Cover layer material on a basis of matting or fabric

The invention relates to a cover layer material on a basis of matting or fabric for the production of boards made of fluid or fluid-containing starting components and provided with cover layers, especially for the production of gypsum boards and polyurethane (PU) hard foam boards and their use in a continuous board producing apparatus.

BACKGROUND OF THE INVENTION AND THE INVENTION 
Boards provided with cover layers on both sides, such as gypsum board and 
foam boards made of polystyrene, polyurethane or urea-formaldehyde resins 
are widely used as structural components such as roof elements and for 
thermal and acoustical insulation, and as packing material. 
These materials are today produced to a very great extent in a continuous 
process in so-called board plants in which the foaming is performed 
between revolving board belts, while the core material or its formation 
from liquid components, as for example in the case of polyurethane foam, 
is shaped against these revolving board belts. To prevent adhesion to 
these revolving board belts, paper layers accompany the upper and lower 
board belts in contact therewith. These layers bond to the core material, 
i.e., the polurethane foam for example, and usually also remain on them as 
bilateral cover layers, because the board thus made thereby gains 
stability and strength, and also the surface quality improves. It has 
already been proposed to use webs of matting or fabric as cover layer 
materials, such as mats or fabrics of cellulose fibers, polyester fibers 
and, glass fiber mats or fabrics on account of their incombustibility. 
Another advantage of such cover layers of matting or fabric consists in 
the fact that the core material, such as the polyurethane foam, is able to 
penetrate the interstices present in them and thus a good anchoring 
between core material and cover layer material is assured. The bond 
between core and cover layer material of paper or film has always been 
problematical. Nevertheless, matting and fabric materials have not 
succeeded as cover layer material, because the liquid components penetrate 
through the interstices present in the matting or fabric and result in 
adhesion to the board bands. Such liquid or liquid-containing starting 
components are present especially in the manufacture of PU hard foams, but 
also in urea-formaldehyde foam materials in which the starting materials 
set or react chemically, and in the manufacture of gypsum boards which set 
hydraulically. 
An attempt has been made to remedy this disadvantage by coating the matting 
or fabric materials with polyethylene or bitumen, it being necessary in 
the latter case to sprinkle the cover layer additionally with sand to 
enable it to be handled. It is disadvantageous in these known materials, 
however, that both polyethylene and bitumen penetrate rather strongly into 
the matting or fabric, which thereby loses its open structure, and the 
bond between matting or fabric and the core of the material forming the 
board thus becomes insufficient. In the case of PU hard foam boards, on 
the example of which the invention is described below, there is another 
disadvantage in the fact that both materials are easily combustible, and 
thus the PU hard foam board made therefrom and provided with cover layers 
has extremely poor properties with regard to its behavior wh. 
Therefore there exists an urgent technical need for a cover layer material 
which does not have the disadvantages indicated above, which permits the 
continuous production of boards from liquid starting components without 
passing through the matting or fabric and sticking to the boards or webs. 
Such a cover layer material is furthermore to conform in its behavior in 
contact with fire as closely as possible with building material group B2 
or B1, but if possible even with building material group A2. It is 
furthermore to be resistant to hot bitumen, so that the cover layer will 
not be destroyed by the tarring so frequently performed on flat roofs, for 
example, and so that no formation of blisters, i.e., partial separation 
between the cover layer and PU hard foam, will occur. 
This problem is solved by a cover layer material with the distinguishing 
features of the patent claim, which is characterized by the fact that the 
matting or fabric has on one side a coating of 70 to 94 wt.-% of a 
powdered inorganic material and 5 to 30 wt.-%, absolutely dry, of a 
binding agent; preferably the powdered inorganic material in the coating 
composition amounts to even 80 to 94 wt.-%, absolutely dry, of the total 
coating. 
In DE-OS No. 31 20 342, with the object of achieving fire retardancy, an 
insulation body is described which has an outer skin composed of glass 
fiber matting and bearing a coating of at least one metal oxide such as 
aluminum hydroxide and/or antimony oxide and plastic copolymers. The 
requirements specified for the invention and set forth above cannot be 
satisfied by the technical teaching of this prior disclosure nor is the 
invention suggested by it. The content of metal oxide in the dried 
composition is between 50 and 70 wt.-%, the coating composition being 
applied in a pasty, foamed state to the glass fiber matting and then dried 
by radiant heat. Such a coating composition may satisfy the requirement of 
fire retardancy, but it does not provide the solution of the problem 
addressed herein. In the case of percentage contents of 50 to 70 wt.-% of 
inorganic material, these are concentrations of solids as they are 
commonly used in brushing and coating compositions. For the purpose 
pursued by the invention, such common coating compositions, with a high 
content of binding agent and liquid, are not suitable because liquid and 
binding agent strike through the matting or fabric and lead to the feared 
adhesion to the board belts of the continuous board machine. The 
considerable amounts of liquid to be removed also lead to bubbles and 
shrinkage in the drying process and the coating does not dry free of 
cracking. 
For this reason a preferred method of producing the cover layer material 
consists in the use of a coating composition with a very high solids 
content, preferably of 70 to 80 wt.-%. Surprisingly, this coating can 
still be applied with a backfilling machine. It is best dried with hot, 
recirculating air and results in a perfectly impermeable coating without 
bubbles, shrinkage or cracking. 
The advantage of the cover layer material according to the invention lies 
in the fact that, due to the unusually high content of inorganic material, 
the matting or fabric becomes impermeable to the liquid starting 
components, so that the open structure of the matting or fabric is 
preserved and good anchoring of the cover layer material to the core 
material of the plate during the later shaping and foaming is assured. 
The high content of inorganic material furthermore brings it about that a 
PU hard foam web provided with this cover layer material is resistant to 
hot bitumen at, for example, 180.degree., the cover layer is not destroyed 
and no bubble formation occurs between cover layer and PU hard foam. 
Moreover, the high content of inorganic material further reduces 
inflammability below that of previously known materials. 
The binding agents can be not only those on an inorganic basis, such as 
water glass, but also those on an organic basis, especially on a plastic 
basis. Since water glass as binding agent makes the cover layer rather 
brittle, mixtures containing binding agents of a plastic basis are also 
recommendable. In organic binding agents have the advantage that they 
further reduce inflammability. 
The binding agents on the basis of plastic are preferably used in the form 
of plastic dispersions with a solids content of 35 to 70% by weight. They 
include especially polyvinylidene chloride and polyvinyl chloride, which 
have the advantage of being fire retardant, and copolymers and terpolymers 
of vinyl acetate with maleic acid and acrylic acid. Especially preferred 
on account of their good binding agent properties in comparison with the 
organic coating components, styrene-butadiene copolymers and polymers or 
copolymers of acrylic acid and methacrylic acid, respectively. The amount 
of plastic dispersion to be used depends to some extent on the solids 
content, and, to keep the energy required for the drying of the coating 
low, dispersions of the highest possible solids content are used. 
The greatest variety of powdered substances are suitable as inorganic 
material, especially those on a mineral basis, such as silicates, clays 
etc. On account of its easy availability, calcium carbonate has proven to 
be especially preferred. 
For the achievement of better values in relation to behavior on exposure to 
fire ["Brandverhalten"] aluminum hydroxide or alumina trihydrate is 
recommendable as an inorganic material, with which a fire retardancy 
rating of A2 can be achieved. 
To remain economical, in a preferred embodiment of the invention the 
inorganic material consists of a mixture of 10 to 50 weight-percent of 
calcium carbonate and 90 to 50 weight-percent of aluminum hydroxide or 
alumina trihydrate. In this case, the higher the content of the aluminum 
hydroxide or the alumina trihydrate content is, the more fire-retardant 
the cover layer material and the PU hard foam board covered with it 
becomes. 
It is desirable for the coating also to contain certain percentages of 
organic or mineral colorants for the purpose of distinguishing different 
quality classes of the board, for example with regard to fire retardancy. 
To counteract the translucency of the cover material and prevent light 
from showing through the often yellowish PU hard foam, coloring the cover 
material with carbon black has proven to be preferable, because even small 
amounts cover large areas. 
For special applications, especially when a white cover layer material and 
thus a white PU hard foam board or white gypsum board is desired, the 
admixture of up to 5 weight-percent of titanium oxide powder, with respect 
to the total amount of inorganic material, has proven to be preferable. 
The matting or fabric used for the cover layer material can best have a 
specific weight between 35 and 350 g/m.sup.2, preferably from 40 g/m.sup.2 
to 150 g/m.sup.2, and the applied weights of the coating are best between 
150 and 450 g/m.sup.2, these weights being dependent to a great extent on 
the application, the thickness of the core material, and other such 
factors. Glass fiber matting and fabric material has proven especially 
desirable as matting and fabric material, since it is incombustible. A 
matting and fabric material on a cellulose basis is desirable for use as a 
matting and fabric material on an organic basis. On account of its good 
strength rating, a polyester fiber matting is preferentially suitable. In 
the case of cover layer material for gypsum boards, it is desirable to use 
both nonwoven and woven fabrics together, because in this manner the 
liability to breakage of the gypsum boards can be very substantially 
reduced. Quite generally, the use of matting and woven fabric together can 
considerably increase the longitudinal and transverse strength. 
Especially preferred is the use of the cover layer material according to 
the invention for the production of boards provided with cover layers on 
both sides in a continuous board producing plant using a top and bottom 
belt. It is also, of course, suitable for use as a laminating material for 
lamination, for example, onto polystyrene foam boards cut from a block of 
foam polystyrene, and here again the uncoated side of the matting or 
fabric is available for a good bonding of the cover layer material to the 
core material through the laminating material.

The invention will be further explained below through preferred examples 
relating to the method of manufacture of the cover layers: 
Example 1 
On a glass fiber mat having a specific weight of about 60 g/cm.sup.2, a 
coating composition is applied in a backfilling machine, the composition 
consisting of CaCO.sub.3 powder of a random average particle size of about 
10 .mu.m and of a polystyrene-butadiene dispersion with a solids content 
of 57% by weight, with the addition of 1.5 g of common adjuvants such as 
antifoaming agents, wetting agents and preservatives, the solids content 
of the coating composition amounting in all to about 75 wt.-%. At the same 
time the percentages of CaCO.sub.3 powder and plastic dispersion in the 
coating composition are selected such that, after drying with hot 
circulating air in a drying tunnel, the coating consists of 92 wt.-% of 
inorganic material and 6.5 wt.-% of binding agent and the balance of 
adjuvants. The coating weight amounts to 250 g/m.sup.2 absolutely dry. 
Example 2 
A mat on a cellulose basis treated for fire retardancy, having a weight of 
50 g/m.sup.2, is coated in a backfilling machine with a coating 
composition made of aluminum hydroxide, calcium carbonate, and a plastic 
dispersion made from a terpolymer of vinyl acetate, maleic acid and 
methacrylic acid ester, with a solids content of 50 wt.-% and 3 g of the 
common adjuvant, the solids content of the coating composition totaling 
about 73 wt.-%. The percentages of aluminum hydroxide, calcium carbonate 
and plastic dispersion in the coating composition are selected such that, 
after drying in hot circulating air in a drying tunnel, the coating 
consists of 60 wt.-% of aluminum hydroxide, 22 wt.-% of calcium carbonate, 
and 15 wt.-% of binding agent, balance adjuvants. The coating rate amounts 
to approximately 250 g/m.sup.2 absolutely dry weight. 
Example 3 
To a mat composed of polyester fibers and weighing 40 g/m.sup.2, there is 
applied a coating composition of 25 g of aluminum hydroxide, 43 g of 
calcium carbonate, 4 g of titanium dioxide, 8 g of a plastic dispersion of 
a terpolymer of vinyl acetate, maleic acid and methacrylic acid ester with 
a solids content of 57 wt.-% and approximately 1 g of common thickening, 
crosslinking and preservative agents, and 23 g of water, by means of a 
backfilling machine, and dried with hot circulating air in a drying 
tunnel. This cover layer material is characterized by its white color due 
to the use of titanium dioxide, and is used in the manufacture of white 
boards which are used a wall covering. The coating rate on the dried cover 
layer consists of about 270 g/m.sup.2 absolutely dry weight.