JPH0655921B2 - Paint composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a coating composition containing a fluorine-containing polymer having a hydroxyl group, which gives a coating film having excellent weather resistance.

[Prior Art] A coating composition containing a solvent-soluble hydroxyl group-containing fluoropolymer as an essential component is known as a coating composition which gives a coating film having excellent weather resistance. For example, JP-A-57-34107
JP-A-59-189108, JP-A-60-67518 and the like describe solvent-soluble hydroxyl group-containing fluoropolymers which are essential components of coating compositions. This hydroxyl group-containing fluoropolymer has a polyfluoroolefin monomer and a hydroxyl group-containing vinyl ether monomer as essential monomers, and optionally a vinyl ether monomer containing no hydroxyl group (which may be a fluorine-containing vinyl ether monomer) or a monomer containing another monomer. It is a copolymer obtained by copolymerizing a mixture. A coating composition containing a hydroxyl group-containing fluoropolymer requires a curing agent for the hydroxyl group-containing fluoropolymer. A polyisocyanate compound is used as one of the curing agents as described in the above-mentioned known examples.
The polyisocyanate compound may optionally be blocked with a blocking agent. The blocking agent is for temporarily protecting the isocyanate group, and when the coating composition is cured, the block is removed to generate an isocyanate group.
The polyisocyanate compound reacts with the hydroxyl groups of the fluorine-containing polymer containing hydroxyl groups and crosslinks them to cure them.

[Problems to be Solved by the Invention] As described in the above-mentioned known examples, a polyisocyanate compound which is a curing agent for a hydroxyl group-containing fluoropolymer is a general-purpose curing agent for a hydroxyl group-containing polymer for paints. A certain polyisocyanate compound was diverted as it was. However, whether or not such a polyisocyanate compound is suitable as a curing agent for a hydroxyl group-containing fluoropolymer has not been sufficiently studied, and according to the study of the present inventor, it is as follows. It has been found that it has problems and is not necessarily the most suitable curing agent for a fluorine-containing polymer having a hydroxyl group.

The first problem is that the compatibility between the hydroxyl group-containing fluorine-containing polymer and the polyisocyanate compound is low. A compound having a certain degree of compatibility can be used depending on the selection of the polyisocyanate compound, but the types thereof are limited and sufficient compatibility is not always obtained. Therefore, the problems such as whitening of the clear coating film and reduction of the gloss of the colored coating film occur, and the properties such as the elongation and hardness of the coating film and the adhesion of the coating film are limited due to the limited kinds of polyisocyanate compounds that can be used. The range of hardener choices for improvement is narrowed.

The second problem is that the characteristic feature of using a hydroxyl group-containing fluoropolymer as a coating polymer is easily restricted by the polyisocyanate compound. The characteristics of the coating material using the fluorine-containing polymer having a hydroxyl group are extremely high weather resistance. However, the polyisocyanate compound is liable to be a cause of deteriorating these characteristics which the hydroxyl group-containing fluoropolymer should have. That is, the polyisocyanate compound itself has insufficient weather resistance as compared with the hydroxyl group-containing fluoropolymer, and when it is used in a considerable amount, it tends to be a major cause of lowering the weather resistance of the coating film.

[Means for Solving Problems] As a result of various studies on polyisocyanate compounds in order to solve the above problems, the present inventor has not hitherto been known as a curing agent for a hydroxyl group-containing fluoropolymer. It has come to find a polyisocyanate compound. This polyisocyanate compound is a polymer having two or more isocyanate groups. This isocyanate group-containing polymer has higher compatibility with the hydroxyl group-containing fluoropolymer as compared with the conventional polyisocyanate compound having a low molecular weight, and therefore the above-mentioned first problem is solved. Further, the isocyanate group-containing polymer usually has a high weather resistance, and in particular, the homo- or copolymer of a (meth) acrylic acid-based monomer having an isocyanate group described below has a high weather resistance, and itself has a hydroxyl group-containing fluorine-containing polymer. Although it does not reach the weather resistance of the coalesced product, by using it as a curing agent for the fluorine-containing polymer having a hydroxyl group, higher weather resistance is exhibited than that using conventional curing agents. Therefore, the use of the isocyanate group-containing polymer as the curing agent also solves the second problem described above.

The present invention is a coating composition containing this isocyanate group-containing polymer as a curing agent for a hydroxyl group-containing fluoropolymer, that is, a polyfluoroolefin monomer / a hydroxyl group-containing copolymerizable monomer / a hydroxyl group-free copolymerizable monomer. 30 to
100 parts by weight of a hydroxyl group-containing fluoropolymer obtained by copolymerization at a copolymerization ratio (mol%) of 70/1 to 45/0 to 69, and a homopolymer or copolymer of an isocyanate alkyl group-containing (meth) acrylate ( Number average molecular weight 400 to 40,
000) 3 to 100 parts by weight of a coating composition.

In the present invention, the isocyanate group of the isocyanate group-containing polymer may be an isocyanate group which is temporarily blocked with a blocking agent as described above. The isocyanate group-containing polymer may be a homopolymer or a copolymer of one or more kinds of isocyanate group-containing vinyl monomers, and is a copolymer of one or more kinds of them with a copolymerizable monomer having no isocyanate group. It may be. Preferred is a homopolymer or copolymer of an isocyanate group-containing vinyl monomer.

Isocyanate group-containing polymers consisting of homo- or copolymers of isocyanate-containing vinyl monomers are known,
For example, JP-A-56-118409 and JP-A-59-227910.
JP, JP-A-60-6712, U.S. Pat.No. 2718516, U.S. Pat.No. 4,222,909, U.S. Pat.
6885, etc. Specifically, isocyanate group-containing vinyl monomers such as isocyanate alkyl acrylate, isocyanate alkyl methacrylate, and isopropenyl-α, α-dimethylbenzyl isocyanate, and homopolymers or copolymers thereof are described. Preferred isocyanate group-containing vinyl monomer has an isocyanate alkyl group having 2 to 6 carbon atoms (excluding carbon atoms of the isocyanate group) such as isocyanate ethyl (meth) acrylate, isocyanate butyl (meth) acrylate, and isocyanate hexyl (meth) acrylate. (Meth) acrylate, and among them, 2-isocyanate ethyl methacrylate (hereinafter I
(Referred to as EM) is most preferable because the polymer has particularly good compatibility with the fluorine-containing polymer having a hydroxyl group.

Examples of the copolymerizable monomer that can be copolymerized with the isocyanate group-containing vinyl monomer include alkyl (meth) acrylate, cycloalkyl (meth) acrylate, acrylic monomers such as acrylonitrile, styrene and α-
There are styrene-based monomers such as methylstyrene, vinyl ester-based monomers such as vinyl acetate, olefin-based monomers such as ethylene and propylene, diene-based monomers such as butadiene, and halogenated vinyl-based monomers such as vinyl chloride. Alkyl (meth) acrylate and styrene are preferable as the copolymerizable monomer, and from the viewpoint of weather resistance, an alkyl (meth) acrylate having an alkyl group having 1 to 10 carbon atoms is particularly preferable. Of course, two or more kinds of these copolymerizable monomers can be used in combination. Polymerization of the isocyanate group-containing vinyl monomer or the copolymerizable monomer is carried out by the method described in the above-mentioned known examples. Usually, it is preferable that the polymerization is carried out in a solvent in the presence of a polymerization initiator, and the polymerization is carried out in the presence of a chain transfer agent such as mercaptan.

The number average molecular weight of the isocyanate group-containing polymer is 400-4
It is preferably 0,000, and particularly preferably 1,000 to 10,000. The number average molecular weight per isocyanate group is preferably 140 to 10,000, particularly 150
It is preferably about 1,000. Also, the average number of isocyanate groups per molecule must be at least 2, preferably 3 to 100, and particularly 4 to 40.
Individuals are preferred. For example, the homopolymer of IEM has a number average molecular weight of 155 per isocyanate group, a number average molecular weight of 620 or more, and 4 or more isocyanate groups per molecule. Further, in the copolymer of IEM and the copolymerizable monomer, the higher the molar ratio of the copolymerizable monomer, the smaller the number of isocyanate groups per molecule. Even in the case of an IEM homopolymer, the number average molecular weight per isocyanate group is usually higher than 155, because residues of the polymerization initiator and residues of the chain transfer agent are usually present.

As the hydroxyl group-containing fluorine-containing polymer, as described above, a monomer that essentially contains a polyfluoroolefin, a monomer and a hydroxyl group-containing vinyl ether monomer, and preferably a vinyl ether monomer that does not further contain a hydroxyl group is used. A polymer obtained by copolymerizing a monomer as a main component is used. Each of these two to three kinds of monomers may be composed of two or more monomers.
As the polyfluoroolefin monomer, tetrafluoroethylene, chlorotrifluoroethylene, vinylidene fluoride, hexafluoropropylene and the like having 2 to 2 carbon atoms
Polyfluoroolefins of 3 are suitable, with tetrafluoroethylene and chlorotrifluoroethylene being particularly preferred. As the hydroxyl group-containing vinyl ether monomer, a hydroxyalkyl vinyl ether is suitable, and a vinyl ether having an ω-hydroxyalkyl group having 3 to 8 carbon atoms is particularly preferable. Specifically, hydroxypropyl vinyl ether, hydroxybutyl vinyl ether, hydroxyisopropyl vinyl ether, hydroxy-2
-Methylbutyl vinyl ether, etc. A particularly preferred hydroxyl group-containing vinyl ether monomer is 4-hydroxy-n-butyl vinyl ether.

The hydroxyl group-containing fluoropolymer can be obtained from two kinds of monomers of the above-mentioned polyfluoroolefin monomer and hydroxyl group-containing vinyl ether monomer, but it is preferably further copolymerized with another copolymerizable monomer. As the copolymerizable monomer, vinyl ether having no hydroxyl group is particularly preferable, but it is not limited thereto. The vinyl ether monomer having no hydroxyl group may also be a vinyl ether having a fluorine atom. Examples of these vinyl ethers include linear, branched, or cyclic vinyl ethers having an alkyl group which may have a fluorine atom, such as alkyl vinyl ethers, cycloalkyl vinyl ethers, and poly (or mono) fluoroalkyl vinyl ethers. Preferred compounds have 1 to 1 carbon atoms
0, in particular, a vinyl ether having a linear or branched alkyl group of 2 to 6, a cycloalkyl vinyl ether which may have a side chain of 6 to 10 carbon atoms, and a carbon number of 3 to 3 having a fluorine atom of 2 or more. 6 is a polyfluoroalkyl vinyl ether. Specific examples include ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, hexyl vinyl ether, cyclohexyl vinyl ether, and 2,2,3,3-tetrafluoropropyl vinyl ether. Further, a polyfunctional vinyl ether such as divinyl ether can be used together with or instead of these vinyl ethers. Particularly preferred vinyl ether monomers having no hydroxyl group are ethyl vinyl ether, butyl vinyl ether and cyclohexyl vinyl ether. Incidentally, a copolymerizable monomer other than vinyl ether can be used instead of or together with these vinyl ether monomers having no hydroxyl group. For example, alkyl (meth) acrylate, olefin, and other copolymerizable monomers can be used. However, the use of a copolymerizable monomer other than vinyl ether often deteriorates properties such as solubility of the hydroxyl group-containing fluorocopolymer, and therefore, even if used, it is a small amount (for example, 5 mol% or less of all monomers). It is preferable and usually not used substantially.

Copolymerization ratio of polyfluoroolefin monomer / hydroxyl group-containing vinyl ether monomer / copolymerizable monomer is mol%
Is preferably 30/70/1 to 45/0 to 69. In particular, 40-60 / 3-40 / 5-57 is preferable, and among them, 40-60 / 5-30 / 10-55 is most preferable. The polymerization method and the like are preferably performed by the method described in the above publication. The obtained hydroxyl group-containing fluoropolymer is usually soluble in a solvent. This polymer in tetrahydrofuran
The intrinsic viscosity measured at 30 ° C. is preferably in the range of 0.05 to 2.0 dl / g.

The coating composition of the present invention essentially comprises two components, the above-mentioned isocyanate group-containing polymer and hydroxyl group-containing fluoropolymer. This composition is usually used after being dissolved in a solvent, and if necessary, various additives for paints are added. The compounding amount of the isocyanate group-containing polymer with respect to the hydroxyl group-containing fluoropolymer depends on the type of the hydroxyl group-containing fluoropolymer (especially the type based on the difference in the hydroxyl group content) and the type of the isocyanate group-containing polymer (especially the isocyanate group content). However, the number is not particularly limited. However, usually 3 to 100 parts by weight of the fluorine-containing polymer containing a hydroxyl group is added to the polymer containing an isocyanate group.
100 parts by weight, especially 5 to 60 parts by weight are used. For applications that require particularly high weather resistance, the amount used should be 5-40.
Parts by weight are preferred. The number of isocyanate groups in the isocyanate group-containing polymer per hydroxyl group in the hydroxyl group-containing fluoropolymer is preferably 0.1 to 2, particularly 0.3 to 1.2, but not limited to this.

As the solvent, various solvents capable of dissolving the above two components are used. However, a solvent that does not have a functional group that reacts with a hydroxyl group or an isocyanate group is used. For example, aromatic hydrocarbons such as xylene and toluene, esters such as butyl acetate, ketones such as methyl isobutyl ketone, and glycol ethers such as ethyl cellosolve can be used. In many cases, a urethanization catalyst is essential as an additive. As this catalyst, various known catalysts such as organometallic compounds and tertiary amines can be used, and organotin compounds such as dibutyltin dilaurate are particularly preferred. In addition, various additives can be optionally mixed, for example, pigments, fillers, dispersion stabilizers, viscosity modifiers, leveling agents, gelation inhibitors, ultraviolet absorbers, light stabilizers, moisture absorbers and the like. You can. In some cases, a modifier capable of reacting with a hydroxyl group or an isocyanate group may be further added. For example, in order to obtain a flexible coating film, an isocyanate group-containing polymer having a high molecular weight per isocyanate group can be used, but instead, a polyol having a relatively high molecular weight per hydroxyl group is blended and coated. The flexibility of the membrane can be increased.

By using an isocyanate group-containing polymer that is not blocked, that is, has a free isocyanate group, a two-component type room temperature curable coating material can be obtained. Further, by using an isocyanate group-containing polymer having a blocked isocyanate group, it is possible to obtain a heat-curable one-pack type coating material. As the blocking agent, known compounds can be used, for example, phenols, ketoxime, lactams, bisulfites and the like can be used.

The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples.
First, the types of raw materials used and the synthetic method will be described below.

Hydroxyl Group-Containing Fluorine-Containing Polymer According to the method described in JP-A-57-34107, polymers A-1 and A-2 having monomer composition ratios shown in Table 1 below are used.
Was manufactured. The number average molecular weight and the like are shown in Table 1. In addition,
The monomer composition ratio (mol%) of (CTFE / HBVE / CHVE / EVE) is (49.5 / 10.1 / 1) for A-1.
5.2 / 25.2), A-2 is (49.5 / 20.1 /
15.0 / 15.4).

Isocyanate Group-Containing Polymer A monomer having a monomer composition ratio shown in Table 2 below was mixed in ethyl acetate at 80 to 100 ° C. in the presence of a polymerization initiator (azobisisobutyronitrile) and a chain transfer agent (1-dodecanethiol). The reaction was carried out for ~ 6 hours to obtain the following isocyanate group-containing polymers B-1 to B-5. The number average molecular weight (Mn) and the number average molecular weight per isocyanate group (Mn / NCO) are shown in Table 2.

[Example] In a solution (solvent: xylene) of the hydroxyl group-containing fluoropolymers A-1 and A-2, 3 × 10 ^-3 parts by weight of dibutyltin dilaurate and the isocyanate were added per 100 parts by weight of the hydroxyl group-containing fluoropolymer. A solution of the group-containing polymers B-1 to B-5 in ethyl acetate was mixed with an isocyanate group-containing polymer in the following third amount.
It was added at a ratio to be the addition amount shown in the table. The coating composition was applied on an aluminum plate, dried at room temperature for 7 days, and then the weather resistance of the coating film was tested with a sunshine weatherometer. The test results are shown in Table 4.

As a comparison, the same test was conducted using a general-purpose polyisocyanate compound-based curing agent instead of the isocyanate group-containing polymer. The mixing ratio is shown in Table 3, and the weather resistance test result is shown in Table 4. The polyisocyanate compounds used for comparison are the following C-1 and C-2.

C-1: trimerized modified hexamethylene diisocyanate (“Coronate EH”) C-2: modified hexamethylene diisocyanate (trade name “Desmodur N”) [Effects of the Invention] The present invention has the effect of further improving the weather resistance of a coating film obtained from a solvent-soluble hydroxyl group-containing fluoropolymer-containing coating composition, as shown in the examples. By appropriately selecting a copolymerizable monomer to be copolymerized with the isocyanate group-containing vinyl monomer, it is also recognized that the hardness, flexibility, and dryness of the coating film can be adjusted as desired.

Claims (1)

[Claims] 1. A copolymer of polyfluoroolefin monomer / hydroxyl group-containing copolymerizable monomer / hydroxyl-free copolymerizable monomer at a copolymerization ratio (mol%) of 30 to 70/1 to 45/0 to 69. A coating composition containing 100 parts by weight of the resulting fluorine-containing polymer containing a hydroxyl group and 3 to 100 parts by weight of a homo- or copolymer of an isocyanate alkyl group-containing (meth) acrylate (a number average molecular weight of 400 to 40,000).