JPH0243774B2 - SUCHIRENNAKURIRUSANKYOJUGOTAIFUOOMU - Google Patents

Description

[Detailed description of the invention]

This invention relates to improved thermoplastic resin foam articles, particularly extruded foam articles of styrene-acrylic acid copolymers, having excellent machinability and solvent resistance. Extruded polystyrene foam is a well-known commercial product and is used primarily for insulation purposes. However, in addition, extruded polystyrene foam is also used for a variety of its end uses. "Extruded form"
The term generally refers to a homogeneous cellular structure that exhibits no appreciable discontinuities in its cross-sectional cell dimensions and is formed by molding a large number of expanded or partially expanded cellular styrene polymer particles. This shows a clear difference from the so-called bead foam prepared by the method. Extruded polystyrene foam has significant use in the decorative field, where it is sometimes cut into desired shapes and used in decoration or as decorative parts. Sometimes the foam is sculpted into various configurations and then painted or otherwise coated to create decorative articles. Cutting and shaping of such extruded foams can be accomplished by a variety of methods. One convenient method for cutting shapes from slabs or rectangular foam bodies is to use a hot wire cutter. A wire, such as a nichrome wire, which has a substantial electrical resistance when hot, is heated by a suitable electric current and passed through the body of the form, melting it in the middle, in a manner similar to using a scroll saw or saber saw. used to make
Saws, scalpels, routers, and abrasive materials can also be used to shape extruded forms. Desirably, in processing shaped articles from extruded foam, cutting and shaping operations should be performed as quickly as possible. Since polystyrene is a thermoplastic, care must be taken in selecting the cutting tool and type of foam used. Machinability tests have been developed for evaluating the machinability of plastic foams, and particularly extruded polystyrene foams. Such testing uses a rotor, a rotary groove cutting tool, which is well known in the art. To be more specific, the router's bits (replacement blades) are 2 inches x 3 3/32 inches (5.1 cm x 7.86 inches).
It has a thin copper blade with dimensions of cm). Attached centrally to its long edge is a cylindrical shank with its axis in the plane of the blade. The opposite edge has a semi-circular cut with a 1 1/2 inch (3.8 cm) radius which acts as a tool and when inserted and rotated by the shank during form testing, it cuts a 3 inch (7.6 cm) radius.
A round sphere with a diameter of cm) is left cut out on the form base. The router bit rotates at 4250 revolutions per minute and makes effective use of the drill press to make the desired cut in one smooth stroke. The time required to produce a hemispherical cut with a smooth surface, ie, no scratches or tears in the form, is recorded. The most desirable forms take about 1 second to achieve a cut on a smooth hemispherical surface, while the less desirable forms take longer and longer times to achieve a cut of about 1.5 to 2.1 lb/ft ^{3 .} (twenty four
For polystyrene foams with rapid machinability in the density range ~33.6 g/),
Most have bubble sizes ranging from about 1.4 to 5 mm. Although often rapid processing is possible, air bubbles can produce an undesirable rough exterior and an unattractive appearance. Foam products are often used for flower arranging, whereupon it is most desirable to be able to easily insert plant pods into the foam mass by hand without prior preparation. The ease of insertion of such plant pods generally corresponds to the machinability of the foam. The easier the form is to machine, the easier it is to push the ends of the flower pods into it and the plant is supported by the form in the desired position. Cutting polystyrene foam by hot wire techniques often results in undesirable or distorted shapes when the operator pauses and changes direction of the cut. If the wire is operated at industrially desirable temperatures, ie, at temperatures where cutting is fast and easy, the phenomenon of "meltback" is observed. When the line is passed through the form at a normal or relatively high cutting speed, the kerf is approximately the width of the line. However, if the operator pauses or slows down the cutting speed substantially, the radiant heat from the wire is sufficient to melt the foam, or at least cause it to collapse and make the cut substantially wider than the wire. give. A convenient shape for handling extruded foam is often in the form of a plate, which is prepared from a larger extruded foam body by conventional woodworking techniques, ie, sawing and planing. Therefore, machinability is a highly desirable property for certain applications. It would be desirable if improved thermoplastic extruded foams of synthetic resins could be obtained that exhibit a high degree of machinability. It would be desirable if thermoplastic extruded foams of synthetic resins could be obtained that exhibit a reduced tendency to melt back when hot wire cut. It would also be desirable if improved synthetic thermoplastic extrusion foams could be prepared using volatile liquid blowing agents with minimal toxicity and environmental impact. It would also be desirable if improved synthetic thermoplastic extrusion foams with better machinability and increased solvent resistance could be obtained. These benefits and other advantages are achieved by a synthetic thermoplastic extruded foam having a large number of generally closed closed gas-containing cells, the foam having at least 8
having a cross-sectional area of 51.6 square inches (51.6 square cm) and a minimum dimension of at least 0.7 inches (1.8 cm), the form comprises about 99.5 parts by weight of styrene to about 0.5 to about 30 parts by weight of acrylic acid therein. It is composed of a copolymer of approximately 70% styrene by weight. The preparation of copolymers of styrene and acrylic acid is well known and disclosed in US Pat. No. 3,035,033. The foam according to the invention has a molecular weight of 100,000 to 100,000 as determined by gel permeation chromatography.
It can be easily prepared using a styrene-acrylic acid copolymer with a molecular weight of 350,000 grams molecule. However, from about 150,000 grams molecules to approx.
Preference is given to using such copolymers having an average molecular weight of up to 300,000 gram molecules. The amount of acrylic acid used is 0.5 to about 30 parts by weight with 99.5 to about 70 parts by weight of styrene. A particularly desirable range is from 1 to 20 parts by weight of acrylic acid.
99 to 80 parts by weight of styrene. The preferred range is 5 to 20 parts by weight of acrylic acid and 95 to 95 parts by weight of acrylic acid.
Up to 80 parts by weight of styrene. The extruded foams of the present invention have densities of about 1.2 to 5 pounds/ft ³ (19.2 to 80.0 g/). The cell size of the foam according to the invention is from about 0.5 to 3 mm, and conveniently from about 0.6 to 2 mm, as measured according to ASTM D3576. The foam according to the invention is advantageously prepared by thermoplasticizing the resin described above, combining the thermoplasticized resin with a suitable volatile liquid blowing agent, such as ethyl chloride, and forming the thermoplastic resin.
The liquid blowing agent mixture is held under sufficient pressure to prevent it from foaming and the foamable gel of thermoplastic resin and blowing agent is subsequently flushed into a low pressure zone, such as atmospheric pressure, to foam the gel. and cooled while the bubbles are free-standing (ie, not collapsed). Generally volatile liquid blowing agents are used per Kg of resin.
Used in amounts of 1.2 to 2.3 mol. Generally, the gel and blowing agent are mechanically combined at a temperature of about 180°C to 220°C, and the temperature of the gel during extrusion is usually about 122°C to 148°C. Conveniently in such mixing, the liquid blowing agent is injected into the barrel and extruder by means of a metering pump to provide the desired mixture of resin component and blowing agent. Extrusion of plastic foam is well known and illustrated in the following US patents: No.
2669751; 2740157; 2838801; 3751377;
3817669; 3954925; 3897528; 3914085 issues. A number of foams were prepared using a copolymer of approximately 92 parts by weight of styrene and 8 parts by weight of acrylic acid having a weight average molecular weight of 196,000 gmol as determined by gel permeation chromatography. The polymer was in pellet or granule form. The polymer was extruded using an extruder with an extruder cylinder internal diameter of 2 1/2 inches (6.35 cm) in which about 12 parts by weight of ethyl chloride were added per 100 parts by weight of copolymer. The extruder barrel temperature was 217°C; the temperature of the resulting gel was 109-125°C, the temperature at which foams of various cell sizes and densities could be prepared from the gel. In each case, a generally homogeneous form is obtained which, when inflated, measures approximately 2 inches by 8 inches (5.1 cm by 20.3 cm).
It had a cross-sectional dimension of. When cooled to room temperature, the foam was cut into sections and the cell size perpendicular to the width was measured. Its vertical dimension is the thickness dimension of the extruded foam plank. Samples were aged for various times and machinability tested as described above. For comparison purposes, a number of polystyrene foam samples of various densities and cell sizes were evaluated for machinability by the method described above. Both the styrene acrylic acid foam and the polystyrene foam were aged for a sufficient period of time, but most of the blowing agent used in the foam preparation was replaced with air. The results are shown in the table in which the abbreviations SAA designates styrene acrylic acid; the abbreviations PS designates polystyrene; PCF designates pounds per ^cubic foot; SEC designates seconds; and MM designates millimeters.

【table】

TABLE From the table it can be easily seen that the samples using styrene-acrylic acid copolymer have substantially improved machinability over the samples using polystyrene. It was observed that the polystyrene samples exhibited some tearing and a rough surface, whereas the samples using the styrene-acrylic acid copolymer did not exhibit any tearing. Foam samples were evaluated for solvent resistance. Samples of styrene-acrylic acid foam were shown to be unaffected by normal pentane, normal heptane, cyclohexane, normal pentanol or normal butanol. Polystyrene foam was severely attacked by both normal pentane and normal heptane and dissolved in cyclohexane. Styrene acrylic acid foam and polystyrene foam were evaluated for hot wire cutting in three different tests. In the first test, a 0.020-inch diameter nichrome wire was connected to a power source and heated to produce a glowing red-hot light. The sample was manually pressed against the line and a vertical cut of about 1 inch (2.54 cm) was made in the sample. The sample remained stationary for a period of time indicated as "Rest Time" in the table, was moved an additional approximately 1 inch (2.54 cm), and was again stationary for a period of time.
When the foam sample is stopped about the line, some meltback of the foam occurs and enlarged holes are obtained in the foam. The pore diameter is reported in the table as "pore diameter versus measured rest time". In a second test using the same wire, a rectangular parallelepiped was cut from one end of the foam sample. Cutting was done at a speed of 1 inch (2.54 cm)/second. At the end of cutting,
Place the piece back into the sample and measure the total gap, divide by 2 and report as gap width at 1 inch/second cutting speed. The third test was conducted by preparing an inclined plane and placing a nichrome wire horizontally below the inclined plane. A foam sample with a cross-sectional area of 4 inches x 4 inches (10.1 cm x 10.1 cm) and a thickness of 2 inches (5.05 cm) was placed on the inclined plane, a weight was placed on top of the foam sample, and an electric current was applied to the nichrome wire. The foam specimen slides down the slope under the weight of the weight above it and onto the hot nichrome wire, causing the nichrome wire to cross its 4 inch by 4 inch (10.1 cm by 10.1 cm) area)×2
Record the time required to cut through the inch (5.05 cm) (thick) foam sample and
Report as "cutting time" for an inch x 4 inch (10.1 cm x 10.1 cm) cross section. Moreover, styrene acrylic acid polymer foams have even better solvent resistance than polystyrene foams.

TABLE It was observed that each sample of polystyrene exhibited some cracking and roughness, whereas the styrene-acrylic acid copolymer did not exhibit any cracking. Other easily machined styrene-acrylic acid copolymers were prepared in a manner similar to the previous illustration. Useful blowing agents for the preparation of styrene-acrylic acid copolymers are ethyl chloride, methyl chloride; dichlorofluoromethane, dichlorodifluoromethane, melmalpentane and dichlorodifluoromethane, ethyl chloride and dichlorodifluoromethane, methyl chloride and dichloromethane. Difluoromethane, methyl chloride and 1-chloro-1,1-difluoroethane, ethyl chloride and 1-chloro-1,1-difluoroethane, carbon dioxide and dichlorodifluoromethane, carbon dioxide and 1-chloro-1,1-difluoroethane, It is a mixture of carbon dioxide and trichlorofluoromethane, and carbon dioxide and methyl chloride. Generally such mixtures contain 30-70 parts by weight of the first component and 70-70 parts by weight of the first component.
30 parts by weight of a second component, such as trichlorofluoromethane and dichlorofluoromethane; normal pentane and dichlorodifluoromethane; ethyl chloride and dichlorodifluoromethane; methyl chloride and difluoromethane; methyl chloride and 1-chloro-
1,1-difluoromethane; ethyl chloride and 1-chloro-1,1-difluoroethane; carbon dioxide and dichlorodifluoromethane; carbon dioxide and 1-chloro-1,1-difluoroethane; carbon dioxide and trichlorofluoromethane; carbon dioxide and methyl chloride; carbon dioxide and ethyl chloride. As is apparent from the foregoing specification, the present invention is susceptible to embodiments with various changes and modifications that may differ individually from those described in the foregoing specification and description. For this reason, everything set forth above is intended to be illustrative only and shall not limit or limit the invention except as defined and indicated in the appended claims. You should fully understand that you should not understand this.

Claims (1)

Claims: 1. a plurality of gas-containing, largely independent cells having a cross-sectional area of at least 8 square inches (51.6 square cm) measured in a plane perpendicular to the axis of extrusion; In a synthetic thermoplastic resin extrusion form having a minimum thickness of 0.7 inches (1.78 cm), the resin contains 70 to 99.5 parts by weight of styrene.
A synthetic thermoplastic resin extrusion foam characterized in that it consists of a copolymer copolymerized with 0.5 to 30 parts by weight of acrylic acid and having a molecular weight of about 100,000 to 350,000 gmol. 2. The foam of claim 1, wherein the copolymer comprises 1 to 20 parts by weight of acrylic acid and 99 to 80 parts by weight of styrene. 3. The foam of claim 2, wherein the copolymer comprises 5 to 20 parts by weight of acrylic acid and 95 to 80 parts by weight of polystyrene. 4. The foam of claim 1 having a density of about 1.2 to 5 pounds/ ^ft3 (19.2 to 80.0 g/). 5. The foam of claim 1 having an average cell size within the range of 0.5 to about 3 mm.