Roll-on Applicator Balls The present invention relates to balls, particularly balls for use in roll-on applicators of the kind which can be used as applicators for deodorants and other surface treatments, and even in some cases as marking devices.

Such balls are often made of blow-moulded or injection moulded polypropylene or high density polyethylene, and after the moulding process are subject to a surface grinding treatment to provide a required accurate dimensional finish. Now it has been a requirement for some while to provide an improved surface feel to the product since some current balls suffer from the problem of having an unsatisfactory hard feel. The present invention aims to overcome this problem.

At this stage it should be mentioned that our earlier US Patent 5,320,887 (and equivalent EP specification 0,552,556) discloses a blow-moulded ball for use in playpens and its method of manufacture. In that case the aim is to produce a ball having certain physical properties in relation to resilience and longevity, while having an attractive gloss surface appearance without the need for any further finishing treatment. Thus no surface grinding is involved and dimensional accuracy is

irrelevant. Indeed a material had to be selected which avoided the production of equatorial sharp edges which would otherwise have to be removed by grinding. It will be appreciated therefore that the disclosures in our earlier patent relate to an entirely different product and problem, and do not solve the surface feel problem since the balls shown there are not subjected to a grinding treatment.

Accordingly the present invention provides a roll-on applicator ball formed by a moulding and a machining treatment and being formed mainly or entirely of low density polyethylene.

Moreover the term low density polyethylene is used here to include either Low Density Polyethylene (LDPE), or Linear Low Density Polyethylene (LLDPE) or mixes of these two forms of low density polyethylene.

The applicator balls in accordance with the present invention can be made by conventional methods of moulding, that is blow moulding or injection moulding, followed by a machining treatment, and have a characteristic soft touch, that is the surface has a feel of lubricity, that is it feels as if it is lubricated even when it is still dry.

The machining treatment is a treatment known per se, to give the ball a dimensionally accurate degree of matt finish and roundness. In this respect in one commercial method an initial coarse grinding treatment is carried out in a centreless rotary grinder, and this is followed by finer grinding to provide a matt finish in a manner known to those in the art.

The invention will now be further exemplified by reference to the following discussion of the consideration and experiments which led to development of the invention.

The objective was to make a new form of roll-on ball with improved surface properties compare with roll-on balls made in polypropylene (PP), and high density polyethylene (H. D. PE) currently on the market. The target was a ball with a surface appearance which gives a soft touch feeling when the ball is held in the hand, that is a feel of lubricity as mentioned above.

Different types of plastic materials were discussed including thermoplastic rubber, but the latter was rejected because of envisage major problems in the grinding process because of the softness of the material.

As mentioned previously, H. D. PE is sometimes used for roll-on balls but these balls do not have the wanted soft touch property. It was thought that a mixture of H. D. PE with low density polyethylene (L. D. PE) in a selected percentage might give the desired result, and it was believed that L. D. PE alone would probably be too soft a material to withstand the subsequent grinding process. <BR> <P>Therefore a mix of 50% H. D. PE and 50% L. D. PE was used for the first test run. It was thought that the stiffness property of H. D. PE might still be retained in a mix of <BR> 40% H. D. PE and 60% L. D. PE and therefore this mix was selected for use in the second test.

Other materials were discussed but rejected because of requirements in the blow moulding and grinding processes.

Linear low density polyethylene (L. L. D. PE) was taken into consideration because of its greater material stiffness compare with L. D. PE. This material can also be supplie in a blow moulding grade. This material was therefore also selected for a test.

Three tests were carried out for: <BR> 1.50% H. D. PE and 50% L. D. PE<BR> 2.40% H. D. PE and 60% L. D. PE 3. Linear Low Density PE alone.

Blow Moulding The three materials were made ready for the blow moulding test.

Specification for test balls: Weight 2.8g to 3.5g <BR> Diameter 25.6-26. lmm<BR> Quantity-5000 The blow mould used for the test was of the kind having 23 single 1"cavities, the cavity being of ball shape design for standard 1"PP balls. lst Test Blow Moulding The balls were on the high side of the blow moulded specification because H. D. PE has more shrinkage.

The balls weight was to specification and the blow moulding process was without problems.

500 balls were produced 2nd Test Blow Moulding This test gave almost the same result in blow moulding as the first test.

500 balls were produced

3rd Test Blow Moulding In this test we found more problems with balls being oversized by up to 26.4mm, but weight was inside specification and Extrusion Blow Moulding occurred without problems.

500 balls were produced Grinding Test The three batches of blow moulded balls were taken to a coarse grinding location and the test process was performed in the same order as for the blow moulding.

The two mixed materials of H. D. PE and L. D. PE gave no significant problems in the grinding treatment except some unground spots occurred on some balls. This was because the blow moulding had produced some balls with low spots. The appearance of balls'surface seemed very even in comparison with roll-on-balls made of H. D. PE but a final jugement needed to be taken after the final grinding process.

The coarse grinding test of the third batch of balls made in L. L. D. PE gave a very different result. As expected the oversized balls gave problems in the mechanical system which loads the grinding wheel. The balls were very hot after the process and gave problems in keeping

to the diameter tolerances. But the appearance on the surface of the balls after the coarse grinding process looked very different and gave some promises for the wanted"soft touch".

The final grinding operation was performed on all three test runs of balls and showed thaï té mixed material balls were of the same quality as existing roll-on-balls made of H. D. PE.

After the final grinding stage the L. L. D. PE balls were found to have the soft touch we were looking for.

Results and conclusion The making of roll-on-balls in the material linear low density polyethylene in a blow moulding-grinding operation, specially set up for homopolymer polypropylene gave some problems because of the two materials different parameters.

The problems in the blow moulding test with oversized balls can be solved by designing a ball shape in the cavities which compensates for the material shrinkage and also takes account of any uneven wall thickness of the ball. This is done basically by calculating the wanted diameter of the ball shape then making test cavities and

correcting for alteration after test balls are made. When the blow moulded balls are within the wanted blow moulded dimension specification we avoid the problems we had in the mechanical overloading of the grinding wheels. Any extra heat which occurs in grinding this material can be removed with additional cold process water sprayed in between the ball and the grinding grooves.

We found out that the finished ball had the wanted appearance and soft feel properties and gives rise to the promise of a new generation of roll-on-balls.

Balls in accordance with the invention had a machining treatment to provide a required uniform dimensional finish.

An embodiment exemplifying the machining treatment is described herein with reference to the accompanying diagrammatic drawings in which: Figures 1 and 2 show plan and side elevations of a coarse grinding machine.

Referring to the Figures a centre less grinding machine provides a preliminary grinding operation. The machine comprises a rotary feed wheel 1, having a plane outer

surface operating in conjunction with a free-running grinding wheel 2 which has circumferential grooves 3 which in cross-section match a half ball profile and thus for 1 inch balls are very slightly above that diameter.

A feed hopper 4 is arrange above the nip of rollers 1 and 2 so that the balls fed through will receive a single pass coarse grinding operation. To ensure suitable pressure is applied to the nip, a hydraulic piston and cylinder arrangement 5 applies pressure to the feed roller 1 so that a suitable pressure is applied between the two rollers during the grinding operation.

During use, the coarse grinding operation is applied to each of the balls as they pass from the hopper 4 and in a single pass operation each ball is brought down to a diameter of approximately 25.5 millimetres.

The balls are then introduced into a further grinding machine in which the balls are subjected to a lapping process which is essentially a similar operation but under finer and tighter conditions to produce a final matt finish to the product to a required dimensional tolerance.

In practice the final finishing operation grinds the balls to a nominal diameter of 25.4 mm plus or minus 0.05

mm with a fine surface roughness, thereby providing the matt finish required.

Following the above discussion and development work further tests have been carried out and the following is a discussion of these further tests.

In the earlier work we had performed 15 different tests in making the Soft Touch Balls in production in both 1" and 1.4".

We tested different grades of Linear Low Density Polyethylene in order to establish the best material for the blow moulding and grinding processes with the best output and balls with the correct size and"Soft Touch".

We found that virtually all Linear low density Polyethylenes have a rather high melt index which produces a"draw down'of tne prison. This mates it difficult to maintain a constant parison and even weight of the balls. We concentrated on an LLD. PE with a melt index lower than the average and made 1"and 1.4" balls, although difficulties were experienced in blow moulding.

The balls which came out of these tests were very uneven in weight but almost within size specification for grinding.

In grinding, we had some difficulties in achieving proper grinding with these balls IDoth in the pre-grinding and in the lapping operations. We were not able to make round balls to specification nor keep to the standard cycle compare to balls of polypropylene.

The reason for this is probably due to the fact that the material is soft and also to the fact that uneven wall- thickness (thin poles) arises, each having a great effect on grinding. In addition there was a problem with LLD. PE grinding dust sticking to the grinding wheel and not being removed by the process water. This meant that the spin of the balls in between the grinding wheel and feeding wheel no longer occurred and therefore that grinding of the complete surface was lost.

We carried out many tests in grinding both 1"and 1.4" balls without achieving the goal of round balls to specifications having a good productivity.

We therefore decided to start again from scratch, making small quantities of different grades and mixes of material in the size of 1".

We chose the following grades and mixes and decided that the ball weight should be increased to 3.5-4.5g.

Approximately 2000 balls were produced in each test.

Test 1 30% LLD. PE 70% LD. PE Test 2 100% LLD. PE Test 3 50% LLD. PE 50% LD. PE Test 4 100% LD. PE Test 5 80% LLD. PE 20% HD. PE Of these five tests, the performance in blow moulding was best for the pure LD. PE. This was to be expected because of the material's low melt index. The ball weight and size were to specifications.

The small quantities we did were not enough to do the lapping process as a full lot (15,000) but the interesting issue here was the pre-grinding process.

Here we found that we were able to grind on a suitable wheel to the right pre-ground size with the same cycle as PP balls. In the lapping process we mixed the balls into a lot of PP balls in order to have enough balls for the process. The results of these tests were as follows: 1 Test 5 did not have the"Soft Touch"appearance.

2. Test 4 gave us the"Soft touch"feeling and balls to size inside tolerances.

3 Test 1-2-3 also gave the"Soft Touch"but the balls were slightly out of roundness.

We decided from experience of previous tests that we had to make a production run with larger amounts of balls.

1 Test (9830) 1"LD. PE 10,000 balls, weight 3.5-4.5G 2 Test (9831) 1"30% LLD. PE + 70% LLD. PE, 10,000 balls, weight 3.5-4.5g The blow moulding process was in control with LD. PE both on weight, cycle time and ball size. We still found problems with the mixed material though with variations in the ball weights.

In the pre-grinding process, we ran both types of balls in the same set up as we used for the 1"PP balls.

In the lapping process, we started slowly. The LD. PE balls came out to specification whereas the balls in mixed material came out more or less out of roundness.

In order to find out what cycle time we could obtain we took both types of bat 1 a second time through the lapping process this time to the size of 0.995". We were able to grind the LD. PE balls from 1"to 0.995" almost in the standard cycle time whereas the balls in mixed material took much longer. We are sure that with more experience we can bring the lapping process cycle time for the LD. PE balls down to the standard cycle time for PP balls.

Measurements of the balls after this last lapping shows that the 100% LD. PE material still gives the best results regarding size and roundness and the balls look nice and have the"Soft Touch".

We concentrated too long on the LLD. PE material even with the lower melt index in attempting to make the"Soft Touch"balls. We think we had a combination of problems: The lightweight balls were oval after the grinding process because of the thin wall thickness.

The material gave problems in the pre-grinding process as explained in part 1.

In conclusion products could be achieved having the"Soft Touch"surface feel by utilising either 100% LD. PE or

100% LLD. PE or any percentage mix of these two materials,, however some were easier to make than others, particularly 1008 LD. PE.

Moreover we also concluded that the good results were dependent on selection of the correct starting material, one or other form of Low Density Polyethylene, and use of a standard machining treatment adjusted as necessary to provide a matt finish ball of the required surface feel. Thus, other forms of moulding such as injection moulding would be equally suitable subject to selection of an appropriate injection moulable grade of polymer, and in this respect the selected resins of low density polyethylene when processed by injection moulding will normally have a higher melt index, and that in turn can result in easier manufacture.