Manufacture of articles of polyvinyl chloride foil with sealed-in reinforcement material

A method of manufacturing articles of softened polyvinyl choride reinforced with a reinforcement material. The method includes the steps of coating one surface of each of two perforated polyvinyl chloride foils with a terpolymer of vinyl chloride, vinyl acetate and an unsaturated carboxylic acid bringing the coated surface of each of the foils into contact with an opposite surface of said reinforcement material, sealing the portions of the foils situated along the edges of the reinforcement material in a high frequency field to form sealed seams and pressing the foils and interposed reinforcing material at an elevated temperature and pressure to secure the foils to the reinforcement material.

BACKGROUND OF THE INVENTION 
This invention relates to a method of manufacturing reinforced articles of 
softened polyvinyl chloride. In particular, an assembly formed by a layer 
of reinforcement material having on each side at least one foil of 
softened polyvinyl chloride is introduced into a high-frequency field, and 
the parts of the foils situated along the edges of the reinforcement 
material are sealed together to form seams. 
The reinforcement material is plate-shaped, may consist of several parts 
and generally has fibrous structure. For example, the reinforcement 
material may be composed of paper, cardboard or a plastic such as 
synthetic foam, cheap, moisture-sensitive but reasonably rigid cardboard 
being frequently used as a reinforcement material in articles made of 
softened polyvinyl chloride. 
According to a conventional method of manufacturing such articles, one or 
several parts or sheets of reinforcement material are laid between foils 
of softened polyvinyl chloride. This assembly, which has a sandwich 
structure, is then placed in a high-frequency sealing machine in which the 
sheets of reinforcement material situated between the foils are sealed-in 
along the edges by means of a high-frequency electric field. For this 
purpose, the polyvinyl chloride foils must extend beyond the peripheral 
edges of the reinforcement material so as to enable the sealing together 
of the polyvinyl chloride foils along the edges. When several sheets of 
reinforcement material are used, some space or clearance is present 
between the various sheets. 
The resulting flat sandwich product with sealed-in parts or sheets of 
reinforcement material, sometimes termed plano product, is then 
mechanically given the desired shape or configuration determined by the 
final product, for example, by folding. 
The kind and quality of high-frequency field generated in the sealing 
machine is determined by the electrodes used therein. By varying the shape 
of the electrodes, the sealed seams obtained in the plano product can be 
varied. This means that the shape of the sealed-in parts of reinforcement 
material may differ considerably in accordance with the electrodes used so 
that a variety of articles can be manufactured from the plano product. 
Examples of such articles are packaging or storage units; for example, 
portfolios, cases, handbags, boxes, suitcases and the like. 
After the shaping of the articles, further mechanical components of metal 
or synthetic resin such as hinges, closures, rings or clamps are nearly 
always provided. These components are fixed in the article in question by 
means of rivets or staples, the rivet or staple perforating the assembly 
of foils with intermediate reinforcement material. 
The disadvantage of the method described is that air can penetrate into the 
various sealed-in compartments via the perforations caused by the staples 
and rivets so that the foil of softened polyvinyl chloride surrounding the 
reinforcement material starts showing ruffles. In the absence of 
perforations, the polyvinyl chloride foils will also show undulations 
after a shorter or longer period of time as a result of heating, for 
example, by sunlight, so that the product becomes unsalable. 
According to another method, each foil is provided on one side over a 
portion of its surface with a layer of aqueous glue. The size and shape of 
any portion of the surface which is provided with the layer of glue must 
accurately correspond to the size and shape of the sheet of reinforcement 
material used. The sheets of reinforcement material are accurately 
disposed on the surface of one of the two foils provided with glue in such 
manner that the glued portions of the foil are exactly covered by the 
reinforcement material. The second foil is then provided in the same 
accurate manner over the surface of the reinforcement material remote from 
the first foil, with the layer of glue facing the reinforcement material. 
The portions of the two foils not provided with glue are then sealed 
together along the edges of the reinforcement material in a high-frequency 
field. The whole process is carried out in an expensive automatic 
glue-sealing machine which is designed especially for this purpose. 
The advantage of this method over the first-mentioned method is that 
ruffles of the foils are substantially suppressed, even if comparatively 
thin foils of softened polyvinyl chloride are used. 
A disadvantage of the method is the high purchasing price of the required 
automatic glue-sealing machine. A further disadvantage is that, as already 
described above, the layer of glue has to be provided very accurately. If 
the layer of glue extends to just beyond the reinforcement material, an 
imperfect seal is obtained; that is, a sealed seam having too low a 
sealing strength so that the seal can easily be broken. If, on the other 
hand, the layer of glue does not extend entirely up to the edges of the 
reinforcement material, an air-filled space will be present between the 
sealed seam and the foils glued to the reinforcement material after the 
sealing process. As a result, ruffles will be formed in the polyvinyl 
chloride foils under the influence of pressure and temperature variations 
of the ambient air and furthermore delamination of the glued foils may 
take place. Another disadvantage of this method is that when switching 
from one product to another, the operations required for readjustment of 
the automatic glue-sealing machine are time-consuming and in addition can 
be carried out only by highly skilled technical personnel. Consequently, 
the method described is less suitable for manufacturing products in 
comparatively small quantities. 
SUMMARY OF THE INVENTION 
Applicants have developed a method which does not exhibit the 
above-mentioned disadvantages. In this method, perforated polyvinyl 
chloride foils are used wherein the entire surface facing the 
reinforcement material is provided with a coating containing a terpolymer 
of vinyl chloride, vinyl acetate and an unsaturated carboxylic acid. After 
the parts of the foils situated along the edges of the reinforcement 
material have been sealed together in a high-frequency field to form 
sealed seams, the parts of the foils situated between the sealed seams are 
glued to the surface of the reinforcement material at elevated temperature 
and pressure. 
The method according to the invention permits manufacturing products having 
excellent quality with simple and non-expensive apparatus. This makes 
economic manufacture of a relatively small quantity of a given product 
possible. For example, the method according to the invention may be 
implemented using only a simple high frequency sealing machine and a 
press. 
With regard to simplicity, the method according to the invention can best 
be compared with the above-described first method in which foils not 
having a layer of glue are used and in which the edges of the foils are 
welded in a high frequency sealing machine albeit, in the present 
invention, a simple after-treating pressing process is necessary. 
The perforated foils of softened polyvinyl chloride which are used in the 
invention and which are provided on one side with the above-mentioned 
terpolymer can be manufactured in a simple manner. For example, the 
perforated foil may be made by unwinding a long rolled-up foil in a 
continuous process and passing it below spraying or nebulizing apparatus 
in which a solution or dispersion of the above-mentioned terpolymer in a 
suitable solvent is nebulized on the surface of the foil track by means of 
nozzles. A suitable solvent is an organic liquid such as ethyl acetate or 
methyl ethyl ketone. The terpolymer may also be provided on the foil by 
means of a pressure process using pressure rollers. The concentration of 
the terpolymer in the solvent is not restricted to narrow limits and in 
general is from 10 to 25% by weight. The foil provided with the terpolymer 
is then passed through a drying zone in which most or all of the solvent 
is sucked off at elevated temperature. The foil which is then ready for 
use is wound on a storage reel. 
The layer thickness of the provided terpolymer is small, preferably from 1 
to 5 .parallel.m. 
The foil provided with the above-mentioned terpolymer remains stable for a 
long period of time and does not show signs of quality deterioration 
during prolonged storage at elevated temperature of approximately 
70.degree. C. The terpolymer provided on the foil is resistant to 
migration of softeners from the softened polyvinyl chloride foil even if a 
softener-sensitive solvent is used during application of the terpolymer. 
The terpolymer surface keeps its non-sticky characteristic after prolonged 
storage. With regard to ease of processing, the foil provided with a 
terpolymer can be compared with a polyvinyl chloride foil not provided 
with a coating. 
Another essential property of a foil of softened polyvinyl chloride 
provided with terpolymer coating is its excellent sealability. Two foils 
provided with terpolymer can be sealed together by coating their surfaces. 
The sealing strength of the resulting sealed seam is significantly higher 
than the tensile strength of the softened foil so that the sealed seam 
cannot be "peeled". This good sealability which corresponds to that of an 
uncoated foil, permits use of a foil which is provided with the terpolymer 
coating throughout its surface. 
It is consequently not necessary or desired in practising the invention to 
use an expensive machine such as an automatic glue-sealing machine with 
which sharply defined surface parts can be provided with a coating. The 
time-consuming and expensive readjusting operations required when such a 
machine is used are not necessary. Also, the above-described disadvantages 
resulting from an incorrect readjustment operation, for example, ruffles 
and delamination of the foil, do not occur in the method according to the 
invention. 
When carrying out the invention, the required layers of reinforcement 
material are placed in the desired pattern between two foils which have 
their coated surfaces facing each other. This sandwich assemby is passed, 
for example, via a transport belt, into a high-frequency sealing machine 
and the foils are then sealed against each other along the edges of the 
inlaid reinforcement material under the influence of the applied 
high-frequency field. The resulting product with sealed-in reinforcement 
material is then passed into a press in which the non-sealed foil parts 
are glued to the reinforcement material under elevated temperature and 
pressure. 
Activation of the terpolymer layer, which is necessary for gluing, must 
take place through the polyvinyl chloride foil at a temperature of at 
least 70.degree. C. but preferably not higher than 120.degree. C. It has 
been found that when so-called decorative polyvinyl chloride foils are 
used, that is, foils having a structured surface, a comparatively high 
activation temperature of 110-120.degree. C. is still possible without 
glossy speckles being formed during the pressing process on the raised 
foil parts. In such a case, a moderate pressing pressure having a maximum 
value of 3 kg/cm.sup.2 should be used on the product to be activated for a 
period of not more than 10 seconds. At a lower activation temperature, the 
pressing pressure and cycle time used are less critical. Depending in part 
on the foil thickness and the temperature, the pressure may generally vary 
from 0.5 to 3 kg/cm.sup.2. In order to promote the speed of processing the 
pressure time is preferably chosen to below, and is roughly from 1 to 5 
seconds. 
The gluing of the foils to the reinforcement material obtained according to 
the invention is excellent. Life tests have demonstrated that the 
resulting products do not show any visible deterioration in quality and, 
in particular, there is no delamination of the foil and reinforcement 
material after storage for weeks under moist conditions and at 
temperatures of 60, 70, 80 and 90.degree. C. 
As stated, a perforated foil is used; that is, before the gluing process 
takes place the foil must be perforated. Experiments performed with 
non-perforated foils and cardboard as a reinforcement material have 
demonstrated that, although good adhesion between the foil and the 
cardboard is obtained, excessive pressure occurs as a result of expanding 
air and water evaporating from the cardboard when the press is opened 
causing delamination of the cardboard structure in layers. 
In the preferred embodiment of the invention, a terpolymer is used 
containing from 80 to 85 parts by weight of vinyl chloride, from 12.5 to 
17.5 parts by weight of vinyl acetate and from 0.5 to 2.5 parts by weight 
of an unsaturated mono- or dibasic carboxylic acid. Examples of suitable 
carboxylic acids are monobasic carboxylic acids such as acrylic acid, 
methacrylic acid or derivatives thereof. Particularly suitable are dibasic 
unsaturated carboxylic acids, such as maleic acid, itaconic acid or 
derivatives thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A softened perforated polyvnyl chloride foil having an extended length, a 
width of 150 cm and a thickness of 0.25 mm was coated on one side by means 
of a coating process with a 3 .mu.m thick coating of a terpolymer 
consisting of 85% by weight vinyl chloride, 14% by weight vinyl acetate 
and 1% by weight maleic acid. For this purpose, the foil was treated with 
a solution of the termpolymer in methyl ethyl ketone containing 200 grams 
of terpolymer per liter, after which the solvent was removed by sucking it 
off at a temperature of 60.degree. C. The foil provided with this coating 
can be rolled without sticking of the foil parts and is stable for a long 
period of time. 
Apparatus for manufacturing an article reinforced by means of reinforcement 
material while using the coated polyvinyl chloride foil is shown in FIG. 
1. 
Reference numeral 1 in FIG. 1 denotes a polyvinyl chloride foil which is 
provided on its upper surface with a terpolymer coating. The foil 1 is 
passed below an automatic cardboard inlay machine 3 by means of transport 
belts 2, which cardboard inlay machine 3 comprises a cardboard store 5 
filled with cardboard parts 4. Foil 1 is fed continuously with the 
cardboard parts 4 on the side of the foil having the terpolymer coating. 
It is to be noted that the cardboard parts are not contiguous but are 
provided on the foil path 1 with a significant intermediate space 6 as a 
result of the operation of the automatic cardboard inlay machine. 
A second softened polyvinyl chloride foil 7, which is also provided on one 
side with a terpolymer coating, is positioned continuously by guide 
rollers 8 over the first foil 1 provided with cardboard parts 4, the 
coating of foil 7 engaging the cardboard parts 4. The resulting assembly 
is further transported by transport belt 2 into an automatic sealing 
machine 9. The automatic sealing machine 9 comprises a pressure plate 10 
of aluminum which is connected on its upper side with a hydraulically 
operated plunger 11 and is provided on its lower side with narrow brass 
electrodes (not shown). Plunger 11 passes through guide member 12 which 
has an aperture 13 and guide member 12 is connected to stand 14 which 
comprises a supporting member 15. By using a high-frequency current in the 
narrow brass electrodes a temperature of approximately 180.degree. C. is 
obtained. At a pressure of approximately 0.5 kg/cm.sup.2 for 2 to 3 
seconds, the foil parts 16 situated along the edges of the cardboard parts 
4 (see FIG. 2) are sealed together by means of the current flowing between 
the brass electrodes. 
FIG. 2 shows the resulting sealed product in which for corresponding 
components the same reference numerals are used as in FIG. 1. The parts 16 
of the foils 1 and 7 situated between cardboard parts 4 are sealed by 
using sealing electrodes 17 while forming sealed seams 18. The outermost 
sealing electrodes shown in FIG. 2 are provided with a cutting edge 19 so 
that the resulting sealed seams 18 comprise a groove 20. The sealed 
product can afterwards be easily torn or separated by tearing along this 
groove. The thickness of the polyvinyl chloride foils below the grooves is 
approximately 0.1 mm. 
The thus sealed product 28 is introduced into a press 21 (see FIG. 1) 
between two press plates 22 and 23 heated at 100.degree. C. The product is 
pressed with a force of 1.5 kg/cm.sup.2 for 4 seconds, the foils 1 and 7 
adhering to the intermediate cardboard parts 4 by means of the terpolymer 
layers present thereon. The upper press plate 22 is connected to plunger 
24 which travels through an opening in guide plate 25 which can be 
operated hydraulically or pneumatically. Guide plate 25 is connected to 
stand 26 and the lower plate 23 has a supporting plate 27. The press 
plates 22 and 23 on their free surfaces, hence facing the sealed product, 
are provided with a collapsible buffer plate (not shown) which is formed 
by an open-pored foam plate. The collapsible buffer plate is of 
considerable importance and presents the advantage that volatile 
constituents which may be present in the cardboard, for example a moisture 
as well as enclosed air, can escape via the pores in foils 1 and 7 and via 
the open foam structure of the buffer plate. Furthermore, the buffer plate 
has a protective function with respect to the sealed product in that 
relief printing or surface structure provided on the foils is completely 
retained. Finally, the buffer plate has the advantage that it compensates 
for differences in cardboard thickness. 
The resulting sealed and glued product 29 is transported by means of 
rollers 30 and finally separated by tearing along the grooves 20 shown in 
FIG. 2. 
It is to be noted that the foils 1 and 7 are glued to cardboard part 4 in 
sealed and glued product 29 shown in FIG. 2. The resulting plano product 
can be folded along the sealed seams between the cardboard part 4 and 
thereby transformed into a three-dimensional article, for example a 
portfolio. The desired closures, clamps, rings and the like can be 
provided in the article by finishing operations. 
It will be understood that the above description of the present invention 
is susceptible to various modifications, changes and adaptations, and the 
same are intended to be comprehended within the meaning and range of 
equivalents of the appended claims.