Process of manufacturing a heat-resistant composite sheet

A process for manufacturing a heat-resistant composite sheet comprising applying a bonding agent with an added cross-linking agent on one of the facing surfaces to be adhered of a thermoplastic resin sheet and a polyolefin foam sheet. The two sheets are then placed one upon another through the bonding agent coated layer and are bonded together while heating the same and applying pressure thereto.

FIELD OF THE INVENTION 
This invention relates to a process for manufacturing a heat-resistant 
composite sheet comprising a foam sheet and a laminating sheet which is 
used as an interior material such as an instrument panel or the like for a 
motorcar or additionally as material for furniture, building or the like. 
PRIOR ART 
In a previously known such process for manufacturing a composite sheet of 
this kind used for an instrument panel, a leather sheet is set in one 
mold, and a hard base member is set in the other mold, and the interior 
mold space formed by closing the two molds is then charged with a foaming 
liquid for polyurethane foam and is foamed. This conventional type of 
manufacturing process, however, has the disadvantages that a harmful 
reaction gas is generated which is detrimental to the environment, and 
additionally the leather sheet previously given a predetermined shape by a 
vacuum shaping treatment is deformed, collapsed or shrunk in stock and 
consequently does not fit well in the mold. 
Accordingly, there has been developed a method of manufacturing a composite 
or laminated sheet wherein a semi-hard leather sheet and a heat-resistant 
foam sheet of the polyolefin type are bonded together. In this case, such 
durable materials that are not deformed even by a change in temperature 
from ambient temperature to about 100.degree. to 110.degree. C., such as, 
for instance, a combination of a polyolefin foam sheet, especially, a 
polypropylene foam sheet and a polyvinyl chloride sheet is preferable. 
However, a satisfactory bonding therebetween has not been obtained by 
simply bonding the two together with various kinds of bonding agents 
interposed therebetween. 
Accordingly, an increase in bonding force has been tried either by treating 
both the surfaces of the foam sheet and the polyvinyl chloride sheet with 
an oxidizing agent such as a chromic acid mixture or the like or by 
subjecting both surfaces to a physical treatment such as sanding or the 
like. However, good results have not been obtained. Further, there has 
been developed a process wherein polyolefin resin powders are spread over 
the polyvinyl chloride and molten by heat sheet in order to bond them or 
wherein a bonding agent is impregnated in the sheet in order to bond them, 
but here again it has not been possible to obtain durable and 
delamination-resistant products which are resistant to a temperature 
change to about 100.degree. C. 
SUMMARY OF THE INVENTION 
The present invention has been made in the light of the above facts, and it 
is characterized in that at least one of the facing surfaces of a 
thermoplastic resin sheet and a polyolefin foam sheet to be bonded 
together is coated with a bonding agent prepared by adding a cross-linking 
agent to a hot-melting type bonding agent of the polyester type or 
polyurethane type, and the two sheets are placed one upon another at the 
bonding agent coated surface and subjected to pressure and heat, so that a 
cross-linking hardening treatment occurs in the bonding agent between the 
sheets. 
Namely, this invention is such that the hot-melting type bonding agent is 
activated by heat, and becomes molten and consequently exhibits a good 
bonding characteristic because of its fluidity, and thereafter the molten 
resin is hardened by being subjected to cross-linking with the 
cross-linking agent, and as a result there is brought about a mutually 
integral and firm bonding between the surfaces of the foam sheet and the 
laminating sheet.

DETAILED DESCRIPTION 
A polypropylene foam sheet 1 of about 4 mm thickness, and a polyvinyl 
chloride type leather sheet 3 of about 0.5 mm thickness are taken as the 
materials to be laminated one upon another, and the surface to be adhered 
of the foam sheet 1 is coated with a bonding agent consisting of a 
hot-melting type adhesive agent of the polyester type or polyurethane type 
or the like containing a cross-linking agent, such as an isocyanate type, 
whereby a thin coating layer 2 thereof is formed on the surface. After the 
coating layer 2 is dried, the foam sheet 1 is heated to temperature in the 
range of from 190 to 220.degree. C. The polyvinyl chloride sheet 3 
previously heated to above 160.degree. C. is put on this heated foam sheet 
surface, and these are passed through a pair of upper and lower pressing 
rolls 4, 4 as illustrated and thereby the two are pressed against each 
other and are bonded. During this time, the bonding agent completes its 
cross-linking action, and thus there can be obtained a composite sheet 
wherein the two sheets are bonded together by the cross-linkage 
connection. 
When this composite sheet was subjected to a bonding strength test, the 
polypropylene foam sheet resisted to the tensile force and the foam sheet 
itself was broken. Further, when this composite sheet, after repeated 
heating several times at about 105.degree. C. for eight hours, was 
subjected to the test in almost the same manner as above, the rupturing of 
the polypropylene foam sheet itself again occured. Thus, it was 
demonstrated that the heat-resistance and bonding force of the bonding 
layer 2 between the boundary surfaces of the two sheets were extremely 
high and excellent. 
Thus, according to this invention, at least one of the polyolefin foam 
sheet and the thermoplastic resin sheet is coated with a coating layer of 
a hot-melting type bonding agent containing a cross-linking agent, and the 
two are then placed together and are heated and pressed against each 
other, so that there can be obtained a composite sheet having excellent 
heat resistant bonding characteristics. 
In the specific embodiment set forth in the example the polyester bonding 
agent was a saturated polyester dissolved in an aromatic hydrocarbon 
solvent and was the ester produced by the reaction of one or more diols 
and one or more dicarboxylic acids and has a melting point of 
70.degree.-100.degree. C. and has an OH valve of 4-8 and an acid value of 
1-2. The cross-linking agent was one or more of a series of "Desmodurs" 
under the trade names of "Desmodur M", "Desmodur RF", "Desmodur R", 
"Desmodur TT". The cross-linking type hot-melting bonding agent was 
prepared by mixing 100 parts, by weight, of the above polyester bonding 
agent and 5--15 parts, by weight, of the above cross-linking agent. 
Numerous modifications and variations of the bonding agent will be evident 
to those skilled in the art particularly where the polyester can be other 
substances while the cross-linking agent can be alternative isocyanates or 
polyisocyanates. The invention is intended to cover all equivalents and 
the breadth of the scope and spirit of the invention is defined by the 
attached claims.