Claims
- 1. In an apparatus for stamping a detergent bar comprising means for locating a detergent bar, at least one die member, and drive means for moving said at least one die member relatively towards said bar to stamp said bar,
- the improvement wherein said at least one die member has a total modulus of elasticity within the range 10.sup.5 to 5.times.10.sup.7 Nm.sup.-2.
- 2. Apparatus according to claim 1 wherein said at least one die member has a total modulus of elasticity within the range 5.times.10.sup.5 to 10.sup.7 Nm.sup.-2.
- 3. Apparatus according to claim 1 comprising a pair of opposing said die members, said means for locating a detergent bar acting to locate said bar between said die members, and said drive means being operative to move said die members relatively towards each other, so as to stamp said bar located between said die members.
- 4. Apparatus according to claim 3 wherein the total modulus of each said die member is substantially the same.
- 5. Apparatus according to claim 1 wherein said at least one die member comprises a non-elastomeric part and an elastomeric part, the non-elastomeric part carrying the elastomeric part at a position to contact the bar during stamping, to the exclusion of the non-elastomeric part.
- 6. Apparatus according to claim 5 wherein said elastomeric part comprises a layer of an elastomer at least 0.2 mm and at most 10 mm thick.
- 7. Apparatus according to claim 5 wherein said elastomeric part is made of a material selected from the group comprising natural rubbers, silicone rubbers, polyurethanes and butyl rubbers.
- 8. Apparatus according to claim 1 wherein said at least one die member is arranged such that in use it substantially retains its shape during stamping.
Priority Claims (1)
| Number |
Date |
Country |
Kind |
| 8701635 |
Jan 1987 |
GBX |
|
Parent Case Info
This is a divisional application of Ser. No. 147,397, filed Jan. 25, 1987, now U.S. Pat. No. 4,793,959.
The present invention relates to a process for stamping a detergent bar, to an apparatus for stamping a detergent bar and to a detergent bar so produced.
By "detergent bar" we mean a tablet, cake or bar comprising substantially of soap, substantially a synthetic detergent or a mixture of soap and synthetic detergent, in each case in optional admixture with one or more additives, e.g. conventional additives used in detergent bars.
Stamping of such bars is performed to give each bar a uniform shape and a smooth glossy surface. Die stamping machines in current use include "pin die" shape machines in which a pair of opposing die members actually meet during the compaction step and a "box die" machine in which a pair of opposing die members stamp a bar held within a through-opening in a box frame but do not meet during compaction, the peripheral face of the bar being restrained by the box frame.
Stamping is also performed to imprint a design such as a logo or trade mark onto an area of the surface of a bar.
With all of the abovementioned stamping operations, problems can be encountered with respect to poor surface finish. This problem is frequently attributable to amounts of residual detergent being left in die members which increase in size with continued use of the die until a visible imperfection is left in the surface of subsequent bars. The problem is traditionally known as die-blocking.
GB 746 769 (Colgate-Palmolive Company) describes, it is claimed for the first time, the use of plastic material for the working face of a die member for pressing detergent material. Detergent bars so produced are said to possess a smoother finish and higher sheen than bars produced with metal dies. The die set described comprising a die box and a pair of companion die members are made of plastic materials which comprise polymers having a modulus of elasticity between 5.times.10.sup.4 and 5.times.10.sup.6, preferably between 2.times.10.sup.5 and 8.times.10.sup.5 pounds per square inch. A wide range of examples of suitable plastic materials are given. In use lubricant is said generally to be necessary to prevent pieces of detergent from adhering to and building up on the dies and marring the surfaces of subsequently pressed cakes.
U.S. Pat. No. 2 965 946 (Colgate-Palmolive Company) describes the use of a particular die box and companion die members made of organic plastic material one of whose intended aims is to reduce marring of detergent cakes on pressing due to adherence of the cake to the die. The plastic chosen should be of sufficient strength to press out the detergent being processed and flexible enough to expand against the die box interior during pressing so as to prevent flashing of the detergent. The plastic must be sufficiently resilient to return quickly to its initial shape when the pressing force is released. The modulus of elasticity is quoted as lying in the range 5.times.10.sup.4 to 5.times.10.sup.6 pounds per square inch, or alternatively being lower, in the region of 1.9.times.10.sup.4 pounds per square inch. A wide variety of suitable plastics material is given. A lubricating material e.g. mineral oil, carbitol, acetic acid, glycerine, salt solutions, pulverised solids etc. may be used.
U.S. Pat. Nos. 3,094,758 and 3,270,110 (Colgate-Palmolive Company) relate respectively to an apparatus for pressing detergents into bars or cakes and a method of making a precision moulded detergent press die member. In each case the press die member described is partly of synthetic polymeric organic plastic. Each die member has embedded therein a comparatively rigid member so located that a pressing force applied to the die will cause it to press detergent material without objectionable distortion of the pressing face of the die, but will allow the peripheral edge of the die to expand to the die box. A wide range of plastics materials are suggested. The modulus of elasticity is quoted as being less than 5.times.10.sup.4 pounds per square inch, preferably less than 3.5.times.10.sup.4 pounds per square inch, but no power limit or significantly lower figure is given.
U.S. Pat. No. 3,242,247 (Colgate-Palmolive Company) relates to a plastic die member for pressing detergent blanks into tablet form having a pressing face with offset embossed or recessed reverse lettering, ornamentation or other indicia with fibrous material embedded in the plastic and adjacent to the lettering, etc. The embedded fibres cause the embossed and/or recessed portions to resist chipping and breakage. A wide range of plastic materials are suggested. The modulus of elasticity is again quoted as 5.times.10.sup.4 to 5.times.10.sup.6 pounds per square inch.
Thus, the lowest modulus of elasticity quoted in the above documents is 1.9.times.10.sup.4 pounds per square inch which is equal to 1.3.times.10.sup.8 Newtons per square metre (Nm.sup.-2).
According to one aspect of the present invention there is provided a process for stamping a detergent bar including moving at least one die member relatively towards the bar so as to contact the bar, in which process the die member, or each of a plurality of die members has a total modulus of elasticity within the range of 10.sup.5 to 5.times.10.sup.7 Nm.sup.-2.
By means of the present process we have found that die-blocking can be reduced. In particular we have found that die-blocking can be attributed to the difference in elastic moduli between the bar and the die members. By means of the present process we believe less shear stress is imparted to the bar during separation of the bar and die members than by use of traditional metal die members and hence the tendency for die-blocking is reduced.
The process of this invention is applicable to any of the stamping operations mentioned initially. It may thus be employed for stamping a design onto an area of a bar, or the invention may be used in a process which entails locating a detergent bar between a pair of opposing die members and stamping the bar by moving the die members relatively towards each other, so as to contact the bar which is located between the die members.
Such a pair of die members may be pin dies or box dies. The use of pin dies is particularly preferred as it produces a detergent bar whose shape is preferred and held in high esteem by consumers. When there is more than one die member it is suitable for the modulus of elasticity of each die member to be substantially the same.
Preferably the total modulus of elasticity of the die member or each of a plurality of die members is within the range 5.times.10.sup.5 to 10.sup.7 Nm.sup.-2. More preferably the total modulus of the or each die member is approximately 10.sup.6 Nm.sup.-2.
Throughout the present specification the "total modulus of elasticity" of each die member refers to that measured by compressing the surface of the die member which in use contacts the bar.
It is strongly preferred that the total modulus of elasticity of the or each die member is less than the modulus of elasticity of the detergent bar being stamped. We have found that the elastic modulus of many types of detergent bars falls within the range 10.sup.6 to 10.sup.8 Nm.sup.-2. Usually the detergent bar has a modulus of elasticity of approximately 10.sup.7 Nm.sup.-2. Preferably the total modulus of elasticity of the or each die member is at least 5% less than the modulus of elasticity it is not more than half that of the detergent bar. Preferably the total modulus of elasticity of the or each die member is up to 15 times less than the modulus of elasticity of the detergent bar being stamped. Accordingly the total modulus of elasticity of the or each die member preferably lies in the range from 1/15 to 95/100 of the modules of elasticity of the detergent bar.
We have found that when the total modulus of elasticity of the die member(s) is substantially less than that of the detergent bar being stamped, the adhesive force between the bar and the die(s) falls markedly. It is desirable to minimise this adhesive force.
Preferably each die member comprises a non-elastomeric part and an elastomeric part, the elastomeric part being attached to the non-elastomeric part and being arranged to contact the bar to the exclusion of the non-elastomeric part. The elastomeric part can be example comprise a layer of elastomer of at least 0.2mm, preferably of at least 0.5mm thickness and up to 10mm, preferably up to 5mm thick. Alternatively the elastomeric part can comprise a substantial part of each die member.
In order that the die member(s) should have a total modulus of elasticity less than that of the detergent bar being stamped, as is preferred, it may be necessary to choose an elastomer of suitable modulus, and/or employ a thickness of elastomer which is in the upper part of the range mentioned above, for example 3 to 8 mm.
The non-elastomeric part of each die member is suitably metallic or made of any other suitable rigid material. The elastomeric part of each die member can be made from any suitable elastomer. Numerous types of elastomer are available, including thermoplastic, chemically-cured thermosetting and heat-cured thermosetting types. We presently prefer elastomers selected from natural rubbers, silicone rubbers, polyurethanes, and butyl rubbers. Use of a heat-cured elastomer may be preferred. In compiling each die member it must be remembered that the requirement of the present invention concerning the modulus of elasticity applies to the total modulus of elasticity of the die member, not merely that of any elastomeric part present.
By means of the present process die-blocking can be reduced and hence a good quality gloss and sheen can be imparted to the bar surface. In contrast to at least some of the prior art processes, the present process can be performed without the employment of a lubricating agent in the die members.
By use of the present process a wide range of detergent bars comprising soap or synthetic detergent or a mixture of soap and synthetic detergent can be successfully stamped. The process can be applied to high speed automatic stamping lines. The process can be suitable for application to soft tacky soap bars which traditionally have proved difficult to stamp successfully. Examples of such bars include transparent soap bars, translucent soap bars and soap bars having a reduced fatty matter content for instance a fatty matter content in the range 63 to 78 wt % with respect to the total bar weight.
According to another aspect of the present invention there is provided an apparatus for stamping a detergent bar comprising at least one die member arranged to move, in use, relatively towards and stamp a detergent bar, wherein the or each die member is such that it has a total modulus of elasticity within the range 10.sup.5 to 5.times.10.sup.7 Nm.sup.-2.
Preferred features of the present apparatus relating to the modulus of elasticity and composition of the die member, or each of a plurality of die members, are those mentioned above with regard to the present process.
It is to be understood that the present invention extends to detergent bars produced by the present process and/or by means of the present apparatus. The present process can be carried out by means of the present apparatus.
US Referenced Citations (6)
Foreign Referenced Citations (2)
| Number |
Date |
Country |
| 746769 |
Mar 1956 |
GBX |
| 831158 |
Mar 1960 |
GBX |
Divisions (1)
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Number |
Date |
Country |
| Parent |
147397 |
Jan 1987 |
|
Patent Grant
4822273
