Stabilization of wood substrates

Details Stabilization of wood substrates Stabilization of wood substrates

1999-03-11

2001-02-13

Beck, Shrive (Department: 1762)

Coating processes

Applying superposed diverse coating or coating a coated base

Synthetic resin coating

C427S160000, C427S393000

Reexamination Certificate

active

06187387

ABSTRACT:

The invention relates to a method of stabilizing wood with a sterically hindered amine N-oxyl or N-hydroxyl against damage by heat and light and to the use of a sterically hindered amine N-oxyl or N-hydroxyl for the stabilization of wood.
Surfaces of wood which are exposed to intense sunlight are damaged primarily by the UV component of sunlight. This process is even enhanced by heat due to the absorbed infrared radiation from the sun. The polymeric constituents of the wood are degraded, leading to a roughening and discoloration of the surface. Subsequently, further damage results from infestation by microorganisms, especially by fungi.
The usual method of protecting wood against damage by light without giving up the visual image of the wood surface is to coat it with a colourless varnish containing a light stabilizer, in particular a UV absorber.
The addition of phenolic antioxidants to wood varnishes is also known. For example, U.S. Pat. No. 3,285,855 discloses the color stabilization of furniture varnishes based on acid-curable urea/formaldehyde alkyd resins by adding 0.2% by weight of a phenolic antioxidant. Wood protective coatings which contain a UV absorber, an antioxidant and an insecticide are disclosed for example in JP-A-59/115 805.
EP-A-0 479 075 discloses sterically hindered amine stabilizers for wood stains which are substituted at the Nitrogen atom by hydrogen, alkyl, allyl, hydroxymethyl, hydroxyethyl, acyl, benzoyl or benzyl.
It has now been found that sterically hindered amine N-oxyls or N-hydroxyls have a marked stabilizing activity against light-induced degradation if they are applied in a stain or impregnation which penetrates the wood. The wood may then additionally provided with a top coat, which top coat may contain other conventional light stabilizers.
The present invention provides superior weatherability to wood substrates as compared to prior art techniques. It is for example possible to leave it without additional coating or to apply only a very thin or transparent coating to the thus impregnated wood. This is in many cases desirable for aesthetical reasons.
Wood is a complex polymeric material containing essentially cellulose, hemicellulose and lignin. Lignin itself is a complex mixture of high molecular weight products which are derived from conyferyl alcohol.
Particularly lignin causes discoloration and undergoes degradation upon exposure to actinic radiation. It is therefore also an object of the present invention to prevent the photochemical degradation of the lignin part of wood. In addition, preventing lignin breakdown may remove a source of nutrition for fungi and thus reduce or prevent fungal attack. Therefore reduced amounts or essentially no biocides may be used in some cases.
Accordingly, the invention relates to a method of protecting wood against light-induced degradation by treatment with
a stain or impregnation which penetrates the surface of the wood comprising
a) at least one organic solvent and
b) a hindered amine compound of formula I or II
 where
G
1
and G
2
are independently alkyl of 1 to 4 carbon atoms or are together pentamethylene,
Z
1
and Z
2
are each methyl, or Z
1
and Z
2
together form a linking moiety which may additionally be substituted by an ester, ether, hydroxy, oxo, cyanohydrin, amide, amino, carboxy or urethane group,
E is oxyl or hydroxyl,
X is an inorganic or organic anion, and
where the total charge of cations h is equal to the total charge of anions j.
Preferred is a method where in the compound of component (b), E is oxyl or hydroxyl; and Z
1
and Z
2
are each methyl or together are a hydrocarbon linking moiety containing 1-200 carbon atoms and 0-60 heteroatoms selected from oxygen atoms and nitrogen atoms.
Examples for X include X as phosphate, carbonate, bicarbonate, nitrate, chloride, bromide, bisulfite, sulfite, bisulfate, sulfate, borate, carboxylate, an alkylsulfonate or an arylsulfonate, or a phosphonate, like, for example, diethylenetriaminepentamethylenephosphonate. X as carboxylate especially is a carboxylate of a mono-, di-, tri- or tetracarboxylic acid, mainly of 1-18 carbon atoms, such as a formate, acetate, benzoate, citrate, oxalate, tartrate, acrylate, polyacrylate, fumarate, maleate, itaconate, glycolate, gluconate, malate, mandelate, tiglate, ascorbate, polymethacrylate, or of nitrilotriacetic acid, hydroxyethylethylenediaminetriacetic acid, ethylenediaminetetraacetic acid or diethylenetriaminepentaacetic acid.
Also preferred is a method where in the compound of component (b), X is phosphate, carbonate, bicarbonate, nitrate, chloride, bromide, bisulfite, sulfite, bisulfate, sulfate, borate, carboxylate, an alkylsulfonate or an arylsulfonate, or a phosphonate.
Most preferably, X is chloride, bisulfite, bisulfate, sulfate, phosphate, nitrate, ascorbate, acetate, citrate or carboxylate of ethylenediaminetetraacetic acid or of diethylenetriaminepentaacetic acid; most especially wherein X is bisulfate or citrate.
h and j are preferably from the range 1-5.
Preferably, Z
1
and Z
2
as a linking moiety are a chain of 2 or 3 carbon atoms or 1 or 2 carbon atoms and a nitrogen or oxygen atom forming together with the remaining structure in formula I or II a saturated 5- or 6-membered heterocyclic ring, which may be substituted as mentioned. The substituents in Z
1
and Z
2
themselves may contain hindered amine moieties. Preferred are compounds of the formula I or II containing 1-4, especially 1 or 2 hindered amine or hindered ammonium moieties. Preferably, Z
1
and Z
2
as a linking moiety is a hydrocarbon containing 1-200, especially 1-60 carbon atoms and 0-60, especially 0-30 heteroatoms selected from oxygen atoms and nitrogen atoms.
Any group denoted as aryl mainly means C
6
-C
12
aryl, preferably phenyl or naphthyl, especially phenyl.
The compounds of component (b) of the invention can be pure or mixtures of compounds.
Groups denoted as alkyl are, within the definitions given, mainly C
1
-C
18
alkyl, for example methyl, ethyl, propyl such as n- or isopropyl, butyl such as n-, iso-, sec- and tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl or octadecyl.
Groups denoted as alkylene are, within the definitions given, for example methylene, 1,2-ethylene, 1,1-ethylene, 1,3-propylene, 1,2-propylene, 1,1-propylene, 2,2-propylene, 1,4-butylene, 1,3-butylene, 1,2-butylene, 1,1-butylene, 2,2-butylene, 2,3-butylene, or —C
5
H
10
—, —C
6
H
12
—, C
7
H
14
, —C
8
H
16
—, —C
9
H
18
—, —C
10
H
20
—, —C
11
H
22
—, —C
12
H
24
—, —C
13
H
26
—, —C
14
H
28
—, —C
15
H
30
—, —C
16
H
32
—, —C
17
H
34
—, —C
18
H
36
—.
Groups denoted as cycloalkyl or cycloalkoxy are mainly C
5
-C
12
cycloalkyl or C
5
-C
12
cycloalkoxy, the cycloalkyl part being, for example, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cycloundecyl or cyclododecyl. Cycloalkenyl is mainly C
5
-C
12
cycloalkenyl including cyclopentenyl, cyclohexenyl, cycloheptenyl, cyclooctenyl, cyclononenyl, cyclodecenyl, cycloundecenyl, cyclododecenyl.
Aralkyl or aralkoxy is preferably phenylalkyl or phenylalkoxy, which is alkyl or alkoxy substituted by phenyl. Examples for phenylalkyl or phenylalkoxy are, within the definitions given, benzyl, benzyloxy, a-methylbenzyl, a-methylbenzyloxy, cumyl, cumyloxy.
Residues alkenyl are mainly alkenyl of 2 to 18 carbon atoms, most preferably allyl.
Residues alkynyl are mainly alkynyl of 2 to 12 carbon atoms, preferred is propargyl.
A group denoted as acyl is mainly R(C═O)—, where R is an aliphatic or aromatic moiety.
An aliphatic or aromatic moiety, such as mentioned above or in other definitions, mainly is an aliphatic or aromatic C
1
-C
30
hydrocarbon; examples are aryl, alkyl, cycloalkyl, alkenyl, cycloalkenyl, bicycloalkyl, bicycloalkenyl, and combinations of these groups.
Examples for acyl groups are alkanoyl of 2 to 12 carbon atoms, alkenoyl of 3 to 12 carbon atoms, benzoyl.
Alkanoyl embraces, for example, formyl, acetyl, propionyl, butyryl, pentanoyl, octanoyl; preferred is C
2
-C
8
alkanoyl, especi

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