GB2100660A

GB2100660A - Stamped plastics sheet

Info

Publication number: GB2100660A
Application number: GB08210640A
Authority: GB
Inventors: Katsushi Jinno; Kenichi Maemoto
Original assignee: Nissan Chemical Corp
Current assignee: Nissan Chemical Corp
Priority date: 1981-04-20
Filing date: 1982-04-13
Publication date: 1983-01-06
Also published as: GB2100660B; DE3214568A1; PH20242A; FR2504055B1; KR830009915A; FR2504055A1; KR870000229B1

Abstract

To produce a stamped sheet of thermoplastics material, film-shaped molten thermoplastics material is supplied from a die (d) to a pair of stamping rollers (r, r') disposed in a bath (v) containing liquid refrigerant (W), such as water. The thermoplastics material passes between the rollers where they engage and is thus stamped by virtue of at least one of the rollers having an uneven outer wall corresponding to a configuration and/or pattern of characters, figures, symbols, pictures or the like. The stamping occurs before the thermoplastics material has solidified to the core, i.e. the core is soft, although a solidified skin layer has formed on the surface of the material. A sheet produced by the method has ribs (1) arranged at regular intervals and extending in a predetermined direction. Each rib is divided by a plurality of hill parts (2) to form individual peak parts (3). The configuration of the sheet means that forces can be absorbed by the peaks (3) to give the sheet an excellent shock absorbing quality. <IMAGE>

Description

SPECIFICATION Stamped plastics sheet, and method of manufacturing same This invention relates to a novel simple method of providing a stamped plastics sheet high in utility value in which a thermoplastics film or sheet (hereinafter referred to as "a sheet", when applicable) is permanently stamped, and to a novel and useful stamped plastics sheet which is provided by the method.

.In general, in stamping a plastics sheet, a sheet-shaped or cylinder-shaped molten thermoplastics material extruded from the nozzle of a T-die, screw die or circular die is allowed to pass through the clearance or gap between stamping rolls, such as emboss rolls, so as to be pressed while being either heated, kept warm or cooled. Especially in manufacturing an uneven wavy sheet, the sheet should be stamped while the core of the sheet is soft.

Accordingly, in the case of a thin sheet, temperature must be strictly controlled before it is stamped. On the other hand, in the case of a thick sheet, two contradictory conditions must be satisfied, that is, while it takes a lot of time to soften the sheet to the core, the stamped sheet must be quickly cooled down to a temperature at which is is not deformed.

Thus, stamping a thick sheet is more difficult than stamping a thin sheet. Therefore, in stamping a thick sheet, it is necessary to reduce the stamping speed to an uneconomical speed or to provide an additional means such as special cooling rollers. In the latter case, the cooling rollers must be precise ones, and a new mechanical problem such as the synchronization in pitch of the unevenness of the cooling rollers is involved.

A primary object of the present invention is to solve the above-described problems accompanying a conventional method of manufacturing stamped sheets, by providing a novel method in which a film is formed and stamped in a single process. A further object of the present invention is to provide a method of readily manufacturing a thick crystalline plastics sheet which is stable in quality.

A still further object of the present invention is to provide an excellent shock absorbing sheet which is special in configuration and structure.

According to the present invention, there is provided a method of manufacturing a stamped plastics material sheet comprising supplying film-shaped molten thermoplastics material to a pair of stamping rollers placed in a liquid refrigerant, and stamping said material by means of said stamping rollers before said material is solidified to the core thereof.

According to another aspect of the present invention, there is provided a stamped sheet of a flexible thermoplastics material, having ribs which are arranged at regular intervals and extend in a predetermined direction, each rib being divided by hill parts, having sides extending downwardly from a top portion of said rib, to form individual peak parts.

Thus in the method of the invention, the material is continuously subjected to stamping by the stamping rollers while the core of the material is soft, although a solidified skin layer has been formed on the surface of the material.

Examples of the thermoplastics employed in the invention are polyesters, such as for instance polyethylene terepthalate; polyamides such as for instance nylon 6; polyolefins such as polyethylene, polypropylene and polystyrene, and the copolymers thereof; and polyvinyl halagenides such as polyvinyl chloride and polyvinylidene chloride. The method of the invention is especially effective with crystalline polymers.

The stamped sheet manufactured by the method of the invention may be a solid sheet which is not foamed, or a foamed sheet which is obtained by extruding at high temperature the above-described thermoplastics material with a foaming agent added. Furthermore, the method of the invention can be used to produce a fiber-reinforced resin (FRR) sheet which includes glass fibers or carbon fibers. In the latter case, the foamed sheet itself is low in heat conductivity. However, stamping can be readily achieved because, in the method of the invention, foaming and sheet formation are carried out substantially at the same time.

In a conventional method, it is difficult to stamp the above-described FRR sheet if it has been cooled and solidified. However, as stated, it can be readily stamped according to the method of the invention. A pigment such as titanium dioxide, a filler such as talc, a plasticizer, a weather resisting agent and/or a thermal-deterioration preventing agent may be mixed, if required.

The molten plastics material is preferably supplied to the stamping rollers directly from an extrusion die such as a T-die, screw die or circular die. However, it may be supplied through rollers which maintain molten the sheet material to be stamped. The stamping rollers are generally arranged in the liquid refrigerant to the engagement line thereof.

However, it is preferable that the stamping rollers are immersed in the liquid refrigerant.

The liquid refrigerant is, in general, water.

However, it may be low aliphatic alcohols or hydrophilic solvent such as polyethylene glycol, or mixtures of the former and the latter.

The molten resin material may be introduced directly into the liquid refrigerant, or it may be introduced into the liquid refrigerant after being guided onto the surface of a drum.

The latter method is advantageous in that the degree of "neck-in" is reduced. Even when the molten plastics material is introduced di rectly into the liquid refrigerant, problems such as foaming are rarely caused. Conditions affecting the stamping, such as the temperature of the liquid refrigerant, the time between the extrusion and the stamping operation, and the arrangement of the stamping rollers must be carefully determined. However, they cannot be simply determined because they depend on the kind of resin employed, the thickness of the sheets, the atmospheric temperature, etc. For instance, the temperature of the liquid refrigerant is in the range of from 0 C to 1 00'C, preferably lower than 60 C.

The lower the liquid refrigerant temperature, the greater the cooling effect, However. as the liquid refrigerant temperature decreases, the stamping speed must be increased. Accordingly, in this case, it is necessary to take the arrangement of rollers and the sheet moving speed into sufficient consideration. If, on the other hand, the temperature of the liquid refrigerant is high, the cooling speed is low.

Therefore, in this case. the degree of freedom is selecting the sheet moving speed is increased, However with crystalline resin, crystallization advances and accordingly stamping becomes difficult In the method of the invention, a variety of stamping rollers may be employed according to the configurations or patterns which are to be given to the sheets. One pair of stamping rollers is employed. Desired configurations and/or patterns are formed on the outer walls of the two stamping rollers. However, one of the two stamping roller may be a roller having a smooth outer wall which is made of elastic rubber material. The patterns employed are of characters, figures, symbols and/or pictures.

The stamping rollers may be a pair of runners, a a pair of engaging rollers, or a pair of unitary rollers, In the case of a conventional pair of stamping rollers, the uneven wall surface of one stamping rollers must be completely engaged with that of the other one, On the other hand, in the case of a pair of stamping rollers, it is not always necessary that the uneven wall surfaces thereof are completely engaged with each other, As was described above, in the shaping stage of the invention, stamping is carried out after a skin layer is formed on the surface of the film-shaped molten plastics material by virtue of cooling carried out by the refrigerant.Therefore, the film-shaped resin to be stamped shows behaviour similar to that of solid resin Accordingly, although the filmshaped molten plastics material is substantially plasticized, it will never be holed even when it hangs down naturally (or it deformed by drive power or centrifugal force) or contacts sharp portions of the rollers. In addition the film-shaped molten plastics material is scarcely wound on the roller or rollers.

On of the specific features of the invention is that it is unnecessary sufficiently to engaqe the ; .n v" and concave parts of one of the rollers ';';th the concave and convex part of the other This means that useful stamped sheets can be manufactured in the method of the Invention even if special stamping rollers, the use of which has never previously been contemplated, are employed, In the method of the invention, a unique stamping sheet can be obtained by using in combination a roller having regular wavv ribs and a roller having recesses everywhere on wavy ribs which are engaged with the former ones, The stamped sheet manufactured by these rollers is useful as a shock absorbing sheet.

When stamping is carried out with the above-described roller under the condition that the respective uneven surfaces are not completely engaged with each other, the resultant sheet is pitched by the convex parts of the roller because of the skin layer on the surface of the film-shaped molten plastics material supplied to the rollers.If, in this case, the roller is of the type in which the recesses are formed everywhere on the wavy ribs, the sheet is pitched by protruding parts on both sides of the recess, as a result of which a unique stamped sheet is obtained which is slackened at the recesses, These stamping mechanisms are completely different from a conventional one for thermoplastics material, In injection molding, stamping is carried out by the pressure of resin filling the cavity between two metal molds, In calendering, embossing is effected by pressing resin between a pair of rollers, In thermo-forming, stamping is carried out with a resin film being brought into contact with the inner surface of a metal mold on the negative pressure side by pressure difference and in a sizing system, stamping is carried out under a partial forcing pressure in the clearance of a sizing plate or sizing mandrel, Thus, they are fundamentally different in mechanism from the stamping according to the invention which utilizes a pitching action.

The reason why the invention utilizes the novel stamping mechanism is that, because of the cooling effect of the refrigerant, the formation of the skin layer on the surface of the molten plastic material and the solidification of the core of the latter occur successively for a very short period of time, It is preferable that, in the method of the invention, the sheet from the stamping rollers is moved in the refrigerant along a tangential line which touches the rollers at a stamping point (at which the rollers engage with each other). In this case, even a rigid stamped sheet having ribs extended in the direction of movement thereof can be formed substantially free from distortion or twist The direction of the tangential line is not strictly critical. That is if the sheet is moved at less than 30 , preferably less than 1 0,, with respect to the tanaential line, then an excellent result can be expected.

What is most intereting in practical use among the various stamped sheets manufactured by the method of the invention is a stamped sheet the ribs of which are formed by the aforementioned pitching action and are divided everywhere.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure la is a plan view of a first type of shock absorbing sheet manufactured according to the present invention; Figure 1b is an inverted plan view of the sheet shown in Fig, 1 a; Figures 1c and 1 d are cross-sectional views on the lines A-A and B-B of Fig, la; Figures 2a and 2b are views equivalent to Figs. 1 a and 1 b but in respect of a second type of shock absorbing sheet manufactured according to the invention; Figures 2c and 2d are cross-sectional views on the lines C-C and D-D respectively in Fig.

2a; Figures 3a and 3b are views equivalent to Figs. 1 a and 1 b, but in respect of a third type of shock absorbing sheet of the invention; Figures 3c-3e are respective cross-sectional views on the lines E-E, F-F and G-G in Fig.

3a; Figure 4 is an enlarged sectional view of the section shown in Fig. 3e; Figures 5 and 6 are diagrams showing apparatus for carrying out two alternative methods of forming stamped sheet in accordance with the invention; Figures 7 and 8 respectively show alternative forms of stamping roller pairs for use in the apparatus of Figs. 5 and 6; Figure 9 is a plan view of a fourth type of shock absorbing sheet of the invention; Figures 10 and 11 are cross-sectional views on the lines A-A and B-B respectively in Fig.

9; Figure 12 is a side view of a pair of rollers for manufacturing the sheet shown in Figs.

1a-1d; Figures 13a and 13b show parts of the outer walls of the two rollers respectively shown in Fig. 12; and Figures 14 and 15 show further alternative types of roller pairs respectively for manufacturing stamped sheets according to the invention.

Figs. 1 through 3 show typical examples of the uneven surface pattern and the structure of respective stamped plastics sheets according to the invention. As shown in Figs. 1 through 2, the patterns are formed with various parts which are different in configuration and in height. In each of the parts (a) and (b) of Figs. 1 through 3, reference symbols 0, X and A designate parts which are highest, lowest and mid-way between highest and lowest in height respectively, so that a peak part (or an edge part), a valley part and a hill part can be readily distinguished from one another.

Further in the parts (a) and (b), the direction of width of the sheet is indicated by the double-headed arrow.

In the exampe shown in Fig. 1, ribs 1 and 1' are provided alternately at equal intervals in such a manner that they are in parallel with the direction of the width of the sheet. On the front side of the sheet, each rib 1 is divided by a plurality of hill parts 2, which are relatively small and are arranged at equal anter- vals, to define separate peak parts 3 along the rib 1. The sheet has a plurality of valley parts 4 4 which are in the form of elongated grooves, which are the edge parts 1 a' of the rear side.

The top surface of each edge part is substantially flat.

In the example of Fig. 2, the sheet has a plurality of ribs 1 and 1' which are in parallel with one another and are arranged at equal intervals. The ribs form an angle of approximately 15 with the direction of the width of the sheet. On the front side, each rib 1 is divided by hill parts 2 which is relatively large in width, thus forming individual peak parts 3. The sheet has valley parts 4 which, similarly as in the example of Fig. 1, are elongated grooves which are the edge parts 11' of the rear side. Similarly as in the example of Fig. 1, the top surface of each edge part is substantially flat. The second sheet type shown in Fig. 2 is similar to that shown in Fig. 1, except that the ribs are inclined with respect to the direction of the width of the sheet.Both of the examples belong to a sheet type having one of the ribs on both its sides divided by hill parts, thus forming the peak parts.

In the example shown in Fig. 3, the sheet has ribs 1 and 1' which extended at angles of 45 and 1 35' respectively with respect to the direction of the width of the sheet. Peak parts are formed at the intersections of the ribs 1 and 1'. A valley part is surrounded by four adjacent-ribs. Each peak part 3 on the front side rises, thus forming a valley part 4 on the rear side. In this example also, the top surface of each peak part 3 and the bottom surface of each valley part are substantially flat.

In the above-described three examples, each valley part between two adjacent peak parts is made concave, thus serving to disperse a pressure which is applied to the flat peak parts. In the case where, as shown in Fig. 1, the hill parts separating the peak parts 3 extend perpendicularly to the direction of the ribs, the hill parts form auxiliary ribs connecting the ribs 1 and 1' a viewed from the rear side (the part (b)). Therefore, elongation perpendicularly to the ribs 1 and 1' is considerably limited, and accordingly the impact withstanding characteristic is significantly improved. In the example shown in Fig. 3, since the ribs are intersected, elongation in all direction is limited, and therefore the compression resisting force is much larger than that of the sheet shown in Fig. 1.

In sheets according to the invention, the top surfaces of the ribs and/or the peak parts are made as flat as possible. As is apparent from Fig. 4, a compression force indicated by the arrow P deforms the top portion 3a of the peak part 3 as indicated by the dotted line.

However, the compression force is transmitted to an article A through the valley parts 4 and two peaks 3,' and 32' on the opposite side.

Therefore, according to a simple calculation, the compression force P is reduced to a quarter (k) when transmitted to the article A, because four peaks (including two more peaks (not shown) on this side are provided. In practice, the flat top portion 3a to which the force is applied directly undergoes brittle fracture, whereby a large part of the energy is absorbed. Accordingly, the force applied to the peaks 3,' and 32' becomes much smaller.

While the top portion 3a of the peak part 3 receives the compression force P completely, the boundary portion between the top portion and the middle portion 3b is acutely bent, as a result of which the brittle fracture occurs more readily. Since the hill part 2 between the peak parts is concave as described before, the peak part will not be broken completely by the compression force. That is, a part of the compression force is transmitted through the hill part 2 and the valley part 4 to the other peak parts, hill parts and valley parts adjacent thereto successively. Thus, the sheet has excellent shock absorbing properties.

The behaviour of the sheet has been described with reference to the case where a compression force is applied to a point on the sheet. However, it can be understood that the same effect is obtained when a compression force is applied to a line in the sheet or on a surface of the sheet. In the latter case, the shock absorbing effect is increased because the compression force is borne by more peaks. The sheet shown in Fig. 3 is sufficiently flexible in any direction, thus being excellent as a shock absorbing sheet.

The shock absorbing sheet shown in Fig. 1 is suitable for wrapping a relatively long arti cle such as a fluorescent lamp, because it is flexible in the longitudinal direction thereof.

The sheet is scarcely expanded in the longitudinal direction, and a number of peak parts supports a compression force. Therefore, the shock absorbing effect thereof is much higher than that of the conventional wavy shock absorbing material.

The shock absorbing sheet shown in Fig. 2 is also considerably flexible in the longitudinal direction thereof, and especially its peak parts are bendable in the direction of width. Therefore, the impact is greatly released by brittle fracture and flexibility.

In addition to the above-described three examples, many other examples of sheet can be provided according to the invention. These examples are in common with one another in that the ribs are arranged regularly in predetermined directions on one or both sides, and in that, in the case where the ribs are provided on one side only, the ribs are divided by a number of recessed parts, and in the case where the ribs are provided on both sides, the ribs on at least one side are divided by a number of recessed parts, the individual peak parts, which are formed by the division with the recessed parts, being connected to one another through the concave hill parts.

In the above-described examples, the top surface of each peak part is flat. However, it is not always necessary to make the top surface flat. For instance, even if the top surface of each peak part in Fig. 3 were to be formed spherical, a sufficient shock absorbing effect through deformation and brittle fracture would still be expected.

The direction of the ribs should be suitably determined according to the purpose of use of the sheet. However, in general, in the case where the sheet is used to wrap a long article in the form of a cylinder, the ribs should extend in the direction of width of the sheet or in the longitudinal direction of the same, or the ribs should extend within an angle of 10' with respect to the widthwise direction or longitudinal direction even when they are formed somewhat inclined. On the other hand, in the case where the sheet is used to wrap an article along the longitudinal direction and widthwise direction, it is most suitable that, as shown in Fig. 3. to provide ribs which intersect at right angles, or ribs which intersect forming angles of 45 and 1 35' with respect to the widthwise direction or the longitudinal direction.A sheet having ribs which extend in the widthwise direction and the longitudinal direction is slightly lower in flexibility in the widthwise direction and the longitudinal direction than the above-described sheet. However, even in the case of the sheet a shown in Fig. 1, which is low in flexibility in the widthwise direction, the flexibility can be substantially improved by providing flexing ribs which are indicated by reference numeral 6 in Figs. 9 through 11, and are arranged at predetermined intervals in the longitudinal direction.

In the case where the sheet is formed by a means for continuously producing sheets (to be described later), the pitch of the ribs is practically limited by the desired height of the ribs, i.e. the thickness of the sheet (not being the thickness of the material for forming the sheet). As the rib's height is increased, the rib's pitch is necessarily increased. If the height of the ribs is large, then the shock absorbing capability is increased to some extent. However, not only is the sheet thickness increased, but also the sheet is weakened with respect to a point compression force or line compression force applied to an intermediate part between the adjacent ribs.Therefore, in practice, it is preferable that the height of the ribs is set to 5mm or less, preferably 1 to 3mm, and instead the thickness and hardness of the sheet material are selected to give a necessary rigidity to the sheet. The thickness of the sheet itself ranges, in general, from approximately 0.1 mm to approximately 0.3mm. The term "sheet" as herein used does not have an exact meaning, and includes thinner films provided the latter can provide the same effects.

The configuration of the peak parts of the sheet according to the invention is not particularly limited. However, it is generally a circular truncated cone, a truncated quadrangular pyramid, a semi-sphere, a prism or a cylinder.

Furthermore, the configuration of the peak parts may be trapezoid which is substantially a parallelogram in section.

Fig. 5 shows one example of a stamped sheet forming method according to the invention. A slit-shaped nozzle n of a die d extrudes molten plastics material m, which is introduced in the form of a sheet into liquid refrigerant W in a liquid refrigerant bath v.

The molten plastics material m thus introduced is shaped while passing through a gap between a pair of stamping rollers rand r'. An uneven pattern such as a geometrical pattern or a pictorial pattern is provided on the outer wall of at least one of the stamping rollers r and r. The uneven pattern is stamped on the sheet surface while the plastics material m passes through the gap between the stamping rollers. The sheet thus stamped is moved in the direction of a tangent line, which extends vertically from a stamping point in a gap C between the stamping roller rand r', substantially without being pulled.After being cooled and solidified to the core, the stamped sheet is pulled out of the liquid refrigerant bath v while the direction of movement of the sheet is being changed by a guide roller r" whose outer wall is on the aformentioned tangential line and by another guide roller rut". The stamped sheet is then subjected to aftertreatments such as thermal setting and drying in a conventional manner.

In this method, the stamping is effected before the molten plastics material is solidified to its core. Therefore, the stamping is achieved momentarily, and the uneven pattern which is formed with parts greatly different in height can be readily stamped on the sheet.

The stamped sheet is moved downwardly along the tangential line from the stamping point while being substantially free from tensile force. Accordingly, no reasonable force is exerted on the stamped sheet, and the uneven pattern stamped thereon is maintained unchanged.

Fig. 6 shows a second example of a stamped sheet forming method according to the invention. Similarly as in the case of the first example in Fig. 5, molten plastics material m is extruded out of a slit-shaped nozzle n n of a die d, so that it is dropped in the form of a sheet directly onto a drum r' having a smooth outer wall. The sheet enters liquid refrigerant W while being kept in contact with the outer wall of the drum r', and passes through the gap between the drum r' and a stamping roller ron which an uneven pattern is formed, so that the uneven pattern is stamped on the sheet. Thereafter, the stamped sheet is moved along a tangential line which touches the stamping roller rat the stamping point. During this movement, the sheet is sufficiently cooled and solidified, and is then pulled out of the liquid refrigerant bath v.

In the second example in Fig. 6, the molten plastics material m contacts the outer wall of the roller r' before going into the refrigerant W. Therefore, the method is advantageous in that the width of the sheet is scarcely reduced. Naturally in this second example, it is essential that the plastics material moves into the refrigerant W immediately it contacts the outer surface of the roller.

Fig. 7 is a front view showing one modification of the stamping roller rand r' in Figs. 5 and 6. Roller according to the modification are intended to provide a wavy stamped sheet having ridges which extend in the longitudinal direction (which is parallel with the direction of extrusion of the molten plastics material).

Disks o and o' are fixedly mounted on the rotary shafts a and a' of the stamping rollers r and r' respectively, in such a manner that they are arranged at equal intervals on the respective rotary shafts and the intertwined.

Therefore, the sheet of molten plastics material m is stamped in a wavy form while passing through the gap between the stamping rollers rand r'.

Fig. 8 is a front view showing another modification of the stamping rollers rand r' in Figs. 5 or 6. In this modification, the outer walls of the rollers rand H are formed wavy.

Therefore, the sheet of molten plastics material m is stamped in a wavy form while passing through the gap between the rollers r and r'.

The methods of the invention shown in Figs. 7 and 8 are especially effective in manufacturing a sheet having a wavy or rib structure which extends in the longitudinal direction. A sheet having a wavy or rib structure extending in the longitudinal direction is liable to collapse when bent by a roller or bar. This tendency is more significant when the sheet is brought into contact with a roller or bar before it has sufficiently solidified. However, in the methods according to the invention, no exces sive force is applied to the sheet before the latter is sufficiently cooled and solidified, and therefore the sheet can be stamped as re quires.

Fig. 9 is a front view of a stamped sheet which is manufactured with a pair of stamping rollers which are obtained by forming annular ribs and recesses on a pair of wavy rollers in the circumferential direction. Fig. 10 is a side view of the stamped sheet a viewed in the direction A-A in Fig. 9, and Fig. 11 is also a side view of the stamped sheet as viewed in the direction B-B. The sheet has transverse ribs 1 and longitudinal ribs 6 which assist flexing, as described previously.

Fig. 12 shows an example of a pair of stamping rollers for manufacturing a sheet having a special uneven pattern by utilizing the aforementioned pitching action, according to the invention. More specifically, the stamping rollers are used to manufacture the sheet as shown in Fig. 1. The pair of rollers rand r' have teeth t and ti which are engaged with each other as the rollers rand r' turn. As molten plastics material m is supplied into the gap between the rollers rand r' from a die d, a stamped sheet S having a wavy uneven pattern corresponding to the configurations of the teeth is produced. In manufacturing the sheet shown in Fig. 1, the roller r is an ordinary wave roller as shown in Fig. 1 3a while shallow grooves g are cut, at regular intervals, in the teeth f of the other roller r' (Fig. 1 3b).Therefore, as the tops and bottoms of the teeth of the two rollers engage, the sheet is naturally arcuately curved at the grooves, being free from tensile force. Thus.

the sheet is stamped as shown in Fig. 1. This phenonemon occurs as long as a gap exists between the side surfaces of the confronted (engaged) teeth of the roller. Accordingly, not only the sheets shown in Figs. 2 and 3, but also other sheets having more complicated uneven patterns can be manufactured in the same manner.

The invention will be further described with reference to some examples.

An extruder (screw diameter 40mm) was used. Under the condition that the number of rivolutions per minute of the screw was set to 72 (only in Example 1 (described below) 100) various kinds of thermoplastics materials were extruded with a T-die having a slit-shaped nozzle 210mm in width. The plastics materials were supplied, in molten film form, to stamping rollers (cf.Figs. 14 and 1 5) which were set in water at about 20 to 30 C, to form wavy sheets under the following conditions described below: Data of the rollers: Type A (Fig. 4) Circular tooth face (dk); 60mm f Tooth form: module m = 1 Deddendum circle diameter (dr) 57.50mm (p Tooth height (h): 2.25mm Number of teeth: (z) 60 Type B (Fig. 15) Boss outside diameter (r,): 30mm Actual vane length (h): 25mm Number of vanes: 10 (provided at equal intervals) Length of the overlap parts of vanes (ho) 15mum Example 1 Polyethylene terephthalate resin was extruded in the form of a film at a resin temperature of 250or from a T-die (having a slit gap of 2.0mum). to manufacture a wavy sheet according to the method shown in Fig. 15.

Water at 30"C was employed as the liquid refrigerant. The time interval which elapsed from the instant that the sheet of molten resin entered the water until the sheet was stamped to a maximum degree was approximately 1 second. and the period of time that the sheet stayed in the water was approximately 25 seconds in total. The resultant wavy sheet (having a thickness of about 1 mm) was correctly stamped, and the configuration thereof was high in stability.

Example 2 Instead of the polyethylene terepthalate resin in Example 1, polypropylene resin containing 50% wt. non organic material (Idemitsu Lion: calp 1400G, Ml = 2) was extruded in the form of a film from a T-die (having a slit gap of 0.6mm) with the resin temperature being at 230 C, so that under the same conditions as those in Example 1, a wavy sheet was manufactured by means of the stamping rollers in Fig. 14. The resultant wavy sheet was stable In configuration, that is, the configuration of the pattern stamped on the sheet was regular.

Example 3 Instead of the polyethylene terepthalate resin in Example 1, ethylene-vinylacetate copolymer resin (containing 10% wt. vinyl acetate, ML = 1.5) having an azo-foaming agent added was extruded in the form of a foamed film from a T-die (having a slit gap of (0.6mm) at 1 70or, so that under the same conditions as those in Example 1, a wavy sheet was formed by using the stamping rollers shown in Fig. 14. The resultant wavy sheet was stable in configuration, that is, the configuration of the pattern stamped on the sheet was regular.

Claims

1. A method of manufacturing a stamped plastics sheet, comprising supplying filmshaped molten thermoplastics material to a pair of stamping rollers placed in a liquid refrigerant, and stamping said material by means of said stamping rollers before said material is solidified to the core thereof.

2. A method as claimed in claim 1, in which an engagement position of said stamping rollers with said material in the form of a film, is substantially at a level of a surface of said liquid refrigerant.

2. A method as claimed in claim 1, in which at least a part of said material in the form of a film, which extends below an engagement position of said stamping rollers, is immersed into said liquid refrigerant.

3. A method as claimed in either claim 1 or claim 2, in which each of said stamping rollers has an uneven outer wall corresponding to a configuration and/or a pattern of characters, figures, symbols, pictures which is to be stamped on said film-shaped material.

4. A method as claimed in any one of claims 1 to 3, in which said pair of stamping rollers are a pair of runners or a pair of engaging rollers.

5. A method as claimed in claim 2, in which said material, after passing through the engagement position of said stamping rollers, is moved substantially along said tangential line which extends from said stamping rollers at said engagement position.

6. A method as claimed in any one of the preceding claims, in which said pair of rollers are a pair of unitary rollers having wavy uneven outer walls, and at least one of said unitary rollers has recesses everywhere on the convex parts of said outer wall thereof.

7. A stamped sheet of a flexible thermoplastics material, having ribs which are arranged at regular intervals and extend in a predetermined direction, each rib being divided by hill parts, having sides extending downwardly from a top portion of said rib, to form individual peak parts.

8. A stamped sheet as claimed in claim 7, in which the top portion of each peak part is substantially flat.

9. A stamped sheet as claimed in either claim 7 or claim 8, in which said peak parts are provided on both sides of said stamped sheet.

10. A stamped sheet as claimed in either claim 7 or claim 8, in which said peak parts are provided on only one side of said stamped sheet.

11. A method of manufacturing a stamped plastics sheet, substantially as hereinbefore described with referenc to and as shown in Fig. 5, or Fig. 6, or Fig. 7, or Fig.

8, or Figs. 12 and 13, or Fig. 14 or Fig. 15 of the accompanying drawings.

12. A stamped plastics sheet substantially as hereinbefore described with reference to and as shown in, Figs. 1a-1d, or Figs.

2a-2d, or Figs. 3a-3e, or Fig. 4 or Figs.

9-11 of the accompanying drawings.

CLAIMS (4 Jun 1982)