Siloxane release agents for the production of derived timber...

Details Siloxane release agents for the production of derived timber... Siloxane release agents for the production of derived timber...

2002-01-17

2004-05-04

Peng, Kuo-Liang (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C264S338000, C264S299000, C427S387000, C156S331400, C156S331700, C525S480000, C525S452000, C525S540000, C428S447000, C428S450000, C428S537100, C524S837000, C528S031000, C528S032000, C528S012000

Reexamination Certificate

active

06730723

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a process for producing derived timber products by hot pressing lignocellulose-containing materials bonded with binder in which a mixture of organosilicon compounds is applied to the surface of the pressing tool facing the material to be pressed.
In the production of derived timber products by hot pressing lignocellulose-containing materials with a binder, polyisocyanates, especially polymeric diphenylmethane diisocyanate (pMDI), are used as the binder mainly in the middle layer. If pMDI is used in the outer layer, problems occur when separating the derived timber product from the pressing tool, or a troublesome layer of residues of release agent and derived timber product builds up on the surfaces of the pressing tool, especially when working at relatively high pressing temperatures (EP-A 634 433, EP-A 1 038 898).
There was therefore a need for a release agent suitable for pMDI-containing binder systems that exhibits an adequate release action at relatively high pressing temperatures, and that causes only minor residues of release agent and/or derived timber product on the pressing tool surface even over relatively long production times.
SUMMARY OF THE INVENTION
It has now been found that a release layer which is effective at pressing temperatures and leaves only a minor residue on the pressing tool and timber product can be produced by curing a mixture of organosilicon compounds satisfying the requirements specified herein, without an additional curing catalyst, at pressing temperatures of from 150° C. to 240° C. on the surface(s) of the pressing plate(s) or pressing belt(s) facing the material to be pressed.
DETAILED DESCRIPTION OF THE INVENTION
The mixture of organosilicon compounds used in the process of the present invention as the release layer includes:
a) at least one organopolysiloxane having at least 2 unsaturated hydrocarbon groups A),
b) at least one methyl hydrogen polysiloxane B),
c) at least one non-reactive organopolysiloxane C),
d) optionally, an inhibitor D),
e) optionally, an emulsifier and/or thickener E),
f) optionally, additives and/or auxiliary substances F), and
g) water as diluent.
Similar mixtures containing a catalyst which includes an element of the platinum group, have been proposed in EP-A 819 735 for the coating of baking papers.
Aqueous emulsions which include organopolysiloxane A), methyl hydrogen polysiloxane B), organopolysiloxane C), inhibitor D), an emulsifier and/or thickener E) are particularly preferred release compositions for the process of the present invention. Additional components F) may be added to components A), B) and/or C) before the emulsification or subsequent to the emulsification. Suitable apparatus for achieving an adequate particle size for the stability of the emulsion are known. Examples of such apparatus include high-pressure homogenizers, colloid mills and the like.
The release agents useful in the practice of the present invention can also be used in mixed binder systems (mixed bonding) composed of pMDI and an aqueous solution of condensation products of formaldehyde with urea and/or melamine and/or phenol which have predominantly been used in the derived timber products industry. A mixing ratio of from 1:10 to 10:1, preferably from 1:5 to 5:1, can be maintained without the release action of the release system being impaired.
The organopolysiloxane having at least 2 unsaturated hydrocarbon groups A) within the scope of the invention is preferably a cyclic, linear or branched polysiloxane containing units of the general formula
(R)
a
(R
1
)
b
SiO
(4−a−b)/2
  (I)
in which
R=a C
2
-C
8
-alkenyl and/or unsaturated C
3
-C
10
-ether radical, such as vinyl, allyl, 1-butenyl, 1-hexenyl and/or —CH
2
—CH
2
CH
2
OCH
2
CH═CH
2
, etc., preferably vinyl or allyl, most preferably vinyl;
R
1
=a monovalent, saturated, optionally substituted hydrocarbon radical having up to 10 carbon atoms selected from the group of substituted and unsubstituted alkyl, aryl and arylalkyl radicals,
a is an integer within the following limits: 0≦a≦3,
b is an integer within the following limits: 0≦b≦3, and
0≦a+b≦4 and each individual R or R
1
within the molecule may be identical or different.
Examples of R
1
include: methyl, ethyl, propyl, isopropyl, butyl, octyl, etc., cyclobutyl, cyclopentyl, cyclohexyl, etc., phenyl, tolyl, xylyl, naphthyl, etc., benzyl, phenylethyl, and phenylpropyl groups. In one embodiment of the invention, some or all of the hydrogen atoms of the alkyl, aryl and arylalkyl radicals R
1
are substituted by fluorine and/or chlorine, bromine, or iodine atoms and/or cyano radicals. In this embodiment, R
1
corresponds, for example, to chloromethyl, trifluoropropyl, chlorophenyl, dibromophenyl, &bgr;-cyanoethyl, &bgr;-cyanopropyl or &ggr;-cyanopropyl radicals. At least 90% of the radicals R
1
are preferably methyl, however.
In a preferred embodiment of the invention, a is 0 or 1.
Using the nomenclature known to the person skilled in the art,
where
M=(CH
3
)
3
SiO
1/2
,
D=(CH
3
)
2
SiO
2/2
,
T=(CH
3
)SiO
3/2
,
M
Vi
=(CH
2
═CH)(CH
3
)
2
SiO
1/2
and
D
Vi
=(CH
2
═CH)(CH
3
)SiO
2/2
,
the following may be given as examples of component A): M
2
D
100
D
Vi
3
, M
Vi
2
D
180
, M
Vi
MD
100
D
Vi
3
, T
5
D
550
M
Vi
7
, T
3
D
500
M
Vi
2
M
3
and/or T
6
D
300
D
Vi
M
4
M
Vi
4
.
The molar amount of unsaturated radicals of type R can be chosen as desired.
In component A), the molar amount of unsaturated radicals of type R should be preferably from 0.01 to 10 mmol./g, more preferably from 0.05 to 1 mmol./g and most preferably from 0.1 to 0.7 mmol./g of component A). The viscosity of component A) at 25° C. is preferably from 10 to 100,000 mPa·s, more preferably from 50 to 10,000 mPa·s.
In a preferred embodiment of the invention, component A) is any of the organopolysiloxanes described in DE-A 43 28 657. Since these polysiloxanes are branched, the ratio of the number of diorganosiloxy units (D units) to the number of branching points is on average from 15 to 40, at least one triorganosiloxy unit (M unit) and not more than half of all M units are free of unsaturated radicals. The remaining M units each carry only one unsaturated radical, and the content of unsaturated radicals is from 0.1 to 1 mmol./g.
The branching points of component A) are preferably monoorganosiloxy units, that is to say trifunctional siloxy units (T units), some of which may, however, also be replaced by tetrafunctional siloxy units (SiO
4/2
units, Q units).
The terminal groups, free of unsaturated radicals, of the branched organopolysiloxane act as an internal plasticizer. The flexibility of the crosslinked film can be controlled via the number of terminal groups (M units) that are free of unsaturated radicals.
Examples of the preferred component A) are compounds of the formulae T
5
D
200
M
Vi
5
M
2
, T
7
D
280
M
Vi
5
M
4
, T
6
D
180
D
Vi
2
M
Vi
4
M
4
and/or T
8
D
250
M
Vi
7
M
3
.
Branched organopolysiloxanes having at least 2 unsaturated hydrocarbon groups A) can be prepared by conventional processes, such as, for example, by hydrolysis of chlorosilanes and subsequent polymerization with low molecular weight cyclic diorganopolysiloxanes.
The methyl hydrogen polysiloxane B) preferably contains units corresponding to the general formula
H
c
(R
2
)
d
SiO
(4−c−d)/2
  (II)
in which
R
2
=a monovalent, saturated, optionally substituted, hydrocarbon radical having up to 10 carbon atoms selected from the group of substituted and unsubstituted alkyl, aryl, arylalkyl and/or C
2
-C
8
-alkenyl radicals,
c is an integer 0≦c≦3, preferably 0≦c≦1 and
d is an integer 0≦d≦2,
provided that 0≦c+d≦4.
The methyl hydrogen polysiloxanes B) are preferably linear. At least half of the D units preferably have hydrogen atoms bonded directly to silicon (H(CH
3
)SiO groups). The number of groups having hydrogen atoms bonded directly to silicon is preferably from 70 to 85% of the difu

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