High clarity, high stiffness films

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length ") is analyzed in column 1; Document USP 5,284,613 and WD Harris, et al in" Effects of Bubble Cooling on Performance and Properties of HMW-HDPE Film Resins ", Polymers, Laminations &amp; Coatings Conference, Book 1, 1990 , pages 306-317 and Moore, EP, Polypropylene Handbook, Hanser, New York, 1996, pages 330-332.

In the formation of blown films, a molten material enters a ring-shaped nozzle either from the bottom or from the side of the nozzle. The molten material is forced through helical grooves around the surface of a mandrel inside the nozzle and is extruded through the nozzle opening like a thick-walled tube. The tube is expanded in a bubble of the desired diameter and the correspondingly decreased thickness as previously described.

The formation of coextruded blown films is known in the art and is applicable to the present invention. Illustrative articles of the technique include Han and Shetty, "Studies on Multilayer Film Coextrusion III. The Rheology of Blown Film Coextrusion," Polymer Engineering and Science, February, (1978), vol. 18, No. 3, pages 187-199; and Morris, "Peel Strength Issues in the Blown Film Coextrusion Process," 1996 Polymers, Laminations &amp; Coatings Conference, TAPPI Press, Atlanta, Ga. (1996), pages 571-577. The term "coextrusion" refers to the process of extruding two or more materials through a single nozzle with two or more holes arranged such that the extrudates are fused into a laminar structure, preferably before cooling or quenching. Coextrusion systems for preparing multilayer films employ at least two extruders that feed a common nozzle assembly. The amount of extruders depends on the amount of different materials that comprise the coextruded film. For each different material, a different extruder is advantageously used. Therefore, a five-layer coextrusion may require up to five extruders, although less can be used if two or more of the layers are made of the same material.

Coextrusion nozzles are used to form coextruded blown films. They have multiple mandrels that feed the different melt streams to the circular flange of the nozzle. When feeding blocks are used to stack the layers of molten material from two or more extruders, the resulting multilayer molten material stream is then fed to the film nozzle.

A distinctive feature of the present invention is the lack of post-biorientation, such as double bubble or tension-frame orientation.

The retraction test is carried out by immersion in a hot oil bath maintained at a temperature of at least 10 ° C above the melting point of the highest melting point layer for at least 30 seconds.

EXAMPLES

The following resins were used in the production of the films of the Examples.

<dl><dt>LDPE 501I </dt><dd>An LDPE of clarity grade with a melt index, I2, of 1.90 g / 10 min (measured by ASTM D-1238), a density of 0.922 g / cm3 (measured by ASTM D-792) , available from The Dow Chemical Co. </dd></dl>

<dl><dt>LDPE 136S </dt><dd>An LDPE of degree of clarity with a melt index, I2, of 0.25 g / 10 min (measured by ASTM D-1238), a density of 0.922 g / cm3 (measured by ASTM D-792) , available from The Dow Chemical Co. </dd></dl>

<dl><dt>LDPE 170A </dt><dd>An LDPE of degree of clarity with a melt index, I2, of 0.70 g / 10 min (measured by ASTM D-1238) and a density of 0.9235 g / cm3 (measured by ASTM D- 792), available from The Dow Chemical Co. </dd></dl>

<dl><dt>LDPE 662I </dt><dd>An LDPE of degree of clarity with a melt index, I2, of 0.50 g / 10 min (measured by ASTM D-1238) and a density of 0.919 g / cm3 (measured by ASTM D-792) , available from The Dow Chemical Co. </dd></dl>

<dl><dt>Dowlex 2038 </dt><dd>A clarity grade LLDPE with a melt index, I2, of 1.0 g / 10 min (measured by ASTM D-1238) and a density of 0.935 g / cm3 (measured by ASTM D-792) , available from The Dow Chemical Co. </dd></dl>

<dl><dt>Dowlex 2049AC </dt><dd>An LDPE with a melt index, I2, of 1.0 g / 10 min (measured by ASTM D-1238) and a density of 0.926 g / cm3 (measured by ASTM D-792), available from The Dow Chemical Co. </dd></dl>

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Examples 5, 8 and 10, Comparative Examples 6, 7 and 9 and Comparative Sample L

5-layer films of high clarity and high rigidity were produced in a conventional coextrusion blown film line without post-biorientation. All the films had an A / B / C / B / A film structure. The layers of the films had the components and percentages (with respect to the total thickness of the film) as shown in Table II. All the films had a total thickness of 38.1 µm (1.5 mils).

As shown in Table II, Examples 5-10 illustrate that films of high clarity and high rigidity can be made by means of the present invention without resorting to post-biorientation processes.

Table II: Results of the film of 5 layers of high clarity and high rigidity.

<dl><dt> image7 </dt><dd><figref>image8</figref><figref>image9</figref><figref>image10</figref><figref>image11</figref><figref>image12</figref><figref>image13</figref>Retraction Retraction Shrinkage,% Shrinkage,% </dd></dl>

<dl><dt>Example Number </dt><dd>A = External /% of total thickness B = Internal /% of total thickness C = Core /% of total thickness BUR Turbidity 2% drying module Voltage 150 C (MD) Voltage 150 C (CD) 150 ° C Average (MD) 150 ° C Average (CD) </dd></dl>

<dl><dt>5 </dt><dd>LDPE 501I / 10% LDPE 136S / 20% HDPE DEGD 1059/40% 2.5 10.67 434.4 (62058) 16.4 very low 79.8 14.4 </dd></dl>

<dl><dt>CS L </dt><dd>LDPE 501I / 10% LDPE 136S / 20% PP DS 6D82 / 40% 2.5 7.50 321.6 (45939) 18.4 very low 81.05 29.1 </dd></dl>

<dl><dt>Comparative 6 </dt><dd>PP DS 4D05 / 10% LDPE 136S / 30% PP DS 4D05 / 20% 3.6 4.54 437.1 (62438) 23.6 very low 81.8 54.7 </dd></dl>

<dl><dt>Comparative 7 </dt><dd>PP DS 6D82 / 10% LDPE 6621/30% PP DS 6D82 / 20% 3.6 7.86 375 (53565) 20.0 very low 82.05 38.7 </dd></dl>

<dl><dt>Comparative 8 </dt><dd>PP DS 6D82 / 10% LDPE 136S / 30% Topas 8007/20% 3.6 7.99 954.6 (136365) 25.4 13.6 73.9 40.7 </dd></dl>

<dl><dt>Comparative 9 </dt><dd>PP DS 6D82 / 10% LDPE 136S / 30% K-resin / 20% 3.6 6.75 415.9 (59412) 23.8 8.5 72.9 51.3 </dd></dl>

<dl><dt>10 </dt><dd>PP DS 6D82 / 10% LDPE 136S / 30% Topas 8007/20% 3.6 6.77 894.5 (127784) 24.9 13.2 75.15 41.6 </dd></dl>

10 Layer percentages are for each layer and are target values.

Examples 8 and 10 are the same, except in the actual ratio of the layer due to the change in the rpm of the screw of the extruder. As a result, the thickness of the core in Example 10 is less than in Example 8.

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