Title of Invention

THERMOPLASTIC RESIN COMPOSITION FOR REFRIGERATOR HAVING IMPROVED ENVIRONMENTAL STRESS CRACK RESISTANCE

Abstract The thermoplastic resin composition for refrigerator according to the present invention comprises (A) 20 to 40 parts by weight of an acrylonitrile-butadiene-styrene graft copolymer resin prepared by grafting in emulsion polymerization 60D30 % by weight of a monomer mixture comprising a cyanide vinyl compound and an aromatic vinyl compound to 40D70 % by weight of a rubber polymer having an average particle size of 0.1 i JO.4μm; (B) 1 to 20 parts by weight of a styrenic copolymer consisting of (b]) 0 to 75 % by weight of a styrenic copolymer prepared by copolymerizing 5G20 % by weight of a rubber polymer having an average particle size of 0.1 □ 10 μm\, 10D30 % by weight of a cyanide vinyl compound, and 65D85 % by weight of an aromatic vinyl compound, and (b2) 25 to 100 % by weight of a styrenic copolymer prepared by copolymerizing 5Q20 % by weight of a rubber polymer having an average particle size of 0.1 H 10 μm and 80D95 % by weight of an aromatic vinyl compound; and (C) 50 to 79 parts by weight of a cyanide vinyl - aromatic vinyl copolymer. MJ/PCT-060/LHJ
Full Text

Thermoplastic Resin Composition for Refrigerator Having Improved Environmental Stress Crack Resistance
Field of the Invention
The present invention relates to a thermoplastic resin composition for refrigerator. More particularly, the present invention relates to a thermoplastic resin composition for refrigerator having good environmental stress crack resistance, vacuum formability and crack resistance by employing an acrylonitrile-butadiene-styrene graft copolymer resin prepared from rubber polymers having a specific average particle size, a styrenic copolymer, and a cyanide vinyl-aromatic vinyl copolymer.
Background of the Invention
An acrylonitrile-butadiene-styrene copolymer (hereinafter "ABS resin') is obtained by grafting an unsaturated nitrile compound (i.e., acrylonitrile monomer) and an aromatic vinyl compound (i.e., styrene monomer) in the presence of butadiene-based rubber polymer. Generally, desired properties of ABS resin can be achieved by controlling the composition of a rubber polymer, a g-ABS resin or a SAN resin used as a matrix resin therein. The ABS resin prepared therefrom has good physical properties such as processability, impact resistance, rigidity, especially, excellent coloration property and glossy appearance. So, the ABS resin has been widely applied to electric or electronic goods and miscellaneous goods. As the trend of the application of ABS resin has been developed from mono-functional mode to multi-functional mode, requirement for a multi-functional ABS resin has been increased recently.
Generally, some connecting part between external steel sheet and internal resin sheet in a refrigerator is manufactured by assembling a table board, a lid and a sash. By injecting polyurethane forming liquid in the space between an internal box and an external box of the assembled refrigerator, allowing the liquid to foam and solidifying in place, an

insulation layer of a refrigerator is formed. For the major components of the polyurethane foam-insulation layer, a mixture comprising a polyol and a diisocyanate compound and a foaming agent, such as freon are used.
However, these major compounds used in the polyurethane foam-insulation layer nay cause chemical erosion at the portion of the internal box of a refrigerator, where »tress is concentrated by contacting with the surface of resin during the manufacturing )rocess or while in use, which results in stress cracking. Therefore, the resin composition or a refrigerator should have stress cracking resistance against these chemical compounds.
As for preparing an internal box of a refrigerator, the ABS resin has-been typically used, because the ABS resin has a good balance of physical properties such as rigidity, impact resistance, processability, glossy appearance, and especially excellent chemical resistance against a freon such as CFC-11 which is used as a foaming agent for a rigid polyurethane foam. CFC-11 is being replaced with HCFC-141b at the present time, because CFC-11 threatens destruction of the ozone layer in the stratosphere. However, HCFC-141b has a problem in that a stress crack appears on the internal box of a refrigerator by melting the resin component.
In order to solve the above problem, Japanese Patent Application Laid-Open No. 2-284906 discloses an internal box of a refrigerator formed with an ABS resin containing a high amount of a vinyl cyanide compound, and Japanese Patent Application Laid-Open No. 6-262713 discloses a method of mixing acrylic rubber during compounding process. However, the resins produced therefrom are susceptible to stress cracking.
Accordingly, the present inventors have developed a thermoplastic resin composition that can apply for a part of a refrigerator having good environmental stress crack resistance, easy vacuum formability, excellent crack resistance and thermal stability by employing an acrylonitrile-butadiene-styrene graft copolymer resin prepared from rubber polymers having a specific average particle size, a styrenic copolymer, and a cyanide vinyl-aromatic vinyl copolymer.
Objects of the Invention

An object of the present invention is to provide a thermoplastic resin composition for refrigerator having excellent environmental stress crack resistance.
Another object of the present invention is to provide a thermoplastic resin composition for refrigerator having easy vacuum formability.
A further object of the present invention is to provide a thermoplastic resin composition for refrigerator having good crack resistance.
A further object of the present invention is to provide a thermoplastic resin composition for refrigerator with good thermal stability.
Other objects and advantages of this invention will be apparent from the ensuing disclosure and appended claims.
Summary of the Invention
A thermoplastic resin composition for refrigerator according to the present invention comprises (A) 20 to 40 parts by weight of an acrylonitrile-butadiene-styrene graft copolymer resin prepared by grafting in emulsion polymerization 60D30 % by weight of a monomer mixture comprising a cyanide vinyl compound and an aromatic vinyl compound to 40G70 % by weight of a rubber polymer having an average particle size of 0.1 GO.4 #m; (B) 1 to 20 parts by weight of a styrenic copolymer consisting of (bi) 0 to 75 % by weight of a styrenic copolymer prepared by copolymerizing 5 [J20 % by weight of a rubber polymer having an average particle size of 0.1 Q 10 /zm, I0G30 % by weight of a cyanide vinyl compound, and 65D85 % by weight of an aromatic vinyl compound, and (b2) 25 to 100 % by weight of a styrenic copolymer prepared by copolymerizing 51220 % by weight of a rubber polymer having an average particle size of
0.1 C110 fm\ and 80G95 % by weight of an aromatic vinyl compound; and (C) 50 to 79 parts by weight of a cyanide vinyl-aromatic vinyl copolymer.
Detailed Description of the Invention

(A) Acrylonitrile-Butadiene-Styrene Graft Copolymer Resin (g-ABS resin)
The acrylonitrile-butadiene-styrene graft copolymer resin of the present invention is prepared by grafting in emulsion polymerization 60D30 % by weight of a monomer mixture comprising a cyanide vinyl compound and an aromatic vinyl compound to 40370 % by weight of a rubber polymer having an average particle size of 0.1 u0.4 //m.
The rubber polymer is for instance chosen from the group comprising a butadiene rubber, an isoprene rubber, a butadiene-styrene copolymer, an alkylacrylate rubber and so forth. Among them, polybutadiene may be preferably used. The average rubber particle size of the rubber polymer is preferably in the range of 0.1-0.4 pm. If the average rubber
particle size is less than 0.1 //m, the resin composition cannot provide sufficient impact strength and environmental stress crack resistance. On the other hand, if the average rubber particle size exceeds 0.4 //m, the time for producing rubber polymer becomes retarded, and the glossy is deteriorated.
The cyanide vinyl compound and the aromatic vinyl compound are well known in the art and are readily commercially available. Also, the cyanide vinyl compound in the monomer mixture may be present in any amount generally known in the art.
As for the g-ABS resin (A), a mixture of two types of g-ABS resins each prepared from two distinct groups of rubber particles having a different average particle size can be used. Preferable example is a mixture comprising (a,) 0 to 100 % by weight of g-ABS resin prepared from a rubber polymer having an average particle size of 0.25 —0.4 //m and (a2) 0 to 100 % by weight of g-ABS resin prepared from a rubber polymer having an average particle size of 0.1 — 0.15 pn\.
In the present invention, the g-ABS resin (A) is used in an amount of about 20 to 40 parts by weight. If the amount of the g-ABS resin (A) is less than 20 parts by weight, the resin composition cannot obtain sufficient environmental stress crack resistance. On the other hand, if the amount of the g-ABS resin (A) is more than 40 parts by weight, the flowability of the resin composition is degraded.

(B) Styrenic Copolymer
The styrenic copolymer of the present invention comprises (b,) 0 to 75 % by weight of a styrenic copolymer prepared by copolymerizing 5FJ20 % by weight of a rubber polymer having an average particle size of 0.1 □ 10 #m, 10G30 % by weight of a cyanide vinyl compound, and 65D85 % by weight of an aromatic vinyl compound, and (b2) 25 to 100 % by weight of a styrenic copolymer prepared by copolymerizing 5E320 % by weight of a rubber polymer having an average particle size of 0.1 □ 10 /zm and 80D95 % by weight of an aromatic vinyl compound;
The average particle size of the rubber polymer in the styrenic copolymer (b,) of the present invention is preferably in the range of 0.1-10 im. If the average rubber
particle size is less than 0.1 #m, the environmental stress crack resistance of the resin
composition is deteriorated. If the average rubber particle size is more than 10 //m, the
glossy appearance is deteriorated.
Further, the content of the cyanide vinyl compound in the styrenic copolymer (b]) is 10D30 % by weight. If the content of the cyanide vinyl compound is out of this range, the environmental stress crack resistance of the resin composition is degraded.
In the styrenic copolymer(b2), the average particle size of the rubber polymer is preferably in the range of 0.1-10 im\. If the average rubber particle size is less than 0.1
/ini, the environmental stress crack resistance of the resin composition is deteriorated. If the average rubber particle size is more than 10 /zm, the glossy appearance is deteriorated. Further, the content of the cyanide vinyl compound in the styrenic copolymer (b2) is 0— 10 % by weight. If the content of the cyanide vinyl compound is more than 10 % by weight, the environmental stress crack resistance and chemical resistance of the resin composition are deteriorated.
The styrenic copolymer (B) of the present invention comprises 0 to 75 % by weight of the styrenic copolymer (b\) and 25 to 100 % by weight of the styrenic copolymer(b2). If the styrenic copolymers (b[ and b2) are out of the above range, the environmental stress crack resistance is deteriorated.

Further, the styrenic copolymer (b2) of the present invention is used in an amount of about 1 —10 parts by weight per 100 parts by weight of total resin composition. If the amount is less than 1 part by weight, the environmental stress crack resistance of the resin composition is deteriorated. If the amount exceeds 10 parts by weight, the impact strength and tensile strength are decreased due to the phase separation.
The styrenic copolymer (B) of the present invention is preferably used in an amount of about 1 ^20 parts by weight. If the amount of the styrenic copolymer (B) is less than 1 part by weight, the resin composition cannot obtain sufficient crack resistance. And if the amount is more than 20 parts by weight, the molecular weight of the total resin composition is decreased, so that it is difficult to obtain good vacuum formability.
(C) Cyanide Vinyl-Aromatic Vinyl Copolymer
The cyanide vinyl-aromatic vinyl copolymer (C) of the present invention is used in an amount of about 50 to 79 parts by weight. The cyanide vinyl-aromatic vinyl copolymer (C) can be used alone or a mixture of at least two distinct groups of cyanide vinyl-aromatic vinyl copolymer having a different molecular weight. Among them, the mixture of at least two distinct groups of copolymer having a different molecular weight is preferred.
The cyanide vinyl-aromatic vinyl copolymer (C) of the present invention comprises (cO 0 to 100 % by weight of cyanide vinyl-aromatic vinyl copolymer containing 25^40 % by weight of cyanide vinyl compound and having a weight average molecular weight (Mvv) of about 50,000 to 150,000 and (c2) 100 to 0 % by weight of cyanide vinyl-aromatic vinyl copolymer containing 20^-30 % by weight of cyanide vinyl compound and having a weight average molecular weight (Mw) of about 150,000 to 1,000,000.
If the weight average molecular weight of the copolymer (c,) is less than 50,000, the resin composition cannot provide a sufficient environmental stress crack resistance. On the other hand, if the weight average molecular weight of the copolymer (c2) exceeds K000,000, the melt viscosity of the resin composition becomes higher, which makes

processing more difficult and appearance of the molded article becomes poor.
In the present invention, a mixture consisting of 34 to 66 % by weight of copolymer (c^ and 34 to 66 % by weight of copolymer (c2) is preferably used.
The cyanide vinyl-aromatic vinyl copolymer (C) of the present invention is preferably used in an amount of about 50 to 79 parts by weight. If the amount of the cyanide vinyl-aromatic vinyl copolymer (C) is less than 50 parts by weight, the fiowability of the resin composition is deteriorated. If the amount is more than 79 parts by weight, the resin composition cannot obtain sufficient crack resistance.
Other additives may be contained in the resin composition of the present invention. The additives include a lubricant, a releasing agent, a light stabilizer, an UV stabilizer, a flame retardant, an antistatic agent, a colorant, a filler, an impact modifier and a mixture thereof. Also, other resin or other rubber component can be contained therein.
The present 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. In the following examples, all parts and percentage are by weight unless otherwise indicated.
Examples
Each component of (A), (B) and (C) used in Examples and Comparative Examples is as follows:
(A)g-ABS Resin
(a0 g-ABS resin having core-shell structure prepared by grafting in emulsion polymerization with a rubber polymer having an average particle size of 0.32 jam was
used.
(a2) g-ABS resin having core-shell structure prepared by grafting in emulsion

polymerization with a rubber polymer having an average particle size of 0.13μm was used.
(B) Styrenic Copolymer Resin
(b,) Styrenic copolymer resin prepared by copolymerizing 7 % by weight of a polybutadiene having an average particle size of 2μm, 25 % by weight of an acrylonitrile, and 68 % by weight of a styrene was used.
(b2) Styrenic copolymer resin prepared by copolymerizing 10 % by weight of a polybutadiene having an average particle size of 0.6 μm and 90 % by weight of a styrene was used.
(C) Cyanide Vinyl-Aromatic Vinyl Copolymer
(C|) SAN resin containing 40 % by weight of acrilonitrile, and having a weight average molecular weight of 120,000 was used.
(c2) SAN resin containing 25 % by weight of acrilonitrile, and having a weight average molecular weight of 450,000was used.
Examples 1-7
The components as shown in Table 1 were mixed and the mixture was extruded through a twin screw extruder with L/D=29 and O=40 mm in pellets. The pellets were molded into test specimens using an injection molding machine at 230G. The test results are shown in Table 2.
Comparative Examples 1-3
Comparative Examples 1 was conducted in the same manner as in Example 1 except that both styrenic copolymer resins (bj and b2) were not used.
Comparative Examples 2 was conducted in the same manner as in Example 1 except that the styrenic copolymer resin (b2) was not used.

Comparative Examples 3 was conducted in the same manner as in Example 1 except that the styrenic copolymer resins (B) was used out of the range of the present invention.

The mechanical properties of the test specimens of Examples and Comparative Examples were measured as follow and the test results are shown in Table 2:
(1) 1ZOD impact strength (kg • cm/cm): The notch Izod impact strength was
measured in accordance with ASTM D256 (1/4" notched).
(2) Flow Index (g/lOmin): The flow index was determined in accordance with
ASTMD1238(10 kg, 220 D).
(3) Gloss (%): Gloss values are determined at an angle of 60 ° using a gloss meter.
(4) Environmental Stress Crack Resistance (ESCR): A test piece in a size of 150 x
20 x 1.6 mm was mold into injection molding machine under 230 □ controlling the
injection speed at 10% so as not to occur a burr and processed into tensile specimen. The
specimen was set on a jig where 6 % of a stress was loaded to the test piece. Then,
polypropylene glycol (hereinafter, MPPGM), methylene diphenyl diisocyanate (hereinafter,

" MDI") and cyclopentane (hereinafter, "CP") were applied to the test piece respectively. Each specimen was left for 5 hours. ESCR was measured in accordance with ASTM D638. It is generally believed that the values of less than 5 indicate poor environmental stress crack resistance. The value required for having crack resistance is considered to be at least 10.
(5) HCFC-141b test (sec): A test piece in the size of 150 x 20 x 1.6 mm prepared as the same as the above was set on a jig where 6 % of a stress was loaded to the test piece. Then, HCFC-141b was applied to the test piece, whereby the time required for cracking on the test piece to appear was judged.

As shown in Table 2, Comparative Example 1 not using styrenic copolymer resin (B) shows that the environmental stress crack resistance and chemical resistance were degraded. Comparative Example 2 not using styrenic copolymer resin (b2) shows that the environmental stress crack resistance against PPG and MDI was deteriorated. Comparative Example 3 using excessive styrenic copolymer resin (B) shows that impact

strength, flow index and gloss were considerably deteriorated.
The present invention can be easily carried out by an ordinary skilled person in the art. Many modifications and changes may be deemed to be with the scope of the present invention as defined in the following claims.









What is claimed is:
I. A thermoplastic resin composition for refrigerator comprising:
(A) 20 to 40 parts by weight of an acrylonitrile-butadiene-styrene graft copolymer resin prepared by grafting in emulsion polymerization 60D30 % by weight of a monomer mixture comprising a cyanide vinyl compound and an aromatic vinyl compound to 40Q70 % by weight of a rubber polymer having an average particle size of 0.1 H0.4;
(B) 1 to 20 parts by weight of a styrenic copolymer consisting of (bf) 0 to 75 % by weight of a styrenic copolymer prepared by copolymerizing 5Μ2G % by weight of a rubber polymer having an average particle size of 0.1 D 10μm, 10D30 % by weight of a
cyanide vinyl compound, and 650 85 % by weight of an aromatic vinyl compound, and (b2) 25 to 100 % by weight of a styrenic copolymer prepared by copolymerizing 5D20 % by weight of a rubber polymer having an average particle size of 0.1 □ 10μm and
80H95 % by weight of an aromatic vinyl compound; and
(C) 50 to 79 parts by weight of a cyanide vinyl-aromatic vinyl copolymer.
2. The thermoplastic resin composition for refrigerator as defined in claim 1, wherein said acrylonitrile-butadiene-styrene graft copolymer (A) is at least one selected from the group consisting of (ai) g-ABS resin prepared from a rubber polymer having an average particle size of 0.2500.4 μm and (a2) g-ABS resin prepared from a rubber polymer having an average particle size of 0.1 DO. 15 μm.
3. The thermoplastic resin composition for refrigerator as defined in claim 1, wherein said rubber polymer is polybutadiene.
4. The thermoplastic resin composition for refrigerator as defined in claim 1, wherein said styrenic copolymer (b2) contains at least 10 % by weight of cyanide vinyl compound.
5. The thermoplastic resin composition for refrigerator as defined in claim 1, wherein

said styrenic copolymer (b2) is used in an amount of about I-10 parts by weight per 100 parts by weight of total resin composition.
6. The thermoplastic resin composition for refrigerator as defined in claim 1, wherein
said cyanide vinyl-aromatic vinyl copolymer(C) is at least one selected from the group
consisting of (c1) cyanide vinyl-aromatic vinyl copolymer containing 25G40 % by weight
of cyanide vinyl compound and having a weight average molecular weight (Mw) of about
50,000 to 150,000 and (c2) cyanide vinyl-aromatic vinyl copolymer containing 20D30 %
by weight of cyanide vinyl compound and having a weight average molecular weight
(Mw) of about 150,000 to 1,000,000.
7. The thermoplastic resin composition for refrigerator as defined in claim 1, further
comprising an additive selected from the group consisting of a lubricant, a releasing
agent, a light stabilizer, an UV stabilizer, a flame retardant, an antistatic agent, a colorant,
a filler, an impact modifier and a mixture thereof.


Documents:

2870-CHENP-2007 CORRESPONDENCE OTHERS 08-06-2010.pdf

2870-chenp-2007-abstract.pdf

2870-chenp-2007-claims.pdf

2870-chenp-2007-correspondnece-others.pdf

2870-chenp-2007-description(complete).pdf

2870-chenp-2007-form 1.pdf

2870-chenp-2007-form 3.pdf

2870-chenp-2007-form 5.pdf

2870-chenp-2007-pct.pdf

2870-CHENP2007 AMENDED PAGES OF SPECIFICATION 29-03-2011.pdf

2870-CHENP2007 AMENDED CLAIMS 29-03-2011.pdf

2870-CHENP2007 POWER OF ATTORNEY 29-03-2011.pdf

2870-chenp2007 form-3 29-03-2011.pdf

2870-CHENP2007 EXAMINATION REPORT REPLY RECIEVED 29-03-2011.pdf


Patent Number 247610
Indian Patent Application Number 2870/CHENP/2007
PG Journal Number 17/2011
Publication Date 29-Apr-2011
Grant Date 27-Apr-2011
Date of Filing 28-Jun-2007
Name of Patentee CHEIL INDUSTRIES INC.
Applicant Address 290 GONGDAN-DONG, GYEONGSANGBUK-DO 730-710, KOREA
Inventors:
# Inventor's Name Inventor's Address
1 PARK, KANG, YEOL 102-503 DAEWOO MIRAESARANG, GWONSEON-DONG, GWONSEON-GU, SUWON-SI, GYEONGGI-DO, KOREA
2 PARK, HEE, JUNG 103-1005 HANJIN GRANDCILL, INCHANG-DONG, GURI-SI, GYEONGGI-DO 471-754, KOREA
3 LEE, JAE, HYUNG 105-406 HYUNDAI APT., SILLIM9-DONG, GWANAK-GU, SEOUL 151-790, KOREA
PCT International Classification Number C08L 25/12
PCT International Application Number PCT/KE05/02035
PCT International Filing date 2005-06-29
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 10-2004-0114011 2004-12-28 Republic of Korea