CA1049684A - Thermosetting powder coating compositions - Google Patents

Abstract

Abstract of the disclosure:
A thermosetting powder costing composition comprising:
(A) a graft copolymer of a) 10 to 40 percent of a linear polyester having a number average molecular weight of 600 to 3,000 and containing one ethylenically unsaturated double bond only at one end of the molecule, b) 5 to 30 percent of at least one of glycidyl esters having the formula wherein R1 is hydrogen or methyl, and c) 10 to 85 percent of at least one of acrylic compounds having the formula of CH2=C(R2)COOR3, wherein R2 is hydrogen or methyl and R3 is alkyl having 1 to 14 carbon atoms cyclohexyl or hydroxyalkyl represented by wherein R4 is hydrogen, methyl or ethyl, said graft copolymer having a softening point of 70 to 110° C
and a number average molecular weight of 2,000 to 30,000;
and (B) at least one of polycarboxylic acids and anhydrides thereof in an amount of 0.6 to 1.2 moles in terms of carboxyl group per mole of the glycidyl group contained in the graft copolymer.

Description

rrhis invention relate6 -to thermosetting powder coating cornpositionG.
With ever increasing severity of pollution of r~ir, wa-ter and the lile~ powcler coating composi.tions are introduced into use whic~l are a~nost unli!sely to cause pollution problems.
Presently, epoxy resin or v:inyl chloride resin is chiefly used as the resin component of powder coa-ting compositions. Because of poor resistance to weather, however, powder coating compositions o~ the epoxy resin type are not usable out-of-doors, whilst those of -the vinyl chloride resin type which are thermoplastic are inferior in their resistance to heat and to solven-ts and there~ore have limited usefulness, In order to overcome these problems~ various powder coating compositions of the acrylic resin type have been recently proposed which contain glycidyl group a3 a functional group.
With such acrylic resin type powder coating composition containing functional glycidyl groups, efforts are made to ingeniously maintain the thermal flowability, ~cross-lin~ing reaction velocity and softening point of the resin in balance with one another BO that the composition exhibits good storage stabi~ity and gives ~mooth COatingG
having high resistance to solvents,

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To ~nsure such balance, there arises the necessity -to accurat~ly determine the kind of the acrylate or meth-acrylate to be used, the amount thereof) the polymerization degree and the amount of the monomer containing the fuctional group to be used. However, even with the optimum combination of these factors, the coating composition is prone to blocking when applied or stored in an environment in which the ambient temperature is likely to exceed 35 C~
The term "blocking" means the phenomenon in which particles of the coating composition cohere one another during storage~ This objection is avoidable when the composition is adapted to have an elevated softening point at the sacrifice of the smoothness of the coating to be prepared therefrom or, otherwise, by providing cooling means for the containers for storing and recovering the coating composition. In the former case~ the powd0r coating com- -position of the thormosetting acr~lic resin type is no ~. longer applicable to decorative surface fini~h for which - the coating composition i~ chiefly intended to use~
whereas the latter case entails hlgher equipment ~ost and operation cost ~nd is unfavorable~
Furthermore, powder coating compositions of the acrylic resin type r~quire baking at high temperatures of at least 180 C~ if it is d~sired to obtain a coating which is ~uperior in me¢hanical propert~e~ such as resist~nce . . , 9~

to impact, Erich.en te~t and flexural streng-th, besause lower bakin~ -temperatures not only impair -the mechanical prop~r-ties of the coa-ting but also reduce its resistance -to weather, solvents and hea-t, For uæe in decorative surface finishing, powder coating compositions, like usual solvent--type coating compositions, should be applicable to a small thickness of about 25 to 50 microns for the sake of economy, but conventional thermosetting powder coating compo~itions of the acrylic resin type involve difficultles in giving thin coatings, because they exhibit a hi~h melt viscosity when applie.d for coating and display. low flowability when heated for fusion. Although such coating compositions may be adapted to form thin coatings by reducing their curability to render them more flowable in molten state, thls is not desirable since the resulting coatings will be inferior in physical properties7 solvent resistance, etc, On the other hand, the coating composition can be made to form thin coatings when reduced in its softening point and thereby lowered in its melt viscosity~ but the composition will then have the disadvantage that the particles cohere together durin~ storage~ resulting in reduced resi~tance to blocking. Such composition is therefore si~ilarly unde~irable~
: 25 Accordingly, an object of this invention is to , ' .
:' '' """ ' provide an improved powder coating composi-tion which is free of the foregoing drawbacks of kno~m acrylic powder coa-ting compositions.
Ano-ther object of -this invention i6 to provide a powcler coating composition capable of giving coatings which are excellent in mechanical strength and in physical properties even when baked at low temperatures.
Another object of this invention is to provide a powder coating composition capable of giving smooth glossy coatings for decorative pu~poses ~ree from undesired blocking, even when applied or stored in a hot environment~.
Still another object of this invention is to provide a powder coating composition which has a low melt viscosity and good flowability and which is therefore capable of readily forming smooth1 glo~sy and yet thin coatings.
The present invention provides a thermosetting powder coating composition which comprises:
(A) A graft copolymer of a) 10 to 40 percent by weight of a linear polyester having a number average molecular weight of 600 to

3~000 and containing one ethylenically un~aturated double bond only at one end of the molecule, b) 5 to 30 percent by weight of a glycidyl ester having the ~ormula 1~9196~

CH2 _ C-COOCH2 - CH - CH2 wherein Rl is hydrogen or methyl, and c) 10 to 85 percent by weight of an acrylic compound having the formula l2 CH2 = C-COOR3 wherein R2 is hydrogen or methyl and I~3 is alkyl having 1 to 14 carbon atoms, cyclohexyl or hydroxyalkyl l4 represented by -CH2-CHOH wherein RL~ ~s hydrogen or alkyl having 1 to 2 carbon atoms, said graft copolymer having a softening point of 70 to 110 C and a number average molecular weight of 2~000 to 30,000; and (B) at least one of polycarboxylic acids and anhydrides thereof in an amount of 0.6 ko 1.2 moles in terms of carboxyl group per mole of the glycidyl group contained in the graft copolymer.
~ he first advantaga of the coating compo~i~ion o~
this invention i8 that when baked for 30 minutes at a temperature of 150 C which is much lower than is the cas~
with conve~tional acrylic powder coating composition~
the composition gives a coating having mechanical propertie~

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~g6~4 such a5 impact resistance, Erichsen test and flexuralstrength, which are comparable to those resulting from.
epoxy resin.powder coati~lg compositions which are the most excellent of presently avai.lable powder coating compositions.
Moreover~ coatings prepared from the present composition are in no way inferior to usual powder coating compositions of the thermosetting acrylic resin type in respect of resistance to weather~ solvents and heat.
The second advantage of the present coating composition is tha-t the above-mentioned unique graft copolymer of polyester and acrylic resin used therein enables the composition to remain in the form of fine particles free of blocking 60 as to be applicable to electrostatic coating or fluidi~d bed coating even under a eevere operation condition of 35 to 40 C as when it is used during eummerJ with the result that the compoeitlon can give smooth and gloæsy eurface finish coatingsO
It ie indeed surprieing that the above-specified graft copolymer o~ linear polyeetor and acrylic polymer~
although containing 10 to L~0 percent by weight o~ polyester grafted on to the polymer~ hae almoet as high a softenlng point as ungrafted acrylic polymers and possesse~ a greatly reduced melt viscosity when heated.
The high softenlng point make~ it less likely ~or the coaLing composit~o ~o undergo blockin6 during .. ..

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storage or coating operation, 50 -that the composi-tion has high resistance -to blocl~ing and goo~ ~nenability to coating operation~
On the other hand, the low melt viscosity of the composition when it is applied for coating en~ures good thermal flowabillty to give a smooth surface finishO
The third advantage of the coating composition of this invention is that because of its low melt viscosity and good thermal f~owability during the formation of coating, the composition is capable of giving s~ooth and glossy coatings having small thicknesses of 25 to 50 ~
while retaining the desired curability and blocking resistance.
Thus these various advantages of the invention are attributable to the use of the specified graft copolymer f acrylic polymer and linear polyesterO
With thi~ invention, the polye~ter constituting the above-identified copolymer must havea number average molecular weight oP 600 to 3,000 and contain one ethyleni-cally unsaturated ~ouble bond only at one end of the molecule. With a number average molecular weight of less than 600, the polye~ter ha~ an poor pla~tioizing ability and is inef~ective in greatly reducing the melt viscosity~
impa~ring the smoothnes~ and ph~ical properties of the resulting coatingO Wlth a number avera~e m~lecular weight f more than 3~000~ the coating compo~ition ha~ a markedly ~04~8~L
reduced so~tening point and poor blocking resistance.
Preferable number average molecular weight is in the range of 1,000 -to 2,000.
The method of preparing the linear polyester having one ethylenically unsaturated double bond at one end o~ the molecule is in no way limitative in this invention but merely has a secondary significance in this invention. Most ~dvantageously, however, it is prepared by condensing a monohydroxymonocarboxylic acid or a mixture of the acid and monocarboxylic acid to obtain a linear polyester having one free terminal carboxyl group and reacting glycidyl acrylate and/or glycidyl methacrylate with the polyester. Useful monohydroxymonocarboxylic acids having one carboxyl group a-t the end of the molecule and one hydroxyl group in the molecule are aliphatic mono-hydroxymonocarboxylic acids having 2 to 18 carbon atoms.
Preferable examples are 12-hydroxystearic acid9 ricinoleic acid~ lactic acid~ etc., among which especially preferable are 12-hydroxystearic acid and ricinoleic acid. The monohydroxymonocarboxylic aicds can be used alone or in admixture with one another. Monocarboxylic acids can be employed in admixture with the monohydroxymonocarboxylic acid, if desired, in order to adjust a molecular weight of the resultant linear polyester~ Usable monocarboxylic acids are aliphatic monocarboxylic acids having 1 to 18 . ~ .

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carbon atoms and aromatic monocarboxylic acids represented by -the formula (R5) ~ COO~I
wherein ~ is al~l having 1 -to L~ carbon atoms and n is 0 or an in-teger of 1 or 2. Preferable examples of the former are acetic acid, caproic acid, caprylic acid, capric acid, lauric acid, myris~ic acid, palmitic acid, stearic acid~ etc. Preferable examples of the latter are benzoic acid, p-tert-butyl benzoic aci~ etc. Especially preferable monocarboxylic acids are palmitic acid~ stearic acid and p-tert-butyl benzoic acid. One or more of -the monocarboxylic acids can be used. The hydroxymonocarboxylic acid is subjected~ singly or as admixed with -the monocarboxylic acid9 to condensation reaction. When the monocarboxylic acid is used, the amount thereof is up to 20 mole %, preferably 10 to 20 mole %, based on the hydroxymonocarboxylic acid.
The condensation reaction is conduc-ted in a conventional manner in the presence or absence of catalyst and with heating~ Suitable catalysts are; for example, sulfuric acid, dimethyl sulfuric acid, methanesulfonic acid, etcO Generally, the condensation temperature is about 130 to about 170 C. The condensation reaction yields a linear polyester having one carboxyl group at the end .:

of the molecule.
In order to introduce.an ethylenically unsaturated double bond in-to the polyester at the end of the molecule, the polyester is then reacted with glycidyl acrylate and/or glycidyl me-thacrylate. For this reaction, an equivalent or excess of glycidyl acrylate and/or methacrylate is used based on the carboxyl group of the polyester. The excess glycidyl ester serves as another rnonomer component A-(b) to ultimately obtain the desired graft copolymer.
Advantageously, the reaction is conducted in the presence ; of catalyst such as trimethylamine~ triethylamine, dimethyl-. aminoethanol, dimethyl coconut amine or like tertiary amine, or tetraethyl ammonium bromide, trimethylbenzyl ammonium chloride or like quaternary ammoni~m salt~ Usually, the reaction is carried out at a temperature of 110 to 150 C, preferably until the acid value of the product reduces to a level not higher than 5.
Another component A-(b) o~ the gra~t copolymer is a glycidyl ester represented by the formula Rl 0 ...
CH2 = C-COOCH2 - CH - CH2 - wherein Rl is hydrogen or methyl. Such esters are glycidyl acrylate and glycidyl methacrylate.
Another component A-(c) of the graft copolymer is an acrylic compound represented by the formula : . .
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~96&14 C~2 = C-COOR3 wherein R~ is hydrogen or methyl, R~ is alkyl havingr 1 to ~ L~
lL~ carbon atoms, cyclohexyl or -CH2-C~IOH wherein Rl is hydrogen or alkyl having 1 to 2 carbon atoms. ~xamples of such compounds are esters of acrylic acid and meth-acrylic acid. The esters include methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, iæo-butyl acrylate, t-butyl acrylateg 2-ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, iso-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, and like alkyl esters; cyclohexyl acrylate and cyclohexyl methacrylate; and 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate and like hydroxyalkyl esters.
Preferable acrylic compounds are methyl acrylate, ethyl acrylate, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, iso-butyl methacrylate, 2-ethylhexyl methacrylate~ 2;hydroxyethyl methacrylate ~nd lauryl methacrylate. They may be uæed alone or in admixture with one ano-tJier.
The graft copolymer to be used in this invention is obtained by subjecting to gra~-t copolymerization the ~9~
above three components, namely linear polyester A-(a) having one ethylenically un,saturated double bond at the end of the molecule, glycidyl ester A-(b) and acrylic compound A-(c). The graft copolymer must have a softening point of 70 to 110 C and a number average molecular weight of 2,000 to 30,000. If the softening point is below 70 C~ the resistance to blocking of the resulting coating composition will be poor. When the softening point is higher than 110 C9 the resulting coating will be poor in surface smoothness. With less than 2,000 number average molecular weight of the graft copolymer~ the coating obtained has low mechanical strength and solvent resis-tance while the coating composition has inferior resistance to blocking. On the other hand~ a molecular weight higher than 30,000 gives no additional effect on the properties of the coating composition as well as of the coating but increases the melt viscosity of the coating composition, making it impossible to obtain a smooth coatingO
Preferable number average molecular weight of the graft copolymer is 4,000 to 20,000~ "' The proportions of the components A-(a), A-(b) ,and A(c) to be copolymerized into the graft copolymer are critical and must be 10 to 40 % by weight of linear polyester A (a), 5 to 30 % by weight of glycidyl ester A~(b) and 10 to 85 % by weight of acrylic compound A-(c).

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If the amoun-t of -the linear polyester is less -than 10 %
by weight9 i-t is impossible to fully ensure the effect con-templated by this invention~
More specifically, as will be apparent from Composition No. 6 in the example ~iven later, a graft copolymer (GP-6) containing about 5 % by weight of the polyester is not particularly distinguishable from ungrafted copolymers~
whereas those containing at least 10 % by weight of polyester have an outstanding effect.
This will be seen from Table 1 given below which shows the softening poin-ts and melt viscosities at 140 C
of copolymers containing varying amounts of polyester.
Table 1 Proportion of polyester in Melt Viscosity Soften~ng the copolymer (Poises) point( C) (wt. %) 5,~00 87 1,500 89 1,300 82 1,250 66 . .' -- - - - . , _ Note: The copolymers are prepared in the same manner as graft copolymer-4 given later, except that the amount of polyester-4 is varied.

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Evidently3 the table shows that use of 10 to 40 % by weight of polyester for graft copolymerization remarl~ably reduces -the melt viscosity without perlllitting a noticeable reduction in the softening point. The table further reveals that use of more than 40 % by weight of polyester is not noticeably effective in reducing the melt viscosity, while markedly lowering the softening point to reduce the resistance to blocking of the coati.ng composition (see Composition No. 10 in the example given later). Preferably the proportion of polyester to be co-polymerized is about 15 to 30 % by weight. `~
When the proportion of glycidyl ester A-(b) is less than 5 % by weight, insufficient cross linking will resul~.~ failing to impart satisfactory solvent resistance and mechanical strength to the coating formed (see Composition No. 13 in the example below), whereas proportions more than 30 % by weight permit the cross-linking reaction to proceed to excess during the coating forming step, resulting in a lower flowability during that step and rendering the coating no longer smooth-surfaced (see Composition No. 14 in the example below), Preferably? 10 to 25 % by weight of glycidyl ester is copolymerized, The acrylic compound A-(c)~ another component of the graft copolymer and represented by the ~ormula CH2=C-COOR3 (wherein R2 and X3 are as defined above) should be used in a proportion of at least 10 % by weight to ensure the adhesion of the resulting coating to the substrate (see Composition No. 22 in the example given below)~
In addition to the foregoing three components, the graft copolymer usable in this invention may further contain, as a copolymerizable monomer A-(d), up to 40 %
by weight of at least one of acrylonitrile, methacrylonitrile, and styrenes represented by the formula ~g~ cx =CH2 wherein R6 is hydrogen or alkyl having 1 to 4 carbon atoms.
The styrenes of the above formula include styrene, vinyl-toluene, etc. They are used singly or in admixture with one another.
When containing the above monomer, the coating composition obtained exhibits better resistance to blocking.

The proportion of the additional monomer must be up to L~0 %
by weight and is usually 5 to 30 % by weight. With more than 40 % by weight of the additional monomer, the resulting coating will be poor in surface smoothness.
The graft copolymer is prepared by block polymerization, solution polymerization, suspension poly merization, emulsion polymerization, etc., among which most preferable is solution polymerization~

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In the solution polymerization are employable various organic solvents such aas aliphatic hydrocarbons, aromatic hydrocarbons, etc. The solution polymerization can be conducted in the presence of polymerization initiators.
Examples thereof are organic peroxides such as benzoyl peroxide, lauroyl peroxide, tert-butylhydroperoxide, tert-butyl peroxyoctate, isobutanoyl peroxide, etc. and azo eompounds such as azobisisobutyronitrile, azobisisovalero-nitrile, etc. The solution polymerization reaction i9 usually carried out under reflux temperature.
The powder coating composition of this i~vention incorporates the graft copolymer described above and at least one of polycarboxylic acids and anhydrides thereof. Useful polycarboxylic acids are aliphatic,alicyclic and aromatic polycarboxylic acids which are known as curing agents for acrylic resins con-taining a functional glycidyl group. More specific examples of polycarboxylic acids are aliphatic polycarboxylic acids such as adipic acid, azelaic acid, sebacic acid~ dodecanedicarbox~lic acid, fumaric acid, male~c acid, succinic acid, tricarballylic acid, etc~; alicyclic polycarboxylic acids such as tetrahydrophthalic acid, hexahydrophthalic acid, etc; and aromatic polycarboxylic acids such as phthalic acida isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid, etc. The anhydrides of such polycarboxylic ~9~4 acids ar~ similarly usable. The polycarboxylic acids and anhyclri~es thereof are used singly or at least two of them are usable in admixture.
To prepare the powder coating composition of this invention, at least one o~ the above polycarboxylic acids and anhydrides thereof is used in an amount of o.6 to 1~2 moles in terms of carboxyl group per mole of the glycidyl group contained in the graft copolymer~ Lesser amounts lead to insufficient curing and there~ore to lower mechanical strength and solvent resistance of the resulting coating (see Composition No. 19 in the example given below), while excess amounts result in reduced surface smoothness and poor physical properties of the coating (see Composition No. 20 in the example).
The powder coating composition of this invention may further incorporate organic and inorganic pigments, flowing agent, curing catalyst, antistatic agent, etc.
which are generally used for coating compositions.
Employable as the curing catalysts are, for example, tert-amine, quaternary ammonium salt,organic tin compound such as triphenyl tin chloride and dibutyl tin laurate ~nd titanium compounds such as tetra-isopropyl titanate.
~ he powder coating composition can be prepared by any conventional method, for example, by blending the ingredients in molten state or by formulating the ingredients into a solution and thereafter removing the solvent.

, For a better understanding of the inventlon examples for preparing linear polye~ters (A)-a, graft copolymers (A) and coatlng composltions are glven below.
<Preparation of polyester>
1. Polyester-l (PE- 1) A 3,000 g quantity of 12-hydroxystearic acid, 150 g of toluene and 5 g of meth~nesulfonic acid serving as a catalyst are placed into a 5-liter reactor equipped with a thermometer, a water separator and a stirrer, and the mixture is subjected to dehydration conden3ation at 150 C for 4 hours to prepare a polyester in the form of a viscous liquid and having an acid value of 32 and a molecular weight of about 1,750. The polyester will be hereinafter referred to as "poly~ster-l"' or "PE- 1"'.
A 1,000 g portion of the polyester- li, 140 g of glycidyl methacrylate, 0.5 g of hydroquinone and 1,000 g of toluene are placed into a 5-liter reactor equipped with a countercurrent conden~er, a thermometer and a stirrer, and the mixture is reacted at 1~0 C under reflux for 10 hour~ to ~ive a polyester (hereinafter referred to as "pclyester- 1" or "PE- 1") havin~ an acid value of 0.2 and a molecular w~i~ht of about 1,890.
2. Pol~estar- 2 (PE- 2) Exactly the came procedure as in the case of 9~i8~
polyester- 1' is followed except that the dehydration condensation is effected for 1.5 hours to obtain a polyester (hereinaf er referred to as "polyester- 2"' or "PE- 2"') in the form of a viscous liquid and having an acid value of 56 and a molecular weight of about 1, 000 ~
The polyester- 2' and the compound listed in Table 2 below in the listed amount, are reacted in the same manner as in the case of polyester- 1 to prepare a polyester (hereinafter referred to as "polyester- 2" or "PE- 2") having the properties given in the same table.
3. Polyester- 3 (PE- 3) Exactly the same procedure as in the case of polyester- 1' is followed except that the dehydration condensation is effected for 10 hours to obtain a polyester (hereinafter referred to a~ "polyester- 3 "' or "PE- 3"') in the form of a vi~cous liquid and having an acid ~alue of 20 and a moleculer weight of about 2,800 The polyester- 3~ and the compound listed in Table 2 below in the li~ted amount, are reacted in the ~ame manner a~ in the case of polyester- 1 to prepare a polye~ter (hereinafte~ referred to as "polyester- 3"
or "P~- 3") havin~ the properties given in the same t~ble.

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4. Polyester- 4 (PE~
Exac-tly the same procedure as in the case of polyester- 1' is followed except -that the dehydration condensation is effec-ted for 3 hours using 2,800 g of ricinoleic acid and 200 g of t-butylbenzoic acid in place of 3,000 g of 12-hydroxystearic acid to obtain a polyester (hereinaftèr referred to as "polyester- 4~ tl or "PE- 4"') in the form of a viscous liquid and having an acid value of 37.4 and a molecular weig~t of about 1,500.
~he polyester- 4' and the compound listed in ~able 2 below in the listed amount, are reacted in the same manner as in the case of polyester- 1 to prepare a polyester (here~inafter referred to as "polyester- 4" or "PE- 4") having the properties given in the sa~e table.

5. Polyester- 5 (PE_ 5) ~xactly the ~a~e procedure as in the case of polyester- 1' is followed except that the dehydration condensation is effected for 2 hours using 2,500 ~ of : 12-hydrox~stearic acid and 500 g of lactic acid to obtain a polyester (hereinafter referred to as "polyester-5"' or "PE- 5"') having an acid value of 80 and a molecular weight of ~bout 700.

The polyester- 5' and the compound listed in Table 2 below in the listed amount, ara reacted in the same manner as in the case of polyester- 1 to prepare a polyester (hereinafter referred to as "polye~ter- 5"
or "PE- 5") having the properties given in the same table.

6. Polye~er- 6 (PE- 6) Exactly the same procedure as in the ca~e of polyester- 1' i8 followed except that the dehydration condensation is effected for 3.5 hours using 2,500 g of 12-hydroxystearic acid and 400 g of coconut oil fatty acid to obtain a polyester (hereinafter referred to as "polyester- 6 "' or "PE- 6 "') in the form of a viscous liquid and having an acid value of 35 and a molecular weight of about 1,600.
~he poly~ter- 6' snd the compound listed in ~able 2 below in the li~ted amount, are reacted in the same manner as in the case of polyester- 1 to prepare a polyestar (hereinafter referred to as "polye~ter-6" or "PE-6") having the properties given in the ~ame table.
.7 A Pol~e~ter- 7 (PE_ 7) E~actly the same procedure as in the Case of polyester- 1' is ~ollowed except that the dehy~ration condensation is effected for 1.5 hours uqing 1,500 g of .

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12-hydrox~stearic acid and 1,500 g of lactic acid to obtain a polyes-ter (hereinafter referred to as "polyester-

7"'or "PE- 7 "') in -the form of a ~iscous liquid and havin~ an acid value of 150 and a molecular weight of about 375.
'~he polyester- 7' and the compounds listed in ~able 2 below, each in the listed amOUnt, are reac-ted in the same manner as in the case of polyester- 1 to prepare a polyester (hereinafter referred to as "polyester- 7"
or "PE- 7") having the properties given in the same table.

8. Yolyester- 8 (PE- 8) Exactly the same procedure as in the case of polyester- 1' is followed except -that the dehydration - 15 condensation is effected for 15 hours to obtain a polyester (hereinafter referred to as "polyester- 8 "' or "PE- 8"') in the form of a viscous liquid and having an acid value of 15 and a molecular wsight of about 3,740.
The pol~ester- 8' and the compound listed in ~able 2 b~low. in the li~ted amount, are reactèd in the same manner as in the ca~e of poiyester- 1 to prepare a polyeater (hereinafter referred to as "polyester- 8" or "P~- 8") having the properties ~iven in the same table.

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o ~ ~ F~ 1 ~o , <Prepar~tion of gr~f-t copol~mer>
1. Graft copolymer~l A 1,000 g quantity of toluene is placed into a 5-liter, four-necked flask equipped with a reflux condenser, a s-tirrer and a dropping funnel and is heated to reflux temperature in nitrogen atmosphere. A
mixture of 700 g of the polyester-l, 150 g of methyl methacrylate, 150 g of n-butyl methacrylate, 200 g of styrene, 150 g of glycidyl methacrylate and 30 g of azobisisobut~ronitrile placed in a dropping funnel i~
added dropwise over a period of 3 hours to the toluene maintained at the same temperature. Further at the same temperature, a mixture of ~ g of azobisisobutyro-nitrile and 30 g of ethyl acetate is added dropwise to the resulting solution three times at an interval of 1 hour. (The catalyst thus added is hereinafter referred to as an "additional ca~alyst"). After maintaining the mixture under reflux for 2 hours, the condenser i9 changed to a concurrent condenser, and the mixture is slowly heated to 150 C while permitting the solvent and unreacted monomers to run off from the flask. After about 60% of the ~olvent charged in has been drawn off, the interior of the flask is maintained at 170 C at a reduced pressure of 30 ~m Hg for 20 minutes, and then, the contents are placed into a stainless steel vat and , . . .... .

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solidified by cooling to prepare a graft copolymer-l (GP-l).
2 - 19. Graft copolymeræ- 2 to - 19.
In exactly the same manner as above, graft copolymers-2 to-19 (GP-2 to GP-19) are prepared using the specified amounts of materials li4ted in ~able 3.
Table 4 shows the compositions and properties of the graft copolymers obtained.

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<Preparation of powder coating compositions>
Powder coating compositions are prepared, using the ingredients given in Table 5 below in the listed amounts.
Compositions Nos. 1 to 5, 7 to 9 and 21 are prepared according to this invention. The other compositions areprepared for comparison.
The ingredients are kneaded with hot rolls at 110 C for 20 minutes, and -the mixture i5 solidified by cooling, roughly crushed, then pulverized and screened to obtain fine particles passing 150-mesh sieves. ~he fine powder is then electrostaticall~
applied to a 0.8-mm thick mild steel sheet treated with zinc phosphate and the coated sheet is heated at 150 C
for ~0 minutes for curing to prepare a test panel~
~he coating has a thickness of 40 ~ 5 ~.
' ;

-- .. . .... .. .. . . .. . .
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Coating compositions are tested with the results given in ~ables 6 and 7.
q`able 6 Blocking resistance Resistance No. _ 30 a 40 C to gasoline Good Good 2H > HB

Partially Blocked H B
blocked 12 " " H ~ 2B
Blocked " H 2B
17 " " HB ~ 6B

~ he r~sults indicate that whereas the composition of this invention (Composition No. 5) exhibits good blocking resistance, Compositions Nos. 10, 12, 15 and 17 ha~e very low blocking resistance because of excess polyester content (No. 10), hi~h molecular weight of polyester (No. 12), exce~dingly small molecular weight of the graft copolymer (No. 15) and exceptionally low softening point (No. 17). The latter four compositions are also inferior in resistance to gasoline.

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_ 1~2 --~ ~4g6~4~

Coatings are tested with the results given in Table 8 below.
~able 8 CompositionFlexural strength Adhesion No. _ _ 9 Good Good 22 Poor Poor __ _ _ <Test methods>
1. Blocking resistance:
~he eomposition is maintained at 40 t 0. 5 C
or 30 + 0.5 C for 7 days while being subjected to a load of 30 g/cm2 and is thereafter inspected. When found unchanged and free of blocking, the specimen is evaluated as "good".
2. Resistance to gasoline:
The test panel is immersed in gasoline ttrade mark: '!Silver Gasoline", product of Nippon Oil Co., ~td., Japan) at 20 C for 24 hours, and the immersed portion i8 thereafter tested for pencil hardness according to the methodof JIS K 5400, 6, 14. ~he result iB indicated in terms of the change from the hardness 'b~fore immersion to the hardness after immersion, for example as "2H ~ HB". The smaller the change, the better is the resi~tance to gasoline.

. . . . . . ~ , , , . . . . :' . . : ' .
: : .
,. :
' . ~

3. Specular gloss:
Determined according to JIS K 5400, 6, 7.
4. Flexural strength:
~he test panel is ben-t, coated surface up, over a 10-mm diameter round bar through an angle of 90 in 1 second, and the coating is inspected for cracking. When the coating cracks, the specimen is evaluated as "poor". The test is conducted at 20 C.
5. Adhesion:
~he test panel is immersed in boiling water for 2 hours, thén allowed to stand in air at 20 C
for 1 hour and the coating is cross-cut to the surface of the substrate. A cellophane tape is adhered to the cross-cut portion and then peeled off quickl~. If the coating i~ peeled off, the composition is evaluated as "poor", 6. Softening point:
D~terminéd according to ring-and-ball method (JIS K 251~).
7. Impact resistance:
After lea~ing a coated plate to qtand in a 'constant temperature and constant humidity chamber at a temperature Or 20 + 1 D C and a humidity Or 75%
for 1 hour, th2 following te~t i8 conducted in the same chamber. A bearer and a center of impact of prescribed _ l~4 -96~L
size~ (1/2 inch in diame-ter) sre fitted to a Du Pont impsct tester and the plate is put between them, turning the coated surface of the plate upward. The preqcribed weight (500 g) is dropped on the center of impact from the prescribed height and the plate i9 -taken out, and after having been left for an hour in the room, the damage of surface is observed. ~he largest height ~cm) of -the weight entailing no cracking in the coating is determined.
8. Erichsen test:
The coated plate is placed in a constant temperature and humidity chamber kept at 20 C and a humidity of 75~/0 for one hour. Thereafter, the plate i5 set on Erichsen test~ng machine with the coating po~itioned outside. A punch having a radius of 10 mm is pu~hed outward predctermined distances in contact wibh the rear face of the plate at as uniform speed as possible of about 0.1 mm/sec~ ~he pushed out portion of the plate is checked by the naked eye for cracking or peeling immediately after pushing out to determine ths maximum distance (mm) of stroke of the punch causing ,no changes on the coatingO
9. Surfàce smoth~ess:
Determin~d wibh the n~ked e~

'

Claims (12)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
FOLLOWS:

1. A thermosetting powder coating composition which comprises:
(A) a graft copolymer of a) 10 to 40 percent by weight of a linear polyester having a number average molecular weight of 600 to 3,000 and containing one ethylenically unsaturated double bond only at one end of the molecule, b) 5 to 30 percent by weight of at least one of glycidyl esters having the formula wherein R1 is hydrogen or methyl, and c) 10 to 85 percent by weight of at least one of acrylic compounds having the formula wherein R2 is hydrogen or methyl and R3 is alkyl having 1 to 14 carbon atoms, cyclohexyl or hydroxyalkyl represented by wherein R4 is hydrogen or alkyl having 1 to 2 carbon atoms, said graft copolymer having a softening point of 70 to 110° C and a number average molecular weight of 2,000 to 30,000; and (B) at least one of polycarboxylic acids and anhydrides thereof in an amount of 0.6 to 1.2 moles in terms of carboxyl group per mole of the glycidyl group contained in the graft copolymer.

2. The thermosetting powder coating composition according to claim 1, in which said linear polyester has a number average molecular weight of 1,000 to 2,000.

3. The thermosetting powder coating composition according to claim 1, in which said glycidyl ester is glycidyl acrylate.

4. The thermosetting powder coating composition according to claim 1, in which said glycidyl ester is glycidyl methacrylate.

5. The thermosetting powder coating composition according to claim 1, in which said acrylic compound has the formula wherein R2 is hydrogen or methyl and R3 is alkyl having 1 to 14 carbon atoms.

6. The thermosetting powder coating composition according to claim 1, in which said acrylic compound has the formula wherein R2 is hydrogen or methyl and R3 is cyclohexyl.

7. The thermosetting powder coating composition according to claim 1, in which said acrylic compound has the formula wherein R2 is hydrogen or methyl and R3 is hydroxyalkyl represented by wherein R4 hydrogen or alkyl having 1 to 2 carbon atoms.

8. The thermosetting powder coating composition according to claim 1, in which said graft copolymer has a number average molecular weight of 4,000 to 20,000.

9. The thermosetting powder coating composition according to claim 1, in which said graft copolymer contains the linear polyester in the range of 15 to 30 percent by weight.

10. The thermosetting powder coating composition according to claim 1,in which said graft copolymer contains the glycidyl ester in the range of 10 to 25 percent by weight.

11. The thermosetting powder coating composition according to claim 1, in which said graft copolymer further contains in an amount of up to 40 percent by weight of at least one compound selected from the group consisting of acrylonitrile, methacrylonitrile and styrenes represented by the formula wherein R6 is hydrogen or alkyl having 1 to 4 carbon atoms.

12. The thermosetting powder coating composition according to claim 11, in which said compound is contained in an amount of 5 to 30 percent by weight.