JPH0238709B2 - - Google Patents

Description

[Detailed description of the invention]

The field of the invention is nonwoven materials. The present invention relates to nonwoven fibrous materials containing hydrophilic fibers interconnected by certain polymers. Much consideration is now being given to the health and environmental impact of the components of sanitary and health care fabrics such as diapers, sanitary napkins, hospital curtains, disposable sheets and bed pads. Nonwovens for these applications also need to have adequate tensile strength and abrasion resistance when wetted with water or aqueous liquids such as body fluids.
Generally, binders currently used in nonwovens are cross-linked to obtain adequate wet strength and abrasion resistance. Cross-linking is usually based on formaldehyde, a harmful substance known to irritate the skin and be a possible carcinogen. This type of cross-linking involves the reaction of methylol groups in polymers such as N-methylolacrylamide, or addition aminoplasts such as methylolated melamine or urea formaldehyde. This type of crosslinking is believed to be a means of imparting adequate wet strength to nonwovens. Such methods are described in US Pat. No. 2,931,749 and US Pat. No. 3,157,562. For similar health reasons, it is desirable that the binder be free of other substances such as acrylonitrile. The inventors have now discovered a type of binder polymer that does not contain methylol group-containing units and to which no aminoplast is added. This polymer surprisingly allows hydrophilic fiber-containing nonwovens to retain the wet strength imparted by similar methylol-containing polymers. An important use of non-woven fabrics is in the manufacture of diapers. Traditionally, hydrophilic fibers such as cellulose, especially rayon, have made up the majority of nonwoven fabrics for diapers. This is because hydrophilic fibers are adsorbent. However, diaper cover stocks are now constructed from non-woven fabrics that allow body fluids to easily pass through the diaper, known as a seepage channel.
Prevents liquid from flowing out of the diaper, known as a wet bag. Such diapers are constructed from hydrophobic fibers such as polyester. However, there remains a significant market for hydrophilic fibers, and it is desirable to adapt hydrophilic fibers to function in much the same manner as hydrophobic fibers. The present inventors have now discovered certain binder polymers that can impart a desirable balance of wicking and wet bag properties to nonwoven fabrics containing hydrophilic fibers. Diapers often have an outer covering known as a cover stock, which is sealed by the application of heat during the manufacturing process. Nonwovens bonded by conventional crosslinked polymers are difficult to seal; they have poor heat sealability. This can be a serious drawback. The inventors have now discovered certain binder polymers that can impart improved heat sealing properties to nonwoven fabrics containing hydrophilic fibers. In methods of manufacturing nonwoven products, binder polymers can create an undesirable degree of sticking to processing equipment. As is obvious, this hinders the smooth conduct of operations. This characteristic is productivity (runnability)
known as. The inventors have discovered certain binder polymers that can have good productivity. According to the invention, the fibers are at least 50% by weight
(dry fiber weight), wherein the fibers are (a) 50-80%, preferably 60-80% by weight;
Acrylic acid and/or such as butyl acrylate and 2-ethylhexyl acrylate
at least one _C4 - _C8 ester, preferably a _C4 - _C8 alkyl ester of methacrylic acid
(b) 10-49% by weight, preferably 15-30% by weight,
at least one of methyl methacrylate, styrene and α-methylstyrene, preferably styrene; and (c) 1-10% by weight, preferably 1-6% by weight.
A nonwoven fibrous product is provided which is interconnected by an emulsion copolymer of: at least one monoethylenically unsaturated dicarboxylic acid, optionally in combination with at least one monoethylenically unsaturated monocarboxylic acid. The term hydrophilic fiber is used in the dry state at 21.1°C (70°C).
) and fibers having a moisture content of greater than 2.5% at 65% relative humidity (see Textile World, August 1978, pages 51 and 52). Preferred fibers for the nonwoven products of this invention include at least 50% by weight cellulosic fibers such as rayon.
(dry fiber weight), with the remainder being one or more other natural or synthetic fibers. Blends of 50% rayon and 50% polyester are preferred, with 100% rayon being more preferred. The copolymer preferably contains up to 10% by weight of units of another functional monomer, such as hydroxyethyl acrylate or methacrylate, hydroxypropyl acrylate or methacrylate, acrylamide or methacrylamide, or mixtures of such monomers. may be present in small amounts, such as up to 5% by weight. However, the copolymer must be substantially free of units containing methylol groups and additional aminoplasts. Preferably, the copolymer does not contain additional functional units, and more preferably consists of units (a), (b), and (c) above. Acid component (c) may consist of a dicarboxylic acid such as itaconic acid or maleic acid and optionally a monocarboxylic acid such as acrylic acid or methacrylic acid. (c) optionally 0.5-3%, preferably
0.5-3 in combination with 0.75-3% monocarboxylic acid
%, more preferably 0.75-3% dicarboxylic acid. In a preferred embodiment of the invention, the binder copolymer contains units of both at least one dicarboxylic acid and at least one monocarboxylic acid as described above. The present inventors have surprisingly discovered that copolymers containing both types of acids generally impart better wet strength to nonwoven fabrics than when containing either acid alone. Therefore, the component (c) preferably consists of itaconic acid and acrylic acid and/or methacrylic acid. Furthermore, we have found that this acid combination increases the productivity conferred by itaconic acid alone. A combination of itaconic acid and acrylic acid is preferred to obtain a desirable balance of improved wet strength and productivity over these individual acids. The weight ratio of dicarboxylic acid to monocarboxylic acid in this acid mixture is preferably from 4:1 to 1:4.
The ratio is more preferably 2:1 to 1:2. Acid component (c) may be present in the free acid form or in salts with alkali metals such as sodium or potassium, water-soluble amines such as methylamine, diethylamine, triethylamine, mono-, di- or tri-ethanolamine or morpholine. or in the form of an ammonium salt. The nonwoven products of the present invention are particularly useful in making diapers. Accordingly, another preferred embodiment of the present invention provides diaper coverstocks and diaper finishes comprising the nonwoven products described herein. Nonwoven fibrous products according to the invention may be formed in any suitable manner, such as by carding, garnetting, or by dry deposition from an air suspension of fibers. When forming this textile product by carding or garnetizing,
The fibers are usually at least partially oriented, whereas in products formed by air deposition the fibers are completely randomly distributed. Although thin webs or fleeces obtained from a single card may be treated with the copolymers described herein, multiple such webs are generally stacked to form mats of sufficient thickness for the intended end use. It is necessary to create
Also desirable. In making such mats, every other layer of carded web may be placed with its fiber orientation oriented at a 60° or 90° angle to the intermediate layer. The copolymer can be applied to the fibers as an aqueous dispersion in any suitable manner such as spraying, dipping or roll transfer. The concentration of the copolymer in the dispersion, at the time of application as an aqueous dispersion, can be from 5 to 60% by weight, preferably from 5 to 25% by weight. The binder dispersion or powder may be applied to the dry fibers after formation or deposition of the web or mat so that it partially penetrates or fully penetrates into the interior of the textile. Alternatively, the binder dispersion or powder can be applied to the fibers as it descends through a settling vessel to its point of deposition. This can advantageously be achieved by spraying the binder dispersion or powder approximately midway between the top and bottom of the settling vessel. By spraying the fibers with the binder down to the aggregation point, the binder can be well distributed within the fibers before it is agglomerated into the product. In some textile products where the hot molten mass of polymer is disrupted by a jet of heated air or steam, the polymer is still present so that after deposition the binder quickly sets and binds the fibers in proper relationship. It is hot and can be sprayed directly onto the fibers just before it is deposited. However, it is preferred that the application of the binder dispersion to the textile product be carried out at room temperature to facilitate cleaning of the equipment associated with the application of the binder dispersion. The binder dispersion can be applied to one or both surfaces of the textile, or distributed throughout its interior. The binders of the present invention may be applied in combination with other binders such as glues. Similarly, the use of strong adhesive fibers within textile products can also be combined with the use of polymeric binders. If desired, an aqueous polymeric dispersion can be used that contains a wetting agent to aid in penetration into the applied fibrous web or mat, and the dispersion can also contain a blowing agent to foam the binder into the final product. or defoamers can be included when the components of the aqueous dispersion have a tendency to foam and in special cases where such foaming is undesirable. Conventional wetting agents such as the sodium salt of dioctyl sulfosuccinic acid can be used and conventional blowing agents such as sodium soaps, including sodium oleate for foaming and octyl alcohol or certain silicones for defoaming. agent can be used. The proportion of polymer applied to the web or mat is 15-50% by weight based on the total weight of copolymer and fibers.
(or even up to 75% in some cases) of the copolymer. After applying the aqueous dispersion of water-insoluble copolymer, the impregnated or saturated web is dried at room temperature or at an elevated temperature. The binder copolymer used in the present invention is disclosed in U.S. Pat.
2754280 and 2795564, nonionic, cationic or anionic emulsifiers or free radical initiators (which may optionally be components of any of the well-known redox systems). They can be prepared by conventional emulsion copolymerization methods using suitable emulsifiers, such as mixtures of nonionic emulsifiers and cationic or anionic emulsifiers (possibly). Examples of emulsifiers that can be used include sodium lauryl sulfate, about 10-50 per molecule;
t-octylphenoxypolyethoxyethanol and laurylpyridinium chloride containing oxyethylene units. The amount of emulsifier can range from about 0.5% to 6% based on the weight of monomer. Any free radical initiator such as azodiisobutyronitrile, t-butyl hydroperoxide and ammonium or potassium persulfate can be used. The proportion of initiator can be from 0.1% to 2% based on the weight of monomer. The following examples more specifically describe some preferred embodiments of the invention. In these examples, all percentages are given by weight and temperatures are given in °C unless otherwise stated. Example 1-27 A nonwoven fabric is made from 100% rayon bonded with the polymers specified in Table 1. Comparative Examples 1-6 demonstrate the performance of methylol cross-linking binders and binders that do not contain methylol groups but also do not contain dicarboxylic acids. Binders containing neither methylol groups nor dicarboxylic acids have low wet strength and generally have poor productivity. Other examples in the table describe nonwoven fabrics according to the invention in which the binder contains a dicarboxylic acid. These materials have improved wet strength. The following test method is used in Table 1: Tensile Strength 22-23% solids binder is applied by impregnation onto a oriented rayon nonwoven web (approximately
31.5g/ ^m2 ). Before impregnation, prepare a web sample (approximately 39.5 cm x
26.5cm) and weighed the cotton/Dacron 54 (35/
65) Insert into fabric. Impregnation is approximately 12.5% in the bath
Performed on solids content. The sample is weighed again and dried in a Werner Mathis oven model LTF No. 1268. Drying and curing conditions are 150°C for 2 minutes. The impregnated nonwoven fabric was kept at 20℃±1℃ and
Condition overnight at 65% ± 10 relative humidity. A 2.5 cm wide sample is tested on an Instron instrument with a 10 cm inter-jaw opening. The test is carried out dry and wet after immersing the sample in water for 10 minutes. Results are paper speed 20cm/min and machine speed
Average value of 10 tests with Instron set at 50 cm/min. Heat-Sealability A binder at 58-62% solids is applied by impregnation using a bath at approximately 20% solids concentration, as in the tensile strength test. The samples are dry cured for 2 minutes at 150°C. A 5 x 7.5 cm sample is taken from the impregnated web in the machine direction and sealed as follows: From the nonwoven sample with two 5 cm long 0.6 cm (1/4 inch) wide strip seals doubled. Made using branded heat sealing equipment. The samples are then conditioned as described above and tested on an Instron device for peel strength when dry and when wet after 30 seconds of immersion in water. Instron was set as above, heat sealing device was 2.8Kg/m ²
(40psi), 200°C and 0.3 seconds.
Take the average value of the tests. Productivity Dilute the copolymer emulsion 50:50 with water. 0.1%
Add Nopco DF-160L and adjust the pH to 9. A Benz putder is modified so that the bottom roller of the vertical putder operates consistently in a prepared manner. The bath level is kept constant by the addition of water and the accumulation on the device is determined visually. Desired tensile and heat sealability values in the wet state are 320 g/2.5 cm and 150 g/5 cm, respectively.

[Table] Examples 28-35 Examples 28-32 from 100% rayon, and Example 33
-35 makes a nonwoven fabric from 50/50% by weight rayon/polyester. The fibers are bonded with the polymers listed in Table 2. It should be noted that the tensile strength results in this table cannot be directly compared with the results shown in Table 1. In Table 2, Comparative Examples 28 and 33 illustrate cases where the binder contains a methylol group, and Comparative Example 29 illustrates a case where the binder does not contain a methylol group and a dicarboxylic acid. Other examples in the table show that the presence of dicarboxylic acids imparts comparable wet strength compared to methylol-containing binders and that the combination of dicarboxylic acids and monocarboxylic acids provides comparable wet wear. and can be seen to impart wet strength. The following test method is used in Table 2: Tensile Strength A web of fibers of the type specified is supported between two layers of glass fiber scrim in a Birch Brothers spudder in a 6% polymer solids bath.
Padder) 18.14Kg at a speed of 6.95m/min
(40 lbs.) Nituprole pressure to saturate with polymeric binder. The padded web was dried in a forced air oven at 65.5°C ((150°C) for 7 minutes,
Cure for 15 minutes at 150°C. The finished fabric
It has a dry weight of 23-26 g/m ² and contains 30% binder. Cut the sample into 2.5 cm x 15.2 cm in the machine direction.
Testing is performed on an Instron machine with a separation distance of 12.7 cm and a drawing speed of 5.1 cm/min. Wet strength is measured after soaking the sample in water for 30 minutes. Wet Abrasion Resistance Nonwoven samples made as described for tensile strength testing are washed repeatedly without soap in a Maytag washing machine. The washing machine was set to circulate sufficient hot water (140°C) and contained eight terry towels as ballast. It is assumed that the web is insufficient when it is cut into two pieces. Each composition is tested twice. Feel Feel or softness is measured on fabrics made as described for the tensile strength test above. Six judges grade the fabrics from 1 (soft) to 5 (hard). Ignore the highest and lowest grades for each fabric and average the remainder to arrive at the final grade.

[Table] Note: The symbols for monomers are the same as in Table 1.

Claims (1)

[Scope of Claims] 1 The fibers are at least 50% (based on dry fiber weight) hydrophilic fibers [hydrophilic fibers are in dry state,
2.5 at 21.1℃ (70〓) and 65% relative humidity
%] and the fiber contains (a) from 50 to 80% by weight of total monomers of acrylic acid;
_C4 to _C8 esters and _C4 to methacrylic acid
at least one of C ₈ esters; (b) at least one of methyl methacrylate, styrene and α-methylstyrene in an amount of 10 to 49% by weight of total monomer; and (c) total monomer 0.5-10% by weight of the body, at least 1
an acid consisting of a monoethylenically unsaturated dicarboxylic acid; the copolymer does not contain a unit containing a methylol group, and A nonwoven fiber product characterized in that no aminoplast is added. 2 At least 50% fiber by weight (dry fiber weight)
of cellulosic fibers, and the remainder, if any, is one or more other natural or synthetic fibers.
Products listed in section. 3. The product according to claim 1 or 2, wherein the fiber is 100% rayon. 4 The fiber contains (a) 60 to 80% by weight of total monomers of acrylic acid;
_C4 to _C8 esters and _C4 to methacrylic acid
at least one of C ₈ esters; (b) at least one of methyl methacrylate, styrene and α-methylstyrene in an amount of 15 to 30% by weight of total monomer; and (c) total monomer 1 to 6% by weight of at least one monoethylenically unsaturated dicarboxylic acid; interconnected by an emulsion copolymer of a monomer composition comprising: The product according to any one of items 3 to 3. 5. A product according to any one of claims 1 to 4, in the form of a diaper cover stock or a finished diaper. 6. Hydrophilic fibers comprising at least 50% fibers (based on dry fiber weight) [hydrophilic fibers are
2.5 at 21.1℃ (70〓) and 65% relative humidity
%] and the fiber contains (a) from 50 to 80% by weight of total monomers of acrylic acid;
_C4 to _C8 esters and _C4 to methacrylic acid
at least one of C ₈ esters; (b) at least one of methyl methacrylate, styrene and α-methylstyrene in an amount of 10 to 49% by weight of total monomer; and (c) total monomer 0.5-10% by weight of the body, at least 1
an acid consisting of at least one monoethylenically unsaturated monocarboxylic acid and at least one monoethylenically unsaturated dicarboxylic acid; 1. A nonwoven fiber product characterized in that it does not contain units containing methylol groups and does not contain added aminoplast. 7 At least 50% fiber by weight (dry fiber weight)
of cellulosic fibers, and the remainder, if any, is one or more other natural or synthetic fibers.
Products listed in section. 8. A product according to claim 6 or 7, wherein the fiber is 100% rayon. 9 The fiber contains (a) 60 to 80% by weight of total monomers of acrylic acid;
_C4 to _C8 esters and _C4 to methacrylic acid
at least one of C ₈ esters; (b) at least one of methyl methacrylate, styrene and α-methylstyrene in an amount of 15 to 30% by weight of total monomer; and (c) total monomer By an emulsion copolymer of a monomer composition consisting of an acid consisting of at least one monoethylenically unsaturated monocarboxylic acid and at least one monoethylenically unsaturated dicarboxylic acid in an amount of 1 to 6% by weight of the body; 9. A product according to any one of claims 6 to 8, which is interconnected. 10 Component (c) comprises 0.5 to 3% by weight of the total monomers of at least one monoethylenically unsaturated dicarboxylic acid and 0.5 to 3% of the total monomers of at least one monoethylenically unsaturated dicarboxylic acid.
Any one of claims 6 to 9, consisting of a species of monoethylenically unsaturated monocarboxylic acid.
Products listed in section. 11. The product according to any one of claims 6 to 10, wherein component (c) consists of itaconic acid and acrylic acid and/or methacrylic acid. 12 The copolymer is butyl acrylate, styrene,
12. A product according to any one of claims 6 to 11, consisting essentially of itaconic acid and acrylic acid and/or methacrylic acid. 13. A product according to any one of claims 6 to 12, in the form of a diaper cover stock or a finished diaper.