MXPA00006242A - Disposable absorbent articles comprising microporous polymer films with registered graphics - Google Patents

Abstract

A disposable absorbent article is disclosed, comprising a topsheet, a backsheet and an absorbent layer between the topsheet and the backsheet, wherein the backsheet is comprised of a microporous polymer film printed with a registered graphic and comprising by weight:from about 30%to about 60%of a polyolefin;and from about 40%to about 80%of calcium carbonate;wherein the film has a"b"value of between about 0 and about 0.5 and exhibits less than about 2%thermal shrinkage at about 50°C and about 50%relative humidity for one week.

Description

DISPOSABLE ABSORBENT ARTICLES THAT COMPRISE MICROPOROSE POLYMER FILMS WITH MARKED GRAPHICS FIELD OF THE INVENTION The present invention relates to disposable absorbent articles comprising microporous polymer films. More specifically, the present invention relates to disposable absorbent articles comprising microporous polymer films that are particularly suitable for printing graphics marked thereon.

BACKGROUND OF THE INVENTION The polymeric materials provided in the form of films or sheets have been used in a variety of commercial products, including diapers, feminine care products, adult incontinence products, and the like. In the manufacture of disposable absorbent articles, such as diapers, microporous polymer films have generally been incorporated into the structure of the article as a part of the layers that are placed away from the user's body during use (often called "the back sheet "). The backsheet provides a liquid impervious barrier such that the exudates absorbed and contained in the absorbent core of the article are prevented from leaking, and particularly in such a way as to prevent urine from staining the outside of the diaper. A nonwoven material is often laminated or otherwise adhered to a microporous polymer film to form the backsheet of a disposable article. The non-woven material provides the fabric appearance and a fabric-like feel on the outer side of the garment so that users and caregivers perceive a comfort similar to the garment. The combination of a non-woven material and a microporous film is suitable for disposable absorbent articles such as diapers, including pull-on diapers and ribbon type diapers, feminine care products, and adult incontinence products. An exemplary pull-on disposable diaper, which is placed by inserting the wearer's legs into the leg openings and sliding the garment upward toward the position around the lower torso, is disclosed in the United States Patent No. 5,569,234, from Buell, "disposable pull-on pants". For disposable absorbent articles, especially disposable diapers, it is also often desired to provide graphic designs on the articles to increase their appearance and customer acceptance. In previously known articles, nonwoven layers have typically been printed with such graphic designs. This is because the printing process for non-woven materials is typically easy to control, because the surfaces of these materials tend to provide stronger mechanical properties that make them more amenable to printing. See, for example, European publication No. 0 604 729; Yeo U.S. Patent No. 5,503,076; Shleinz patent of the United States No. 5,458,590. However, graphics marked in multiple colors as high resolution, which are preferred by the consumer, can not normally be printed on such materials. In this way, the quality of the graphics that can be printed on the nonwoven materials is typically much lower than those that can be achieved by printing on the microporous film. Microporous polymer films provide excellent surface characteristics that make them suitable for printing high resolution graphics. However, existing polymer microporous films, see, for example, Japanese Patent Laid-Open No. 9-25372, (Kokai), are not mechanically stable enough to support the printing of high-color multi-color graphics. resolution, which are preferred by the consumer. This is due in large part to its thermal instability. The thermal contraction associated with existing microporous materials has made it difficult to exploit its ability to support the application of high resolution graphics. It has also been found that a high degree of whiteness, that is, the visual appearance of the white color of the item as seen by the consumer, is very important for the customer. Customers tend not to accept articles that incorporate films that have a yellowish or non-white hue. In addition, breathability, the ability of the item to allow water vapor to escape, is important for the user's comfort and for the acceptance of the client's skin care. A lack of breathability can result in a hot, more ventilated product, not benevolent with the skin, for the user. Based on the foregoing, there is a need for disposable absorbent articles that comprise a microporous polymer film that is mechanically stable enough to support high resolution printing, multi-color marked graphics, while also providing breathability and a degree of high whiteness. None of the existing absorbent articles provides all the advantages and benefits of the present invention.

BRIEF DESCRIPTION OF THE INVENTION The present invention is directed to a disposable absorbent article comprising a topsheet, a backsheet and an absorbent layer between the topsheet and the backsheet, wherein the backsheet is composed of a microporous polymer film printed with a marked graphic and comprising by weight: from about 30% to about 60% of a polyolefin; and from about 40% to about 80% calcium carbonate; wherein the film has a "b" value between about 0 and 0.5 and exhibits less than about 2% thermal contraction at about 50 ° C and about 50% relative humidity for one week. These and other features, aspects and advantages of the invention will be apparent to those skilled in the art from a reading of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS Although the description concludes with the claims that point in particular and claim the invention differently, it is believed that the present invention will be better understood from the following description of the preferred embodiments taken in conjunction with the accompanying drawings in the drawings. which: Figure 1 is a representation of a coordinate system for the colorimetric measurement; Figure 2 is a partial top view of a preferred embodiment of the film of the present invention printed with the marked graphics; Figure 3 is a front view of a preferred embodiment of a disposable absorbent article having the graphics marked; and Figure 4 is a simplified plan view of another preferred embodiment of a disposable absorbent article having the graphics marked.

DETAILED DESCRIPTION OF THE INVENTION All the references cited here are incorporated by reference in their totalities. The citation of any reference is not an admission with respect to any determination as to its availability as the prior art for the claimed invention. All percentages herein are by weight of the compositions unless specifically stated otherwise. All proportions are weight proportions unless specifically stated otherwise. As used herein, the term "comprising" means that other steps or other ingredients that do not affect the final result can be added. This term encompasses the terms "consisting of" and "consisting essentially of". The microporous polymer films which are preferred for use in the disposable absorbent articles of the present invention are formed from a mixture of polyolefin, normally supplied as a resin, and calcium carbonate particles (CaCO3). Preferred exemplary polyolefins for use herein include polyethylene and polypropylene. Because polyethylene has a lower modulus and a lower melting point than polypropylene, it is generally easier to process than polypropylene. For this reason, polyethylene is more preferred. Alternatively, other thermoplastic polymers may be used for the films of the present invention. Preferably, about 30% to about 60% of a polyolefin is used in the films of the present invention; more preferably, from about 45% to about 55% polyethylene. CaCO3 is used to provide microporosity, as described more fully below. However, this may tend to impart a light yellow hue to the film. It is believed that any yellow hue is highly unacceptable to consumers, who tend to prefer an intense, bright white appearance. A bright white appearance can be achieved by selecting a grade of CaCO3 that has a very white color. A bright white appearance can also be achieved by adding a small amount of titanium dioxide (TiO2) to the polyolefin and CaCO3 during the mixing step of the film forming process, if the grade of CaCO3 used is not white enough to provide the finished film with the desired whiteness. In this case, the addition of TiO2 counteracts the yellowing effect of CaCO3. CaCO3 is generally whiter than CaCO3, but is also generally more expensive and more difficult to mix during extrusion. If TiO2 is added, it should preferably be added in an amount less than about 5% by weight, since amounts greater than about 5% by weight can be difficult to process. "Whiteness" as used here generally refers to the absence of yellow. The whiteness of the microporous films here can be measured using the color model of the ColorQUEST 45/0 instrumentation available from HunterLab, 11491 Sunset Hills Road, Reston, VA 22090 USA. See also, The Measurement of Appearance, Hunter, Richard S., Hunter Associates Laboratories, 9529 Lee Highway, Fairfax, VA 22030 USA. The color model describes the color of any material based on three parameters: L, a, and b. The color model can be graphically represented by a coordinate system shown in Figure 1. Referring to Figure 1, in the coordinate system shown, "L" is a measurement of the clarity of a sample, which varies from L = 0 (blackness) to L = 100 (whiteness). The quantities "a" and "b" are called opponents-type coordinates. These indicate the degree of redness (values "a" positive), greenness (values "a" negative); and the degree of yellowing (values "b" positive), azulez (values "b" negative). For neutral colors (for example, white, gray, black), "a" and "b" should be approximately zero. The highest values of "a" and "b" for a given sample, the most saturated or chromatic is the color of that sample. The very important parameter for the films of the present invention is the "b" value, due to the lack of acceptance by the consumer of the yellow films. Using the ColorQUEST instrument under the conditions of the international standard 10 D65 and a reflection angle of 10 °, the value of "b" for the films of the present invention is preferably between about 0 and about 0.5, more preferably as close to 0 as may be possible. In addition to polyethylene and CaCO3, small amounts of other additives such as antioxidants or lubricants may be added during the initial step of mixing the film forming process. These other additives should preferably be added in the range from about 0.01% by weight to about 0.05% by weight. "Microporosity" refers to the functional property of the film that allows an article such as a diaper to provide improved health to the skin, because the microporous orifices allow the transmission of moist vapor between the interior of the diaper, is say, the user's skin, and the outside of the diaper. Good wet steam transmission, or "breathability", also increases user comfort by providing a less suffocating feeling. The microporous orifices in the films of the present invention are generally concentrically formed around the particles of the CAC03 during the stretching step of the film formation, as described more fully below. The microporous orifices form on the surfaces of the film as well as throughout the thickness of the film, with the size of the microporous orifices being related to the size of the CaCO3 particles. In general, the size of the holes surrounding the particles is directly related to the size of the particle. In this way, small particles will cause the formation of small holes, while large particles will create large holes. However, limiting the size of the microporous holes is also important, because even when the larger holes result in greater breathability, they also increase the risk of leaks. The size of the holes can also be affected by the stretch ratio during the stretching stage of film making. Preferably, CaCO3 particles with small size are used to achieve optimum breathability and the stretch ratio is approximately 2 to 3 times. The wet vapor transport velocity ("MVTR") is a characteristic measure of the breathability and "microclimate" within the diaper. The MVTR refers to the permissible wet volume from one film side to the other side of the film per unit area (eg, per square meter) and per unit of time (eg, per day). The elevated MVTR is desirable for good skin care because the air can be well ventilated between the inside and the outside of the diaper. However, if the MVTR is too high, the risk of odor, noticeable moisture leaks or both is present. The control of MVTR is therefore important in applications involving microporous film technology. The MVTR of a breathable film can be measured by the cup test method. This method is described as follows. A known quantity of calcium chloride (CaCl2) is placed inside a stainless steel container. The CaCl2 with the water level measurement used here can be purchased from Wako Puré Chemical Co., Ltd. A film sample is placed on top of the container, and the container is closed hermetically with a lid and screws. The lid has a hole through it and in this way the external moisture of the container can diffuse towards the container through the film. The container with the film test sample is then placed in a constant temperature and humidity environment for a fixed period of time. The amount of moisture absorbed by the CaCl2 within the container is a measure of the moisture permeability of the film. Using the cup test method where the stainless steel container is a cylindrical container with a diameter of 30 mm and a depth of 50 mm, with constant environmental conditions of 75% relative humidity and 40 ° C, the films of The present invention preferably has an MVTR of at least about 3200 grams / m2 per day, with approximately 3700 grams / m2 per day which is more preferable for diapers. Preferably, the MVTR is as high as possible without leakage. The microporous polymer films of the present invention are preferably formed according to the following process. The polyolefin polymer, preferably from about 30% to about 60% and more preferably from about 35% to about 55% polyethylene, and CaC03, preferably from about 40% to about 80% and more preferably from about 45% to about 65% are mixed at an elevated temperature, preferably higher than the melting point temperature of the polymer. For example, if polyethylene is used the mixing temperature should be in the range of about 120 ° C to about 130 ° C. If the TiO2, and the other additives are to be included in the film, these should also be added to this initial raw material mix at the beginning of the process. If T0O2 is to be added, it is preferable to add it to a level less than about 5%. After mixing, the mixture is fed through pulleys and then pumped to an extruder. After extrusion, the mixture is emptied as a thin film. Generally, the pour temperature is also higher than the melting point temperature of the raw material polyolefin polymer.

After emptying, the film is stretched, while remaining at a higher ambient temperature. The stretch step is the point at which the microporous orifices form around the CaCO3 particles. The stretching rollers are preferably used for the stretching step. The speed of each stretching roller must basically be greater than that of the preceding drawing roller. In this way, the speed of the second stretching roller is greater than the speed of the first stretching roller, with the first stretching roller having the lowest speed of all the stretching rollers. The stretch stage interlaces or locks in the residual stress. After the film has been stretched, it is not thermally stable due to the energies between the molecules of the film. Therefore, in order to achieve the thermal stability necessary to sustain the printing of the high resolution graphics on the film, additional processing is necessary. The film in the stretched state is then tempered. It is believed that the tempering step removes tensions between the micro molecules of which the film is composed, and thus it is critical to provide the film with thermal stability. The tempering step provides the release of tension that would otherwise occur during storage and transport conditions at elevated temperatures above its vitreous transition temperature Tg of the polyethylene used (or other polymer). In other words, if tempering is not carried out as described herein, this release of tension will occur when the finished product incorporating the film, eg, a diaper, experiences the elevated temperatures associated with storage and transportation. At that point, the stresses will release, which will generally distort the appearance of both the product itself and especially the appearance of the marked graphics, and which can affect the overall quality of the film's integrity.

However, if the tempering conditions are not too strict, for example if the tempering temperature is too high, the tempering time is too long, or both, many of the microporous orifices will contract at high tension, decreasing this. way the breathability of the film. After tempering, the film is preferably subjected to a corona treatment in which it is placed in a sealed environment at about room temperature. O3 ions are radiated throughout the environment. It is believed that the corona treatment increases the level of dyna for the printing side of the film, ie, on which the graphics will be printed. The high dyne levels indicate that each area of the printing ink will require less surface area on the film for adhesion; In this way, the level of superior dyna, the superior graphic resolution and the best that can be done. The films of the present invention preferably have a dyne level of more than about 35 and more preferably greater than about 40. After the corona treatment, the finished film can be rolled or packed in the preparation for printing the marked graphics on the film, for example, as shown in Figure 2. The printing techniques used here to provide the multi-color graphics marked include the flexographic printing process and the gravure printing processes with flexographic printing being preferred. An exemplary part of a film of the present invention is shown in Figure 2. The film 10 is shown printed with the graphics 20 separated by a separation length P. It will be well understood by those skilled in the art that the graphics 20 may be in any way, design color or size, and that individual or multiple designs can be used. Alternatively, pre-packed, pre-filled, pre-cut or pre-cut objects can be used. Regulating marks 30 having a width W1 and a length L are also shown. Regulating marks 30 are used in such a way that the optical sensors of the combination and cutting mechanisms can detect the marks and therefore properly align and cut the film or the combination of film / non-woven backsheet. Preferably the regulating marks are sized and positioned so that they are removed when the film is cut, such that they do not form a part of the finished product and therefore are not visible to the consumer. Alternately, these may be part of the finished product but invisible to the consumer, while still being detectable by the machinery. The distance between the regulation mark and the edge of the film is referred to as a shaded mark. The shaded marks 40 are shown as having the width W2 in Figure 2. For a disposable diaper manufacturing line, the separation length P of about 475 mm to about 485 mm, the width of the regulation mark W1 of about 7 mm to approximately 10 mm, the length of the adjustment mark L from approximately 20 mm to 25 mm, the width of the shading mark W2 from approximately 0 to approximately 10 mm, and the red color of the adjustment mark for the contrast they are exemplary parameters for the regulation marks. As noted above, the films of the present invention exhibit high thermal stability as a result of the selection of raw materials and processing conditions, particularly the stretching and quenching steps. After the film has formed and during the time in which it is subsequently stored, often in a warehouse where it is exposed to elevated temperatures after production, the film material tends to contract. This contraction is a function of the conditions of time, temperature and humidity of storage and transport, parameters that can not be easily controlled. For example, during a week at 50 ° C, contraction levels of up to 5 to 10% have been observed for certain conventional films. Different contraction levels can even vary within a single film roll depending on the level of tension that was used to wind the roll. This thermal instability has typically made it difficult to incorporate these films into consumer products in a phase relationship. The coefficient of thermal shrinkage of the microporous films can also be measured under the following conditions. Film samples are cut as long as 500 mm in the machine direction and 150 mm in width in the transverse direction. As used herein, "machine direction" means the direction of movement along the manufacturing line, and "transverse direction" means the direction substantially perpendicular to the direction of the machine. The machine direction is represented by the arrow labeled MD in Figure 2. Two straight lines are drawn as 250 mm in the machine direction and 100 mm in the transverse direction. The film samples are placed in a controlled oven at 150 ° C and 50% relative humidity for one week. The contracted lengths of the lines are calculated as the coefficient of thermal contraction, based on the original lengths. Under the test conditions described above, the films of the present invention typically only experience from about 0% to about 5% machine direction shrinkage, more preferably less than about 2%. In the transverse direction, the films typically experience negligible shrinkage. In this way, the films of the present invention provide both of the good surface characteristics of the microporous polymer films that readily sustain the high resolution printed graphics while being susceptible to only negligible degrees of thermal shrinkage. The films of the present invention also preferably have other desirable properties that are beneficial in the processing of the film in relation to the manufacture of the absorbent articles. Although it will be understood by those skilled in the art that the films of the present invention have many uses, for purposes of illustration the following description will focus on the use of the film as a backsheet for a disposable papal. The frame module is important for the stable operation of the marked graphics phase system. As used herein, "raster modulus" means the property defined as the inclination of a material in the stress / strain curve. Although the absolute value of the weft module is not as important as its standard deviation within a roll of film, the modulus determines the amount of tension required to force an adjustment to the phase position of the film during processing. Films having a raster modulus in the range of about 4000 g / in to about 13,000 g / in have been found to be preferred for the printing of high resolution graphics on the films used as the backsheets of the diaper. The control of the film gauge is important for the winding of a back sheet film roll and its processing capacity. The term "film size" refers to the thickness of the film. During the process of making the film, several localized levels of film shrinkage sometimes occur in the case of microporous films. A wide variation in the size of the film can cause wrinkles or uneven surfaces or both on a film roll. During processing, gauge variations can cause film deformation, film breakage in thinner areas, line interruptions due to problems caused by the tension control problem. The exemplary scales for the sizes of the film here are in the range of approximately 0.022 mm to approximately 0.038 mm, with gauge variations of + 6.3%. Thermal enthalpy (H) is another important feature in providing thermal resistance to the polymer film, especially during processes such as thermal fusion bond lamination that can be part of a diaper manufacturing line. A high enthalpy property can provide a wide scale for temperature adjustment of the adhesive because the film materials have strong thermal resistance. As the enthalpy increases, however, the stiffness of the microporous film material also increases, resulting in possible problems with comfort and other manufacturing processes that depend on the thermal response of the film. Without being bound by the theory, it is believed that the link between the additional stiffness and the ascending enthalpy is due to the rising forces between the macro molecules. The basis weight refers to the weight of one square meter of raster material. Exemplary base weights here are between about 20 grams per square meter (gm2) and about 40 g / m2 of films useful as a backsheet diaper. Other parameters of the film that impact the printing process, the diaper manufacturing process, or both, include the width of the film, the length of the film roll, the core diameter of the film roll, splices, markings regulation, and printing orientation. Print orientation refers to the direction of travel of the printed film with graphics through the manufacturing line. For a disposable diaper manufacturing line, it has been found useful that the printed side of the microporous polymer film is rolled into the roll, with the area that will become the front of the product leading out of the roll, with the orientation of the regulating mark on the left and the regulation shading mark on the right. Referring to Figure 3, there is shown a preferred embodiment of a pull-on disposable diaper 50, which is generally placed on the wearer's body by inserting the legs into the leg openings 62 and carrying the article upwards over the waist . Generally, "pull-on diaper" refers to pull-on garments worn by young children and other incontinent individuals to absorb and contain exudates from the body. It should be understood that other pull-on garments such as training pants, incontinence briefs, feminine trusses, garments or panties for feminine hygiene, and the like, are included herein. It should also be understood that diapers of tape type are included here. Referring to Figures 3 and 4, the diaper 50 is generally composed of a backsheet 52, a top sheet 54 and an absorbent layer 66 (shown by dotted lines in Figure 4) located between the back sheet 52 and the sheet upper 54. Upper sheet 54 is positioned to be positioned facing or near the body when the diaper is worn and is generally provided with a liquid-permeable region such that exudates from the body can flow through the upper sheet 54 towards the absorbent layer 66. The backsheet 52, which is placed away from the body during use, is typically impervious to liquid such that the outer garment or other items are not wetted by body exudates. Preferably, the backsheet 52 is composed of at least one microporous polymer film printed with marked graphics, as described herein. The backsheet 52 may further comprise a layer of nonwoven material laminated to the microporous film layer, in which case there is provided a more fabric-like and garment-like feel that is typically obtained with only the backsheet of film. The elastically extensible side panels 56 are provided to ensure the most comfortable and contour fit by initially comfortably adjusting the pull-on diaper 50 to the wearer and holding this adjustment throughout the time of use even after it has been loaded with the exudates. The elastics of the leg 58 and the elastic waist region 60 are also provided to increase the fit around the legs and waist, respectively. Figure 3 shows the front view of the diaper 50 with an exemplary graphic 20 positioned in approximately the upper region of the backsheet, on the front side of the diaper 50. In Figure 4, there is shown a simplified plan view of an embodiment of a disposable absorbent article in its flat state, not contracted prior to forming. In this embodiment, graph 20 is shown in the posterior region of the diaper with the graphics 22 shown additionally in the frontal region. As will be understood by those skilled in the art, many other aspects for disposable absorbent articles are within the scope of the present invention. For example, barrier folds as described in the Lawson and Dragoo patents Nos. 4,695,278 and 4,795,454 are a desirable aspect for disposable absorbent articles. In addition, the upper skin care type sheets that are provided with lotion thereon for the purpose of reducing irritation and skin abrasion are a desirable feature here. The aspects and embodiments of the present invention set forth herein have many advantages, including the glossy white appearance, the ability to support the graphics marked in multiple colors., high resolution, and thermal stability.

EXAMPLES The following example further describes and demonstrates a preferred embodiment of the microporous polymer film for disposable absorbent articles within the scope of the present invention. The example is only given for the purpose of illustration, and should not be construed as a limitation of the present invention since many variations thereof are possible without departing from its spirit and scope. Polyethylene and CaCO3 are used as starting materials. The film is emptied and stretched in the direction of the machine. The movie has the following properties: Base Weight 34.3 + 0.42 gm2 Thickness by Gauge 0.042 + 6.3% mm Thermal shrinkage MD 1.4% CD 0.0% Mechanical Property MD: Load at 1% 114 g / in Load at 3% 269 g / in Load at 5% 389 g / in Maximum load 1260 g / in. Maximum effort 188% CD Maximum load 460 g / in Maximum effort 386% MVTR (Cup test) 3600 g / m2 / 24hr Whiteness L: white / black 93.46% a: red / green -0.24 b: blue / yellow 0.35 Separation size for registered marks 480 + 4 mm Brand width 10 + 0.2 mm Brand length 20 + 0.5 mm Shade mark width 0.0 + 1.0 mm The mechanical property of the film refers to the tensile strength at a percent strength or at the maximum, where stresses on the scale of about 1% to 5% represent the stresses on the elastic scale of the material. After the film has been formed it can be printed with the marked graphics and incorporated in the disposable absorbent article, for example as part of the back sheet of a disposable diaper. It is understood that the examples and embodiments described are for illustrative purposes only and that various modifications or changes in the light thereof will be suggested by one skilled in the art without departing from the scope of the invention.

Claims (10)

1. A disposable absorbent article comprising a topsheet, a backsheet and an absorbent layer between the topsheet and the backsheet, wherein the backsheet is comprised of a microporous polymer film printed with a marked graphic and comprising by weight: to. from about 30% to about 60% of a polyolefin; and b. from about 40% to about 80% calcium carbonate; wherein the film has a "b" value of between about 0 and about 0.5 and exhibits less than 2% thermal contraction at about 50 ° C and about 50% relative humidity for one week.

2. The article according to claim 1, wherein the polyolefin is selected from the group consisting of polyethylene and polypropylene.

3. The film of the article according to claim 2 which comprises by weight from about 35% to about 55% polyethylene; and from about 45% to about 65% calcium carbonate.

4. The article according to claim 3, further comprising up to about 5% by weight of titanium dioxide.

5. The article according to claim 1, wherein the film has a wet steam transmission coefficient of at least about 3200 grams / m2 per 24 hours.

6. The article according to claim 1, wherein the film has a raster modulus of about 4,000 g / in. To about 13,000 g / in.

7. The article according to claim 1, wherein the film has a print side having a dyne level greater than about 35. The article according to claim 1, wherein the backsheet further comprises a film layer. a non-woven material laminated to the film. 9. The article according to claim 1, wherein the marked graphic is printed on a flexographic printing process. 10. The article according to claim 1, wherein the marked graphic is printed by a gravure printing process.