JPH0432104B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to polypropylene compositions with improved extrudability. such as paper, paperboard, textiles and metal foils,
Extrusion coating of substrates with thin plastic layers is practiced on a large scale. A frequently used plastic is low density polyethylene, a polymer that is easily extruded as a thin coating onto the surface of a rapidly moving substrate. Although crystalline polypropylene is a more desirable coating material than polyethylene for some coating applications, the use of polypropylene as an extrusion coating is exemplified by lower coating speeds, edge netting, and edge instability. is severely limited by the relatively poor extrudability of polypropylene. Even low molecular weight polypropylene can be used, e.g. in paper coatings.
It is not possible to extrude at the desired speed without severe netting or a reduction in the width between the extrusion point (die lip) and the paper contact point. Meltresonance, which causes non-uniform coating thickness, is also a common problem with polypropylene. In addition, extrusion coatings of polypropylene are often characterized by poor adhesion of the substrate and the presence of pinholes. As is known from US Pat. No. 3,652,725, the extrudability of polypropylene can be improved by blending it with a small amount of low density polyethylene and a small amount of a copolymer of vinyltoluene and alpha-methylstyrene. Also, as is known from U.S. Pat. There are no reports on improvement in extrusion suitability due to the presence of chemical copolymers. In accordance with the present invention, there is provided an extrudable polymer composition containing a quantity of (a) crystalline polypropylene, (b) low density polyethylene, and (c) a copolymer of vinyltoluene and alpha-methylstyrene, comprising: the copolymer (c) is hydrogenated to the point that at least 50% of its aromatic unsaturation has been reduced and has a falling softening point of 100°C to 160°C; b) has a density of 0.915 to 0.920, 3 to
Melt index of 15, and at least 2.5 x 10 ⁵
The copolymer (c) has a G _c value of
(a) in the range of 2 to 10 parts per 100 parts, and the total weight ratio of said polyethylene (b) and said copolymer (c) per 100 parts of said polypropylene (a);
An extrudable polymer composition characterized in that the amount is at least 7 parts and less than 20 parts. Blends of polypropylene with both low density polyethylene and a hydrogenated copolymer of vinyltoluene and alpha-methylstyrene according to the present invention are prepared by blending polypropylene with either low density polyethylene or the hydrogenated copolymer alone, i.e. low density polyethylene or a hydrogenated copolymer alone in combination with polypropylene, or a combination of polypropylene, low density polyethylene and a copolymer of unhydrogenated vinyltoluene and alpha-methylstyrene. I found out. In addition to being extrudable at high speeds, the compositions of the present invention are also characterized by the ability to produce coatings that are free of pinholes and have excellent adhesion to substrates such as paper. The crystalline polypropylene used in the present invention is
It is desirable to have a molecular weight well below the commercially available range to provide melt flow rates suitable for extrusion coating. As used herein, the term "polypropylene" refers to homopolymers of propylene as well as primarily crystalline copolymers of propylene and other olefins, such as containing up to about 7% by weight ethylene or up to 15% by weight butene-1. Random copolymers of propylene containing ethylene or butene-1, and crystalline copolymers of propylene and ethylene, or polypropylene and polyethylene containing up to about 25% by weight ethylene made by alternating polymerization of propylene and ethylene. Includes alloys. The low density polyethylene component has a high G _c value (at least 2.5 x 10 ⁵ dynes/cm ² ), about 0.915 to 0.920.
and a melt index of about 3 to about 15. G _c is the value of the elastic modulus at the dynamic shear rate at 180°C, that is, the torsional stiffness modulus G′;
G _c loss modulus at the same temperature and shear rate
Equal to G″. A means of measuring the values of G′ and G″ by varying the shear rate was published by K. Walter, London, 1975.
It is described in the book “Rheometry” by Chapman and Hall, Ltd.
The method used to obtain G _c values for the polyethylene samples used in the present examples was a rheometric mechanical spectrometer with a cone and plate arrangement with a 25 mm surface plate and a 0.1 radian cone. Meter (Rheometrics Mechanical
Spectrometer). The top plate (cone) was vibrated in a sinusoidal manner and the torque was measured at the bottom plate. The above polyethylene is made by methods known in the art, and representative materials are shown in the table below.

[Table] The hydroxylated copolymer of vinyltoluene and α-methylstyrene used in the present invention is an amorphous polymerized material that is a hard, brittle solid at room temperature, and ring and ball softening at about 100°C to 160°C. It has an elevated temperature softening range as shown by dots, an average molecular weight of about 500 or more (Rast method), an iodine number of about 2 or less, and is compatible with polyolefins. These are made by hydrogenating polymers containing about 25 to 85 weight percent vinyltoluene and the balance alpha-methylstyrene until at least 50% of the aromatic unsaturation is removed. A commercially available copolymer consisting of about 25% by weight α-methylstyrene and about 75% by weight vinyltoluene and having a ring and ball softening point of 75°C to 120°C was hydrogenated to make the copolymer useful in the present invention. These are the typical materials you get. The copolymerization of vinyltoluene and alpha-methylstyrene can be carried out using known catalysts such as sulfuric acid, phosphoric acid, Fuller's earth, amphoteric metal chlorides such as boron trifluoride, zinc chloride or aluminum chloride, with or without solvents. This can be carried out by a known method using a material or the like. Preferably, the polymerization is conducted under conditions that cause substantially all of the hydrocarbon monomer to react to minimize dimer formation. Hydrogenation of the above copolymers can be carried out using catalysts such as nickel on diatomaceous earth, copper chromite, palladium on carbon, platinum on alumina, or cobalt and zirconia on diatomaceous earth. This hydrogenation is carried out in the presence of a solvent such as methylcyclohexane, toluene, p-menthane, etc., at a pressure ranging from 500 to 10,000 psi, from 150°C to 300°C.
Preferably it is carried out using a temperature of .degree. Average molecular weight of about 500 or more [Rast method],
Any of the hydrogenated hydrocarbon polymers described above having an iodine number of about 2 or less, a ring and ball softening point of about 100°C or more, and compatibility with polyolefins may be used in the present invention, but may not provide the improvements of the present invention. Preferred hydrogenated hydrocarbon polymers that are particularly effective in
Average molecular weight of 600 or more (last method), softening point of about 130℃ or more, iodine value of about 2 or less, and
Compatibility with polyolefins corresponding to a haze of less than or equal to about 25% as measured on a 5 mil film pressed at 232°C and cooled using the test method described in ASTM D1003-61 (reauthorized 1977). Characterized by. The compositions of the present invention can be made by a variety of methods, such as dry blending, dry blending followed by passage through a compounding extruder, compounding by blending in the melt or solution on kneading rolls or a Banbury mixer. Any method by which the above components can be blended together will produce the desired blend. For example, fine pellets of each polymer having an average size of about 1/16 inch, with up to about 20% of the pellets being about 1/8 inch in diameter and some pellets smaller than 1/16 inch. The pellets are mechanically blended and the blend is fed to an extruder where it is melted and extruded. The above compositions can be extruded or fabricated at melt temperatures up to about 335°C, but about 290°C.
A melt temperature in the range .about.305 DEG C. is preferred and has been found to give excellent results with maximum coating speed and minimum defects such as pinholes. The compositions of the present invention include additives such as antioxidants, stabilizers to inhibit heat, UV and weather degradation, opaque pigments such as titanium dioxide and carbon black, plasticizers and small amounts (up to about 20%). Other compatible polymers may be included. Similarly,
For some applications, small amounts of other polyolefins or copolymers thereof, such as copolymers of ethylene and propylene, may be blended with the compositions of the present invention. The invention will be explained in more detail by the following examples. Examples 1-3 The ingredients for these examples are: Polypropylene - commercially available polypropylene with an intrinsic viscosity of 2.0 and a melt flow of 12. Polyethylene - Commercially available low density polyethylene with a density of 0.917, a G _c value of 2.7 x 10 ⁵ and a melt index of 6.5. Hydrogenated hydrocarbon polymer - A commercially available copolymer of 75% by weight vinyltoluene and 25% by weight alpha-methylstyrene hydrogenated until about 97% of its aromatic unsaturation is reduced. This hydrogenated polymer has a ring and ball softening point of about 140°C. The non-hydrogenated hydrocarbon polymer of Example D is the same as the commercially available copolymer of vinyltoluene and alpha-methylstyrene described above, except that it is not hydrogenated. This polymer has a ring and ball softening point of about 120°C. The first step is to blend the ingredients with 0.1 part phenolic antioxidant and 0.1 part calcium stearate in a Henschel mixer at high speed for 2 minutes and then at low speed for 1 minute. The blended materials are then fed into the first barrel of a co-kneader compounding extruder. The co-kneader was set under the following conditions: First barrel temperature range 1 163°C Region 2 163°C Screw speed Maximum L/D ratio 8:1 The second barrel was installed at an angle of 90° to the first barrel. The mixed molten material was transferred from the first barrel to the second barrel where it was prepared for pelletization. This second barrel is set to the following conditions: First barrel temperature range 1 163°C Region 2 232°C Die 204°C Screen pack
The 60/100/60 mesh size pelletizing die has 30 holes each 0.070 inch diameter. The molten “string” exits the die and is cut into small beads (hot cuts).
This is cooled in a water bath, collected and dried. For extrusion coating tests, the following procedures and conditions are applied to all formulations prepared. The extruder is a 2-1/2 inch Davis Standard with a 24:1 L/D ratio and a 2.87:1 compression ratio. The die is a 12 inch Johnson Flex. Rip. coat-hanger (Johnson flex lip coat-hunger)
It is a type film die. Extrusion speed is 70 in all cases
±3lb./hr. Just before the paper enters the nip between the chill roll and the nip roll, the formulation is extruded onto a web that passes through the 24 inch wide paper. The following extrusion coating conditions are used for all formulations: Extruder barrel temperature: 204°C, 260°C, 288°C, 316°C
℃, 316℃ Adapter temperature: 316℃ Die temperature: 316℃ Air gap: 2-3/4 inch Paper substrate: 40#/ream kraft paper The die opening is set to 12 mil, but the edge In the section, the aperture is reduced to provide an oval wire die profile and the end bead is reduced. When starting with new material, a 10 minute purge is required to minimize previously used material in the new melt. The melt is then collected for 2 minutes and weighed to determine the extrusion rate. Once the speed is adjusted, start the converter roll and set up the extruder and die. Start coating. The coating speed is started at 200 feet per minute (fpm) and increased in 50 fpm increments until an edge wave or melt resonance occurs. The maximum speed at which the device can be operated is approximately
It is 600fpm. The coated paper on the winder is flagged at each speed. Samples are collected with splice targets at each speed. Measure the coverage width of each sample. Fiber tear results were obtained from all coated samples using the pressure sensitive tape test method, which indicated good adhesion for the example products. The results of all seven formulations and control tests A, B and C are shown in Table 1. From the above results, it can be concluded that the present invention is effective in improving the extrusion coating processability of polypropylene. Examples 4-9 A 16-inch Egan keyhold die was replaced with a 12-inch Johnson keyhold die.
Flex Rip Coat - Used in Examples 1-3 except that the hanger type film die was replaced, the air gap was increased by 1/4 inch, and the winder was modified for a maximum coating speed of 900 fpm. Using the same operations as above. All extrusion speeds are
93lb./hr. The formulations and results obtained, including controls E and F, are shown in the table. In all cases, the adhesion of the coatings to the paper was good and the coatings were free of pinholes. Examples 10-18 Using the procedures of the previous examples, paper is coated with several different compositions. Each composition consisted of 100 parts of the polypropylene specified in Example 1, 5 parts of the hydrogenated copolymer specified in Example 1, and 5 parts of low density polyethylene. The various polyethylenes used are shown in the table together with the results obtained. This data indicates the desirability of using polyethylene having the properties specified above. Example 19 Extrusion coating tests are carried out using the formulation of Example 1 on commercially available paper coating equipment. Coating equipment includes: 6-inch Beloit extruder 80-inch Egan Series 32 coating die 80-inch Beloit coater Coating conditions are as follows: Extruder barrel temperature: 150°C , 232℃, 288℃, 304
℃, 304℃. Adapter Temperature: 304°C Die Temperature: 304°C in all areas Melt Temperature: 288°C Air Gap: 5 inches 40# continuous blend paper without added adhesion promoters is first coated at the following speeds.

[Table] 17#/ream without adhesion promoter is then coated with the same temperature distribution for use as oil can liner and the following speeds are easily obtained:

Table: In both cases, good adhesion is obtained without priming the substrate and there are no pinholes in the coating.

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Claims (1)

[Scope of Claims] 1 (a) a large amount of extrudable crystalline polypropylene; (b)
Low density polyethylene and (c) vinyltoluene and α
- an extrudable polymer composition containing a copolymer with methylstyrene, said copolymer (c) being hydrogenated to the point that at least 50% of its aromatic unsaturation has been reduced; , and has a drop softening point of 100°C to 160°C, the polyethylene (b) has a density of 0.915 to 0.920, and a density of 3 to 160°C.
Melt index of 15, and at least 2.5 x 10 ⁵
The copolymer (c) has a G _c value of
(a) in the range of 2 to 10 parts per 100 parts, and the total weight proportion of said polyethylene (b) and said copolymer (c) is at least 7 parts and less than 20 parts per 100 parts of said polypropylene (a); An extrudable polymer composition characterized by: 2. The polymer composition of claim 1, wherein the extrudable crystalline polypropylene has a melt flow rate of at least 3 at 230°C. 3. The polymer composition according to claim 1, wherein component (b) is present in an amount of 3 to 15 parts by weight per 100 parts of component (a). 4 Component (c) has an average molecular weight of 600 or more (last method)
The polymer composition according to claim 1. 5. The polymer composition according to claim 1, wherein component (c) has an iodine value of 2 or less.