Method of production of a plastic laminate

A method of production of a plastic laminate having a protective layer on a foamed layer comprising coating plastisol containing a vinyl chloride resin or an acrylic resin having epoxy group and having average particle diameter of 0.05 to 5 mm and plasticizer as the essential components on the surface of vinyl chloride resin layer containing an organic foaming agent, then forming the combined layers by heating and foaming is provided. A plastic laminate having a protective layer of polyvinyl chloride having excellent surface strength, abrasion resistance and resistance to chemicals on a foamed layer can be produced efficiently.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a novel method of production of a plastic 
laminate comprising a protective layer on the surface of a foamed layer of 
a polyvinyl chloride, More particularly, the present invention relates to 
a method of efficiently producing a plastic laminate comprising a 
crosslinked protective layer of a polyvinyl chloride or a polyacrylate 
having excellent strength, abrasion resistance and resistance to chemicals 
of the surface on a foamed layer of polyvinyl chloride. 
2. Description of the Prior Art 
Foamed materials of polyvinyl chloride have excellent ability for design 
and flame retarding property and have heretofore been used as raw 
materials for building materials, such as wall materials and floor 
materials. As the wall papers and floorings, laminates having protective 
layer for protecting the surface of the foamed materials are frequently 
used. 
For the formation of the protective layer on the surface of the foamed 
materials, materials and methods of processing are suitably selected 
depending on the purpose. For example, when durability, such as resistance 
to chemicals, strength and abrasion resistance, is enhanced, a method in 
which a polyvinyl chloride pastisol containing a vinyl chloride resin of 
high degree of polymerization, such as a resin having average degree of 
polymerization of 1600 or more, or a polyvinyl chloride plastisol 
containing crosslinking agent, such as triazine, is coated on the surface 
of the foamed material and then heated to form a protective layer and a 
method in which a polyvinyl chloride film by calender processing 
containing a plasticizer in a smaller amount, such as 35 weight parts per 
100 weight parts of the vinyl chloride resin, is laminated are adopted. 
In another method, emulsion or film of other than polyvinyl chloride, such 
as polyacrylate and the like, is laminated or coated. 
Recently, prevention of fouling of wall papers and floorings are strongly 
desired because of change of style of living. Organic solvents are 
frequently used in household generally for cleaning fouled materials. When 
an organic solvent which dissolves polyvinyl chlorides is used for this 
purpose, the protective layer is reduced to be ineffective. By this 
reason, the method in which a crosslinked protective layer is formed by 
using a plastisol containing a crosslinking agent, such as triazine 
compounds and the like, has been adopted as the preferable method. 
However, this method has drawbacks that the polyvinyl chloride tends to be 
thermally degraded during processing and that formed articles have 
inferior weatherability, tending to cause loss of transparency and 
whitening with humidity. 
On the other hand, the method of using raw materials other than polyvinyl 
chloride, such as emulsions and films of polyacrylate, has drawbacks that 
it cannot exhibit the properties sufficiently and that cost of the product 
is increased. 
SUMMARY OF THE INVENTION 
The present invention accordingly has an object to provide a method of 
production of a plastic laminate which comprises a foamed layer having a 
protective layer made of a crosslinked polyvinyl chloride or a crosslinked 
polyacrylate having sufficient durability, such as resistance to 
chemicals, strength and abrasion resistance, without using a crosslinking 
agent. 
As the result of intensive study by the present inventors to achieve the 
object described above, it was particularly mentioned that a vinyl 
chloride resin or an acrylic resin containing epoxy group is crosslinked 
during the process of foaming by decomposition of an organic foaming agent 
and it was discovered that a layer of plastisol of polyvinyl chloride or 
polyacrylate containing epoxy group coated on the surface of the polyvinyl 
chloride layer containing an organic foaming agent is crosslinked by 
decomposition of the foaming agent in the foaming layer to form a 
protective layer having sufficient resistance to chemicals, strength and 
the like and a laminate having the excellent foamed layer can be easily 
obtained. The present invention was completed on the basis of the 
discovery. 
Thus, the present invention provides a method of production of a plastic 
laminate which comprises coating a plastisol comprising a vinyl chloride 
resin or an acrylate resin containing epoxy group and having an average 
particle diameter in the range of 0.05 to 5 .mu.m and a plasticizer on the 
surface of a substrate made by curing of a polyvinyl chloride composition 
containing an organic foaming agent at a temperature lower than the 
decomposition temperature of the organic foaming agent and then forming a 
foamed layer and a crosslinked protective layer on the surface of the 
foamed layer by heating to a temperature equal to or higher than the 
decomposition temperature of the organic foaming agent. 
Other and further objects, features and advantages of the invention will 
appear more fully from the following description.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is described in detail in the following. 
The vinyl chloride resin or the acrylate resin containing epoxy group which 
is used in the protective layer of the present invention is particles of 
spherical shape. It is necessary that average diameter of the particles is 
in the range of 0.05 to 5 .mu.m and preferably in the range of 0.5 to 5 
.mu.m. 
When the average diameter is larger than this range, melting by heating 
becomes slower and the advantage of the present invention is not 
sufficiently exhibited. When the average diameter is smaller than this 
range, viscosity of the plastisol is too high and workability is inferior. 
The vinyl chloride resin or the acrylic resin containing epoxy group 
described above which is used in the protective layer of the present 
invention preferably has concentration of epoxy group at the surface of 
the particle of 1.times.10.sup.-2 weight % or more and total concentration 
of epoxy group of 10 weight % or less. Particularly preferably, it has the 
concentration of epoxy group at the surface of the particle in the range 
of 5.times.10.sup.-2 to 5.times.10.sup.-1 weight % and the total 
concentration of epoxy group in the range of 0.5 to 5 weight %. 
When the concentration of epoxy group at the surface of the particle is 
less than 1.times.10.sup.-2 weight %, the crosslinking property is 
inferior. When the total concentration of epoxy group is more than 10 
weight %, viscosity of the plastisol is too high. Thus, conditions out of 
the specified range are not preferable. The concentration of epoxy group 
at the surface of the particle and the total concentration of epoxy group 
can be measured by the methods described later. 
As the vinyl chloride resin containing epoxy group used in the present 
invention, (1) a copolymer comprising a repeating unit of vinyl chloride 
as the main component thereof, a repeating unit of a monomer containing an 
epoxy group and repeating units of monomers copolymerizable with these 
monomers which are introduced according to desire or (2) a polymer 
obtained by adding an epoxy group to a copolymer comprising a repeating 
unit of vinyl chloride as the main component thereof and repeating units 
of monomers copolymerizable with vinyl chloride which are used according 
to desire is used. 
Examples of the monomer copolymerizable with vinyl chloride and the monomer 
containing epoxy group or copolymerizable with vinyl chloride which is 
used according to desire are: esters of unsaturated monocarboxylic acids, 
such as methyl ester, ethyl ester, propyl ester, butyl ester, octyl ester, 
cyclohexyl ester, benzyl ester and the like esters of methacrylic acid or 
acrylic acid; diesters of unsaturated dicarboxylic acids, such as dimethyl 
ester, diethyl ester, dipropyl ester, dibutyl ester, dioctyl ester, 
dicyclohexyl ester, dibenzyl ester and the like diesters of maleic acid or 
fumaric acid; vinyl ethers, such as methyl vinyl ether, ethyl vinyl ether, 
propyl vinyl ether and the like; vinyl esters of organic acids, such as 
vinyl acetate, vinyl propionate and the like; olefins, such as ethylene, 
propylene, butene-1, pentene-1 and the like; aromatic monovinyl compounds, 
such as styrene, .alpha.-methylstyrene and the like; cyanovinyl compounds, 
such as acrylonitrile, methacrylonitrile and the like; polymerizable 
unsaturated compounds having no reactive functional group, such as 
vinylidene chloride and the like; unsaturated monocarboxylic acids, 
unsaturated dicarboxylic acid and anhydrides of these acids, such as 
acrylic acid, methacrylic acid, ethacrylic acid, maleic acid, cinnamic 
acid, maleic anhydride, fumaric acid, itaconic acid, itaconic anhydride 
and the like; polymerizable unsaturated compounds containing carboxyl 
group, such as maleic acid monoalkyl esters, fumaric acid monoalkyl 
esters, itaconic acid monoalkyl esters, like other monoalkyl esters of 
unsaturated dicarboxylic acids and the like compounds; polymerizable 
unsaturated compounds containing amino group, such as 2-aminoethyl 
methacrylate, 2-aminoethyl acrylate, 2-aminopropyl methacrylate, 
2-aminopropyl acrylate, 3-aminopropyl methacrylate, 3-aminopropyl 
acrylate, 2-aminobutyl methacrylate, 2 -aminobutyl acrylate, 3-aminobutyl 
methacrylate, 3-aminobutyl acrylate, 4-aminobutyl methacrylate, 
4-aminobutyl acrylate, methacrylamide, acrylamide, 
N-2-aminoethylmethacrylamide, N-2-aminoethylacrylamide, 
N-2-aminopropylmethacrylamide, 
N-2-aminopropylacrylamide, N-3-aminopropylmethacrylamide, 
N-3-aminopropylacrylamide and the like; and polymerizable unsaturated 
compounds containing hydroxyl group, such as 2-hydroxyethyl methacrylate, 
2-hydroxyethyl acrylate, 2-hydroxypropyl methacrylate, 2-hydroxypropyl 
acrylate, 3-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, 
2-hydroxybutyl methacrylate, 2-hydroxybutyl acrylate, 3-hydroxybutyl 
methacrylate, 3-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, 
4-hydroxybutyl acrylate, dipentaerythritol hexamethacrylate, 
dipentaerythritol hexaacrylate and the like; and the like compounds. The 
unit of the copolymerizable monomer used according to desire may be 
introduced as a single kind or as a combination of two or more kinds. The 
unit of the monomer used according to desire is introduced to the vinyl 
chloride resin containing epoxy group preferably in the amount 10 weight % 
or less. 
Examples of the monomer containing epoxy group used in the vinyl chloride 
resin containing epoxy group (1) are: glycidyl ethers, such as allyl 
glycidyl ether, methallyl glycidyl ether and the like; glycidyl esters of 
unsaturated acids, such as glycidyl methacrylate, glycidyl acrylate, 
glycidyl p-vinylbenzoate, methyl glycidyl itaconate, glycidyl ethyl 
maleate, glycidyl vinyl sulfonate, glycidyl (meth)allyl sulfonate and the 
like; and epoxyolefins, such as butadiene monooxide, vinylcyclohexene 
monooxide, 5,6-epoxyhexene, 2-methyl-5,6-epoxyhexene and the like. The 
monomer containing epoxy group may be used as a single kind or as a 
combination of two or more kinds. 
As the method of preparation of the vinyl chloride resin containing epoxy 
group (1) described above, a method of copolymerizing the monomer 
described above by emulsion polymerization or microsuspension 
polymerization suited for production of vinyl chloride resins for paste 
processing can be adopted. A latex in which resin particles having average 
particle diameter of 0.05 to 5 .mu.m are dispersed uniformly can be 
obtained by this method. 
As the method of addition of epoxy group in the vinyl chloride resin 
containing epoxy group (2), a method in which vinyl chloride resin for 
paste processing is dehydrochlorinated by heat treatment or by contact 
with an alkali compound and then epoxidized by an organic peracid or the 
like can be adopted. 
It is preferable that the vinyl chloride resin containing epoxy group used 
in the method of the present invention has average degree of 
polymerization in the range of 600 to 4000. When the average degree of 
polymerization is less than 600, mechanical strength is insufficient. When 
the average degree of polymerization is more than 4000, a large amount of 
heat is required for melting completely. 
The acrylic resin containing epoxy group used in the method of the present 
invention can also be obtained by either the method of copolymerization or 
the method of addition of epoxy group to an acrylic polymer in the 
treatment after polymerization. 
For obtaining the acrylic resin containing epoxy group by copolymerization, 
at least one kind of monomer selected from the group consisting of 
monomers containing epoxy group, at least one kind of monomer selected 
from the group consisting of methacrylate monomers or the group consisting 
of acrylate monomers and other monomers used according to necessity are 
copolymerized in a medium and then the copolymer is separated from the 
medium and dried. In an example of obtaining the acrylic resin containing 
epoxy group by graft copolymerization which is one of the forms of 
copolymerization, monomers containing a methacrylate or an acrylate as the 
main component thereof are polymerized at first and a monomer containing 
epoxy group is added and polymerized. 
Examples of the method of obtaining the acrylic resin containing epoxy 
group by addition in the treatment after polymerization are a method in 
which an acrylic resin is epoxidized by the same treatment as that shown 
as an example of the method of obtaining the vinyl chloride resin 
containing epoxy group (2) described above and a method in which a monomer 
containing epoxy group is brought into contact with and added to a 
methacrylate polymer or an acrylate polymer. 
Examples of the methacrylate monomer and the acrylate monomer are: alkyl 
methacrylates, such as methyl methacrylate, ethyl methacrylate, stearyl 
methacrylate and the like; alkyl acrylates, such as methyl acrylate, butyl 
acrylate and the like; alkylglycol methacrylates and alkylglycol 
acrylates, such as butoxyethyl methacrylate, butoxyethyl acrylate and the 
like; alkyleneglycol monomethacrylates and alkyleneglycol monoacrylate; 
and the like. Among these monomers, methyl methacrylate is preferable. 
In the method of the present invention, plasticizer compounded with the 
vinyl chloride resin or the acrylic resin containing epoxy group described 
above is not particularly limited and plasticizers generally used as 
plasticizers of vinyl chloride resins heretofore can be used. Examples of 
the plasticizer are: phthalic acid derivatives, such as dimethyl 
phthalate, diethyl phthalate, dibutyl phthalate, di-(2-ethylhexyl) 
phthalate, di-n-octyl phthalate, diisobutyl phthalate, diheptyl phthalate, 
diphenyl phthalate, diisodecyl phthalate, ditridecyl phthalate, diundecyl 
phthalate, di-(heptyl, nonyl, undecyl) phthalate, benzyl phthalate, butyl 
benzyl phthalate, dinonyl phthalate, dicyclohexyl phthalate and the like; 
isophthalic acid derivatives, such as dimethyl isophthalate, 
di-(2-ethylhexyl) isophthalate, diisooctyl isophthalate and the like; 
tetrahydrophthalic acid derivatives, such as di-(2-ethylhexyl) 
tetrahydrophthalate, di-n-octyl tetrahydrophthalate, diisodecyl 
tetrahydrophthalate and the like; adipic acid derivatives, such as 
di-n-butyl adipate, di-(2-ethylhexyl) adipate, diisodecyl adipate, 
diisononyl adipate and the like; azelaic acid derivatives, such as 
di-(2-ethylhexyl) azelate, diisooctyl azelate, di-n-hexyl azelate and the 
like; sebacic acid derivatives, such as di-n-butyl sebacate, 
di-(2-ethylhexyl) sebacate and the like; maleic acid derivatives, such as 
di-n-butyl maleate, dimethyl maleate, diethyl maleate, di-(2-ethylhexyl) 
maleate and the like; fumaric acid derivatives, such as di-n-butyl 
fumarate, di-(2-ethylhexyl) fumarate and the like; trimellitic acid 
derivatives, such as tri-(ethylhexyl) trimellitate, tri-n-octyl 
trimellitate, triisodecyl trimellitate, triisooctyl trimellitate, 
tri-n-hexyl trimellitate, triisononyl trimellitate and the like; 
pyromellitic acid derivatives, such as tetra-(2-ethylhexyl) pyromellitate, 
tetra-n-octyl pyromellitate and the like; citric acid derivatives, such as 
triethyl citrate, tri-n-butyl citrate, acetyl triethyl citrate, acetyl 
tri-(2-ethylhexyl) citrate and the like; itaconic acid derivatives, such 
as monomethyl itaconate, monobutyl itaconate, dimethyl itaconate, diethyl 
itaconate, dibutyl itaconate, di-(2-ethylhexyl) itaconate and the like; 
oleic acid derivatives, such as butyl oleate, glyceryl monooleate, 
diethyleneglycol monooleate and the like; ricinolic acid derivatives, such 
as methyl acetyl ricinolate, butyl acetyl ricinolate, glyceryl 
monoricinolate, diethyleneglycol monoricinolate and the like; stearic acid 
derivatives, such as n-butyl stearate, glycerine monostearate, 
diethyleneglycol distearate and the like; other fatty acid derivatives, 
such as diethyleneglycol monolaurate, diethyleneglycol diperalgonate, 
pentaerythritol fatty acid ester and the like; phosphoric acid 
derivatives, such as triethyl phosphate, tributyl phosphate, 
tri-(2-ethylhexyl) phosphate, tributoxyethyl phosphate, triphenyl 
phosphate, cresyl diphenyl phosphate, tricresyl phosphate, trixylenyl 
phosphate, tris(chloroethyl) phosphate and the like; glycol derivatives, 
such as diethyleneglycol dibenzoate, dipropyleneglycol dibenzoate, 
triethyleneglycol dibenzoate, triethyleneglycol di-(2-ethylbutyrate), 
triethyleneglycol di-(2-ethylhexoate), dibutyl methylenebisthioglycolate 
and the like; glycerine derivatives, such as glycerol monoacetate, 
glycerol triacetate, glycerol tributyrate and the like; epoxy derivatives, 
such as epoxidized soy bean oil, epoxybutyl stearate, di-(2-ethylhexyl) 
epoxyhexahydrophthalate, diisodecyl epoxyhexahydrophthalate, 
epoxytriglyceride, epoxidized octyl oleate, epoxidized decyl oleate and 
the like; polyester plasticizers, such as polyesters of adipic acid, 
polyesters of sebacic acid, polyesters of phthalic acid and the like; 
liquid epoxy resins, such as water bisphenol A type liquid epoxy resins, 
novolac type liquid epoxy resins, polyglycol type liquid epoxy resins, 
alicylic epoxy resins, aliphatic epoxy resins, tetrafunctional epoxy 
resins having tertiary amino nitrogen atom, epoxy resins modified with 
urethane, epoxy resins modified with nitrile rubbers and the like; 
adhesive plasticizers; polymerizable plasticizers, such as diallyl 
phthalate, oligomers of acrylic monomers and the like; and the like other 
plasticizers. These plasticizers may be used as a single kind or as a 
combination of two or more kinds. 
The plasticizer is used in an amount generally in the range of 20 to 80 
weight parts, preferably 40 to 80 weight parts, based on 100 weight parts 
of the vinyl chloride resin or the acrylic resin containing epoxy group 
described above. When the amount is higher than the specified range, 
physical properties are deteriorated and, when the amount is lower than 
the specified range, the product becomes too hard. Thus, conditions out of 
the specified range are not preferable. 
In the plastisol of the present invention, other additives which are 
generally used in vinyl chloride plastisols, such as inorganic fillers, 
heat stabilizers, viscosity adjusting agents, diluents, coloring agents, 
flame retardants and the like, may be compounded according to desire. 
Examples of the inorganic filler are: calcium carbonate, such as 
precipitating calcium carbonate, heavy calcium carbonate, ultrafine 
calcium carbonate and the like; magnesium carbonate; silicic acid salts, 
such as silica, tarc, diatomaceous earth, clay, mica and the like; 
aluminum hydroxide; alumina; and the like. 
Examples of the heat stabilizer are: metal soaps, such as magnesium 
stearate, aluminum stearate, calcium stearate, barium stearate, zinc 
stearate, calcium laurate, barium laurate, zinc laurate and the like; 
metal salts, such as sodium salts, zinc salts and barium salts of phenol 
and naphthol and the like salts; organic tin compounds, such as dibutyltin 
dilaurate, dibutyltin dimaleate and the like; esters of phosphorous acid, 
such as diethyl phosphite, dibutyl phosphite, dioctyl phosphite, diphenyl 
isodecyl phosphite, tricresyl phosphite, triphenyl phosphite, 
tris(nonylphenyl) phosphite, triisooctyl phosphite and the like. 
Examples of the viscosity adjusting agent and the diluent are solvents, 
such as xylene, solvent naphtha, mineral spirit, diisobutyl ketone, butyl 
acetate and the like, suitable surface active agents and the like. 
Examples of the flame retardant are antimony trioxide, red phosphorus, 
zinc borate, organic bromides, chlorinated paraffins and the like. 
To the plastisol, conventional vinyl chloride resins for plastisol 
processing having no epoxy group may be compounded as well. 
The foamed layer which forms the base of the protective layer of the 
invention essentially comprises an organic foaming agent and a vinyl 
chloride resin. 
The organic foaming agent is not particularly limited and a suitable 
organic foaming agent can be selected from the foaming agents generally 
used for foaming of vinyl chloride resins and used in the present 
invention. Examples of such organic foaming: agent are azodicarbonamide, 
benzenesulfonyl hydrazide, p-toluenesulfonyl hydrazide, 
p,p'-oxybis(benzenesulfonyl)hydrazide, dinitrosopentamethylenetetramine, 
N,N'-dinitroso-N,N'-dimethylterephthalamide, trihydrazinotriamine and the 
like. The organic foaming agent may used as a single kind or as a 
combination of two or more kinds. The amount compounded in the plastisol 
is selected generally in the range of 0.5 to 15 weight parts based on 100 
weight parts of the vinyl chloride resin. When the amount is less than 0.5 
weight parts, foaming is insufficient. When the amount is more than 15 
weight parts, the foaming ratio is not increased as expected from the 
amount and the condition is economically unfavorable. 
The vinyl chloride resin used for the foamed layer is homopolymer of vinyl 
chloride monomer, a copolymer containing vinyl chloride monomer unit as 
the main component thereof and monomer units copolymerizable with vinyl 
chloride or the like polymer. 
Examples of the monomer copolymerizable with vinyl chloride are the same 
compounds as those described as examples of copolymerizable monomer 
constituting the vinyl chloride resin used for the protective layer 
described above. 
As the vinyl chloride resin used in the foamed layer, a vinyl chloride 
resin for paste processing is preferable. To the foamed layer, other 
additives generally used for vinyl chloride plastisols, such as inorganic 
fillers, heat stabilizers, diluents, coloring agents, flame retardants and 
the like, may be compounded according to desire in addition to the 
plasticizer described above. More specific examples of the other additives 
are the same as those described above. 
In the present invention, a layer of vinyl chloride resin containing the 
foaming agent as the essential component thereof is molded to form a 
foaming layer at a temperature which does not decompose the foaming agent 
and the plastisol comprising the vinyl chloride resin or the acrylic resin 
containing epoxy group as the main component thereof is coated on the base 
material thus formed. The combined layers are heated at a temperature 
preferably in the range of 150.degree. to 300.degree. C. for 30 seconds to 
10 minutes to make foam in the foaming layer and the laminate having the 
crosslinked protective layer can be obtained. It is considered that the 
crosslinking reaction occurs through scission of the epoxy group by 
decomposition products of the foaming agent. 
Thickness of the protective layer is preferably in the range of 2 to 3000 
.mu.m and more preferably in the range of 5 to 400 .mu.m. When the 
thickness is less than 2 .mu.m, desired resistance to chemicals and 
strength are not readily obtained. When the thickness is more than 3000 
.mu.m, a large amount of heat is required for melting completely. 
Apparatuses and conditions generally used in the production of foamed 
materials by vinyl chloride plastisols can be adopted in the operations in 
the present invention, such as preparation of plastisol, coating of 
plastisol, gel formation by heating, foaming, pre-treatment, 
post-treatment and the like. 
To summarize the advantages obtained by the invention, the foamed laminate 
having a protective layer of a crosslinked polyvinyl chloride or a 
crosslinked polyacrylate having excellent physical properties, such as 
surface strength, abrasion resistance and heat resistance, and resistance 
to chemicals can be produced without using a crosslinking agent according 
to the method of the present invention. 
The invention will be understood more readily with reference to the 
following examples; however, these examples are intended to illustrate the 
invention and are not to be construed to limit the scope of the invention. 
In Examples and Comparative Examples, "part" and "%" show weight part and 
weight %, respectively, unless otherwise mentioned. 
Properties in Examples and Comparative Examples were obtained by the 
following methods. 
(1) Concentration of epoxy group at the surface of a vinyl chloride resin 
containing epoxy group 
In a 300 ml wide top glass vessel with a glass stopper, 5 g of a vinyl 
chloride resin containing epoxy group, 1 ml of a 1N aqueous solution of 
hydrochloric acid and 100 ml of methanol were charged and mixed with a 
magnetic stirrer for 1 hour. The mixture was then treated with ultrasonic 
wave at 40.degree. C. and titrated with a 1/10N alcohol solution of KOH 
(amount of the titration, a ml). Separately, the same operation was 
conducted without adding the vinyl chloride resin to obtain the blank 
value (amount of the blank titration, b ml). Concentration of epoxy group 
at the surface was obtained by the following equation: 
concentration of epoxy group at the surface (weight 
%)=43.times.[(b-a)f.sub.1 .times.0.1]/w.times.10.sup.-1 
wherein 
f.sub.1 : factor of the 1/10N KOH solution 
w: weight of the sample (g). 
(2) Total concentration of epoxy group in a vinyl chloride resin containing 
epoxy group 
In a 300 ml wide top glass vessel with a glass stopper, a solution which 
had been prepared by dissolving 1 g of a vinyl chloride resin containing 
epoxy group in 100 ml of methyl ethyl ketone and 2 ml of a 1N aqueous 
solution of hydrochloric acid were charged and mixed with a magnetic 
stirrer for 1 hour. The mixture was then titrated with a 1/10N alcohol 
solution of KOH (amount of the titration, a ml). Separately, the same 
operation was conducted without adding the vinyl chloride resin to obtain 
the blank value (amount of the blank titration, b ml). Total concentration 
of epoxy group in the resin was obtained by the following equation: 
total concentration of epoxy group (weight %)=43.times.[(b-a)f.sub.1 
.times.0.1]/w.times.10.sup.-1 
wherein 
f.sub.1 : factor of the 1/10N KOH solution 
w: weight of the sample (g). 
(3) Foaming ratio of a foamed layer 
Foaming ratio was obtained by the following equation: 
foaming ratio=thickness of foamed layer after the foaming/thickness of the 
coated layer before the foaming (thickness of semi-cured sheet) 
(4) Degree of volume swelling of a protective layer 
A piece of a laminate of 20 mm square was dipped in tetrahydrofuran (THF) 
for 10 minutes and degree of volume swelling was obtained by the following 
equation: 
##EQU1## 
A lower value of the degree of volume swelling is considered to show a 
higher degree of crosslinking. 
(5) Resistance of a protective layer to chemicals 
A piece of gauze impregnated with THF was pushed against surface of a 
protective layer and rubbed 10 times. Then, condition of the surface was 
evaluated by visual observation. 
(6) Average degree of polymerization 
Average degree of polymerization was obtained according to the viscosity 
method of Japanese Industrial Standard K6721. 
(7) Average particle diameter 
Average particle diameter was obtained by measuring and averaging lengths 
of 1000 particles in an electron microscopic photograph of .times.10000 
magnification by using a transmission type electron microscope. 
(8) Fouling test for evaluation of surface abrasion 
A laminate having a protective layer was attached to the whole part of the 
inner surface of a stainless steel vessel of 120 mm.phi. inner diameter 
and 100 mm depth. In the stainless steel vessel, 200 g of glass beads of 3 
mm.phi. and 500 g of steel balls of 18 mm.phi. as abrasion accelerators 
and 7 g of carbon black as a fouling agent were charged. The vessel was 
placed on a roll mill and rotated at 80 rpm for 1 hour. 
After 1 hour, the laminate attached to the inner surface of the vessel was 
taken out, washed with water and dried. Condition of fouling of the 
surface of the sample was visually observed and evaluated according to the 
following criterion: .smallcircle.: scratch and fouling scarcely found on 
the surface; white foamed layer seen through the protective layer. 
.times.: significant scratches and foulings found on the surface; white 
foamed layer not seen through the protective layer. .DELTA.: some 
scratches and foulings found on the surface; white foamed layer seen 
through the protective layer. 
Examples 1 to 4 and Comparative Examples 1 to 3 
A plastisol was prepared according to the following compounding formulation 
by mixing with stirring for 10 minutes by using a planetary mixer (a 
product of Ishikawa Kojo Co., Ltd., No. 18.RTM.). The plastisol thus 
prepared was coated on a flame retarded paper to the thickness of 180 
.mu.m by using Mattice Oven.RTM. (a product of Warner-Mattice Corp.) and 
hardened by heating at 150.degree. C. for 45 seconds to form a foamed 
layer. 
______________________________________ 
vinyl chloride resin for paste processing 
100 weight parts 
dioctyl phthalate 60 weight parts 
heavy calcium carbonate 
80 weight parts 
titanium oxide (rutile form) 
15 weight parts 
azodicarbonamide 5 weight parts 
Na--Zn liquid stabilizer 
3 weight parts 
mineral spirit 10 weight parts 
______________________________________ 
For preparation of a protective layer, compounding ingredients shown in 
Tables 1 and 2 were mixed in the planetary mixer described above and then 
defoamed for 10 minutes by using a vacuum stirred defoaming machine to 
prepare a plastisol. Then, this plastisol was coated on the foamed layer 
prepared above to the thickness of 100 .mu.m by using Mattice Oven.RTM. 
and hardened by heating at 150.degree. C. for 45 seconds. Samples of 
5.times.5 cm square each were cut out from the laminate thus prepared and 
heated in four conditions of 30, 45, 60 and 75 seconds in Mattice 
Oven.RTM. at 200.degree. C. to prepare foamed materials. 
The results are shown in Tables 1 and 2. 
TABLE 1 
__________________________________________________________________________ 
Example 1 2 3 -- -- 
Comparative Example 
-- -- -- 1 2 
__________________________________________________________________________ 
Composition of plastisol for surface 
protective layer (weight part) 
PVC1 100 -- -- -- -- 
PVC2 -- 100 50 -- -- 
PVC3 -- -- 50 100 -- 
PVC4 -- -- -- -- 100 
dioctyl phthalate 50 50 50 50 50 
Ba--Zn heat stabilizer 
3 3 3 3 3 
Properties 
foaming ratio of foamed layer, 
30 
2.3 2.7 2.6 2.4 2.3 
heating at 200.degree. C. 
40 
3.8 4.6 4.3 3.8 4.0 
(second) 60 
5.2 6.6 6.1 5.5 5.4 
75 
8.8 9.7 9.0 9.1 9.1 
degree of volume swelling 
30 
.infin. 
.infin. 
.infin. 
.infin. 
.infin. 
(in THF, 10 min.) 
heating time of sample 
40 
8.0 7.9 7.9 .infin. 
.infin. 
(second) 60 
7.9 8.1 8.0 .infin. 
.infin. 
75 
8.1 8.0 8.0 .infin. 
.infin. 
resistance to chemicals; heating 
no no no surf.lyr. 
surf.lyr. 
time of sample: 60 seconds 
change 
change 
change 
dislvd. 
dislvd. 
fouling at the surface; heating 
.smallcircle. 
.smallcircle. 
.DELTA. 
x .DELTA. 
time of sample: 75 seconds 
__________________________________________________________________________ 
Notes for Table 1: 
PVC1: a vinyl chloride resin for paste processing containing epoxy group; 
average particle diameter, 0.9 .mu.m; average degree of polymerization, 
700; concentration of epoxy group at the surface, 0.09 weight %; total 
concentration of epoxy group, 0.92 weight %. 
PVC2: a vinyl chloride resin for paste processing containing epoxy group; 
average particle diameter, 1.0 .mu.m; average degree of polymerization, 
1250; concentration of epoxy group at the surface, 0.10 weight %; total 
concentration of epoxy group, 1.03 weight %. 
PVC3: a vinyl chloride homopolymer resin for paste processing; average 
particle diameter, 1.2 .mu.m; average degree of polymerization, 850. 
PVC4: a vinyl chloride homopolymer resin for paste processing; average 
particle diameter, 1.2 .mu.m; average degree of polymerization, 3500. 
.infin.: dissolved. 
surf.lyr.dislvd.: surface layer dissolved. 
no change: no change at the surface. 
TABLE 2 
______________________________________ 
Example 4 -- 
Comparative Example 
-- 3 
______________________________________ 
Composition of plastisol for 
surface, protective layer 
(weight part) 
PMMA1 100 -- 
PMMA2 -- 100 
dibutyl phthalate 80 80 
Properties 
foaming ratio of foamed layer, 
30 2.4 2.4 
heating at 200.degree. C. 
heating time of sample 
40 3.8 3.7 
(second) 60 5.4 5.5 
75 8.9 8.7 
degree of volume swelling 
30 .infin. (dissolved) 
.infin. (dissolved) 
(in THF, 10 min.) 
heating time of sample 
40 5.0 .infin. (dissolved) 
(second) 60 4.9 .infin. (dissolved) 
75 4.9 .infin. (dissolved) 
resistance to chemicals; heating 
no change surface layer 
time of sample: 60 seconds 
at the surface 
dissolved 
______________________________________ 
Notes for Table 2: 
PMMA1: a methyl methacrylate resin for paste processing containing epoxy 
group; average particle diameter, 1.0 .mu.m; average degree of 
polymerization, 30000; concentration of epoxy group at the surface, 0.11 
weight %; total concentration of epoxy group, 2.0 weight %. 
PMM2: a methyl methacrylate homopolymer for paste processing. 
While the invention has been particularly shown and described with 
reference to preferred embodiments thereof, it will be understood by those 
skilled in the art that the foregoing and other changes in form and 
details can be made therein without departing from the spirit and scope of 
the invention.