Resin composition for coating and molded resin product obtained therefrom
Provided is a resin composition for coating, including: 35-65 wt % of a high-molecular weight polypropylene resin (A) having a weight average molecular weight of 100,000-300,000 and an isotactic chain molar fraction, L, of 0.30-0.70; 30-60 wt % of a low-molecular weight polypropylene resin (B) having a weight average molecular weight of 10,000-50,000 and an isotactic chain molar fraction, L, of 0.30-0.70; and 0.1-5.0 wt % of a highly crystalline, low-molecular weight polypropylene resin (C) having a weight average molecular weight of 5,000-50,000 and an isotactic chain molar fraction, L, of 0.70-0.75. The polypropylene resin composition for coating is amenable to spray coating while avoiding a need for a complicated process such as discharge treatment, flame treatment or acid treatment of a polypropylene substrate, in the absence of chlorine, and is effective for forming a coating film having excellent scratch resistance and adhesive property and showing no tagging property.
1. A resin composition for coating, comprising:
35-65 wt % of a high-molecular weight polypropylene resin (A) having a weight average molecular weight of 100,000-300,000 and an isotactic chain molar fraction, L, as defined in the following Mathematical Formula 1, of 0.30-0.70;
30-60 wt % of a low-molecular weight polypropylene resin (B) having a weight average molecular weight of 10,000-50,000 and an isotactic chain molar fraction, L, as defined in the following Mathematical Formula 1, of 0.30-0.70; and
0.1-5.0 wt % of a highly crystalline, low-molecular weight polypropylene resin (C) having a weight average molecular weight of 5,000-50,000 and an isotactic chain molar fraction, L, as defined in the following Mathematical Formula 1, of 0.70-0.75
1
T
m
-
1
T
m
0
=
-
R
Δ
H
U
ln
L
[
Mathematical
Formula
1
]
wherein T m is melting point of a resin, T m 0 is melting point of a perfect crystal, R is the gas constant, ΔH u is melting enthalpy per mol of crystallizable units, and L is an isotactic chain molar fraction.
2. The resin composition for coating according to claim 1 , wherein the high-molecular weight polypropylene resin (A) has a polydispersity (Mw/Mn) of 5 or less.
3. The resin composition for coating according to claim 1 , wherein each of the high-molecular weight polypropylene resin (A) and the low-molecular weight polypropylene resin (B) comprises structural units derived from a heterogeneous monomer in an amount less than 20 mol %.
4. The resin composition for coating according to claim 1 , wherein the highly crystalline low-molecular weight polypropylene resin (C) comprises structural units derived from a heterogeneous monomer in an amount less than 5 mol %.
5. The resin composition for coating according to claim 3 , wherein the heterogeneous monomer is at least one selected from ethylene, 1-butene, 1-pentene, 1-hexene, 1-methyl-1-pentene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene and 1-dodecene.
6. The resin composition for coating according to claim 1 , which further comprises water and a surfactant.
7. A coating agent comprising the resin composition for coating as defined in claim 1 and at least one dispersion solvent selected from water and an organic solvent.
8. The coating agent according to claim 7 , wherein the dispersion solvent is a basic material.
9. A laminate obtained by stacking a layer comprising the resin composition for coating as defined in claim 1 on a substrate.
10. A coated molded article obtained by using the resin composition for coating as defined in claim 1 .
11. A polypropylene resin having a weight average molecular weight of 100,000-300,000 and an isotactic chain molar fraction, L, as defined in the following Mathematical Formula 1, of 0.30-0.70, characterized by comprising structural units derived from a heterogeneous monomer:
1
T
m
-
1
T
m
0
=
-
R
Δ
H
U
ln
L
[
Mathematical
Formula
1
]
wherein T m is melting point of a resin, T m 0 is melting point of a perfect crystal, R is the gas constant, ΔH u is melting enthalpy per mol of crystallizable units, and L is an isotactic chain molar fraction.
12. A polypropylene resin having a weight average molecular weight of 100,000-300,000 and an isotactic chain molar fraction, L, as defined in the following Mathematical Formula 1, of 0.30-0.70, characterized by comprising structural units derived from a heterogeneous monomer:
1
T
m
-
1
T
m
0
=
-
R
Δ
H
U
ln
L
[
Mathematical
Formula
1
]
wherein T m is melting point of a resin, T m 0 is melting point of a perfect crystal, R is the gas constant, ΔH u is melting enthalpy per mol of crystallizable units, and L is an isotactic chain molar fraction, wherein the heterogeneous monomer is at least one selected from ethylene, 1-butene, 1-pentene, 1-hexene, 1-methyl-1-pentene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene and 1-dodecene.
13. A polypropylene resin having a weight average molecular weight of 5,000-50,000 and an isotactic chain molar fraction, L, as defined in the following Mathematical Formula 1, of 0.70-0.75, characterized by comprising structural units derived from a heterogeneous monomer in an amount less than 5 mol %:
1
T
m
-
1
T
m
0
=
-
R
Δ
H
U
ln
L
[
Mathematical
Formula
1
]
wherein T m is melting point of a resin, T m 0 is melting point of a perfect crystal, R is the gas constant, ΔH u is melting enthalpy per mol of crystallizable units, and L is an isotactic chain molar fraction.
14. The polypropylene resin according to claim 13 , wherein the heterogeneous monomer is at least one selected from ethylene, 1-butene, 1-pentene, 1-hexene, 1-methyl-1-pentene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene and 1-dodecene.
15. The resin composition for coating according to claim 1 , which further comprises an unsaturated compound comprising a carboxyl or acid anhydride group.
16. The resin composition for coating according to claim 15 , wherein the unsaturated compound comprising a carboxyl or acid anhydride group is introduced by an unsaturated carboxylic acid or anhydride selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, aconitic acid, aconitic anhydride, fumaric acid, crotonic acid, citraconic acid, mesaconic acid, and allylsuccinic acid.
17. The resin composition for coating according to claim 15 , wherein the unsaturated compound comprising a carboxyl or acid anhydride group is used in an amount of 1-20 parts by weight based on 100 parts by weight of the polypropylene resins.
18. The resin composition for coating according to claim 15 , which further comprises a radical initiator.
19. The resin composition for coating according to claim 18 , wherein the radical initiator is at least one selected from the group consisting of peroxyketals, dialkyl peroxides, diacyl peroxides, peroxyesters and hydroperoxides.
20. The resin composition for coating according to claim 18 , wherein the radical initiator is used in an amount of 5-50 parts by weight based on 100 parts by weight of carboxyl groups or anhydride groups contained in the propylene resins.