Adhesive and method of jointing articles of polyolefin using the same

An adhesive, suitable for joining cured polyolefin articles, comprising a water curable polyolefin having a melt index of from 0.1 to 20, and a method of joining cured polyolefin articles, especially cured polyethylene pipes, comprising a step to apply the above adhesive to the surface of the articles and a step to join both of the surfaces to each other with the melt of the adhesive.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to a novel adhesive suitable for jointing a 
variety of articles, especially shaped articles of cured polyolefin and a 
method of jointing articles of cured polyolefin using the adhesive. 
(2) Description of the Prior Art 
Since cured polyolefin is superior to uncured polyolefin in heat 
resistance, mechanical strength, especially in resistance to environmental 
stress cracking, shaped articles of cured polyolefin are increasing more 
and more in kind and amount product. For instance, a cured polyolefin pipe 
appear useful as gas pipe, tap water pipe, and hot water pipe. 
There have been proposed several methods of jointing cured polyolefin pipe 
without using metallic joints which have been used heretofore and have 
shortcomings, such as high cost and corrosiveness. Those methods, however, 
have not found practical use yet. For example, a method of heat adhering 
two cured polyolefin pipes has the drawback that because the cured 
polyolefin does not melt well due to its crosslinked molecular structure, 
joining strength is not very good so that flow of a pressurized liquid or 
heat cycles of the pipe often cause disconnection of the joint portion. 
A method of using an adhesive consisting of a polar organic material has 
been tested. However, its adhesion is not enough, owing to the 
non-polarity or low polarity of cured polyolefin. 
On the other hand, experiments of the inventors of the present invention 
had revealed that ordinary polyolefin, such as polyethylene, will function 
as an adhesive for cured polyolefin. Ordinary polyolefin, which has 
excellent adhesion for a short period of time, such as for about one month 
after the joining, however, has a problem that its adhesion gradually 
deteriorates. In this case, at an early stage after joining, temporal 
entanglements and physico-chemical adherence between the molecules on the 
surface of a cured polyolefin article and the polyolefins of adhesive 
provide excellent joining strength, which is gradually weakened by the 
action of various forces such as a force due to thermal expansion and 
contraction of the joint portion. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a novel adhesive with 
excellent adhesion for a long period of time. 
Another object of the present invention is to provide an adhesive for 
joining cured polyolefin articles. 
A further object of the present invention is to provide an adhesive for 
joining cured polyolefin pipe. 
A still further object of the present invention is to provide a method of 
joining shaped articles of cured polyolefin, especially cured polyolefin 
pipes by using said adhesive. 
Therefore, the present invention provides, in one aspect, an adhesive 
comprising a water curable polyolefin having a melt index of from 0.1 to 
20, and, in another aspect, a method of joining polyolefin articles one or 
both of which surfaces to be joined have a gel fraction of at least 5% by 
weight, which comprises a step of applying an adhesive comprising a water 
curable polyolefin to one or both of the above surfaces and a step of 
joining both of the surfaces to each other with said adhesive.

DETAILED DESCRIPTION OF THE INVENTION 
The adhesive of this invention not only improves the mechanical strength of 
the adhesive itself by gradually curing even at normal temperature, thanks 
to the actions of water contained in the atmosphere and of moisture moving 
from adhered articles after the adhesive has been used for adhesion, but 
also is excellent in long-term stability of adhering power because the 
adhering power gradually increases, due to the curing between the surface 
layer molecules of the adhered article and the molecules in the adhesive. 
Particularly, this adhesive is useful in adhering or joining cured 
polyolefin articles which have conventionally been extremely difficult to 
join, especially cured polyolefin pipes. In this invention, the term 
"joining cured polyolefin articles" means adhering or joining between 
articles composed of cured polyolefin when one or both of the paired 
surfaces to be joined have the degree of cure (or crosslinking) equivalent 
to a gel fraction of at least 5%, preferably at least 10% (in this 
invention, % is always by weight) as determined according to ASTM D-2765, 
Method A. 
For the water curable polyolefin which composes the adhesive of this 
invention, one may use those having hydrolizable silane radicals in its 
main or side chain, expressed by the general formula 
##STR1## 
where Y is a hydrolizable organic radical having less than 20 carbon 
atoms, and R.sup.1 and R.sup.2 are radical Y or a monovalent saturated 
organic radical having less than 20 carbon atoms. Radical Y is exemplified 
by alkoxy radical such as methoxy, etoxy and butoxy, acyloxy radical such 
as formyloxy, acetoxy and propionoxy, oximo radical such as 
--ON.dbd.C(CH.sub.3).sub.2, --ON.dbd.C(CH.sub.3)C.sub.2 H.sub.5 and 
--ON.dbd.C(C.sub.6 H.sub.5).sub.2, substituted amino radical such as 
--NHCH.sub.3, --NHC.sub.2 H.sub.5 and --NH(C.sub.6 H.sub.5), etc. R.sup.1 
and R.sup.2 are, for example, methyl, ethyl, propyl, tetradecyl, 
octadecyl, phenyl, benzyl, tolyl, etc. or may be radical Y. 
It is desirable to set the content of the above-mentioned hydrolyzable 
silane radical at 0.001% to 20%. That is because polyolefin with said 
silane radical content of less than 0.001% has low curability from water 
curing and therefore lacks sufficient adhesive power. On the other hand, 
polyolefin with said content of over 20% is not easy to handle because 
water curing gradually progresses during heating in the jointing operation 
on articles of the cured polyolefin. Therefore the preferable content of 
hydrolyzable silane radical is 0.05% to 5%. 
In the present invention, water curable polyolefins having a melt index 
(MI) of 0.1 to 20 measured by ASTM D-1238 are employed. That is because 
any water curable polyolefin whose MI is smaller than 0.1 has too large a 
melting viscosity to apply to the surfaces to be joined, whereas if MI 
exceeds 20, it does not adhere well due to the weak mechanical strength of 
the adhesive itself no matter how well it is water cured. Therefore the 
most desirable MI ranges from 0.5 to 5. 
The water curable polyolefin of this invention may be obtained by, for 
instance, heating a mixture of polyolefin, free radical producing 
compound, and unsaturated organic silane compound presented by the formula 
EQU RR'.sub.n SiY.sub.(3-n) (II) 
(where R is a monovalent unsaturated radical having less than 20 carbon 
atoms directly connecting to Si atom; Y is a hydrolyzable organic radical 
in the same concept described in the above-mentioned formula (I); R' is a 
monovalent saturated radical having less than 20 carbon atoms or radical 
Y; and n is 0, 1 or 2) at the temperature higher than the decomposition 
temperature of said free radical producing compound. 
Examples of the polyolefin are homopolymers and copolymers of 
.alpha.-olefins, such as ethylene, propylene, butene-1 and 
4-methylpentene-1, homopolymers and copolymers of .alpha.-olefins 
containing halogens, carboxylic acids or derivatives thereof, and 
copolymers of .alpha.-olefins and carboxylic acids or derivatives thereof, 
such as polyethylene, polypropylene, polybutene-1, poly-4-methylpentene-1, 
ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, 
ethylene-ethyl acrylate copolymer and chlorinated polyethylene. Examples 
of more preferable polyolefins are as follows. 
(1) Copolymers of ethylene and at least one of .alpha.-olefins having 3 to 
10 carbon atoms. 
Examples of .alpha.-olefins having 3 to 10 carbon atoms and useful as one 
of the components of such copolymers are propylene, butene-1, 
pentene-1,4-methylpentene-1 and hexene-1. 
The ratio of the .alpha.-olefin in the copolymer is 0.5 to 50%, preferably 
50 to 30%. If the ratio is less than 0.5%, reduced bond strength tends to 
result, whereas if the ratio exceeds 50%, the composition requires a 
higher temperature in forming thereof. This imposes a limitation on the 
kinds of organic peroxides usable. Especially preferable among such 
copolymers are those having a density of less than 0.915 g/cm.sup.3 as 
measured according to ASTM D-2839 since they are amenable to processing 
and shaping. 
The copolymer may further contain in the molecule thereof at least one of 
nonconjugated dienes, ethylenically unsaturated carboxylic acids and acid 
anhydrides thereof as its third component. The presence of the third 
component in a small amount is effective in affording improved adhesion. 
However, the third component, if present in an excessive amount, 
conversely results in reduced bond strength, so that the content of the 
third component should preferably be not more than 10%. 
Useful nonconjugated dienes are those used as the third component of EPDM 
and including, for example, methylenenorbornene, ethylidenenorbornene and 
like norbornenes, 1,11-tridecadiene, 11-ethyl-1,11-tridecadiene, 
6-methyl-1,6-heptadiene, dicyclopentadiene, methyltetrahydroindene and 
like nonconjugated dienes. 
Examples of useful ethylenically unsaturated carboxylic acid are those 
amenable to radical polymerization and represented by the formula 
##STR2## 
Wherein R.sup.1, R.sup.2 and R.sup.3 are the same or different and are 
each a hydrogen atom, halogen atom, carboxyl, alkyl having 1 to 10 carbon 
atoms or carboxyalkyl having 1 to 10 carbon atoms, or acid anhydrides 
thereof. More specific examples are acrylic acid, maleic acid, itaconic 
acid, himic acid and acid anhydrides thereof. 
(2) Polyolefins modified with an ethylenically unsaturated carboxylic acid 
or an acid anhydride thereof (hereinafter referred to as "modified 
polyolefins"). 
The modified polyolefins are polymers of .alpha.-olefins containing a 
compound represented by the formula (III) or an acid anhydride thereof as 
a copolymer component or graft component. 
Examples of useful .alpha.-olefins are ethylene, propylene, butene-1 and 
4-methylpentene-1. These compounds are used singly or in admixture in 
producing the polymers of .alpha.-olefins. 
The ethylenically unsaturated carboxylic acid is incorporated in an amount 
of 0.001 to 10%, preferably 0.01 to 1%, based on the modified polyolefin. 
With less than 0.001% of the acid present, reduced bond strength will 
result, whereas if the acid content exceeds 10%, bubbles tend to occur at 
the interface between the adherend and the adhesive, entailing impaired 
bond strength. 
Examples of preferred modified polyolefins are ethylene-acrylic acid 
copolymer (acrylic acid content: 0.01 to 1%), ethylene-maleic acid 
copolymer (maleic acid content: 0.01 to 1%), etc. 
(3) Copolymers of an .alpha.-olefin and a carboxylic acid or an acid 
anhydride thereof. 
Examples of such copolymers are the copolymers of (i) .alpha.-olefins, such 
as ethylene, propylene, butene-1 and 4-methylpentene-1, and (ii) 
carboxylic acids or derivatives thereof, such as vinyl acetate. Of these 
examples, the ethylene-vinyl acetate copolymer preferably contains 5 to 
30%, most preferably 10 to 20%, of vinyl acetate. 
(4) Polyethylene having a melting point (mp, .degree.C.) and a density (d, 
g/cm.sup.3) which fulfill the conditions of: 
EQU mp.gtoreq.500d-345 (1) 
EQU 0.915.ltoreq.d.ltoreq.0.970 (2) 
The melting point (mp) is a value determined by the method shown in B. Ke 
(ed.), "Newer Methods of Polymer Characterization", chap. IX, Pages 
350-354 (1964), John Wiley & Sons, Inc., N.Y. The density is a value 
measured according to ASTM D-2839 (20.degree. C.) Examples of useful 
polyethylenes are those known as linear low-density polyethylenes and 
linear medium-density polyethylenes. Preferably such polyethylenes are up 
to 130.degree. C. in melting point. 
The free radical producing compound above-mentioned are those which, when 
heated at a temperature over the melting point of the polyolefin, give 
rise to free radicals. Examples of the compound are organic peroxides, 
especially dialkyl peroxides heretofore known as curing agents for 
polyethylenes, such as dicumyl peroxide, 
2,5-dimethyl-2,5-di-(t-butylperoxy)-hexyne-3,1,3-bis-(1-butylperoxyisoprop 
yl)benzene, 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, t-butyl-cumyl 
peroxide, di-t-butyl peroxide and 4,4'-di-t-butylperoxyvaleric acid 
n-butyl ester, hydroperoxides, such as 
2,5-dimethylhexyne-2,5-di-hydroperoxide, and peroxy acids, such as 
t-butylperoxybenzoate, di-t-butyl-di-peroxyphthalate and 
2,5-di-(benzoylperoxy)hexane, or esters of such acids. Of these, dialkyl 
peroxides are especially preferable since they generally effect grafting 
described later within a shorter period of time. 
In the above-mentioned formula (II) for the unsaturated organic silane 
compound, radical R is, for instance, vinyl, allyl, butenyl, cyclohexenyl, 
cyclopentadienyl, cyclohexadienyl, CH.sub.2 
.dbd.C(CH.sub.3)COO(CH.sub.2).sub.3 --, CH.sub.2 
.dbd.C(CH.sub.3)COO(CH.sub.2).sub.2 O(CH.sub.2).sub.3 --, 
##STR3## 
etc. Radical R' is, for example, methyl, ethyl, propyl, tetradecyl, 
octadecyl, phenyl, benzyl, tolyl, etc. or may be a kind of the 
above-mentioned radical Y. 
Of the above-mentioned unsaturated organic silane compounds, the most 
preferable are vinyl trimethoxysilane and vinyl triethoxysilane. 
To manufacture water curable polyolefin using the above-mentioned 
polyolefin, free radical producing compound and unsaturated organic silane 
compound, a compound mixed with polyolefin, 0.05 to 10 parts (in this 
invention, parts are always by weight), preferably 0.1 to 2 parts of the 
free radical producing compound and 0.001 to 20 parts, preferably 0.1 to 5 
parts of the unsaturated organic silane compound, per 100 parts of the 
polyolefin, are heated at a temperature above the polyolefin melting 
temperature and for a period of time long enough for the employed free 
radical producing compound to fully decompose. By this heating, the 
unsaturated organic silane compound is grafted onto the polyolefin 
radicalyzed by the action of the free radical producing compound, and thus 
water curable polyolefin is obtained. For instance, when dicumyl peroxide 
is employed as free radical producing compound, and vinyl trimethoxysilane 
as unsaturated organic silane compound, their mixture may be held for 5 to 
10 minutes at 140.degree. to 180.degree. C. 
The reaction of the above-mentioned three components normally progresses 
with great ease, and polyolefin changes into water curable polyolefin in 
as short a period of time as just a few minutes. For that reason, the 
mixture composed of unchanged polyolefin, free radical producing compound 
and unsaturated organic silane compound may be used for the adhesive of 
this invention. While this mixture is held in the melting state in order 
to apply it on an article of cured polyolefin to be joined, the 
above-mentioned graft reaction goes on and the polyolefin changes into a 
water curable polyolefin. 
Another example of the water curable polyolefin of this invention is a 
copolymer of .alpha.-olefin, particularly ethylene, and at least one of 
the unsaturated organic silane compounds represented by the 
above-mentioned formula (II), especially vinyl trimethoxysilane or vinyl 
triethoxysilane. 
The process for manufacturing such a copolymer is revealed by Japan Patent 
Disclosure (Kokai Tokkyo Koho) No. 9611 of 1980. 
The adhesive of this invention may contain a small amount, for example up 
to about 1 part, of a chemical that accelerates the curing by water of the 
water curable polyolefin, e.g. silanol condensation catalyst, per 100 
parts of water curable polyolefin. As the silanol condensation catalyst, 
one may use tributyltin laurate, dibutyltin dilaurate, dibutyltin 
diacetate, or other chemicals shown in British Pat. No. 1,357,549. 
However, the adhesives of this invention including the above-mentioned 
silanol condensation catalyst have the shortcomings that they have to be 
held dry because of their quick water curing, while quick action is 
required for bonding operation, and so on. 
Therefore, the preferable adhesive in this invention should either never 
contain any of the chemicals considered under the criteria listed below to 
have a water curing accelerating effect (hereinafter such chemical is 
defined as high water curing accelerator) or not contain such a high water 
curing accelerator in excess of 0.01 part per 100 parts of the water 
curable polyolefin. Such adhesives are very easy to store and handle. 
Also, although the adhesive does not cure immediately after the bonding 
operation of articles, the water curing of the adhesive steadily 
progresses and the bonding strength gradually increases even when the 
bonded portion is left at room temperature. 
(Criteria of Water Curing Accelerators) 
A compound composed of 100 parts of polyethylene having a density of 
0.925-0.930 and MI of 1-2, 0.5 part of dicumyl peroxide, 2.0 parts of 
vinyl trimethoxysilane and 0.1 part of sample water curing accelerator, is 
extruded through an extruder, which is 20-28 in L/D and is provided with a 
T-die, to a sheet measuring 1 mm in thickness under the extrusion 
temperature of 150.degree.-170.degree. C. and the extrusion retension time 
of 10-20 minutes. Then the sheet thus obtained is held in the atmosphere 
at 150.degree. C. for 5 hours. After that the gel fraction of the sheet is 
measured according to ASTM D-2765, Method A. If the gel fraction is over 
10%, it is judged as a high water curing accelerator. 
Some of the silanol condensation catalysts, e.g. dibutyltin dilaurate, can 
be regarded as such a high water curing accelerator. 
Various other chemicals, e.g. oxidation inhibitors, coloring agents, 
temperature sensing agents, discoloring agents, etc. may be mixed with the 
adhesive of this invention as long as they do not interrupt its bonding 
performance. 
The adhesive of this invention can be handled in various forms. To handle 
the adhesive in its solid shape, it is desirable to mold the same 
beforehand into bar, sheet, tape, ring or any other adaptable form. The 
adhesive of this invention can also be used together with a chemically 
stable voltatile organic liquid as dissolved or dispersed therein. 
As the above-mentioned organic liquid, chemicals with various chemical 
structures are utilized as long as they do not adversely affect the water 
curability of the water curable polyolefin. For example, one may use 
hydrocarbons such as benzene, toluene, xylene, durain, mesitylene, 
decalin, liquid olefin oligomers, and petroleum products like light oil, 
kerosene, naphtha, gasoline, etc.; hydrocarbons containing oxygen such as 
tetrahydrofuran, methylisobutylketone, cyclohexanone, diphenylether, 
2-ethylhexanol, etc.; or other organic compounds such as dichlorobenzene, 
trichloroethylene etc. Of the volatile liquids, excessively volatile ones 
are hard to handle, whereas insufficiently volatile ones require a long 
period of time to disperse after the application of the adhesive. The 
preferred boiling point of the volatile liquid ranges from 100.degree. C. 
to 200.degree. C. If the water curable polyolefin is polyethylene based, 
or if its melting point is from 100.degree. to 140.degree. C., the 
particularly desirable organic liquid is a hydrocarbon whose boiling point 
is from 130.degree. C. to 170.degree. C., e.g. petroleum fractions such as 
gasoline, naphtha, etc. and xylene. 
The amount of the organic liquid to be used may be freely determined. One 
may use a solution made by dissolving a small amount of water curable 
polyolefin in a large quantity of organic liquid. On the other hand, a 
composition made by dispersing a bit of organic liquid in the water 
curable polyolefin will also do. Although water curable polyolefin has 
high melting viscosity in general, if even a small amount of organic 
liquid is dispersed, it reduces the melting viscosity of the polyolefin, 
thus facilitating its application to the surface to be jointed. Generally 
the appropriate amount of the organic liquid ranges from 10 parts to 2000 
parts, preferably from 200 parts to 800 parts per 100 parts of the water 
curable polyolefin. 
Although including a great amount of high water-curing accelerator in the 
adhesive of this invention has the above-mentioned disadvantage, if the 
high water-curing accelerator and the water curable polyolefin are 
contained in separate vessels respectively but quickly mixed immediately 
before the application, then the accelerator will work perfectly. To 
employ the high water-curing accelerator in this fashion, each of the two 
components is preferably either dissolved or dispersed in said organic 
liquid beforehand so as to facilitate quick mixing with each other. 
The adhesive of this invention is very useful as an adhesive for various 
articles, such as wood, materials for construction, shaped plastic 
articles, particularly for cured polyolefin goods like cured polyolefin 
pipes, because the curing progresses after the jointing operation has been 
finished and its jointing power increases even if it does not contain any 
high water curing accelerator, much more if it contains the accelerator. 
To use the adhesive of this invention for joining cured polyolefin 
articles, especially cured polyolefin pipes, it is desirable that the 
adhesive has a tensile strength (So, kg/mm.sup.2) in the water curable and 
cured state which is greater than that (S, kg/mm.sup.2) of the cured 
polyolefin pipe to be jointed, particularly greater than (S+0.1) 
kg/mm.sup.2. 
Next the preferred joining method of cured polyolefin articles using the 
adhesive of this invention will be descriped. 
Earlier, as an example of water curable polyolefin, the substance obtained 
from mixing polyolefin, free radical producing compound and unsaturated 
organic silane compound has been mentioned and so a detailed description 
of the polyolefin has been made. As the polyolefin articles serving as 
objects of joining in this invention, one may list an article comprising a 
cured one of a polyolefin selected from the concept of the above-mentioned 
polyolefin, which is cured with a curing agent such as organic peroxide, 
by irradiation, or by water curing, and so on. A molded article of cured 
polyolefin, which enables particularly good adhesion to be made, is an 
article comprising a water cured one of a water curable polyolefin 
selected from those of the same concept as the water curable polyolefin 
that composes the adhesive of this invention (mixed with silanol 
condensation catalyst or water curing accelerator as required). When a 
water curable polyolefin is molded with an extruder, calender, injection 
molding machine and other normal molding machines, the gel fraction of the 
polyolefin has often reached over 5% immediately after the molding, due to 
the effect of the heat during the molding process on the moisture 
originally contained in the water curable polyolefin or the polyolefin 
serving as its raw material and/or moisture in the atmosphere. Such molded 
articles right after being molded can be the object of adhesion in this 
invention just like objects brought to the highly cured state through the 
curing process after molding. 
In the joining method of this invention, it is generally essential for the 
adhesive to be brought in the melted state on the surface of molded 
articles to be joined, before or after, or at the very time when the 
molded articles are brought into contact with each other. Then, the 
polyolefin molecules which compose the adhesive will better adhere the 
surface of the cured polyolefin article. To attain tighter and stronger 
joining, it is desirable to bring the adhesive to a temperature 20.degree. 
C. higher, especially 50.degree. C. higher, than the melting point (To, 
.degree.C.) of the water curable polyolefin which composes the adhesive. 
Such heating of the adhesive can be achieved in various ways. For example, 
there are (1) a method in which the surface of a cured polyolefin article 
to be joined is heated in advance at a required high temperature and then 
the adhesive at normal temperature is applied to the surface, (2) a method 
in which the adhesive heated in advance at a required high temperature is 
applied to a molded article's surface kept at normal temperature, (3) a 
method in which the adhesive at normal or high temperature is applied to a 
molded article's surface kept at normal or high temperature and then the 
adhesive on the molded article's surface (preferably together with the 
molded article's surface at the same time) is heated by a metal heater 4 
shown in FIG. 2, a hot plate, a torch lamp, or by any other proper means, 
and so forth. 
Hereinafter the method of this invention will be explained by examples of 
joining cured polyolefin pipes. 
In FIGS. 1 to 3, first the adhesive of this invention is applied to the end 
surface of a pipe 1 made of cured polyolefin. Then, using a metal heater 4 
having a ring-shaped projection 41 whose inside diameter is equal to the 
pipe's outside diameter or slightly larger than that and a column-shaped 
projection 42 whose outside diameter is equal to the inside diameter of a 
joint 2 made of cured polyolefin or slightly larger than that, the end of 
pipe 1 is inserted into the projection 41 and joint 2 into projection 42 
as shown in FIG. 2, and all are heated. 
Next, pipe 1 and joint 2 are separated from the metal heater, and while 
adhesive 3 on pipe 1 is still in the melted state, pipe 1 is quickly 
inserted into joint 2 as shown in FIG. 3. Thus the connection of pipe 1 to 
joint 2 is completed. The adhesive may be applied either only to the 
inside of the joint or preferably to both articles to be bonded. Joint 2 
is a socket, elbow, cheese, etc. If the inside diameter of joint 2 before 
being heated is smaller than the outside diameter of pipe 1, the inside 
diameter of joint 2 is expanded by heating and then jointed to pipe 1 for 
tighter connection. 
If the inside diameter of the ring-shaped projection 41 of the metal heater 
is equal to or only slightly larger than the outside diameter of pipe 1, 
only a very thin film of adhesive remains on the surface at the end of 
pipe 1, because most of the adhesive is pushed back in the pipe by 
inserting the pipe 1 into the said projection 41. In the method of this 
invention, however, if, immediately before the pipe is inserted into the 
joint, a very thin film of the adhesive of this invention in the melted 
state is present, then adequate connection can be achieved. 
To use the adhesive of this invention in solid shapes such as bar, sheet, 
etc. at normal temperature, it may be applied to the pipe surface or the 
like while the adhesive is being melted by a heating means, such as gas 
burner. Also when the aforementioned organic liquid is added to the 
adhesive of this invention and is used as a low-viscosity liquid at normal 
or high temperature, it can be easily applied with brush or the like not 
only to the outer surface of the pipe but also to the inner surface of the 
joint. When an organic liquid is employed, it is desirable that the 
remaining amount of organic liquid in adhesive 3 is minimized right before 
pipe 1 is inserted into joint 2, but a slight amount may be allowed to 
remain. 
Actually, however, there is no problem about the use of organic liquid in 
the jointing method of this invention because most of the organic liquid 
is dispersed thanks to its own volatility and by being heated to a high 
temperature at which the adhesive of this invention is melted. 
In the perferred mode of joining pipes using joints, prior to the 
application of the adhesive the surface of the pipe and/or joint to which 
the adhesive is to be applied are preheated at least to the melting point 
(T.sub.o), preferably at least to (T.sub.o +20).degree.C., of the water 
curable polyolefin that composes the adhesive. 
The higher the above-mentioned preheating temperature, the better the 
joining power of the adhesive. However, since excessive heating might 
cause heat deformation of the pipe and/or the joint, it is desirable to 
set the temperature at over (T.sub.o +50).degree.C. and under (T.sub.o 
+180).degree.C. If the adhesive, the pipe, and the joint are each composed 
of different materials, it is preferable to preheat them to a temperature 
higher than the highest melting point of all the materials. 
Although the preheating may be conducted in any manner, the most desirable 
method is such that, of the whole thickness of the zone to be joined, only 
the surface and the upper half of the thickness, preferably only the 
surface and about the upper tenth of the thickness are heated to the 
above-mentioned high temperature. That is because heat deformation is 
inevitable on the pipe and joint if the whole layers of the pipe and joint 
become as hot as the said temperature. Such heating can be achieved by 
bringing the pipe and joint for the period of from several seconds to 
several minutes into direct contact with a metal heater held at a 
temperature as high as 200.degree.-300.degree. C., for example. 
After the preheating process, and while the surface of the preheated pipe 
and/or joint keeps the temperature at least T.sub.o .degree.C., the 
adhesive is applied. As long as the adhesive is applied all over the 
surface to be joined, a thickness of about 0.5 mm is sufficient for the 
amount of applied adhesive. 
Immediately before inserting the pipe into the joint, both of the surfaces 
of the pipe and joint are heated at least to (T.sub.o +20).degree.C., even 
if adhesive is not applied to either one of the two members and whether 
preheating of pipe, joint, and/or adhesive is conducted or not. The 
heating is particularly preferable to smoothly insert the pipe in the 
subsequent step and to maintain sufficient joining strength at the 
interface between pipe and joint after insertion. 
As the temperature of the heating is raised, the insertion becomes easier 
and smoother due to the drop in the melt viscosity of the adhesive, and 
the adhesion strength after insertion improves accordingly. However, 
excessive heating is likely to worsen the mechanical strength of either or 
both of the pipe to be inserted and the joint to receive it, resulting in 
obstructed and unsmooth insertion. For that reason, it is essential to 
heat only the surface of the jointing zone or its vicinity at a high 
enough temperature. It is desirable to quickly heat the surfaces of the 
joining zone to a temperature over (T.sub.o +50).degree.C. but under 
(T.sub.o +180).degree.C., particularly at over (T.sub.o +80).degree.C. but 
under (T.sub.o +140).degree.C., using metal heater 4 or the like. 
The preferred time required for the heating using metal heater 4 shown in 
FIG. 2, depends on the thickness (A mm) and outside diameter (D mm) of the 
pipe and the joint respectively. If the joint heating time is t.sub.1 
sec., the pipe heating time t.sub.2 sec., they are expressed as follows: 
##EQU1## 
where .alpha. is a constant and is from 0.01 to 0.05 and T is the 
temperature (.degree.C.) of the metal heater. Also it is desirable to make 
t.sub.1 &gt;t.sub.2, particularly t.sub.1 ranging from 1.1t.sub.2 to 
3t.sub.2. 
After the above-mentioned heating is finished, it is desirable to insert 
the pipe into the joint as soon as possible, especially desirable to do it 
within 10 seconds right after the heating. Generally the deeper the 
insertion of pipe 1 into joint 2, the greater the strength of joining, 
however the insertion resistance increases according to the increase in 
the length of the inserted portion of the pipe. The proper length of the 
inserted portion is about 0.5-2 times the pipe's outside diameter. So when 
the pipe has been inserted to that extent and has reached the point where 
the insertion resistance has risen abruptly, it is desirable to stop 
inserting and cool the pipe and joint without changing their relative 
positions so that the jointed interface between the pipe and the joint may 
not be damaged. Then the adhesion strength will become more stable. 
Although it depends on the size of the pipe and joint, it is generally 
desirable to stop inserting after pressing and inserting the pipe for 2-20 
sec. following the start of insertion, and keep the joined zone immobile 
as mentioned above to cool it. 
Cured polyolefin pipes can be firmly joined by the butt method, without 
using any joint. Hereinafter some examples of pipe connection by the butt 
method will be described. 
The ends of two pipes to be joined are correctly cut in advance so as to 
minimize the clearance which might be caused when the two ends are put in 
contact. Then adhesive of this invention is interposed between the two 
ends, and while the adhesive is in the melted state, the two pipes are 
lightly pressed against each other. The adhesive will do either in the 
solid shape of sheet, etc. at normal temperature, or in the shape of paste 
added with organic liquid at normal or high temperatures. By pressing the 
pipes against each other the adhesive between the pipe ends is turned into 
a layer as thin as less than 1 mm, sometimes even under 0.1 mm, but this 
causes no problem as far as the strength of the pipe connection is 
concerned. 
Prior to joining pipes in the butt method, it is desirable to preheat at 
least the ends of the pipes to a temperature higher than the melting point 
(T.sub.o) of the adhesive, and preheat the adhesive to a temperature 
higher than (T.sub.o -40).degree.C., preferably higher than T.sub.o 
.degree.C. The pipes can be firmly joined by doing so. In some case, the 
adhesive may be separately heated apart from the ends of the pipes and 
interposed between the ends of the pipes. However, in order to obtain a 
more stable high jointing strength, it is more desirable to keep the 
adhesive in contact with at least one of the pipes to be jointed and 
preheat it together with the ends of the pipes. 
The present invention will be described in greater detail with reference to 
the following examples and comparison examples. 
EXAMPLES 1-24, COMISON EXAMPLES 1-3 
Prepared for these examples were pipes of cured polyolefins listed in Table 
1 and measuring 21 mm in inside diameter and 27 mm in outside diameter, 
and socket joints of cured polyolefins listed in Table 1 and measuring 27 
mm in inside diameter, 34 mm in outside diameter, and 7.5 cm in length. 
Grease and water were removed from the outer surfaces of the spigot ends 
of the pipes and the inner surfaces of the socket ends of the joints with 
dry cloth. An adhesive comprising a polyolefin composition listed in Table 
1 was applied to the outer surface of the pipe spigot end about 1 mm in 
thickness and about 4 cm in length. 
The outer surface of the pipe spigot end and the inner surface of the 
socket joint end were heated for about 20 seconds by using an electrically 
heated iron heater maintained at a temperature of 220.degree. C., which 
was the type shown in FIG. 2 and had a cylinder-shaped projection of 27 mm 
in outside diameter and 5 cm in length and a ring-shaped projection of 27 
mm in inside diameter and 5 cm in length. After this the pipe was inserted 
into one socket end of the joint. The same procedure was repeated for the 
other socket end of the joint. 
Each adhesive used in Examples 1-13, and 17-24 were prepared by mixing and 
extruding a composition consisting of 100 parts of the base polymer listed 
in Table 1, 0.2 part of dicumyl peroxide and 2 parts of vinyl 
trimethoxysilane through a mixtruder held at a temperature of about 
150.degree. C. Each adhesive used in each of Examples and Comparison 
Examples were mixed with each organic solvent listed in Table 1 at a 
temperature of around 100.degree.-150.degree. C. and applied. 
Comparison Example 1 and Comparison Example 2 were different from Example 1 
and Example 2 respectively in only the point that each adhesive used was 
not water curable. In Comparison Example 3 the jointing operation of 
Example 14 was conducted with the exception of using no adhesive. In this 
case, the pipe and the socket joint are joined by the action of heat 
fusion. 
WATER PRESSURE TEST 
An approximately 30 cm long specimen including the socket joint portion at 
its midportion was ruptured by increasing the pressure of the water 
(20.degree. C.) filled in the specimen at a rate of 20 kg/cm.sup.2 per 
minute. Table 1 shows two pressure values at which the specimen ruptured, 
one indicating the initial value which was obtained from the test 
conducted 2 hours after the end of pipe joining, the other indicating the 
value after heat-cycles of 1 month, in which the specimen was heated at 
80.degree. C. for 12 hours and then cooled at 25.degree. C. for 12 hours. 
For the interpretations of abbreviations representing the names of 
materials and chemicals listed in Tables 1 and 2, see the remarks in Table 
5. 
3 TABLE 1 
Example No. 1 2 3 4 5 6 7 8 9 10 11 
Pipe Material PE (d: 0.945, PE(d: 0.945, PE (d: 0.945, PE (d: 0.945, 
PE (d: 0.945, PE (d: 0.945, PE (d: 0.945, PE (d: 0.935 PE (d: 0.935 PE 
(d: 0.935 PE (d: 0.935 (Parts) MI: 0.8) MI: 0.8) MI: 0.8) MI: 0.8) MI: 
0.8) MI: 0.8) MI: 0.8) MI: 0.5) MI: 0.5) MI: 0.5 MI: 0.5) 100 100 
100 100 100 100 100 100 100 100 100 DCP 2.2 DCP 2.2 DCP 2.2 
DCP 2.2 DCP 2.2 DCP 2.2 DCP 2.2 VMS 2.0 VMS 2.0 VMS 2.0 VMS 2.0 
DCP 0.2 DCP 0.2 DCP 0.2 DCP 0.2 BTL 0.05 BTL 0.05 BTL 0.05 BTL 
0.05 Gel fraction (%) 82 82 82 82 82 82 82 73 73 73 73 Joint Material 
PE (d: 0.945, PE (d: 0.945, PE (d: 0.945, PE (d: 0.945, PE (d: 0.945, PE 
(d: 0.945, PE (d: 0.945, PE (d: 0.945, PE (d: 0.935, PP (d: 0.92, PP (d: 
0.91, (Parts) MI: 0.8) MI: 0.8) MI: 0.8) MI: 0.8) MI: 0.8) MI: 0.8) MI: 
0.8) MI: 0.8) MI: 5) MI: 2.0) MI: 0.5) 100 100 100 100 100 100 
100 100 100 100 100 VMS 2.0 VMS 2.0 VMS 2.0 VMS 2.0 DCP 1.5 VMS 
2.0 VMS 2.0 VMS 2.0 VMS 2.0 TAIC 6.0 TMPAF 3 DCP 0.2 DCP 0.2 DCP 0.2 
DCP 0.2 DCP 0.2 DCP 0.2 DCP 0.2 DCP 0.2 DCP 0.25 DCP 0.2 BTL 0.05 BTL 
0.05 BTL 0.05 BTL 0.05 BTL 0.05 BTL 0.05 BTL 0.05 BTL 0.05 BTL 0.05 
Gel fraction (%) 73 73 73 73 67 73 73 73 73 20 35 Adhesive Base polymer 
EB (d: 0.88, EH (d: 0.88, LPE (d: 0.925, LPE (d: 0.935 EM (d: 0.93, EAC 
(d: 0.91, EVA (d: 0.93, EEA (d: 0.93, PE (d: 0.920, EVA (d: 0.93, PE-M 
50 (Parts) (100 parts) MI: 3.2, MI: 0.5, mp: 119.degree. C., mp: 
123.degree. C., MI: 4, MI: 13, MI: 3.0, MI: 0.8, MI: 2.0) MI: 1.5, EE-A 
(d: 0.93, B: 5%) H: 10%) MI: 2) MI: 0.8) M: 0.2%) A: 0.4%) VA: 10%) 
EA: 8%) 40 VA: 10%) MI: 1.5, EPDM 60 80 EA: 0.4%) 
EB (d: 0.89, 50 MI: 4, B: 5%) 20 Solvent, 
(parts) Xylene, 400 Tetradecane, 400 Decalin, 400 Decalin, 400 Decalin, 
400 Decalin, 400 Xylene, 400 Xylene, 400 Xylene, 500 Xylene, 500 Xylene, 
500 Water Initial .gtoreq.56 (note 1) .gtoreq.56 (note 1) .gtoreq.56 
(note 1) .gtoreq.56 (note 1) .gtoreq.56 (note 1) .gtoreq.56 (note 1) 
.gtoreq.56 (note 1) .gtoreq.56 (note 1) .gtoreq.56 (note 1) .gtoreq.56 
(note 1) .gtoreq.56 (note 1) pressure After heat .gtoreq.56 (note 1) 
.gtoreq.56 (note 1) .gtoreq.56 (note 1) .gtoreq.56 (note 1) .gtoreq.56 
(note 1) .gtoreq.56 (note 1) .gtoreq.56 (note 1) .gtoreq.56 (note 1) 
.gtoreq.56 (note 1) .gtoreq.56 (note 1) .gtoreq.56 (note 1) (kg/cm.sup.2) 
cycle 
Example No. 12 13 14 15 16 17 18 19 20 21 22 
Pipe Material PE (d: 0.935 PE (d: 0.935 PE (d: 0.935 PE (d: 0.935 PE 
(d: 0.935 PE (d: 0.935 PE (d: 0.935 PE (d: 0.935 PE (d: 0.935 PE (d: 
0.935 PE (d: 0.935 (Parts) MI: 0.5) MI: 0.5) MI: 0.5) MI: 0.5) MI: 0.5) 
MI: 0.5) MI: 0.5) MI: 0.5) MI: 0.5) MI: 0.5) 100 100 100 100 100 1 
00 100 100 100 100 100 VMS 2.0 VMS 2.0 VMS 2.0 VMS 2.0 VMS 2.0 
VMS 2.0 VMS 2.0 VMS 2.0 VMS 2.0 VMS 2.0 VMS 2.0 DCP 0.2 DCP 0.2 DCP 
0.2 DCP 0.2 DCP 0.2 DCP 0.2 DCP 0.2 DCP 0.2 DCP 0.2 DCP 0.2 DCP 0.2 
BTL 0.05 BTL 0.05 BTL 0.05 BTL 0.05 BTL 0.05 BTL 0.05 BTL 0.05 BTL 0.05 
BTL 0.05 BTL 0.05 BTL 0.05 Gel fraction (%) 73 73 10 20 30 73 73 73 73 
10 73 Joint Material XEP - 1 XPECl - 1 PE (d: 0.935, PE (d: 0.935, PE 
(d: 0.935, EVA (d: 0.93, LPE (d: 0.935, PE (d: 0.935, PE (d: 0.935, PE 
(d: 0.935, PE (d: 0.935, MI: 0.5) MI: 0.5) MI: 0.5) MI: 3, mp: 123, 
MI: 0.5) MI: 0.5) MI: 0.5) MI: 0.5) 100 100 100 VA: 10%) MI: 0.8) 
100 100 100 100 VMS 2.0 VMS 2.0 VMS 2.0 100 100 VMS 2.0 VMS 
2.0 VMS 2.0 VMS 2.0 DCP 0.2 DCP 0.2 DCP 0.2 DCP 2.0 VMS 2.0 DCP 0.2 
DCP 0.2 DCP 0.2 DCP 0.2 BTL 0.05 BTL 0.05 BTL 0.05 DCP 0.2 BTL 0.05 
BTL 0.05 BTL 0.05 BTL 0.05 BTL 0.05 Gel fraction (%) 78 81 12 
23 35 81 73 73 73 73 73 Adhesive Base polymer EVA (d: 0.93, EVA (d: 
0.93, ES (MI: 0.5, ES (MI: 2, ES (MI: 10, EGM (d: 0.93, LPE (d: 0.922, 
EGA (d: 0.91, EB (d: 0.89, EEA (d: 0.93, PE (d: 0.935, (Parts) (100 
Parts) MI: 0.8, MI: 0.8, VMS: 4%) VMS: 5%) VMS: 5%) MI: 14, MI: 2.5, MI: 
13, MI: 4) MI: 0.8, MI: 0.5) VA: 15%) VA: 15%) M: 0.2%) mp: 
124.degree. C.) A: 0.4%) 50 EA: 8%) 100 EPDM 50 VMS 2.0 
DCP 0.2 BTL 0.05 Solvent, (parts) Solvent, 
(parts) Xylene, 800 Xylene, 800 Xylene, 800 Xylene, 800 Tetradecane, 800 
-- -- -- -- -- Water Initial Initial .gtoreq.56 (note 1) .gtoreq.56 
(note 1) .gtoreq.56 (note 1) .gtoreq.56 (note 1) .gtoreq.56 (note 1) 
.gtoreq.56 (note 1) .gtoreq.56 (note 1) .gtoreq.56 (note 1) .gtoreq.56 
(note 1) .gtoreq.56 (note 1) pressure After heat After heat .gtoreq.56 
(note 1) .gtoreq.56 (note 1) .gtoreq.56 (note 1) .gtoreq.56 (note 1) 
.gtoreq.56 (note 1) .gtoreq.56 (note 1) .gtoreq.56 (note 1) .gtoreq.56 
(note 1) .gtoreq.56 (note 1) .gtoreq.56 (note 1) (kg/cm.sup.2) cycle 
cycle 
Example No. 23 24 1 2 3 
Pipe Material PE (d: 0.945, PE (d: 0.945, PE (d: 0.945, PE (d: 0.945, 
PE (d: 0.935 (Parts) MI: 0.88) MI: 0.88) MI: 0.8) MI: 0.8) MI: 0.5) 
VMS 100 VMS 100 100 100 100 VMS 2.0 VMS 2.0 DCP 2.2 DCP 2.2 VMS 2.0 
DCP 0.2 DCP 0.2 DCP 0.2 BTL 0.05 BTL 0.05 BTL 0.05 Gel 
fraction (%) 73 10 82 82 10 Joint Material PE (d: 0.935, PE (d: 0.935, 
PE (d: 0.945, PE (d: 0.945, PE (d: 0.935, (Parts) MI: 0.5) MI: 0.5) MI: 
0.8) MI: 0.8) MI: 0.5) 100 100 100 100 100 VMS 2.0 VMS 2.0 VMS 
2.0 VMS 2.0 VMS 2.0 DCP 0.2 DCP 0.2 DCP 0.2 DCP 0.2 DCP 0.2 BTL 0.05 
BTL 0.05 BTL 0.05 BTL 0.05 BTL 0.05 Gel fraction (%) 73 10 73 73 12 
Adhesive Base polymer PE (d: 0.935, PE (d: 0.935, EB (d: 0.88, LPE (d: 
0.925, -- (Parts) (100 Parts) MI: 0.5) MI: 0.5) MI: 3.2, mp: 119.degree. 
C., 100 100 B: 5%) MI: 0.8) VMS 2.0 VMS 2.0 (not water- (not 
water- DCP 0.2 DCP 0.2 curable) curable) BTL 0.05 BTL 0.05 Solvent, 
(parts) Tetradecane, 500 Tetradecane, 500 Xylene, 400 Decalin, 400 -- 
Water Initial Initial Initial .gtoreq.56 (note 1) .gtoreq.56 (note 1) 
.gtoreq.56, (note 2) pressure After heat After heat After heat 22 24 10 
(kg/cm.sup.2) cycle cycle cycle 
(note 1): ruptured at pipe portion 
(note 2): ruptured at joint portion 
EXAMPLES 25-31 
The composition of an adhesive used in each example, the results of the 
water pressure test conducted on the water cured polyethylene pipe 
connected by the procedure described below were shown in Table 2. 
PROCEDURE OF JOINING PIPES 
Both surfaces, to be joined mutually, of a cured polyethylene pipe 
measuring 26 mm in outside diameter and 3 mm in thickness and a water 
cured polyethylene socket joint measuring 26 mm in inside diameter and 3.5 
mm in thickness were heated at 230.degree. C., and then an adhesive held 
at 113.degree.-150.degree. C. was applied thinly on both the surfaces. 
After the surfaces were heated again at 230.degree. C., the pipe was 
inserted into the socket joint in about 15 mm insertion length, and thus 
the connected portion was cooled with air. 
WATER PRESSURE TEST 
(1) Short time test 
The pressure of water, maintained at 80.degree. C., filling an 
approximately 50 cm long specimen including the socket joint portion was 
progressively increased at a rate of 20 kg/cm.sup.2 /min. to rupture the 
specimen, and the pressure when the specimen ruptures was determined. 
(2) Long time test 
The water filling a specimen prepared in the same manner as above was 
maintained at 14 kg/cm.sup.2 and at 80.degree. C., and the time when water 
leakage did start from the joint portion was determined. 
TABLE 2 
__________________________________________________________________________ 
Example No. 25 26 27 28 29 30 31 
__________________________________________________________________________ 
Adhesive 
LPE (d: 0.92, MI: 2.5, mp: 124.degree. C.) 
100 -- -- -- 100 100 100 
(Parts) PE (d: 0.95, MI: 5) 
-- 100 -- -- -- -- -- 
PE (d: 0.92, MI: 1.5) 
-- -- 100 -- -- -- -- 
ES -- -- -- 100 -- -- -- 
VMS 2.0 2.0 2.0 -- 2.0 2.0 2.0 
DCP 0.1 0.1 0.1 -- 0.1 0.1 0.1 
BTL -- -- -- -- -- -- 0.05 
PF-1 -- -- -- -- 500 -- -- 
PF-2 -- -- -- -- -- 500 -- 
Xylene 500 300 1000 500 -- -- 500 
Temperature of Adhesive, when applied (.degree.C.) 
150 130 135 130 130 130 130 
Handling of Adhesive good good good good good good good 
Water pressure 
Short time test 20 20 20 20 20 20 20 
test Water pressure (kg/mm.sup.2) 
Long time test &gt;120 &gt;120 &gt;120 &gt;120 &gt;120 &gt;120 &gt;120 
Time (hr.) 
__________________________________________________________________________ 
EXAMPLE 32 
A compound consisting of 100 parts of polyethylene (d: 0.95 g/cm.sup.2), 
0.15 part of dicumyl peroxide, 2 parts of vinyl trimothoxysilane, and 0.05 
part of dibutyltin dilaulate was extruded at a temperature of 170.degree. 
C. to prepare a pipe measuring 60 mm in outside diameter and 4.5 mm in 
thickness. The same compound as above was injected to prepare a socket 
joint measuring 60 mm in length of pipe-insertion portion, 60 mm in inside 
diameter and 5.0 mm in thickness. To prepare an adhesive, 20 parts of a 
compound consisting of 100 parts of polyethylene (d: 0.95 g/cm.sup.2, mp: 
130.degree. C.), 0.15 part of dicumyl peroxide and 2 parts of vinyl 
trimethoxysilane was heat-dissolved in 100 parts of xylene. At the time of 
pipe joining, the gel fractions of the polyethylenes constructing the 
pipe, the socket joint and the adhesive were 20%, 15%, and a value lower 
than 1%, respectively. 
The adhesive was applied to the surfaces of connection portions of the pipe 
and the socket joint without preheating the surfaces, and then the 
surfaces were heated by using a heater held at a temperature of 
150.degree. C. for 20 seconds for the surface of the pipe, while for 40 
seconds for the surface of the socket joint in the same manner as shown in 
FIG. 2. After the heating, the pipe was inserted into the socket joint for 
about 60 mm in insertion length, while the insertion of pipe took 4 
seconds. The connected portion was allowed to cool under a careful 
management wherein the connected interface of the pipe and the joint was 
maintained stationary. 
Ten specimens, each of which includes the socket joint, thus obtained were 
subjected to the test described below. 
Although water-leakage was found in 5 specimens, there was no water-leakage 
in the remaining 5 specimens. 
WATER-LEAKAGE TEST 
Water at 80.degree. C. and 10 kg/cm.sup.2 was filled in the specimen for 
170 hours, thereafter it was inspected whether or not the water would leak 
from the connected portion of the specimen. 
EXAMPLE 33 
The joining operations of Example 32 were repeated except that the surfaces 
of the pipe and the socket joint were heated at 240.degree. C. for 20 
seconds, and after the adhesive was applied to the surfaces, the pipe was 
heated at 240.degree. C. for 20 seconds, while the socket joint was heated 
at 240.degree. C. for 40 seconds. 
EXAMPLE 34 
The joining operations of Example 33 were repeated except that in advance 
of joining operation the pipe and the socket joint were immersed in hot 
water held at a temperature of 80.degree. C. for 43 hours to be further 
water-cured. 
The polyolefin constructing the pipe and the socket joint had a gel 
fraction of 50% and 48% respectively, when the joining operation had 
started. 
EXAMPLE 35 
The joining operations of Example 33 were repeated with the exceptions of 
preheating (220.degree. C., 20 seconds) and heating after the application 
of adhesive (pipe: 220.degree. C., 30 sec.; socket joint: 220.degree. C., 
60 sec.). 
EXAMPLE 36 
The joining operations of Example 33 were repeated with the exception of 
using an adhesive which was prepared by dissolving 20 parts of a compound 
consisting of a linear polyethylene (d: 0.92 g/cm.sup.2, MI: 12.5 g/10 
min., mp: 120.degree. C.) 100 parts, vinyl trimethoxysilane 2.0 parts and 
dicumyl peroxide 1 part to 100 parts of decalin. 
The same water-leakage tests as described in Example 32 were conducted on 
the specimens of Examples 33-36. No water-leakage was found on 10 
specimens of each example. 
EXAMPLE 37 
By extruding (in the case of a pipe) or injecting (in the case of a socket 
joint) and heat-curing of a compound consisting of 100 parts of 
polyethylene (d: 0.945 g/cm.sup.3), 2.0 parts of dicumyl peroxide, 0.3 
part of 2,6-t-butylmethylphenol and 0.8 part of carbon black, was a pipe 
prepared having an outside diameter of 27.0 mm, a thickness of 3.0 mm, and 
a socket joint having an inside diameter of 27.0 mm and a thickness of 3.5 
mm. The cured polyethylene of the pipe and the socket joint had a gel 
fraction of 80%, and a tensile strength of 2.3 kg/mm.sup.2. 
A water-curable film to be used as adhesive, having a thickness of 0.2 mm 
and a tensile strength of 2.6 kg/mm.sup.2, was made of a compound 
consisting of polyethylene (d: 0.956 g/cm.sup.3, MI: 0.8 g/10 min) 100 
parts, vinyl trimethoxysilane 2.0 parts and dicumyl peroxide 0.2 part. 
The joining portions of the pipe and the socket joint were cleaned, covered 
with the adhesive film, and heated by using an iron heater held at a 
temperature of 200.degree. C., and then the pipe was inserted to the 
socket joint. 
EXAMPLE 38 
The joining operations of Example 37 were repeated with the exception of 
using a water curable polyethylene film having a density of 0.943 
g/cm.sup.2 and a tensile strength of 2.0 kg/mm.sup.2. 
EXAMPLE 39 
A compound consisting of polyethylene 100 parts, vinyl trimethoxysilane 2.0 
parts, dicumyl peroxide 0.2 part, dibutyltin dilaurate 0.05 part, 
2.6-t-butylmethylphenol 0.3 part and carbon black 0.8 part was used to 
prepare a pipe (outside diameter: 48.0 mm, thickness: 4.5 mm, gel 
fraction: 30%, and tensile strength: 2.5 kg/mm.sup.2) and a socket joint 
(inside diameter: 48.0 mm, thickness: 5.0 mm, gel fraction: 30%, tensile 
strength: 2.5 kg/mm.sup.2). 
The joining operations of Example 37 were repeated with the exception of 
using the above pipe and socket joint, and a pasty adhesive prepared by 
dissolving 1 part of a water curable polyethylene of silane graft type 
having a tensile strength of 2.8 kg/mm.sup.2 to 5 parts of xylene. 
EXAMPLE 40 
As an adhesive, a water curable polyethylene of silane graft type having a 
density of 0.952 g/cm.sup.3, and a tensile strength of 2.3 kg/mm.sup.2 
instead of the adhesive used in Example 39 was used to repeat the joining 
operations of Example 39. 
EXAMPLE 41 
A water cured polyethylene pipe (outside diameter: 48 mm, thickness: 4.5 
mm, gel fraction 30%, and tensile strength: 2.7 kg/mm.sup.2) is joined to 
a water cured polyethylene socket joint (inside diameter: 48 mm, 
thickness: 5.0 mm, gel fraction: 30%, and tensile strength: 2.7 
kg/mm.sup.2) using a pasty adhesive which was prepared by dissolving 1 
part of a water curable polyethylene (tensile strength: 3.2 kg/mm.sup.2) 
to 5 parts of xylene in the same manner as described in Example 37. 
EXAMPLE 42 
A water cured polyethylene pipe (outside diameter: 60 mm, thickness: 5.5 
mm, gel fraction: 30%, tensile strength: 2.5 kg/mm.sup.2) was joined to a 
water cured polyethylene socket joint (inside diameter: 60 mm, thickness: 
6.0 mm, gel fraction: 30%, tensile strength: 2.5 kg/mm.sup.2) by using a 
pasty adhesive which was prepared by dissolving 1 part of a water-curable 
polyethylene (tensile strength: 3.5 kg/mm.sup.2) to 5 parts of xylene in 
the same manner as described in Example 37. 
CREEP TEST 
Three specimens, each of which included the socket joint portion, were 
subjected to the Creep Test of JIS K 6774, Section 6.10 at 80.degree. C. 
for 1500 hours. Of the 3 specimens of Example 38, two specimens developed 
a leak from the joint portion after a 800 hours lapse (one specimen) and a 
1200 hours lapse (the other). The remaining one specimen had stood for 
1500 hours without any water leak. Of the 3 specimens of Example 40, one 
specimen developed a leak after a 1200 hours lapse, and the remaining two 
had stood for 1500 hours without any leak. While 3 specimens from each 
example of Example 37, 39, 41 and 42 had stood for 1500 hours without any 
leak. 
EXAMPLES 43-45 
A polyethylene, 0.92 g/cm.sup.3 in density, and 1.1 g/10 min in MI was 
extruded and heat-cured with use of dicumyl peroxide to obtain two pipes 
each having an outside diameter of 91 mm and a thickness of 5 mm and made 
of cured polyethylene having a gel fraction of 65%. The pipes were cut to 
form end faces perpendicular to the pipe axis and fittable to each other 
for joining. 
Each end face of the pipes was contacted by a hot plate held at a 
temperature of 235.degree. C. for several minutes to heat to a desired 
temperature. While, a film of adhesive, having a thickness of 2 mm, made 
of a water curable polethylene (d: 0.925 g/cm.sup.3, mp: 120.degree. C.) 
grafted with vinyl trimethoxysilane with the aid of dicumyl peroxide was 
put onto an above-mentioned hot plate to heat melt. At the time when the 
film as heated at a temperature over its melting point (heating for about 
60 seconds), the film was pressed by the end face of one pipe preheated, 
and then the end face covered with the adhesive was pressed by the end 
face of the other pipe also preheated to join each other. 
Temperatures at which the end faces of the pipes were preheated before the 
butt joint operation and the results of the water pressure test (rate of 
increasing water pressure: 20 kg/cm.sup.2 /min., water temperature: 
20.degree. C.) were listed in Table 3. 
TABLE 3 
______________________________________ 
Example No. 43 44 45 
______________________________________ 
Temperature of end faces (.degree.C.) 
160 200 240 
Water Strength against Water 
27 28 26 
Pressure 
Pressure (kg/cm.sup.2) 
Test Broken Portion pipe (not " " 
joint 
portion) 
______________________________________ 
EXAMPLES 46-47, COMISON EXAMPLE 4 
Two wooden pieces each measuring 5 mm in thickness, 10 cm in length and 2 
cm in width were heated at a temperature of 130.degree. C. for 1 hour, and 
an adhesive held at a temperature of 140.degree. C. was applied to both of 
the surfaces of the pieces. Thereafter each half length of the pieces were 
mutually superposed to press and bond by the action of adhesive. 
Adhesives used and force necessary to peel off determined according to peel 
off test described below were listed in Table 4. 
TABLE 4 
______________________________________ 
Compar- 
ison 
Example 46 
Example 47 
Example 4 
______________________________________ 
Adhesive Same as Same as Same as 
Ex. 4 Ex. 3 Com. Ex. 2 
Force Initial 30 30 30 
necessary to 
After heat 
50 45 10 
Peel Off (kg) 
cycle 
______________________________________ 
PEEL OFF TEST 
Force necessary to peel off is tensile strength (kg) at which a bonded 
wooden specimen subjected to tensile test separates into two pieces. Table 
4 shows two values. One is the initial value which was obtained on a 
specimen taken after a 2 hours lapse of bonding operation. The other is 
the value after heat-cycles of 1 month, in which the specimen was heated 
at 80.degree. C. for 12 hours and then cooled at 25.degree. C. for 12 
hours. 
TABLE 5-1 
______________________________________ 
A Acrylic acid 
B Butene-1 
BTL Dibutyltin dilaulate 
DCP Dicumyl peroxide 
EA Ethyl acrylate 
EAC Ethylene-acrylic acid copolymer 
EB Ethylene-butene-1 copolymer 
EEA Ethylene-ethyl acrylate copolymer 
EGA Acrylic acid grafted PE 
EGM Maleic acid grafted PE 
EH Ethylene-hexen-1 copolymer 
EM Ethylene-maleic acid copolymer 
(maleic acid: 1%, d: 0.92 g/cm.sup.3, MI:3.5 g/10 min.) 
EPDM Ethylene-propylene-dieneterpolymer (MI: 1.0) 
ES Water curable ethylene-silane copolymer 
EVA Ethylene-vinyl acetate copolymer 
H Hexen-1 
LPE Linear polyethylene 
M Maleic acid 
PE Polyethylene 
PE-A Acrylic acid grafted PE 
(acrylic acid: 0.4%, d:0.91 g/cm.sup.3, MI:13 g/10 min.) 
PE-M Maleic acid grafted PE 
(maleic acid: 0.2%, 0.93 g/cm.sup.3, MI:4 g/10 min.) 
PECl Chlorinated PE 
PF-1 Petroleum fraction (BP: 130-140.degree. C.) 
PF-2 Petroleum fraction (BP: 140-150.degree. C.) 
PP Polypropylene 
TAIC Triallylisocyanurate 
TMPAF 3-Trimethoxysilyl propylazido formate 
VA Vinyl acetate 
VMS Vinyl trimethoxysilane 
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TABLE 5-2 
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XEP-1 Cured EPDM compound: 
EPDM (d: 0.87 g/cm.sup.3 
100 parts 
Moony viscosity/ML.sub.1+4, 100.degree. C./:20, 
diene: dicyclopentadine) 
ZnO 5 parts 
Stearic acid 1 part.sup. 
HAF carbon 55 parts 
Naphthene oil 10 parts 
Sulfur 1 part.sup. 
2-Mercaptobenzothiazole 0.5 part.sup. 
Tetramethylthiuram monosulfide 
1.5 parts 
XPECl-1 Cured flame-resisting PECl compound: 
PECl (Cl: 32%, d:1.15 g/cm.sup.3, 
100 parts 
MI: 0.4 g/10 min.) 
Sb.sub.2 O.sub.3 10 parts 
Tribasic lead sulfide 1.5 parts 
DCP 3.5 parts 
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