Thermoplastic Resin Compositions with Good Extruding Ability Field of the Invention The present invention relates to a thermoplastic resin composition with good extruding ability. More particularly, the present invention relates to a thermoplastic resin composition having excellent extruding ability by addition of an ultramacromolecular styrene-acrylonitrile copolymer (SAN) and a metal salt so that the resin composition may have an increased stability for decomposition, cross- linking, gelation, networking or carbonization and, at the same time, have a uniform thickness, no variation of extrusion output and no surface defect such as die-line.

Background of the Invention In general, a resin composition can be prepared by blending a raw resin material with appropriate additives according to its use and making into pellets form.

The resin composition in the form of pellets may be made into a desired molded article by any known molding methods, such as injection molding, extrusion molding or compression molding. Among them, injection molding and extrusion molding are generally employed for thermoplastic resin composition, and these are conducted through a continuous process or a continuous cycling process. During the molding process, the resin composition is melted or plasticized by friction between the cylinder and resin and by thermal history from the surface of the heating cylinder, transferring through empty space between the screw and cylinder of the molding machine to produce a sheet form through the extruder die and polishing roll or to produce a molded article though a nozzle by cooling in the mold.

In these melting or plasticizing processes, the thermal history of the resin and the flow thereof are locally different, and the stagnation or turbulence of the

resin tends to occur in a certain area of the molding machine, which leads to excess of or long-term thermal history of the resin so that the resin may have uniform configuration, composition, appearance or color. As a result, this ununiform fraction becomes hard spots, fish eyes or hard lumps due to chemical or physical reaction such as cross-linking, gelation, networking, carbonization and agglomeration etc, so that a protruding point, silver streak or die line are generated on the surface of the molded article, which cause deterioration in the quality of the molded products.

Especially, in case of a sheet form article, this appearance defect will be apparently noticeable during drawing in the vacuum forming process. And this appearance defects are intensified in a large-sized article or in a large scale process. Further, in case of a conventional thermoplastic resin, problems may be brought about that the resin will suffer from variation of extrusion output, lack of uniform thickness, and die-line during the extrusion molding process due to inferior extruding ability.

A number of researches have been made to solve the above-mentioned problems occurred in the molding process to improve the extrusion stability and moldability. Japanese Patent Publication No. 6-16897 discloses a styrene resin composition prepared by adding an anti-oxidant composition such as a hindered phenol stabilizer during the molding step. It is taught that this styrene resin composition may have improved colors and physical properties by addition of an anti-oxidant composition to prevent oxidation reaction during the molding process.

However, it has a drawback that the resin cannot maintain a stable state under the excess thermal history caused by stagnation or residence during the molding process.

Korean patent application No. 93-18486 discloses a styrenic resin composition prepared by adding a low molecular weight polyethylene wax, an ethylenebisstearamide or a metal soap type lubricant composition excessively.

According to the above application, the lubricant acts to decrease friction between the metal and the resin so that the resin composition may have a good moldability.

However, it could not overcome occurrence of cross-linking and carbonization of the resin under the excess thermal history caused by stagnation during the molding process. Moreover, if a lubricant composition is added excessively, a low molecular

weight composition is increased, which causes deterioration in color stability and drawing property of the resin during the second molding process such as vacuum forming.

In order to solve the above problems, Korean Paten Applications Nos. 97- 75567,98-62769 and 99-3735 disclose resin compositions prepared by adding a compound selected from the group consisting of a + 2 valence metal salt, such as + 2 valence metal chloride, + 2 valence metal carbonate, + 2 valence metal oxide and a mixture thereof. However, it fails to improve variation of extrusion output, lack of uniform thickness and die-line during the extrusion molding process sufficiently because of poor extrusion workability.

Accordingly, the present inventors have developed a resin composition which is capable of overcoming the above-described problems by addition of an ultra macromolecular SAN copolymer and a metal salt so that the resin composition may not suffer from not only inferior appearance regardless of long-time stagnation during the molding process but also variation of extrusion output, lack of uniform thickness and die-line owing to poor extrusion workability.

Objects of the Invention An object of this invention is to provide a thermoplastic resin composition having good extrusion stability thereby the resin composition may not suffer from inferior appearance regardless of long-time stagnation during the extrusion molding process.

Another object of the invention is to provide a thermoplastic resin composition having good extrusion workability thereby the resin composition may not suffer from variation of extrusion output, lack of uniform thickness and die-line.

Other objects and advantages of this invention will be apparent from the ensuing disclosure and appended claims.

Summary of the Invention

The resin composition according to the present invention comprises (A) 20- 60 parts by weight of a graft copolymer obtained by copolymerizing a cyanide vinyl compound and an aromatic vinyl compound onto a rubbery polymer; (B) 80-40 parts by weight of a copolymer obtained by copolymerizing a cyanide vinyl compound with an aromatic vinyl compound; (C) 0.1-2 parts by weight of a + 2 valence metal compound; and (D) 0. 1-30 parts by weight of an ultramacromolecular copolymer having a weight average molecular weight 1,000, 000-5,000, 000 obtained by copolymerizing a cyanide vinyl compound with an aromatic vinyl compound.

Detailed Description of the Invention The resin composition according to the present invention comprises (A) 20- 60 parts by weight of a graft copolymer obtained by copolymerizing a cyanide vinyl compound and an aromatic vinyl compound onto a rubbery polymer; (B) 80-40 parts by weight of a copolymer obtained by copolymerizing a cyanide vinyl compound with an aromatic vinyl compound; (C) 0.1-2 parts by weight of a + 2 valence metal compound; and (D) 0. 1-30 parts by weight of an ultramacromolecular copolymer obtained by copolymerizing a cyanide vinyl compound with an aromatic vinyl compound.

The detailed descriptions of the present invention are as follows.

(A) Graft Copolymer The graft copolymer (A) of the present invention can be prepared by copolymerizing a cyanide vinyl compound and an aromatic vinyl compound onto a rubbery polymer. The rubbery polymer includes a polybutadiene, a styrene- butadiene rubber, an acrylonitrile-butadiene rubber and an acryl rubber and the like.

The cyanide vinyl compound may include acrylonitrile, methacrylonitrile and the like. The aromatic vinyl compound may include styrene, alpha-methylstyrene, vinyl toluene and the like.

Specifically, it is preferable to use a copolymer prepared by graft copolymerizing 70-30 parts by weight of an aromatic vinyl compound and a cyanide vinyl compound onto 30-70 parts by weight of a butadiene rubber, wherein more than 90% of butadiene rubber have an average rubber particle size of 500-3500 A in which the butadiene rubber has a gel content of more than 50%. The graft copolymer (A) used in the present invention has 50-100% of graft ratio and 50,000- 100,000 of weight average molecular weight. In the present invention, the graft copolymer (A) is used in an amount of 20-60 parts by weight based upon the total weight of the resin composition.

(B) Copolymer The copolymer (B) of the present invention can be obtained by copolymerizing an aromatic vinyl monomer with a vinyl cyanide monomer.

Specifically, it is preferable to use a copolymer prepared by graft copolymerizing 50-90 parts by weight of an aromatic vinyl monomer and 80-50 parts by weight of an unsaturated nitrile monomer. A vinyl cyanide monomer is preferably used for the unsaturated nitrile monomer. In the present invention, the copolymer (B) is used in an amount of 40-80 parts by weight based upon the total weight of the resin composition.

(C) + 2 valence metal compound The + 2 valence metal compound of the present invention is added to improve process stability of the resin composition. The + 2 valence metal compound will react with an activating group of a polymer or a component of additives, which causes an appearance problem to thereby form an inactivating compound. The + 2 valence metal compound used in the present invention includes a + 2 valence metal salt, such as + 2 valence metal chloride, +2 valence metal carbonate, + 2 valence metal oxide. The examples of the + 2 valence metal

compound are magnesium carbonate, calcium carbonate, zinc chloride, magnesium chloride, calcium chloride, zinc oxide, magnesium oxide, calcium oxide and so forth.

The + 2 valence metal compound (C) can be used in an amount of 0.1-2 parts by weight per 100 parts by weight of the sum of (A) and (B).

(D) Ultramacromolecular SAN copolymer The ultra high molecular SAN copolymer (D) acts to prevent variation of extrusion output, lack of uniformity in thickness and die-line to improve extrusion workability. In the present invention, the ultramacromolecular SAN copolymer (D) is added to the base resin with a + 2 valence metal compound (C) to provide a thermoplastic resin composition with an excellent extrusion workability as well as an extrusion stability whereby the resin composition may not suffer from inferior appearance owing to long-term stagnation during the molding process.

The ultramacromolecular SAN copolymer (D) according to the present invention can be prepared by copolymerizing an aromatic vinyl monomer with a vinyl cyanide monomer. It is preferable to copolymerize 50-90 parts by weight of an aromatic vinyl monomer and 10-50 parts by weight of an unsaturated nitrile monomer. The copolymer (D) of the present invention has a weight average molecular weight of 1,000, 000-5,000, 000 of converted to that of polystyrene (PS).

The ultramacromolecular copolymer (D) is used in an amount of 0.1-30 parts by weight per 100 parts by weight of the sum of (A) and (B).

The thermoplastic resin composition of the present invention may contain customary additives such as heat stabilizers, anti-oxidants, lubricants, release agents, light and UV stabilizers, flame retardants, antistatic agents, coloring agents, fillers, impact modifiers and other resins or rubber components.

The invention may be better understood by reference to the following examples that are intended for the purpose of illustration and are not to be construed as in any way limiting the scope of the present invention, which is defined in the

claims appended hereto.

Examples Each component of (A), (B), (C) and (D) used in Examples 1~2 and Comparative Examples 1-3 was prepared as follow: (A) Graft copolymer To a reactor, 50 parts by weight of polybutadiene latex having average rubber particle size of 0. 3, um were charged and then 150 parts of deionized water, 0.9 part of rosin soap, 0.3 part of cumene hydroperoxide, 0.2 part of mercaptane- containing chain transfer agents and 0.3 part of glucose were added. The temperature was maintained at 70 °C. 35 parts of styrene and 15 parts of acrylonitrile were dropped into the mixture for 3 hours and the polymerization was started by means of redox initiator to obtain styrene-acrylonitrile-butadiene graft copolymer latex. The resultant was coagulated by adding 1.5 % of magnesium sulfate aqueous solution and dried to produce styrene-acrylonitrile-butadiene graft copolymer resin powder.

(B) Copolymer A styrene-acrylonitrile copolymer by Cheil Industries Inc. of Korea (Product name: SAN HR-5330) was used.

(C) + 2 valence metal compound Magnesium oxide (MgO) was used.

(D) Ultramacromolecular copolymer

71 parts by weight of styrene monomer, 29 parts by weight of acrylonitrile monomer, 150 parts of ion-exchanged water, 0.4 part of tricalciumphosphate, 0.03 part of carboxylic anionic surfactant, 0.01 part of polyoxyethylene alkyl ether phosphate and 0. 001-1 part of 2, 2'-azobisisobutylonitrile as an initiator were blended and added to a reactor, and the reactor was sealed completely. The mixture was agitated sufficiently to disperse. The reactor was heated up to 75 °C for 3 hours, and again further heated up to 120 C for 3 hours to carry out polymerization. After the polymerization was terminated, the reactor was cooled to room temperature to terminate the reaction. The resultant was washed, dehydrated and dried to obtain a copolymer in the form of beads. The weight average molecular weight of the copolymer was 4,000, 000.

Example 1-2 Each component were mixed by means of Henschel mixer and the mixture was extruded with a conventional twin screw extruder in pellets. The resin pellets were molded into test specimens.

Each specimen was melt blended in a Torque Rheometer (available from Haake Inc. ) operated at 260 °C at mixing speed of 10 rpm for 1 hour, and the torque fluctuation was observed. The increased torque (GQ) was calculated by comparing a minimum torque value at which the resin has been melted (generally 20 minutes later after mixing) with the torque value after 1 hour to evaluated the degree of molding stability. When the Torque was decreased continuously, the decreased torque (zBTQ) was calculated by comparing the torque value after 20 minutes with the torque value after 1 hour. If Q exceeds zero, gelation occurs. Therefore, the higher the z ! TQ is, the worse the molding stability is. If ZfTQ is near zero, it means the resin has good molding stability. In addition, if GQ is less than zero, the resin will be decomposed, which also means low molding stability. Z ? TQ was calculated from following formula:

ZJTQ (increased torque) = (Torque after 1 hour-minimum Torque) or Z ? TQ (decreased torque) = (Torque after 1 hour-Torque after 20 minutes.) Additionally, extrusion processability was evaluated by observing surface appearance including variation in extrusion output, thickness deviation and die-line by extruding a sheet with a thickness of 3 mm at 230 °C for 12 hours by means of sheet extruder with a screw diameter of 120 mm, T-Die width of 1,200 mm. The results are shown in Table 1.

Comparative Example 1-3 Comparative Examples were carried out the same as in Example 1 except that Comparative Example 1 was prepared without using the ultramacromolecular copolymer (D), Comparative Example 2 was prepared without using the + 2 valence metal compound (C) and Comparative Example 3 was prepared using neither ultramacromolecular copolymer (D) nor +2 valence metal compound (C).

The results are shown in Table 1.

Table 1<BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> Examples Comparative Examples<BR> <BR> <BR> <BR> <BR> <BR> 1 2 1 2 3<BR> Examples Comparative Examples<BR> 12123 (A) Graft copolymer 30 30 30 30 30 (B) Copolymer 66.5 66.5 70 60 60 (C) + 2 valence metal compound 0.3 0.5 0. 5-- (D) ultramacromolecular copolymer 3 3 - 3 - <BR> <BR> <BR> Extrusion Torque<BR> <BR> <BR> 0 -5 -5 +80 +70<BR> <BR> stability fluctuation(##Q)<BR> 0-5-5 +80 +70<BR> stability fluctuation (Z ? TQ) Extrusion Variation of extrusion @ O X O x<BR> <BR> <BR> processability output<BR> <BR> <BR> <BR> <BR> Thickness uniformity # # # # # Die-line (Q) A x A x * : excellent, 0 : good, A : normal, X : bad As shown in Table 1, when both ultramacromolecular copolymer (D) and + 2 valence metal compound (C) are used, the torque fluctuation was near zero, and variation of extrusion output, thickness uniformity and die-line were also improved.

So the resin composition of the present invention is good not only in extrusion stability but also in extrusion workability. Comparative Example 1 shows a low extrusion workability due to use of + 2 valence metal compound (C) only. And, Comparative Example 2 shows a low extrusion stability to have +80 of Torque fluctuation value due to use of the ultramacromolecular copolymer (D) only.

Comparative Example 3 shows a low extrusion workability and stability, because neither + 2 valence metal compound (C) nor ultramacromolecular copolymer (D) is used.

The thermoplastic resin composition according to the present invention shows good extruding ability by addition of an ultramacromolecular styrene- acrylonitrile copolymer (SAN) and a metal salt so that the resin composition may

not suffer from inferior appearance due to long-time stagnation and, at the same time, have uniform thickness and extrusion output and no appearance defect such as die- line during the extrusion step.

It is apparent from the above that many modifications and changes are possible without departing from the spirit and scope of the present invention.