CA2013868A1 - Thermosetting resin composition and powder coating composition therefrom - Google Patents

Abstract

Abstract of the Disclosure:

A thermosetting resin composition comprising the following components (a) to (c) wherein the ratio of (a)/(b) is in the range of 0.1 to 1.0 by weight:
(a) an ethylene copolymer containing 0.5 to 10 by weight of a structure derived from a monomer having an acid anhydride group and 3 to 40 % by weight of a structure derived from an .alpha.,.beta.-unsatureated carboxylic acid ester monomer in the molecule, (b) a resin having an epoxy group, and (c) a curing agent for an epoxy resin, and a powder coating composition prepared therefrom, which are useful for coating underfloor parts of automobiles, building materials, various industrial materials, etc. which require corrosion protection and anti-chipping property.

Description

THERMOSETTING R~SIN COMPOSITION AND
POWDER COAT I NG COMPOS I T I ON T~EREFROM

Technical Field of the Invention This invention relates to a thermosetting resin composition and a powder coating composition prepared therefrom, more particularly to a thermosetting resin composition and a powder coating composition which are useful for coating underfloor parts of ~utomobiles, building materials, various industrial materials, etc. which require corrosion protection and further resistance to e.Yternal impact such as impact with jumped stones, so-called "anti-chipping property".
Technical Backqround and Prior Art The coating of the outer covering of automobiles is usually carried out by the steps of electrodeposition coating, intercoatinq and outercoating. Recent attention has focused on the problem of durability of the multiple coat on the outer covering of automobiles, particularly the lowering in beutiful sight of the coat and the corrosion of the steel plate of the body due to peeling off of the coat by impaGt du}ing running. Especially, in cold regions in United States of America, European countries, and the like, the road is occ~sionally covered t~ith gravel mixed with a large amount of comparative coarse rock salt for preventing from freezing of the road surface in winter season, and when automobiles run on such a road, the coating surface of the - 2 ~

automobiles will be suffered from impact by the rock salt particles or stones jumped up with the wheel, by which the coat is partially injured by the impact and results in peeling off of whole coat, so-called "chipping" phenomenon.
Due to this phenomenon, the metallic surface of the outer covering at the injured area is exposed, by which the steel plate will rust and corrode rapidly.
In order to prevent such a chipping and the corrosion of the steel plate, there has hitherto been studied various means such as chemical treatment of the outer surface of metallic base material Oe the body and the improvement of the electrodeposition coating, intercoating and outercoating, but there has never been found any suitable coating composition which has excellent anti-chipping property and also has sufficient adhesion property.
There have also been proposed various means for preventing the chipping of the outer covering of automobiles, such as a method of applying an anti-chipping coating composition comprising a soft thermopIastic resin such as polyethylene powder, powder of polyethylene foam, polyvinyl chloride ~PVC) paste, bituminous substance, elastomers, and the like; and a method of using thermo-setting resin composition having improved anti-chipping property, such as epo~y resin coating composition, polyester coating composition.
However, in the method of using the conventional thermoplastic resin as an anti-chipping coating composition, ~ 3 ~ 2~ 8 since the thermoplastic resin per se has little adhesion property, an anti-corrosive primer should previously be applied to the substance to be coated in order to exhibit both anti-corrosive property and adhesion property, followed by applying thereto the thermoplastic resin composition as the anti-chipping coating composition. Even by applying or the anti-corrosive primer, the adhesion property is still not sufficient, and hence, there are still various problems.
For instance, during running of automobiles for a long period of time, the anti-chipping coating composition is peeled off from the primer~ The thermoplastic anti-chipping coating composition is so~t and can absorve the e4~ternal energy of the ~umped stones, etc. and thereby can prevent to reach the impact to the anti-corrosive primer, but there is produced a hole passing through the coating composition layer to reach to the primer layer. AS a result, water penetrates through the hole into the thermoplastic resin coating layer and the anti-corrosive primer layer, and thereby, the weak adhesion between the thermoplastic resin coating composition layer and the anti-corrosive primer layer is further weakened. Particularly, when the penetrated water is fro~en, the volume thereof expands, by which the other region havinq no penetration of water is newly peeled off, and then, water is again penetrated into the newly peeled region. By repeating this, the peeling or the layers extends very rapidly. .~oreover, according to tr.-above method, when the jumped stones, etc. attack repreatedly at the same portion, the e~ternal energy will directly be siven to the anti-corrosive primer layer through the holes of the thermosetting resin coating layer, by which crack and crazing are produced at said portion and thereby the desired anti-corrosive efect can not be obtained.
Thus, this method is somewhat useful for anti-chipping coating, but is still not sufficient.
On the other handr for improving the anti-chipping property of the thermosetting resin coating composition such as an epoxy resin coating composition or a polyester resin coating composition, various methods have been proposed.
The thermosetting resins are originally more brittle and breakable in comparison with thermoplastic resins, but the defect is improved by blending with a soft thermoplastic resin or by using a flexible curing- agent, and the composition thus improved shows satisfactory anti-chipping property at an ordinary temperature (0 to 30C). However, in a cold region of a temperature of -20C or lower, these methods can still not be used, because the thermosetting resins such as an epoxy resin and polyester resin have a glass transition temperature higher tnan that of thermo-plastic resins and hence the anti-chipping coating composition prepared therefrom is brittle and breakable like a glass at the cold region of a temperature of -20C or lower. There have been known some coating compositions similar to the composition of the present invention, for e~ample, in Japanese Patent First Publication (Kokai) Nos.

- s - 20~

10142~/1973 and 85832/1978, but these known compositions are intended to use for other purposes diîferent from the objects oE the present invention, and hence, most of them are not useful for the purpose of the present invention.
Brief Description of the Invention The present inventors have intensively studied as to various compositions suitable for the purpose of the present invention among the compositions disclosed in the above Japanese Patent First Publication (Kokai) No.
101424~1973 and have Eound that the structure and reactivity of some ethylene copolymer have very important effect on the desired properties oE the coa~ing composition and that there can be obtained a suitable thermosetting resin composition naving the desired excellent propertiesl and further that the powder coating composition prepared from the resin composition has excellent properties.
Detailed Description oE the Invention This invention provides a thermosetting resin composition (1) and a powder coating composition (2) comprising the following components, respectively.
(1) A thermosetting resin composition comprising the foliowing components (a~ to (c) wherein the ratio of ~a)/(b) is in the range of 0.1 to 1.0 by weight:
(a) an ethylene copolymer containing 0.5 to 10 by weight of a structure derived from a monomer having an acid anhydride group and 3 to 40 ~ by weight oE a structure ~L3~

derived from an ~ unsaturated carboxylic acid ester monomer in the molecule, (b) a resin having an epoxy group, and (c) a curing agent for an epoxy resin.
~ 2) A powder coating composition comprising the following components (a) to (c) wherein the ratio of (a)/(b) is in the range of 0.1 to 1.0 by weight:
(a) an ethylene copolymer containing 0.5 to 10 %
by weight of a structure derived from a monomer having an acid anhydride group and 3 to 40 ~ by weight of a structure derived from an ~B-unsaturated carboxylic acid ester monomer in the molecule, (b) a resin having an epoxy group, and (c) a curing agent for an epoxy resin.
In the above compositions, the ethylene copolymer (a) contributes to the improvement of impact resistance, and the molecular structure thereof is very important. In order to improve the impact resistance of the composition, the ethylene copolymer should have the Eollowing properties.
(i) It has a glass transition temperature of -20C
or lower.
(ii) It is an elastic material suitable for relieving the impact.
(iii) It has a functional group so as to be able to transmit the stress to the epoxy resin matrix, preferably it is reactive with the epoxy group.

- 2~3~

(iv) It has an affinity with the epoxy resin of the matrix so that it can microscopically dispersed into the matrix resin.
(v) It has heat resistance and chemical resistance and has less variation in the physical properties.
Among the above requirements, the items (i) and ~v) are satisfied by all ethylene copolymers. The requirement (ii) is predominantly participated by the ~ unsat~lrated carboxylic acid ester component. That is, when the ~,3-unsaturated carbo~ylic acid ester co~ponent is contained in an amount of less than 3 % by weight in the ethylene copolymer, the copolymer has a large crystallinity at the ethylene chain region and hence has less elasticity. On the other hand, when the component is contained in an amount of more than 40 ~ by weight, it is no problem in the elasticity but it becomes completely non-crystalline, and further show excess tackiness and less heat resistance and chemical resistance, and hence, it is not preferable from the practical ~iet~point. As to the requirement (iii), the acid anhydride component takes a role. When the acid anhydride component is contained in an amount of less than 0.5 % by weight, the ethylene copolymer has less functional group and hence has insufficient ability of transmitting the stress to the matri~ resin. On the other hand, when the acid anhydride component is contained in more than 10 % by weight, it gives various troubles on the production oE
ethylene copolymer, and hence, such a product can not - 8 - ~ 8S8 practically be obtained by the present available technique.
As to the requirement (iv), both of the ~,B-unsaturated carboxylic acid ester component and the acid anhydride component participate, and when both components are contained in a small amount, the copolymer is hardly microscopically dispersed in the matrix resin. On the other hand, when both components are contained in a too large amount, the copolymer has too high affinity to the epoxy resin and becomes almost compatible in molecular level, and hence, the copolymer can not microscopically be dispersed within the matrix resin in a degree suitable for relieving the impact and the impact resistance o~ the product is not so improved.
The acid anhydride used in the present invention includes maleic anhydride, citraconic anhydride, etc. which are preferable in view oE the copolymerizability wlth ethylene.
The ~B-unsaturated carboxylic acid ester used in the present invention includes preferably Cl-C4 alkyl esters of acrylic acid, such as methyl acrylate, ethyl acrylate, butyl a_rylate, etc., and Cl-C4 alkyl esters of methacrylic acid, such as methyl methacrylate, ethyl methacrylate, etc.
The component (a) in the present composition is a terpolymer which is prepared by copolymerizing the above acid anhydride, ~ unsaturated carboxylic acid ester and ethylene in the ratios as mentioned above, i.e. in such ratios that the acid anhydride-derived structure becomes in 38~B

the range of 0.5 to 10 % by weight and the ~ unsaturated carboxylic ester-derived structure becomes in the range of 3 to 40 ~ by weight, in a usual manner, that is, by a radical reaction at a high temperature under high pressure using an appa~atus ~hich is usually used for the production of a low-density polyethylene. A commercially available product thereof is "Bondine~" (sold by Sumika CDF, Ltd., Japan). In view of the object and mechanism of the present invention, it is not necessarily limited to the above process.
The resin having an epoxy group used in the present invention includes any resins which are usually used as a component oE the conventional epoxy resin coating compos-ition, and includes, for example, aliphatic diglycidyl ethers, such as ethylene glycol diglycidyl ether, poly-ethylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, polypropylene glycol diglycidyl ether, etc.; aromtic diglycidyl ethers, such as bisphenol A type epoxy resins, bisphenol F type epoxy resins, etc.; aliphatic triglycidyl ethers, such as glycerin triglycidyl ether;
aromatic polyglycidyl ethers, such as epoxy-novolac resin;
acyclic aliphatic epoxy compounds, such as epoxylated oil;
cyclic aliphatic epoxy compounds, such as dicyclopentadiene dioxidei and the like. These epoxy compounds have preferably an epoxy equivalent of 100 to 5,000.
The curing agent for epoxy resin used in the present invention includes polyesters having carboxyl terminus comprising as the main components an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid and ~
polyhydric alcohol (said aromatic dicarboxylic acid includes phthalic acid, terephthalic acid, isophthalic acid, phthalic anhydride, etc.; said aliphatic dicarboxylic acid includes succinic acid, adipic acid, sebacic acid, azelaic acid, maleic anhydride, fumaric acid, itaconic acid, etc.; and said polyhydric alcohol includes ethylene glycol, propylene glycol, diethylene glycol, 1,3-butylene glycol, neopentyl glycol, butenediol, glycerin, trimethylolpropane, penta-erythritol, etc.); organic acid dihydrazides such as adipic acid dihydrazide ~ADH), isophthalic acid dihydrazide (IDH), sebacic acid dihydrazide (SDH), etc.; dicyandiamide (DICY);
aromatic amides such as diaminodiphenylmethane, aniline-formalin condensate, m-phenylenediamine, toluenediamine, etc.; acid anhydrides such as methyltetrahydrophthalic anhydride, metnylnadic anhydride, methylhexahydrophthalic anhydride, hexahydrophthalic anhydride, polyazetic poly-anhydride (PAPA), chlorendic anhydride (HET), phthalic anhydride, trimellitic anhydride (TMA), pyromellitic anhydride (PMDA), benzophenonetetracarboxylic anhydride (BTD~), ethylene glycol bistrimellitate (TMEG), etc.
In the composition of the present invention, when the ratio of (a)~(b) is less than 0.1, the product shows insufficient impact resistance, and on the other hand, when it is over 1.0, the composition shows a different structure, that is, the component (a) becomes the matrix, and hence, the composition has the same problem as the conventional i8 -thermoplastic anti-chipping coating composition. According to the composition of the present invention satisfying the ratio o~ (a)/(b) as specified, the component (a) is microscopically dispersed within the hard and brittle component ~b) and the components (a) and (b) are reacted and strongly adhered each other, by which the desired properties are exhibited.
The amount of the component (c) in the present invention varies largely depending on the kinds of the component (b) and the kinds o the component (c) and further is determined by the conditions for subsequent bakin~, and hence, it is hardly speciied. In examples disclosed hereinafter, a standard range of amount is shown in a representative example where there are used Epo-tohte YD902 (manuEactured by Toto Seikei K.K., Japan) as component (b), Epotote ZX798 (manufactured by Toto Seikei K.K., Japan) as component (c), and Curezol 2MZ (manufactured by Shikoku Kasei K.K., Japan), but the range of amount is not limited thereto.
The theremosetting resin composition of the present invention can be used as a powder coating composition which is prepared by mixing and heat-melting the components (a), (b) and (c) with an extruder, various mixer, or the like, followed by pulverizing. In this procedure, the temperature for mixing and melting may vary depending on the kinds of the component (b), but preferably at a temperature of not higher than 12GC, for the purpose of keeping the component - 12 ~ 8~8 (b) in the semi-cured state and completing the curing of the composition during the subsequent electrostatic baking and coating or fluidi~ation dip coating.
The compos~tion of the present invention may directly be applied to the substance to be coated with an extruder, or the like.
Moreover, the composition of the present invention may be used in the form of a solution coating composition where the components are dissolved in an organic solvent, or in the form of an emulsion coating composition where the components are emulsified and dispersed in water or an organic solvent.
The composition of the present invention may also be incorporated with various pigments for coloring and various inorganic substances as an extender pigment and further optionally with other additives, such as ultraviolet absorbers, antioxidants, lubricants, and the like.
Examples The present invention is illustrated by the following examples, but should not be construded to be limited thereto.
Examples 1 to 4 The components of the compositions of the present invention are shown in Table 1. The components (a), (b) and ~c~ as shown in Table 1 are mixed with stirring with Henschel mixer, and the mixture is extruded in the sheet-li~e form at 105 - 120C with an extruder. ~fter cooling, - 13 - 2~

the product is roughly pulverized with a crusher and further finely pulverized with a mill to obtain powders having a particle size of 35 to 45 ~m.
The powder thus prepared was coated on a primer-electrodeposited steel panel (70 mm x lS0 mm) in a thickness of 200 ~m with an electrostatic coating machine, followed by baking at 200C for 20 minutes to give a test piece. Each test piece thus prepared was subjected to various tests.
The results are shown in Table 3.
Re~erence Examples 1 to 7 The compositions of the reference examples are shown in Table 2.
In the same manner as described in Examples except the composition was different, there were prepared test pieces, and the test pieces were subjected to the tests, likewise. The results are shown in Table 3.
Test methods (1) Test for chipping at room temperature:
Crush stones (6~, 500 9) were sprayed onto the test piece under a spray pressure of 5 mg/cm2, which procedure was repeated S times, and the test piece was obser~ed whether any peeling of the coated layer was present or not.
The test piece having no peeling or cracking of the layer was evaluated as "o".
(2) Test for chipping at -30C:
The test piece cooled at -30C was subjected to the ~est for chipping in the same manner as in the above test at room temperature. The test piece having no peeling or cracking of thè layer ~as evaluated as "o".

(3) Test for adhesion:
The test piece was slitted in two lines with a width of 3 mm, and the T-peel strength per 3 mm width was measured. The test piece having a T-peel strength of 1 kg/3 mm width or more was evaluated as "o".
(4~ Test of flaw:
After being subjected to the test for chipping at room temperature, the test piece was observed as to the degree of flaw with naked eyes. The test piece having an unevenness of more than O.3 mm in depth was evaluated as "x" .

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2~38~

Table 3 Example No. Test items .
Chipping Chipping ~dhesion Flaw at room temp. at -30C

Example 1 ~ o ~ o o o Ref. Ex. 1 o x x x ., 4 o x x o x ~ o As is clear from Table 3, the products in all Examples had no problem in all testings, but on the other hand, the products in Reference Examples had defects of anyone of cracking or flaw and was insufficient as an anti-chipping coating composition.
Thus, the thermosetting resin composition and powder coating composition of the present invention are useful for coating thermosetting resin composition and a powder coating composition which are useful ror coating underfloor parts of automobiles, building materials, various industrial materials, etc. which require corrosion protec-tion and further resistance to external impact such as impact with jumped stones, so-called "anti-chipping property".

Claims (6)

1. A thermosetting resin composition comprising the following components (a) to (c) wherein the ratio of (a)/(b) is in the range of 0.1 to 1.0 by weight:
(a) an ethylene copolymer containing 0.5 to 10 %
by weight of a structure derived from a monomer having an acid anhydride group and 3 to 40 % by weight of a structure derived from an .alpha.,.beta.-unsatureated carboxylic acid ester monomer in the molecule, (b) a resin having an epoxy group, and (c) a curing agent for an epoxy resin.

2. The composition according to claim 1, wherein the monomer having an acid hydride group is a member selected from maleic anhydride and citraconic anhydride, and the .alpha.,.beta.-unsaturated carboxylic acid ester monomer is a member selected from C1-C4 alkyl esters of acrylic acid and C1-C4 alkyl esters of methacrylic acid.

3. The composition according to claim 1, wherein the component (a) is a termpolymer prepared by copolymerizing the monomer having an acid anhydride group, the .alpha.,.beta.-unsaturated carboxylic acid ester monomer and ethylene.

4. A powder coating composition comprising the following components (a) to (c) wherein the ratio of (a)/(b) is in the range of 0.1 to 1.0 by weight:
(a) an ethylene copolymer containing 0.5 to 10 %
by weight of a structure derived from a monomer having an acid anhydride group and 3 to 40 % by weight of a structure derived from an .alpha.,.beta.-unsatureated carboxylic acid ester monomer in the molecule, (b) a resin having an epoxy group, and (c) a curing agent for an epoxy resin.

5. The composition according to claim 4, wherein the monomer having an acid hydride group is a member selected from maleic anhydride and citraconic anhydride, and the .alpha.,.beta.-unsaturated carboxylic acid ester monomer is a member selected from C1-C4 alkyl esters of acrylic acid and C1-C4 alkyl esters of methacrylic acid.

6. The composition according to claim 4, wherein the component (a) is a termpolymer prepared by copolymer-izing the monomer having an acid anhydride group, the unsaturated carboxylic acid ester monomer and ethylene.