero to forty percent propylene homopolymer. The term high density polyethylene refers to polyethylene having a density greater than 0.94. The polyisobutylene has a molecular weight of at least 50,000 as measured in accordance with ASTM D2503-82. The use of polyisobutylene having a much lower molecular weight to increase the coefficient of friction of the surface layer of a plastic bag is disclosed in US-A-4,560,598, but the increased coefficient of friction, being at least 0.8, is greater than the coefficient of friction that is desirable for purposes of this invention. The film of this invention has a coefficient of friction of between 0.2 and 0.7, preferably between 0.3 and 0.5, as measured in accordance with ASTM D1894. The matte surface layer has a gloss of less than ten percent, preferably less than eight percent, as measured in accordance with ASTM D1223. The other layer or layers of the coextruded film are not critical as long as they provide other desired properties. The other surface layer of the film is preferably a heat seal layer, such as a layer of ethylenevinyl acetate copolymer or ethylene-methyl acylate copolymer. The film preferably includes a core layer providing strength and bulk, such as a polyolefin layer. Suitable polyolefins include low density polyethylene, linear low or medium density polyethylene, and blends thereof. The core layer also preferably contains a pigment. The thickness of the film of this invention is preferably between 25.4 and 76.2 µm (1.0 and 3.0 mils), with the thickness of the matte surface layer preferably being between 2.54 and 7.62 µm (0.1 and 0.3 mil). The best mode contemplated for practicing the invention is illustrated by the following example, in which all percentages are by weight. Example A film having a matte surface layer, a core layer and a heat seal layer was prepared by coextrusion. The ratio of the thicknesses of the layers was 10:83:7. The matte surface layer consisted of a blend of 75 percent high density polyethylene having a melt index of 12 and 25 percent polyisobutylene having a Mooney viscosity of 80, which corresponds to a molecular weight between 64,000 and 81,000. The core layer consisted of a blend of 50.5 percent low density polyethylene, 33.5 percent linear medium density polyethylene, and 16 percent of a color concentrate. The color concentrate consisted of 50 percent red and white pigments in low density polyethylene. The heat seal layer consisted of ethylene-vinyl acetate copolymer having a vinyl acetate content of 23 percent. Physical properties of the film were determined and compared with a film prepared under the same conditions except a layer consisting of a blend of 75 percent high density polyethylene and 25 percent linear medium density polyethylene was substituted for the matte surface layer. The results are reported in the following table. The film of the invention illustrated by this example is especially suitable as an overwrap for packaging consumer products in an automatic packaging machine wherein the film is formed and heatsealed to itself. The film has low gloss and low stiffness, giving a cloth-like appearance for consumer appeal. The film has a medium coefficient of friction on both surfaces, which is especially desirable for good machinability. The film has a high surface energy for good printability, good tear strength, and good puncture resistance. The matte surface layer has excellent heat resistance, which facilitates heat sealing of the film. The film may be heat sealed at a temperature of 260°C without having the heatseal jaws stick to the matte surface layer.

Claims: A coextruded film having a nonembossed matte surface layer having a gloss of less than ten percent, characterized in that the matte surface layer consists essentially of a blend of from ten to forty percent polyisobutylene, fifty to ninety percent high density polyethylene, and zero to forty percent propylene homopolymer, the polyisobutylene having a molecular weight of at least 50,000 and the film having a coefficient of friction between the matte surface layers of between 0.2 and 0.7. The film of claim 1 characterized in that the coefficient of friction is between 0.3 and 0.5. The film of claim 2 characterized in having a heatseal layer on the opposite surface. The film of claim 3 characterized in that the matte surface layer has excellent heat resistance, whereby the heatseal layer may be heatsealed to itself using heatseal jaws having a temperature of 260°C without having the jaws stick to the matter surface layer. The film of claims 1-4 characterized in having a thickness of from 25.4 µm to 76.2 µm (1.0 and 3.0 mils). The film of claim 5, characterized in that the thickness of the matte surface layer is between 2.54 µm to 7.62 µm (0.1 and 0.3 mils). The film of claim 6, characterized in having three layers wherein the third layer is a polyolefin core layer.

Inventors: DEW JIMMY S, DEW, JIMMY S.
Applicants: JAMES RIVER PAPER CO, JAMES RIVER PAPER COMPANY, INC.
Application year: 1989
Main classification: B23B27
IPC codes: B29C47, B29L9, B32B27, B65D65, B29K23, C08J5, B32B7