WO2004112472A1

WO2004112472A1 - Frame for and bee hive foundation and method of manufacture

Info

Publication number: WO2004112472A1
Application number: PCT/SE2004/001033
Authority: WO
Inventors: Tommy Lundquist; Jan CEDERSTRÖM
Original assignee: Bhf Bee Hive Foundation Ab
Priority date: 2003-06-24
Filing date: 2004-06-23
Publication date: 2004-12-29
Also published as: SE0301838L; SE0301838D0

Abstract

The present invention relates to a frame for supporting a bee hive foundation. According to the invention the frame consists of foldable material, which is folded into a rectangular frame with the aid of folding indentions in the frame material. The invention also relates to a method and apparatus for manufacturing such a frame and bee hive foundation.

Description

Frame for and bee hive foundation and method of manufacture.

FIELD OF INVENTION

The invention is concerned with components for honey bee hives.

BACKGROUND OF THE INVENTION

Bee hives and parts thereof are mostly made from wood. To some small extent polymer materials are also used in solid or expanded (foamed) execution. Foundations are normally made from bees wax. These are good materials but have some drawbacks in comparison with the present invention: They are relatively costly, they often require considerable work to assemble and to put to use and the use of wax foundations has brought problems of pesticide contamination.

Beekeepers install in beehives perpendicular sheets or plates that are called

foundations. These serve two main purposes: to facilitate handling of the

honey stored in the beehive and to promote honey production by saving time

for bees in that they do not have to build complete honey combs, saved time

that will be spent to collect honey. Foundations can thus be termed semi-

finished honeycombs.

By far the most common foundation is a plate of beeswax embossed with a

pattern on both sides indicating size and shape of the cells that the bees will

build. The pattern serves as a starting blueprint for the bees. The plates are

mounted in frames, usually wooden, that are hung in the beehives. Mounting of the plates in the frames is done either by affixing them by

melting onto metal wires suspended across the frames or by affixing them by

melting the plate onto the upper bar of the frame. While such foundations are

well accepted by bees, the stringing of wires to frames and the melting

procedure is quite laborious. The frame parts also have to be assembled and

joined together. Alternative methods of mounting foundations into frames are

fitting them into grooves made along the center of the insides of the parts

making up the frames and applying tacks to the insides of the frames to keep

the foundations in place.

The predominant frame material is wood, mostly from rainforest wood origin.

To a small extent, plastic frame parts are used, see e g US Patents 4,402,099

and 4,374,440.

There exists also an industrial foundation being a wax coated plastic sheet

where the desired cell bottom pattern is profiled in the plastic material. An

example of such a foundation is given by US Patent 3,105,978. An advantage

of such foundations is that there is no need for stringing metal wires on which

to melt affix the foundation; however requirement of special frames and tools

makes the use of this product rather expensive. There is also a variant of such plastic sheets without a wax layer, in which

case the beekeeper has the option to apply such. Unless the plastic sheet is to

be wax coated by the beekeeper, the use of this type of foundation does not

require much work; however it is at least two to four times as expensive as

wax foundations.

US Patent 4,992,073 teaches the use of a material mixture of polypropylene

copolymer and 7.5 to 15% of beeswax that is moulded into shapes of bee hive

components.

The above executions of foundations occur with and without profiling of the

bottoms of cell indications in such manner that the center of the hexagonal cell

pattern is recessed seen from one side of the foundation with such a mirrored

profile seen from the other side of the foundation that the bottom of the recess

seen from one side forms the corner of the hexagonal cell pattern seen from

the other side.

It is the purpose of the present invention to lower the cost of materials used as

bee hive components and to reduce the amount of work associated with the

use of traditional materials. Another objective of the present innovation is to provide a frame for

foundations and a foundation integrated with the frame, or being a separate

part, offering excellent economy in that the material cost is very low and that

work to prepare foundations and frames is minimized.

Yet another objective is to provide a method and a means for beekeepers to

apply by printing or stamping techniques a pattern of pure, uncontaminated

wax onto the foundations.

Further, the invention aims at solving the problem of foundations made of wax

being contaminated by pesticides used inside the hive.

The invention further provides the principle of folding the materials used for

frames and frames integrated with foundations.

These goals are reached by using suitable materials, by applying a wax pattern

onto them, and by folding techniques.

SUMMARY OF THE INVENTION

The present invention aims at minimizing the need for time consuming work

to prepare bee hives foundations and the frames they are mounted in and to lower the material cost, while avoiding the risk of foundations being

contaminated by pesticides. This is achieved by choosing an inexpensive

material and an efficient production method for the manufacture of

foundations, frames and frames integrated with foundations.

The materials used should be foldable exemplified by but not limited to

corrugated or single-, twin- or multiwalled cardboard paper, or polymer or

polymer slabs, sheet or strips. The slabs, sheets or strips may have pre¬

punched or cut grooves or indentations to guide and facilitate the folding of

them into frames of predetermined shape and size. The sheets or strips further

have slots and tabs to allow fixation of folded segments.

These goals are accomplished by a frame for supporting a bee hive foundation, characterised in that it consists of foldable material, which is folded into a rectangular frame with the aid of folding indentions in the frame material.

In a preferred embodiment the frame comprises an integrated bee hive foundation and consists of folded peripheral portions of at least one sheet being folded into a three-dimensional shape, the central part of the at least one sheet constituting a bee hive foundation. Advantageously the frame can consist of two sheets having folded peripheral portions holding the two sheets together. The frame comprising an integrated bee hive foundation can alternatively consists of a double- walled central part and peripheral portions folded into a three-dimensional shape, the frame being made from a single blank.

In the preferred embodiment the frame consists of folded peripheral portions of at least one sheet and a bee hive foundation is a separate piece attached to the frame.

The invention also relates to a blank for a frame supporting a bee hive foundation, characterised in that it consists of sheet material having folding creases for facilitating folding of the sheet material into a frame having three- dimensional shape.

Furthermore, the invention also relates to a method of manufacturing a bee hive foundation, characterised by printing a pattern of beeswax onto one or both sides of a sheet of material.

In a preferred embodiment the method includes leaving peripheral portions of the sheet free from beeswax, and thereafter folding the peripheral portions of one or two such sheets to form a frame around the pattern of beeswax.

Preferably the method includes forming a pattern of beeswax by applying molten beeswax onto form surfaces in a form, said form surfaces forming a pattern, so that a volume of beeswax extend above a plane comprising said form surfaces; thereafter applying a first side of a sheet of material to the form while the beeswax is still in a molten state, the sheet of material having a temperature below the solidifying temperature of beeswax; and finally removing the sheet of material from the form, wherewith with a pattern of beeswax is attached to the sheet of material. In an advantageous embodiment the method includes the step of applying a pattern of beeswax onto a second side of a sheet of material, the first side of the sheet of material being provided with a pattern of beeswax. Said form surfaces forming a pattern are constituted by grooves or by planar surfaces.

Beeswax in molten state can be applied to the form surfaces in a patterned form by dipping the form in a bath of molten beeswax.

The invention also relates to a form for applying a pattern of beeswax onto a sheet material, characterised in that the form comprises a body having form surfaces in a hexagonal pattern, all surfaces of the form extending from the edges of the form surfaces being inclined and leading to openings having edges on a lower level than the edges of the form surfaces so that any surplus of molten beeswax supplied to the form will run away along said surfaces. The form surfaces be planar or consist of grooves. The form surfaces have preferably a width of 0.2-2.0 mm.

The invention also relates to an apparatus for applying a pattern of beeswax onto a sheet material, characterised in that it comprises a container for molten beeswax, means for melting beeswax filled into the container and means for maintaining beeswax in a molten state, a form as described above, means for moving said form into and out of the container and means for position a sheet of material onto said form when said form is placed outside the container.

Finally, the invention relates to a bee hive foundation comprising a sheet of material, onto which a pattern of beeswax is attached, characterised in that the pattern of beeswax has a height of 0.1-1.0 mm, preferably 0.3-0.4 mm. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the enclosed figures. The

drawings are merely examples that illustrate how frames with or without

integrated foundations may be prepared for easy assembly and preparation by

beekeepers and illustrations of a method and means to apply by printing or

stamping techniques a wax pattern to the foundations. All sizes and

configurations of frames and foundations used in the bee-keeping industry are

suited for this method and the invention includes any suitable or desirable size,

shape and pre-punched folding pattern of the sheets or strips used.

Figure 1 shows a foundation according to the invention and thereon applied

pattern of wax cell wall indications.

Figure 2 shows a plan view of a blank according to a first embodiment of the

invention, where one half-part of a foundation is to be integrated into its frame

parts.

Figures 2 A through 2D show different stages of the folding procedure for the

blank in figure 2. Figure 3 shows a plan view of a blank according to a second embodiment.

Figure 3 A shows a profile view of an integrated frame according to figure 3 in

the final stage of folding.

Figure 3B shows a profile view of an integrated frame according to figure 3

after folding.

Figure 4 shows a perspective view of a blank for a frame according to a third

embodiment.

Fig. 5 A shows a side view of a foundation manufacturing apparatus with the

form raised above the wax bath.

Fig. 5B shows the foundation manufacturing apparatus in figure 5 A with the

form lowered into the wax bath.

Fig 6 A is a view of the pattern of a form and a side view of the form.

Fig. 6B is a sectional view along the line A - A in figure 3 A. Fig. 7A - 7C show stepwise the process of applying the substrate to the form

to transfer beeswax onto the substrate.

DESCRIPTION OF EMBODIMENTS

Individual beekeepers have different preferences with regard to size and

material of foundations and can be expected to have different attitudes also to

the advantages of foundations being integrated with frames respectively being

separate components.

The present invention aims at satisfying most such preferences by providing a

low cost, labour saving system of frames and foundations and foundations

integrated with frames.

The following description will involve plastic coated cardboard paper as base

material. It is understood that the invention also applies to any other material

such as plastic coated corrugated paper or polymer, e g so called bi- or multi¬

walled plastics, starch, etcetera, that lends itself to being pre-treated to

facilitate folding to achieve a specific shape suitable as bee hive frames and

foundations and foundations integrated with frames.

The meeting of the objectives of the claimed invention requires that onto the

foundation material can be printed or stamped a wax pattern of hexagonal cells, this pattern serving as guidance and starting point for bees to build cells.

When foundations integrated with frames are used, this procedure should take

place before the folding of the material into frames is undertaken.

Thus the first step to realize the invention is to apply the wax pattern to the

foundation substrate. This may be done by any suitable printing or stamping

method such as silk screen printing, ink jet printing, suitably modified to

dispense molten bees wax, paint roller printing with the roller surface of e g

porous rubber having a suitable surface pattern.

Bees will accept to build cells to suitable height from such foundations, using

wax that they produce and available wax that they redistribute. When the cells

are filled with honey, the bees will cap them with a layer of wax that they

produce.

When the beekeeper harvests the honey, he will scrape or cut off these caps.

This wax and wax fragments form the walls of the cells is separated from the

honey and sold to such industries that manufacture foundations and to other

industries. An important wax source for industrial production is also all the

wax from such foundations that are taken out of production e g because of

damages.

One very important problem stems from the need to protect bee colonies from

attacks by parasites and spoors like e g the varroa mite and the American foul brood. This is done with the aid of pesticides such as for instance formic acid

and bromopropylate used inside the beehives. Unfortunately pesticide agents

are deposited in the wax of the foundations and from there the honey stored in

the cells will be contaminated. Such honey is not suitable for human

consumption and consequently many beekeepers run the risk of not being able

to pursue their activity.

With the practice of reusing the wax for the production of foundations this

problem is aggravated in that wax that has been exposed to pesticides several

times is still recirculated. No economically feasible method of purifying the

wax from residuals of pesticides used is known.

The objective of eliminating or substantially reducing this problem is to

provide a system that enables the beekeeper to safeguard the quality of the

honey he can supply, in respect of contamination of chemical agents used to

control e g parasites and spoors. This is achieved by a system that permits him

to use virgin wax that has not been exposed to pesticides, or in a special case

to use virgin wax that has been exposed to pesticides once, but that has not

been recycled and repeatedly picked up residuals of pesticides, thus ensuring

that the contents of harmful agents that can be transmitted from the wax to the

honey is safely below a critical limit and that the content will be lowered each

time this somewhat contaminated wax is mixed with wax that has not been

exposed to pesticides. Another objective is to enable the beekeeper to lower his cost for foundations.

This objective is reached by the fact that the system allows the use of very low

cost material as a substratum onto which is applied an indication pattern for

cells to be built by the bees and by the fact that the method may use as little as

only about 1/20 of the amount of beeswax compared to what is used for

foundations made entirely from beeswax.

This circumstance also has the effect that the absolute amount of contaminated

wax in a foundation, according to the invention, that is filled with honey and

capped will be much less than the amount of contaminated wax in a

foundation made by traditional methods.

Not only does the invention enable the beekeeper to manufacture himself

foundations at low cost, it also puts him in the position of having excess fresh,

virgin, uncontaminated, wax that can be sold at a premium.

Also, inherent properties of the foundations manufactured according to the .

invention are such that no stringing of wires in frames or affixing of

foundations by melting procedures is needed, thereby bringing labour savings.

Simple stapling of or fitting the foundations into grooves in the frames are

preferred methods of affixing foundations to the frames. When foundations integrated with frames are used, naturally no measure needs to be taken to

affixing them.

Here will be shown one embodiment of printing equipment designed

specifically for use by the individual beekeeper to apply a hexagonal wax

pattern onto the foundation substrate. For simplicity of explanation the use of

the method and the equipment is illustrated by the application of a wax pattern

onto a simple foundation substrate; however the same principle applies when

the pattern shall be given to the foundation parts of integrated foundations and

frames.

In Figure 1 a substratum material 1 for foundations according to the invention

is a thin sheet of polypropylene or other plastic material or paper. Some other

sufficiently stiff materials such as starch or wood are also suitable. This

substratum, unless made by a plastic material, may be covered with a thin

layer of food quality surface protection material such as plastic, wax,

aluminum or lacquer (not shown).

The substratum 1 is processed in a specially developed apparatus, being one

element of the invention, by the aid of which a pattern 2 of wax in an outline

of hexagonal cell wall indications is attached to the substratum, each wall section being common for two adjoining cell patterns. The height of the wax

cell indications is 0.1 to 1.0 mm, preferably 0.3 - 0.4 mm.

The width of the wax cell indications is 0.2 to 2.0 mm, preferably 0.5 to 1.5

mm. These dimensions will bring about the savings in wax consumption

earlier mentioned and will give good pregnancy to the pattern.

The size of the cells indicated by wax pattern, as measured from one wall to

the opposite wall is from 4.5 to 7.0 mm, depending on e g local preferences,

preferably 4.9 to 5.5 mm.

The size of the foundations shall be according to the various standards in the

industry predominantly between 111 x 300 mm to 285 x 448 mm.

The apparatus for applying the wax cell wall indications will now be explained

by references to the Figures 5-7.

In Figures 5A and 5B, 3 indicates a tray containing beeswax 10, the tray being

made from metal or other strong material that will withstand temperatures

between minus 30°C and at least plus 80°C and that will not discolour the wax. Figures 5 A and 5B, 4 and 5 shows a device, attachable by cord 11 to a mains

outlet, for controlling the temperature of the wax and a means of limiting the

maximum temperature thereof to avoid overheating and fire hazard. The

device includes one or several thermal sensors in the tray (not shown).

Mounted on supports 12 is a system of levers 6 to which is attached a

stabilizing frame or grid 8 that will let molten wax flow through it. This frame

or grid serves to hold a form shown in Figure 6A. Operating handle 9 permits

the lowering of the frame or grid with the form into the molten wax bath and

raising it out of the bath.

The form, Figures 6 A and 6B, is manufactured from a material that will

withstand temperatures between minus 30°C and at least plus 80°C and that

will not absorb nor discolour beeswax. Figure 6A shows the form having been

raised out of the bath of beeswax, with the shadowed area 13 being the

remaining molten beeswax in the grooves intended for this purpose, where

surface tension results in some wax above the plane of the peaks surrounding

the grooves. Figure 6 A, 14 indicates holes in the form for evacuation of

surplus beeswax during raising of the form.

In Figure 6B, 13a illustrates non-filled grooves of a hexagonal pattern being

given to the form, 14a shows a hole in the form that will let wax run back into the tray when the form is lifted out of the wax bath. Symbol 15 represents the

section surface A - A of the material of the form.

Figures 7A - 7C show the sequence of transferring beeswax from the form to

the foundation substratum. Onto the lifted form is positioned the foundation

substratum 16. The molten wax in the hexagonal grooves of the form will

adhere and form the desired cell wall indications on the substratum. As

previously indicated, surface tension of the molten wax will cause the wax to

assemble in the grooves with some wax volume extending above the plane

formed by the peaks of the grooves. It is only this amount of wax that is

intended to be transferred to the foundation substratums. This transfer can be

achieved quickly because the substratum material will and should have a

lower temperature than the molten wax. The solidification of the transferred

wax commences immediately upon lifting the substratum from form. The

duration of the contact between the substratum and the form and the

temperature difference will influence the height of the cell wall indications

transferred to the substratum.

In the foregoing description of wax in grooves 13a being transferred to the

substrate, pregnancy of pattern and minimizing of wax consumption are the

objectives. Should the beekeeper wish to apply more wax to the substrate,

thereby supplying more wax for redistribution by the bees and in doing so speed up the building of cells, a form may be used that has wider and deeper

grooves, or the grooves replaced by plane, horizontal surfaces to which wax

will adhere by surface tension.

The handling of the foundation substratum is shown in sequence as the shape

of the substratum, in contact with the form 7, changes according to what is

indicated by 16 - 16a - 16b.

This operation is done on both sides of the substratum, with a drying period in

between.

The foregoing description of the invention is one non-limiting execution

thereof. To anyone skilled in the art it is obvious that additional features can

be included, such as a stand for the apparatus, a thermally insulating hood and

means to protect the operator of the equipment from touching the hot wax. The

addition is also foreseen of such functions as automation of filling the tray

with wax, lowering and raising of the form, feeding foundation substrata in

and out and applying those onto the form, drying chamber for foundations and

equipment for turning over and for stacking of foundations. Dual form

arrangement to attach cell indications to both sides of foundation substrata is

yet another execution. For production of larger quantities than most individual beekeepers need, the

cell wall indications may be applied to foundation substrata by e g equipment

for silk screen printing or for ink jet printing, suitably modified to dispense

molten beeswax.

The second step to realize the invention, in the case of using an integrated

foundation and frame or using a foldable frame only, is to perform the folding

operation. This will now be shown by two preferred but not limiting

embodiments.

The first embodiment is an integrated foundation and frame consisting of two

identical pre-treated cardboard sheets that shall be mounted onto each other.

Figure 2 shows the blank 17 for the integrated foundation and frame having

tabs 18, slots 19 and folding creases or indentions 20. The mounting operation

is simplified by placing the two blanks 17 congruously onto each other,

thereafter commencing the folding sequence as outlined for one sheet in

figures 2 A - 2D. The tabs are pushed through the slots of both sheets in the

same operation, thereby ensuring that the assembly is firm and precise. In this

embodiment all the folding is done in the same direction resulting in a semi-

finished product that is plane on one side, with the exception of protruding

flaps, while the opposite side has a half-frame shape. The complete product

includes also a mirrored copy of the fist semi-finished product. The slots 19 in each semi-finished product are of a size that permits passing through them of

the flaps of both semi-finished products; thus the two semi-finished products

can easily and securely be fitted together. The flaps 18 may have partial cut¬

outs that can be bent out of plane, or twisted, after passing them through the

slots 19, to prevent loosening of the firm connection between the semi¬

finished products.

The second embodiment is an integrated foundation and frame made up of a

single sheet that is shown in figure 3. Components similar to corresponding

components in the embodiment shown in figure 2, such as indicate folding

creases 20' in the blank 17', are indicated with the same reference with the

addition of a prime sign. The folding procedure is essentially the same as

described for the blank 17 in the first embodiment with the exception that the

operation commences by folding sections a-a, b-b and c-c first and securing

the folds by inserting in the same operation tabs d through opposing slots e in

both congruously positioned parts of the sheet. Sections b to be folded at an

acute angle to sections a and c as illustrated in the cross-sectional views in

Figure 3 A and 3B, showing the last stage in the folding of the blank 17' into

an integrated frame and bee hive foundation and such a frame, respectively.

Thereafter the folding of side and bottom frame parts is done as in the first

embodiment. Thus, with the exception of the part that will make up the top bar of the frame it blank 17' is essentially folded in the same manner as the

integrated frame and foundation illustrated in figure 2.

The third embodiment shown in Figure 4 is one preferred but non-limiting

execution of a foldable frame without an integrated bee hive foundation. In

this embodiment the frame 21 is made of multiwalled plastic coated

corrugated paper and consists of two elements 22, 23. The free ends of the

foldable element 22 having folding indentions in the form of cut-outs as is

shown in figure 4, may be shaped in a manner suitable for firm attachment to

the upper member 23 of the frame, e g as shown or dove-tailed. To increase

stability of the assembled frame, nails 24 or the like may be driven into the

corners of the frame and into the joint between the side members and the

upper member. Grooves may be cut out for holding a foundation along the

inside center of the upper and lower members.

Naturally, entire bee hives may be manufactured using the materials and

techniques employed above.

Advantages of the invention

Employing the described system, materials and equipment will allow the beekeeper to lower cost, reduce work input and control his situation in terms of quality of his production. It is a means of becoming independent of industrial sources of foundations, frames and wax.

Claims

1. A frame for supporting a bee hive foundation, characterised in that it consists of foldable material, which is folded into a rectangular frame with the aid of folding indentions in the frame material.

2. A frame according to claim 1 comprising an integrated bee hive foundation, wherein the frame consists of folded peripheral portions of at least one sheet being folded into a three-dimensional shape, the central part of the at least one sheet constituting a bee hive foundation.

3. The frame according to claim 2, wherein the frame consists of two sheets having folded peripheral portions holding the two sheets together.

4. The frame according to claim 1 comprising an integrated bee hive foundation, wherein the frame consists of a double-walled central part and peripheral portions folded into a three-dimensional shape, the frame being made from a single blank.

5. A blank for a frame supporting a bee hive foundation, characterised in that it consists of sheet material having folding creases for facilitating folding of the sheet material into a frame having three-dimensional shape.

6. A method of manufacturing a bee hive foundation, characterised by printing a pattern (2) of beeswax onto one or both sides of a sheet of material (16).

7. The method according to claim 6, characterised by leaving peripheral portions of the sheet free from beeswax, and thereafter folding the peripheral portions of one or two such sheets to form a frame around the pattern of beeswax.

8. The method according to claim 6 or 7, characterised by forming a pattern of beeswax by applying molten beeswax onto form surfaces (13a) in a form (7), said form surfaces forming a pattern, so that a volume of beeswax extend above a plane comprising said form surfaces (13a); thereafter applying a first side of a sheet of material (16) to the form while the beeswax is still in a molten state, the sheet of material having a temperature below the solidifying temperature of beeswax; and finally removing the sheet of material from the form, wherewith with a pattern (2) of beeswax is attached to the sheet of material.

9. The method according to claim 6, 7 or 8, characterised by applying a pattern of beeswax onto a second side of a sheet of material (16), the first side of the sheet of material being provided with a pattern (2) of beeswax.

10. The method according to claim 8 or 9, wherein said form surfaces forming a pattern are constituted by grooves (13a).

11. The method according to claim 8 or 9, wherein said form surfaces forming a pattern are constituted by planar surfaces.

12. The method according to claim 6, 7 , 8, 9, 10 or 11, wherein beeswax in molten state is applied to the form surfaces (13a) in a patterned form (7) by dipping the form in a bath (10) of molten beeswax.

13. A form (7) for applying a pattern of beeswax onto a sheet material, characterised in that the form comprises a body (15) having form surfaces (13a) in a hexagonal pattern, all surfaces of the form extending from the edges of the form surfaces being inclined and leading to openings having edges on a lower level than the edges of the form surfaces so that any surplus of molten beeswax supplied to the form will run away along said surfaces.

14. The form according to claim 13, wherein the form surfaces are planar,

15. The form according to claim 13, wherein the form surfaces (13a) are grooves.

16. A form (7) according to claim 13, 14 or 15, wherein the form surfaces (13a) have a width of 0.2-2.0 mm.

17. Apparatus for applying a pattern of beeswax onto a sheet material, characterised in that it comprises a container (3) for molten beeswax, means (4,5,11) for melting beeswax filled into the container and means (4,5,11) for maintaining beeswax in a molten state, a form (7) according to claim 13, means (6,9) for moving said form into and out of the container and means for position a sheet of material onto said form when said form is placed outside the container.

18. Bee hive foundation comprising a sheet of material (1), onto which a pattern (2) of beeswax is attached, characterised in that the pattern of beeswax has a height of 0.1-1.0 mm, preferably 0.3-0.4 mm.